The Chajul Tropical Field Station is located to the South of the Montes Azules Integral Biosphere Reserve, at the border off the Marques de Comillas region, Southeast Mexico (16°01’N, 90°55’ W). The climate is warm-humid with an average annual temperature of 25–27ºC, and an annual rainfall of 3,000 mm, of which 80% falls between June and October (Garcia, 1981). The February–April dry season has less than 100 mm precipitation per month.
Haplic Luvisol and Humid Acrisol soil types (FAO 1988) support associations of Tropical Rain Forest and Lower Montane Rain Forest (Pennington & Sarukhán, 1968, Meave 1990). In forested sites within the low-hill areas, soil have low pH (< 5.5), very low phosphorous (< 0.1 mg/Kg) and moderate nitrogen (13–28 mg/Kg) availability (Siebe et al. 1996). Ecological research conducted in Chajul has been recently reviewed by Martínez-Ramos (2006).
Marques de Comillas, once covered with tropical rainforest (Miranda & Hernàndez-X, 1963), is now a complex and dynamic matrix of forest remnants, secondary forests, pastures, and agricultural lands—rain forest area has been reduced to less than half its original area ((Dichtl 1988, Pérez-G. 1991, Sarukhán 1991, Lazcano et al. l992, De Jong et al. 1999). Permanent successional plots were established on abandoned milpas, the primary form of agriculture, located on sandy and limestone soils of the low-hills. In 2000, 11 sites were selected with fallow ages ranging of 1.5–17 years; sites had been under agricultural use once or twice, for one year before abandonment.
Each 0.5 ha site contains a 10 x 50 m permanent plot. All trees >1 cm dbh were identified, tagged and measured for height and DBH. Plots were censused every 6 mo for the first two years and annually thereafter. Five 20 x 500 m permanent plots in mature, old-growth forest in low-hill areas have also been monitored (DBH ≥ 10 cm) annually since 1995. Additionally we have two sets of chronosequence data in the same area, one set from 1998 (21 plots of 0.05ha) and one set from 2000 (66 plots of 0.015 ha), encompassing the five major soil types in the area.