Comparison of Nitrogen Content in Tree Litterfall in Three Dry Dipterocarp Forests Under Different Fire Regime in Northeast Thailand
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TROPICS Vol. 17 (3) Issued May 30, 2008 Comparison of nitrogen content in tree litterfall in three dry dipterocarp forests under different fire regime in northeast Thailand 1,* 2 3 1 4 Tetsuya TODA , Hiroshi TAKEDA , Naoko TOKUCHI , Seiichi OHTA , Chongrak WACHARINRAT and 4 San KAITPRANEET 1 Laboratory of Tropical Forest Resources and Environments, Division of Forest Science, Graduate School of Agriculture, Kyoto University, Kyoto 606−8502, Japan 2 Laboratory of Forest Ecology, Division of Environmental Science and Technology, Graduate School of Agriculture, Kyoto University, Kyoto 606−8502, Japan 3 Field Science Education and Research Center, Kyoto University, Kyoto 606−8502, Japan 4 Department of Silviculture, Faculty of Forestry, Kasetsart University, Bangkok 10900, Thailand * Corresponding author: Tel: +81−75−753−6361, Fax: +81−75−753−6372, E-mail: [email protected] ABSTRACT Tree litterfall was measured and of forest. In addition, transformations of N are variable nitrogen (N) return by tree litterfall was estimated and dynamic in forest ecosystems. Consequently, many in three plots, F0, F10, and F35, with different studies on nutrient cycling place special emphasis on N fire histories (protected from fire for 0, 10, and 35 dynamics. years, respectively) in dry dipterocarp forests (DDF) Fire is a major disturbance and causes substantial in northeast Thailand. Annual litterfall was 3.92, loss of N from terrestrial ecosystems, especially through 7.13, and 8.79 Mg ha−1, for F0, F10, and F35, volatilization (Gillon and Rapp, 1989). The frequency respectively. Leaf litter was the main component of fire affects the extent of N loss from the ecosystem in all the plots, ranging from 67.4 % to 77.9 %, (Marafa and Chau, 1999). In Thailand, dry deciduous peaking in the dry season. Other components dipterocarp forest (or dry dipterocarp forest, DDF) is of the litterfall had no clear seasonality. The N a major forest type and occupies over 30 % of the total concentration of the tree litterfall increased in the forest area (Royal Forest Department, 2000). The DDF rainy season and decreased in the dry season in all in northeast Thailand is a biotic forest that has been three plots. The N return due to the tree litterfall maintained by human disturbances such as forest fires. was estimated to be 33.4, 75.2, and 123.8 kg ha−1, Generally speaking, forest fires in the dry season are for F0, F10, and F35, respectively. Fire protection almost inevitable because of the extremely dry conditions increased the N return by tree litterfall, as well as that occur for a couple of months a year (around January tree litter production in DDF. to February). Local people burn forest floors of DDF to improve the yield of non-timber forest products such as Key words: Dry dipterocarp forest, Forest fire, mushrooms, tree vegetables, etc (Akaakara, 2002). In Litterfall, Nitrogen dynamics, Thailand DDF, forest fires influence the forest ecosystems through the removal of understory vegetation and the litter layer. Frequent fire often led a species-rich forest into the INTRODUCTION simple combination of fire-resistant trees and perennial In forest ecosystems, litterfall is an important flux of grass (Tsutsumi, 1989). Fires play a role in maintaining N carbon (C) and mineral nutrients into the soil decomposer limitation for plant growth in such ecosystems (Vitousek system where nutrients are mineralized. The amount of and Howarth, 1991). mineral nutrients returned by litter is a good indicator Since 1970s, Thai government has started practicing of nutrient cycling (Proctor, 1983; Spain, 1984). Thus, the fire protection in DDF for multiple uses on a measurement of litterfall and estimation of nutrient return sustained yield basis (Komkris, 1971). Recently, some via litterfall have been carried out, not only for temperate study has been discussed on the effect of fire protection forest ecosystems but also for tropical forest ecosystems in DDF. Kanzaki et al. (1995) reported the change and (e.g., Vitousek, 1984; Jaramillo and Sanford, 1995) in study increase of tree species by the practice of fire protection on nutrient cycling. Among forest nutrients, nitrogen (N) in DDF. Sakurai et al. (1998) suggested the recovering is known to be greatly affected the primary productivity effect on soil properties by the fire protection. Both 200 Tetsuya TODA, Hiroshi TAKEDA, Naoko TOKUCHI, Seiichi OHTA, Chongrak WACHARINRAT and San KAITPRANEET of the approaches are quite recommendable for the dry evergreen forest, plantation forest, and grassland and comprehensive understanding of the relation between bamboo forest. There is 13.4 km2 of DDF in the SERS. In DDF and fire protection. However, the effect of fire the fire protection area of the DDF, fire was excluded by control on N cycling in DDF is not known. Here, we 10-m wide fire belts in a part of the SERS (Sahunalu and focused on the relationship between the N return via tree Dhanmanonda, 1995; Phongamfai, 1997). litterfall