Marine Communities in the Intertidal Zone

Alvarez, Ma. Lemie G.                                                                                               May 20, 2015

2013-98581                                                                                                                 BIO 150 F-1L

Exercise 4C. Tropical Rainforest and Tropical Grassland

A community can be characterized based on its physical, chemical, and biological structure. It also undergoes patterns of development commonly known as community development or succession (Botkin and Keller, 1982). Succession is the process by which the communities we see in nature were establishment of a climax community. These stages involve changes in both the biological and physical component of the habitat. There are two kinds of succession, namely; primary and secondary succession. Primary succession is referred to as the initial establishment of an ecosystem. Smith and Smith (2004) further described it as a succession occurring in an area which has never been occupied by other community. Secondary succession, on the other hand, is a reestablishment of an ecosystem wherein the series of changes occur in a preoccupied area that has been already disturbed yet not all individual components have been destroyed or totally removed (Botkin and Keller, 1982). During a community succession, different species undergo changes. There are species that tend to be dominant at the early succession stages while there are species which tend to dominate the late succession stages. The latter species are termed as the late successional species while the other group of species is known as the early successional or pioneer species (Botkin and Keller, 1982). In addition, the latest successional stage of a community is termed as the climax community. This stage is also known as the mature stage wherein the community has finally achieved a dynamic equilibrium and a steady state.

The tropical rainforest is earth’s most complex biome in terms of both structure and species diversity. It occurs under optimal growing conditions: abundant precipitation and year round warmth. There is no annual rhythm in the forest; rather each species has evolved its own flowering and fruiting seasons. Sunlight is a major limiting factor. A variety of strategies have been successful in the struggle to reach light or to adapt to the low intensity of light beneath the canopy. A primary forest are undisturbed forest having high canopies and several layered understories resulting to a poor ground vegetation and high diversity whereas secondary forest are described as the forest having “less developed canopy structure and less diversity”. It can also be characterized by buttresses, having a large leaves and drip tips. Many species in primary growth forest have broad, woody flanges at the base of the trunk. Originally believed to help support the tree, now it is believed that the buttresses channel stem flow and it’s dissolved nutrients to the roots. Large leaves are common among trees of the C layer. Young individuals of trees destined for the B and A layers may also have large trees. When the reach the canopy new leaves will be smaller. The large leaf surface helps intercept light in the sun-dappled lower strata of the forest. Drip tips facilitate drainage of precipitation off the leaf to promote transpiration. They occur in the lower layers and among the saplings of species of the emergent layer (A layer).

Some indicators of stage of succession are: grass and short-statured species found along the road/trail to forest study site, tree and shrub species found along the road/trail to grassland study site and indicators of agricultural activities in the grassland study site. Different species found along the trail were recorded in Tables 4C.1

Table 4C. 1. Species present along the trail to tropical forest and tropical grassland study sites.

The climax community which is the most stable characteristic community (esp. vegetation) in an area as allowed by the climatic condition (Climatic climax community) is composed of species that are very competitive and highly specialized for a narrow set of environmental conditions (k-strategists). One example is the Dipterocarp trees (White Lauan), growing seedlings require protection from intense sunlight, excessive water loss and strong winds, hence, it only grows under the canopy of older taller trees that serve as nurse trees. The climatic climax community for the Philippines is the tropical forest. However, the specific local conditions may not allow the development of a forest in the area. In that case, the grassland there is said to be an edaphic climax community (climax community allowed by specific local conditions, differing from the climatic climax). Philippines, is predominated by Imperata cylindrica and Saccharum spontaneum. This was due to the shifting cultivation assisted by fire which is occurring in most Philippine grasslands. Because of the high dominance of the two species, it can also be concluded that there is a very low diversity in most Philippine grasslands. Factors affecting succession include: environmental conditions - rainfall/moisture, temperature, etc),  type of parent material - volcanic material is more conducive for colonization than bare rock, presence/recurrence of disturbance - fire, human disturbance, etc., neighboring communities – source of propagules and time.