Rapid Understory Restoration of a Thinned Red Pine Plantation in Algonquin Provincial Park

Abstract

Tree plantations can be used as a restoration tool to quickly re-establish canopy cover in degraded areas. A red pine plantation was established in the 1970s for just this purpose in Algonquin Provincial Park, Ontario. Plantation ecosystems, however, are substantially different in composition, structure, and function compared to old growth forests, and their understory communities develop more slowly. Therefore, in 2021, the Park initiated a 4-year project to rapidly restore the plantation understory. This thesis documents the first 2 years of the project, during which a restoration experiment was designed and implemented. The experiment goals are to determine which treatments improve soil quality and increase native vegetation abundance, as well as to test of the effectiveness of windthrow guards, a novel treatment that does not appear in the literature.

Two treatments are being applied universally: thinning and invasive species management. Two additional treatments are being tested experimentally using a variant of the randomized complete block design. The first of these experimental treatments is a simplified version of applied nucleation, where small clusters of plants are planted with the expectation that they will enhance seedling recruitment and spread outwards over time. We transplanted 128 individual beaked hazel shrubs as our nuclei. The second experimental treatment is windthrow guards, which use rings of herbaceous plants around woody species to protect them from being uprooted by strong winds. Canada goldenrod was used for this treatment, with 768 transplants forming rings around the hazel shrubs. Mortality censuses conducted one month after transplanting determined that 99% of shrubs and 87% of goldenrod survived the transplanting process. Preliminary results also show that thinning increased average understory light availability to 38.8% of full sun across the site. Vegetation surveys have revealed the presence of native understory species in the plantation, as well as a significant number of non-native species, especially generalist species.

After the 4-year project ends, the Park will continue to thin the plantation every 10-12 years. It is expected that the periodic canopy openings will allow more understory recruitment, including native hardwood saplings. As the red pines are removed, the hardwoods will dominate, and a young hardwood forest will be established in 30-40 years.