Rapid Understorey Restoration of a Red Pine Plantation in Algonquin Provincial Park

Abstract

The understorey of a forest provides essential habitat for wildlife, increases habitat heterogeneity, and enhances soil nutrients through the nutrient-rich litterfall of understorey vegetation. In red pine plantations (a common plantation type in southern Ontario and Algonquin Park), the understorey is sparse to non-existent. This is due to the dense overstorey reducing light, and the thick layer of fallen pine needles, which suppresses vegetation growth and acidifies the soil. This thesis documents the results of a four-year (2021-2024) collaboration between the University of Waterloo and Algonquin Provincial Park to restore the understorey of a 50-year-old red pine plantation. The treatments tested were tree thinning and herbicide application to invasive species (applied to the entire site), applied nucleation and windthrow guards. Applied nucleation is the planting of trees and/or shrubs scattered throughout an area, to mimic natural succession. Beaked hazel shrubs and yellow birch trees were used as the applied nuclei in this experiment. Windthrow guards are when an herbaceous species is planted around a woody species to reduce wind damage. The term windthrow guard was coined for this project, as this method has not been tested in scientific literature before. Canada goldenrod was used as the windthrow guard in this experiment. The five treatment types used were: (1) control: received no additional treatments other than the tree thinning and herbicide application, (2) applied nucleation, (3) windthrow guard, (4) applied nucleation with windthrow guard, (5) unthinned: received to restoration treatments and acts as a reference state for statistical analysis. To determine the effectiveness of the windthrow guards and overall restoration success, mortality surveys of the transplanted trees and shrubs were performed. To determine the short-term outcomes of this experiment and establish monitoring best practices, vegetation surveys, insect trapping and identification and soil sampling and testing for pH, NO3, P and K occurred. A Cochran’s Q test with a post-hoc pairwise McNemar test with a Bonferroni correction was run on the mortality data. Differences in native and non-native vegetation community metrics (species richness, Simpson diversity and Hill-Shannon diversity) between the different treatment types were assessed with generalized linear mixed models with a post-hoc Tukey-adjusted estimated marginal means. Two-way mixed ANOVA’s were used to assess the impact of treatment type and sampling time on insect community metrics (species richness, Simpson diversity and Shannon diversity). Kruskal-Wallis tests with a post-hoc Dunn test were run on each year of soil data, due to changes in sampling strategy, to determine the impacts of treatment type on each of the soil parameters (pH, NO3, P, K). There was a high transplant survival rate (over 80% in 2024). There were differences in the mortality of transplants between 2022 and 2024 in the applied nucleation treatment type (p = 0.04), but not the applied nucleation with windthrow guard plot type (p > 0.05) indicating that windthrow guards may reduce the mortality of transplanted trees and shrubs. The only statistically significant results of vegetation metrics between the reference and restored treatment types were in nonnative species richness and Hill-Shannon diversity in 2024 (p > 0.05), however, post-hoc tests did not show statistically significant differences of either of the metrics between the different treatment types. There were no statistically significant two-way interactions or main effects of treatment type or sampling time on any of the arthropod metrics (p > 0.05). These results suggest that the understorey restoration had an acceptable outcome, and the area is recovering as expected, without many short-term changes in most monitoring metrics. The thesis ends with recommending further monitoring to assess the impacts of restoration impacts on the long-term site trajectory.