scholarly journals Climate Change Decreased Net Ecosystem Productivity in the Arid Region of Central Asia

2021 ◽  
Vol 13 (21) ◽  
pp. 4449
Author(s):  
Jingjing Zhang ◽  
Xingming Hao ◽  
Haichao Hao ◽  
Xue Fan ◽  
Yuanhang Li
Keyword(s):  
Climate Change ◽  
Carbon Source ◽  
Central Asia ◽  
Net Primary Productivity ◽  
Regional Distribution ◽  
Source Area ◽  
Terrestrial Ecosystems ◽  
Net Ecosystem Productivity ◽  
Ecosystem Productivity ◽  
Source Sink

Numerous studies have confirmed that climate change leads to a decrease in the net ecosystem productivity (NEP) of terrestrial ecosystems and alters regional carbon source/sink patterns. However, the response mechanism of NEP to climate change in the arid regions of Central Asia remains unclear. Therefore, this study combined the Carnegie–Ames–Stanford approach (CASA) and empirical models to estimate the NEP in Central Asia and quantitatively evaluate the sensitivity of the NEP to climate factors. The results show that although the net primary productivity (NPP) in Central Asia exhibits an increasing trend, it is not significant. Soil heterotrophic respiration (RH) has increased significantly, while the NEP has decreased at a rate of 6.1 g C·m−2·10 a−1. Spatially, the regional distribution of the significant increase in RH is consistent with that of the significant decrease in the NEP, which is concentrated in western and southern Central Asia. Specifically, the NPP is more sensitive to precipitation than temperature, whereas RH and NEP are more sensitive to temperature than precipitation. The annual contribution rates of temperature and precipitation to the NEP are 28.79% and 23.23%, respectively. Additionally, drought has an important impact on the carbon source/sink in Central Asia. Drought intensified from 2001 to 2008, leading to a significant expansion of the carbon source area in Central Asia. Therefore, since the start of the 21st century, climate change has damaged the NEP of the Central Asian ecosystem. Varying degrees of warming under different climate scenarios will further aggravate the expansion of carbon source areas in Central Asia. An improved understanding of climate change impacts in Central Asia is critically required for sustainable development of the regional economy and protection of its natural environment. Our results provide a scientific reference for the construction of the Silk Road Economic Belt and global emissions reduction.

Quantitatively assessing the effects of climate change and human activities on ecosystem degradation and restoration in southwest China

2019 ◽  
Vol 41 (4) ◽  
pp. 335
Author(s):  
Z. G. Sun ◽  
J. S. Wu ◽  
F. Liu ◽  
T. Y. Shao ◽  
X. B. Liu ◽  
...  
Keyword(s):  
Climate Change ◽  
Primary Productivity ◽  
Human Activities ◽  
Southwest China ◽  
Net Primary Productivity ◽  
Terrestrial Ecosystems ◽  
Ecosystem Degradation ◽  
Relative Contribution ◽  
Degraded Ecosystem ◽  
Annual Means

Identifying the effects of climate change and human activities on the degradation and restoration of terrestrial ecosystems is essential for sustainable management of these ecosystems. However, our knowledge of methodology on this topic is limited. To assess the relative contribution of climate change and human activities, actual and potential net primary productivity (NPPa and NPPp respectively), and human appropriation of net primary productivity (HANPP) were calculated and applied to the monitoring of forest, grassland, and cropland ecosystems in Yunnan–Guizhou–Sichuan Provinces, southwest China. We determined annual means of 476 g C m–2 year–1 for NPPa, 1314 g C m–2 year–1 for NPPp, and 849 g C m–2 year–1 for HANPP during the period between 2007 and 2016. Furthermore, the area with an increasing NPPa accounted for 75.12% of the total area of the three ecosystems. Similarly, the areas with increasing NPPp and HANPP accounted for 77.60 and 57.58% of the study area respectively. Furthermore, we found that ~57.58% of areas with ecosystem restored was due to climate change, 23.39% due to human activities, and 19.03% due to the combined effects of human activities and climate change. In contrast, climate change and human activities contributed to 19.47 and 76.36%, respectively, of the areas of degraded ecosystem. Only 4.17% of degraded ecosystem could be attributed to the combined influences of climate change and human activities. We conclude that human activities were mainly responsible for ecosystem degradation, whereas climate change benefitted ecosystem restoration in southwest China in the past decade.

