Revista Mexicana de Ciencias Forestales Vol. 15 (83)

Mayo - Junio (2024)

Fecha de recepción/Reception date: 8 de diciembre de 2023.

Fecha de aceptación/Acceptance date: 28 de febrero de 2024.

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¹El Colegio de la Frontera Sur (Ecosur), Unidad Tapachula. México.

²Colegio de Postgraduados (Colpos) Campus Montecillo. México.

*Autor para correspondencia; correo-e: vin.bertolini@gmail.com

*Corresponding author; e-mail: vin.bertolini@gmail.com

Abstract

Urban vegetation is a vital part of urban infrastructure due to the environmental services it provides and the benefits to the population; therefore, it is important to know its diversity and structure. The objective of this work was to assess the structure and floristic composition of trees, palms and shrubs located in public urban areas of the city of Tapachula, state of Chiapas. Mensuration information was collected from eight public parks; five public green areas, four medians and 38 streets, with a total area of 27.32 ha. Normal diameter (1.30 m base from the ground) and total height were recorded. The density of species per urban green area was calculated. Diversity was evaluated using the Shannon-Weiner and Margalef indexes. Taxonomically, 130 species, 109 genera and 44 families were identified. Of the 130 specific taxa recorded, 65 belong to native species and 65 exotic. The total number of individuals was 1 927 exotic and 550 native. Ficus microcarpa is the predominant exotic with 6.14 Importance Value Index (IVI). Of the native species, Roseodendron donnell-smithii stands out as the most representative (IVI=1.45). The Shannon-Weiner Index calculated for different green areas registered 2.7≤H'≤3.3 and the Margalef Index 5.2≤D_Mg≤15.2, showing that the streets have a great species diversity.

Key words: Urban trees, urban forestry, exotic species, native species, diversity index, landscaping.

Resumen

La vegetación es una parte vital de la infraestructura urbana por los servicios ambientales y los beneficios que provee a la población, por lo que es importante conocer su diversidad y estructura. El objetivo del presente trabajo fue evaluar la estructura y composición florística de árboles, palmas y arbustos ubicados en áreas urbanas públicas de la ciudad de Tapachula, en el estado de Chiapas. Se recabó información dasométrica de ocho parques públicos, cinco áreas verdes públicas, cuatro camellones o jardineras y 38 calles, con una superficie total de 27.32 ha. Se registró el diámetro normal (1.30 m de la base del suelo) y la altura total. Se calculó la densidad de especies por área verde. La diversidad fue evaluada mediante los índices de Shannon-Weiner y de Margalef. Taxonómicamente, se identificaron 130 especies, 109 géneros y 44 familias. De los taxa registrados, 65 pertenecen a especies nativas (550 individuos) y 65 a exóticas (1 927 individuos). Ficus microcarpa es el taxón exótico preponderante con un Índice de Valor de Importancia (IVI) de 6.14. De las especies nativas, Roseodendron donnell-smithii destaca como el elemento más representativo (IVI=1.45). El Índice de Shannon-Weiner calculado para diferentes áreas verdes registró 2.7≤H’≤3.3 y el Índice de Margalef 5.2≤D_Mg≤15.2, lo cual evidencia que las calles poseen una gran diversidad de especies.

Palabras clave: Arbolado urbano, dasonomía urbana, especies exóticas, especies nativas, índice de diversidad, paisajismo. 

Introduction

Rapid and uncontrolled urbanization causes the loss of biodiversity, soil degradation, high levels of fragmentation of green spaces and low connectivity between the city and the natural environment (Velasco et al., 2014). In this sense, the importance of studying urban trees to have concrete data on what is happening at the present and provide solutions that can mitigate environmental problems at a local scale is indisputable (Martínez-Trinidad et al., 2021). Green areas for public use can conserve and preserve biological variability within the city, being reservoirs of fauna and flora species from each region (Mexia et al., 2018). The trees intercept and store rainwater to recharge the soil aquifers, absorb polluting particles and the canopy functions as a barrier against noise, and at the same time offers shelter for birds, squirrels, bats, insects, among other animals (Guillen-Cruz et al., 2021).

