Assessing early-stage effects of defoliation by the Hemlock Looper on Himalayan Blackberry (Rubus armeniacus) abundance in Stanley Park in winter 2026

Himalayan Blackberry (HIBL; Rubus bifrons/R. armeniacus) is an invasive species, whose presence in Stanley Park threatens to reduce ecosystem biodiversity. In collaboration with Stanley Park Ecology (SPE), this project aimed to quantify the relationship between the defoliation from the most recent Western Hemlock Looper (LM; Lambdina fiscellaria lugubrosa) outbreak and HIBL growth in Stanley Park. Additionally, this study assessed general HIBL habitat suitability and trends across the park. To quantify the relationship between HIBL abundance and LM defoliation, Stanley Park was divided into four strata, looking at areas of high and low defoliation and areas with and without historical HIBL recordings. We randomly generated 60 sampling plots, with an equal number (15) in each stratum. Each plot was surveyed for HIBL density, percent coverage, and average stand height. We found no statistically significant relationship between HIBL biomass or presence and LM defoliation, but suggest the potential for one to develop over time. Overall, this study can be used to support future research initiatives about how HIBL responds to defoliation disturbances in the long-term, and help identify general areas vulnerable to HIBL invasion.