Foliar respiration in an old-growth Pseudotsuga-Tsuga forest

2006 ◽  
Vol 36 (1) ◽  
pp. 216-226 ◽  
Author(s):  
Clifton E Cooper ◽  
Sean C Thomas ◽  
William E Winner
Keyword(s):  
Carbon Sources ◽  
Interspecific Variation ◽  
Net Ecosystem Productivity ◽  
Seasonal Temperature ◽  
Ecosystem Productivity ◽  
Old Growth ◽  
Old Growth Forest ◽  
Canopy Position ◽  
Eddy Covariance Measurements ◽  
Source Sink

Old-growth forest ecosystems accrue carbon at small mean rates and may function as carbon sinks in some years and as carbon sources in others. Foliar respiration is a large component of stand carbon balance and could be variable enough to substantially affect source–sink behaviors. However, foliar respiration has not been well studied in old-growth canopies. We examined seasonal, interannual, spatial, and interspecific variation of foliar respiration in an old-growth Pseudotsuga–Tsuga stand in Washington, USA, with measurements made on three species at 3-month intervals, for 4+ years. There were strong seasonal differences, with rates being much larger in June than in December. Rates in March were significantly (p ≤ 0.0001) larger than expected for all species. For data pooled across seasons, the exponential respiration-temperature relationship indicated that a seasonal temperature increase of 10 °C caused rates to increase by 1.78 times. For respiration based on leaf area, but not on leaf mass, rates varied strongly with canopy position (p ≤ 0.0001). Temperature-corrected rates were compared among four consecutive years and declined from 1999 to 2001. Correlation with eddy covariance measurements suggests that interannual changes in foliar respiration did not cause the decline in net ecosystem productivity observed at the site through the same period, but may have instead partially offset a trend toward decreasing net ecosystem productivity caused by other factors.

scholarly journals Carbon uptake and water use in woodlands and forests in southern Australia during an extreme heat wave event in the ‘Angry Summer’ of 2012/2013

2016 ◽  
Author(s):  
Eva van Gorsel ◽  
Sebastian Wolf ◽  
Peter Isaac ◽  
James Cleverly ◽  
Vanessa Haverd ◽  
...  
Keyword(s):  
Heat Flux ◽  
Heat Wave ◽  
Forest Ecosystem ◽  
Land Surface ◽  
Bowen Ratio ◽  
Terrestrial Ecosystems ◽  
Carbon Uptake ◽  
Temperature Extremes ◽  
Net Ecosystem Productivity ◽  
Ecosystem Productivity

Abstract. As a result of climate change warmer temperatures are projected through the 21st century and are already increasing above modelled predictions. Apart from increases in the mean, warm/hot temperature extremes are expected to become more prevalent in the future, along with an increase in the frequency of droughts. It is crucial to better understand the response of terrestrial ecosystems to such temperature extremes for predicting land-surface feedbacks in a changing climate. During the 2012/2013 summer, Australia experienced a record-breaking heat wave with an exceptional spatial extent that lasted for several weeks. We synthesized eddy-covariance measurements from seven woodland and forest sites across climate zones in southern Australia, which we combined with model simulations from the CABLE land surface model to investigate the effect of this summer heat wave on the carbon and water exchange of terrestrial ecosystems. We found that the water-limited woodlands and the energy-limited forest ecosystem responded differently to the heat wave. During the most intense part of the heat wave, the woodlands experienced decreased latent heat flux, an increased Bowen ratio and a reduced carbon uptake while the forest ecosystem had increased latent heat flux, reduced Bowen ratio and increased carbon uptake. Ecosystem respiration was increased at all sites resulting in reduced net ecosystem productivity in the woodlands and constant net ecosystem productivity in the forest. Importantly all ecosystems remained carbon sinks during the event. Precipitation after the most intense first part of the heat wave and slightly cooler temperatures led to a decrease of the Bowen ratio and hence increased evaporative cooling. Carbon uptake in the woodlands also recovered quickly but respiration remained high. While woodlands and forest proved relatively resistant to this short-term heat extreme these carbon sinks may not sustainable in a future with an increased number, intensity and duration of heat waves.

Climate change impacts on CO2 and CH4 exchange in an Arctic polygonal tundra depend on changes in vegetation and drainage

2020 ◽  
Author(s):  
Robert Grant
Keyword(s):  
Climate Change ◽  
Boundary Conditions ◽  
Net Primary Productivity ◽  
Climate Change Impacts ◽  
Ecosystem Productivity ◽  
Climate Change Effects ◽  
Net Uptake ◽  
Soil Temperatures ◽  
Rcp 8.5 ◽  
Thawing Permafrost

