Understory in the composition and diversity of managed forest areas in Santa Catarina Ixtepeji, Oaxaca

 

El sotobosque en la composición y diversidad de áreas bajo manejo forestal en Santa Catarina Ixtepeji, Oaxaca

 

Lizbeth Luna-Bautista¹, Patricia Hernández-de la Rosa¹, Alejandro Velázquez-Martínez¹*, Armando Gómez-Guerrero¹, Miguel Acosta-Mireles²

 

¹ Colegio de Postgraduados, Campus Montecillo. km 36.5 Carretera México-Texcoco. C. P. 56230. Montecillo, Texcoco, Edo. de México. MÉXICO. Correo-e: alejvela@colpos.mx, tel.: (595) 952 0200 ext. 1470 (*Autor para correspondencia).

² Instituto Nacional de Investigaciones Forestales y Agropecuarias. Campo Experimental Valle de México. Carretera Los Reyes-Texcoco km 13.5. C. P. 56250. Coatlinchán, Texcoco, Edo. de México. MÉXICO.

 

Received: August 28, 2014.
Accepted: March 10, 2015.

 

ABSTRACT

In the present study, the effect of silvicultural practices on richness, composition and diversity of tree species, herbaceous and shrub species in a forest community of Santa Catarina Ixtepeji, Oaxaca was evaluated. To this end, the following silvicultural treatments were evaluated: selective cutting (1998), light thinning (2011) and seed tree cutting (1998 and 2011). Alpha and beta diversity indices of tree communities (shrub and herbaceous) were estimated, and also the Importance Value index (IVI) of the tree layer. The results showed that the herbaceous component is the most diverse in both stands with and without silvicultural management, followed by the shrub component. According to the IVI, Pinus oaxacana Mirov was the most important ecological species in all treatments evaluated, including unmanaged forest. The results indicate that logging modifies richness, diversity and composition of the tree strata (shrub and herbaceous), these two tree strata are the largest contributors to diversity. Therefore it is important to assess the understory, because it helps giving a better explanation of the total plant diversity of the forest.

Keywords: Silvicultural treatments, understory vegetation, stand structure, biodiversity indices.

 

RESUMEN

En el presente estudio se investigó el efecto de las prácticas silvícolas sobre la riqueza, composición y diversidad de las especies arbóreas, herbáceas y arbustivas en un bosque de la comunidad de Santa Catarina Ixtepeji, Oaxaca. Para tal fin, los siguientes tratamientos silvícolas fueron evaluados: corta de selección 1998, aclareo ligero 2011 y árboles padre 1998 y 2011. Los índices de diversidad alfa y beta de las comunidades arbórea, arbustiva y herbácea se estimaron, así como el índice de valor de importancia (IVI) del estrato arbóreo. Los resultados mostraron que el componente herbáceo es el más diverso tanto en rodales bajo manejo silvícola como sin manejo, seguido del componente arbustivo. De acuerdo con el IVI, la especie de mayor importancia ecológica fue Pinus oaxacana Mirov. en todos los tratamientos evaluados, incluyendo el bosque sin manejo. Los resultados indican que el aprovechamiento forestal modifica la riqueza, diversidad y composición de los estratos arbóreo, arbustivo y herbáceo, siendo los dos últimos estratos los que más contribuyen a la diversidad. Por lo anterior resulta importante evaluar el sotobosque, ya que ayuda a dar una mejor explicación de la diversidad vegetal total del bosque.

Palabras clave: Tratamiento silvícola, vegetación del sotobosque, estructura del rodal, índices de biodiversidad.

 

INTRODUCTION

Species richness and diversity of each of the strata forming a forest under silvicultural management have become topics of interest, because of the need to know the most important components of the ecosystem from an ecological, economic, social and cultural perspective. The adoption of new paradigms on forest management at international level, promote the need to employ practices imitating natural succession dynamics and enhancing biodiversity, specially flora and fauna (Ares, Berryman, & Puettmann, 2009; Puettmann, 2011). Silvicultural treatments used to control species composition, growth and development of a forest are essentially simulations of natural disturbances (Fujimori, 2001; Smith, Larson, Kelty, & Ashton, 1997) modifying structure, composition, diversity and function of the stand (Ares et al., 2009; Fujimori, 2001; Oliver & Larson, 1996). Due to the above, assessing forest ecosystems through ecological indicators such as structure and diversity, focus on the analysis of the relationship among species in a population (Jiménez, Aguirre, & Kramer, 2001) and the effect of both natural and human-induced disturbances.

