Karl Ramjohn
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Ecological Character: Northern Range, Trinidad
« Thread started on: Sep 20th, 2008, 3:47pm » |
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The Definition of “Ecological Character” and “Change in Ecological Character” with Reference to Tropical Rainforest: Acono – El Tucuche Trail, Northern Range
The Northern Range of Trinidad provides an example of a “Mountain Ecosystem”, particularly a forest and associated stream system. A forest is a complex ecosystem, with trees comprising the dominant biota. The predominance of trees provides other diverse flora and fauna, all of which form an integrated and inter-dependent system. The distinctive qualities featured in such a system, inclusive of flora, fauna, processes and interactions define the “ecological character”. This is important in defining its stability and viability. The purpose of this article is to define the “ecological character” and “change in ecological character”, based on field observations (September 23, 1998) in the forested environments along the Acono-El Tucuche Trail of the Northern Range.
Vegetation
The “ecological character” indicative of forests was more evident higher up the trail. There was an apparent stratification of plants into three distinct layers: an upper storey of taller-than-average trees, a middle storey with shorter trees (more regular and dense), and a ground layer of juvenile trees, seedlings and shrubs, with ground-level plants such as herbs, ferns and Selaginella. The leaves and upper branches of the trees form an almost closed canopy. This canopy restricts the entry of sunlight, resulting in higher humidity, and limiting undergrowth. However, in places where there was a break in the canopy, the undergrowth was more profuse.
On the forest floor, there was an accumulation of leaf litter, broken twigs and other plant materials. This is only temporary, however, as it provides food for animals, and is also acted upon by bacteria and fungi, which decompose the material. This is important for the production of humic material, which enriches the forest soils. The soils observed were generally light and spongy in nature (predominantly schists). Several trees had buttressed roots, possibly as a physical support mechanism on the light shallow soils on steeply sloping ground. Also, rather than having deeply penetrating roots, the trees tend to have a system of laterally spreading rootlets. This allows them to take advantage of the nutrients in the humic material near the surface, with the assistance of Mycorrhizae, fungi which assist the trees in nutrient uptake.
In addition to the trees, a number of associated forest plants were observed. These include plants mechanically dependent on trees, such as lianes and vines. Epiphytes, including lichens, mosses and bromeliads were observed growing on the trunks and branches of most trees. Some heterotrophic plants (without chlorophyll) were also present, mainly mushrooms growing on fallen branches in the shade. All of these plants assist in the breakdown of organic matter for soil formation, or manufacture additional material through photosynthesis.
Hydrology and Fauna
The “ecological character” of the forest also influences hydrology and drainage. The density of vegetation results in rainwater taking much longer to reach the ground. Also certain plants, such as Heliconia bihai hold water. This assists in the protection of the thin, light forest soils, as it does not bear full impact of rainfall.
A number of forest streams were observed adjacent to, and at times crossing, the trail. These have unidirectional flow, with a relatively high current speed. The streams and adjacent areas were somewhat different to other parts of the forest. There was evidence of a higher abundance of fauna, primarily indicated by higher noise levels caused by birds and insects. Some differences in plants were also observed, such as mosses and algae growing on rocks and boulders in the streams. Differences in riparian vegetation growing along the banks were also observed. Bamboo, an exotic species was found growing along the river banks, although it is possible that it arrived at the present location via “natural” colonization.
River fauna were also observed in pools and other places where the current speed was reduced. Observed fauna included insects such as water striders, fish such as Poecillia (guppies) and larvae including tadpoles. The presence of tadpoles implies frogs or other amphibian, although adults were not observed. Water-holding plants, such as Heliconia also provide micro-habitats for some species. Larger fauna are also associated with forests, including invertebrates such as scorpions and manicou-crabs, and mammals, snakes and birds. Not surprisingly, these were not readily evident. Birds were heard among the trees, as forest birds are very vocal and generally not brightly coloured, as a result of reduced visibility. Insects, most notably the Emporer Butterfly and leaf-cutting ants (bachacs), were observed.
Human Impacts: Change in Ecological Character
Human intervention in forests invariably leads to changes in their “ecological character”. The system becomes simplified, and this adversely affects processes and interactions. These changes were observed in the lower parts of the trail, closer to human settlements. Some of the most readily observed changes included the presence of introduced species, such as cacao, adjacent to the trail. There was also a less defined plant stratification, and more sunlight, resulting in grasses growing at the ground level. On some adjacent slopes there was evidence of forest vegetation being replaced by a “fire succession” vegetation, mainly grasses with a few clumps of fire-resistant palms forming effective savanna-type systems. Earlier writers in Trinidad, described rainforests as “climax vegetation” under optimal conditions. The integrated and complex interactions of such a system are crucial for the retention of its “ecological character”, and maintenance of stability and sustainable productivity, as even small changes are observed to have significant impacts.
References
Based on:
Ramjohn, Karl. The Definition of “Ecological Character” and “Change in Ecological Character” with Reference to Tropical Rainforest: Acono – El Tucuche Trail, Northern Range. Tropical Environment Research and Management Center, Trinidad & Tobago. September 1998.
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