<p>Model projections of CO<sub>2</sub> and CH<sub>4</sub> exchange in Arctic tundra during the next century diverge widely.  In this modelling study, we used ecosys to examine how climate change will affect CO<sub>2</sub> and CH<sub>4</sub> exchange through its effects on net primary productivity (NPP), heterotrophic respiration (R<sub>h</sub>) and thereby on net ecosystem productivity (NEP) in landform features (troughs, rims, centers) of a coastal polygonal tundra landscape at Barrow AK. The model was shown to simulate diurnal and seasonal variation in CO<sub>2</sub> and CH<sub>4</sub> fluxes associated with those in air and soil temperatures (T<sub>a</sub> and T<sub>s</sub>) and soil water contents (q) under current climate in 2014 and 2015. During RCP 8.5 climate change from 2015 to 2085, rising T<sub>a</sub>, atmospheric CO<sub>2</sub> concentrations (C<sub>a</sub>) and precipitation  (P) increased NPP from 50 – 150 g C m<sup>-2</sup> y<sup>-1</sup>,  consistent with current biometric estimates, to 200 – 250 g C m<sup>-2</sup> y<sup>-1</sup>, depending on feature elevation. Concurrent increases in R<sub>h</sub> were slightly smaller, so that net CO<sub>2</sub> exchange rose from values of -25 (net emission) to +50 (net uptake) g C m<sup>-2</sup> y<sup>-1</sup> to ones of -10 to +65 g C m<sup>-2</sup> y<sup>-1</sup>, again depending on feature elevation. Large increases in R<sub>h</sub> with thawing permafrost were not modelled. Increases in net CO<sub>2</sub> uptake were largely offset by increases in CH<sub>4 </sub>emissions from 0 – 6 g C m<sup>-2</sup> y<sup>-1 </sup>to 1 – 20 g C m<sup>-2</sup> y<sup>-1</sup>, depending on feature elevation, reducing gains in NEP. Increases in CH<sub>4</sub> emissions with climate change were mostly attributed to increases in T<sub>a</sub>, but also to increases in C<sub>a</sub> and P. These increases in net CO<sub>2</sub> uptake and CH<sub>4</sub> emissions were modelled with hydrological boundary conditions that were assumed not to change with climate.  Both these increases were smaller if boundary conditions were gradually altered to increase landscape drainage during model runs with climate change. The model was then applied to the entire permafrost zone of North America to project RCP 8.5 climate change effects on active layer depth and ecosystem productivity by 2100.  </p>

scholarly journals Spatiotemporal Simulation of Net Ecosystem Productivity and Its Response to Climate Change in Subtropical Forests

Forests ◽  
2019 ◽  
Vol 10 (8) ◽  
pp. 708 ◽  
Author(s):  
Junlong Zheng ◽  
Fangjie Mao ◽  
Huaqiang Du ◽  
Xuejian Li ◽  
Guomo Zhou ◽  
...  
Keyword(s):  
Climate Change ◽  
Relative Humidity ◽  
Correlation Coefficient ◽  
Zhejiang Province ◽  
Annual Growth Rate ◽  
Net Ecosystem Productivity ◽  
Carbon Sinks ◽  
Ecosystem Productivity ◽  
Subtropical Forests ◽  
Relative Contribution

Subtropical forests have great potential as carbon sinks; however, the relationship between net ecosystem productivity (NEP) and climate change is still unclear. This study took Zhejiang Province, a subtropical region, as an example. Based on remote sensing classification data of forest resources, the integrated terrestrial ecosystem carbon cycle (InTEC) model was used to simulate the spatiotemporal dynamics of the forest NEP in Zhejiang Province during 1985–2015 and analyze its response to meteorological factors such as temperature, precipitation, relative humidity, and radiation. Three patterns emerged: (1) The optimized InTEC model can better simulate the forest NEP in Zhejiang Province, and the correlation coefficient between the simulated NEP and observed NEP was up to 0.75. (2) From 1985 to 2015, the increase in the total NEP was rapid, with an average annual growth rate of 1.52 Tg·C·yr−1. During 1985–1988, the forests in Zhejiang Province were carbon sources. After 1988, the forests turned into carbon sinks and this continued to increase. During 2000–2015, more than 97% of the forests in Zhejiang Province were carbon sinks. The total NEP reached 32.02 Tg·C·yr−1, and the annual mean NEP increased to 441.91 gC·m−2·yr−1. The carbon sequestration capacity of forests in the east and southwest of Zhejiang Province is higher than that in the northeast of Zhejiang Province. (3) From 2000 to 2015, there was an extremely significant correlation between forest NEP and precipitation, with a correlation coefficient of 0.85. Simultaneously, the forest NEP showed a negative correlation with temperature and radiation, with a correlation coefficient of −0.56 for both, and the forest NEP was slightly negatively correlated with relative humidity. The relative contribution rates of temperature, precipitation, relative humidity, and radiation data to NEP showed that the contribution of precipitation to NEP is the largest, reaching 61%, followed by temperature and radiation at 18% and 17%, respectively. The relative contribution rate of relative humidity is the smallest at only 4%. During the period of 1985–1999, due to significant man-made disturbances, the NEP had a weak correlation with temperature, precipitation, relative humidity, and radiation. The results of this study are important for addressing climate change and illustrating the response mechanism between subtropical forest NEP and climate change.

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