Accepted Manuscript

Title: Species diversity of urban forests in China

Authors: Pengbo Yan, Jun Yang

PII: S1618-8667(17)30225-X
DOI: http://dx.doi.org/10.1016/j.ufug.2017.09.005
Reference: UFUG 25977

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Received date: 14-4-2017

Revised date: 7-9-2017
Accepted date: 12-9-2017

Please cite this article as: Yan, Pengbo, Yang, Jun, Species diversity
of urban forests in China.Urban Forestry and Urban Greening
http://dx.doi.org/10.1016/j.ufug.2017.09.005

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 Species diversity of urban forests in China

Pengbo YAN1, Jun YANG2,3*

1. College of Forestry, Beijing Forestry University, Beijing, 100083, China

2. Ministry of Education Key Laboratory for Earth System Modeling, Department of

Earth System Science, Tsinghua University, Beijing, China, 100084

3. Joint Center for Global Change Studies (JCGCS), Beijing 100875, China

*Contact information for the corresponding author

Dr. Jun Yang

Mailing address:

S721 Mong Man Wai Science Building, Tsinghua University

Haidian District, Beijing, China 100084

Tel: +86 10 62786859

Fax: +86 10 62797284

E-mail: larix001@gmail.com

Highlights
 A total of 2,640 woody plant species were found in urban forests in China
 These species consisted of 1,671 trees, 743 shrubs, and 226 lianas
 About 23.98% of all woody plant species are exotic species
 There was a latitudinal pattern in compositional similarity of urban forests

Abstract

A good knowledge of species diversity is essential for urban forest planning and

management. In this study, we analyzed species diversity of urban forests in China using

data synthesized through a systematic review. Our analysis showed that 3,740 taxa of

1
woody plants at species level and below have been reported in urban forests in 257

cities. Merging to the species level, there were 2,640 species, including 1,671 trees, 743

shrubs, and 226 lianas. Salix babylonica L. was the most widely distributed urban tree

species in China. Overall, native species accounted for 76.02% of the observed species

while the rest were exotic species. Inside cities, parks contained more species than

other types of land use. Among cities, composition similarity of urban forests decreased

as spatial distances among them increased. Besides, there was a latitudinal pattern in

compositional similarity of urban forests in China. The relatively low ratio of the number

of woody plant species in urban forests to these naturally distributed in China indicates

that there is plenty of room for increasing species diversity of urban forests in China.

However, cautions must be taken to avoid increasing compositional similarity of urban

forests in China at the same time.

Keywords: Woody plants; land use; species composition; dissimilarity; spatial distance

Introduction

The species diversity–the number of different species in an area–of an urban forest is a

key component of urban biodiversity. On the one hand, many rare species and even

endangered species grow in urban forests (Alvey, 2006; Jim and Chen, 2008). On the

other hand, alien species are frequently introduced into urban forests through planting

and managing activities, which may replace native species and cause the loss of local

biodiversity (Gaggini et al., 2017; Moro and Castro, 2015). Species diversity is also

important for the resilience of urban forests. Diversity can provide urban forests with

2
protection from impacts of pests and diseases, climate changes, and other unfavorable

environmental conditions (Kendal et al., 2014). Furthermore, studies have shown that

there is a linkage between species diversity of urban forests and their supply of

ecosystem services (Dallimer et al., 2012; Nowak et al., 2016). An urban forest with high

species diversity can provide multiple ecosystem services sustainably (Escobedo et al.,

2015).

Due to its importance, species diversity of urban forests in different cities has

been studied extensively (Jim and Liu, 2001; Kendal et al., 2012b; Sudha and

Ravindranath, 2000). These studies produced information that are important for

understanding patterns of species diversity of urban forests and the underlying

mechanism that shape these patterns. Nevertheless, studies at a single city level are less

conductive for reaching generalizations that are necessary for informing practitioners

beyond the studied cities. This led to the call for more studies that include multiple

cities, regions, and countries (McDonnell and Hahs, 2013). In recent years, there is a

steady increase in the number of studies covering multiple cities and regions (Avolio et

al., 2015; Blood et al., 2016; Kendal et al., 2014; Kirkpatrick et al., 2011; Nowak, 2012;

Sæbø et al., 2005; Sjöman et al., 2012). In North America, species compositions of

planted tree populations in 14 cities in the United States and Canada were analyzed

(Nowak, 2012). In Europe, a survey of tree diversity in 10 Nordic cities found that

species belonging to genera Tilia, Acer, Betula, and Sorbus added up to 58.3% of the

total tree stock (Sjöman et al., 2012). At the global scale, using data from 108 cities,

Kendal et al. (2014) found that the relative abundance of the most common tree species

3
and genus was higher in streetscapes and gardens and in cities with continental

climates. Another study found that compositional similarity of urban forests among 38

cities was scale-dependent, i.e., the similarity diminished as the scale of study increasing

from local to global (Yang et al., 2015).

