**1. Introduction**

134 The Dynamical Processes of Biodiversity – Case Studies of Evolution and Spatial Distribution

Veiga, M.P. da , Martins, S.S., Silva, I.C., Tormena, C.A. & Silva, O.H. da. (2003). Avaliação

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*Scientiarum*, Maringá, Vol. 25, No. 2, pp. 519-525, ISSN 1679-9275

Janeiro

Paraná, Brasil

dos aspectos florísticos de uma mata ciliar no Norte do Estado do Paraná. *Acta* 

*adaptada a um Sistema Universal*, Instituto Brasileiro de Geografia e Estatística/Departamento de Recursos Naturais e Estudos Ambientais, Rio de

composição florística e estrutura de uma Floresta Ombrófila Mista, no Município de General Carneiro (PR). *Ambiência*, Vol. 1, No. 2, p. 229-237, ISSN 1808-0251 Zacarias, R.R. (2008). O componente arbóreo de dois trechos de Floresta Ombrófila Densa

Aluvial em solos hidromórficos, Guaraqueçaba, Paraná. M.Sc Dissertation. Pósgraduação em Ciências Biológicas, Universidade Federal do Paraná. Curitiba,

> Southern Mexico is well known for its high biodiversity (CONABIO, 2008). This biodiversity is a result of several factors like its geographic position, geographic diversity, and physiographic richness (Ferrusquilla-Villafranca, 1998). In particular, Chiapas, Mexico's southernmost state holds seven physiographic zones, including valleys, mountain chains, plateaus, and coastal plains (Müllerried, 1957). Most of this biological richness is to be found in the eastern moist forest, northern mountains, central plateau, and Sierra Madre (Breedlove, 1981). The Sierra Madre mountain chain harbors some of the very last patches of Cloud Forest, which is one of the most endangered ecosystems both in Mexico and at a global scale (Challenger, 1998; Toledo-Aceves et al., 2010). Fortunately, three existing biosphere reserves namely El Triunfo, La Sepultura and Volcán Tacaná, aim to protect and maintain this highly threatened ecosystem.

> As elsewhere, natural areas compete for land with human activities such as agriculture and cattle ranching, recently, climate change has added up to the list of threats. Only at El Triunfo reserve between 1983 and 1993 were lost 8,946 ha, including 5,084 ha of Cloud Forest (March & Flamenco, 1996). As a region, the Sierra Madre de Chiapas, was between 1998 and 2005, the region that suffered the greatest impact related to climate change in the form of massive landslides. For example, more than 15,000 ha of Cloud Forest were affected in Chiapas by Hurricane Isis (Richter, 2000), while this phenomenon has also occurred in other parts of the Americas (Restrepo & Alvarez, 2006).

> The loss of forest cover in the upper parts of the mountain chain generates a reduction of water retention and filtering capability which results in soil loss and consequently in river sedimentation. This also has occasioned an increment of water flow volume which augments flood risk. One way to help to reduce flood risk is through the ecological restoration of forest systems in the upper basin, and subsequent recovery of the ecological services associated to forest. Hence, information on the structure of natural plant communities, including structure and floristic composition, is central to establish sound ecological restoration strategies and policies. Our research objective, was thus, to evaluate and analyze the natural successional process in a cloud forest along a successional gradient

Structure and Floristic Composition in

a Successional Gradient in a Cloud Forest in Chiapas, Southern Mexico 137

We selected three study sites at ETBR, all localized in the core zone I, based on accessibility and disturbance history. We established sampling plots in three different successional stages according to the time elapsed since disturbance: 1.- Early growth, 20-25 years old (n = 10); 2.-

We modified the method proposed by Ramírez-Marcial et al. (2001) to describe the physiognomy and structure of plant communities. We used 0.1 ha circular plots, with a radius of 17.8 m. Inside each circular plot we set smaller circular sub-plots (Figure 2). To avoid border effect, plots were placed at least 50 meters from the border. We randomly selected a point to be used as the center of the plot, and then we placed four straight lines 17.8 m long to each cardinal direction with marks at 5.6, 12.6 y 17.8 m. Then, beginning from the plot center, we traced a circle at the 5.6 m mark (circle "A"), another at the 12.6 m mark (circle "B"), and finally one at the 17.8 mark (circle "C"). Then we measured different vegetation features in each circle. Circle A: all trees with DBH ≥5 cm and ≤ 10 cm; circle B:

all trees with a DBH >10 cm and ≤ 30 cm; circle C: all trees with a DBH > 30 cm.

Fig. 2. Plot sampling layout (modified from Ramírez-Marcial et al., 2001)

17.8 m

*Dominance* (D): Due to the difficulty of measuring horizontal crown projection to estimate dominance (Lamprecht, 1990), we used basal area, expressed in m2, for each species to

A

5.6 m

12.6 m

B

C

**AD** = (π/4) x dbh2

**2.1 Data analysis** 

Where:

estimate Absolute Dominance (AD):

π = 3.1416, dbh = diameter at breast height

old growth 30-35 years old (n = 7); and 3.- Mature forest (n = 10).

(20-25 years old, 30-35 years old, and mature forest), and to determine the floristic composition, vegetation structure, and species replacement along this gradient.
