Ground-layer disturbance and initial conditions influence gap partitioning of understorey vegetation

1. Differential species responses to canopy gap formation may dominate organization of understorey plant community composition in many forests. Gap creation may enhance heterogeneity in understorey plant communities and could influence biodiversity patterns in young managed forests. 2. Our objective was to determine whether understorey plant communities exhibit patterns indicative of gap partitioning and to quantify environmental variables related to these patterns. 3. Patterns in understorey vegetation were studied on transects across harvested canopy gaps in four young, Douglas-fir (Psuedotsuga menziesii) dominated forest stands in western Oregon. Variation in ground-layer disturbance and resource gradients in relation to patterns in understorey plant community composition was also assessed. 4. Understorey plant community composition differed significantly by location relative to gap in 0.4-ha gaps, but not 0.1-ha gaps, supporting the gap-size partitioning hypothesis. 5. The concurrent effects of ground-layer disturbance, gap size-related differences in resource gradient intensity, and pre-gap community composition and vegetation structure interact to influence the existence of gap partitioning in understorey plant communities. 6. Gap creation can influence small-scale heterogeneity in understorey plant communities and thus could be an important management tool in efforts to increase heterogeneity and biodiversity in stands and landscapes dominated by young, second growth forests.