While the number of cross-city studies is increasing, there is an obvious

geographic bias. Most works were carried out in North America and Europe. China is

seriously underrepresented in literature on this topic. In the last two decades, studies

on species diversity of a single urban forest have increased quickly in China (He et al.,

2016; Jim and Liu, 2001; Song et al., 2011; Xiao et al., 2016; Yang et al., 2005; Zhang et

al., 2016; Zhang and Jim, 2014). However, studies include urban forests in more than

two cities in China are still difficult to find, not to mention studies at the regional

(Regions are defined by geographical, political, physiographic, or climatic factors, e.g.,

North China and Qinghai-Tibet Plateau) and national levels. Only in recently researchers

start to pay more attention to species diversity of urban forests at the regional scale

(Qian et al., 2016; Wang et al., 2014). The lack of cross-city studies becomes a hurdle for

better understanding of species diversity of urban forests in China. It also impedes the

effort to reach generalizations in urban forestry since China has a large share of

populous cities in the world. In 2017, globally there are 1,040 urban area with a

population 500,000 and over and 247 of them are located in China (Demographia,

2017).

In this study, we conducted an analysis on species diversity of urban forests in

China at the national scale. Specifically, we wanted to achieve the following objectives:

4
(1) to assess plant species richness and diversity of urban forests, and (2) to determine

differences in woody plants composition in urban forests, based on specific traits, and

(3) to provide potential indications useful for improving species diversity of urban

forests.

Methods

Data collection

We conducted a systematic literature review by following the PRISMA statement for

reporting systematic reviews and meta-analyses of studies (Liberati et al., 2009). We

first run a systematic literature search using both international (Google Scholar, Scopus,

and the Web of Science) and domestic (China National Knowledge Infrastructure,

Wanfang Data, and China Science and Technology Journal Database) literature

databases. The following keyword search was used:

(Urban or city) and (tree or woody plant or vegetation or forest) and (species or

diversity).

We included all woody plant species in urban areas in our search because urban

forest is defined as the sum of all woody and associated vegetation in and around dense

human settlements (Miller, 1988).

We performed the initial screening of the retrieved publications based on their

titles and abstracts. Then a more detailed review was conducted to exclude publications

that could not meet the following selection criteria: (1) species lists contained in

5
publications must be based on data collected from field surveys, and (2) the survey must

be conducted at citywide, not at a single site, e.g., a park. Species lists were then

extracted from the selected publications and merged into a database for further

analysis. We excluded records containing species from botanic gardens because they

would bias the study. Besides data extracted out from literature sources, we also

included data collected through field surveys. These data were collected by us and

colleagues between 1998 and 2012 following the protocol specified in the UFORE Field

Data Collection Manual (Nowak et al., 2003).

Data analysis

We looked up the traits of all recorded taxa, including species and these below the

species level such as cultivars and subspecies from Dirr’s Encyclopedia of Trees and

Shrubs (Dirr, 2011) and online databases (Table 1).

We merged all records to the species level and verified names of species against the

Plant List (www.theplantlist.org). The merge allowed us to make comparisons among all

cities because not all cities reported taxonomic information below the species level. We

summarized occurrences of species, genus, and families in all cities. In order to find out

how species diversity of urban forests compares to species diversity of woody plants

naturally distributed in China, we compared our data with records in Atlas of Woody

Plants in China (Fang et al., 2011).

Occurrences of species by types of land use were recorded in some publications. So

we summarized occurrences of species in six types of land use, including streets, parks,

6
residential areas, commercial areas, institution lands, and open lands (i.e., Non-built-up

land with no, or insignificant vegetation cover) using these publications. This allowed us

to look into the distribution of species at the sub-city level.

We compared compositional similarity between urban forests using Simpson

dissimilarity index 𝛽𝑆𝐼𝑀 , which is calculated as:

𝑀𝑖𝑛(𝑏,𝑐)
𝛽𝑆𝐼𝑀 = 𝑀𝑖𝑛(𝑏,𝑐)+𝑎 (1)

Where a is the number of species shared by two urban forests, b and c are numbers

of species that are unique to each urban forest, respectively. Min is a logical function,

which returns the smaller value between b and c. Values of 𝛽𝑆𝐼𝑀 range between zero

and one, with higher value indicating higher dissimilarity of species compositions

between two urban forests.

