Guoqiang Shi

Winter imposes severe ecological constraints on Eurasian otters (Lutra lutra), yet the environmental characteristics of their winter marking sites remain poorly understood. We characterized winter sprainting sites along a human disturbance gradient in Changbai Mountain, northeastern China. In January 2025, 55 sites were recorded along three rivers and assigned to urban or wild river-reach contexts based on the broader spatial and management context of each reach. We measured topographic, hydrological, riparian, fish-diversity, and anthropogenic variables. Broad environmental gradients were summarized using Factor Analysis of Mixed Data (FAMD), and five local variables were compared between river-reach contexts using exploratory tests with Holm adjustment. Of the 55 sites, 54 were beside flowing, unfrozen water. Intermediate-to-deep water, natural banks and forested riparian backgrounds were common. The first two FAMD dimensions explained 52.5% of environmental variation, representing a spatially coupled gradient involving anthropogenic remoteness and river-section fish resource background, and a topographic and channel-structure contrast. Urban and wild sites differed in water depth, bank type, and vegetation cover, while sprainting sites occurred in both. These findings show that winter marking activity was concentrated within accessible river sections embedded in contrasting landscape contexts.

Species diversity has been shown to be influenced by environmental factors, but the mechanism underlying their relationship remains unclear across spatial scales. Based on field investigation data collected from 3,077 sample plots in temperate forest ecosystems, we compared tree species richness, evenness and dominance at 10 km × 10 km, 30 km × 30 km and 90 km × 90 km spatial scales. Then, we detected the scale dependence of changes in tree species composition on climate, topography and forest structure using variation partitioning and quantified their contribution to tree diversity with gradient boosted models (GBMs) and fitted their relationships. The magnitude of tree richness, evenness and dominance significantly increased with spatial scale. Ecological factors jointly accounted for 24.3%, 26.5% and 38.5% of the variation in tree species composition at the three spatial scales, respectively. Annual mean temperature had a strong impact on tree richness, evenness and dominance and peaked at an intermediate scale. Tree evenness and dominance increased with the variation of temperature but had upper and lower limits. Tree richness obviously increased with annual precipitation on multiple scales and decreased with annual sunshine duration at large spatial scale. Tree richness, evenness and dominance obviously increased with the variation elevation and diameter at breast height at large scales and small scales, respectively. Tree dominance decreased with tree height in a hump at small scale. The dependence of tree diversity on ecological factors increased with spatial scales. Furthermore, different factors exert various controls on tree diversity at different spatial scales, representing a comprehensive mechanism regulating tree diversity.