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Relationship of Some Environmental Factors with the Tree Layer and Other Plant Communities in a Lowland Rainforest of Palawan, Philippines
Abstract:
The study was conducted in Sitio Kayasa, Brgy. Tagabinit, Puerto Princesa City, Palawan from August 1, 1995 to February 20, 1996. A patch of virgin forest surrounds this limestone rock. Thirty-two square plots in a line plot layout, each with 20 x 20 m2 dimension were established. Two more plots were located 3 km northeast from Kayasan and another two 13 km away.
The study discovered that 31 percent of the variations among 36 stands in terms of 15 soil variables may be explained by a function which was a linear combination of soil variables clay, N, OM, sand, CEC, and pH while another 22 percent of the same may be explained by a second function which was a linear combination of mostly micronutrients, namely: Ca, Mn, Zn, Cu, and Mg. Stepwise regression analysis extracted from the first function showed only clay, N, and sand as significant while Ca, Mn, Zn, and Cu from the second function. Principal component analysis (PCA) and regression scores when independently plotted in two scattergrams showed similar results.
Ordination by PCA and multidimensional scaling (MDS) found that the line plot layout of 35 samples can be classified into the following groupings: young second growth forest (SGF), advanced SGF, outlier old growth forest (OGF) with some SGF characteristics, OGF with Magpanggamot (cf. Shore sp.), and OGF without Magpanggamot. Using stepwise multiple regression analysis (SMRA), the study
found that some of the PCA scores correlated with some environmental variables measured, namely: CEC, clay, N, OM, sand, silt, P, Ca, Cu, Mn, Zn, pH, Fe, Mg, land post (plot position on valley, mid-slope or ridge), longitude, latitude, altitude (meters above sea level), and slope (percent gradient).
The study estimated that the timber volume in OGF stands may amount to 258 m3/ha—23 percent belonged to Apitong group (Dipterocarpus spp.); 4 percent, Ebony group; 2 percent, Nato group; 1 percent, Makaasim group; 9 percent, various commercial groups; and 61 percent, non-commercial. The area was virgin in terms of the timber resources but not in terms of commercial rattan. Rattan attributes did not show any relationship with measured environmental factors and may be attributed to its disturbed condition.
An improved sampling design using the above multivariate methods can be a powerful tool for detecting relationships between vegetation and environmental factors.