We excluded cities where less than 30 species were recorded in their urban forests

to reduce the influence of incomplete lists of species on comparison. We used 30 as the

threshold value because the northernmost city― Heihe (50.24N, 127.47E) and the city

with the highest elevation―Lhasa (3,605 m above the sea level) included in this study

reported 34 and 31 species, respectively. We assumed that the number of woody plant

species in an urban forest in China should be no less than 30.

Based on values of Simpson dissimilarity index, we classified urban forests into

groups using the Ward hierarchical clustering method. The matrix of dissimilarities (i.e.,

Simpson dissimilarity index between any pair of urban forests) was used as input for

7
clustering. The dendrogram was cut into groups by referring to Silhouette plots. We

chose the number of groups that has the highest value of Silhouette coefficient.

We conducted a Mantel test to test whether there is a spatial decay of species

compositional similarity among urban forests, i.e., species compositional similarity of

two urban forests decreases as the spatial distance between them increases. The matrix

of dissimilarities was compared with the matrix of spatial distances (i.e., spatial

distances between any pair of urban forests). Statistics of Mantel test include a

correlation coefficient and the significance level. When the correlation is significant, a

higher value of correlation coefficient indicates stronger association between spatial

distances and species composition similarity of urban forests.

We further explored how variation in species composition of different urban forests

were affected by climate, human population size, and geographic locations (latitude and

longitude) by using distance-based redundancy analysis (db-RDA). We obtained six

bioclimatic variables from WorldClim (Hijmans et al., 2005), including mean annual

temperature, mean coldest monthly temperature, temperature seasonality, mean

annual precipitation, precipitation of driest month, and seasonality of precipitation. We

conducted a principle component analysis (PCA) to reduce the collinearity between the

bioclimatic variables. Population of each city was obtained from the China City

Statistical Yearbook 2016 (National Bureau of Statistics, 2016).

All data analysis was carried out using R (version 3.3.1,). The Simpson dissimilarity

index was calculated using Vegan package. Spatial distances between urban forests

8
were calculated using Field package. The clustering analysis was conducted using cluster

package. The Vegan package was also used to conduct the mantel test and the db-RDA

analysis.

Results

Result of the systematic literature search

The systematic literature search resulted in 66,450 publications initially. Judging from

titles and abstracts, we kept 2,380 publications for detailed review. Among them, 1,018

publications met the selection criteria. Through further examination, we removed 44

publications that included botanic gardens in surveys. At the end, 954 publications were

kept in the analysis. These publications were published between 1979 and 2015, with

the majority published after 2003. Among them, 716 publications contained

occurrences of species by types of land use.

We extracted out 954 taxon lists for 257 Chinese cities from these publications.

Combined with survey data, we obtained 71,239 records of occurrences of woody plant

species in total (see supplementary material Table S1 for a list of cities and Table S2 for

a list of species). Our compiled data gave a good representation of species diversity of

urban forests in China. The number of cities covered in our study account for 39.2% of

total number of cities in China.

Overall species diversity of urban forests in China

9
The compiled data contained 3,738 taxa of woody plants. After merging to the species

level, there were 2,640 species, which belong to 745 genera and 155 families. The

numbers of families and genera of tree species found in urban forests in China were

more than these naturally distributed in China (Table 2). Nevertheless, the total number

of species reported in 257 cities was only 23.14% of these distributed naturally in China.

The ratio of the number of species in urban forests to the number of species naturally

distributed in China was 0.53 for tree species and 0.10 for shrub species.

Table 2 Numbers of families, genera, and species of woody plants in urban forests and
these distributed naturally in China (Fang et al., 2011)
Family Genus Species
Growth habit
Urban Nature Urban Nature Urban Nature
Tree 122 104 529 493 1,671 3,165
Shrub 82 135 251 796 743 7,205
Lianas 45 46 96 152 226 1,035

Around 26.55% of species came from five families (Table 3). It was less

concentrated at the genus level. The top five genera only contained 9.54% of all species.

Table 3 Numbers of species in the top five families and genera and their percentages to
the total
Rank Family Genus
Name Number % Name Number %
1 Rosaceae 274 10.38 Magnolia 56 2.12
2 Leguminosae 187 7.08 Prunus 51 1.93
3 Salicaceae 85 3.22 Rhododendron 50 1.89
4 Oleaceae 79 2.99 Acer 48 1.82
5 Arecaceae 76 2.88 Ficus 47 1.78

Some families, genera, and species were widely distributed (Supplementary

table S3). For example, the top three widespread species–Salix babylonica L., Juniperus

10
chinensis L., and Prunus cerasifera Ehrh.–occurred in more than 75% of studied cities.

The genus Prunus appeared in more than 90% of studied cities.

