Research Article / 1 Application of Forest Gap Model for Sal (Shorea robusta) Forest Succession การประยกตุ ใช์ แบบจ้ าลองชํ ่องวางในป่ ่าสาหรํ ับการทดแทนของป่าซาล ์ Dipak Jnawali, Raywadee Roachanakanan and Kulvadee Kansuntisukmongkol Faculty of Environment and Resource Studies, Mahidol University, Nakhonpathom 73170 Abstract The Shorea roubsta (sal) forest dominated in lowland of Nepal has ecologically and economically significant values. Chitawan National Park (CNP), a protected area in central lowland of Nepal was selected for the study and species composition, basal area and stem density were recorded and measured from 20 sampling plots. Together with secondary and primary data from consultation with experts, all data were used to reparameterize the KIAMBRAM model. The KIAMBRAM model is an individual-based forest gap model in the JABOWA-FORET model family and is developed for subtropical rainforest in Australia. The application of the KIAMBRAM model for prediction of the natural sal forest stand dynamics of subtropical region of Nepal is the goal of the study. Four major components (subroutines); GROW, BIRTH, KILL and CHABLI of the KIAMBRAM model were selected. The model was first test through the qualitative comparison of species composition of each successional stage, i.e., early successional stage, mid-successional stage, late successional stage and mature stage. Species composition from the simulated model results at mature stage was compared with field data, whereas for other stages the simulated model results were compared with those of available literature. The results showed that the best match between the simulated model results and data of CNP forest was for mature stage and also for early successional stage where the results were satisfactorily matched whereas for mid-successional and late-successional stages, the results were fairly matched. It can be concluded that the KIAMBRAM model has a potential to be used as a tool to gain knowledge on the succession of sal forest dynamics in Nepal. Key words : the KIAMBRAM model, individual-based gap model, Shorea roubsta, forest succession ป่าซาล ์ (Sal) (Shorea robusta ) เป็นป่าที่ตั้งอยในบรู่ ิเวณพ้ืนที่ราบตาของประเทศเนปาลํ่ ซึ่งมีความสาคํ ญในทางั นิเวศวิทยาและเศรษฐกิจ และเป็นป่ าในเขตสงวนของอุทยานแห่งชาติชิตวนซั ึ่งเป็นพ้ืนที่ราบตาตอนกลางของํ่ ประเทศเนปาล ได้ถูกคดเลั ือกข้ึนมาใชเป้ ็นกรณีศึกษา คลอบคลุมพ้ืนที่ตัวอยางท่ ้งหมดั 20 แปลง ซึ่งเป็นป่าที่มี ช่วงการเจริญเติบโตสมบูรณ์เต็มที่แล้ว เพื่อใชเป้ ็นเครื่องมือในการศึกษาการทดแทนป่าโดยได้นําแบบจาลองํ ช่องว่างในป่ามาประยุกตใช์ ในป้ ่าซาล์ซึ่งสามารถใชเป้ ็นตนแบบของป้ ่ าในเขตร้อนได ้ ซึ่งการศึกษาดงกลั ่าวมี การศึกษาใน 4 ปัจจยหลั กทั ี่สําคัญ คือ การเจริญเติบโต การเกิด การตาย และ การเกิดช่องวางของแบบจ่ าลองชํ ื่อ KIAMBRAM โดยใช้ตัวแปรของชนิดที่ไดจากการทบทวนวรรณกรรม้ ในแบบจาลองเพํ ื่อศึกษาพลวตของปั ่ า ซาลในช์ ่วงต่างๆ ของการทดแทน ไดแก้ ่ ช่วงต้น ช่วงกลาง ช่วงปลาย และช่วงสมบูรณ์เตมท็ ี่ จากการศึกษาวิจัย สามารถสรุปผลได้วาการน่ าแบบจํ าลองชํ ่องวางในป่ ่าสามารถนามาประยํ ุกตใช์ ในการศ้ ึกษาการทดแทนในป่า 2 / Environment and Natural Resources Journal Vol.6, No.2, December 2008 คําสําคัญ : แบบจาลองํ KIAMBRAM/ แบบจาลองชํ ่องวางแบบป่ ัจเจก/ Shorea robusta/ การทดแทนของป่า 1. Introduction Sal forest is prevalent in tropical and subtropical regions of South Asia and distributed on the plain and lower foothills of Himalayas (Gautam and Devoe, 2006), Siwalik hills and river valleys (Jackson, 1994). This forest covers about 10 million ha in India (Tiwari, 1995), 1 million ha in Nepal (HMGN, 1988), 0.11 million ha in Bangladesh (Alam, 1996) and some parts in Bhutan (Gautam and Devoe, 2006). In Nepal, sal forest is the major component (more than 70%) of Terai forest (lowland tropical and subtropical forests). Sal forest is ecologically and economically important (commercial and subsistence purposes) for tropical and subtropical area of Nepal (Kandel and Shrestha, 2001; Webb and Sah, 2003). The Terai forest in Nepal is broadly categorized into two types; protected area based management system and open access government managed forest outside the protected area. Total five protected areas including two National Parks and three Wildlife Reserves are executing under the protected area based management system in the Terai forest of Nepal and they cover almost half of the Terai forest area (Timilsina, 2005). Forests outside the protected area in the Terai forest of Nepal are partly managed under community based management system such as community forest and the rest are managed by government but are open access for local people. Despite their widespread occurrence and importance of sal forest in Nepal, little information exists on ecological aspects. Past studies on sal forest inside the protected area (natural forest) focused