Climate extremes and grassland potential productivity

Yi, Chuixiang; Rustic, G. T.; Xu, Xiyan; Wang, Jingxin; Dookie, A.; Wei, Suhua; Hendrey, George R.; Ricciuto, D. M.; Meyers, Tilden P.; Nagy, Zoltán; Pintér, Krisztina

doi:10.1088/1748-9326/7/3/035703

Cited by 37 publications

(42 citation statements)

References 19 publications

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“…An increasing trend in global net primary productivity, particularly in tropical forests, has also been identified on the basis of satellite imagery for 1982-1999 and is attributed primarily to CO 2 fertilization [2]. On the other hand, in boreal areas, warming has been a major driver of longer growing seasons and higher productivity [51,52], while in arid and semiarid areas, moisture availability is a primary modulator of vegetation growth [15,[53][54][55]. The small positive impact of precipitation on NDVI trends, concentrated during and after the summer monsoon, is consistent with the increasing trend in monsoon precipitation found for recent decades over much of Nepal [56], although dry spells have also increased [57,58].…”

Section: Discussionmentioning

confidence: 99%

Mapping and Attributing Normalized Difference Vegetation Index Trends for Nepal

2017

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Global change affects vegetation cover and processes through multiple pathways. Long time series of surface land surface properties derived from satellite remote sensing give unique abilities to observe these changes, particularly in areas with complex topography and limited research infrastructure. Here, we focus on Nepal, a biodiversity hotspot where vegetation productivity is limited by moisture availability (dominated by a summer monsoon) at lower elevations and by temperature at high elevations. We analyze the normalized difference vegetation index (NDVI) from 1981 to 2015 semimonthly, at an 8 km spatial resolution. We use a random forest (RF) of regression trees to generate a statistical model of the NDVI as a function of elevation, land use, CO 2 level, temperature, and precipitation. We find that the NDVI increased over the studied period, particularly at low and middle elevations and during the fall (post-monsoon). We infer from the fitted RF model that the NDVI linear trend is primarily due to CO 2 level (or another environmental parameter that is changing quasi-linearly), and not primarily due to temperature or precipitation trends. On the other hand, interannual fluctuation in the NDVI is more correlated with temperature and precipitation. The RF accurately fits the available data and shows promise for estimating trends and testing hypotheses about their causes.

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Section: Discussionmentioning

confidence: 99%

Mapping and Attributing Normalized Difference Vegetation Index Trends for Nepal

2017

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“…Drought-induced tree mortality has been shown to greatly reduce terrestrial carbon uptake (Zhao and Running 2010). However, the relationship between tree mortality and drought is reported to be more complex than that between grassland production and drought (Yi et al 2012). This is thought to be mainly due to the greater ability of trees to access water sources at greater depths leading to lower sensitivity to moisture levels in shallow soil horizons.…”

Section: Introductionmentioning

confidence: 99%

Tipping point of a conifer forest ecosystem under severe drought

Huang

et al. 2015

Environ. Res. Lett.

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Drought-induced tree mortality has recently received considerable attention. Questions have arisen over the necessary intensity and duration thresholds of droughts that are sufficient to trigger rapid forest declines. The values of such tipping points leading to forest declines due to drought are presently unknown. In this study, we have evaluated the potential relationship between the level of tree growth and concurrent drought conditions with data of the tree growth-related ring width index (RWI) of the two dominant conifer species (Pinus edulis and Pinus ponderosa) in the Southwestern United States (SWUS) and the meteorological drought-related standardized precipitation evapotranspiration index (SPEI). In this effort, we determined the binned averages of RWI and the 11 month SPEI within the month of July within each bin of 30 of RWI in the range of 0-3000. We found a significant correlation between the binned averages of RWI and SPEI at the regional-scale under dryer conditions. The tipping point of forest declines to drought is predicted by the regression model as SPEI tp = −1.64 and RWI tp = 0, that is, persistence of the water deficit (11 month) with intensity of −1.64 leading to negligible growth for the conifer species. When climate conditions are wetter, the correlation between the binned averages of RWI and SPEI is weaker which we believe is most likely due to soil water and atmospheric moisture levels no longer being the dominant factor limiting tree growth. We also illustrate a potential application of the derived tipping point (SPEI tp = −1.64) through an examination of the 2002 extreme drought event in the SWUS conifer forest regions. Distinguished differences in remote-sensing based NDVI anomalies were found between the two regions partitioned by the derived tipping point.

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“…A recent study using flux tower measurements over semi-arid grasslands in southwest United States identified a precipitation threshold that a semi-arid system could switch from a net sink or a net source of carbon from year to year32. Meanwhile, a common temporal and spatial sensitivity of gross CO 2 uptake to water-availability over a broad diversity of semi-arid ecosystems in North America has also been reported33, indicating that fast ecophysiological responses are useful for predicting semi-arid carbon sink/source dynamics under future climatic water availability34. Global semi-arid ecosystems are currently threatened by increasing aridity and enhanced warming3536, posing concerns on their sustainable ability to absorb carbon, maintain biodiversity, and support human livelihood.…”

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confidence: 97%

Drought rapidly diminishes the large net CO2 uptake in 2011 over semi-arid Australia

Huete

Cleverly

et al. 2016

Sci Rep

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Each year, terrestrial ecosystems absorb more than a quarter of the anthropogenic carbon emissions, termed as land carbon sink. An exceptionally large land carbon sink anomaly was recorded in 2011, of which more than half was attributed to Australia. However, the persistence and spatially attribution of this carbon sink remain largely unknown. Here we conducted an observation-based study to characterize the Australian land carbon sink through the novel coupling of satellite retrievals of atmospheric CO2 and photosynthesis and in-situ flux tower measures. We show the 2010–11 carbon sink was primarily ascribed to savannas and grasslands. When all biomes were normalized by rainfall, shrublands however, were most efficient in absorbing carbon. We found the 2010–11 net CO2 uptake was highly transient with rapid dissipation through drought. The size of the 2010–11 carbon sink over Australia (0.97 Pg) was reduced to 0.48 Pg in 2011–12, and was nearly eliminated in 2012–13 (0.08 Pg). We further report evidence of an earlier 2000–01 large net CO2 uptake, demonstrating a repetitive nature of this land carbon sink. Given a significant increasing trend in extreme wet year precipitation over Australia, we suggest that carbon sink episodes will exert greater future impacts on global carbon cycle.

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Climate extremes and grassland potential productivity

Cited by 37 publications

References 19 publications

Mapping and Attributing Normalized Difference Vegetation Index Trends for Nepal

Mapping and Attributing Normalized Difference Vegetation Index Trends for Nepal

Tipping point of a conifer forest ecosystem under severe drought

Drought rapidly diminishes the large net CO2 uptake in 2011 over semi-arid Australia

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