There were 210 cities where more than 30 woody plant species were reported

for their urban forests. The median number of tree species reported in 210 cities was

85. The median number of tree species reported in 210 cities was only 2.69% of the

total number of tree species naturally distributed in China. At the individual city level,

the urban forest in Xi’an had 627 woody plant species, which was the largest number of

species reported in all cities (Fig. 1a). The median proportion of exotic woody plant

species in urban areas was 20.69%. A few cities had higher percentages of exotic species

(Fig.1b). For example, proportion of exotic species in Guangzhou was 51.26%.

Figure 1 The number of woody plant species and their origins found in 210 cites. (a)

Numbers of trees, shrubs, lianas, and all woody plants (All) in cities, (b) percentages of

native and exotic species in each urban forest

11
Distribution of species in different land use

Parks had more woody plant species than other types of land uses while commercial

lands had the least number of species. Parks also had the largest number of exotic

species (Fig.2).

Figure 2 Total number of woody plant species found in different types of land use by

origins

While the total number of species reported in different types of land use varied

significantly, the most frequent species in different types of land use were quite similar

(supplementary table S4). S. babylonica, J. chinensis, P. cerasifera, and Ginkgo biloba L.

appeared frequently in different types of land use. The most frequent species in open

lands were slightly different from other types of land use. Two ruderal species Robinia

pseudoacacia L. and Broussonetia papyrifera (L.) L'Hér. ex Vent. were frequently

reported in this land use.

12
Traits of urban woody plants

There were 633 exotic woody plant species. Most exotic species are originated from

Paearctic, Nearctic, and Neotropic (Table 4).

Table 4 Origins of exotic woody plant species in urban forests in China

Origin Number of exotic species % of all exotic species
Palearctic 173 27.33
Nearctic 125 19.75
Neotropic 171 27.01
Indo-Malay 99 15.64
Australasia 79 12.48
Afrotropic 69 10.9
Oceania 15 2.37

Urban forests in China were dominated by broadleaf species (Table 5). There

were also more tree species than shrub and lianas. The number of evergreen species

was roughly the same as the number of deciduous species.

Table 5 Leaf persistence, origin, and leaf forms of woody plant species in urban forests
in China
Leaf form
Leaf persistance/origin Broadleaf Conifer
Tree Shrub Lianas Tree Shrub Lianas
Exotic 223 82 26 48 1 0
Evergreen
Native 534 228 101 84 3 0
Exotic 183 56 11 3 0 0
Deciduous
Native 589 373 88 7 0 0

Compositional similarity of urban forests

Based on values of Simpson dissimilarity index, urban forests in 210 cities could be

classified into six groups (Fig.3).

13
 The result of Mantel test showed that there was a strong spatial decay effect (r =

0.56, P-value = 9.9×10-5). The positive correlation value indicated that as the spatial

distance between cities increased, species compositions of urban forests in cities

became more dissimilar.

Figure 3. Groups of urban forests in China based on their values of Simpson dissimilarity

index.

The first two principle components of the PCA, accounting for 91% of total

variance in the six bioclimatic variables, were retained for subsequent analysis. PC1

14
represented a north-south gradient of temperature and precipitation and PC2

represented an east-west gradient of precipitation. The result of db-RDA showed that

together the five variables could explain about 41% of variation in species composition

among urban forests (Adjusted R2=0.41). Latitude and PC1 had more impacts on

variation of species composition than other variables while population had the least

impact (Fig.4).

Figure 4 Correlation triplots based on db-RDA depicting the relationship between the

selected geographic, climatic, and anthropogenic variables and the variation of species

composition among different urban forests. Lat = latitude; Long = longitude; Pop =

population.

Discussion

15
Patterns of species diversity in China’s urban forests

Our study has revealed several distinctive patterns of species diversity of urban forests

in China.

First, tree species were more abundant than shrub species in urban forests in

China. This pattern may be partially explained by urban greening practices in China.

Many Chinese cities favor trees over shrubs in urban greening. For example, Chengdu

requires that tree species should cover 70% of areas of greenspaces (Municipal Bureau

of Forestry and Landscape of Chengdu, 2003). Beihai requires that the ratio of tree

species to shrub species should be 7 to 3 (Municipal Bureau of Housing and Urban

Construction of Beihai, 2011).

Secondly, there was a significant proportion of exotic species in urban forests in

China. Aronson et al. (2014) viewed the significant proportion of exotic plants a threat

to global biodiversity after analyzing vascular plants in 110 cities worldwide. China

should have the same worry. Another notifiable finding was more families and genera of

trees were found in urban forests than those distributed naturally in China. This

indicates that many exotic tree species have been first introduced into cities in China

from other parts of the world.