mostly on floristic structure and composition (Dinerstein, 1979; Shrestha and Jha, 1997; Timilsina et al, 2007). No information is available on dynamics of the sal forest. Wesche (1997) described different types of the sal forest in natural forest of Central Nepal. Nagendra (2002) also studied the forest condition outside the protected area in Chitawan (Central Nepal). Rautiainen (1999) and Rautiainen et al (2000) focused on growth and yield models of sal species (not sal forest) however they did not incorporate the stand and sub-stand level dynamics. There is completely lack of knowledge on disturbance, growth, birth and kill factors influencing on successional change of forest composition in natural sal forest. Information on forest dynamics is very important at the managerial level to make the decision on biodiversity conservation and management because sal forest in Nepal is the habitat for large and endangered mammals such as rhinoceros, Asian tiger and Asian elephant (Shrestha, 2004). Establishment of the sal seedling at the initial phase requires special soil condition and such soils could be new alluvial deposits, sand dunes and land slips (Troup, 1921). The early stages of the Research Article / 3 succession are generally easily recognized as they are generally uniform, but in the later stages, great divergence is noticeable due to moisture and soil conditions (Khanna, 1993) and it becomes difficult to identify and correlate with environmental factors. Succession of sal forest on Gangetic riverine alluvium of Uttar Pradesh of India was observed by Khanna (1993) and it was described that at the very beginning stage special types of grasses took place as the pioneer species in the early successional process. Most common pioneer grasses were Saccharum spontaneum and Tamarix dioica. After the time, two major tree species i.e., Acacia catechu and Dalbergia sissoo replaced the grassland. Then, in the course of the time A. catechu and D. sissoo were slowly replaced by three species i.e., Holoptelia sp., Adina cordifolia and Albizzia procera. In the mid-successional stage, some new species such as Lagerstroemia parviflora, Bombax ceiba and Terminalia belerica existed in the community whereas A. cordifolia, L. parviflora and T. belerica played dominant roles in the stand. In the late successional stage, Shorea robusta established in the community and other species which were similar with those of the mid successional stage. In this stage Terminalia alata also took place if the soil contained moisture. At the climax stage, S. robusta became the most dominant species. Other dominant species at the climax stage could be L. parviflora, Terminalia spp. and A. cordifolia. At this stage, Syzygium cumini also appeared at the lower canopy level in the site with moisture content. Formation of gap and gap dynamics are the important driving force that maintains the tropical diversity (Young and Hubbell, 1991). Gap models are developed for better understanding of the ecological mechanism and patterns of structure and functional dynamics in natural forest ecosystems over a long period of time (Liu and Ashton, 1995; Kolstrom, 1998). Individual-based forest gap models are a potential tool for addressing succession dynamics because of their focus on individual tree growth and species-specific life history parameters (Botkin et al, 1972; Botkin, 1993; Shugart et al, 1980; Shugart, 1984). Most of the gap models in tropical and subtropical forests are developed from the JABOWA-FORET model (Roachanakanan, 2002). Among the ancestors of the JABOWA- FORET model, there are only few models that were developed for tropical forests. The KIAMBRAM model was developed by Shugart et al (1980) for the complex subtropical rainforest in Australia and was further reparameterized to another two subtropical and tropical rainforests in Australia by Roachanakanan (2002). For the present study, the KIAMBRAM model was reparameterized without any change on the model structure to the lowland sal forest in Nepal. Four major components (subroutines); GROW, BIRTH, KILL and CHABLIS of the KIAMBRAM model were selected. The objective of the present study is to test the model performance through the qualitative comparison of species composition of each successional stage, i.e., early successional stage, mid-successional stage, late-succession stage and mature stage. 4 / Environment and Natural Resources Journal Vol.6, No.2, December 2008 2. Materials and methods 2.1 The Study area Chiawan National Park (CNP), a natural undisturbed forest of subtropical region of Nepal was selected for the study. CNP is also in UNESCO world heritage list since 1984 for its internationally important on flora and fauna diversities (Straede et al, 2002). The CNP covers a pristine area