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Rehabilitation of a Degraded Tropical Lowland Dipterocarp Forest Using Three Indigenous Timber Species in Peninsular Malaysia
Abstract:
Seedlings of Azadirachta excelsa, Hopea odorata, and Vitex pinnata were line and gap planted on a logged-over site in Pasoh Forest Reserve, Negeri Sembilan, Malaysia.
After two and a half years of planting, H. odorata exhibited the highest average survival percentage of 97 percent in the large discontinuous gaps of 20 x 20 m (G3 method), followed by V. pinnata (91%), and A. excelsa (82%).
In G4 (10 x 10 m x 9/ha gaps), the survival percentage of H. odorata was 95 percent, followed by V. pinnata (89%), and A. excelsa (84%). In G2 (10 x 10 m x 5/ ha gaps), H. odorata showed 90 percent survival, followed by V. pinnata (71%) and A. excelsa (64%). In the line planting, H. odorata attained 93% survival; V. pinnata, 84%; and A. excelsa, 75%.
Relatively high survival percentages of the seedlings were due to the capacity of the seedlings to survive under situation typical of degraded lands. Moreover, relatively high light environment and high organic matter content may have contributed also to low mortality. Mortality can be attributed to the activities of the wild boars that collect small twigs and seedlings as nest during breeding periods. The broken stems (reduced heights) that sometimes led to seedling death were mainly due to strong winds which are typical of Malaysia, the monkeys who play with and eat the top shoots, and the weeds that strangled and pulled the seedlings downwards. The relatively high survival rates were indicative of the species capacity to colonize and regenerate degraded lands.
In terms of stem growth, A. excelsa exhibited the highest growth among the species. It showed higher increments than H. odorata and V. pinnata in basal diameter, basal area, volume, and relative crown depth. H. odorata had comparable increments with V. pinnata except in total height. V. pinnata had comparable increments with A. excelsa except in relative height where H. odorata had a lower relative height than V. pinnata.
In terms of crown growth, A. excelsa developed larger increments than H. odorata in crown diameter and crown surface area. V. pinnata had the highest foliage depth increment and had comparable crown surface area with A. excelsa. Both A. excelsa and H. odorata had the desirable lower crown-basal diameter ratio than V. pinnata.
Based on stem growth dynamics, all three species can be mix-planted for enrichment planting and plantation establishment. H. odorata was the best survivor whereas A. excelsa exhibited the best growth performance among the species. V. pinnata showed moderate survival and growth performance.
Correlation and regression results showed that the growth indicators, namely: basal diameter, total height, crown height, and crown diameter can be used to predict seedling growth efficiency at this stage of their development and thus eliminate guess work.