Third, parks and institutional lands had higher species richness than other types

of land use. This pattern has also been observed in cities around the globe (Celesti-

Grapow et al., 2006; Jim and Chen, 2008; Nielsen et al., 2014). Parks tend to have high

species richness because of people’s planting efforts as well as the diversity of habitats

16
and microhabitat heterogeneity contained in urban parks (Nielsen et al., 2014).

Institutional lands in China such as schools and government agencies are often well

planted and gated. The greening efforts in institutional lands are generally more intense

than residential areas due to the attention to good images (Jim and Liu, 2001).

Fourth, although species richness in different types of land use varied, the most

frequent woody plant species in different types of land use were largely the same

except for open lands. This reflected the wide use of few common species in urban

greening in China (Wang et al., 2014). The exception of open lands is due to their status

as a type of land use in transition, so they are managed less intensively by human.

Ruderal species often grow spontaneously on open lands.

There were two obvious spatial patterns of species compositions of urban

forests in China: (1) there was a clear spatial decay effect, which was supported by the

result of Mantel test, and (2) there was a latitudinal pattern–compositional similarity of

urban forests at the same latitude tended to be more similar (Fig.3). This pattern was

supported by the result of db-RDA, which showed that latitude had a strong impact on

variation in species compositions among urban forests. Other than latitude,

temperature and precipitation (represented by PC1) had strong effects on variation in

species compositions too while population had the least impact. These patterns

indicated that at the national scale, species compositions of urban forests in China are

still largely constrained by ecological factors including climate and geography. This

discovery is in accordance with findings in Europe and North America (La Sorte et al.,

2014; Winter et al., 2010).

17
 However, there were also some exceptions. For example, the red dot that was

far from other red dots in the group six represented Lhasa (Fig.3), which was classified

into the same group as Beijing even the two cities were 2,500 km apart. This gave a

good example that anthropogenic forces could override the influence of ecological

factors on species diversity of urban forests under certain circumstances. Because the

main vegetation type in Lhasa area is Alpine steppe and scrubs, where diversity of

woody plants is low, the contribution of the natural species pool to its urban forest was

low. It was found that 20 out of the 24 street tree species planted in Lhasa are

extralimital and exotic species and are widely planted in Beijing too. Only four species

are local native species (Yang et al., 2012).

Comparing with other regions

Some comparison can be made between urban forests in China and urban forests in

other parts of world. In terms of total number of species, the 1,671 tree species

recorded in urban forests in China were more than the 1,360 taxa of trees reported in

urban sites in the United Kingdom while the later might include taxa below the species

level (Johnson, 2005). This is the only number on tree diversity at the national level

which we could found.

In terms of species composition, the similarity between urban forests in china

and these in other parts of the world was low. In 10 Nordic cities, Acer, Tilia, Betula, and

Sorbus were dominant genera (Sjöman et al., 2012). Only Acer made to the sixth place

of the top 10 most frequent genera in China. Species such as Acer platanoides L.,

18
Platanus× acerifolia (Aiton) Willd., Quercus robur L. and Betula pendula Roth were

common in cities in the UK, the U.S., and Australia (Kendal et al., 2012a) but all did not

make to the top 10 list of China. The low similarity attested to the finding that people do

not cultivate the same plants in urban areas around the world (Kendal et al., 2012a).

Furthermore, the low similarity attested to the finding that urban biotas have not yet

become taxonomically homogenized at the global scale (Aronson et al., 2014; Yang et

al., 2015).

Implications for urban forest management

Our results clearly show that there is plenty of room to increase species diversity of

urban forests in China. Blood et al (2016) reported that the number of tree species

found in eight urban forests in the U.S. ranged between 63 and 124, which were 9.26%

and 18.24% of the total number of tree species (about 680) naturally distributed in

North America (Wang et al., 2009). Compare to cities in the U.S., cities in China had a

much lower ratio when comparing number of tree species in urban forests to that of

naturally distributed tree species. The abundant natural resource provides excellent

opportunities for urban foresters in China to select and test species and use them to

increase species diversity of urban forests in China.

There is a need to increase the use of shrub species in urban forests in China.

The number of shrub species used in cities was much lower than the number of tree

species (Fig.1a). At the same time, there are more naturally distributed shrub species

than naturally distributed tree species in China, which allows for increasing the use of

19
shrub species. Currently a single tree layer or a two-layer structure of trees plus lawns

are common in urban forests in China, which has already been shown to have lower

ecosystem services and biodiversity than urban forests with more complicated structure

(Sandström et al., 2006; Schmitt-Harsh et al., 2013). At the same time, the use of woody

liana species can be increased, which cannot only improve the structural complexity of

urban forests by adding interlayer plants but also can be very useful in vertical greening.