In Mexico studies have been performed reporting the response of tree species to silvicultural treatments, evaluating tree structure differences in time and space (Alanís-Rodríguez et al., 2013; Castellanos et al., 2008; Leyva-López, Velázquez-Martínez, & Ángeles-Pérez, 2010; Návar-Cháidez & González-Elizando, 2009; Solís et al., 2006), and studies documenting the response to a disturbance such as forest fires (Alanís-Rodríguez et al., 2010). However, studies addressing the response of understory silvicultural practices such as regeneration cutting and thinning are scarce, even knowing that the composition of tree structure can influence the diversity of understory (Barbier, Gosselin, & Balandier 2008) and that it can intervene in changing the environment for the establishment of natural regeneration (Kuehne & Puetmman, 2008). The application of thinning leads to high levels of biodiversity and richness of tree species under logging (Ares, Neill, & Puettmann, 2010; Berger, Puettmann & McKenna, 2012; Burton, Ares, Mulford, Deanna, & Puettmann, 2013).

Understory is a key component of forest ecosystems because it provides habitat for wildlife and contributes to nutrient cycling, resulting in the maintenance of productive capacity in managed forests (Ampooter, Beaten, Koricheva, Vanhellemont, & Verheyen, 2014; Berger & Puettmann, 2000; Davis & Puettmann, 2009). This study considers that the understory (shrubs and herbs) is an integral component of the structure of managed forest. The general hypothesis is that the composition and species richness and alpha and beta diversity indices in a managed ecosystem differ between silvicultural treatments and application time.

Therefore, the objectives of this study were 1) to obtain richness, species composition and diversity indices (alpha and beta) of the tree layer and understory in forests managed under different silvicultural treatments and application times and 2) determine whether there are differences in the variables analyzed in a managed forest (silviculture and application time), when compared with unmanaged forest.

 

MATERIALS AND METHODS

Location of the study area

The study area is located in the communal lands of Santa Catarina Ixtepeji, Oaxaca (Figure 1) between the geographical coordinates 17° 26' N and 96° 34' W, and average altitude of 1,920 m (Zacarías-Eslava & Del Castillo, 2010). The climate is temperate subhumid with summer rains and average annual temperatures of 17.6 °C. The type of soil is silty medium textured humic acrisol (Ah) (Zacarías-Eslava & Del Castillo, 2010; Vázquez & Givnish, 1998). Pine-oak and oak forest are the predominant vegetation; Pinus oaxacana Mirov., P. teocote Schiede ex Schltdl., P. leiophylla Schiede ex Schltdl. & Cham., Quercus crassifolia Humb. & Bonpl., Q. castanea Née and Q. rugosa Née are among the most common species (Zacarías-Eslava & Del Castillo, 2010).

Background of forest management

Forest management in the community of Santa Catarina Ixtepeji began 45 years ago. During the first 25 years, management was under Mexican method of irregular forest management (MMOBI) with selective cutting, which influenced determinedly the composition and structure of forests. In the past 20 years, the system of conservation and forestry development (SICODESI) has been used for regular stands with a rotation period of 60 years (liberation cutting, pre-thinning, four thinning and regeneration cutting) and for irregular stands with cutting cycles of10 years and selective tree cutting as main method of regeneration. In both cases it is considered that a stand with regeneration of commercial species (predominating oak and other hardwoods) has not been generated, especially due to low intensity in the application of silvicultural treatments that have created favorable conditions for the species.

Sampling sites and measurement of variables

Cutting areas correspond to annualities 1998-1999 and 2010-2011. Stands with regeneration cutting with seed tree cutting, selective cutting and light thinning were chosen in these areas. Nearby areas with similar characteristics in composition, altitude, slope and aspect were selected in order to compare the effect of these treatments on structure, composition, richness and diversity of species in unmanaged stands. Table 1 reports the number of sites sampled by silvicultural treatment and annuality. A sampling intensity of 5 % for each annuality and silvicultural treatment was established. Sampling sites were chosen randomly from a grid of dots superimposed on an image of the work area. Nested circular sites were established. At the first place (400 m², 11.28 m radius) the total height of all trees with greater normal diameter of 2.5 cm was measured and the respective species was recorded. 200 m² (7.97 m radius) sites were established in a concentric manner and the coverage percentage of shrub species and their height were measured; finally, four sites (1 m²) were placed within such areas, these sites were located systematically at 7 m from the center of each site (400 m²) in the four free zones and in the direction of clockwise. At 1 m² sites, the coverage percentage of each herbaceous species was estimated and the frequency was recorded. All species not identified in the field were collected for subsequent taxonomic identification in the herbarium at the Colegio de Postgraduados.

