Ge Nature YS) Conservation

Nature Conservation 54: 179-202 (2023) DOI: 10.3897/natureconservation.54.110257

Research Article

Vegetation changes along an urbanisation and atmospheric pollution gradient in Mexico

Edmar Meléndez-Jaramillo’®, Laura Sanchez-Castillo'®, Ma. Teresa de Jesus Segura Martinez'™®,

Uriel Jeshua Sanchez-Reyes?®

1 Facultad de Ingenieria y Ciencias, Universidad Autonoma de Tamaulipas, Centro Universitario Victoria, C.P 87149 Ciudad Victoria, Tamaulipas, Mexico 2 Tecnoldgico Nacional de México - Instituto Tecnologico de Cd. Victoria, Boulevard Emilio Portes Gil No.1301, C.P. 87010, Ciudad Victoria, Tamaulipas, Mexico Corresponding author: Edmar Meléndez-Jaramillo (edjaramillo@uat.edu.mx)

OPEN Qaccess

Academic editor: Cassio Cardoso Pereira Received: 29 July 2023

Accepted: 25 November 2023 Published: 21 December 2023

ZooBank: https://Zoobank.org/ ASAB18E6-E50C-4932-8084- 76453E584C7A

Citation: Meléndez-Jaramillo E, Sanchez-Castillo L, Segura Martinez MatTJ, Sanchez-Reyes UJ (2023) Vegetation changes along an urbanisation and atmospheric pollution gradient in Mexico. Nature Conservation 94: 179-202. https://doi.org/10.3897/ natureconservation.54.110257

Copyright: © Edmar Meléndez-Jaramillo et al. This is an open access article distributed under terms of the Creative Commons Attribution License (Attribution 4.0 International -

CC BY 4.0).

Abstract

Green areas are important places for biodiversity conservation within cities, but their vegetation is affected by various anthropogenic factors. This study used an exploratory approach to examine the influence of urbanisation and air pollution-related factors on the indicators for the composition and structure of vegetation in an urban area in northeast Mexico. Based on the spatial analysis of the major air pollutants, four sampling categories were delimited (rural, low, moderate and high urbanisation). The differences between categories, based on vegetation structure, were determined using non- parametric Kruskal-Wallis tests. The Importance Value was calculated for the species. The floristic similarity was compared using NMDS and PERMANOVA unidirectional. The relationship between environmental variables and abundance of species was evaluated using CCA. One hundred and ten plant species were collected, including ten alien species. The highest abundance and species richness were registered in the rural site. The general tendency of vegetation structure is to plants decreasing with respect to the increase in the levels of urbanisation and air pollution present in the study area. The association between the environmental variables and plant communities along the urbanisation gradient was significant, being the relative humidity, the particles lower than 2.5 um, the dew point and the heat index as the most important variables. The understanding of the nature and variability of vegetation within green areas contributes to increasing our knowledge about the distribution of the environmental services they provide and the composition of the faunal communities that depend on them. For this reason, this study relates the plants of a specific area of northeast Mexico with the environmental quality present in an urban area.

Key words: air pollution, environmental variability, Monterrey Metropolitan Area, urbani- sation, vegetation structure

Introduction

The demographic growth dynamics faced by cities represent a serious threat to the environment, as well as to the health and quality of life of its inhabi- tants (Vlahov and Galea 2002). The unsustainable use of natural resources, in- tense land-use changes, increasing density of urban/industrial centres and the

179

Edmar Meléndez-Jaramillo et al.: Vegetation change on an urbanisation gradient

growing emission of pollutants irreversibly damage the environment (Garcia et al. 2013). These effects not only harm living beings, but also generate phenom- ena that affect the ecosystem (Ldpez et al. 2001). Likewise, the accelerated urbanisation changes the structure of cities and affects their climate and that of their surrounding area (Tang et al. 2008). This urbanisation process occurs more rapidly in countries located in regions classified as developing econo- mies. Particularly in Latin America, where it is estimated that 75% of the popu- lation live in cities (UN-HABITAT 2010).

In Mexico, air pollution has deteriorated air quality in various cities, including the Metropolitan Area of the Valley of Mexico, the Metropolitan Area of Guada- lajara and the Monterrey Metropolitan Area (MMA) (Garcia et al. 2012; Ceron et al. 2014; Mancilla et al. 2015; Menchaca et al. 2015). It is appropriate to point out that there is a perception problem in society as there is no clear awareness of pollutant emissions, their concentrations and damage to health, urban infra- structure and ecosystems (Lezama and Graizbord 2010). The State of Nuevo Leon, in the northeast of Mexico, has an unregulated urban growth. Its main ur- ban sprawl, the MMA presents serious environmental problems: geological and hydrological risks, water scarcity, loss of green areas, air pollution, amongst many others (Badillo et al. 2015; Orta et al. 2016; Sanchez-Castillo et al. 2016; Sisto et al. 2016; Ybafez and Barboza 2017).

Studies of species diversity in urban ecosystems are needed to understand the effect of anthropogenic development on ecosystem integrity and suste- nance (Mukherjee et al. 2015). To study the effects of urbanisation on eco- system structure and function, researchers have used the urban-rural gradient methodology (Pennington et al. 2010). Urban-rural gradients are generally real- ised on large spatial scales and, in some cases, have been conceived as a lin- ear transect radiating from the city centre towards less disturbed landscapes. Studies employing this method have documented declines in plant species diversity, basal area and density of native species as sites become more ur- banised. These studies, which show a decrease in species richness as urban- isation increases, follow a general disturbance hypothesis (Porter et al. 2001; Moffatt et al. 2004; Burton et al. 2005; Duguay et al. 2007).

On the other hand, the intermediate disturbance hypothesis has been one of the main models used to interpret urban plant diversity patterns (Johnson and Swan 2014). The theory has been applied to explore the co-existence of native and non-native species along urban-rural gradients or within the urban environment between patches that vary in level of disturbance (e.g. Porter et al. (2001); ManSecak and Wein (2006); Catford et al. (2012)). The expectation is that species diversity will be maximised in intermediate locations, where native and invasive species are found in the same communities, in relatively uniform proportions.

Previous studies of large-scale urban-rural gradients have documented that those urban forests are more deteriorated than their “natural” or rural coun- terparts (Paul and Meyer 2001; Giller 2020). Consequently, they reduce the perceived ecological value of remnant vegetation within highly modified land- scapes. However, it is important to understand the potential ecological and so- cial value of remnant urban vegetation (Turner et al. 2004; Czaja et al. 2020). Given that more than 60% of the world’s population will reside in urban areas by 2050, these forest fragments in urban settings could provide critical ecosystem

Nature Conservation 54: 179-202 (2023), DOI: 10.3897/natureconservation.54.110257 180

Edmar Meléndez-Jaramillo et al.: Vegetation change on an urbanisation gradient

services for both people and other species (Bernhardt and Palmer 2007; Zeg- eye et al. 2023).