Finally, attentions should be paid to maintain the compositional dissimilarity of

urban forests in China. At the national scale, compositional dissimilarities among urban

forests in different regions were still high. However, there were already examples such

as Lhasa, whose urban forest has similar species composition as an urban forest

thousand kilometers away. Furthermore, several species like S. babylonica and J.

chinensis were widely distributed in urban forests in China. Although these species are

native species in China, they are extralimital species in certain regions. Their wide use

can potentially displace local native species and lead to similar species compositions

among urban forests. Therefore, urban foresters in China should not only increase

richness of native species of individual urban forest but also work to maintain the

compositional dissimilarity of urban forests.

Limitations of the current study

While our study provides the first-ever description of species diversity of urban forests

at the national scale in China, there are limitations that should be kept in mind when

using data and findings from this study. First, our findings are mainly based on species

20
richness. We could only get abundance data of species for nine urban forests so we

focused on species richness but not their abundances. The data limitation prevented us

from giving a more complete picture of species diversity of urban forests in China.

Secondly, a portion of studies (394 out of 954) did not present complete lists of species

founded in studied cities. Although we compiled the list of species for each city using

multiple literature sources and removed cities with less than 30 species when making

comparisons, bias could not be removed entirely. Despite these limitations, we feel

confident that the main pattern of species diversity of urban forests in China has been

revealed by our study since abundant species in urban forests are more likely to be

identified and reported in literature.

Conclusions

A better understanding of patterns of species diversity of urban forests and the forces

that shaping those patterns is needed for improving planning and management of urban

forests. Without cross-city studies, it is difficult to achieve this goal. In this study, we

analyzed species diversity of urban forests in China at the national scale by using data

compiled from 257 cities. We identified 3,740 taxa of woody plants–2,640 species when

merged to the species level. While species diversity of urban forests in China was

relatively high comparing to other countries, there is a great potential for improvement.

Utilization of species that are naturally distributed in China after careful planting trials

can help to realize that potential. Findings from this study can contribute to a better

understanding of species diversity of urban forests in China and improved planning and

management. Nevertheless, the data availability limited our ability to give a full picture

21
of species diversity of urban forests in China, e.g., dominance of specific species. In the

future, more cross-city studies based on species abundance information are urgently

needed.

Acknowledgements

We want to thank people who helped us in field surveys. We also want to thank Dr. Joe

McBride from University of California, Berkeley for generously sharing his data with us.

Manuscript feedback from the editors and two anonymous referees was much

appreciated. This research was supported by the National Natural Science Foundation of

China (grant number 31570458, 2016).

22
References

Alvey, A.A., 2006. Promoting and preserving biodiversity in the urban forest. Urban Forestry &
Urban Greening 5, 195-201.

Aronson, M.F.J., Sorte, F.A.L., Nilon, C.H., Katti, M., Goddard, M.A., Lepczyk, C.A., Warren, P.S.,
Williams, N.S.G., Cilliers, S., Clarkson, B., Dobbs, C., Dolan, R., Hedblom, M., Klotz, S., Kooijmans,
J.L., Kühn, I., MacGregor-Fors, I., McDonnell, M., Mörtberg, U., Pyšek, P., Siebert, S., Sushinsky,
J., Werner, P., Winter, M., 2014. A global analysis of the impacts of urbanization on bird and
plant diversity reveals key anthropogenic drivers. Proceedings of the Royal Society B: Biological
Sciences 281, 20133330.

Avolio, M.L., Pataki, D.E., Gillespie, T.W., Jenerette, G.D., McCarthy, H.R., Pincetl, S., Clarke, L.W.,
2015. Tree diversity in southern California's urban forest: the interacting roles of social and
environmental variables. Frontiers in Ecology and Evolution 3, art. 73.

Blood, A., Starr, G., Escobedo, F., Chappelka, A., Staudhammer, C.L., 2016. How Do Urban
Forests Compare? Tree Diversity in Urban and Periurban Forests of the Southeastern US. Forests
7, 120.

Celesti-Grapow, L., Pysek, P., Jarosík, V., Blasi, C., 2006. Determinants of native and alien species
richness in the urban flora of Rome. Diversity and Distributions 12, 490-501.

Dallimer, M., Irvine, K.N., Skinner, A.M.J., Davies, Z.G., Rouquette, J.R., Maltby, L.L., Warren,
P.H., Armsworth, P.R., Gaston, K.J., 2012. Biodiversity and the feel-good factor: understanding
associations between self-reported human well-being and species richness. BioScience 62, 47-
55.

Demographia. 2017. World Urban Areas, 13th Annual Edition. Retrived August, 2017 from
http://demographia.com/db-worldua.pdf

Dirr, M. 2011. Dirr’s Encyclopedia of trees and Shrubs. Firs Edition. Timber Press, Portland, USA.

