Successional analysis of post agricultural forests using light detecting and ranging (LiDAR)

The successional trajectories of post-agricultural forests in Northeastern Nova Scotia either presently or formerly dominated by white spruce (Picea glauca (Moench.)Voss) were investigated. Comparative analysis was performed for post-agricultural stands under conditions of natural disturbance (AN) and harvest disturbance (AH), versus non-agricultural control sites under a natural disturbance regime (NAN). Canonical Correspondence Analysis (CCA) ordination of species and environmental data was performed for 81 ground reference plots to ascertain successional trajectories. CCA input included variables derived from Light Detecting and Ranging (LiDAR), including surface roughness, insolation and pulse return intensity. Separate ordinations were performed for the herbaceous layer (<1 m height) and woody overstorey. Herbaceous layer succession was influenced by gradients of canopy closure, live basal area and ground microtopography (CCA Axis 1) and accretion of coarse woody material (CCA Axis 2). Woody overstorey characteristics were similarly driven by succession (Axis 1) and canopy openness (Axis 2). Significant linkage between herbaceous layer and overstorey were observed for all sites under a natural disturbance regime (AN, p=0.002; NAN, p=0.005) as opposed to those harvested (AH, p=0.07). CCA revealed a disclimactic, non-forested community which appears to have reverted to conditions similar to those of early agricultural abandonment. Both harvested and unharvested post-agricultural plots in close proximity to primary forest stands supported herbaceous layer species similar to primary forest plots, and regression analysis of CCA scores versus distance from seed source yielded a significant (p <0.0001) result. A conceptual model of disturbance-related succession for post-agricultural sites is proposed. P.glauca may play a role in reintroducing site complexity on post-agricultural sites through deposition of coarse woody material, generation of microsites for seed germination and by modifying the light environment.