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

Abstract. During the past several decades, observational data have shown a faster increase in hot temperature extremes than the change in mean temperature. Increasingly high extreme temperatures are expected to affect terrestrial ecosystem function. The ecological impact of hot extremes on vegetation production, however, remains uncertain across biomes in natural climatic conditions. In this study, we investigated the effects of hot temperature extremes on vegetation production by combining the MODIS enhanced vegetation index (EVI) data set and in situ climatic records during the period 2000 to 2009 from 12 long-term experimental sites across biomes and climate. Our results show that higher mean annual maximum temperatures (T_max) greatly reduced grassland production, and yet enhanced forest production after removing the effect of precipitation. The relative decrease in vegetation production was 16% for arid grassland and 7% for mesic grassland, and the increase was 5% for forest. We also observed a significantly positive relationship between interannual aboveground net primary production (ANPP) and T_max for the forest biome (R² = 0.79, P < 0.001). This line of evidence suggests that hot temperature extremes lead to contrasting ecosystem-level responses of vegetation production between grassland and forest biomes. Given that many terrestrial ecosystem models use average daily temperature as input, predictions of ecosystem production should consider such contrasting responses to increasingly hot temperature extreme regimes associated with climate change.