title: Forest Development in Response to Climatic and Environmental Changes in the Miyun Reservoir Basin, Beijing, China
Creators: name: Fu, Li
Publisher: name: Griffith University
Year: 2017
Subjects: subject: Forest development
subject: Climate change
subject: Miyun Reservoir Basin

description: The rising atmospheric carbon dioxide (CO2) concentration along with the ongoing climate change is predicted to substantially influence terrestrial ecosystems from local to global scales. Forest ecosystems not only provide multiple ecological services to human, but also play a critical role in regulating climate conditions and mitigating regional pollutions. Site-specific variations call for more local forest dynamic studies to be undertaken in response to both global climate change and local environmental changes. For instance, the rapid city expansion of Beijing, the capital city of China, and severe air pollutions have yielded great stress on forest development. Although afforestation efforts have been implemented since early 1960s and forest covers have significantly increased, very limited information is available about the functions and services of the forest ecosystems surrounding Beijing, and their responses to the regional climatic and environmental changes. Thus, the overarching goal of this thesis was to quantify the responses of forest ecosystems surrounding Beijing, within the Miyun Reservoir Basin (MRB) in response to the rising CO2, atmospheric warming, increased pollution and other climatic and environmental changes. Specifically, three questions are important if the objective of the study needs to be addressed appropriately: Question 1: Are forest ecosystems within the study area well established? Question 2: Will different tree species respond differently to climatic and environmental changes? Question 3: Will local pollutions influence forest development and tree growth in response to the rising CO2 and changing climate? In pursuing the answers to the above questions, three interlinked research components are proposed. Both remote sensing based biomass estimation and tree ring sampling experiments were used. Major research findings are listed below: The aboveground biomass (AGB) estimations were based on remote sensing technology and the results showed that the AGB density in MRB experienced overall increase since 1990. In 2010, total AGB was estimated to be 4.5 × 107 t, which increased by 8% when compared with the level in 1990. While the absolute AGB density values were in the similar range of AGB density reported in the Northern China studies, its spatiotemporal variations indicated that regions with less external interventions presented more consistent biomass accumulations. Ecological programs including Three-North Shelter Forest Project and Returning Farming to Forest promoted the forest expansion and development during this period, while local farming activities exerted certain negative effects on the surrounding forest ecosystems. The study of examining responses of different tree species at two selected sites (northern and southern sites) found that: the three studied tree species would respond to climate and environmental change differently, but the site-related variation was dominant. At the northern site, basal area increment (BAI) for Pinus tabuliformis and Larix gmelinii showed similar increasing trend, while rising atmospheric CO2 concentration (ca) was found to be the primary controlling factor which accounted for 92% and 74% of the BAI variations for each of the tree species. The N deposition was found to have positive effect on tree growth at this site. At the southern site, ca could explain 52% and 44% of the BAI variations for Pinus tabuliformis and Pinus massoniana, respectively, while the negative influences from the pollution intensified. All tree species at both sites showed consistently increased intrinsic water use efficiency (iWUE), but quadratic correlations between iWUE and BAI were observed, indicating that the rising ca initially stimulated photosynthetic procedures and contributed to the initial BAI and iWUE increase, but the intensified water stress resulted from reduced precipitation and increased temperature, leading to the reduction in tree leaf stomatal conductance and thus subsequently increase in iWUE which decreased the BAI. It is noteworthy that the phenomenon also suggested the reduced ability of local forests in capturing forest C and delivering into the forest C pools. The study of testing the impacts of air pollution through the pollutant gradient analysis found that: Pinus tabuliformis at the five studied sites presented overall increase in iWUE, but its relationship with BAI differed among the sites, either with different level of significances of the relationship, or adverse correlations were acquired. At the sites 1 and 5 (S1 and S5) which were considered as remote areas free of heavy air pollution, ca was found to stimulate tree growth, even though the recently increasing water deficit had caused the reduction in tree stomatal conductance which would lead to the reduced BAI. While at the pollution-affected sites 2, 3 and 4 (S2, S3 and S4), the combined effects of ca and pollutants over BAI change were observed. Multiple regression models revealed that the effect of ca on tree growth was much higher in the remote areas (&gt; 90% of the contributions), while in the pollution-affected areas, including dust, nitrogen (N) and sulfur (S) depositions into the models apparently increased the performance of the models, indicating contributions from the listed pollutants. Overall, air pollution caused further stomatal closure as evidenced with less negative δ13C levels (about 0.5‰ to 1‰ higher) at the sites closer to the pollution source during heavy pollution periods (e.g. prior to 1996). Pollution was also considered as the reason for the poor growth observed at the juvenile stage of the trees at S5. The fast growth at this site for recent periods indicated a possible adaptation mechanism for Pinus tabuliformis to the sever air pollution. It was concluded that forest ecosystems in the Miyun Reservoir Basin (MRB) experienced consistent development, either from the perspective of spatial distribution or its quality (AGB). Trees, as indicated with the selected tree species, presented site- and species-related responses to the rising atmospheric CO2, climatic and environmental changes, while the site-related responses dominated the overall variations. The gradient analysis indicated that Pinus tabuliformis showed the responses to the changing climate and environmental conditions. In the regions subjected to frequent exposures to heavy pollutants, Pinus tabuliformis growth was suppressed due to the stomatal limitations caused by the combined effects of pollution and water deficit. Meanwhile, different BAI trajectories along the gradient also suggested that Pinus tabuliformis had the ability to adapt to the harsh environment in the studied area. It was concluded that forest ecosystems in the Miyun Reservoir Basin (MRB) experienced consistent development, either from the perspective of spatial distribution or its quality (AGB). Trees, as indicated with the selected tree species, presented site- and species-related responses to the rising atmospheric CO2, climatic and environmental changes, while the site-related responses dominated the overall variations. The gradient analysis indicated that Pinus tabuliformis showed the responses to the changing climate and environmental conditions. In the regions subjected to frequent exposures to heavy pollutants, Pinus tabuliformis growth was suppressed due to the stomatal limitations caused by the combined effects of pollution and water deficit. Meanwhile, different BAI trajectories along the gradient also suggested that Pinus tabuliformis had the ability to adapt to the harsh environment in the studied area.