Guild structure and litterfall production in a mature secondary forest: its implications to silviculture and natural resources management

Results of the study revealed that the mature secondary forest in Mt. Makiling [College, Laguna, Philippines] is a complex and diverse forest community composed of forest trees of palms belonging to 44 families, 126 genera and 179 species. The area has an average density of 192 trees/ha and the average basal area was 43 sq m/ha. The highest density was obtained by Celtis luzonica (magabuyo) representing 21 percent of the total number of trees, followed by Diplodiscus panicolatus (balobo), Pinanga insignis (sarawag), Chisocheton cumingianus (balukanag), Ficus congesta (malatibig), Pterocymbium tinctorium (taluto), and Laportea luzonensis (lipa). The highest dbh was obtained by balete (Ficus balete), binuang (Octomeles sumatrana), haguimit (Ficus minahassae), and bangulo (Litsea garciae). The most dominant species in terms of basal area were balobo, magabuyo and bangulo which gave values of 6.74, 6.36 and 1.51 sq m/ha. The average height of the forest trees was 11.81 m and the tallest trees were Drypetes maguilinginses, Dillenia philippinensis with average height of 21 and 19.6 m, respectively. Based on population structure, 17 percent of the total number of trees were magabuyo followed by balobo and balukanang which were 8 and 4 percent, respectively of the total population. Based on canopy classes, magabuyo was composed of 20 percent, 13 percent and 67 percent canopy, subcanopy and understories, respectively. Balobo gave values of 42, 19 and 39 percent, respectively for canopy, subcanopy and understory crowns, suggesting an older age distribution than magabuyo. Other trees followed the trend of higher populations (50 to 60 percent) for the understories. Based on mortalities, it was observed that higher values were noted for pugahan (45 percent), hamindang (42 percent), haguimit (40 percent) and bangulo (37 percent). Balobo and magabuyo had mortalities of 12 percent and 11 percent, respectively. The fastest growers in terms of dbh increment were binuang (17 mm/year), bangulo (13.18 mm/year), lamog (5.03 mm/year) and magabuyo (2.37 mm/year). Bagtikan had 3.1 mm/year diameter increment. Seven species were noted to have distributed naturally at the ridge such as bolobo, bagtikan, taluto, anuling, bangulo, hamindang and pugahan. Those trees found in the slopes were malak-malak, binuang, apanang and malasaging. On the other hand, balukanag preferred the valley. Many species were found to be generalist and these were magabuyo, kapulasan, tambalau, tinaang pantai, katong matsing and many others. Canopy trees were magabuyo (13 percent), balukanag (20 percent), balobo (47 percent), taluto (18 percent) and bagtikan (17 percent). Other species had values less than 1 percent. Non canopy forming trees were pugahan, apanang, malasaging, sarauag, malatibig, lipa and katong matsing. The diversity using the Shannon-Weiner index was 4.72 for trees greater than 5 cm in diameter and 4.65 for trees greater than 10 cm in diameter, suggesting a moderate value. Gaps constitute 5 percent of the total area. This ranged from 25 to 275 sq m. The densiest regenerations were noted for magabuyo (3.33 individuals/sq m). Balobo had 1.25 individuals/sq m while bagtikan has 1/sq m. Litterfall production in the area was 15 tons per ha/yr and 25 percent of which was contributed by magabuyo, followed by balobo (18 percent) and bagtikan (9 percent). About 65 percent of the total litter produced were leaves while wood falls, flowers and seeds and trash had values of 19, 4 and 12 percent, respectively. In order to enhance succession in the area, it was suggested that the area should be subjected to enriched using the autogenic and allogenic succession principles where shade loving trees should be planted in the natural gaps while intolerant trees should be planted in the chablis. The planting material should be raised following the same principles. It was also suggested that some promising trees in the subcanopy and understorey crown levels should be released and be given chance to improve their growth and take the canopy level position. Crown thinning was likewise suggested. In order to enhance the watershed values of the forest, it was suggested that 3 canopy levels be maintained, the natural and induced gap areas be regenerated and the forest litter be maintained. The understorey trees should be maintained for microenvironmental modification and stability.