Data analysis

In order to know if the sampling intensity per silvicultural treatment and annuality caught the total of richness present on the site, species-area curves were created using the program Species diversity and richness 4.1 (Seaby & Henderson, 2006). Analyses and comparisons were generated for managed and unmanaged forest (silvicultural treatment and annuality). Tree stratum, shrub and herbaceous were analyzed separately in each condition, considering the last two as main components of the understory. The floristic composition at the study sites was determined for each layer at family, genus and species level.

The importance value index (IVI) was calculated only for tree species based on density, coverage and relative frequency according to Magurran (2004). Simpson and Fisher's alpha indices, both considered robust, were calculated to define the alpha diversity (Moreno, 2001). The first is influenced by the most abundant species in the sample and is less sensitive to the richness of species; the second, besides not being influenced by the sample size, is less affected by the less abundant species, allows comparison between sites and different sample sizes as long as it has more than 1,000 observations. The beta diversity or index of similarity between communities was obtained with Jaccard and Sorensen indices using the program Species diversity and richness 4.1 (Seaby & Henderson, 2006). Table 2 shows alpha and beta diversity indices used in this study. Subsequently a nonparametric statistical analysis was performed with the Kruskal-Wallis test (Wheater & Cook, 2005), and a Wilcoxon rank sum under the null hypothesis of equal silvicultural treatments and life forms.

 

RESULTS AND DISCUSSION

Species richness and composition

Area-species curves indicated that the number of samples was sufficient to capture most of the species in all conditions under analysis. The total richness in the study area corresponds to 43 species of vascular plants belonging to 31 genera and 25 families. Figure 2 shows the families and number of genera found per silvicultural treatment and annuality. A total of 30 species belonging to 23 genera and 20 families were recorded in the unmanaged forest, highlighting the Asteraceae (8) and Fagaceae (5) family. A total of 41 species belonging to 31 genera and 25 families were found in managed forests; the families with highest species richness were Asteraceae, Fabaceae and Fagaceae.

Litsea glauscences Kunth is a species recorded in the NOM-059 (Secretaría del Medio Ambiente y Recursos Naturales [SEMARNAT], 2010), which had the highest density in unmanaged forests. Moreover, two exotic herbaceous species (Geranium rutundifolium L. and Acmella papposa [Hemsl.] R. K. Jansen) and two endemic herbaceous from the state of Oaxaca (Matudanthus nanus [M. Martens & Galeotti] D. R. Hunt and Schoenocaulon oaxacense [Frame] Zomlefer & Judd) were found in managed forests.

Pinus and Quercus had higher IVI. P. oaxacana had values of 34 % for unmanaged forests and 58 % for light thinning (2011), while Quercus sp. had10 % for unmanaged forests and up to 15.9 % for seed tree cutting (1998). This coincides with the information provided by Leyva-López et al. (2010), Alanís-Rodríguez et al. (2010) and Alanís-Rodríguez et al. (2013) who found that in temperate forests, after applying silvicultural treatments, the genera with higher IVI were Pinus sp. and Quercus sp. which represent the biggest ecological weight of the ecosystem. Louman, Quirós, and Nilsson (2001) found that, generally, there is smaller proportion of dominant species in stands with greater diversity and the permanence of the few species in the stand can be influenced by silvicultural practices.

Life forms

Figure 3 shows there is greater density from trees and shrubs, regardless of the silvicultural treatment and age of application; however, density is even higher in unmanaged forest. Changes in tree density and composition influence the increase or decrease of richness and abundance of understory species (Ampoorter et al., 2014; Ares et al., 2010). Diversity and greater vertical stratification when advancing natural succession in the absence of disturbances (Smith et al., 1997) is promoted in unmanaged forests. In areas with high conservation value and low tree diversity stand out the shrub species as the most representative (García, Tapias, Fernández, Vázquez, & Salvador, 2010).

