Effects of Forest Fire and Logging on Forest Degredation in Monglia

Forests in Mongolia have been severely degraded by forest fi re and exploitive logging. This study investigated changes in vegetation and soil properties after forest fi re or clearfelling. Microclimate conditions such as temperature and relative humidity (RH) changed drastically after forest fi re or logging; temperature increased 1.6-1.7 oC on average, whereas RH decreased up to 15.7 percent after logging. Thus, burned and logged stands became drier and it mainly affected understory species composition such as the succession of steppe xerophytes from taiga and meadow mesophytes. Soil moisture signifi cantly decreased after forest fi re or logging, and the extent of decrease was more severe in the logged stand. The chemical properties of the organic layer were signifi cantly changed, more so than the properties of the mineral soil horizons. 1Visiting Scientist, Center for Forest Disturbance Science, U.S. Forest Service, Athens, GA; Professor, Dept. of Forest Sciences, Seoul National University, Seoul Republic of Korea; Director, Institute of Geoecology, Mongolian Academy of Sciences, Ulaanbaatar, Mongolia; Research Ecologist, Center for Forest Disturbance Science, U.S. Forest Service, Athens, GA, respectively. Citation for proceedings: Stanturf, John A., ed. 2010. Proceedings of the 14th biennial southern silvicultural research conference. Gen. Tech. Rep. SRS-121. Asheville, NC: U.S. Department of Agriculture, Forest Service, Southern Research Station. 614 p. INTRODUCTION Forest degradation is one of the main environmental concerns globally because degradation constrains environmental functions of forests (Daily and Ehrlich 1995, Burley 2002). Global attention to forest degradation in northeast Asia including the Russian Far East, China, Mongolia and the Democratic People’s Republic of Korea (DPRK), has been greatly heightened by dramatic changes in climate in recent years (Lee and Park 2001). Forests in Mongolia have been severely degraded by wildfi re and exploitive logging (World Bank 2002, Tsogtbaatar 2004), and this degradation has negatively affected the environment of neighboring countries including Korea. Between 1971 and 1997, approximately 2,700 largeand small-scale fi res occurred and destroyed over 14 million ha of forests. Particularly in 1997, 2.7 million ha burned (FAO, 2001). During the last decade, Mongolia lost approximately 4 million ha of forests, averaging 40,000 ha annually but between 1990 and 2000, the rate of deforestation increased to 60,000 ha/year. As a result of this ongoing loss and degradation, 1.6 million ha of forest area has been completely lost between 1974 and 2000 due to fi re, improper clearfelling, overgrazing, and mining activities (UNEP, 2002). The objectives of this study were (1) to investigate the changes in vegetation and soil properties after forest fi re or clearfelling, and (2) to discuss the effects on forest degradation and future restoration work in Mongolia. MATERIALS AND METHODS The fi eld study was conducted at southern area of Khenti in Mongolia, which lies between the southern fringe of the Siberian boreal forest and the Mid-Asia Steppe zone. This area is very sensitive and vulnerable to external disturbances such as forest fi re and logging. A total of 17 study sites were selected: six for reference sites, seven for burned sites, and four for clearfelled sites. In each site, three 30 by 30 m square plots were randomly established to investigate the composition of overstory species. In each main plot, three 5 by 5 m square subplots were established to investigate natural regeneration and fi ve 2 by 2 m square subplots were included to investigate the composition of understory vegetation. For all identifi ed vegetation, we calculated importance value, species diversity, and similarity in order to examine the changes in vegetation after forest fi re or logging. In each main plot, soils were sampled using a soil auger at three soil depths: the forest fl oor (O) and two mineral horizons (A and B), with four replications for each horizon. All samples were air-dried after collection and analyzed for physical and chemical properties such as moisture content, pH, soil texture, organic matter, nitrogen, phosphorous and cation exchange capacity (CEC). Three portable HOBO data loggers were launched in each stand to collect daily mean temperature and relative humidity at one-hour intervals. The differences in vegetation and soil properties among the study plots were determined by analysis of variance (ANOVA) using Tukey’s Studentized Range to test separation of means (SAS 8.2). The signifi cance for all analyses was set at α=0.05. RESULTS AND DISCUSSION Changes in Vegetation Composition after Forest Fire or Logging Stand development and natural regeneration—The patterns of stand development after fi re or clearfelling in Larix sibirica stands mainly progressed in four stages: (1) secondary Larix sibirica stand, (2) hardwood stand mainly composed of birch (Betula spp.) and willow (Salix spp.), (3) bush stand, and (4) grassland (steppe). Stand development strongly depended on the intensity of degradation and the potential for natural regeneration (Oliver and Larson 1996). The intensity of degradation in secondary larch and hardwood forests was slight after forest fi re and these forests progressed easily into a natural regeneration stage with more than 5,000 seedlings/ha. The bush stand and steppe, however, were affected by severe degradation after clearfelling, and progressed slowly into, or did not reach the natural regeneration stage; there were less than 100 seedlings/ha. Natural regeneration usually occurs more readily on burned as opposed to logged sites as a result