Abstract. Changes in snow water equivalent (SWE) over Northern Hemisphere (NH) landmasses are investigated for the early (2016-2035), middle (2046-2065) and late (2080-2099) 21st century using a multi-model ensemble from 20 global climate models from the Coupled Model Intercomparison Project Phase 5 (CMIP5). The multi-model ensemble was found to provide a realistic estimate of observed NH mean winter SWE compared to the GlobSnow product. The multi-model ensemble projects significant decreases in SWE over the 21st century for most regions of the NH for representative concentration pathways (RCPs) 2.6, 4.5 and 8.5. This decrease is particularly evident over the Tibetan Plateau and North America. The only region with projected increases is eastern Siberia. Projected reductions in mean annual SWE exhibit a latitudinal gradient with the largest relative changes over lower latitudes. SWE is projected to undergo the largest decreases in the spring period where it is most strongly negatively correlated with air temperature. The reduction in snowfall amount from warming is shown to be the main contributor to projected changes in SWE during September to May over the NH.

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Questions What are the primary types of intraspecific distribution patterns and interspecific associations of tree species in the temperate–subtropical transition region? Can potential ecological mechanisms such as habitat heterogeneity, dispersal limitation, density dependence, spatial segregation, and competition between species regulate these patterns? Location The Qinling Mountains, north‐central China. Methods Ripley's K‐function, D‐function and pair correlation function were applied to assess the spatial distribution of 15 dominant tree species in a fully mapped 25‐ha plot. Complete spatial randomness (CSR), heterogeneous Poisson (HP) and random‐labelling (RL) null models were used to reveal the potential process of community construction. Results (a) Thirteen of 15 adult tree species displayed an aggregation distribution at various scales. (b) Eleven adult species (73.3%) showed significant aggregation, especially at small distances, after removing the effect of habitat. (c) The percentage of species showing additional aggregation relative to adults decreased from saplings to juveniles. The maximum strength of density dependence was negative with species abundance. (d) Only 29 (13.8%) of the species pairs showed significant small‐scale interactions. Most of the significant small‐scale associations did not occur in abundant species pairs. (e) Negative interactions of interspecific associations were more prevalent than positive ones, yet there was no consistency of the characteristics among species pairs. Conclusions Habitat heterogeneity and dispersal limitation likely contribute to the spatial pattern of tree species at different life stages. Density dependence remains the important factor in maintaining species diversity in this forest stand. Moreover, spatial segregation generates the interspecific spatial patterns of segregation and partial overlap. Unexpectedly, the species herd protection hypothesis and the low‐frequency hypothesis cannot well explain the mechanism of interspecific interaction at small distances. Resource competition might be responsible for negative associations being more frequent among species pairs.

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