Urbanization and riparian forest woody communities Diversity, composition, and structure
Urbanization and riparian forest woody communities:Diversity,composition,and structure within a metropolitan landscape
Derric N.Pennington a,*,James R.Hansel b,1,David L.Gorchov c
a
Conservation Biology Graduate Program,University of Minnesota,200Hodson Hall,St.Paul,MN 55108,United States b
Institute of Environmental Science,Miami University,Oxford,OH 45056,United States c
Department of Botany,Miami University,316Pearson Hall,Oxford,OH 45056,United States
a r t i c l e i n f o Article history:
Received 17November 2008
Received in revised form 24September 2009Accepted 9October 2009
Available online 7November 2009Keywords:Development Disturbance Exotic species Indicator species Land cover
Riparian forests Urbanization
a b s t r a c t
Understanding how urban land-use structure contributes to the abundance and diversity of riparian woody species can inform management and conservation efforts.Yet,previous studies have focused on broad-scale (e.g.,urban to exurban)land-use types and have not examined more local-scale changes in land use (e.g.,the variation within ‘‘urban”),which could be important in urban areas.In this paper we examine how local-scale characteristics or ?ne-scale urban heterogeneity affect(s)the diversity,com-position,and structure of temperate woody riparian vegetation communities in the highly urbanized area of Cincinnati,Ohio,USA.We use an information-theoretic approach to compare vegetation models and canonical correspondence analyses to compare species responses to urban variables.We found that urban riparian areas can harbor a high diversity of native canopy and shrub species (38and 41,respec-tively);however,native and exotic woody plant species responded differently to urbanization.Exotic canopy species increased with the level of urbanization while native canopy and understory species declined.Understory species diversity displayed a greater response to urbanization than did canopy diversity,suggesting temporal lags in canopy response to disturbances associated with present and recent land-use changes.Certain native and exotic woody species represent ecological indicators of dif-ferent levels of urbanization.Native species characteristic of pre-European settlement conditions were restricted to the wide riparian forests with little urban encroachment.Several native early-successional species appear tolerant to urbanization.Two exotic species,the tree Ailanthus altissima and the shrub Lonicera maackii ,were the most abundant and ubiquitous woody species and appear to exploit urban dis-turbances.These exotic species invasions have the potential to modify forest composition and ecological function of urban riparian systems.In addition,altered hydrology may be a contributing factor as canopy and understory stem density of high-moisture-requiring species decreased with an increase in impervi-ous surface and grass cover and with proximity to roads and railroads.In the face of urbanization,main-taining wide riparian forests and limiting building,road and railroad development within these areas may help reduce the invasion of exotic species and bene?t hydrological function in temperate riparian areas.
Published by Elsevier Ltd.
1.Introduction
Urbanization,the ‘‘city building process”(Gottdiener and Hutch-inson,2006),has substantially in?uenced vegetation on a global scale (Rebele,1994;Vitousek et al.,1997;McKinney,2002).Urban-ization directly impacts ecosystems through the replacement of
vegetation with urban infrastructure (e.g.buildings,roads,utilities)and indirectly by altering vegetation composition and structure through fragmentation and degradation (e.g.,altered hydrology),which reduces habitat quality for certain native species and in-creases the opportunity for early colonizers and some non-native species (McKinney,2002).Studies of urban forests that identify spe-ci?c factors of urbanization that affect the structure and function of urban ecosystems will improve our understanding of these unique systems and inform conservation and restoration decisions (Bern-hardt and Palmer,2007;Pickett and Cadenasso,2008).
To study the effects of urbanization on ecosystem structure and function,researchers have employed urban–rural gradient meth-odology (McDonnell and Pickett,1990).Urban–rural gradients are generally conducted at large spatial scales and have in some
0006-3207/$-see front matter Published by Elsevier Ltd.doi:10.1016/j.biocon.2009.10.002
*Corresponding author.Present address:Department of Applied Economics,University of Minnesota,337Classroom Of?ce Building,St.Paul,MN 55108,United States.Tel.:+15133132185.
E-mail addresses:penn0107@https://www.wendangku.net/doc/6f16022001.html, (D.N.Pennington),hanselj@https://www.wendangku.net/doc/6f16022001.html, (J.R.Hansel).1
Great Oaks,Diamond Oaks Career Campus,6375Harrison Avenue,Cincinnati,OH 45247-7898,United States.
Biological Conservation 143(2010)
182–194
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cases been conceived of as a linear transect radiating out from a city center to less-altered or more‘‘natural”landscapes.Studies employing this method have documented changes along urban–rural gradients for stream hydrology(Nilsson and Berggren, 2000;Groffman et al.,2003),degradation in stream habitat(Milt-ner et al.,2004),changes in both aquatic and terrestrial species abundance and diversity(McKinney,2002;Morley and Karr, 2002;Price et al.,2006;Pennington and Blair,2009),and biogeo-chemical processes(Pouyat et al.,2002;Groffman et al.,2006). Gradient studies have documented declines in plant species diver-sity,basal area,and native species density(Porter et al.,2001; Moffatt et al.,2004;Godefroid and Koedam,2007)and an increase in the presence of non-native species(Burton et al.,2005;Duguay et al.,2007)as sites become more urbanized.
Previous large-scale urban–rural gradient studies have docu-mented that urban riparian forests are more impaired than their ‘‘natural”or rural counterparts(Paul and Meyer,2001);and conse-quently,their conclusions often diminish the perceived ecological value of small remnant vegetation within highly modi?ed land-scapes.Yet,it is increasingly vital for researchers,managers,plan-ners,and citizens to understand the potential ecological and societal value of remnant urban vegetation(Miller and Hobbs, 2002;Turner et al.,2004).Given that over60%of the world’s pop-ulation will reside in urban areas by2030(UNPD,2003),these‘‘less than pristine”forests could provide critical ecosystem services for both people and other species(Miller and Hobbs,2002;Bernhardt and Palmer,2007).
Large-scale gradient analyses often assume a single urban–rural gradient that views urban areas as a dense,highly developed urban core,surrounded by irregular rings of declining development (McDonnell and Pickett,1990).In reality this‘‘gradient”is a com-plex mosaic of patches representing small gradients associated with each patch(Alberti et al.,2001).Urbanized landscapes contain numerous gradients that range in intensity and scale over land area and land-cover/land-use types(Cadenasso et al.,2007).Few studies have explicitly examined more local-scale changes in a particular land-use category along this gradient(Pickett and Cadenasso,1995).For this study,we examine the variation within a complex and spatially heterogeneous urban area to identify the important gradients for woody riparian vegetation.
Understanding how urban structure in?uences riparian forests is important because these vegetation communities provide a vari-ety of critical ecosystem services and harbor a high diversity of species(Naiman et al.,1993;Richardson et al.,2007).Fundamen-tally,people have been drawn to the areas adjacent to rivers and streams for transportation,power production,food,and waste disposal needs(Hedeen,1994;Naiman and Decamps,1997).The collective effect of these activities has resulted in the‘‘urban stream syndrome,”typi?ed by a?ashy hydrograph,elevated concentrations of nutrients and contaminants,altered channel morphology,and reduced species diversity,with increased domi-nance of disturbance tolerant species(Walsh et al.,2005).
In addition to the ecosystem services provided to people,urban riparian areas also function as a dispersal route for aquatic organ-isms and plant propagules(vegetative or seed),provide habitat for aquatic and terrestrial resident and migrant animal species(Rot-tenborn,1999;Pennington et al.,2008),and buffer sediment and nutrient runoff into the stream channel(Tabacchi et al.,2000).Fur-ther,riparian forests function as important habitat in urban sys-tems by connecting adjacent natural areas,such as parks to contiguous vegetation communities for wildlife mobility and over-all habitat enhancement(Botkin and Beveridge,1997;Savard et al., 2000;Sinclair et al.,2005).
The integrity of riparian forest communities is vulnerable to the intense land-use modi?cation associated with urbanization(Rich-ardson et al.,2007).Signi?cant changes in species composition of riparian forests along urban–rural gradients have been reported for Columbus,Georgia(Burton et al.,2005),Baltimore,Maryland (Groffman et al.,2003),and Winnipeg,Manitoba(Moffatt et al., 2004).Species diversity,tree basal area,and native plant density were shown to decrease near urban areas(Porter et al.,2001;Moff-att et al.,2004)and invasive exotic richness and density increased with development in the southeastern United States(Burton et al., 2005).These studies applied an urban-to-rural gradient approach to study sites located across a large geographical region from a densely populated urban landscape to a relatively unpopulated rural landscape and did not examine?ne-scale responses.
For our study,we characterize riparian forests along a gradient of urban land-use types(commercial,industrial,residential and parklands)in the highly urbanized landscape of Cincinnati,Ohio, USA.Our purpose is twofold:(1)to determine whether canopy and understory woody plant community composition and struc-ture respond differently to?ne-scale land use and land cover fac-tors(vegetation,surfaces,and infrastructure)used to describe urbanization;in particular,to determine how urbanization in?u-ences the prevalence of exotic species;and(2)to identify potential indicator species of eastern deciduous riparian vegetative commu-nities in densely urbanized areas.By addressing these objectives we seek to improve our understanding of the potential processes in?uencing urban ecosystem functioning and the conservation and management of vegetation in urban areas.
2.Methods
2.1.Study area/site selection
The Mill Creek watershed covers42,994hectares and is located in Butler and Hamilton Counties in Southwestern Ohio(Fig.1). Within this watershed,we selected a4243ha study area com-prised of a portion of the Mill Creek and sections of two tributaries, Sharon Creek and West Fork Mill Creek(Fig.1).This area is located on the geologically homogeneous Pre-Wisconsinan Drift Plains ecoregion within the urbanizing greater Cincinnati metropolitan area(39.2°N84.5°W).The selected sub-watersheds represent some of the fastest growing areas in Ohio,with more than half a million people living and working in the Mill Creek watershed(US Census Bureau,2000).At least three continental glacial events shaped the terrain,removing accumulated soil and in?uencing regional river-ine systems(USDA,1992).The pre-settlement vegetation of the area was predominately Beech forests(Fagus grandifolia,Acer sac-charum,Plantanus occidentalis,Populous deltoides;authorities cited in Appendix A)and mixed mesophytic forests(Gordon,1966).The climate of the region is temperate with cold winters and hot sum-mers and an annual precipitation of approximately100cm with over50%from April to September(USDA,1992).The Mill Creek has been designated as one of the most threatened urban rivers in the United States(American Rivers,1997)because of the various effects of human settlement common to many urban rivers.
