Impacts of global change on peak vegetation growth and its timing in terrestrial ecosystems of the continental US

Abstract Vegetation phenology and peak growth are important indicators reflecting the response of ecosystems to global changes, yet the trends in peak vegetation growth and its drivers have not been well analyzed across different ecosystems. Here, we used time series of satellite-derived Normalized Difference Vegetation Index (NDVI) (1985–2015) to track recent changes in maximum vegetation growth (the maximum of NDVI (NDVImax) and the peak of growing season (POS)) in the continental US, and explored their responses to both climatic drivers (i.e. temperature, precipitation and cloud cover) and atmospheric changes (i.e. nitrogen (N) deposition and atmospheric CO2 concentration [CO2]). We found that precipitation had the greatest impact on NDVImax, accounting for 31.7% of vegetated area, followed by cloud cover (17.1%), temperature (16.4%), [CO2] (13.7%), and N deposition (10.4%), respectively. However, temperature showed the largest contribution to POS change in about 41.9% of vegetated areas, followed by precipitation (18.6%), cloud cover (15.0%), N deposition (6.7%) and [CO2] (5.9%), respectively. Interestingly, the effects of cloud cover highly depended on moisture regime, that is, more cloud cover was associated with a delayed POS and a decreased NDVImax in wetter regions, but could advance POS and increase NDVImax in dry areas. In addition, we also found that an earlier POS was accompanied by a higher NDVImax in most ecosystems, but with lower NDVImax in arid ecosystems. These results reveal the control of both climatic and atmospheric drivers on peak growth, and consequently are of great significance for understanding of the responses and feedbacks of vegetation to global change and improve models of terrestrial ecosystem carbon cycle.