Escobedo, F.J., Clerici, N., Staudhammer, C.L., Corzo, G.T., 2015. Socio-ecological dynamics and
inequality in Bogotá, Colombia's public urban forests and their ecosystem services. Urban
Forestry & Urban Greening 14, 1040-1053.

Fang, J., Wang, Z., Tang, Z., 2011. Atlas of woody plants in China: distribution and climate. Higher
Education Press,Beijing, China.

Gaggini, L., Rusterholz, H.-P., Baur, B., 2017. Settlements as a source for the spread of non-
native plants into Central European suburban forests. Acta Oecologica 79, 18-25.

23
He, R., Yang, J., Song, X., 2016. Quantifying the impact of different ways to delimit study areas
on the assessment of species diversity of an urban forest. Forests 7, 42.

Hijmans, R.J., Cameron, S.E., Parra, J.L., Jones, P.G. & Jarvis, A. 2005. Very high resolution
interpolated climate surfaces for global land areas. International Journal of Climatology, 25,
1965–1978.

Jim, C.Y., Chen, W.Y., 2008. Pattern and divergence of tree communities in Taipei's main urban
green spaces. Landscape and Urban Planning 84, 312-323.

Jim, C.Y., Liu, H.T., 2001. Species diversity of three major urban forest types in Guangzhou City,
China. Forest Ecology and Management 146, 99-114.

Johnson, O., 2005. A study of biodiversity in UK urban tree populations. Arboricultural Journal
29, 55-62.

Kendal, D., Dobbs, C., Lohr, V.I., 2014. Global patterns of diversity in the urban forest: Is there
evidence to support the 10/20/30 rule? Urban Forestry & Urban Greening 13, 411-417.

Kendal, D., Williams, N.S.G., Williams, K.J.H., 2012a. A cultivated environment: exploring the
global distribution of plants in gardens, parks and streetscapes. Urban Ecosystems 15, 637-652.

Kendal, D., Williams, N.S.G., Williams, K.J.H., 2012b. Drivers of diversity and tree cover in
gardens, parks and streetscapes in an Australian city. Urban Forestry & Urban Greening 11, 257-
265.

Kirkpatrick, J.B., Daniels, G.D., Davison, A., 2011. Temporal and spatial variation in garden and
street trees in six eastern Australian cities. Landscape and Urban Planning 101, 244-252.

La Sorte, F.A., Aronson, M.F.J., Williams, N.S.G., Celesti-Grapow, L., Cilliers, S., Clarkson, B.D.,
Dolan, R.W., Hipp, A., Klotz, S., Kühn, I., Pyšek, P., Siebert, S., Winter, M., 2014. Beta diversity of
urban floras among European and non-European cities. Global Ecology and Biogeography 23,
769-779.

Liberati, A., Altman, D.G., Tetzlaff, J., Mulrow, C., Gøtzsche, P.C., Ioannidis, J.P.A., Clarke, M.,
Devereaux, P.J., Kleijnen, J., Moher, D., 2009. The PRISMA statement for reporting systematic
reviews and meta-analyses of studies that evaluate health care interventions: explanation and
elaboration. PLoS Medicine 6, e1000100.

McDonnell, M.J., Hahs, A.K., 2013. The future of urban biodiversity research: Moving beyond the
'low-hanging fruit'. Urban Ecosystems 16, 397-409.

Miller, R.W., 1988. Urban Forestry: Planning and Managing Urban Greenspaces. In: Miller, R.W.
(Eds.), Prentice Hall, New Jersey.

Moro, M.F., Castro, A.S.F., 2015. A check list of plant species in the urban forestry of Fortaleza,
Brazil: where are the native species in the country of megadiversity? Urban Ecosystems 18, 47-
71.

24
Municipal Bureau of Forestry and Landscape of Chengdu, 2003. Planning of the urban green
space system in Chengdu (2003-2020). Chengdu, China.
Municipal Bureau of Housing and Urban Construction of Beihai, 2011. Urban Green Space
System Planning of Beihai City in Guangxi Zhuang Autonomous Region (2010-2025). Beihai,
China.

National Bureau of Statistics, 2016. China City Statistical Yearbook 2016. National Bureau of
Statistics of the People's Republic of China Beijing, China.

Nielsen, A.B., Bosch, M.v.d., Maruthaveeran, S., Bosch, C.K.v.d., 2014. Species richness in urban
parks and its drivers: A review of empirical evidence. Urban Ecosystems 17, 305-327.