Along Mill Creek,West Fork Mill Creek and Sharon Creek,we identi?ed71study plots systemically from a random starting point using ArcViewòGeographic Information Systems(GIS)version8.2 and the2002Cincinnati Area Geographic Information System(CA-GIS)dataset(using high-resolution color aerial photos taken in 2001that distinguish physical and surface features including topography,waterways,buildings,and roads).All plot centers were located along the streamside edge and separated by a minimum distance of150m.Stream channel width was similar across plots($10m).The elevation among plots ranges from200 to300m above sea level.Permission was obtained from commer-cial and residential landowners prior to data collection.These selected waterways traverse various metropolitan land-use types:
D.N.Pennington et al./Biological Conservation143(2010)182–194183
commercial,industrial,residential and parkland (Fig.1).Each waterway has been directly altered by people in the past:Mill Creek has some channelized sections;Sharon Creek has an unreg-ulated dam upstream of study sites;West Fork Mill Creek has a regulated dam upstream of study sites.Given the scope of our study,we were not able to directly examine the role of hydrologic disturbances via dam regulation on riparian vegetation.
https://www.wendangku.net/doc/6f16022001.html,ndscape parameters
To examine varying levels of urbanization within our study area,we used classi?ed land-cover data derived from 2000IKONOS satellite imagery for Hamilton County,Ohio.IKONOS imagery pro-duces 1m high-resolution color images that can be directly used for land-use classi?cation and surface feature data (Dial et
al.,
Fig.1.Location of the 71study plots used to examine woody riparian plant communities in the Mill Creek watershed in the greater Cincinnati metropolitan area Hamilton county,Ohio,https://www.wendangku.net/doc/6f16022001.html,nd use/land cover map derived from IKONOS satellite imagery area shows land-use classes and survey plots.
184 D.N.Pennington et al./Biological Conservation 143(2010)182–194
2003).Land-cover data were previously classi?ed into categories,including trees,grass,impervious surfaces,agriculture/soil and water (Fig.1).We veri?ed the accuracy of land-cover classi?cation data for each plot by visually comparing IKONOS data to high-res-olution (0.5m)color aerial photos taken in 2002,which was the same year vegetation data was collected.
From IKONOS-based land-cover data,we calculated three land-scape variables to serve as components of urbanization:percent impervious surface (pavement and rooftops),percent tree cover,and percent grass (agricultural ?elds,meadows,and lawns)within 250m of each plot origin (Table 1).We calculated ?ve additional landscape variables using the CAGIS dataset:distance to nearest road and railroad from plot center,road density,building density,and building area within a 250m radius of the plot center (Table 1).We chose to include distance to nearest road and railroad because of the potential in?uence of these factors on seed dispersal (Tikka et al.,2001).
2.3.Woody plant sampling
Trees and shrubs were sampled mid-August to October 2002.For each site,we located one 70m diameter circular sampling plot (3848.5m 2)on the stream bank to capture vegetation data from both sides of the waterway (see Fig 2).The plot center was located as close to the edge of the stream as possible.We identi?ed all trees >10cm diameter at breast height (dbh)and recorded dbh within the plot.We sampled woody plants with stems <10cm diameter in ?ve 10m diameter subplots (78.5m 2per subplot;392.5m 2total),one along each of ?ve 35m radial transects from the circular plot origin.The compass bearing of the ?rst radial
transect was randomly selected.Subsequent transects were equi-distantly spaced with a 72°interval between each transect.Along each transect one point was randomly selected 5–35m from the plot origin;this served as the center of the subplot.If a subplot in-cluded the stream,the radial transect was reselected or shifted in 10°increments so no part of the subplot was located in the water-way.In each 78.5m 2subplot,every woody stem <10cm dbh was identi?ed and total stem density https://www.wendangku.net/doc/6f16022001.html,position and structure measures
We calculated several diversity and composition measures of woody plant communities for each plot (Table 1).For canopy and understory species,we calculated Shannon–Weiner’s index (H),Simpson’s index (D 0)and evenness (E),using the multivariate eco-logical software package PC-ORD version 4.14(McCune and Mef-ford,1999;Magurran,2004).We also calculated species richness for native and exotic species separately.Exotic or non-native spe-cies were de?ned as those absent from the study area prior to European settlement (Braun,1989).We used importance values for canopy and understory species to describe woody species com-position of riparian plant communities.We calculated importance values for each plot for canopy stems (>10cm dbh)by summing relative density and relative basal area and dividing by two (Bar-bour et al.,1987).For understory stems (<10cm dbh),relative fre-quency and relative stem density were summed and divided by two to calculate importance values for each plot.
We characterized canopy forest structure using basal area and stem densities.For stems >10cm dbh,absolute basal area of can-opy species was calculated for both native and exotic species,as well as total absolute basal area.Canopy absolute native tree den-sity,absolute exotic tree density and total absolute density were also calculated for stems >10cm dbh.For stems <10cm dbh,abso-lute stem density values were calculated for understory native,exotic and total species.
Table 1
Variable codes for landscape measures and riparian plots in the Mill Creek watershed located within the Cincinnati Metropolitan area,Ohio,USA.Variable code Description
Landscape variables Imp_250Percent impervious surface in a 250m radius from plot center
T-250Percent trees in a 250m radius from plot center G_250Percent grass in a 250m radius from plot center RD_D
Distance to nearest road from plot center in meters BDEN_250Total number of buildings in a 250m radius from plot center divided by the area
RR_D Distance to nearest railroad from plot center
B_250
Total building area in a 250m radius from plot center
Woody vegetation variables Total canopy_BA Absolute basal area of native canopy trees Native canopy_BA Total absolute basal area of canopy trees Exotic canopy_BA Absolute basal area of exotic canopy trees Total canopy_DEN Total absolute density of canopy trees Native canopy_DEN Absolute density of native canopy trees Exotic canopy_DEN Absolute density of exotic canopy trees H_canopy Shannon–Weiner index of diversity for canopy plants
D 0_canopy
Simpson index of diversity for canopy plants E_canopy Evenness or distribution of individuals among species
for canopy plants
S_native_canopy Species richness of native woody canopy species S_exotic_canopy Species richness of exotic woody canopy species Total understory_DEN Total absolute stem density of understory woody plants Native understory_DEN Absolute stem density of understory native woody plants Exotic understory_DEN Absolute stem density of understory exotic woody plants H_understory Shannon–Weiner index of diversity for understory
plants
D 0_understory
Simpson index of diversity for understory plants E_understory Evenness or distribution of individuals among species
for understory plants
S_native_understory Species richness of native woody understory species S_exotic_understory Species richness of exotic woody understory
species
D.N.Pennington et al./Biological Conservation 143(2010)182–194185
To explore the importance of altered hydrology on the riparian woody community in the study area,we?rst categorized species based on moisture requirement using Burns and Honkala(1990) and USDA-NRCS(2006)(Appendix A),then analyzed vegetation structure and diversity measures separately for each category. 2.5.Statistical analysis
Vegetation data were log-transformed to down weight the con-tribution of highly abundant or rare species on community struc-ture.We examined multicollinearity among the eight landscape variables to determine which variables to use or drop as predictors in multiple regression analyses.Road density was highly correlated with building density(r=0.85);we chose to remove road density and keep building density because landscape plantings associated with buildings can escape to adjacent areas(Dirr,1998).Percent tree cover was highly correlated with percent impervious surface (r=à0.87);consequently,we removed percent trees and included percent impervious surface in the model as a measure of urbaniza-tion because impervious surface represents human-mediated dis-turbances including altered hydrology and forest fragmentation. The remaining variables were not highly correlated(Table2),so were used as explanatory variables in our analyses.
2.5.1.Multiple regression model selection
To determine the effect of landscape variables on woody vege-tation community measures we used a model-ranking approach that does not rely on conventional hypothesis testing and signi?-cance to reject variables or models(Cunningham and Johnson, 2006;Diniz-Filho et al.,2008).We ranked models using a multi-ple-model inference approach rather than attempting to determine only a single‘‘best”model that described the data(Burnham and Anderson,2002).By using this approach we could rank possible explanatory models and retain all models that?t our data well based on the assumption that several models(and variables)could be similarly important in explaining woody vegetation measures.
To identify competitive landscape feature models,we took an exploratory‘all possible models’approach to model selection, including all six explanatory variables characterizing the surround-ing landscape,which is in contrast to developing a suite of candi-date models based on a priori hypotheses.Given that our goal was to gain insight into the relative importance of landscape vari-ables and to assess unanticipated relationships,not prediction,we felt obliged to take an exploratory approach(Diniz-Filho et al., 2008).
Speci?cally,we used an information theoretic method to evalu-ate a set of models based on their explanatory value determined by corrected Akaike’s information criterion(AIC c;adjusted for small sample-size in relation to number of parameters),and identi?ed the best-?tting models(or strongest)based on D AIC c values(Burn-ham and Anderson,2002);D AIC c=0represented the‘‘best”model and we considered all models with D AIC c<3to be competitive candidate models(Cunningham and Johnson,2006).We computed Akaike weights for models in order to assess the evidence of a particular model based on the observed data.We also computed Akaike weights for each explanatory variable so that we could compare the relative importance of each variable,which prevented us from discarding variables that might be important for explain-ing vegetation measures yet do not appear in the‘‘best”selected model(Burnham and Anderson,2002).For each analysis,we ranked models by running a model selection routine in SAS(PROC MIXED SAS version9.2,SAS Institute,Cary,NC,USA)that calcu-lated AIC c,D AIC c,model weights,and variable weights;each model included one or more explanatory variables.We report adjusted R2 values for the‘‘best”model based on linear regression as a way to evaluate goodness of?t.
2.5.2.Canonical correspondence analysis
To further investigate how urbanization in?uences riparian community composition,ordination methods were used to de-scribe dominant patterns and complex relationships in species composition(McCune and Grace,2002).We chose to use canonical correspondence analysis(CCA)in order to determine how commu-nity composition was related to the selected environmental https://www.wendangku.net/doc/6f16022001.html,A is a direct gradient analysis ordination technique,and represents a special case of multivariate regression,and differs from indirect gradient analysis in that species composition is di-rectly and immediately related to measured environmental vari-ables(Ter Braak,1986).Ordination of plot scores is based on CCA operations that perform a least-squares regression of sampling plot scores as dependent variables and environmental variables as independent variables(Jongman et al.,1995).PC-ORD(McCune and Mefford,1999)was used to perform CCA of riparian woody plant species composition(importance values at plot-level)and landscape variables(Table1).A Monte Carlo simulation with 1000permutations was used to determine if a linear relationship existed between the landscape(environmental)variables and woody plant species.Results from the CCA produce eigenvalues that are used to describe how much variance is explained by each ordination axis,thus measuring the importance of each axis(Jong-man et al.,1995;McCune and Grace,2002).Separate CCA analyses were evaluated for canopy plants(stems>10cm dbh)and under-story plants(stems<10cm dbh).
