Disentangling exogenous and endogenous memory in global vegetation productivity: dominant role and future strengthening of vegetation carryover effects.

Vegetation productivity is not only determined by current environmental conditions but also reflects the lagged influence of past climate and vegetation states. This temporal dependency, often referred to as ecological memory, arises from both antecedent climate conditions (exogenous lagged climatic effects, LCE) and prior vegetation states (endogenous vegetation growth carryover effects, VGC). However, their spatiotemporal variability, relative importance, and responses to future climate change remain poorly understood at the global scale. Here, we develop a unified analytical framework by integrating vector autoregressive model and impulse response functions to disentangle the roles of LCE and VGC in regulating global gross primary productivity (GPP) across space, time, and future climate scenarios. Both components exhibit rapid initial responses followed by gradual decay within approximately five months, yet differ markedly in magnitude, direction, and persistence. LCE show strong hemispheric asymmetry: in the Northern Hemisphere, increases in temperature exert the strongest positive effect on GPP, whereas increases in atmospheric dryness (vapor pressure deficit) produce the strongest negative effect. In contrast, in the Southern Hemisphere, increased precipitation is the dominant positive driver of GPP, while negative responses exhibit greater spatial heterogeneity and show no clear dominant controlling factor, suggesting more complex and regionally varying climatic influences. In contrast, VGC display globally consistent positive responses with substantially greater intensity (17.35 gC m