Spatial–temporal pattern of vegetation carbon sequestration and its response to rocky desertification control measures in a karst area, in Guangxi Province, China

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Abstract

The terrestrial ecosystem in southwestern China has been a long‐term carbon sink, but its spatial–temporal pattern during the previous two decades and its response to karst rocky desertification control measures (KRDC) still merit further quantification, particularly where higher levels of carbon capture by vegetation are proposed in the context of a ‘carbon neutrality’ goal. Satellite datasets, field data from previous studies, and the geostatistical soil respiration model enabled a focus on the karst landscape in Guangxi Province in Southwest China, to probe the spatial–temporal pattern of the ability to capture carbon during 2001–2020 and assess its response to KRDC. The results showed that the interannual variation in the average net ecosystem productivity (NEP) exhibited a remarkable tendency to increase at a rate of 4.15 g C m ⁻² yr ⁻¹ ( p < 0.01). A major period of increase was identified from 2006 to 2011, which represented the second stage of the KRDC. The terrestrial ecosystems of karst area have always acted as carbon sinks. Human activity was the dominant factor in the development of NEP and covered an area of 79.30%. The karst area offers climate change characteristics of ‘wetness’ and ‘light stress,’ which can promote the ability of vegetation carbon to serve as a carbon sink (0.18 g C m ⁻² yr ⁻¹). Furthermore, the closing mountains for afforestation is the most effective way to artificially increase the carbon sink. Quantifying vegetation ecosystem carbon sinks and sources in this study is highly significant for understanding regional carbon dynamics and guiding carbon capture policies to design and mitigate land degradation.

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The carbon balance of terrestrial ecosystems in China.

Shilong Piao, Jingyun Fang, Philippe Ciais … (2009)

Global terrestrial ecosystems absorbed carbon at a rate of 1-4 Pg yr(-1) during the 1980s and 1990s, offsetting 10-60 per cent of the fossil-fuel emissions. The regional patterns and causes of terrestrial carbon sources and sinks, however, remain uncertain. With increasing scientific and political interest in regional aspects of the global carbon cycle, there is a strong impetus to better understand the carbon balance of China. This is not only because China is the world's most populous country and the largest emitter of fossil-fuel CO(2) into the atmosphere, but also because it has experienced regionally distinct land-use histories and climate trends, which together control the carbon budget of its ecosystems. Here we analyse the current terrestrial carbon balance of China and its driving mechanisms during the 1980s and 1990s using three different methods: biomass and soil carbon inventories extrapolated by satellite greenness measurements, ecosystem models and atmospheric inversions. The three methods produce similar estimates of a net carbon sink in the range of 0.19-0.26 Pg carbon (PgC) per year, which is smaller than that in the conterminous United States but comparable to that in geographic Europe. We find that northeast China is a net source of CO(2) to the atmosphere owing to overharvesting and degradation of forests. By contrast, southern China accounts for more than 65 per cent of the carbon sink, which can be attributed to regional climate change, large-scale plantation programmes active since the 1980s and shrub recovery. Shrub recovery is identified as the most uncertain factor contributing to the carbon sink. Our data and model results together indicate that China's terrestrial ecosystems absorbed 28-37 per cent of its cumulated fossil carbon emissions during the 1980s and 1990s.

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Evaluation of terrestrial carbon cycle models for their response to climate variability and to CO2 trends.

Shilong Piao, Stephen Sitch, Philippe Ciais … (2013)

The purpose of this study was to evaluate 10 process-based terrestrial biosphere models that were used for the IPCC fifth Assessment Report. The simulated gross primary productivity (GPP) is compared with flux-tower-based estimates by Jung et al. [Journal of Geophysical Research 116 (2011) G00J07] (JU11). The net primary productivity (NPP) apparent sensitivity to climate variability and atmospheric CO2 trends is diagnosed from each model output, using statistical functions. The temperature sensitivity is compared against ecosystem field warming experiments results. The CO2 sensitivity of NPP is compared to the results from four Free-Air CO2 Enrichment (FACE) experiments. The simulated global net biome productivity (NBP) is compared with the residual land sink (RLS) of the global carbon budget from Friedlingstein et al. [Nature Geoscience 3 (2010) 811] (FR10). We found that models produce a higher GPP (133 ± 15 Pg C yr(-1) ) than JU11 (118 ± 6 Pg C yr(-1) ). In response to rising atmospheric CO2 concentration, modeled NPP increases on average by 16% (5-20%) per 100 ppm, a slightly larger apparent sensitivity of NPP to CO2 than that measured at the FACE experiment locations (13% per 100 ppm). Global NBP differs markedly among individual models, although the mean value of 2.0 ± 0.8 Pg C yr(-1) is remarkably close to the mean value of RLS (2.1 ± 1.2 Pg C yr(-1) ). The interannual variability in modeled NBP is significantly correlated with that of RLS for the period 1980-2009. Both model-to-model and interannual variation in model GPP is larger than that in model NBP due to the strong coupling causing a positive correlation between ecosystem respiration and GPP in the model. The average linear regression slope of global NBP vs. temperature across the 10 models is -3.0 ± 1.5 Pg C yr(-1) °C(-1) , within the uncertainty of what derived from RLS (-3.9 ± 1.1 Pg C yr(-1) °C(-1) ). However, 9 of 10 models overestimate the regression slope of NBP vs. precipitation, compared with the slope of the observed RLS vs. precipitation. With most models lacking processes that control GPP and NBP in addition to CO2 and climate, the agreement between modeled and observation-based GPP and NBP can be fortuitous. Carbon-nitrogen interactions (only separable in one model) significantly influence the simulated response of carbon cycle to temperature and atmospheric CO2 concentration, suggesting that nutrients limitations should be included in the next generation of terrestrial biosphere models. © 2013 Blackwell Publishing Ltd.