3.Results
A total of6482canopy and39,182understory stems were iden-ti?ed,comprising51canopy and52understory species encoun-tered in the71study plots(Appendix A).Of all canopy species recorded,12were exotic and39were native.Three of the exotic species,tree of heaven(Ailanthus altissima),Osage-orange(Maclura pomifera)and white mulberry(Morus alba)were each encountered in>75%of the plots.Native canopy plants were more evenly dis-tributed with16species found in>75%of plots.Among understory stems,13exotic and39native species were identi?ed.Three understory species,Amur honeysuckle(Lonicera maackii),white mulberry(M.alba)and multi?ora rose(Rosa multi?ora)were found in75%of plots and accounted for most of the exotic stems.Amur
Table2
Correlations among landscape variables across71riparian study plots in the Mill Creek watershed(see Table1for codes).
T_250G_250Imp_250RDEN_250RR_D RD_D BDEN_250B_250
T_250 1.00
G_250à0.15 1.00
Imp_250à0.87à0.32 1.00
RDen_250à0.34à0.150.44 1.00
RR_D0.640.17à0.70à0.40 1.00
RD_Dà0.010.28à0.21à0.610.25 1.00
BDEN_250à0.28à0.080.360.85à0.32à0.56 1.00
B_250à0.60à0.260.720.65à0.46à0.390.63 1.00 186 D.N.Pennington et al./Biological Conservation143(2010)182–194
honeysuckle was the only woody plant species found at all71 plots.Each of?ve native understory species(Acer negundo,Celtis occidentalis,Fraxinus spp.(F.americana and pennsylvania),Ulmus spp.(Ulmus amer and Ulmus red),and Plantanus occidentalis)were found at>75%of the plots.Ten species were classi?ed as having high moisture requirements,nine as having low moisture require-ments,and41as having moderate moisture needs(Appendix A).
3.1.Multiple regression results
Among the‘‘best”landscape models for woody vegetation mea-sures,percent impervious cover within250m was the most com-mon variable and frequently the heaviest weighted or most important variable followed by grass cover within250m(Table 3).The best models for a given vegetation measure re?ected the landscape variables with the highest cumulative Akaike weights across all models.Of the19best models,six yielded relatively weak models with adjusted R2values<0.10(Table3).
3.1.1.Canopy trees
Percent impervious cover within250m was the most important variable for four of the six best models describing canopy structure followed by building density within250m(Table3).Total canopy basal area,total canopy stem density,native canopy basal area and native canopy density,were all positively correlated with the amount of impervious surface and negatively correlated with increasing building density in the landscape(Table3).Interest-ingly,percent grass cover was the most important and heavily weighted variable for exotic canopy measures.Exotic canopy basal area and exotic stem density were positively correlated with the amount of grass;exotic basal area was positively associated with impervious cover within250m and exotic stem density was posi-tively associated with building area(Table3).Exotic canopy basal area and density decreased with increasing distance to railroads (Table3).
For canopy diversity measures,only the best models for native and exotic species richness displayed relatively good?ts(adjusted R2>0.10;Table3).Native canopy species richness was negatively associated with percent impervious surface and grass cover and positively associated with distance to railroad(Table3).Exotic canopy richness was positively associated with percent grass cover and building area and negatively associated with distance to near-est road(Table3).
When the canopy data were re-analyzed separately for species with high,medium,and low species’moisture requirements,stem density of high moisture species displayed the best?t across can-opy models,and was negatively associated with percent impervi-ous surface and positively associated with distance to nearest railroad(adj.R2=0.24;Table4).Canopy stem density of species with medium moisture requirements was negatively associated with percent grass cover and percent impervious surface and pos-itively with distance to nearest railroad(Table4).The best model for canopy density of low-moisture-requiring species was rela-tively weak(adj.R2<0.10).Canopy species richness for medium-moisture-requiring species decreased with percentage of impervi-ous surface and increased with distance from nearest railroad track;models for canopy richness for low and high moisture-requiring species were relatively weak(adj.R2<0.10).
3.1.2.Understory woody plants
Best models for understory structure were relatively weak when compared to canopy structure models with native under-story density re?ecting the best?t(Table3).Total understory den-sity was positively associated with distance to nearest road and railroad(Table3).Native understory density was negatively asso-ciated with increases in impervious surface and grass cover(Ta-ble3).Exotic understory density was positively associated with distance to nearest road(Table3).
In contrast,understory diversity models re?ected stronger rela-tionships to landscape variables(Table3).Percent impervious sur-face was the most important landscape measure for three of the
Table3
Woody vegetation community measures,best landscape model,and variable weights(for variable codes refer to Table1).
Community measure Best model Variable Akaike weights
Imp_250G_250BDEN_250B_250RD_D RR_D Adj.R2
Canopy structure
Total canopy_BAàIMP_250+BDEN_250à0.93à0.26+0.78à0.29+0.29à0.270.15 Native canopy_BAàIMP_250+BDEN_250à0.93à0.27+0.77à0.30+0.31à0.270.19 Exotic canopy_BA+G_250+IMP_250àRR_D+0.59+1.00+0.39+0.58à0.60à0.600.28 Total canopy_DENàIMP_250+BDEN_250à0.99+0.30+0.99+0.25+0.40+0.270.35 Native canopy_DENàIMP_250+BDEN_250à0.99à0.37+0.98à0.25+0.45+0.290.36 Exotic canopy_DEN+G_250+B_250àRR_D+0.41+0.98+0.45+0.71à0.41à0.530.21
Canopy diversity
H_canopyàIMP_250à0.43à0.27+0.42+0.31à0.33+0.360.00 D0_canopyàIMP_250à0.39à0.28+0.36+0.31à0.32+0.330.00 E_canopyàRR_D+0.31à0.32+0.30+0.29à0.29+0.320.00 S_native_canopyàIMP_250+RR_DàG_250à0.73à0.48+0.39+0.32à0.25+0.650.19 S_exotic_canopy+G_250+B_250àRD_DàRR_D+0.35+0.90+0.31+0.82à0.54à0.500.19
Understory structure
Total understory_DEN+RD_D+0.25+0.25+0.26à0.25+0.94+0.260.08 Native understory_DENàG_250àIMP_250à0.76à0.95+0.26à0.50+0.44+0.320.16 Exotic understory_DEN+RD_D+0.40+0.60+0.27+0.29+0.70+0.330.04
Understory diversity
H_understoryàIMP_250àG_250+RD_Dà0.98à0.99+0.26à0.25+0.53+0.240.27 D0_understoryàIMP_250àG_250à0.98à0.94+0.32à0.25+0.39+0.300.21 E_understoryàIMP_250àG_250+0.90à0.56+0.44à0.31+0.31+0.370.11 S_native_understoryàG_250àIMP_250+RD_Dà0.82à1.00+0.33à0.35+0.66+0.570.34 S_exotic_understoryàBDEN_250à0.33à0.49à0.48+0.29+0.40+0.520.02
Note:For best local landscape models,variables and signs of coef?cients(positive or negative effects)are shown.For example,the best landscape model for total canopy basal area(Total canopy_BA)included a negative response to impervious surface and a positive response to building density.Strengths of effects are indicated by cumulative weights.Variable weights are the cumulative Akaike weights of models in which a variable occurred.In general,the best proximate models include the most important variables.Where secondary variables have comparable weights,omitted variables may contribute to alternative competitive models.
D.N.Pennington et al./Biological Conservation143(2010)182–194187
?ve best models for understory diversity(Table3).Shannon–Wei-ner index was negatively associated with impervious surface and grass cover within250m and positively associated with distance to nearest road.Simpson index of diversity and evenness were neg-atively associated with percent impervious surface and grass cover (Table3).Understory native species richness was negatively asso-ciated with grass cover and impervious surface and positively asso-ciated with distance to road(Table3).
Analyzing understory community measures separately for sets of species with different moisture requirements revealed trends similar to those found for canopy measures.Understory density for high moisture-requiring species was negatively associated with percent grass cover and positively associated with distances to nearest road and railroad(Table4).Low moisture understory den-sity was negatively associated with percent grass cover and posi-tively associated with distance to nearest railroad,but the relationship was weak(adj.R2=0.12;Table4).Understory richness of medium moisture-requiring species displayed the best?t(adj. R2=0.33;Table4),and was negatively associated with percent grass cover and percent impervious surface and positively associated with distance to nearest road.Richness of species with high and low moisture requirements was not well explained by our models.
3.2.Ordination
3.2.1.Canopy trees
Patterns in species composition of canopy trees,based on plot-level importance values entered in the CCA,were related to measures of urbanization and the resulting biplots illustrate the ?ne-scale heterogeneity present in a highly urbanized area (Fig.3).Results of the CCA ordination of the canopy community are summarized in the correlations between CCA species ordina-tion scores and environmental variables(Table5)and biplots of species scores along the?rst two axes of the ordination(Fig.3). The eigenvalues for both axes were signi?cant based on Monte Car-lo simulations(axis1=0.26,P=0.001;axis2=0.06,P=0.001),and the species-environment correlations,indicating the ability of landscape variables to explain canopy composition,were0.89 and0.69,for axis1and axis2,respectively.Axis1was positively in?uenced by distance to nearest railroad and negatively by per-cent impervious surface,building area and building density(Table 5;Fig.3).Because impervious surface cover was highly negatively correlated with tree cover,axis1can be interpreted as the urban-ization gradient represented by heavily urbanized areas with rela-tively low tree cover at the negative end to less urbanized areas with greater tree cover at the positive end(Table5;Fig.3).Axis 2was negatively in?uenced by percent grass cover and distance to nearest road and railroad(Fig.3),and separates plots along a gradient consisting of open grassy riparian areas further away from roads and railroads at the negative end of axis1to areas containing little or no grass cover,closer to roads at the positive end(Fig.3). Several unique patterns emerged along these land use gradients. Canopy composition of more urban plots was characterized by sev-eral exotic species(e.g.,A.altissima,Alnus glutinosa,Ulmus pumila, M.alba,Acer platanoides),as well as native pioneer species(e.g., Robinia pseudoacacia,Acer negundo,Populus deltoides);however, the least urbanized plots were characterized almost exclusively by native canopy species,many of which characterize late-succes-sional forests in the area(e.g.,Aesculus glabra,Acer saccharum,T. americana,Quercus muehlenbergii)(Fig.3B).
