Individual response traits of understory plants vary along linked-press and compounded-pulse disturbance gradients in northern temperate and boreal forests

Abstract

Community-weighted means (CWM) and functional dispersion (FDis) of response traits of woody and herbaceous understory plants in northern temperate and boreal forest communities were studied to determine how these traits respond to linked-press (i.e., climate, historic fire regimes, and silviculture systems) and compounded-pulse (i.e., harvest, site preparation, and release treatments) disturbances. We used fifth year post-harvesting disturbance data from the NEBIE plot network (NEBIE), a large-plot field experiment in northern temperate and boreal forests in Ontario, Canada. To analyze treatment effects, a randomized complete block design was assumed. Treatments were applied in a semi-operational manner to two-hectare experimental units. Individual response traits were affected by linked-press and compounded-pulse disturbances in unique ways, with logarithmic (stress-gradient hypothesis) or hump-shaped (intermediate disturbance hypothesis) patterns typically observed. Some traits (i.e., lateral spread of clones, seed weight) did not differ between disturbance types. Results suggest that all interactions between linked-press and compounded-pulse disturbances typically exert non-linear effects on CWM and FDis of individual plant response traits for both woody and herbaceous understory plants in boreal and temperate forests. Specific responses varied with trait, understory layer, and type of disturbance.