On the Effect of Thinning on Tree Growth and Stand Structure of White Birch (Betula platyphylla Sukaczev) and Siberian Larch (Larix sibirica Ledeb.) in Mongolia

Abstract

The forests of North Mongolia are largely dominated either by larch (Larix sibirica Ledeb.) or birch (Betula platyphylla Sukaczev). The increasing demand for timber and firewood is currently met by removal of wood from these forest stands. Therefore, silvicultural approaches that account for both utilization and protection are needed. Thinning trials were established in the research area Altansumber, in the mountain forest steppe west of the town of Darkhan. We analyzed the response of non-spatial and spatial structure and growth of birch and larch stands on thinning. Before thinning, spatial tree distribution was largely clumped. Thinning promoted regular tree distribution. Ingrowth of new stems after thinning tended to redirect stand structure towards clumping. Both relative and absolute tree growth and competition were evaluated before, directly after, and three years after the thinning. Competition played a significant role in tree growth before thinning. A reduction in competition after thinning triggered significantly increased growth of both birch and larch. The observed positive growth response was valid in absolute and relative terms. A methodically based forest management strategy, including thinning operations and selective cuttings, could be established, even under the harsh Mongolian conditions. Our findings could initiate the development of broader forest management guidelines for the light-taiga dominated stands.

Forest Management In Mongolia – A Review Of Challenges And Lessons Learned With Special Reference To Degradation And Deforestation

“…Already in the second half of the 20th century, research trials for the evaluation of logging impact concluded that in Mongolia the impact of selective logging is ecologically more positive than clearcutting (Savin et al 1988). The shortterm effects of thinning from below on individual tree growth was recently studied in larch and birch stands near the steppe border (Gradel et al 2017c). The authors found that the growth response of the remaining trees was significantly positive and directly related to the reduction of surrounding competitor trees.…”

Special issue «environmental change on the Mongolian plateau: atmosphere, forests, soils and water»

“…Land cover changes in the region are related to both climate change Miao et al 2015) as well as anthropogenic impacts related to urbanization (Allington et al 2017;Fan et al 2016), livestock herding (Allington et al 2017, Sternberg 2012, mining (Batbayar et al 2019;Jarsjö et al 2017) and logging (Batkhuu et al 2011;Tsogtbaatar 2004). In vast parts of the Mongolian Plateau, forest degradation and losses (Gradel et al 2017;Juřička et al 2019a) as well as desertification of grasslands (Khodolmor et al 2013;Wei et al 2019) have modified a natural land cover. The key drivers of these processes are mining, agriculture / urbanization and deforestation, which are at the same time major water users and polluters (Batbayar et al 2019;Jarsjö et al 2017;Karthe et al 2017).…”

Which Selective Logging Intensity is Most Suitable for the Maintenance of Soil Properties and the Promotion of Natural Regeneration in Highly Continental Scots Pine Forests?–Results 19 Years after Harvest Operations in Mongolia

“…To gain a better understanding of the character of the different treatments, we analyzed the type and intensity of the logging events [45,46] carried out in February 1998. We assessed the selective logging weight (originally referred to as the thinning weight, or "rG ratio"; [47]), which represents the intensity of the selective logging.…”

“…We compared relevant stand measures and index values [46] directly before and after the harvest events in order to better quantify potential changes in diameter size classes and forest structure caused by the logging event. We analyzed the following variables: basal area (m 2 ), diameter coefficient of variation (CV; also denoted as DBH-differentiation [49]), quadratic mean diameter of all trees (Dg), arithmetic mean diameter of all trees (D), quadratic mean diameter of the 200 strongest trees (Dg_200), and the arithmetic mean diameter of the 200 strongest trees (D_200).…”

“…We evaluated every initial model run using standard regression diagnostics in which outliers were detected and eliminated based on the distribution of internally studentized residuals in Q-Qplots with a 95% confidence envelope [62]. The best models were selected according to the following criteria: Akaike's information criterion (AIC), Bayesian information criterion (BIC), the value of the log likelihood, the plausibility of the intercept, the distribution of residuals, and the plausibility of the respective model from an ecological point of view [46]. The mean values of soil property variables or the mean regeneration numbers of the sample i of a research plot j represent one sample unit.…”