Herbaceous plant diversity in forest ecosystems: patterns, mechanisms, and threats
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Studies conducted in forests have resulted in much of the ecological theory we build upon today. However, our basic understanding of forest ecology comes almost exclusively from the study of trees, even though they represent only a small fraction of the plant diversity present in forests. In recent decades there has been an increasing number of studies of forest herbs, broadening our understanding of plant community ecology in forest ecosystems. Here we highlight ten recent studies examining patterns and drivers of, as well as threats to, herbaceous plant diversity in forests. We first examine local, regional, and global patterns of herbaceous diversity in forests and how such patterns differ for woody versus herbaceous species. We then focus on ecological mechanisms that contribute to forest herb diversity, including the role of abiotic and biotic interactions. We end by discussing some major anthropogenic impacts on forest herb diversity, identifying where herbs are particularly susceptible or particularly resilient to current and predicted changes in comparison to trees. The studies we feature demonstrate that patterns and drivers of diversity often differ between woody and herbaceous plant communities. To facilitate cross-site comparisons, there is great need for more standardized survey methods for herbaceous plants, for simultaneous measurements of multiple plant growth forms, and for incorporating herbs into long-term forest monitoring networks. In addition, the selected studies reveal how land-use history, overabundant herbivores, invasive species, and climate change are all impacting forest herb communities. Some common characteristics of herbaceous plants, such as limited dispersal and small stature, may make forest herb communities more susceptible to these anthropogenic impacts, while others (e.g., resprouting ability, clonal reproduction) may make them more resilient compared to forest trees. More research is needed from both plant ecologists and applied forest practitioners to predict how herbaceous forest diversity will change in the future.