3.2.2.Understory woody plants
Patterns in species composition for the riparian understory were directly related to landscape measures and again illustrated the?ne-scale heterogeneity within an urban area.Results of the CCA for the understory community are summarized by correlations between CCA species ordination scores and environmental vari-ables(Table5)and in the biplot of species scores along the?rst two axes of the ordination(Fig.4).Both eigenvalues were signi?-cant based on Monte Carlo simulations(axis1=0.19,P=0.002; axis2=0.07,P=0.01),and the species-environment correlations were0.84and0.72for axis1and axis2,respectively.Axis1was positively in?uenced by distance to nearest railroad and negatively in?uenced by percentage of impervious surface,building area and building density,and represents a gradient of more to less urban development(Table5;Fig.4).Axis2was negatively in?uenced by percent grass cover and distance to nearest road and railroad (Table5;Fig.4).A pattern in species composition was apparent with most exotic species(e.g., A.altissima,Catalpa speciosa,U. pumila,M.alba)being associated at the negative,‘urbanized’end of axis1and native species characteristic of late-successional for-ests(e.g.,A.saccharum,F.grandifolia,Carya cordiformis,Carya ovata, Cercis canadenis,Cornus?orida)located at the positive end(Fig.4B). Several native early-successional species(e.g.,R.pseudoacacia,P. deltoides,A.negundo,Celtis occidentalis)were plotted toward the urbanized end of the axis1gradient.In contrast to the canopy CCA,A.altissima saplings were most common in more urbanized areas.The exotic shrub species,L.maackii,was found throughout the study area(Fig.4B).Several of the native shrubs were only found at the least urbanized sites(e.g.,Hydrangea arborescens,Rhus aromatica).Species scores on axis2were dif?cult to interpret,with exotic and native species distributed at both ends.
Table4
Woody vegetation community measures based on moisture dependence,best landscape model,and variable weights(for variable codes refer to Table1;moisture dependence based on Burns and Honkala(1990)and USDA-NRCS(2006;see Appendix A).
Community measure based on moisture requirement Best model Variable Akaike weights
Imp_250G_250BDEN_250B_250RD_D RR_D Adj.R2
Low
Canopy density+BDEN_250à0.30+0.36+0.73+0.35+0.27à0.420.06 Understory densityàG_250+RR_Dà0.44à0.92+0.27+0.27à0.25+0.660.12 Canopy SàRD_Dà0.47+0.30+0.44+0.44à0.67à0.450.06 Understory SàG_250àIMP_250à0.45à0.72à0.29à0.32+0.27+0.290.05
Medium
Canopy densityàG_250àIMP_250+RR_Dà0.82à0.89+0.45+0.32+0.25+0.460.18 Understory density+RD_Dà0.26+0.30à0.26à0.26+0.89à0.290.08 Canopy S+RR_DàIMP_250à0.45à0.36+0.35+0.29à0.42+0.840.17 Understory SàG-250àIMP_250+RD_Dà0.84à1.00+0.24à0.36+0.56+0.340.33
High
Canopy densityàIMP_250+RR_Dà0.69+0.38+0.37à0.34+0.34+0.690.24 Understory densityàG_250+RD_D+RR_Dà0.53à0.99à0.27à0.40+0.92+0.560.23 Canopy S+G_250à0.28+0.82+0.31+0.27+0.25à0.330.05 Understory S+RD_Dà0.41à0.52+0.37+0.32+0.57+0.430.01 188 D.N.Pennington et al./Biological Conservation143(2010)182–194
4.Discussion
Our results indicate that urban riparian areas can harbor a high diversity of native canopy and shrub species and also relatively high exotic species diversity as well;however,native and exotic woody plant species responded differently to urbanization in the Cincinnati area.Riparian forests of highly urbanized areas (i.e.,more impervious surface,higher building density,and closer prox-imity to buildings and roads)were more likely to have a canopy characterized by native early-successional species and exotic spe-cies with an understory dominated by exotic shrubs.In contrast,riparian forests of less urbanized areas were likely to have a more diverse composition of understory and subcanopy species with few exotic species.In general,riparian forest understory diversity dis-played a greater response to measures of urbanization than canopy diversity measures.Native canopy and native understory structure measures both had a negative association with percentage of impervious surface within a 250m buffer (Table 3),similar to re-sponses seen for riparian forests in Manitoba,Canada,and Mary-land and Georgia,USA.(Groffman et al.,2003;Moffatt et al.,
2004;Burton and Samuelson,2008).Interestingly,native canopy density also had a positive relationship with the number of build-ings in the 250m buffer,which for this study area likely represents residential developments within and around the riparian forest.It is tenable these native species were either planted for landscape purposes or represent early-successional species that are able to thrive as development increases and consequently fragments riparian forests in urban environments (Reichard and White,2001;McKinney,2006).
Exotic canopy and understory vegetation structure measures were positively associated with the landscape variables of percent impervious cover and percent grass cover (Table 3).Interestingly,exotic canopy species measures were the only variables to have a positive association with percent grass cover.It is possible that per-centage grass cover re?ects transition areas between grass and for-est edge.It is likely that the exotic species encountered in this study are plants that have escaped adjacent developed landscapes over time and have become an established part of the riparian plant community,since we sampled few obviously planted stems.For example,U.pumila,A.altissima and L.maackii were introduced to North America as ornamental plants during the 1800s (Dirr,1998),and all were commonly found throughout the study area.For L.maackii ,fragmentation has been shown to mediate its inva-sion into southwestern Ohio forests (Hutchinson and Vankat,1998).Other studies report correlations between exotic plant inva-sion and urbanization (Barton et al.,2004;Duguay et al.,2007).We also found that exotic woody measures increased while na-tive woody measures decreased with proximity to railroads and roads.Railway routes and roads represent another possible mech-anism of exotic species invasion (Watkins et al.,2003).Railways and roads have historically been situated along waterways because ?oodplains and valleys often provided a relatively level landscape for infrastructure construction.These factors may adversely affect native species diversity by mediating exotic invasion by
directly
Fig.3.Canonical correspondence analysis (CCA)ordination of canopy (>10cm dbh)species composition of 71plots in the Mill Creek watershed,southwestern Ohio.For biplot A,codes correspond to individual study plots;‘‘A”represents plots along Sharon Creek and Mill Creek and ‘‘B”represents plots located along West Fork Mill Creek.For biplot B,codes of individual species (Appendix A )show their scores as a function of the ?rst two axes.Arrow length indicates the importance of each landscape variable and its in?uence on each species.
Table 5
Correlations between the environmental matrix and the ?rst two axes of the CCA canopy and understory species ordination scores (based on intraset scores,Ter Braak,1986).Variable
Canopy Understory Axis 1
Axis 2Axis 1Axis 2IMP_250à0.8660.436à0.7790.256G_250à0.159à0.943à0.323à0.415BDEN_250à0.2990.141à0.279à0.076B_250à0.5590.397à0.444à0.211RD_D 0.077à0.4460.082à0.794RR_D
0.712
à0.424
0.622
à0.381
D.N.Pennington et al./Biological Conservation 143(2010)182–194189
aiding seed dispersal (Tikka et al.,2001)or indirectly by increasing light availability via fragmentation (Medley,1997;Tilman and Leh-man,2001).
Canopy diversity was also negatively affected by urbanization,but to a lesser degree (Table 3).This ?nding appears due to com-plementary responses of native vs.exotic canopy species,similar to that reported by Burton and Samuelson (2008).In our study,exotic canopy richness increased with measures of urbanization,whereas native canopy richness decreased (Table 3).These ?ndings suggest that many native canopy species are sensitive to impacts associated with urbanization (i.e.fragmentation,competition with invasive plants,hydrological changes;Didham et al.,2007).This interpretation is supported by our ordination,which shows many native tree species to be associated with the least urbanized sites,as we discuss below (Fig.3B).Species richness of native understory woody plants,over 65%of which were tree saplings,was even more negatively affected by urbanization (Table 3).We strongly suspect that the impacts of the landscape in the present and recent decades are manifest in the understory,but of course this under-story composition shapes the composition of the future canopy.Research on the composition of riparian seed banks has docu-mented a shift from native to exotic species with increasing levels of urbanization (Moffatt and McLachlan,2003).Canopy trees are several decades old and likely re?ect the landscape conditions that existed at the time they were established,when human impact was less apparent than indicated by current measures.
Our results are consistent with the hypothesis that altered site hydrology in?uences riparian woody plant composition and struc-ture within urban areas.In general,medium-and high-moisture-requiring species,canopy stem density was lower in plots within landscapes having a higher proportion of impervious surface,and understory stem density was lower where there was more grass cover;both were lower in plots closer to railroad tracks (Table 4).Low-moisture-requiring species were widely distributed across the study area.Changes in hydrology associated with urbanization,such as the replacement of pervious natural vegetation with impervious surfaces and an increase in stormwater discharge via sewers,can lead to lower water tables.This ‘‘urban drought”phe-nomenon in turn in?uences associated soil,vegetation,and micro-bial processes (Groffman et al.,2003).Our results provide further support for this hypothesis,and are similar to ?ndings from Balti-more and the Georgia Piedmont (Groffman et al.,2003;Burton and Samuelson 2008).In addition,our results on species’moisture requirements suggest that railroad and road construction near the stream might also affect streambank hydrology.The construc-tion of these structures parallel to stream channels can result in lateral hydrological disconnections leading to drier soil conditions (Blanton and Marcus,2009).Such ?oodplain disconnections can have a signi?cant impact on the ecological function of riparian landscapes by negatively affecting ?oodplain evolution,riparian ecosystem processes,side-channel habitats,and associated biodi-versity (Snyder et al.,2002;Forman,2003).
For the Cincinnati metropolitan area,the CCA for both canopy and understory species composition revealed a diffuse pattern rather than a distinct ordering of sites on a single gradient of urbanization (Figs.3A and 4A).The presence of a diffuse rather than a distinct gradient differs from what has been documented for other large-scale urban-to-rural gradient vegetation studies (e.g.,McDonnell et al.,1997;Burton et al.,2005);and illustrates the complex heterogeneity comprised of both built and vegetative elements found within an urban area (Cadenasso et al.,2007).This is important since urban areas are often incorrectly assumed to represent a homogenous landscape or land-use type.Indeed,our ?ndings reveal a complex patterning of species composition on the landscape that is directly in?uenced by landscape changes within and surrounding urban riparian forests.
