The resilience of the forest field layer to anthropogenic disturbances depends on site productivity

Abstract

The resilience of the boreal forest field layer (herbs plus dwarf shrubs) to anthropogenic disturbances is insufficiently understood because of the multitude of direct or indirect driver pathways and environmental conditions involved. We hypothesized that the impact of the forest-management-induced disturbances on field layer varies along the gradient of site productivity. To explore that we proposed a method for estimating the proportional effect of each driver on the field-layer composition, in a survey data of 273 mature or overgrown boreal forests, by combining variogram analysis with multifactorial general linear modelling. In forest types of very low and high productivity, field-layer composition was sensitive to the management disturbances in general and, particularly, to the management-controlled variations in the structure of the stand and its understory, i.e., in environmentally stressful conditions the main limiting factors were light availability and its spatiotemporal variability. At intermediate productivity, instead, the natural heterogeneity of ground layer conditions was the dominant driver, pointing to the limitation of regeneration microsites. Accordingly, on soils with low and high productivity, biodiversity-oriented sustainable forestry should diversify silvicultural approaches among stands and (or) enhance the within-stand mosaic, whereas small-scale natural disturbances of the ground-level “organic blanket” should be promoted in forests of intermediate productivity.