Forest
Laguna del Tigre belongs to the Tehuantepec rainforest ecological region (Dinerstein et al, 1995). Studies show that flora is heterogeneous and composed of numerous families that have adapted to several environments. There are three vegetation zones in the area, each with a particular composition and structure, and 14 natural ecosystems (FIPA/USAID, 2004)(2). Eighty-one tree species have been reported in the eastern zone and 98 in the central area (CONAP, 1999). The Laguna del Tigre management unit's master plan - which includes the biotope and the surrounding national park - states that the predominant habitat is transition woodlands (between wetlands and elevated forests), covering approximately 55% of the protected area. Nearly 30% of the area is covered by floodable savannah and marshes, while elevated forests cover the rest, along with scattered oak (Quercus oleoides) communities, riparian vegetation, lakes, lagoons, and rivers.
An important part of Laguna del Tigre is under very heavy human intervention; the forest is being cleared for grasslands and agricultural lands and forest fires are a constant menace. The eastern and northern zones are less disturbed; the central area, most of the southern portion, and some plots in the west have been severely fragmented by human actions.
Elevated forest
This type of forest is quite scarce in Laguna del Tigre, and only a handful of patches remain to the southeast, east, and west (ProPetén, 1998). Elevated forests cover approximately 6% of the area (CONAP Master Plan, 1999); the trees in these woods are sturdy, well developed, leafy, and exuberant, and normally thrive atop knolls or small elevations. Although the canopy can grow to 25 m, some odd individuals protrude 30 to 35 meters above average.
The more sheltered places reveal an intermediate stratum, from 12 to 15 m, and underbrush that can grow to 6m. Brosimum alicastrum ("breadnut") is one of the most abundant species, as are Pouteria reticulata, P. amygdalina, P. campechiana, and Manilkara zapota (CONAP, 1999). The leaves of some species fall off during the dry season, especially atop hills, which are characteristically very dry (Schulze y Whitacre, 1999) due to exposure to light, air, and overland flows. The underbrush of the highest and shadiest areas harbors many palms (Orbignya cohune, Sabal morrisiana, Chamaedorea sp., and Desmoncus ferox). The park has an elevated and sparse forest ecosystem that floods during the rainy season, one of the very few of its kind in the total Mayan Biosphere (FIPA/USAID, 2004).
Transition forest
This type of forest is the most prevalent in Laguna del Tigre, with several plots in the central, eastern, and northeastern territories, although an important extension has been heavily fragmented and impacted by human intervention. The transition woodlands are a group of plots that exhibit mixed elevated and lowland forests as well as savannahs (CONAP, 1999). This habitat is very much dependent on water, because most of it, including the elevated forest, is flooded during at least part of the year. Floods determine the composition of the vegetation. Therefore, the areas with thick, murky soils and poor drainage become flooded during the rainy season, and dry and eroded upon the onset of the dry season, exhibiting characteristics of lowland forests, with associations of Bucida buceras, Haematoxylum campechianum, Nectandra membranacea, Coccoloba sp., and palms such as Sabal morrisiana and Chryosophila argentea (CONAP, 2001a). The areas that collect most of the water give way to savannahs.
Flooded Savannahs and Marshes
Savannahs cover most of the northern quarter: approximately 15% of the total protected area (CONAP, 1999), mainly inside the national park. Flora has adapted to extreme climate conditions; the land floods during the rainy season and erodes upon the onset of the dry season (Pennington and Sarukhan, 1998), which fosters herbaceous vegetation with a few trees such as Bucida buceras, Pachira acuatica, and Spondias sp., among others. The western savannahs gradually transform into marshes, especially in the south near the biotope. Abundant water transforms the northeastern savannahs - characterized by "jimbal," a bamboo species that, although not yet adequately described, is presumed to be Bambusa longifolia - into marshes.
The marshes are permanently covered by surface waters or are located very close to them. The most prevalent vegetation is Cladium jamaicensis. Southeastern marshes cover approximately 12% of the surface of the national park and almost 35% of the biotope, and are surrounded by transition woodlands. The landscapes of the park and the biotope are smooth, with herbaceous vegetation that can grow up to 1.5 to 2 m high, with a handful of isolated trees and palms. These habitats are prone to forest fires, which foster the gradual expansion of the savannahs (Méndez et al., 1998).
Oak forest
A secluded population of oaks (Quercus oleoides) thrives in 2,367 hectares in the southeastern corner of the protected area (CONAP, 1999). An unreported small plot of the same species was discovered during a field visit to the northeastern area of the biotope, not far from an oil well. The southeastern oak woodlands prosper in a flooded area along with other species such as Bucida buceras and Haematoxylum campechianum, which are usually found in lowland forests. Inside the biotope, oak grows in a rippled area that surrounds small flooded savannahs, and the underbrush fosters some labiatae and palm species. In both areas, trees do not grow beyond 15 m, the canopy is open, and the underbrush is packed and thick. Forest fires and cattle herding jeopardize the oak in the southeast: the trees have almost completely disappeared.