The CCA also demonstrated that riparian canopy and under-story species composition responded to landscape
metrics
Fig.4.Canonical correspondence analysis (CCA)ordination of understory (<10cm dbh)species composition of 71plots in the Mill Creek watershed.For biplot A,codes correspond to individual plots:‘‘A”represents plots along Sharon Creek and Mill Creek and ‘‘B”represents plots located along West Fork Mill Creek.For biplot B,codes of individual species (Appendix A )show their scores as a function of the ?rst two axes.Arrow length indicates the importance of each landscape variable and its in?uence on each species.
190 D.N.Pennington et al./Biological Conservation 143(2010)182–194
(Fig.2).From these analyses,we can identify indicator species of the riparian plant community associated with urbanization(Kre-men,1992).For example,it is clear from species biplot scores that certain species are identi?ed with more or less urbanized areas.Exotic canopy species M.alba, A.platanoides,U.pumila and Pyrus ornamentalana were found at the most urbanized sites. These species are highly tolerant of urban growing conditions and appear capable of exploiting the environmental conditions associ-ated with urbanization,and could be described as urban exploit-ers(Mckinney,2002).Little research has investigated the invasiveness of M.alba,but the species’high phenotypic plasticity has been suggested as a reason for its success in highly disturbed environments(Gray,1990).A.platanoides has been documented as being highly invasive of disturbed Midwestern forests(Web-ster et al.,2005)and to negatively impact native understory regeneration(Galbraith-Kent and Handel,2008),but in our study area it is currently limited to only the very most urbanized sites. The shade-intolerant exotic species,A.altissima,is a known inva-der of open areas(Kowarik and S?umel,2007),but more rarely an invader of forests;however,this species was found at nearly all sites(Fig.3B,center),and appears to be the most invasive exotic tree species in the study area.
Early-successional native species,such as A.negundo,P.delto-ides and Salix nigra,were among the most common canopy spe-cies at urbanized sites and possibly represent urban adapters capable of tolerating disturbances associated with urbanization. Conversely,native canopy species characteristic of late-succes-sional forests such as,A.saccharum,Fagus grandifolia,Diospyros virginiana,Carya spp.,T.americana and Quercus spp.,were found at only the least urbanized sites(Fig.2),often large urban parks –indeed,the only sites having all three species present were lo-cated in a state nature preserve.Consequently,these species rep-resent possible urban avoiders that are highly intolerant to the novel interactions and a process associated with urbanization, and highlights the importance of urban remnant woodland areas and parks as havens for these species.These results are consis-tent with the large-scale studies of Moffatt et al.(2004)and Bur-ton and Samuelson(2008),who reported a dominance of exotic and pioneer species in more developed riparian areas compared to rural areas.
As stated above,understory diversity and structure were greatly in?uenced by urbanization.The CCA of the composition of under-story species revealed similar results to that of canopy species. These results provide a glimpse of what the riparian forest compo-sition could be in the future.For example,the native species that are characteristic of late-successional forests,such as Carpinus car-oliniana,Carya ovata,Fagus grandifolia,Hydrangea arborescens,Os-trya virginiana,and Quercus alba,are likely to be replaced by a combination of early-successional native species,such as C.occi-dentalis,P.deltoides,P.occidentalis,and R.pseudoacacia,and exotic species including A.altissima,U.pumila,P.ornamentalana,and M. alba.It is not clear if shifts in species composition along the urban gradient suggest a permanent shift in forest successional trajec-tory.Our?ndings indicate that many native shrubs and saplings of subcanopy and upper canopy species regenerate poorly in the moderately to highly urbanized sites.The most abundant under-story shrub,L.maackii,dominated the understory of all but the least urbanized sites,and we observed few herbaceous or other woody species growing under this species.As discussed below,this particular species could signi?cantly impact future forest structure and function.
The exotic understory species,L.maackii,is of particular inter-est because of its ubiquitous presence throughout the study area. Hutchinson and Vankat(1997)showed that cover of the invasive shrub L.maackii is correlated to canopy openness and inferred that canopy disturbance promotes invasion by this shrub in Southwest Ohio.However,Bartuszevige et al.(2006)found that landscape parameters,such as the amount of edge habitat in a 1500m buffer,predicted L.maackii density better than any other woodlot parameters.In upland forests this exotic shrub reduces native tree seedling survival(Gorchov and Trisel,2003),survival and reproduction of native annual herbs(Gould and Gorchov, 2000),growth and reproduction of perennial herbs(Miller and Gorchov,2004),and canopy tree growth increments(Hartman and McCarthy,2007).Furthermore,chronosequences indicate that L.maackii invasion reduces density and diversity of herbs and tree seedlings and saplings(Hartman and McCarthy,2008).Similar ef-fects are likely for riparian forests.The invasive tree A.altissima is also likely to negatively impact riparian plant communities,as it suppresses seedling growth of native trees through allelopathy (Gómez-Aparicio and Canham,2008).In addition,another con-tributing factor that could in?uence woody species composition is excessive browsing from the overabundance of whitetail deer (Odocoileus virginianus)in our study area,which can negatively affect the growth and survival of many shrub and trees species (Cute et al.,2004).Further research is needed to fully understand the potential importance of species invasion on the functioning of riparian systems.
Our?ndings are important because compositional and struc-tural changes in riparian plant communities by exotic species invasions could diminish the ecological functioning of these sys-tems(Hooper et al.,2005;Richardson et al.,2007).For example, exotic species have been shown to in?uence biogeochemical cy-cles in deciduous forests(Ashton et al.,2005).Chen et al.(2007) documented that invasion of exotic plants can alter ecosystem functions indirectly by in?uencing soil decomposers such as nematodes.In addition,it has been documented that the diver-sity of riparian leaf litter can in?uence decomposition rates by stream invertebrates(Lecerf et al.,2005),and the presence of exotic species leaf litter can cause cascading ecological effects that alter the composition of benthic invertebrate communities (Lecerf et al.,2007).A recent study of the invasive A.altissima showed its litter decomposes more rapidly in streams than litter of native trees,and is preferred by aquatic detritivores(Swan et al.,2008).
This research also illustrates the complex heterogeneity that ex-ists within cities,and underscores the importance of urban green-spaces,such as riparian areas,in harboring native biodiversity. Even though our study focused on a highly urbanized area,we still identi?ed relatively large fragments of diverse riparian forest.Ef-forts by land-use planners and managers should focus on limiting building,railroad and road development within and surrounding these remaining and unique riparian forests.Such efforts may help reduce the spread of exotic species whose invasions pose unknown changes to future successional trajectories.Finally,additional re-search is needed to determine the relative in?uence that can be attributed to hydrologic disturbances,past land-use legacies,and habitat fragmentation and loss on the structure and function of ur-ban riparian systems.
Cities represent what Hobbs et al.(2006)describe as‘‘novel ecosystems”that are comprised of new combinations of species that result from the direct interaction with people(Hobbs et al., 2006).These new biotic assemblages comprised of native and introduced species can signi?cantly alter important interactions and processes of ecosystem functioning(Richardson et al.,2007), and will become more important with increasing urbanization. Further research is needed to examine the provisioning of various ecosystem services by urban riparian areas.For example,several of the riparian forests we sampled represented mixtures of native and exotic species,and although altered,these forests have been shown to provide important migratory habitat for avian species(Penning-ton et al.,2008)and mitigate local?ooding(Thurston et al.,2003).
D.N.Pennington et al./Biological Conservation143(2010)182–194191
This study poses an important management and restoration ques-tion for future research:how can we manage these urban riparian ecosystems for maximizing their bene?cial aspects,while reducing their more deleterious ones?
Acknowledgements
We thank M.Carreiro,L.Frelich,S.Galatowitsch,K.Pennington, A.Primack,and G.Willeke for insightful comments and discussion on earlier drafts of this paper.We also thank A.Primack and T.Ar-bour for providing extensive geographic information system(GIS) data interpretation and other technical assistance.Mr.Arbour pro-vided the GIS land-cover data used in this study.We would also like to acknowledge assistance from The Cincinnati Park Board and The City of Cincinnati for providing key GIS data used in this study.This manuscript is based on a practicum submitted by J. Hansel in partial ful?llment of the requirements of the M.En.de-gree at Miami University.
Appendix A
Canopy and understory woody plant species found tributaries of the Mill Creek watershed in Cincinnati,Ohio.Native status is native(N)or exotic(E)in North America(Braun,1989);Strata refers to whether species was found in canopy(C)or understory (U)in this study.Moisture requirement is high(H),medium(M), low(L),or no information(NI),and were classi?ed based on Burns and Honkala(1990)and USDA-NRCS(2006).
