Ecological restoration and ecosystem memory of wildlife forage and understory diversity in a young pine monoculture plantation in central-interior British Columbia

Ecological restoration has recently taken center stage in the rehabilitation of degraded forest ecosystems to improve multifunctionality, biodiversity, and wildlife habitat conservation. The research summarized herein assessed the efficacy of variable stand density thinning (200, 400, and 600 stems/ha) and artificial canopy gaps (0.2, 0.5, 1.0, 2.0 ha in size) as potential restoration treatments to enhance wildlife forage and native biodiversity in a young lodgepole pine (Pinus contorta var. latifolia Engelm. ex S. Wats.) forest in central-interior British Columbia. Field data collection was conducted from May-August, 2023 to assess the early response (1-3 years post-treatment) of the forest understory plant community to the treatments. The effects of the restoration treatments and time since treatment on the cover, richness, diversity, and composition of the shrub and herbaceous layer species were analyzed using linear mixed-effects models and permutational multivariate analysis of variance. Additionally, linear models were used to examine the influence of forest floor characteristics (leaf litter, bare ground, downed woody debris, and duff depth) on understory cover, richness, and diversity as well as the impact of the treatments on presence of wildlife activity (based on presence or absence of feces). Both restoration thinning and canopy gap treatments resulted in an increase in understory herbaceous species cover and richness compared to the untreated controls. Species cover, richness and diversity were generally higher in 3-years post-treatment plots compared to 1-year post-treatment plots. Furthermore, herbaceous species composition varied significantly between the restoration treatments versus the controls, with treated plots dominated by shade-intolerant, disturbance-dependent species. Forest floor characteristics, such as percent cover of leaf litter and bare ground, were associated with reduced herbaceous species cover and richness. There was evidence of increased wildlife presence in the thinning and canopy gap treatments (as compared with the untreated controls), where certain species of importance to moose, such as aspen (Populus tremuloides) and willow (Salix spp.), were found. Overall, these results suggest that reducing forest stand density through thinning and artificial canopy gaps may be effective for restoring native plant biodiversity and wildlife habitat in dense monoculture plantations. Soil samples were also collected from the study area for a seedling emergence trial to assess the viability of the soil seed bank. After 6 months of germination under favorable conditions in the greenhouse, predominantly graminoids and ruderals germinated from the seed bank. There was no difference found in the count or identities of the germinants between the restoration treatments, untreated controls, and old-growth reference stands when analyzed using permutational multivariate analysis of variance. Notably, the absence of seeds from target forage species, such as aspen, willow, and birch, from the soil seed bank suggested that we cannot rely solely on the seed bank for passive regeneration of native plant biodiversity in these young pine-dominated forests. Rather, active restoration methods, such as seeding and planting of native forage species, may be needed to rehabilitate and restore understory plant diversity and wildlife habitat in these stands.