Knowing the diversity and floristic structure contributes to properly managing trees in urban green areas to maximize environmental services (Morales-Gallegos et al., 2023). Inside a city, the tree composition becomes an integral part of it; it positively interacts with the atmosphere and soil, and adapts to the difficult conditions dictated by the urban environment (Liu et al., 2022). Based on the above, the objective of the present study was to evaluate the structure, composition of trees and shrubs, as well as compare the richness and diversity of species between avenues, streets, squares, parks and public medians of the city of Tapachula, state of Chiapas, in order to have a representative estimate of the tree heritage and set a guideline for better future planning.

Materials and Methods

Study area

The city is located within the Soconusco region, Chiapas, and is located between 14°53'28.34" N and 92°16'15.74" W (Martínez-Camilo et al., 2019). Two types of climate prevail: Am (warm humid with intense rains in summer) with an annual precipitation greater than 2 500 mm and annual average temperature of 26 °C, and Aw₂ (warm subhumid with rains in summer) with a higher average annual temperature of 22 °C and an annual average precipitation of 500 to 2 500 mm (Murcia and Macías, 2009). The Tapachula municipality covers about 51.74 km² with an average elevation of 170 masl. Geomorphologically, the city is located between the low mountain range with steep slopes and the coastal plain with hills, which rest on Mesozoic metamorphic rocks (García-Palomo et al., 2006). The sampling areas were located throughout the central part of the city with the aim of recording the oldest specimens (Figure 1). It was also decided to evaluate the south-west axis that coincides with the road to the airport and the exit to the east of the city, until reaching the Bonanza roundabout, which coincides with the end of the city before the highway to Guatemala. Field data were collected during 2018-2020.

Source: Prepared by the authors based on an image from https://www.google.com/intl/es-419/earth/.

Figure 1. Location of the sampling points inside the city of Tapachula, Chiapas, Mexico.

55 green areas were selected, all with free access to the public, and the typology of urban green spaces was described as: 38 streets, eight public parks, four planters or medians and five public green areas. In addition, the surface area of the types of urban green areas was determined and a database was generated in Microsoft Excel^® in which the infrastructure of the urban typology was included (Alanís-Rodríguez et al., 2022, Morales-Gallegos et al., 2023).

Floristic inventory

A tree, palms and shrubs census established in the types of urban green areas was carried out. Individuals of interest were georeferenced using a GPS/GNSS navigator for Android^® (Dangullaa et al., 2020). All census individuals were measured in terms of total height (h) with a PM-5 Suunto^® hypsometer, normal diameter at 1.30 m (d_{1.30 m}) from the ground with a model TP30ME Truper^® crosshead 30 m fiberglass measuring tape (Cruz-Salazar et al., 2020; Holguín-Estrada et al., 2021).

The species were identified by common and scientific name, using botanical keys (Macías et al., 2015) and to verify the correct and updated nomenclature, the Tropicos^® platform was used (Tropicos, 2023). The taxa that could not be identified in the field were collected for determination in the ECO-TA-H herbarium of El Colegio de la Frontera Sur (Ecosur). Their origin was determined (native or exotic) and the total number of trees, palms and shrubs per urban green area was counted (Alanís-Rodríguez et al., 2022, Morales-Gallegos et al., 2023).

Structure and diversity

The abundance for each individual of each species was calculated, based on the number of individuals, its dominance according to its basimetric area and its frequency based on its presence in the sampling sites. The relative values of the structural attributes were combined into the Importance Value Index (IVI) (Holguín-Estrada et al., 2021). Richness and alpha diversity were estimated with the Shannon-Wiener entropy index, which is based on the proportional distribution of the abundance of each species, and the Margalef richness index, which considers the quantification of the number of species present and the Shannon true diversity index (¹D) (Moreno et al., 2011); in addition, a Foreign index (Sa) was used that indicates the percentage of species not native to the geographical area based on the native species and species native to the region (Morales-Gallegos et al., 2023) (Table 1). 

Table 1. Formulas used to calculate the richness, diversity, foreign species and Importance Value Index in the types of urban green areas within the city of Tapachula, Chiapas, Mexico.

