Plant community assembly 15-37 years after clearcutting, clearcutting plus prescribed burning, and wildfire in jack pine (Pinus banksiana Lamb.) forest of Central Canada

Abstract

Study area: Northwestern Ontario.It has been suggested that clearcutting be followed by prescribed burning as a means of reconciling effects of clearcutting and wildfire on plant communities. To address the effectiveness of clearcutting followed by prescribed burning (PB), I assessed understorey communities in northwestern Ontario using fifty 10 ? 10 m plots, located in 15-37 year old jack pine (Pinus banksiana Lamb.) stands established after clearcutting, PB, and wildfire. My findings are presented in two chapters, first I examined structural and compositional differences in plant communities originating from the three disturbance types, and secondly I examined the relationship of species' traits to disturbance type. In Chapter 1, I hypothesized that understorey communities established after PB would resemble those established after wildfire more closely than those established after clearcutting alone. However, I found that all three disturbance types had similar understorey species richness and diversity, while species composition within PB sites differed significantly from clearcut and wildfire sites. Compositional differences associated with PB were comparable to those found after successive short-interval wildfires. Indicator species of PB sites were mostly ruderai and disturbance tolerant species; suggesting that PB created a compound effect on plant communities. Since application of prescribed burning after clearcutting does not involve a novel disturbance, compositional differences may be related to the short-interval between clearcutting and PB. In Chapter 2, I hypothesized that compositional differences between communities originating from PB correspond to the interaction of short-interval disturbance with species' life history and regeneration traits. I analyzed traits related to post-disturbance regeneration to quantify relationships with disturbance type. For trait analysis I used the abundance-weighted analyses RLQ, Fourth-Corner Analysis, calculation of functional diversity indices (functional richness, evenness, and dispersion), and community weighted means. I found no significant relationship between the suite of traits and disturbance type. However I found significant relationships between PB and species' traits such as Raunkiaer's lifeform, seed banking, wind dispersal, deciduous foliage, rosettes and alien status. My hypothesis was supported by the prevalence of seed banking and wind dispersal in the PB sites, both of which are known to increase with short-interval disturbances. From these results I conclude that application of PB following clearcutting causes compositional differences that result from disturbance-mediated plant trait selection by short-interval disturbances.