Response of taxonomic and functional diversity to disturbance severity in temperate hardwood forests

Abstract

AbstractAims:Quantify changes in taxonomic and functional diversity (FD) and identity to determine if responses to a disturbance severity gradient follow a “colonization/competition” hypothesis: diversity will (a) increase with disturbance severity as more open conditions favor species with traits linked to colonization; and (b) become more similar between regeneration and overstorey layers as environmental filtering favors species with traits linked to increasing competition for light.Location:North Carolina, USA.Methods:Taxonomic (richness [S], evenness [E], and Shannon diversity [H′]) and functional diversity (richness [FRic], evenness [FEve], and dispersion [FDis]) and identities were calculated for regeneration and overstorey before and after restoration treatments: control (CONT); “undesirable” subcanopy stems removed via herbicide (HERB); repeated burning (RRXF); and timber harvest followed by burning (HARV).Results:In the overstorey, HARV affected taxonomic and FD. In HARV, S and H′ were lower than in other treatments. At high levels of species richness, FEve was lower in HARV than in HERB and RRXF. Similarly, at high levels of species richness, FDis was greater in HARV than other treatments. In the regeneration layer, taxonomic and FD did not differ across treatments during any of the post‐treatment years. In the regeneration stratum, HARV increased the means of traits associated with rapid post‐disturbance establishment, carbon capture, and maximum height. Greater dissimilarity in composition between the overstorey and regeneration suggests stronger treatment effects on regeneration in HARV than less severe treatments.Conclusion:Patterns do not support the hypothesis that taxonomic diversity increases with disturbance severity or decreases with time after disturbance in the regeneration layer. Of the restoration treatments tested in this study, only HARV affected aspects of functional identity of the regeneration stratum; even so, FD remained unchanged. In mixed Quercus forests, functional identity rather than taxonomic or FD may provide insight into nuanced effects of restoration treatments on ecosystem function.