Ecological dynamics in the Tabunan forest fragment in Cebu City, Philippines

The Tabunan forest remnant predominantly lies on limestone geology. It sits on the ridge with elevation ranging from 400 to 880 masl and slope of 11% to as high as 50%. Soil analysis reveals low levels of nitrogen, phosphorus, and potassium in the forest. However, organic matter content is high and soil pH and temperature are within the range favorable for plant regeneration, growth and development. The air temperature inside the forest is lower (24 deg C) compared with the open areas in the forest edge (27 deg C). Consequently, relative humidity is higher inside the forest (93.6%) than in open areas (78.5%). The profile of the Tabunan forest fragment revealed at least three vertical strata: the emergent, canopy and lower canopy layers. Furthermore, it has a closed canopy with an average of 82.66% crown closure. One hundred eleven species belonging to 71 genera and 36 families were observed in a total area of 600 sq m. The Shannon-Weiner index of diversity ranges from 2.29 to 2.54 and is comparable to that of the Dipterocarp midmontane forest (3.899) and mossy forest (3.57) in Mt. Makiling as observed by Gruezo (1997). The evenness of distribution between sites ranging from 0.89 to 0.94 approaches the highest value of 1, indicating equitable distribution of species. Sorensen's community coefficient is low (range=19.23% to 31.68%), with Plots 2 and 3 having the least similar species composition. The forest edge is composed of cultivated and abandoned farms. In the abandoned farms where succession has already proceeded, herbs, shrubs, and pioneer trees characteristic of secondary vegetation dominate. On the other hand, cash crops of various kinds dominate the cultivated farms. Land use history generated thru key informant interviews indicated that the expansion of agriculture and settlements resulted in forest fragmentation and consequently, the decline of population of some economically important plants and animals. Furthermore, results of the key informant interview shows that there are two groups of forest users: the local community, and visitors who utilize different goods and services of the forest. Increasing awareness as to the importance of the Tabunan forest fragment to the community was also observed. The community likewise recognizes the economic as well as the ecological functions of the forest