For our study, we characterised the remnant vegetation of the MMA, north- east Mexico, along an urbanisation gradient, based on parameters of atmo- spheric pollution. The objectives of this study were: (1) Identify the plant species richness in the MMA, northeast Mexico; (2) Compare the variation in richness, abundance and diversity of plant species amongst urbanisation cate- gories; (3) Quantify the value of importance of the species by urbanisation cat- egory; and (4) Analyse the influence of environmental variation (air pollutants, climatic factors and soil) on the abundance and richness of plant species. Our hypothesis is that the structure and composition of the vegetation decrease with respect to the increase in urbanisation levels in the MMA.

Methods Study area

The MMA is the largest urban area in northeast Mexico and the third largest urban centre in the country, extending from 25°15' to 26°30' north latitude and from 99°40' to 101°10' west longitude (Fig. 1A, B). The area is bounded by the coastal plain of the Gulf of Mexico and the Sierra Madre Oriental Moun- tain Range. Several municipalities compose the geographical area of MMA: Apodaca, Cadereyta, Garcia, General Escobedo, Guadalupe, Jiménez, Juarez, Monterrey, Salinas Victoria, San Nicolas de los Garza, San Pedro Garza Garcia, Santa Catarina and Santiago (Alanis 2005; Gonzalez et al. 2011; Mancilla et al. 2015). The main vegetation cover found at MMA is forest, scrubs and grass- lands (Carpio et al. 2021). The MMA has a vehicle fleet of 2.5 million vehicles (Castillo-Nava et al. 2020) and 5.3 million inhabitants (INEGI 2021), which is probably even higher today. Likewise, there is a variety of industrial complexes that include the production of glass, steel, cement and paper, amongst others (Menchaca et al. 2015). The city centre has an average altitude of 540 ma.s.l., the characteristic climate is dry steppe, hot and extreme with temperatures above 35 °C during the summer and below 8 °C during the winter (Alanis 2005; Gonzalez et al. 2011; Menchaca et al. 2015).

Delimitation of the urbanisation gradient

Since November 1992, the MMA has operated a network of air quality monitor- ing stations known as the Integral Environmental Monitoring System (SIMA). The SIMA network is currently made up of 14 recording stations distributed according to criteria from meteorological, land use and population densi- ty studies. The measurements recorded at these monitoring stations are: PM.,, (particulate matter less than 10 um), PM, (particulate matter less than 2.5 um), carbon monoxide (CO), ozone (O,), nitrogen oxides (NO_) and sulphur dioxide (SO,). In addition, some meteorological variables are reported, such as barometric pressure, rainfall, relative humidity, solar radiation, temperature and wind direction and magnitude (Arreola and Gonzalez 1999; Gonzalez et al. 2011; Mancilla et al. 2015). The data recorded by the SIMA stations for air qual- ity and meteorological variables (2009-2018) were obtained from the National

Nature Conservation 54: 179-202 (2023), DOI: 10.3897/natureconservation.54.110257 181

Edmar Meléndez-Jaramillo et al.: Vegetation change on an urbanisation gradient

-110°30' _-102°0' _ -93°30!' -100°30.589"

A | YT We ag Nar ,

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Gulf of Mexico

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No “3 8 Map Legend MM Nuevo Leon, Mexico Air Pollution Sampling Sites a [_]MMA, Nuevo Leon [ij Free @ Site 1 we {1 Political Divisions [_] Low O Site 2 5 | Federal NPAs Moderate © Site 3 @ SIMA Stations (4 High @ Site 4

-101°36' -99°49/ -98°2! Figure 1. Study area and location of sampling sites A location of Nuevo Leon in Mexico B location of the MMA inside Nuevo Leon C location of sampling sites according with the air pollution levels.

Air Quality Information System (SINAICA). Obtaining descriptive measures for each year and for each of the recording stations was carried out in the Statisti- ca 13.3 programme (TIBCO Software Inc. 2017).

To identify the main pollutants that describe air quality in the MMA during the 2009-2018 period, a Principal Component Analysis (PCA) was carried out. Subsequently, to differentiate the changes in the spatial distribution of pollut- ants that are indicators of air quality in the MMA, maps were created using the annual average information on each monitoring station. Mapping was done us- ing Inverse Distance Weighting (IDW) interpolation, with a Distance Coefficient of 2 and the output raster pixel size reset to 15 metres. As a reference of the extension, the minimum and maximum distances of the vector sections corre- sponding to the urban areas that make up the MMA were taken; these sections were obtained from the national layer of Land Use and Vegetation Series 6 (IN- EGI 2016). The procedures described above were performed using Quantum GIS 3.2 software (Quantum GIS Development Team 2018). As a result, four cat- egories of urbanisation by atmospheric pollution were generated: rural (lower than 3.22 g/m? of PM, .), low (3.22 to 10.56 g/m? of PM, .), moderate (10.56 to 17.92 g/m? of PM, .) and high (17.92 to 25.3 g/m of PM, ,) (Fig. 1C).

Selection of sampling sites

Four permanent sampling sites were delimited, based on the spatial superposi- tion of three geographic elements: (1) the interpolation of the main air pollutants

Nature Conservation 54: 179-202 (2023), DOI: 10.3897/natureconservation.54.110257 182

Edmar Meléndez-Jaramillo et al.: Vegetation change on an urbanisation gradient

was used for determination of the urbanisation gradient in the study area (Fig. 1C); (2) images obtained from the Google Earth Pro software were used to differentiate the spatial presence or absence of vegetation cover and (3) amesh with a grid size of 150 x 150 m was delimited to select sampling areas with complete vegetation cover. Overlay and selection procedures were performed in Quantum GIS 3.2 software. The rural site is located in the Municipality of San- tiago, a rural area without substantial urbanisation or air pollution and with sec- ondary submontane scrub vegetation (25°30'41.184"N, 100°11'53.159"W). The low urbanisation site is located in the central zone of the Municipality of Gua- dalupe with low values of air pollution and secondary vegetation of submon- tane scrub (25°40'4.944"N, 100°14'45.564"W). The moderate urbanisation site is located in the northern zone of the Municipality of Guadalupe with moderate air pollution and secondary vegetation of submontane scrub (25°42'44.017'N, 100°13'58.825"W). The high urbanisation site is in the Municipality of San Pedro Garza Garcia with high air pollution and anthropogenic submontane scrub veg- etation (25°38'11.112"N, 100°21'30.815"W) (Fig. 1C).

