Báo cáo lâm nghiệp: "PAR conversion efficiencies of a tropical rain forest"

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PAR conversion efficiencies of rain forest tropical a R.J. Luxmoore 1 J.G. 2 Saldarriaga 1 Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, U.S.A., and Environmental 2 Tropenbos Program, Bogoti, Colombia ed with allometric Introduction regression relationships using diameter, height, dry weight and wood density data from each of the 23 sites. Recently avail- The mean annual quantities of photosyn- able data for 1 and 3 yr regrowth forest stands thetically active radiation (PAR) absorbed also included in this analysis. were during various stages of regeneration of a Regression equations for converting leaf phy- tropical rain forest in the upper Rio Negro tomass to leaf area were used with number of region of Colombia and Venezuela were trees per hectare (Saldarriaga et aL, 1986) to derive leaf area index (LAI) values for the forest estimated for the intervals between clear- stands. The value of LAI for the 1-3 yr period cut and 1, 3, 10, 20, 35, 60, 80, and 200 yr was 3.9, and this increased up to a mean value of growth. The forest phytomass and litter- of 6.7 for the oldest stand (80-200 yr). fall at each stage were obtained from pre- vious studies, and the data were used to calculate the mean annual quantity of net dry matter production per unit of absorbed Results PAR, the PAR conversion efficiency. The annual quantities of PAR absorbed by the forest stands (Table I) were calculated from the Bouguer-Lambert (Beers) Law Methods using appropriate LAI values with an extinction coefficient for PAR of 0.74 and The basic for the calculation is equation given an annual net incoming PAR of 2.75 by: GJ-m-2!yrl. This latter value was ob- Total dry matter PAR conversion Absorbed (1 ) x = tained from the mean annual solar radia- PAR production efficiency tion (5.2 GJ measured in the ) 1 yr 2 m- ’ ) 1 yr 2 m- ’ (g ) 1 MJ- ’ (g ) 1 yr 2 m- ’ (MJ area since 1971, by using a factor of 0.55 et al. (1986) investigated forest Saldarriaga for the proportion of PAR (Stigter and succession at 23 sites representing a chronose- Musabilha, 1982) and a PAR albedo of quence ranging from recently abandoned areas 0.04 (Dickinson, 1983). after slash-and-burn agriculture to mature rain Dry matter production for the 8 growth forest. Aboveground and belowground living periods (Fig. 1) shows the highest rates phytomass, litter and root production, standing during the first 10 yr. A significant change dead mass, and leaf indices estimat- area were
about 60-80 Acknowledgments in stand structure occurs at yr with the replacement of several early mature stand successional species by the The authors thank the staff of the Ministry of increment in species. This results in no Environment at San Carlos de Rio Negro, the living phytomass. Venezuela, for providing solar radiation data. Research was sponsored in part by the Na- The PAR conversion efficiencies deter- tional Science Foundation’s Ecosystem Studies mined from eqn 1 show the highest values Program under Interagency Agreement no. in the first year, decreasing to zero by year BSR-831585 with the U.S. Department of Ener- 70 (Fig. 2). When above- and below- gy and in part by the Carbon Dioxide Research Division, Office of Basic Energy Sciences, U.S. ground production is combined with litter- Department of Energy, under contract DE- fall (net primary production), the PAR AC05-840R21400 with Martin Marietta Energy conversion efficiencies are much higher Systems, Inc. The research is a contribution to for years 20-140. the Solar Conversion Project of the Interna- tional Union of Forestry Research Organiza- tions. Publication no. 3182, Environmental Sciences Division, ORNL. Discussion and Conclusion for The PAR conversion efficiency values References much lower aboveground growth are very than the 1.7 g-MJ- 1 reported by Linder (1985) for several temperate forests; Dickinson R.E. (1983) Land surface processes however, the results are consistent with and climate - surface albedos and energy balance. Adv. Geophys. 25, 305-355 the low-end values in the 0.2-1.0 g-MJ- 1 range of PAR energy conversion values Jordan C.F. (1971) Productivity of tropical forest and its relations to a world pattern of energy derived from Jordan (1971) for 17 forest storage. J. Ecol. 59, 127-142 types, including temperate and tropical Leith H. (1968) Calorific values of biological ecosystems. The analysis by Jordan in- materials. In: UNESCO Symposium on the cluded coarse roots in the dry matter pro- Functioning of Terrestrial Ecosystems. UNES- duction. A value of 20 kJ!g-1 for the heat CO, Paris, pp. 233-240 of combustion of dry matter, as suggested Linder S. (1985) Potential and actual production by Leith (1968), was used in the conver- in Australian forest stands. In: Research for sion of Jordan’s values from an energy to Forest Management (Landsberg J.J. & Par- a mass basis. sons W., eds.), CSIRO, Melbourne, pp. 11-34 This analysis shows that PAR conver- Saldarriaga J.G., West D.C. & Tharp M.L. (1986) Forest succession in the Upper Rio sion efficiency decreases with the in- Negro of Colombia and Venezuela. ORNL/TM- crease in successional stage and that ef- 9712. Oak Ridge National Laboratory, Oak ficiency values are generally low in Ridge, TN, pp.164 comparison with data for temperate Stigter C.J. & Musabilha V.M.M. (1982) The forests. One implication for agroforestry in conservative ratio of photosynthetically active to tropical areas similar to the upper Rio total radiation in the tropics. J. Appl. Ecol. 19, Negro valley is that short rotation times 853-858 (