and history of forest fires. The climate type of the SERS is tropical monsoon In the present study, we performed a comparative (Fig. 2): mean annual temperature is 22.5 ˚C; annual study in DDFs with different forest fire histories. The precipitation is 1097 mm, characterized by a pattern of objective of this study was to compare N return of three two peaks of precipitation (one in May and the other in stands with different forest fire histories via tree litterfall September). The monthly precipitation is less than 100 to the forest floor. We hypothesized that: (1) the tree mm during the dry season, from November to March. litterfall would increase, and (2) the N return via tree Because of the extremely dry conditions and human litterfall would increase, with the time after the fire activities in the dry season, DDF without fire protection protection, due to the change of tree species composition. almost inevitably has annual surface fires. The soil in the study area is stony red-yellow podzolic soil, with a depth of 60 cm or less (Bos and Thunduan, 1968; Sakurai et al. MATERIALS AND METHODS 1998). The soil is equivalent to that of Orthic Acrisols Study area (FAO/UNESCO, 1974) or Haplustults (USDA, 2006). The study was performed in the Sakaerat Environmental Research Station (SERS) located in Nakhonrachasima Plot setting and tree census Province, approximately 180 km northeast of Bangkok, Three study stands with different fire histories were , , Thailand (lat. 14˚30 N, long. 101˚56 E, 200−800 m in established in the DDF of the SERS. The forest fire elevation, Fig. 1). SERS is an 81 km2 biosphere reserve history of each stand is as follows: (1) a stand without established in 1978 that consists of four forest types, DDF, fire protection that was burned in January 2000 (F0), �������� �0 �35 �10 0 2 4��� ���������������������������� �������������������������� ��������������� ���������������������������� Fig. 1. Location of research site and the vegetation map of the Sakaerat Environmental Research Station. (Modified, after Sakurai et al., 1998) Comparison of nitrogen return by litterfall in three dry dipterocarp forests, Thailand 201 250 35 30 200 25 � 150 ℃ 20 15 100 10 ������������� ������������������������ 50 5 0 0 ��� ��� ��� ��� ��� ��� ��� ��� ��� ��� ��� ��� ��� ��� ��� ��� ��� ��� ��� ��� ��� ��� ��� ��� 2000 2001 2002 Fig. 2. Monthly precipitation and temperature during March 2000−Februar y 2002 at the Sakaerat Environmental Research Station. (2) a stand protected for 10 years (F10), and (3) a stand The oven-dried and sorted litter samples collected protected for 35 years (F35). In each stand, a 50 m × 50 m in January, April, June, August, October, and December plot was established in February 2000. 2001 were ground up separately. The amount of Each plot was further divided into 25 subplots (10 m reproductive organs was so small that we mixed them × 10 m). In each subplot, we recorded the tree species with the miscellaneous litter. For the same reason, we and measured the diameters at breast height (DBH, 1.3 also mixed the leaf litter of the three species Mitragyna m above the ground) of all trees with a DBH of 3 cm or brunonis (Rubiaceae), Sindra siamensis (Leguminosae), lager. and Bauhinia spp. (Leguminosae) with the other species The lower layer was composed of saplings of canopy in F0. trees. A dwarf bamboo-like grass, Arundinaria pusilla (= Vietnamosasa pusilla, Poaceae), occupied the understory Statistical analysis both in F10 and F0. The grass was dense in F0. We found The total litterfall and weights of the four sorted no understory grass in F35. litter samples were analyzed for variability using non- parametric tests. Significant differences of the litterfall Litter trap setting and litter collection among the three plots were examined by the Kruskal- In each plot, litterfall was measured over a 2 year period Wallis test and Mann-Whitney U-test (SPSS, 1999). from March 2000 to February 2002. Thirteen litter traps, 1 m high with a diameter of 60 cm, were arranged in Chemical analysis the centers of the subplots in a staggered pattern. In F0, Total N concentrations of the sorted litter samples in 2001 forest fires occurred at the end of January 2001 and 2002. were analyzed with an NC analyzer (Sumigraph NC900, We successfully collected litter samples and removed Sumika Chemical Co. Ltd., Japan). litter traps from F0 2 to 6 days before burning and reset the traps immediately after burning. Estimation of nitrogen content in litterfall Trapped litter was collected at monthly intervals We calculated N content in the tree litterfall in 2001 as and then oven-dried at 105 ˚C for 48 h. The litter was follows: (monthly N content in litter component) = (dry sorted into the following categories, (1) leaves; (2) weight of monthly litter component) × (N concentration woody material including branches, twigs, and bark; in each litter component). For February, March, May, (3) reproductive organs such as flowers and seeds; July, September, and November, we used the average and (4) miscellaneous material such as insects, feces, concentrations of the values of the two neighboring and amorphous material.