Sample collection and processing

During April 2019, the analysis of preliminary samples obtained in the study area was Carried out. The Clench model was used to calculate the minimum sample size to be used, based on the method and parameters indicated by Jiménez-Valverde and Hortal (2003). According to the analysis, between 5 to 8 sampling units are needed to register the 95% of the richness of each site. Veg- etation was assessed using 20 quadrats of 10 x 10 m (0.01 hectares), which were evenly distributed amongst the four categories of urbanisation by air pol- lution (five quadrats per category). The quadrats were located from inside the sampling site (150 x 150 m) (2.25 hectares) randomly and they were placed using the tool random points inside a polygon in Quantum GIS 3.2 software. The quadrats are located in patches of natural and native vegetation. The eval- uation was carried once per season: dry season (November to April) and rainy season (May to October), during the period from May 2019 to April 2020. The seasons were defined, based on the historical data of the monthly total values of temperature and rainfall (average from 2009 to 2018), which were obtained from the SIMA stations located within the study area (Fig. 2).

Measurements were carried out independently for each of the vegetation strata. For the herbaceous stratum, five sub-quadrats of 1 x 1 m (5 m’ in total per quadrant) were delimited. In the shrub stratum, two 5 x 5 m sub-quadrats (50 m? in total per quadrant) were evaluated. Finally, the tree stratum was eval- uated in the entire quadrat, 10 x 10 m (100 m? in total per quadrat). The dimen- sion of the quadrat and sub-quadrats was established according to the criteria described by Brower et al. (1998).

In each quadrat/sub-quadrats, the following measurements were made: (1) height of the plant (from its base at ground level to the highest branch); (2) largest and (3) smallest diameter of the aerial projection of the plant. The number of individuals of each morphospecies assigned in the field was quan- tified and their identification in the laboratory was carried out using the works of Alanis and Gonzalez (2003), Stubbendieck et al. (2003) and Zurita and Eli- zondo (2009); likewise, the botanical nomenclature was homogenised using

Nature Conservation 54: 179-202 (2023), DOI: 10.3897/natureconservation.54.110257 183

Edmar Meléndez-Jaramillo et al.: Vegetation change on an urbanisation gradient

40

Temperature (°C) i) th ey) oe) fom) tn com) Nn

— tn

10 Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct

300

Rainfall (mm) — i) ho a > ea —) S S

— S So

Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct

Figure 2. Monthly average variation of temperature and rainfall in the MMA. Dry season (red colour) and Rainy season (blue colour).

the International Plant Names Index base (IPNI 2022). Villasefior and Espino- sa-Garcia (2004) were mainly followed to determine which plant species were not native to the MMA region.

Microenvironment measurement

The microenvironmental variables were measured in each of the quadrants us- ing a Kestrel 5500 portable weather station, a CEM — DT1308 digital luxmeter, a CEM — DT9881 particle counter and a HB -— 2 soil moisture and pH meter, si- multaneously with the sampling of the vegetation, recording the following vari- ables: maximum wind speed (MWS) and average wind speed (AWS) (obtained during five minutes of exposure), temperature (T), relative humidity (RH), heat index (HI), dew point (DP), evapotranspiration (E), solar radiation (SR), particles of 2.5 (PM,,) and 10 microns (PM.,), soil pH (SpH) and soil moisture (SM). Measurements were carried out in the centre of each quadrat during the early hours of the morning, noon and before sunset, avoiding direct solar radiation.

Data analysis

Species richness was measured as the total number of species observed in the study area, as well as in each of the sites. Significant differences in the

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Edmar Meléndez-Jaramillo et al.: Vegetation change on an urbanisation gradient

number of species between sites were determined using non-parametric Kru- skal-Wallis tests, in Statistica 13.3 software. Sampling efficiency was calcu- lated for the entire study area and for each site using the interpolation and extrapolation methodology proposed by Chao and Jost (2012), available in the iNEXT package (Hsieh et al. 2016) for version 3.5.3 of R (R Development Core Team 2019).

Differences in plant abundance between sites were calculated with a Kru- skal-Wallis test. For the analysis of alpha diversity, we adopted the analytical method of Chao and Jost (2015) to obtain profiles in which diversity is evaluat- ed in terms of “effective numbers of species” (qD), an approach that is equiv- alent to the numbers of Hill (Hill 1973). Hill numbers include three widely-used measures as special cases: species richness (q = 0), Shannon diversity (the exponential of Shannon entropy, q = 1) and Simpson diversity (the inverse of Simpson concentration, q = 2), all of which are expressed in units of “species equivalents”. The analysis was performed for the entire study area and for each site using the SpadeR package (Chao et al. 2016), in R 3.5.3.

Vegetation cover was calculated according to the criteria described by Ramirez (2006). Differences in vegetation cover between sites were deter- mined with a Kruskal-Wallis test. To examine differences in species composi- tion between sites, we performed non-metric multidimensional scaling (NMDS) analysis, using the Bray-Curtis Index as the similarity matrix. A PERMANOVA was also performed to test for differences in species composition between sites. Both analyses were performed using the Vegan package (Oksanen et al. 2019) in R 3.5.3.

For each species, its abundance was determined according to the number of individuals, its dominance based on cover and its frequency based on its pres- ence in the sampling quadrats. These results were used to obtain a weighted value at the taxon level called Importance Value (IV), which acquires percent- age values ona scale from 0 to 100 (Mueller-Dombois and Ellenberg 1974). The IV was calculated for each site separately.

Finally, a canonical correspondence analysis (CCA) was carried out to de- termine the relationship between the microenvironmental variables and the abundance of the recorded species in each plot, which also includes a Monte Carlo permutation test to evaluate the significance of the microenvironmental variables in the analysis. For the CCA, the average values of the microenviron- mental variables of each season of the year were used (dry and rainy season). The CCA was done using the Vegan package in R 3.5.3.

Results

A total of 12,878 plants of 42 families, 104 genera and 110 species were quan- tified. From this total, 17 species (594 individuals) were trees, 34 (2,595 individ- uals) were shrubs and 59 (9,689 individuals) were herbaceous (Table 1). The greatest abundance and richness of tree species in the study area was found in the Fabaceae family with 35.0 and 23.5% of the total registered, respectively. Likewise, Fabaceae presented the highest abundance and richness of shrub species with 29.3 and 29.4% of the total registered, respectively. Asteraceae showed the highest abundance and richness of herbaceous species with 21.6 and 18.6% of the total recorded, respectively (Table 1).