Code Latin name Common name Native status Strata Moisture
requirement Woody plant species
ACNE Acer negundo L.Boxelder N C,U M
ACNI Acer nigrum Michx.f.Black Maple N C,U M ACPL Acer platanoides L.Norway Maple E C,U M ACRU Acer rubrum L.Red Maple N C,U H ACSAN Acer saccharinum L.Silver Maple N C,U M ACSA Acer saccharum Marshall Sugar Maple N C,U M AEGL Aesculus glabra Willd.Ohio Buckeye N C,U M AIAL Ailanthus altissima(Mill.)Swingle Tree of Heaven E C,U M ALGL Alnus glutinosa(L.)Gaertn.European Alder E C M AMFR Amorpha fruticosa L.Indigobush Amorpha N U H ASTR Asimina triloba(L.)Dunal Common Pawpaw N C,U M BENI Betula nigra L.River Birch N C H CACA Carpinus caroliniana Walter American Hornbeam N C,U M CACO Carya cordiformis(Wang.)K.Koch Bitternut Hickory N C,U M CAOV Carya ovata(Mill.)K.Koch Shagbark Hickory N C,U M CASP Catalpa speciosa(Warder ex Barney)Englem.Northern Catalpa E C,U L
CEOC Celtis occidentalis https://www.wendangku.net/doc/6f16022001.html,mon Hackberry N C,U
CECA Cercis canadensis L.Eastern Redbud N C,U L
COFL Cornus?orida L.Flowering Dogwood N C,U L
COSE Cornus sericea L.Redosier Dogwood N U
CRPH Crataegus phaenopyrum(L.f.)Medik.Washington Hawthorn N C,U M DIVI Diospyros virginiana https://www.wendangku.net/doc/6f16022001.html,mon Persimmon N C M EUAL Euonymus alatus(Thunb.)Sieb.Winged Euonymus E U M FAGR Fagus grandifolia Ehrh.American Beech N C,U M FRQU Fraxinus quadrangulata Michx.Blue Ash N C,U NI FRSP Fraxinus sp.Ash N C,U H GLTR Gleditsia triacanthos https://www.wendangku.net/doc/6f16022001.html,mon Honeylocust N C,U M GYDI Gymnocladus dioicus(L.)K.Koch Kentucky Coffeetree N C M HISY Hibiscus syriacus L.Shrub Althea E U NI HYAR Hydrangea arborescens L.Smooth Hydrangea N U M JUNI Juglans nigra L.Black Walnut N C,U H JUVI Juniperus virginiana L.Eastern Redcedar N C,U L
LIVU Ligustrum vulgare L.European Privet E U M LIST Liquidambar styraci?ua L.American Sweetgum N C M
LOMA Lonicera maackii(Rupr.)Maxim.Amur Honeysuckle E U M
MAPO Maclura pomifera(Raf.)Schneid.Osage-orange E I M MASP Malus https://www.wendangku.net/doc/6f16022001.html,l Flowering Crabapple N I M MOAL Morus alba L.White Mulberry E I L
NYSY Nyssa sylvatica Marsh.Black Tupelo N C M OSVI Ostrya virginiana(Mill.)K.Koch American Hophornbeam N I L
PIAB Picea abies(L.)Karst.Norway Spruce E C M PIPU Picea pungens Engelm.Colorado Spruce E C M PINI Pinus nigra Arn.Austrian Pine E C M PLOC Platanus occidentalis L.Sycamore N I H PODE Populus deltoides Bartr.ex Marshall Eastern Cottonwood N I H
192 D.N.Pennington et al./Biological Conservation143(2010)182–194
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Appendix A(continued)
Code Latin name Common name Native status Strata Moisture
requirement
(continued on next page) PRSE Prunus serotina Ehrh.Black Cherry N I M
PRVI Prunus virginiana https://www.wendangku.net/doc/6f16022001.html,mon Chokecherry N C M
PYCA Pyrus ornamentalana Decne.Ornamental Pear N I M
QUAL Quercus alba L.White Oak N I M
QUMA Quercus macrocarpa Michx.Burr Oak N I M
QUMU Quercus muehlenbergii Engelm.Chinkapin Oak N I M
QURU Quercus rubra L.Red Oak N I M
RHCA Rhamnus cathartica L.European Buckthorn E C NI
RHAR Rhus aromatica Ait.Fragrant Sumac N U L
RHTY Rhus typhina L.Staghorn Sumac N U L
RISP Ribes sp.Currant N U NI
ROPS Robinia pseudoacacia L.Black Locust N I M
ROMU Rosa multi?ora Thunb.Ex Murray Multi?ora Rose E U M
RUSP Rubus L.Blackberry E U L
SABA Salix babylonica L.Weeping Willow E C H
SANI Salix nigra Marsh.Black Willow N I H
TIAM Tilia americana L.American Linden N I M
ULPU Ulmus pumila L.Siberian Elm E I M
ULSP Ulmus sp.Elm N I H
VITR Viburnum opulus L.European Cranberrybush E U M
VIRH Viburnum rhytidophyllum Hemsl.Leatherleaf Viburnum E U M
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Problems_of_urbanization
Problems of urbanization Today I want to discuss problems of urbanization / in particular I want to talk about those problems which are peculiar to developing economies and to discuss three possible policies / which could be used to control or uh / to stem / uncontrolled urbanization in developing counties / Certain urban problems of course are common to both developed and developing countries / for example / poor housing, unemployment, problems connected with traffic / for example air pollution, congestion and so on / however there there are problems which are very peculiar to developing economies / and this is due to the fact that developing countries need to create a basic infrastructure / which is necessary for industrialization / and consequently for economic growth / in fact it’s the provision of this infrastructure which constitutes the urbanization process itself / and this uh infrastructure / or rather the / provision of this infrastructure / may have undesired effects on the economy as a whole / now it’s these undesirable consequences of … or effects which I’d like to deal with first / I’m going to talk about five main consequences of this uncontrolled urbanization // in the first instance there’s the problem of the migration of people from the country to the city / people living in the country often see the city as a more desirable place to live / whether they’re living in developing or developed countries / but the problem is much more serious in a developing country / because there are in fact more people who wish to migrate to the city / now the fact of people migrating to the city causes a certain depopulation of rural areas // and a second consequence / is the result / or the result of this is a decrease in the production of food / and in the supply of food to the country as a whole / this in turn can also lead to a rise in prices / because of the law of supple and demand // as a result of people moving to the city / you get a high urban population growth rate / now this isn’t not this isn’t due to only to the fact of more adults moving to the city / but can also be due to traditions of these people from the country / who perhaps from rural areas have a tradition of large families and so on / so the ci…population of the cities increases with these numerous children of large families // this leads to a fourth consequence / which is a dramatic pressure on the supply of social services in urban areas / in particular / services related to health and education / in relation / in relation to health services / we can see that there are endemic diseases which could be made worse by overcrowding / people coming from the country to the city / and for example in the stresses on services in education / with more children there’s a need for more schools and more teachers and so on and so on // a fifth area which is affected by uncontrolled urbanization is that of the labour supply / often uncontrolled urbanization leads to an excess of labour supply in the cities / and this can lead in turn to an informal kind of labour activity / which might be called low-prod…productivity activities / for example people selling things in the streets / or for example you often find in large urban areas in a developing country / children who watch cars while their owners are doing something else / and then they ask for tips when the owners return / this is really a sort of undesirable type of labour / so these are in fact the main consequences of uncontrolled urbanization / now I’d like to move on to three possible policies which could be developed / to stem this kind of uncontrolled urbanization in developing countries / the first one would be to promote a more equal land distribution / in this way farmers would be more motivated to stay on the land / they would be able to work more land and thus be
关于中国联通公司提升服务质量的对策研究剖析
中国联通分公司提升服务质量的对策研究 内容摘要：自中国21世纪加入WTO以来，国际电信运营商的即将进入，国内各大电信运营商的崛起，中国电信市场的竞争硝烟愈来愈浓。当今经济社会中，服务占有重要的地位，无论在传统的服务性行业还是制造业领域，人们都把创造增值性的服务当作竞争优势的重要手段，这种针对于服务的变革是时代的需要，是自助服务技术的广泛应用，是服务外包、业务网络化以及竞争日趋激烈的结果。越来越激烈的竟争迫使企业不能仅依赖于单纯靠生产创造出的价值。今日的顾客看重的是服务带来的增值、综合性的整体解决方案及其对服务的体验。本文为中国联通分公司面对竞争、开拓市场，从提升自身服务质量做起，赢得市场竞争等方面提供了较有力的理论依据和实践指导，具有一定的现实意义和借鉴作用。 关键词：中国联通提升服务质量对策研究
目录 内容摘要-------------------------------------------------------------1 第一章引言----------------------------------------------------------3 第二章服务质量概述--------------------------------------------------3 一、服务质量的概念-------------------------------------------------4 二、服务质量的评价方法---------------------------------------------4 1、目标顾客--------------------------------------------------------5 2、连贯性----------------------------------------------------------5 3、服务质量要素----------------------------------------------------5 3.1、功能性--------------------------------------------------------5 3.2、经济性--------------------------------------------------------5 3.3、安全性--------------------------------------------------------6 3. 4、时间性--------------------------------------------------------6 3. 5、舒适性--------------------------------------------------------6 3.6、文明性--------------------------------------------------------6 4、服务质量差距----------------------------------------------------6 三、影响服务质量的因素---------------------------------------------7 第三章中国联通海南分公司服务质量的现状分析--------------------------7 一、中国联通海南分公司概况-----------------------------------------7 二、中国联通海南分公司服务质量现状分析-----------------------------8 1、中国联通竞争优势------------------------------------------------8 2、中国联通竞争劣势-----------------------------------------------10 3、中国移动的竞争优势---------------------------------------------10 4、中国移动的竞争劣势---------------------------------------------12 三、中国联通海南分公司服务质量存在问题的原因----------------------13 第四章中国联通海南分公司提升服务质量的对策与措施-------------------13 第五章结束语-------------------------------------------------------15 参考文献------------------------------------------------------------16
小蜜蜂的作文100字
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篇四：一只小蜜蜂 上语文课的时候，嗡嗡嗡一只小蜜蜂从窗外飞了进来。只见那只小蜜蜂在倪瑜跃的头上飞来飞去，好像把倪瑜跃当成了小花一样。 倪瑜跃吓坏了，一个劲儿东躲西藏，和蜜蜂玩起了躲猫猫的游戏。他的动作引起了大家的注意。老师和同学们看到都笑了。 篇五：有趣的小蜜蜂 上课了，我们突然发现了一只小蜜蜂飞进了教室。李老师大喊一声：“看!”大家转头一瞧，发现了一只小蜜蜂在教室的窗上爬，不知它在干什么，可真有趣。我仔细地观察，发现它着急地趴在窗户上：“bzzzbzzz”的叫，我想，小蜜蜂在说：“我要飞回大自然，但我爬不出去，谁来帮帮我!”它爬了半天还是没有爬出去。最后，李老师说：“它一定能靠自己的本领爬出去的。” 不一会儿，小蜜蜂不见了，它终于爬出去了，飞回了大自然的怀抱中。 多么有趣的小蜜蜂啊! 有关小蜜蜂的作文100字 1.有关小蜜蜂的作文500字 2.有关写小蜜蜂的作文 3.有关小蜜蜂的作文 4.和小蜜蜂有关的作文 5.《小蜜蜂》作文 6.小蜜蜂的作文
Urbanization in China Policy Issues and Options
China Economic Research and Advisory Programme Urbanization in China: Policy Issues and Options1 J. Vernon Henderson Brown University and NBER 14 November 2009 1 The research assistance of Zhi Wang and Zhichao Wei is gratefully acknowledged. The help of Cai Fang, Du Yang and Wang Meiyan of CASS is gratefully acknowledged. They shared data, ideas and various background papers, which have improved the accuracy and relevance of the report. I am indebted to them but remaining errors are mine. Comments from participants in a seminar hosted by Lu Mai and CDRF on July 2009, as well as meetings with CDRC and DRC, were helpful in preparation of this draft. Ian Porter made helpful comments on a first draft. There was an original version of this report from 2007 with contributions from John Quigley and Edwin Lim. Comments on that draft by Du Yang and Gao Shiji were very helpful in preparing this report. Comments by Mike Spence, Tony Venables, Wu Jinglian, Qiu Baoxing, Lou Jiwei, Li Jiange, and Lin Zhongli in preparation of that original draft are gratefully acknowledged. Parts of that report were were based on two background papers: Managing Urban Development in Chinese Cities by Alain Bertaud, Jan K. Brueckner, and Yuming Fu and Evaluating China's Urbanization Experience and Prospects by J. Vernon Henderson.
