Stable or unstable? Landscape diversity and ecosystem stability across scales in the forest–grassland ecotone in northern China

Context Forest–grassland ecotones, the transitional zones between forests and grasslands, often harbor high levels of biodiversity. According to the portfolio theory, communities with such high biodiversity should exhibit high stability in ecosystem functioning. On the contrary, the theory of ‘bi-stability’ or ‘multistability’ predicts that ecosystems exhibiting multiple states or regimes (e.g. forest and grassland) are less stable. Understanding the stability of forest–grassland ecotone has broad implications for forest management and restoration. Objectives In this study, by quantifying landscape heterogeneity and temporal invariability of regional climatic and vegetational metrics, we aimed to reveal how landscape diversity influences the stability of ecosystem functioning in the forest–grassland ecotone. Methods We focused on the forest–grassland ecotone in northern China (i.e. from the forest belt in the Greater Khingan Mountains to the steppe grassland in Inner Mongolia) and used remote sensing data of land cover dynamics from 1992 to 2015 to analyze the landscape diversity and ecosystem dynamics at different grain sizes. To measure the temporal stability of climatic variables and vegetational dynamics, we calculated the interannual variation of temperature ( T ), wind speed ( WS ), precipitation ( P ), and the net primary productivity ( NPP ) on the grided sampling cells at different spatial scale over the same period. Results Our results showed that landscape diversity across this forest–grassland ecotone was positively related to the stability of T and NPP , but negatively related to that of WS and P . These opposite patterns may be explained by the differential nature of ecosystem variables, namely whether they involve transporting substance across space ( WS and P ) or not ( T and NPP ). We also found that as the spatial scale increases, the diversity-stability relationships strengthened for all three climatic variables (i.e., T, P, WS). However, the stabilizing effects of landscape diversity on NPP first increased but then decreased with increasing grain size, peaking at ~ 30 km. Conclusions Our empirical analyses demonstrate strong, but context-dependent diversity-stability relationships, shedding light on the paradox in the stability of ecosystem functioning in the ecotone. These findings also have implications for the management of landscape resources to maintain the sustainability of forest–grassland ecotones.