Nature Conservation 54: 179-202 (2023), DOI: 10.3897/natureconservation.54.110257 185

Edmar Meléndez-Jaramillo et al.: Vegetation change on an urbanisation gradient

Table 1. Taxonomic list, abundance and IV of the species found in an air pollution gradient in the MMA. Legend: Site 1 = Rural, Site 2 = Low urbanisation, Site 3 = Moderate urbanisation, Site 4 = High urbanisation.

sata Kaye | Abundance IV Site 1 Site 2 | Site3 | Site4 Site 1 Site2 | Site3 Site4

Tree Boraginaceae Juss. Ehretia anacua (Teran & Berland.) I.M. Johnst. Eana 16 6 0 0 8.1 4.7 0.0 0.0 Cannabaceae Martinov | Celtis laevigata Willd. Clae 26 22 0 0 2d Daal ted 0.0 0.0 Ebenaceae Giirke Diospyros texana Scheele Dtex 22 0 0 0 10.7 | 0.0 0.0 0.0 Fabaceae Lindl. Ebenopsis ebano (Berland.) Barneby & J.W. Grimes Eeba 20 28 16 0 NOES. | 82A.61) TAS |, 0:0 Havardia pallens (Benth.) Britton & Rose Hpal 18 12 6 0 9.6 8.7 5.7 0.0 Leucaena leucocephala (Lam.) de Wit* Lleu 0 26 16 0 0.0 | 12.6 | 18.9 | 0.0 Prosopis glandulosa Torr. Pgla 26 18 22 0 2 AP |) OMe || Zl |) 0 Fagaceae Dumort. | Quercus fusiformis Small Qfus 0 0 0 24 0.0 0.0 0.0 | 22.4 Juglandaceae DC. ex Perleb | | Carya illinoinensis (Wangenh.) K. Koch Cill 0 0 0 6 0.0 0.0 0.0 5.1 Oleaceae Hoffmanns. & Link Fraxinus americana L.* Fame 0 0 14 16 0.0 0.0 T1630" | 1:6:9 Ligustrum lucidum W.T. Aiton* Lluc 0 0 0 22 0.0 0.0 0.0 18.0 Rutaceae Juss. Sargentia greggii S. Watson Sgre 20 0 0 0 9.3 0.0 0.0 0.0 Salicaceae Mirb. | | Salix nigra Marshall Snig 0 22 0 0 0.0 11.8 0.0 0.0 Sapindaceae Juss. | Koelreuteria elegans (Seem.) A.C. Sm.* Kele 0 30 22 16 0.0 | 14.1 | 21.0 | 14.1 Sapindus saponaria L. Ssap 34 0 0 0 15.4 0.0 0.0 0.0 Ungnadia speciosa Endl. Uspe 0 0 0 26 0.0 0.0 Os || 235 Sapotaceae Juss. Sideroxylon celastrinum (Kunth) T.D. Penn. Scel 24 18 0 0 | 122%, |) 1152!) 0.6 0.0 Shrub Asparagaceae Juss. Yucca treculeana Carriére Ytre 33 0 0 0 2.9 0.0 0.0 0.0 Asteraceae Bercht. & J. Presl | | Gochnatia hypoleuca (DC.) A. Gray Ghyp 34 0 0 0 3.0 0.0 0.0 0.0 Bignoniaceae Juss. | Tecoma stans (L.) Juss. ex Kunth Tsta 0 59 0 0 0.0 75 0.0 0.0 Boraginaceae Juss. Cordia boissieri A. DC. Cboi 54 44 0 0 4.4 6.3 0.0 0.0 Cactaceae Juss. Opuntia engelmannii Salm-Dyck ex Engelm. Oeng 40 0 0 0 | 3.6 0.0 0.0 0.0

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Edmar Meléndez-Jaramillo et al.: Vegetation change on an urbanisation gradient

Taxon

Cannabaceae Martinov

Celtis pallida Torr.

Capparaceae Juss.

Capparis flexuosa Vell.

Euphorbiaceae Juss.

Adelia vaseyi (JM Coult.) Pax y K. Hoffm. Fabaceae Lindl.

Acacia berlandieri Benth.

Acacia farnesiana (L.) Willd.

Acacia rigidula Benth.

Bauhinia mexicana Vogel

Caesalpinia mexicana A. Gray

Dalea scandens (Mill.) R.T. Clausen Erythrina herbacea L.

Eysenhardtia texana Scheele

Mimosa monancistra Benth.

Parkinsonia aculeata L. Lythraceae J. St.-Hil.

Punica granatum L.*

Malpighiaceae Juss.

Malpighia glabra L.

Mascagnia macroptera (Moc. & Sessé ex DC.) Nied. Myrtaceae Juss.

Psidium guajava L.*

Oleaceae Hoffmanns. & Link

Forestiera angustifolia Torr.

Rhamnaceae Juss.

Condalia hookeri M.C. Johnst.

Karwinskia humboldtiana (Schult.) Zucc. Ziziphus obtusifolia (Hook. ex Torr. & A. Gray) A. Gray Rubiaceae Juss.

Randia obcordata S. Watson

Rutaceae Juss.

Helietta parvifolia (A. Gray ex Hemsl.) Benth. Zanthoxylum fagara (L.) Sarg.

Salicaceae Mirb.

Neopringlea integrifolia (Hemsl.) S. Watson Scrophulariaceae Juss.

Leucophyllum frutescens (Berland.) I.M. Johnst. Simaroubaceae DC.

Castela erecta Turpin

Verbenaceae J. St.-Hil.

Citharexylum berlandieri B.L. Rob.

Key

Cpal Cfle Avas Aber Afar Arig Bmex Cmex Dsca Eher Etex Mmon Pacu

Pgra

Mgla

Mmac

Pgua

Fang

Choo

Khum

Zobt

Robc

Hpar Zfag

Nint

Lfru

Cere

Cber

Abundance

IV

53

39

43

46 34

29

49

31

33

42

45 47

58

35

49

43

Nature Conservation 54: 179-202 (2023), DOI: 10.3897/natureconservation.54.110257

32

36

40

33 50

45

56

53

41

36

48

41

Al

4.2

3.4

37

4.7

0.0

4.1

3.4

0.0

3.9

3.8

3.0

0.0

319 4.3

0.0

2.8

4.0

4.3

2.9

3.6

3.8 3.8

4.5

2.9

3.5

3.2

4.9

0.0

3.4

9.9

0.0

50

0.0

na

5.8

0.0

5.1 6.7

0.0

6.2

Fiat)

0.0

riers

a7 59

0.0

5.4

0.0

12.8

0.0

12.6

0.0

11.0

Ale?

14.2

0.0

0.0 12.3

0.0

12.5 0.0

0.0

19:6

0.0

1B:2

0.0

15,41

0.0 19.6

14.6

0.0

0.0 0.0

0.0

187

Edmar Meléndez-Jaramillo et al.: Vegetation change on an urbanisation gradient

Taxon

Lantana camara L.

Herb

Acanthaceae Juss.

Elytraria bromoides Oerst.

Justicia pilosella (Nees) Hilsenb.

Ruellia nudiflora (Engelm. & A. Gray) Urb. Tetramerium nervosum Nees Apocynaceae Juss.

Asclepias curassavica L.

Telosiphonia lanuginosa (M. Martens & Galeotti) Henrickson

Asteraceae Bercht. & J. Presl

Bidens odorata Cav.