Santa Catarina Ixtepeji reports that shrub species in the areas studied are dominant at lower altitudes around 2,000 m, due to weather conditions, while trees dominate when the altitudinal gradient increases (Zacarías-Eslava & Del Castillo, 2010). According to Alanís-Rodríguez et al. (2010), life forms change with respect to climate, altitude and type of ecosystem that is being evaluated.

In the study area is evident that the history of forest management with the application of different silvicultural treatments, not always with the right intensity, has led to mixed composition for the upper canopy (Leyva-López et al., 2010), and this in turn influences the presence of life forms of temperate forests (Ampoorter et al., 2014).

Alpha diversity

Simpson diversity indices and Fisher's alpha indices reported in Table 3 indicate that regardless of the silvicultural treatment and annuality, there is greater diversity in herbaceous plants and in some cases the shrub component exceeds the tree layer. This confirms the importance of high diversity represented by the understory in forest ecosystems and the significance of incorporating it when evaluating the diversity in managed forests, even if the contribution of the understory to the total biomass may not be as important (Ampoorter et al., 2014; Ares et al., 2010; Berger & Puetmman, 2000; Elliott & Knoepp, 2005).

Specially, unmanaged forest has the highest diversity index of herbs and a significant contribution from the bushes. Theoretically, greatest diversity of life forms and further stratification of the vertical structure is promoted, when there is no logging (Davis & Puettmann, 2009), this reflects, in many cases, a high diversity.

This study shows that silvicultural treatments performed in 1998 (seed tree and selective cutting) have similar Simpson indices, although statistically different for the tree component; in contrast, light thinning and seed tree cutting in 2011 had the lowest indices. In the case of the Fisher's alpha index, diversity was lower in the tree and shrub layer, regardless of the silvicultural treatment and time of application. Several studies have reported the modification of the diversity and composition of tree layer as a result of logging (Alanís-Rodríguez et al., 2010; Castellanos et al., 2008; Leyva-López et al., 2010; Solís et al., 2006). In particular, Alanís-Rodríguez et al. (2013) reported that forest management in a temperate forest in the ejido El Largo, Durango, modified the alpha diversity in the forest, and although species richness remained, indices of Margalef and Shannon-Wiener decreased. Moreover, Zacarías-Eslava and Del Castillo (2010) report that in the area of Ixtepeji, Oaxaca, shrub species have greater variation of species richness than the trees, and that shrubs diversity decreases with altitude. In general terms, it is evident that the herbaceous component contributes significantly to the total plant diversity in the area.

Beta diversity

The similarity of species between the evaluated treatments increases with time of application of silvicultural treatment. Table 4 shows the floristic similarity indices for silvicultural treatment and annuality. The highest values of Jaccard and Sorensen indices are presented between the selective cutting and seed tree cutting in 1998. As the forest develops, a larger number of species is seen due to the stand opening and to the both, biotic and abiotic conditions that are modified when silvicultural practices are applied (Alanís-Rodríguez et al., 2010; Ares et al., 2009; Berger & Puettmann, 2000).

The unmanaged forest had the lowest similarity values, indicating that a significant percentage of species is exclusive to this condition and, therefore, beta diversity increases, although the species richness is relatively similar (Table 4). Leyva-López et al. (2010) and Alanís-Rodríguez et al. (2013) reported the above and say the number of species decreases when silvicultural treatments are performed; however, the species richness of forest remains.

 

CONCLUSIONS

Alpha diversity indices were higher in herbaceous and shrubs for all silvicultural treatments and years of application. This indicates the importance of incorporating the understory in the evaluation of plant diversity in managed ecosystems. Beta diversity indices indicate that the similarity increases over the years in the silvicultural treatments evaluated; however, the unmanaged forest has low similarity values when compared with other silviculture treatments. The explanation of composition, richness and diversity of managed forest by including understory components is complex, since they are determined by multiple biotic and abiotic factors.

