Effects of past pollution on zoochory in a recovering mixed temperate-boreal forest

Abstract

In landscapes perturbed by industrial mining, seed dispersal limitations could affect the potential for forest recovery. We measured seed removal in different vegetation layers by different dispersal vectors to examine the potential for natural recovery of a severely stressed forest in Greater Sudbury, Canada. Vegetation structure was measured and causal relationships with seed removal along a stress gradient of past pollution were estimated using path analysis. There was almost no seed removal in the most degraded sites, and birds removed fewer seeds than other animal groups in all sites. An increasing trend across the pollution gradient was identified for both seed types examined (blueberries and oaks), and it was strongly correlated with basal area per hectare, distance to decommissioned smelter, and understory cover. A negative effect of an invasive slug species on the seed consumption process was detected. We show slow recovery in more degraded sites, the importance of forest structure for animal activity, and the need for considering structural and functional components when analyzing regeneration from past pollution.