Calyptocarpus vialis Less. Chromolaena odorata (L.) R.M. King & H. Rob. Helianthus annuus L.

Jefea lantanifolia (S. Schauer) Strother Sanvitalia ocymoides DC.

Simsia eurylepis S.F. Blake Thymophylla pentachaeta (DC.) Small Tridax coronopifolia (Kunth) Hemsl.* Verbesina persicifolia DC.

Wedelia acapulcensis Kunth Commelinaceae Mirb.

Commelina erecta L.

Convolvulaceae Juss.

Evolvulus alsinoides (L.) L.

Ipomoea hederacea Jacq.

Merremia dissecta (Jacq.) Hallier f. Euphorbiaceae Juss.

Acalypha monostachya Cav. Cnidoscolus rotundifolius (Mull. Arg.) McVaugh Croton cortesianus Kunth

Euphorbia hirta L.

Fabaceae Lindl.

Canavalia villosa Benth.

Desmanthus virgatus (L.) Willd. Mimosa malacophylla A. Gray Lamiaceae Martinov

Ocimum micranthum Willd.*

Salvia coccinea Buc'hoz ex Etl. Loasaceae Juss.

Cevallia sinuata Lag.

Key

Lcam

Ebro Jpil Rnud

Tner

Acur

Tlan

Bodo Cvia Codo Hann Jlan Socy Seur Tpen Tcor Vper

Waca

Cere

Eals lhed Mdis

Amon Crot Ccor Ehir

Cvil Dvir

Mmal

Omic

Scoc

Csin

66

99

91

Nature Conservation 54: 179-202 (2023), DOI: 10.3897/natureconservation.54.110257

26

89

102

v2.

oOo, 0o;oO);| oO

103

95

119

106

47

o;1,o;o);| oOo

87

105

89

4.5

3.0 3.0 0.0 3.5

3.5 0.0

3.8 0.0 3.8 0.0 0.0 2.1 0.0 0.0 3.4 2.1 3.5

3.3

0.0 3.3 0.0

0.0 0.0 3.6 0.0

3.5

3.4

3:7

3.1 3.4

0.0

4.1

0.0 4.2 4.3 0.0

SA 0.0

3.7 3.8 0.0 0.0 3.6 3.8 3.3 0.0 3.8 0.0 0.0

3.5

0.0 3.3 3.7

0.0 3.9 4.3 3.3

0.0

See. 3.9

0.0

12,9

0.0 0.0 0.0 0.0

4.0 4.3

4.5 4.1 0.0 a9 0.0 0.0 4.0 0.0 4.2 0.0 0.0

3.9

4.6 aa 3.9

0.0 0.0 0.0 4.3

0.0

0.0 4.1

0.0

15.9

0.0 0.0 0.0 0.0

5-5 29

6.3 Sirs 0.0 0.0 0.0 0.0 0.0 #1 6.8 0.0 0.0

5.3

0.0 0.0 0.0

5.1 0.0 0.0 0.0

0.0

0.0 5.9

9.3

188

Edmar Meléndez-Jaramillo et al.: Vegetation change on an urbanisation gradient

Taxon

Malvaceae Juss.

Abutilon trisulcatum (Jacq.) Urb. Malvastrum americanum (L.) Torr. Melochia pyramidata L.

Waltheria indica L.

Nyctaginaceae Juss.

Cyphomeris crassifolia (Standl.) Standl. Oleaceae Hoffmanns. & Link Menodora heterophylla Moric. ex DC. Onagraceae Juss.

Oenothera rosea LHér. ex Aiton Papaveraceae Juss.

Argemone grandiflora Sweet Passifloraceae Juss. ex Roussel Passiflora foetida L.

Petiveriaceae C. Agardh

Rivina humilis L.

Poaceae Barnhart

Aristida adscensionis L.

Bouteloua curtipendula (Michx.) Torr. Cenchrus spinifex Cav.

Eragrostis barrelieri Daveau*

Melinis repens (Willd.) Zizka* Panicum hallii Vasey

Paspalum unispicatum (Scribn. & Merr.) Nash Setaria leucopila (Scribn. & Merr.) K. Schum. Pteridaceae E.D.M. Kirchn. Adiantum tricholepis Fée Cheilanthes aemula Maxon Ranunculaceae Juss.

Clematis dr'ummondii Torr. & A. Gray Rubiaceae Juss.

Spermacoce glabra Michx. Sapindaceae Juss.

Cardiospermum halicacabum L. Solanaceae Juss.

Solanum elaeagnifolium Cav. Solanum triquetrum Cav. Verbenaceae J. St.-Hil.

Lantana canescens Kunth

Phyla nodiflora (L.) Greene

Verbena canescens Kunth

*Introduced species.

Key

Oros

Agra

Pfoe

Rhum

Aads Bcur Cspi Ebar Mrep Phal Puni

Sleu

Atri

Caem

Cdru

Sgla

Chal

Sela Stri

Lcan Pnod

Vcan

69

68

122

04

98

Nature Conservation 54: 179-202 (2023), DOI: 10.3897/natureconservation.54.110257

64

60

107

98

67

103

63

oi)

63

134

106

84

a

0.0 3.4 flee 0.0

2.1

0.0

tS |

2.3

3.0

0.0

3.3

0.0

30)

3.4 Bil

4.1

Ae

0.0

0.0 1.9

3.4 0.0 0.0

3.9 0.0 = 0.0

0.0

aes,

2.3

0.0

4.2

0.0

3.5

0.0

3.9

0.0 0.0

3.8

ZS

3.8

0.0 0.0

3.5 0.0 0.0

IV

4.3 0.0 4.0 4.0

0.0

29

ie

2.4

0.0

oe

3,9

0.0

2a

0.0

0.0 0.0

5.0

0.0

4.1

4.0 0.0

4.2 0.0 0.0

0.0

3.9

0.0

9.9

0.0

9.4

0.0

0.0 0.0

0.0

RZ

0.0 0.0

5.6

Al 6.4

189

Edmar Meléndez-Jaramillo et al.: Vegetation change on an urbanisation gradient

Koelreuteria elegans (Seem.) A.C. Sm. was the species with the highest abundance of trees (68 individuals), 11.4% of the total number of individuals recorded in the study area. On the other hand, Mascagnia macroptera (Moc. & Sessé ex DC.) Nied. presented the highest abundance of shrubs (215 individ- uals) (8.3%). Bidens odorata Cav. was the species with the highest abundance of herbaceous plants (441 individuals) (4.6%) (Table 1). From the total of the reported species, ten are alien species, amongst which, Koelreuteria elegans (Seem.) A.C. Sm. and Tridax coronopifolia (Kunth) Hemsl. are present in most of the sampling sites (Table 1).

