Contrasting responses of terrestrial ecosystem production to hot temperature extreme regimes between grassland and forest

Abstract

Abstract. Observational data during the past several decades show faster increase of hot temperature extremes over land than changes in mean temperature. Towards more extreme temperature is expected to affect terrestrial ecosystem function. However, the ecological impacts of hot extremes on vegetation production remain uncertain across biomes in natural climatic conditions. In this study, we investigated the effects of hot temperature extremes on aboveground net primary production (ANPP) by combining MODIS EVI dataset and in situ climatic records during 2000 to 2009 from 12 long-term experimental sites across biomes and climates. Our results showed that higher mean annual maximum temperatures (Tmax) greatly reduced grassland production, and yet enhanced forest production after removing the effects of precipitation. Relative decreases in ANPP were 16% for arid grassland and 7% for mesic grassland, and the increase were 5% for forest. We also observed a significant positive relationship between interannual ANPP and Tmax for forest biome (R2 = 0.79, P < 0.001). This line of evidence suggests that hot temperature extreme leads to contrasting ecosystem-level response of vegetation production to warming climate between grassland and forest. Given that many terrestrial ecosystem models use average daily temperature as input, predictions of ecosystem production should consider these contrasting responses to more hot temperature extreme regimes associated with climate change.

Changing Trends and Abrupt Features of Extreme Temperature in Mainland China from 1960 to 2010

“…Abrupt changes in climate factors, especially abrupt changes in extreme temperatures, have been pointed out as a major threat to ecosystems [27,28], because extreme temperature is an important physical restriction for some plants [29,30]. Several researchers investigated abrupt changes in the trends in temperature extremes in the northern hemisphere, North America, the northwest of China and mainland China [31][32][33][34][35]; for example, an abrupt change in both temperature and precipitation extremes in Northwest China occurred in around 1986 [34], but studies of the abrupt changes in temperature extremes in mainland China used the moderate extremes temperature indices based on the 10th (90th) percentiles.…”

Topographic, soil, and climate drivers of drought sensitivity in forests and shrublands of the Pacific Northwest, USA

“…Vegetation responses to drought were discernible across two markedly different biomes at a regional scale, with EVI reduced under drought conditions relative to baseline conditions in over 95% of shrub-steppe pixels and 80% of forest pixels. Drought sensitivity in this study likely reflected drought-induced changes to vegetation canopies—such as reductions in leaf area—that can interact with other drought-induced physiological stresses to impact ecosystem productivity 18 , 23 , 24 , 37 . The sensitivity of ecosystem productivity to climate variability has implications for ecosystem services and processes including habitat availability and stability through time, nutrient cycling and carbon storage, watershed hydrology, and diversity of species and plant functional groups 1 , 30 .…”

“…Previous studies have similarly found greater drought sensitivity in non-forest ecosystems relative to forested ones 28 and in semi-arid regions compared to humid ones 30 . Water-limited biomes with relatively low gross primary productivity have shown stronger coupling between hydroclimate variation and vegetation greenness 20 , greater productivity decreases in response to extreme precipitation patterns 26 and heat extremes 24 , and slower recovery after droughts 8 . Thus, at broad spatial scales spanning large climate gradients, our results agree with a general pattern of greater spectral sensitivity to drought in biomes with greater water limitation and lower biomass.…”

“…Remote sensing has enabled regional- and global-scale assessments of vegetation responses to drought that generally agree with information from other sources such as land-surface models, dendrochronology, flux-tower data, and field observations 18 , 20 – 22 . For example, annually integrated Enhanced Vegetation Index (EVI) from the Moderate-resolution Imaging Spectroradiometer (MODIS) is strongly correlated with field measurements of aboveground net primary productivity (ANPP), allowing its use as a proxy for ANPP 18 , 23 , 24 . For representing ANPP across a range of biomes, EVI is preferable to other spectral indices such as Normalized Difference Vegetation Index (NDVI), due to the tendency of NDVI to saturate in high-biomass areas 25 , 26 .…”

“…We conceptualized drought sensitivity as the reduction in ecosystem productivity in response to drought and quantified that sensitivity using EVI, which is representative of ANPP 18 , 23 , 24 . This conceptualization of drought sensitivity is slightly different from—and complementary to—how other studies have assessed drought sensitivity, i.e., as the slope or correlation coefficient of the relationship between a meteorological metric and a vegetation metric such as EVI, NDVI, or ANPP 18 , 20 , 28 , 30 .…”