Chonggang Xu

Long-term forest landscape responses to fire exclusion in the Great Xing'an Mountains, China

Understanding of long-term forest landscape dynamics under fire exclusion, which have not been studied in north-eastern China, is increasingly needed for designing sound forest management and protection plans. In the present study, we examine whether long-term fire exclusion leads to catastrophic fires and whether the fire regimes altered by fire exclusion have changed the course of natural succession of dominant tree species. We designed two simulation scenarios - fire exclusion and no fire exclusion - and used LANDIS to study the long-term (300 years) fire regime dynamic and the succession of dominant tree species in terms of species abundance, age structure and spatial pattern. Our simulated results show that fire exclusion can lead to catastrophic fires with return intervals ranging from 50 to 120 years, increase the proportion of coniferous forests and decrease the proportion of deciduous forests, simplify tree species composition, and alter forest age structures and landscape patterns. Based on these simulated results, we suggest that prescribed burning or coarse woody debris reduction, uneven age management, and a comprehensive wildlife habitat suitability analysis should be incorporated in forest management plans in this region.

Elasticity and loop analyses: tools for understanding forest landscape response to climatic change in spatial dynamic models

Spatially explicit dynamic forest landscape models have been important tools to study large-scale forest landscape response under global climatic change. However, the quantification of relative importance of different transition pathways among different forest types to forest landscape dynamics stands as a significant challenge. In this study, we propose a novel approach of elasticity and loop analyses to identify important transition pathways contributing to forest landscape dynamics. The elasticity analysis calculates the elasticity to measure the importance of one-directional transitions (transition from one forest type directly to another forest type); while the loop analysis is employed to measure the importance of different circular transition pathways (transition from one forest type through other forest types back to itself). We apply the proposed approach to a spatially explicit dynamic model, LANDIS-II, in a study of forest landscape response to climatic change in the Boundary Waters Canoe Area (BWCA) incorporating the uncertainties in climatic change predictions. Our results not only corroborate the findings of the previous studies on the most likely future forest compositions under simulated climatic variability, but also, through the novel application of the elasticity and loop analyses concepts, provide a quantitative assessment of the specific mechanisms leading to particular forest compositions, some of which might remain undetected with conventional model evaluation methods. By quantifying the importance of specific processes (transitions among forest types) to forest composition dynamics, the proposed approach can be a valuable tool for a more quantitative understanding of the relationship between processes and landscape composition/patterns.

Ecological footprint and biological capacity time series assessment for a forest region in northeastern China

Anthropogenic disturbances have caused major landscape changes in the forests of northeastern China during the past 50 years. In particular, continuous over-deforestation has greatly decreased the regions forest quality. Ecological footprint analysis generates aggregated information about a populations demand on nature and the population regional biological capacity. To show the forest change and the populations ecological demand on the study area, this paper presents an ecological footprint time series for the Songling Forestry Bureau in northeastern China from 1965 to 2000. The paper shows conventional ecological footprint time series and area demand time series – under global, Chinese and local yearly yields – to study the biological productivity of Songling. In this study, biological capacity was calculated based on a conventional approach. The results demonstrate that the ecological footprint has increased slightly and continuously during the 35-year timespan, while the biological capacity has decreased dramatically. These effects have been caused mainly by the depletion of forest resources. The results also yield much information about natural changes and socioeconomic dynamics, as well as the driving factors for these changes, of which the most important is forest management policy.