Variation per urbanisation category

Sapindus saponaria L. was the tree species with the highest IV (15.4%) in the rural site. On the other hand, Ebenopsis ebano (Berland.) Barneby & J.W. Grimes was the most important tree species (14.61%) in the low urbanisation site. Pro- sopis glandulosa Torre. was the most important species (21.21%) in the moder- ate urbanisation site. Likewise, Ungnadia speciosa Endl. was the most import- ant species (23.48%) in the high urbanisation site (Table 1).

Acacia berlandieri Benth. was the shrub species with the highest IV (4.68%) in the rural site. On the other hand, Tecoma stans (L.) Juss. ex Kunth was the most important shrub species (7.53%) in the low urbanisation site. Parkinsonia aculeata L. was the most important species (14.23%) in the moderate urban- isation site. Likewise, Caesalpinia mexicana A. Gray was the most important species (19.63%) in the high urbanisation site (Table 1).

Clematis drummondii Torr. & A. Gray was the herbaceous species with the highest IV (4.06%) in the rural site. On the other hand, Ruellia nudiflora (Engelm. & A. Gray) Urb. was the most important herbaceous species (4.31%) in the low urbanisation site. Clematis dr'ummondii Torr. & A. Gray also turned out to be the most important herbaceous (5.02%) in the moderate urbanization site. Like- wise, Phyla nodiflora (L.) Greene turned out to be the most important species (7.12%) in the high urbanisation site (Table 1).

Comparisons between sites showed significant differences (P < 0.05) for species richness, height and coverage between all sites (Table 2). Abundance was significantly different (P < 0.05) between all sites, except for the compar- ison between the sites with moderate and high urbanisation (Table 2). All the parameters (abundance, species richness, height and coverage) decreased with increasing levels of urbanisation or pollution. In the rural site, 425.2 + 87.7 individuals and 61.8 + 3.4 species were registered, representing a sampling coverage of 99.9%. In the low urbanisation site, the values were reduced to 350 + 68.5 individuals and 50.9 + 1.6 species (coverage of 99.9%). For the moderate urbanisation site, 296.9 + 62.4 individuals and 36.2 + 1.6 species were regis- tered (coverage of 99.9%), while for the high urbanisation site, 215.7 + 35.5 individuals and 27.2 + 0.6 species (coverage of 100%).

For °D, 'D and 2D, the rural site had the highest diversity. All comparisons between sites were significantly different (with 95% confidence intervals) (Ta- ble 2). The one-way PERMANOVA test detected significant differences in spe- cies composition between all sites (SS,,.,. = 7-05; SS ithingroup = 1-25; F = 55.81, P< 0.001). Plant communities sampled formed separate groups in the NUDS diagram (Stress = 0.11) (Fig. 3).

Nature Conservation 54: 179-202 (2023), DOI: 10.3897/natureconservation.54.110257 190

Edmar Meléndez-Jaramillo et al.: Vegetation change on an urbanisation gradient

Table 2. Richness, abundance, height, coverage and diversity profiles along the urbanisation gradient in the MMA. Leg- end: °D = species richness expressed in units of species; 'D = Shannon diversity expressed in units of species; 7D = Simp- son diversity expressed in units of species.

Ecological parameter Rural Low urbanisation Moderate urbanisation High urbanisation Richness * 61.8+3.4a 50.9 + 1.6b 36.2 + 1.6c 27.2 + 0.6d Abundance* 425.2 + 87.7a 350 + 68.5b 296.9 + 62.4c 2157 +35.5¢ Height * lee aeOela 0.9 + Ob 0.7+0c 0.8+0.1d Coverage * 558.3 + 103.1a 205.72311b 117.4 +22.9c 118.5 +19.9d i ar 68 + 0a 54 + 0b 40 +0.2c 29 +0d Ty s* 61.2 +0.8a 47.3 +0.8b 35:5 O:5c 25.1 + 0.5d “p** 56.5+1.2a 43.4+1b 33.4.4:0;7¢ 23:3:4'077d

* Values with different letters between columns are significantly different using Kruskal-Wallis test: richness between sites, K = 36.6, DF = 3, P= 0-0001; abundance between sites, K = 17.5, DF = 3, P = 0:0001; height between sites, K = 32.5, DF = 3, P= 0:0001; coverage between sites, K = 31.2, DF = 3, P=0-0001. ** Diversity values with different letters between columns are different, using 95% confidence intervals.

0.254 Moderate urbanisation

Rural ; 0.20; Low urbanisation Big High urbanisation

0.10;

0.055

0.00 -0.45 -0.30 0.15 0.15 0.30 0.45

Axis 2

-0.20- Axis 1

Figure 3. Non-Metric Multidimensional Scaling (NMDS) ordination of plant communities by urbanisation categories.

Plant responses to environmental variation

The MWS, T, RH, HI, DP, E, PM, , and SpH were the significant environmental variables (P < 0.05) used in the CCA (Table 3). CCA showed significant association between the environmental variables and the plant communities along the urbanisation gradient (Total inertia = 81.3%; P < 0.001). The variables most related with the plant abundance in the gradient were: RH and PM,,, for Axis 1 (Eigenvalue = 0.441; Inertia = 56.6%). For Axis 2 (Eigenvalue = 0.193; Inertia = 24.7%), DP and HI were the most important variables. Quercus fusiformis Small, Carya illinoinensis (Wangenh.) K. Koch, Fraxinus americana L., Ligustrum lucidum W.T. Aiton, Koelreuteria elegans (Seem.) A.C. Sm., Caesalpinia mexicana A. Gray, Punica granatum L., Psidium guajava L., Lantana camara L., Thymophylla pentachaeta (DC.) Small, Tridax coronopifolia (Kunth) Hemsl., Eragrostis barrelieri Daveau, Melinis repens (Willd.) Zizka and Verbena canescens Kunth are associated with conditions of high concentration of PM, ,, higher RH and alkaline SpH. On the other hand, Fhretia anacua (Teradn & Berland.) I.M. Johnst., Diospyros texana Scheele,

Nature Conservation 54: 179-202 (2023), DOI: 10.3897/natureconservation.54.110257 191

Edmar Meléndez-Jaramillo et al.: Vegetation change on an urbanisation gradient

Table 3. Environmental values registered along the urbanisation gradient in the MMA. Environmental variables marked (*) are significant (p < 0.05) according to the Monte Carlo permutation test. MWS = maximum wind speed; AWS = average wind speed; T = temperature; RH = relative humidity; HI = heat index; DP = dew point; E = evapotranspiration; SR = solar radiation; PM, , = 2.5 um particles; PM,, = 10 um particles; SpH = soil pH; SM = soil moisture.

