Dark diversity in temperate forests of northeastern China: drivers and implications

Understanding the species composition of a community, including those species present and those absent but potentially able to occur, is vital for assessing biodiversity changes and informing conservation planning. Typically, studies focus on observed taxonomic diversity but ignore undetected species expected to be present based on co-occurrence patterns—referred to as dark diversity. Dark diversity serves as a sensitive indicator of biodiversity change, often responding earlier than observed diversity. However, its underlying drivers, especially environmental and anthropogenic factors, remain poorly understood in forest ecosystems. In this study, we quantified both dark and observed diversity and applied logistic regression to identify traits influencing species’ likelihood of belonging to dark diversity at the species level. Variance partitioning and spatial autoregressive models were used to disentangle the effects of environmental and human drivers at the plot level. Our results revealed that key traits such as mycorrhizal type, specific leaf area and tree height determine a species’ likelihood of belonging to dark diversity, and that dark and observed diversity respond differently to environmental and anthropogenic factors. Dark diversity was mainly influenced by the interaction of environmental factors and human impacts, with annual mean temperature being the strongest environmental driver. Observed diversity, in contrast, was most influenced by annual mean precipitation. Dark diversity increased with mean annual temperature, declined under the combined influence of human footprint and precipitation, and increased with the interaction between human footprint and precipitation seasonality. Observed diversity was positively affected by precipitation and altitude, and negatively influenced by human footprint-temperature and altitude-roadless area interactions. Our findings highlight the importance of addressing climate and human pressures in conservation planning, as dark diversity signals hidden constraints on species establishment and persistence.