Dynamic Global Vegetation Models (DGVM) are powerful tools for studying complicated ecosystem processes and global changes. This review article synthesizes the developments and applications of the Integrated Biosphere Simulator (IBIS), a DGVM, over the past two decades. IBIS has been used to evaluate carbon, nitrogen, and water cycling in terrestrial ecosystems, vegetation changes, land-atmosphere interactions, land-aquatic system integration, and climate change impacts. Here we summarize model development work since IBIS v2.5, covering hydrology (evapotranspiration, groundwater, lateral routing), vegetation dynamics (plant functional type, land cover change), plant physiology (phenology, photosynthesis, carbon allocation, growth), biogeochemistry (soil carbon and nitrogen processes, greenhouse gas emissions), impacts of natural disturbances (drought, insect damage, fire) and human induced land use changes, and computational improvements. We also summarize IBIS model applications around the world in evaluating ecosystem productivity, carbon and water budgets, water use efficiency, natural disturbance effects, and impacts of climate change and land use change on the carbon cycle. Based on this review, visions of future cross-scale, cross-landscape and cross-system model development and applications are discussed.
The National Forest Inventory (NFI) is an important resource for estimating the national carbon balance (These data were unpublished data, and we could only obtain the data before 2008 through data search by now). Based on the data from sample plots, the literature, and NFI, as well as the relationships between volume, biomass, annual litterfall and soil respiration of different forest types, the net ecosystem production (NEP), changes in forest biomass carbon storage (△Cbiomass) and non-respiratory losses (NR) of China’s forests during 1999-2008 were estimated, and the forest soil carbon sequestration (△Csoil) was assessed according to the carbon balance principle of the forest ecosystem (△Csoil = NEP - NR - △Cbiomass). The results showed that the total NEP, △Cbiomass, NR and △Csoil values for China’s forests were 157.530, 48.704, 31.033 and 77.793 Tg C yr-1 respectively, and average NEP, △Cbiomass, NR, and △Csoil values were 101.247, 31.303, 19.945 and 49.999 g C m-2 yr-1 respectively. There were large spatial differences in forest soil carbon sequestration in different parts of China. The forest soil in Jiangxi, Hunan, Zhejiang, Fujian, Anhui, Shanxi, Shaanxi, Guangxi and Liaoning served as carbon sources and the carbon released was about 25.507 Tg C yr-1. The other 22 provinces served as carbon sinks and the average carbon sequestration by forest soil came to 103.300 Tg C yr-1. This research established a method for evaluating soil carbon sequestration by China’s forests based on the NFI, which is a useful supplement to current statistical data-based studies on the forest ecosystem carbon cycle, and can promote comparable studies on forest soil carbon sequestration with consistent research methods at the regional scale.
Vegetation restoration is the primary task of ecological reconstruction and rocky desertification control in Karst areas. With vegetation net primary productivity and coverage as two key indicators, a vegetation ecological quality evaluation model was built based on meteorological and remote sensing data. Spatiotemporal variation of vegetation ecological quality index and its response to climate change in rocky desertification areas in Southwest China during 2000-2020 were also analyzed by using the difference method and linear trend method. The results showed that: (1) Vegetation ecological quality in rocky desertification areas in Southwest China showed a fluctuating upward trend during 2000-2020. In 2020, the vegetation ecological quality index reached 69.7, which was 19.9% and 9.3% higher than the averaged values for 2000 and 2000-2019, respectively, ranking the fourth highest since 2000. (2) Vegetation ecological quality of the rocky desertification areas in Yunnan, Guangxi and Guizhou provinces have been improved by 89.2%, 99.2% and 98.5%, respectively, from 2000 to 2020, with their vegetation ecological quality index values increasing by 0.5-0.75 per year in southeast Yunnan, most areas in Guizhou and northwest Guangxi. (3) Precipitation was an important meteorological factor affecting the vegetation ecological quality in rocky desertification areas. The vegetation ecological quality index in the northwest and central Yunnan rocky desertification areas has been rising slowly, but with localized declines at a yearly rate of nearly 0.25 caused by climatic warming and drying.
Leaf longevity is an important adaptive strategy that allows plants to maximize photosynthetic carbon gain. Due to the difficulty of identifying overwintering bud scars and distinguishing the age sequence of twigs, leaf longevity is rarely studied in Cupressaceae species, which further limits our understanding of the leaf economic spectrum (LES) for these populations. Here, we investigated the leaf longevity, as well as mass-based leaf nitrogen concentration (Nmass), of Juniperus saltuaria at different canopy heights for both subalpine and alpine timberline forests in the Sergymla Mountains, southeastern Tibet. We found that the mean leaf longevity was 4.2±1.2 years, and overall it did not differ significantly between different elevations. Along the vertical profiles of juniper canopies, the leaf longevity did not reflect a linear trend. With increasing leaf longevity, Nmass showed declining trends. We further analyzed the relationship between leaf longevity and the corresponding length of green twigs, and found that the length of green twigs could only explain 1%-3% of the variation in leaf longevity, indicating that the length of green twigs is a poor predictor for the variation in leaf longevity. In summary, for the J. saltuaria species in timberline or nearby subalpine forests, the effects of elevation and canopy depths on leaf longevity are minor, and the leaf trait analysis is in accordance with the prediction of LES.