小学语文《想象作文》教案设计之一
小学语文《想象作文》教案设计之一 小学语文《想象作文》教案设计之一 一、教学目的 1．启发学生自由地想象，培养学生的创新思维能力。 2．指导学生有序地、重点突出地、主次分明地说和写。 3．培养学生热爱学校、热爱生活、热爱科学的思想感情。 二、教学重点 启迪学生展开大胆、丰富、新奇的想象，并指导学生有序地、主次分明地说和写。 三、课前准备 1．课前学生绘制自己心目中《未来的......》构想图。 2．制作多媒体课件。 四、教学时间 二课时（第二课时为写作及讲评） 五、教学过程 第一课时 （一）导入
1．谈话：(出示课件1后)小的时候，我就曾经幻想过，如果我能够像小鸟一样，有那样一对翅膀，那该多好啊！现在你们又有怎样的想象呢？（板书：想象） 2．结合学生回答表扬“你的想象真大胆！”.“你的想象真丰富！”.“你的想象真新奇！”（教师板书：大胆.丰富.新奇） 3．小结：希望同学们能把大胆.丰富.新奇的想象，在自己的作文中体现出来。（4分钟） （二）本次作文指导经过。 1.让我们乘上宇宙飞船，穿越时空隧道，去未来看一看吧！（出示课件2）（1分钟） 2.我们还在去未来的路上，但是伟大的科学家爱因斯坦曾经说过：“想象是一切创造之源。”（出示课件3）这节课让我们用想象创设一下未来吧！同学们，今天这节课，我们就来写一写未来的......（板书：未来的......）（出示课件4）（1分钟） 1．读一下课题，你觉得可以写什么？进行讨论。（3分钟） 提示：人物、事物、军事、科技、农业、环境、体育等等。 估计可能有的题目：《未来的我》、《未来的生日》、《未来的母校》、《未来的教师》、《未来的祖国》，以及《未来的地球》、《未来的汽车》、《未来的学校》。 明确：在现实生活的基础上，随着科技发展，将来可能实现的设想或可能拥有的事物才可写。 2．我们选好了要写的题目，那么怎么来写，具体写些什么呢？ 3．学习小组进行讨论，要求：
三年级下册语文第五单元作文《奇妙的想象》
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写作素材 一、题目 《瞌睡虫多多》《小豆苗历险记》《白雪公主后传》《月亮又瘦了》 二、好词 无影无踪大摇大摆活灵活现转瞬即逝 神秘莫测窃窃私语一模一样大吃一惊 远走高飞 三、好句 开头 1.晚上，一道金光闪过，我突然发现睡在身边的妹妹变成了一个巨大的金蛋。我急坏了，怎么才能把妹妹救出来呢?把蛋砸破，可能会伤到里面的妹妹。把蛋刹开妹妹会不会变成蛋清流出来呢?我想了又想，最后决定把妹妹从蛋里孵 出来。 2.在离天河不远的地方，有三颗小星星。说来也巧，这三颗小星星是同年、同月、同日、同时生的，可它们彼此都不一样：一颗是蓝的，一颗是红的，第三颗最小，似乎没有什么颜色，只有一点儿微弱得可怜的光。 结尾 1.从此，绿森林里多了一个永久性的居民，绿森林的动物们多了一个永远的朋 友，绿森林的故事里多了一份传奇。 2.大力士风孩子回来了，呼呼吹了几口气，白烟被吹跑了，烟筒和房子被吹倒了那几个黑衣人被吹到了森林外。大树们开心地笑了。
一年级小学生作文100字(六篇)
一年级xx作文100字（六篇） 【篇一】 今天，我和爸爸妈妈去踏春，暖暖的春风吹在我的脸上，就像妈妈的手温柔地抚摸着我的脸。走着走着，我发现路两边的树干上都冒出了嫩嫩的小芽芽，成片成片的麦苗绿油油的，大地就像穿上了一件绿色的大衣，一排排麦苗排列的整整齐齐，就像小朋友们在做早操。 快看，一群小白羊在草地里，有的在吃草，有的在玩耍，还有两只小羊头抵着头在打架呢！好可爱呀！ 【篇二】 哗哗的大雨过去了，晴朗的天空又来了。天空出现了彩虹，雨后的空气比原来更清新了，雨后的花儿比原来更美丽了，雨后的草地更绿了，雨后的天空特别的蓝……雨后让我感觉到了万物变了样，比原来更美了。 我喜欢雨后！ 【篇三】 冬天像一位和蔼可亲的老奶奶，脸上总是带着幸福的微笑。她手里拿着一只大篮子，里面装满了洁白的雪花。老奶奶日夜不停地忙着给房屋、田野、大树穿上了一件件羽绒服。人们围上了围巾，穿上了厚厚的大棉袄，戴上了漂亮又可爱的帽子。小朋友都跑出来玩了：有的在打雪仗，有的在堆雪人，还有的在跟小狗一起赛跑……玩得开心 极了。 冬天，是个既好看又好玩的季节。我爱您，美丽的冬天！ 【篇四】 寒冷的冬天过去了，春姑娘悄悄的来到了我们身旁。春天在哪里呢？星期天，妈妈带我到山上找春天。一路上，我看见桃花红了，像春天的笑脸，朝着我们微笑。油菜花黄了，一阵微风吹来，花儿散发出阵阵清香，引来
了一只只勤劳的小蜜蜂它们不停地采着花粉。山涧的小溪哗哗哗的往下流，溪水清澈见底。几条小鱼在石头缝里，游来游去，好像在捉迷藏。小溪旁的柳树也发芽了，长长的柳枝垂到了溪水里，像少女的头发。 春天的景色多美呀！ 【篇五】 在回家的路上，我看见了日落。 太阳先是金黄的，慢慢的，太阳挂在了树上，真像大树结了一个大大的果实啊！一刹那，它的颜色从黄变成了红彤彤的脸，很红很红，好像见我在看她，脸刷刷地红了，说：“不要看我嘛！多不好意思啊！”阳光照在玻璃上，一闪一闪的，漂亮极了！转眼间，这害羞的小姑娘已经在山顶了，脸更红了，旁边是她扔的纱巾。短短的几十秒，她的大半边脸已经落下去，她说：“再见啊！明天见”渐渐地，她不见了，连旁边的纱巾也被她拿走了…… 【篇六】 刘老师带我们找春天，有的同学发现树枝软了，树梢绿了；有的同学发现松树长出了细小的绿针；有的同学发现向阳的地方小草发芽了……我在一棵不高的树上发现了淡粉色的圆球。刘老师告诉我那是花苞，我还会继续观察的。多么盼望花苞快点变成美丽的花瓣啊！ xx果真悄悄地回来了！我喜欢春天。 网络搜集整理，仅供参考
小学语文想象类作文的构思技巧整理
小学语文想象类作文的构思技巧整理 给文字插上想象的翅膀，想象类作文的构思技巧整理！ 学生在作文时，往往觉得没有合适的素材可写，或是不知从何想象。其实呢，不是生活中没有作文素材，而是学生缺少善于捕捉作文素材的能力。连素材都有限，自然就很难展开想象了。因此，培养学生的观察生活的能力，养成留心观察周围事物的习惯显得十分重要。 01 怎样指导孩子观察呢？ 1．观察周围尽可能看到的所有事物，捕捉典型材料。 孩子的视线往往局限于一个小圈子，觉得一些司空见惯的小事没什么可写的。其实，平常的小事也可写出新意来。要选择最佳的观察对象，安排合理的观察顺序，认真观察。2．动用多种感官，丰富写作素材。 心理学认为，观察是思维的知觉，没有思维的观察是肤浅的，不是真正的观察。观察不仅仅是看，要动用耳、口、鼻、手、脑等感官去多方面地感知或判断，获得真实、全面、深刻的印象，为作文提供丰厚的材料。3．填写观察记录，养成观察习惯。 观察不应只是一次作文之前的例行公事。还应填写观察记录（观察顺序、观察方法）。 02 如何构思 以《卖火柴的小女孩》为例题，小女孩五次擦燃火柴所看到的奇异景象是作者的想象。这些想象奇特而大胆，而读者仍然觉得合情合理。
为什么呢？因为作者亲眼目睹了穷苦孩子的悲惨遭遇，深深地理解他们的内心需求。在文章中，想象与现实有着相似的地方，那就是穷孩子对幸福生活的渴望。 作者想象小女孩在神志不清时见到了温暖的火炉，喷香的烤鹅，美丽的圣诞树，慈祥的奶奶并和奶奶一起飞走，就显得自然而合理了。 无论写哪类想象作文，我们都必须做到以现实生活为基础，想象要合理、丰富，表达要真实、具体。 03 以现实生活为基础 现实生活是我们想象的源泉，离开了现实生活，想象就如同空中楼阁，成为无本之木、无源之水，变成空想或幻想。 所以，写想象作文必须勤于观察，丰富自己的生活，积极思考，驰骋想象，创新思维，这样才能引发你进行写作的灵感，进而写出优秀的想象作文。 04 怎样做到想象合理、丰富呢 1．再现 侧重于写景状物或叙事的想象作文，可以搜寻脑海中对相关事物的印象，加以再现。2．移植 有时候，想象可以进行嫁接、移植，把优美的景色移为一处，或把有趣的现象归为一物，或把美好的品质浓缩在一人之身。即，学生可以按自己的意愿中的特定形象，结合生活实际，进行移植想象。只有善于把想象与现实生活中的事实联系起来，巧妙地设计人物之间的关系，才能使文章生动有趣。3．幻想
英语作文 城市化的利弊(Advantages and Disadvantages of Unbanization)-精品
城市化的利弊(Advantages and Disadvantages of Unbanization) urbanization has been a subject of heated discussion for a long time. some people are in favor, while others are opposed. in my opinion, urbanization has both advantages and disadvantages. generally, the advantages of urbanization can be listed as follows. first,urbanization can quicken our pace to catch up with the developed countries. we all know that the developed countries are all highly urbanized. second, urbanization will help to solve the problem of unemployment. it will create more job opportunities for the unemployed. in addition, urbanization will free a great number of farmers from the fields, thus realizing the dream of agricultural mechanization in our country. finally, urbanization can improve the standards of living of the migrants who move to the urban area. however,the disadvantages of urbanization are also obvious. to begin with,administration of the increasing population in urban area might be a great challenge to the government. moreover, more problems, such as increasing crime rate, over crowding, might increase, since more people are concentrated in a relatively smaller place. it is evident that the advantages outweigh the disadvantages. therefore, i am in favor of urbanization. 2019年12月21日
小学语文教学论文 想象作文教学浅谈
小学语文教学论文：想象作文教学浅谈 作文是语文教学的重点，也是难点，而想像作文更是难中之难，小学生大都有“恐作症”，老师也常常为此头疼不已。那么怎样才能让学生在想象作文中有内容可写，有话可说呢？我认为可以从以下几方面训练。 一、观察现实生活，激发相关想象。 想像离不开现实，离开现实的想象是空洞的，无论哪一类想象作文都脱离不了现实生活。例如童话式想象作文，它是根据小学生喜爱动物的特点，用动物代替人类的形象来表达他们对世界的认识，在想像力作用下的动物附上了人的动作、语言、神态和思维。这类作文实际上是对现实的再现。 如想像作文“未来的×××”，这一类写未来生活的想象作文对学生而言有难度。未来是什么样的，学生除了接触到一些科幻片、科幻小说以外，其他的十分抽象，不知如何写。教师可引导学生仔细观察现实生活，展开想像的翅膀。例如现在的房屋，一旦完工，它便固定下来。如果让学生大但想象，让未来的建筑由一个个组装件构成，根据不同的需要进行不同的组合，这样既适合不同人的需求，又便于搬迁、移动，还可以维修，那该多好。又如当看到学校操场只有一处，空间过于狭小时，可以引导学生想象地下或空中操场，用电梯或升降机来回启用……这些现实中人们追求的更加便捷、完美的东西，都可以大胆想象它的样子、形状、功能。如果激发了学生想象的火花，那么展现在学生面前的空间不知有多大！ 二、结合课文内容，进行再造想象。