The 10-20-30 rule was also used, which assumes that a tree species should not exceed 10 %, a genus 20 % and a family no more than 30 % as an indicator of diversity (Dangulla et al., 2020; Martínez-Trinidad et al., 2021). The calculations were performed in a Microsoft Excel^® spreadsheet (Morales-Gallegos et al., 2023).

Results

The total area explored was 27.32 ha. The total number of individuals (2 477) grouped into 130 species, 109 genera and 44 families. The most representative families in number of species were Fabaceae with 19 taxa, Arecaceae with 12, Bignoniaceae with 10, Rutaceae with eight, Moraceae with seven and Malvaceae with six. Angiosperms represented 96.92 %, while gymnosperms represented 3.08 %. Due to their origin, of the 130 taxa recorded in the study, 65 were native and 65 exotic. Cedrela odorata L. and Roystonea regia (Kunth) O. F. Cook are declared as species subject to special protection (Pr) in the NOM-059-SEMARNAT-2010 Mexican regulation (Semarnat, 2010) (Table 2). 

Table 2. Tree species, palms and shrubs, and average dasometric variables found in 55 green areas of the city of Tapachula, Chiapas, Mexico.

No. Ind. = Number of individuals; Dn = Normal diameter (cm); At = Total height (m); Ab = Basimetric area (cm²); Na = Native; Ex = Exotic. *Specie in NOM-059-SEMARNAT-2010 (Semarnat, 2010) in status subject to special protection. 

In relation to the height class, the greatest presence of trees, shrubs and palms was recorded in the 5.04-7.31 m category with 904 individuals, followed by the 2.77-5.04 m category in which 593 individuals and 31 individuals with a height greater than 18.65 m. The distribution of individuals in height classes had an asymmetric distribution (Figure 2). Most urban trees are made up of young specimens and few mature and long-lived individuals.

Figure 2. Number of individuals of trees, shrubs and palms according to total height class (m).

With regard to the diametric classes, it is observed that a low number of individuals with small diameters and a greater number of specimens with large diameters (>21 cm) prevail; there is heterogeneity in its distribution, which means that it is not strictly normal. In total, 555 individuals smaller than 21 cm in normal diameter and 1 922 individuals larger than 21 cm were counted; however, the highest abundance was recorded in the diameter classes of 13.5-20.0, 59.0-65.5 and 72.0-78.5 cm with 407, 344 and 305 individuals, respectively. The distribution of individuals in diametric classes was asymmetric, probably due to the wide diversity of present species (Figure 3).

Figure 3. Number of individuals of trees, shrubs and palms according to the normal diameter class (cm).

The most abundant species were: Ficus microcarpa L. f. (16.39 %), Terminalia catappa L. (9.41 %), Elaeis guineensis Jacq. (8.16 %), Polyalthia longifolia (Sonn.) Thwaites (8.03 %), Ficus benjamina L. (7.63 %), Dypsis lutescens (H. Wendl.) Beentje & J. Dransf. (6.26 %) and Murraya paniculata (L.) Jack (4.52 %) (Table 3). Those with the highest Importance Value Index were: Ficus microcarpa (exotic), Elaeis guineensis (exotic), Ficus benjamina (exotic) and Terminalia catappa (exotic) (Table 3).

Table 3. Ecological parameters of abundance, dominance, frequency and Importance Value Index of the most frequent tree species, palms and shrubs in the green areas of the city of Tapachula, Chiapas, Mexico.

*Native species

According to the richness and diversity indexes, the city of Tapachula has a greater richness of species in alignment trees (streets) and in public green areas, while in the flower beds or medians the results were lower (Table 4). 

Table 4. Diversity indexes obtained by type of green area in the city of Tapachula, Chiapas, Mexico.

No. Ind. = Number of individuals.  

