Cover Diversity of Understory Vegetation in Managed Forests: Patterns, Drivers, and Implications for Biodiversity-Oriented Management

Forest management strongly influences understory plant communities, yet their responses to management remain context-dependent and scale-sensitive. This review synthesizes current knowledge on understory vegetation in managed forests by combining a bibliometric analysis of global research trends (1986–2025) with a comprehensive qualitative evaluation of empirical studies. The bibliometric assessment identified 726 publications, with a marked increase in output after 2017 and a predominance of research articles within Environmental Sciences, forestry, and biodiversity conservation. Research activity is geographically concentrated in North America and Europe, while other biomes remain comparatively underrepresented. The classical review highlights canopy structure and light availability as primary drivers of understory diversity. Management interventions such as thinning, harvesting, gap creation, and prescribed fire frequently increase local (α) species richness and vegetation cover in the short term by promoting early-seral and light-demanding species. However, these gains are often accompanied by compositional shifts toward ruderal and generalist taxa, reductions in bryophytes and forest specialists, and declines in spatial heterogeneity at broader scales. Consequently, β-diversity and landscape-level distinctiveness may decrease despite stable or elevated plot-level richness. Management intensity, retention of structural legacies (e.g., large trees and deadwood), soil and hydrological conditions, landscape context, and interactions with global change drivers (e.g., nitrogen deposition and climate warming) strongly mediate vegetation responses. Low-to-moderate-intensity systems that maintain structural heterogeneity and approximate natural disturbance regimes appear most effective at balancing production objectives with biodiversity conservation. Understory vegetation responses to forest management reflect trade-offs between short-term richness increases and long-term risks of compositional homogenization and specialist decline. Evaluating biodiversity outcomes therefore requires multi-scale, trait-informed approaches that move beyond species richness alone. This synthesis provides an integrative framework to support evidence-based, biodiversity-oriented forest management in increasingly human-modified landscapes.