Environment variable Rural Low urbanisation Moderate urbanisation High urbanisation MWS (Km/h) * B25 4.2+0.7 4.9+2.3 15 97 AWS (Km/h) ot] 1.94+0.4 2.2+0.8 Te? #'0.8 TeGG)* 26.4+0.5 ZF O17 26530156 20.8 42.7 RH (%) * 49.1+6.1 62.24:3.7 65.6 £336 74.6 43.4 ALEC! 26, 2017, 32:244,3 26.8 +1.2 22+2.8 DP (°C) * 14.1+1.9 20.9 + 2.1 TBS: 4127 16.642 E@G).* 18.44 1.5 22,.2.31.3 20.4+1.4 19.3+1.9 SR (Klux) 9:4 2135 Toe 15 9.1+1.8 FE B32 PM, .* 25621 101.4 410.4 + 94.6 396.7 + 33.4 1181.4 + 455.6 PM,, 47 +20 T19 £22,4 41.4+8 69.2 + 23.5 SpH * 7.1404 7.2+0.6 L340:5 8+0.7 SM (%) 11.6448 162722 1.7 #43 1445

Ebenopsis ebano (Berland.) Barneby & J.W. Grimes, Prosopis glandulosa Torr., Sapindus saponaria L., Gochnatia hypoleuca (DC.) A. Gray, Tecoma stans (L.) Juss. ex Kunth, Forestiera angustifolia Torr., Randia obcordata S. Watson, Zanthoxylum fagara (L.) Sarg., Citharexylum berlandieri B.L. Rob., Verbesina persicifolia DC., Croton cortesianus Kunth, Cenchrus spinifex Cav., Clematis drummondii Torr. & A. Gray, Solanum triquetrum Cav. and Lantana canescens Kunth are related to the low PM, , concentration, RH and neutral

SpH (Fig. 4). nud hal pp2.0 Jlan & Crt Ehir sew sta « Snig HI - dis Sela _ ere Hae “Leu Low urbanrtisati Moderate pS DAta sae Pasa Eeba him ” ia) eu

Cmex Cviae Kele 6 0. LU FP Robe cn: Scoc Lean Cspie ¢Scel

‘ : : : : PY --Ger Pela, Chod’sssClae

A -3.0 De: -2.0 -1,5 Fame 19 Ftexgs 0.5, Zag", o 1.5 — _Mrep. ¢Tlan Hpa! Aber High urbanisation <3 — Rural e Eana Cill, Qfus. ° Uspe PM2Z.5 — S -1.0 Cera Zobt * a 2 Pgua ¢ Lluc 4s Vper® St Dvir Pager 3 Pnodys «fee : Ebro ty « Nint Vean Cogn 20 a SM

Figure 4. Canonic Correspondence Analysis (CCA) of the plant communities and significant environmental variables corresponding to the urbanisation gradient. MWS = maximum wind speed; T = temperature; RH = relative humidity; HI = heat index; DP = dew point; E = evapotranspiration, PM, , = 2.5 um particles; SpH = soil pH.

Nature Conservation 54: 179-202 (2023), DOI: 10.3897/natureconservation.54.110257 192

Edmar Meléndez-Jaramillo et al.: Vegetation change on an urbanisation gradient

Discussion

We use the air quality records to define an urbanisation gradient in the MMA, where the height, cover, abundance, species richness and diversity were the parameters recorded in sites with different levels of urbanisation. It was found that all the pa- rameters decreased with increasing urbanisation levels; thus, in accordance with the general disturbance hypothesis, the general tendency of plant distribution at the levels of urbanisation and pollution present in the MMA is to decrease.

It is important to note that urban gradient studies are clearly a simplification of the complex patterns produced by urbanisation, such as air pollution (Alberti et al. 2001; Hahs and McDonnell 2006; McKinney 2008). The negative effect of urbanisation on plant species richness has been related to a variety of factors ranging from the pollution and habitat degradation to introduction of alien spe- cies and others societal impacts (McKinney 2002, 2006; Hope et al. 2003; Grimm et al. 2008; Vila et al. 2011). While the impact of urbanisation on plant richness depends upon the size of an urban area, the overall loss of habitable areas in urban zones normally results in a lower richness of plants. On the other hand, the expansion of urban areas is associated with an influx of non-native plant species that tend to counterbalance this urban effect by increasing overall plant richness (Duguay et al. 2007; Gavier-Pizarro et al. 2010; Cameron et al. 2015). These pat- terns were observed in the MMA region, notably, we recorded a decrease in the number of species as urbanisation levels increase and an increase in the abun- dance of introduced species in sites with higher urbanisation level.

The integrity of plant communities is vulnerable to intense land-use modifi- cation associated with urbanisation (Richardson et al. 2007). Significant chang- es in species composition along urban-rural gradients have been reported in Baltimore, Maryland (Groffman et al. 2003), Winnipeg, Manitoba (Moffatt et al. 2004) and Columbus, Georgia (Burton et al. 2005; Styers et al. 2010). Species richness and density of native plants were shown to decrease near urban areas (Porter et al. 2001; Moffatt et al. 2004), whereas invasive richness and density increased with urban development in the south-eastern United States. (Burton et al. 2005). These studies applied an urban-to-rural gradient approach to study sites located over a large geographic region from a densely populated urban landscape to a relatively unpopulated rural landscape. Our results corroborate similar studies of declining plant populations in urban-rural gradients, suggest- ing that habitat degradation may be a devastating threat to the persistence of certain sensitive taxa, such as plants present only in rural sites.

The replacement of local native species by alien species causes the floras of cities in different biogeographic regions to be increasingly homogeneous (i.e. beta diversity is reduced) (KUhn and Klotz 2006; Schwartz et al. 2006). However, the introduction of non-native species in urban areas can make them relatively biologically diverse at smaller scales. Our results show a clear differentiation in species composition (beta diversity) between sites on the urban-rural gradient. Hope et al. (2003) and Turner et al. (2005) demonstrate that certain anthropogen- ic habitats may have similar or greater alpha diversity than the more natural hab- itats of the region. However, our results show a greater diversity for sites without apparent urbanisation, but it decreases as urbanisation levels increase. The low diversity in such habitats may reflect a high degree of land change, thus causing significant stress to the plant community in urban areas (Pennington et al. 2010).

Nature Conservation 54: 179-202 (2023), DOI: 10.3897/natureconservation.54.110257 193

Edmar Meléndez-Jaramillo et al.: Vegetation change on an urbanisation gradient

Certain native and alien species represent ecological indicators of different levels of urbanisation (LaPaix and Freedman 2010). Sapindus Saponaria, Aca- cia berlandieri and Clematis dr'ummondii were the species with the highest IV value in the rural site. On the other hand, Ungnadia speciosa, Caesalpinia mex- icana and Phyla nodiflora were the most important species in the high urban- isation site. Our species with the highest IV differ from those mentioned by Alanis-Rodriguez et al. (2015) for areas contiguous to the MMA. In contrast, Estrada-Castill6n et al. (2012) report plant associations made up of species mentioned in our study, clarifying that the plant communities with the highest deterioration are associated with the areas adjacent to the metropolitan zone.