 

REFERENCES

Alanís-Rodríguez, E., Jiménez-Pérez, J., Aguirre-Calderón, O. A., Treviño-Garza, E. J., Hernández-Salas, J., González-Tagle, M. A., ...Domínguez-Pereda, L. A. (2013). Efecto del manejo forestal en la diversidad y composición arbórea de un bosque templado del noroeste de México. Revista Chapingo Serie Ciencias Forestales y del Ambiente, 19(2), 189-199. doi: 10.5154/r.rchscfa.2012.08.052.         [ Links ]

Alanís-Rodríguez, E., Jiménez-Pérez, J., Pando-Moreno, M., Aguirre-Calderón, O. A., Treviño-Garza, E. J., & García-Galindo, P. C. (2010). Efecto de la restauración ecológica post-incendio en la diversidad arbórea del Parque Ecológico Chipinque, México. Madera y Bosques, 16(4), 39-54. Obtenido de http://www.scielo.org.mx/pdf/mb/v16n4/v16n4a3.pdf.         [ Links ]

Ampoorter, E., Baeten, L., Koricheva, J., Vanhellemont, M., & Verheyen, K. (2014). Do diverse overstoreys induce diverse understoreys? Lessons learnt from an experimental-observational platform in Finland. Forest Ecology and Management, 318, 206-215. doi:10.1016/j.foreco.2014.01.030.         [ Links ]

Ares, A., Berryman, S. D., & Puettmann, K. J. (2009). Understory vegetation response to thinning disturbance of varying complexity in coniferous stands. Journal of Applied Vegetation Science, 12(4), 472-487. doi: 10.1111/j.1654-109X.2009.01042.x.         [ Links ]

Ares, A., Neill, A. R., & Puettmann, K. J. (2010). Understory abundance, species diversity, and functional attribute response to thinning in coniferous stands. Forest Ecology and Management, 260(7), 1014-1113. doi: 10.1016/j.foreco.2010.06.023.         [ Links ]

Barbier S., Gosselin, F., & Balandier, P. (2008). Influence of tree species on understory vegetation diversity and mechanisms involved-A critical review for temperate and boreal forests. Forest Ecology and Management, 254, 1-15. doi: 10.1016/j.foreco.2007.09.038.         [ Links ]

Berger, A., & Puettmann, K. J. (2000). Overstory composition and stand structure influence herbaceous plant diversity in the mixed aspen forest of northern Minnesota. American Midland Naturalist, 143, 111-125. Obtenido de http://www.jstor.org/stable/3082988.         [ Links ]

Berger, A. Puettmann K. J., & McKenna, J. (2012). Understory response to repeated thinning in Douglas-fir forests of Western Oregon. Journal of Sustainable Forestry, 31(6), 589-605. doi: 10.1080/10549811.2011.628523.         [ Links ]

Burton, J. I., Ares, A., Mulford, S. E., Deanna, H., & Puettmann, K. J. (2013). Above-ground carbon storage, down wood, and understory plant species richness after thinning in Western Oregon. In P. D. Anderson, & K. L. Ronnenberg (Eds), Density management for the 21^st century: West side story. Portland, OR, USA: U. S. Department of Agriculture-Forest Service-Pacific Northwest Research Station.         [ Links ]

Castellanos, B. J. F., Treviño, G. E. J., Aguirre, C. O. A., Jiménez, P. J., Musalem, S. M., & López, A. R. (2008). Estructura de bosques de pino patula bajo manejo en Ixtlán de Juárez, Oaxaca, México. Madera y Bosques, 14(2), 51-63. Obtenido de http://www1.inecol.edu.mx/myb/resumeness/14.2/MB_2008_14-2_051-064.pdf.         [ Links ]

Davis, L. R. & Puettmann, K. J. (2009). Initial response of understory vegetation to alternative thinning treatments. Journal of Sustainable Forestry, 28, 904-934. Obtenido de http://www.fs.fed.us/pnw/pubs/journals/pnw_2009_davis001.pdf.         [ Links ]

Elliott, K. L. & Knoepp, J. D. (2005). The effects of three regeneration harvest methods on plant diversity and soil characteristics in the southern Appalachians. Forest Ecology and Management, 211, 296-317. doi:10.1016/j.foreco.2005.02.064.         [ Links ]

Fujimori, T. (2001). Ecological and silvicultural strategies for sustainable forest management. Ámsterdam, The Netherlands: Elsevier Science B. V.         [ Links ]

García, F. J., Tapias, R., Fernández, M., Vázquez, F. J., & Salvador, L. (2010). La biodiversidad como herramienta en la gestión y certificación forestal zonas de alto valor de conservación en montes madereros del sureste peninsular. Boletín Informativo CIDEU, 8(9), 57-73. Obtenido de http://dialnet.unirioja.es/ejemplar/275337.         [ Links ]