Discussion

The city streets presented a greater diversity of species: this is probably due to the fact that this type of surface shown, along with the green areas, were the largest. However, the diversity of the former had double the records compared to green areas. It is considered that this data reflects the probable renewal of the road's own trees, which are more susceptible to intervention by the city council, because the conditions of the sidewalks cause more stress on the vegetation than larger spaces. 130 species were recorded in the city of Tapachula, a figure much higher than the 38 defined by Alanís-Rodríguez et al. (2022) in the center of Hualahuises, Nuevo León, and at 33 by Molina et al. (2023) in urban forests of six rural areas of said town, northeast of Mexico. It is worth mentioning that the ecological situation of Tapachula offers more favorable conditions for biological diversity than those of Nuevo León, since it is a humid tropical environment.

The Fabaceae family was the most representative with 19 species. Equal numbers of native and exotic species were recorded (65 and 65, respectively). Generally, for other Mexican cities, more exotic than native species have been recorded (Alanís-Rodríguez et al., 2022; Molina et al., 2023; Morales-Gallegos et al., 2023). This pattern can be observed in much of the world and is related to the increase in the production of ornamental trees introduced in nurseries (Alanís-Rodríguez et al., 2022). The high presence of exotic species in the city of Tapachula is related to the increase in their use in the green areas of the cities of southern Mexico in the 80s and 90s, due to their attractiveness and the low availability of species native (Morales-Gallegos et al., 2023).

On the other hand, under the aim of protection and conservation against exotic or native pests and diseases, Santamour (1990) proposed the 10-20-30 rule to promote the diversity of urban forests (10% abundance at the specie level, 20% abundance at the generic level and 30% abundance at the plant family level). In addition, a range of ages should be maintained to rationally plan the removal and replacement of dead specimens and pruning (Flores et al., 2018). In the case of the city of Tapachula, Ficus microcarpa exceeds 10 % presence, Citrus 20 % in terms of the genus, and the Fabaceae family exceeded 30 % in accordance with what was recommended by Santamour (1990).

In a diagnosis of the urban trees of “El Vedado” in Havana, Cuba, 33 tree species were counted, of which Ficus sp., Calophyllum antillanum Britton and Terminalia catappa represent 42 % of the total; 34 % of urban trees showed serious health problems, mainly in the crowns (Castillo and Pastrana, 2015), data similar to those identified in the present study. In 17 urban green spaces in the city of Recife, Pernambuco, Brazil, 49.1 % native species and 50.9 % exotic species were calculated, similar to the proportion in the study of interest (De Souza e Silva et al., 2020). In contrast, Dangullaa et al. (2020) evaluated the composition, diversity, structural characteristics and provenance of trees in two cities in northwestern Nigeria, and concluded the predominance of native species over exotic ones, as well as the highest populations of exotic origin.

In Mexico, the structure, diversity and ecosystem services of trees were evaluated in four parks in the city of Texcoco, State of Mexico (Martínez-Trinidad et al., 2021), and in a similar way to the study described here, Ficus benjamina it was an abundant species with 23 % of the total. For the state of Chiapas, specifically for the city of Tuxtla Gutiérrez, Román-Guillén et al. (2019) reported a total of 7 539 trees, distributed in 38 families, 88 genera and 114 species; 74 % were introduced individuals. Although the urban trees of Tapachula have a lower percentage of exotic species, due to its climatic regime and geographical position, it is important to promote tree diversity to reduce phytosanitary problems, mainly due to the lack of planning in the selection of species and their relationship with ecosystem benefits.

Conclusions

Angiosperm tree species are the most numerous in the city. Unlike other cities in Mexico and the world, the percentage of exotic and native species is similar. The alignment trees and in public green areas gather the greatest richness of species. Ficus microcarpa is a species that does not comply with the 10-20-30 rule, so its presence should be reduced, while the Citrus genus is also overrepresented. This study is the first approach and historical record published about the trees of the city of Tapachula, and provides information for better management of the trees in the selection and replacement of tree species.

Acknowledgements

The authors thank the people who participated in the field activities as practitioners.

Conflict of interests

The authors declare no conflict of interest.

Contribution by author

Carlos Mario Almeida-Cerino: field work, preparation of the manuscript, information collection and data analysis; Vincenzo Bertolini: preparation and review of data and manuscript; Tomás Martínez-Trinidad: preparation and review of the manuscript.

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