From the CCA, we identified plant species associated with urbanisation (Kremen 1992). Amongst which, invasive alien species, such as Ligustrum lu- cidum, Koelreuteria elegans, Tridax coronopifolia, Eragrostis barrelieri and Melinis repens, were found in the more urbanised sites. These species are highly tolerant to urban growth conditions and appear capable of exploiting environmental con- ditions associated with urbanisation (McKinney 2002). Native species, such as Quercus fusiformis, Carya illinoinensis, Caesalpinia Mexicana, Lantana camara, Thymophylla pentachaeta and Verbena canescens, were amongst the most com- mon species to observe in urbanised sites and likely present adaptations capa- ble of tolerating disturbance associated with urbanisation. In contrast, native species, such as Diospyros texana, Sapindus saponaria, Gochnatia hypoleuca, Zanthoxylum fagara, Citharexylum berlandieri, Verbesina persicifolia, Solanum triquetrum and Lantana canescens, were found only in the less urbanised sites. Consequently, these species are highly intolerant to process associated with urbanisation, highlighting the importance of green areas as refuges for these species. These results are consistent with the large-scale studies by Moffatt et al. (2004) and Burton and Samuelson (2008), who reported a predominance of exotic and pioneer species in more urbanised areas compared to rural areas.

The composition and structure of vegetation in peri-urban and urban areas can vary due to climate, soil conditions, ecological disturbances and human influences (Jim and Liu 2001; Jim 2002; Pedlowski et al. 2002; Escobedo et al. 2006). For this study, the conditions of RH, DP, HI and PM,,, were the variables that best describe the vegetation structure in the MMA. Other studies have documented these characteristics. For example, Stewart et al. (2009) in New Zealand and Godefroid and Koedam (2003) in Belgium studied different plant assemblages in urban and peri-urban temperate forests. In Latin America, Grau et al. (2008) in Tucuman, Argentina and Baumgardner et al. (2012) in Mexico City, analysed the role of the structure and composition of peri-urban forests as a function of the watershed and regional air quality, respectively. In addition, Puric-Mladenovic et al. (2000) in Canada and Christopoulou et al. (2007) in Greece, discussed the loss of peri-urban natural areas due to urbanisation.

Other anthropogenic factors of vegetation structure and composition have been found in other urban and subtropical areas of the world (Jim 2002; Grau et al. 2008). For example, people in southern China prefer green areas character- ised by high tree cover and large trees (Jim and Chen 2006). Furthermore, so- cioeconomic and educational levels may play a role in the structure and com- position of forests in Brazilian urban areas (Pedlowski et al. 2002). In Kenya, peri-urban mangroves have been affected by industrial pollution and sewage (Mohamed et al. 2009).

Nature Conservation 54: 179-202 (2023), DOI: 10.3897/natureconservation.54.110257 194

Edmar Meléndez-Jaramillo et al.: Vegetation change on an urbanisation gradient

The approach used in this research implies a relationship between microclimat- ic variations and plant species at the plot level. This analysis assumes the influence of environmental variables (independent variables) on the species (Dolédec et al. 2000). However, the relationship between both factors is interdependent. That is, the structure of the vegetation and the characteristics of the plants influence the abiotic variation (Guariguata and Ostertag 2001; Renaud et al. 2010; Lienard et al. 2015; Hardwick et al. 2015) and, at the same time, the presence of certain microcli- matic conditions allows the development of each plant species (Arroyo-Rodriguez et al. 2017). Therefore, the microclimate is one of the first factors to change after disturbance (Norris et al. 2012; Parr 2012; Hardwick et al. 2015).

Overall, our study analysed the effects of urbanisation on vegetation and changes in vegetation structure were detected as levels of urbanisation in- creased. However, studies in subtropical regions of North America show how, in addition to urbanisation, demography also affects the structure of the veg- etation, mainly tree structure in built-up areas (Zhao et al. 2010; Flocks et al. 2011). Additionally, other studies in South America document the effect of so- cioeconomics in vegetation structure (De la Maza et al. 2002; Pedlowski et al. 2002; Escobedo et al. 2006). The ability of parks and areas of remaining native vegetation to promote biodiversity depends largely on their design and the types of management activities to which they are subjected. For example, while regionally rare native species can be found within cities, they are often associated with habitats that have not been greatly altered (Godefroid 2001; Godefroid and Koedam 2003). Such partnerships strengthen the call to pro- tect plant communities within the urban landscape and emphasise the need for ecological knowledge to guide park design and management.

Conclusions

For the first time in north-eastern Mexico, the vegetation structure was moni- tored on a rural-urban gradient, where the height, cover, abundance, species rich- ness and diversity were the parameters recorded in sites with different levels of urbanisation. It was found that all the parameters decreased with increasing urbanisation levels; thus, in accordance with the general disturbance hypothesis, the general tendency of plant distribution at the levels of urbanisation and pollu- tion present in the MMA is to decrease. The association between environmental variables and the plant community along the urbanisation gradient was signifi- cant, the conditions of RH, DP HI and PM, , being the variables that best describe the vegetation structure in the MMA. Understanding the nature and variability of vegetation within green spaces contributes to increasing our knowledge about the distribution of the environmental services it provides and the composition of the faunal communities that depend on it. Likewise, it provides valuable infor- mation to prioritise the strategic management of the vegetation of urban green spaces so that it provides the greatest benefit for humans and biodiversity.

Acknowledgements

The first author recognises the great support of the family Cantu Bendeck for their kindness during the developing of the data collection. Bernal Herrera Fernandez gave support and recommendations during the planning of this investigation.

Nature Conservation 54: 179-202 (2023), DOI: 10.3897/natureconservation.54.110257 195

Edmar Meléndez-Jaramillo et al.: Vegetation change on an urbanisation gradient

Additional information

Conflict of interest

The authors have declared that no competing interests exist.

Ethical statement

No ethical statement was reported.

Funding

The National Council of Sciences and Technology of Mexico (CONACyT), Ph.D scholar- ship No. 704911), EMU.

Author contributions

Edmar Meléndez-Jaramillo, sampling sites selection, fieldwork, plants identification, data analysis and document writing; Laura Sanchez-Castillo, fieldwork, database com- pilation and document writing; Ma. Teresa de Jesus Segura Martinez, sampling sites selection, plants identification and completed document review; Uriel Jeshua San- chez-Reyes, data analysis, results interpretation and completed document review.

Author ORCIDs

Laura Sanchez-Castillo ® https://orcid.org/0000-0002-1028-2449

Ma. Teresa de Jesus Segura Martinez © https://orcid.org/0000-0001-8123-5773 Uriel Jeshua Sanchez-Reyes © https://orcid.org/0000-0003-3528-2610

Data availability

All of the data that support the findings of this study are available in the main text.

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