Dipterocarps as forest restoration species: environmental and economic implications of ecophysiological studies in the nursery

September 22, 2006 by

E. L. Tolentino, Jr. and L. D. Camacho

College of Forestry and Natural Resources, University of the Philippines Los Baños, College, Laguna 4031, Philippines

E-mail: eltj@mudspring.uplb.edu.ph, lcamacho@laguna.net



Abstract



The potential of dipterocarp species for restoring degraded lands was examined using ecophysiological parameters. The photosynthesis, conductance, transpiration and water use efficiency of the following dipterocarps species were evaluated for two years in a nursery in the Philippines: Shorea almon, Hopea plagata, Parashorea malaanonan, Anisoptera thurifera and Shorea contorta. Hopea plagata consistently gave high photosynthetic rates ranging from 4.28 to 8.7 μmol CO2 m-2 s-1. In terms of conductivity, Anisoptera thurifera had the highest rate ranging from 0.05 to 0.17 H2O m-2 s-1. The same species showed the highest transpiration rate ranging from 0.98 to 3.33 mmol m-2 s-1. The most water use efficient dipterocarp species tested was Hopea plagata with values ranging from 5.56 to 7.11. The potential utility of basic ecophysiological parameters for species selection in forest restoration was discussed. The tool could assist forest managers or silviculturists in choosing appropriate dipterocarp species for the varying conditions in the field particularly adverse sites common in degraded lands. Ecophysiological assessments which could be performed in the nursery or in smaller plots in less time periods could facilitate and economize selecting dipterocarps for use in restoring degrading. Limitations of the analysis was also explained.



Introduction



Dipterocarp log production in the Philippines in 1990 was estimated at 2.1 million cu m representing 83.5% of the country’s total log production (Forestry Statistics 1990). By 2003, the volume precipitously dropped to 82 093 cu m and contributed only a measly 16.2% to the country’s total log production (Forestry Statistics 2003). In 1985, dipterocarp forests were estimated at 31% of the country’s total land area (The Committee on Forestry 1985) while the latest available forestry statistics in 1997 estimated it at only 12% of the total land area (Forestry Statistics 2002). The significant drop in dipterocarp log production and area covered by dipterocarps is a reverberating distress signal sounded off long time ago indicating that this precious timber resource is seriously threatened and is becoming scarce in the wood market. In the latest campaign to recapture lost forest cover, the Department of Environment and Natural Resources Secretary announced an ambitious forest plantation of 4 M ha spread in every town of the Philippines (http://denr.gov.ph/articleprint/3313-1/355/). While it is an admitted fact that fast growing species like Gmelina, Swietenia, Acacia, Paraserianthes and Eucalyptus, dominate the Philippine forest plantations, dipterocarps for all its desirable wood properties and high trade value, has an important niche in wood production not only in the Philippines but on a regional basis.


With a staggering 2.8 million ha of uplands needing immediate rehabilitation, dipterocarps offer a major alternative as a forest restoration species in the Philippines and even on a regional basis. Unfortunately, its widespread use as a plantation species is beset by many problems, one of which is the limited basic information about its ecophysiology. A comprehensive compilation of average photosynthetic capacity of different broad leafed and coniferous trees was earlier made by Ceulemans and Saugier (1991). Most of the species included in the review are species from temperate zones. Maruyama et al. (1997) studied the photosynthesis and water use efficiency of 19 tropical tree species including 11 dipterocarp species. The dearth in basic information about dipterocarps provided sufficient reasons for the ASEAN-Korea Environmental Cooperation Project (AKECOP-Philippines) to include in its long list of researches, an investigation on the ecophysiology of several indigenous tree species including dipterocarps. This paper will present the two-year result of a nursery study on the performance of selected dipterocarp species. Specifically, it examined the photosynthesis, conductivity, transpiration and water use efficiency of five dipterocarp species. From the ecophysiological information generated, potential field performance of the species in degraded sites was elaborated. Additionally, the utility of ecophysiological studies in improved species selection was elucidated venturing both in its environmental and economic implications.



Materials and methods



The following dipterocarp species were evaluated in the nursery of the College of Forestry and Natural Resources, University of the Philippines Los Baños for two years: Hopea plagata (saplungan), Anisoptera thurifera (palosapis), Parashorea malaanonan (Bagtikan), Shorea contorta (White lauan) and S. almon (almon). One-year-old seedlings were planted in 25 x 30 cm black polyethylene plastic bags. The soil media used was a mixture of garden soil, coconut coir dust, rice hull, compost and ash (6:4:2:2:1 parts by volume) with soil pH of 6.31. A LICOR 6400 portable photosynthesis machine was used to measure photosynthesis, conductivity, and transpiration. The species light curve was developed under the following conditions: 300 μmol CO2 and photosynthetically active radiation (PAR) from 0 to 1 500 μmol m-2 s-1. Water use efficiency was computed as the ratio of the net photosynthesis to the transpiration rates. There were three measurement periods: February 2004, April 2004 and April 2005. Measurements were timed when the portable photosynthesis machine is made available by the Korean scientists. One fully expanded and healthy leaf per species was measured in two replications. The average of the measurements was presented.


Sources: 8th Round-Table Conference on Dipterocarps

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