Nowak, D.J., Crane, D.E., Stevens, J.C., Hoehn, R.E., 2003. The urban forest effects (UFORE)
model: field data collection manual. V1b. Newtown Square, PA: US Department of Agriculture,
Forest Service, Northeastern Research Station. Retrived July, 2003 from
http://www.magicoflandscape.com/Research/UFORE-Field_Data_Collection_Manual.pdf

Nowak, D.J., 2012. Contrasting natural regeneration and tree planting in fourteen North
American cities. Urban Forestry & Urban Greening 11, 374-382.

Nowak, D.J., Hoehn, R.E., Bodine, A.R., Greenfield, E.J., O'Neil-Dunne, J., 2016. Urban forest
structure, ecosystem services and change in Syracuse, NY. Urban Ecosystems 19, 1455-1477.

Qian, S., Qi, M., Huang, L., Zhao, L., Lin, D., Yang, Y., 2016. Biotic homogenization of China’s
urban greening: a meta-analysis on woody species. Urban Forestry & Urban Greening 18, 25-33.

Sæbø, A., Borzan, Ž., Ducatillion, C., Hatzistathis, A., Lagerström, T., Supuka, J., García-
Valdecantos, J.L., Rego, F., Slycken, J.V., 2005. The selection of plant materials for street trees,
park trees and urban woodland. In: Konijnendijk, C., Nilsson, K., Randrup, T., Schipperijn, J.
(Eds.), Urban forests and trees. Springer, pp. 257-280.

Sandström, U.G., Angelstam, P. and Mikusiński, G., 2006. Ecological diversity of birds in relation
to the structure of urban green space. Landscape and urban planning, 77, 39-53.

Schmitt-Harsh, M., Mincey, S.K., Patterson, M., Fischer, B.C. and Evans, T.P., 2013. Private
residential urban forest structure and carbon storage in a moderate-sized urban area in the
Midwest, United States. Urban forestry & urban greening, 12, 454-463.

Sjöman, H., Östberg, J., Bühler, O., 2012. Diversity and distribution of the urban tree population
in ten major Nordic cities. Urban Forestry & Urban Greening 11, 31-39.

Song, Y., Hao, R., Shi, Z., Yu, S., 2011. Heterogeneity and pattern of tree in Shenzhen special
economic zone's urban forest, China, 2011 International Conference on Remote Sensing,
Environment and Transportation Engineering, RSETE 2011, June 24, 2011 - June 26, 2011. IEEE
Computer Society, Nanjing, China, pp. 5018-5021.

25
Sudha, P., Ravindranath, N.H., 2000. A study of Bangalore urban forest. Landscape and Urban
Planning 47, 47-63.

Wang, G.-m., Zuo, J.-c., Li, X.-R., Liu, Y.-h., Yu, J.-b., Shao, H.-b., Li, Y.-z., 2014. Low plant diversity
and floristic homogenization in fast-urbanizing towns in Shandong Peninsular, China: Effects of
urban greening at regional scale for ecological engineering. Ecological Engineering 64, 179-185.

Wang, Z., Brown, J.H., Tang, Z., Fang, J., 2009. Temperature dependence, spatial scale, and tree
species diversity in eastern Asia and North America. PNAS 106, 13388-13392.

Winter, M., Kühn, I., Sorte, F.A.L., Schweiger, O., Nentwig, W., Klotz, S., 2010. The role of non-
native plants and vertebrates in defining patterns of compositional dissimilarity within and
across continents. Global Ecology and Biogeography 19, 332-342.

Xiao, L., Wang, W., He, X., Lv, H., Wei, C., Zhou, W., Zhang, B., 2016. Urban-rural and temporal
differences of woody plants and bird species in Harbin city, northeastern China. Urban Forestry
& Urban Greening 20, 20-31.

Yang, J., McBride, J., Zhou, J., Sun, Z., 2005. The urban forest in Beijing and its role in air
pollution reduction. Urban Forestry & Urban Greening 3, 65-78.

Yang, J., Zhou, J., Ke, Y., Xiao, J., 2012. Assessing the structure and stability of street trees in
Lhasa, China. Urban Forestry & Urban Greening 11, 432-438.

Yang, J., Sorte, F.A.L., Pyšek, P., Yan, P., Nowak, D., McBride, J., 2015. The compositional
similarity of urban forests among the world's cities is scale dependent. Global Ecology and
Biogeography 24, 1413-1423.

Zhang, D., Zheng, H., He, X., Ren, Z., Zhai, C., Yu, X., Mao, Z., Wang, P., 2016. Effects of forest
type and urbanization on species composition and diversity of urban forest in Changchun,
Northeast China. Urban Ecosystems 19, 455-473.

Zhang, H., Jim, C.Y., 2014. Contributions of landscape trees in public housing estates to urban
biodiversity in Hong Kong. Urban Forestry & Urban Greening 13, 272-284.

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