Understory Species Identity Rather than Species Richness Influences Fine Root Decomposition in a Temperate Plantation

Different silvicultural treatments that are applied at plantation establishment may drive different vegetation succession pathways. These divergent vegetation types subsequently feed back to influence soil carbon and nitrogen cycles. One potential mechanism of feedback is through litter decomposition, and in particular fine root decomposition (FRD; <2 mm roots). In the present study we investigated how blade scarification, fertilization, and vegetation control influenced over- and understory vegetation 27 years after plantation, and whether these different vegetation communities affected FRD. In a design using factorial combinations of the three treatments at the Petawawa Research Forest (Laurentian Hills, ON, Canada), we conducted an in situ FRD experiment, with fine roots from the entire vegetation community (both over- and understory) of each plot. The different silvicultural treatments affected overstory basal area, understory species richness and FRD. No correlation was noted between understory species richness and FRD. Instead, we found that understory vegetation (especially fern and herb) cover best explained FRD. We conclude that silvicultural treatments affect FRD through subsequent vegetation succession and that this effect is more likely due to species-specific effects inducing a favorable soil environment than to a higher species richness per se.