课文是学生学习文化知识的重要材料，也是学生写作的典型范例。教师可充分利用课文资源，结合课文内容，让学生练习改写、续写、扩写等想象性作文，是一种行之有效的再造想象途径，能有效提高学生的想像能力。 例如《凡卡》一文，当凡卡满怀希望地把信寄出去后，爷爷能收到吗？爷爷在乡下会怎样想念凡卡呢？小凡卡后来的命运又会如何呢？让学生大胆去想象，续写出符合事情发展的故事，这样既加深了对课文内容的理解，又激活了学生想象的火花。 另外，还可以根据文中的插图进行补充或扩写。如《我的战友邱少云》一文在的插图，邱少云被烈火烧身时的巨大痛苦，是通过作者的心理活动侧面描写的，那么邱少云的心理感受会怎样呢？可引导学生观察他的神态、动作进行想象。 三、填补一些空白，设置整体形象。 在教学中选取一些相关的事物或词语，让学生进行整合，填补其中的空白，也是提高学生想象能力的重要手段。例如：画下几种不同的小动物，让学生按照自己的思维说出它们之间的关系，并想象出这些小动物之间会发生什么样的故事，然后进行口述表演，这样激起学生的童趣，他们的想象力就会更活跃。或者随便写下几个词语，让学生编上一段故事，用上这几个词语。这类填空白的训练，可以让学生的想象能力得到逐步提高。坚持长期训练，会收到意想不到的效果。 总之，学生作文能力的提高与教师的训练密不可分。我们应该在平时的作文教学中善动脑子，力求科学、有效，为学生作文插上想像的翅膀，让他们飞得更高、更远。
小动物作文100字_作文100字
小动物作文100字 我家的小动物陈恺曦我家里有很多可爱的小动物，你看一只小猫，它是我们人类的好朋友，帮助我们抓老鼠，它最喜欢吃鱼了。 小狗也是我们的人类的好朋友，它帮助我们看门，它最喜欢吃肉了，一看见肉啊，口水滴滴的流。而在门口草地上市小马和小牛，它们最喜欢就是吃草了，绿绿的青草是它们的最爱。这些可爱的动物都是我们的朋友，大家一起爱护它们吧。 池塘里的小动物仲梓文我在花园里的池塘里看到了两只天鹅、三只鸭子。那两只天鹅浑身长着雪白的羽毛，黑黄相见的嘴巴，黑色的脚蹼，它们游到岸上突然朝我和妈妈扑过来，掐我们，把我和妈妈吓得赶紧往上跑；它们一会又游到岸上来吃草，吃了一会后就张开翅膀，伸长了脖子，咯咯地叫，好像吃饱了要跳舞的样子。 我还发现有一只陌生的鸟飞过来，它看起来像是一只幼小的鹤吧。 我家的小动物们胡逸尧我们家有许多小动物，有兔子、狗、仓鼠、乌龟、金鱼。我们家的兔子是去年买的，买回来的时候只有我掌心这么大，现在已经有十斤了！然后是狗，狗已经听得懂命令了。还有仓鼠，今天我爸爸给它洗澡，洗完以后，它头上一点毛都翘起来了。乌龟嘛，它吃食的时候把嘴巴张的大大的，差点咬到我妈妈的手。金鱼在荷叶间游泳，有红的、黑的、白的、金的还有花的，金鱼的尾巴像剪刀一样，还有像丝带一样。 我们家的小动物可爱极了！ 我最喜欢的小动物朱俊林我最喜欢的小动物是小狗，有一次大姨送给我一只西施狗。我非常喜欢它，给它取名叫“史努比”。它有一双又黑又亮的眼睛，它的毛是三色的，尾巴翘翘的，很好看。 它给我带来了许多快乐，它不仅不吵不叫，还会照顾我不让别的小朋友欺负我。可是妈妈却把它送人了，因为妈妈怕影响到我的学习和健康，“史努比”走后我很伤心，每当我看见别人家的小狗时我就会想起它，我盼望我快点长大，再自己重新养一条和史努比一样的小狗。 小动物们的聚会解付义薄风和日丽的一天，小动物们都到池塘边来玩耍了，有长得色彩斑斓的小公鸡，有蹦蹦跳跳专为庄稼除害虫的小青蛙，还有整天飞来飞去忙忙碌碌的小蜜蜂，他们在一起谈论着，说这里的景色可真美呀！小公鸡说岸边有绿油油的青草，小青蛙说清澈见底的湖面飘着像盘子一样的荷叶，蜜蜂说到处都开着红艳艳的鲜花。 这时小公鸡说咱们也叫其他的小动物们来这里一起玩吧！大家齐声说好。然后小公鸡就喔喔喔大声的叫了起来。 我喜欢的一种小动物我家曾经养过一只小兔子，小兔子的耳朵长长的，而且小兔子的耳朵上的毛特别特别的柔软，让人摸了小兔子的耳朵就感觉特别的舒服。小兔子的耳朵里面还有一条粉色的竖线。 小兔子的头圆圆的，真像一个长满白色的毛的小皮球，小皮球可以摸，摸了之后很舒服！小兔子的眼睛是红色的，在我小的时候，我还以为小兔子的眼睛流血了。我一见小兔子我就向爷爷要一张纸，去擦小兔子的眼睛。可是小兔子跑得太快了，我连追都没有追上！。
英语学术写作作文The effects of urbanization in China
Directions:Urbanization in China The effects of urbanization in China Since the founding of new China, China's urbanization process has been accelerating. After the reform and opening up, China's urbanization process is proceeding at an unprecedented speed and will persist in the coming decades. Nowadays, China's urbanization level has entered a higher stage. Urbanization promotes the development of economy to a certain extent. However, the rapid development of urbanization has also brought many negative effects. The most prominent effect of urbanization is on livelihood issues. The acceleration of urbanization has affected people from all walks of life, especially the farmers living in the countryside. For the rural farmers, urbanization reduces the area of farmland and expel them from the original cultivated land in large quantities which will lead to a reduction in agricultural production. The decrease of grain production will cause the increase of China's grain import rate. As a result, the hidden danger of China's provision security will become a significant problem. Besides, there are many unreasonable restrictions on the peasants to work in the city, and their wages, welfare and medical care are not guaranteed which shows the poverty gap with the procession of urbanization. Such bad results brought by urbanization to farmers are not conducive to China's national development and political stability. Another area affected by urbanization is the social problems. For one thing, with the continuous development of urbanization, more and more people can afford their own vehicles, which contribute to a growing number of private cars. The roads are congested with a large number of vehicles, especially during the rush hours. For another thing, the rapid increase of migrant workers and floating population have greatly raised the urban population. Urban resources become scarce due to the population expansion. Too many people are concentrated in cities in a short time will inevitably leads to mass unemployment, shortage of fresh water and energy supply. In addition, the amount of garbage in the city increases rapidly, but the utilization rate
【部编人教版】最新版语文六年级上册-小学分类作文全攻略之怎样写好想象类作文
小学分类作文全攻略之怎样写好想象类作文未来因为不可预知而显得神秘莫测，令人神往；想象，因为未能定格而让人激情膨胀。当我们置身于高科技时代，我们其实就是在不断地享受着人类的创造之果给我们的生活带来的舒适、方便与快捷。人类社会，在想象中不断完善，在创造中走向壮大。 <一>想象 1.定义：想象是人在头脑里对已储存的表象进行加工改造形成新形象的心理过程。想象作文与平时作文中的“想象”有所不同。如写桃花，可根据桃花的形想象它像一颗颗五角星，根据它盛开的样子想象它像小姑娘绽开的笑脸，这样就可以把桃花这个事物写具体生动。以上例子只能说是平时作文中一个想象的小节，并不代表它就是想象作文，想象作文不是细节和局部情节的想象，而是整篇作文的想象。 2.想象的分类 （1）再造想象含义：根据别人的描述或图样，在头脑中形成新形象的过程。意义：使人能超越个人狭隘的经验范围和时空限制，获得更多的知识；使我们更好理解抽象的知识，使之变得具体、生动、易于掌握。 形成正确再造想象的基本条件：一是能正确理解词与符号、图样标志的意义；二是有丰富的表象储备。 （2）创造想象含义：不根据现成的描述，而在大脑中独立地产生新形象的过程。创造想象的特殊形式——幻想：与个人生活愿望相联系并指向未来的想象。两个特点：体现了个人的憧憬或寄托，不与当前的行动直接联系而指向于未来。具有积极意义：积极的幻想是创造力实现的必要条件，是科学预见的一部分；是激励人们创造的重要精神力量；是个人和社会存在与发展的精神支柱。 <二>想象类作文的分类： 【1】童话 童话写作时，首先要有一定的故事情节，在设计情节时不要太复杂，可采用拟人的手法，把物当做人来写，让物具有人的思想感情。其次要充分发挥想象，把生活中本质的事物，通过想象编成趣味性的故事，展现在读者面前。再次要注意想象与现实生活的联系。现实生活时想象的基础，通过艺术加工后，表达一种
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