Jiménez, J., Aguirre, O., & Kramer, H. (2001). Análisis de la estructura horizontal y vertical en un ecosistema multicohortal de pino-encino en el norte de México. Investigación Agraria: Sistemas y Recursos Forestales, 10(2), 355-366. Obtenido de http://www.inia.es/IASPF/2001/vol10-2/jimen.PDF.         [ Links ]

Kuehne, C. & Puetmann, K. J. (2008). Natural regeneration in thinned Douglas-fir stands in western Oregon. Journal of Sustainable Forestry, 27, 246-274. doi: 10.1080/10549810802256221.         [ Links ]

Louman, B., Quirós, D., & Nilsson, M. (2001). Silvicultura de bosques latifoliados húmedos con énfasis en América Central. Turrialba, Costa Rica: CATIE.         [ Links ]

Leyva-López, J. C., Velázquez-Martínez, A., & Ángeles-Pérez, G. (2010). Patrones de diversidad de la regeneración natural en rodales mezclados de pino. Revista Chapingo Serie Ciencias Forestales y del Ambiente, 16(2), 227-239. doi: 10.5154/r.rchscfa.2010.06.038.         [ Links ]

Magurran, A. E. (2004). Measuring biological diversity. Oxford, UK: Blackwell Publishing Company.         [ Links ]

Moreno, C. E. (2001). Métodos para medir la biodiversidad. Zaragoza, España: Programa Iberoamericano de Ciencia y Tecnología para el Desarrollo (CYTED)-Oficina Regional de Ciencia y Tecnología para América Latina del Caribe (ORCYT-UNESCO)-Sociedad Entomológica Aragonesa (SEA).         [ Links ]

Návar-Cháidez, J. J. & González-Elizondo, S. (2009). Diversidad, estructura y productividad de bosques templados de Durango, México. Polibotánica 27, 71-87. Obtenido de http://www.scielo.org.mx/pdf/polib/n27/n27a5.pdf.         [ Links ]

Oliver, C. D. & Larson, B. C. (1996). Forest stand dynamics. New York, USA: John Wiley & Sons, Inc.         [ Links ]

Puettmann, K. J. (2011). Silvicultural challenges and options in the context of global change: "Simple" fixes and opportunities for new management approaches. Journal of Forestry, 109, 321-331. Obtenido de http://www.cof.orst.edu/cof/fs/kpuettmann/JoF%20109%202011.pdf.         [ Links ]

Secretaría del Medio Ambiente y Recursos Naturales (SEMARNAT). (2010). Protección ambiental-Especies nativas de México de flora y fauna silvestres-Categorías de riesgo y especificaciones para su inclusión, exclusión o cambio-Lista de especies en riesgo. México: Diario Oficial de la Federación. Obtenido de http://biblioteca.semarnat.gob.mx/janium/Documentos/Ciga/agenda/DOFsr/DO2454.pdf.

Seaby, R. M. H. & Henderson, P. A. (2006). Species diversity and richness version 4.1. Lymington, England: Pisces Conservation Ltd.         [ Links ]

Smith, D. M., Larson, B. C., Kelty, M. J., & Ashton, P. M. S. (1997). The practice of silviculture: Applied forest ecology. New York, USA: John Wiley & Sons, Inc.         [ Links ]

Solís, M. R., Aguirre, C. O. A., Treviño, G. E. J., Jiménez, P. J., Jurado, Y. E., & Corral-Rivas, J. (2006). Efecto de dos tratamientos silvícolas en la estructura de ecosistemas forestales en Durango, México. Madera y Bosques, 12(2), 49-64. Obtenido de http://www.redalyc.org/articulo.oa?id=61712205.         [ Links ]

Vázquez, G. A. & Givnish, T. J. (1998). Altitudinal gradients in tropical forest composition structure and diversity in the Sierra de Manantlán. Journal of Ecology, 86(6), 999-1020. doi: 10.1046/j.1365-2745.1998.00325.x.         [ Links ]

Wheater, C. P. & Cook, P. A. (2005). Using statistics to understand the environment. London, UK: Routledge Taylor & Francis.         [ Links ]

Zacarías-Eslava, Y. & Del Castillo, F. R. (2010). Comunidades vegetales templadas de la Sierra Juárez, Oaxaca: Pisos altitudinales y sus posibles implicaciones al cambio climático. Boletín de la Sociedad Botánica de México, 87, 13-28. Obtenido de http://www.scielo.org.mx/pdf/bsbm/n87/n87a2.pdf.         [ Links ]