Char gardens: vegetation trends in planted conservation burn piles in the San Juan Islands, WA

Conservation Burns are a technique that burns slash material in such a way to maximize charcoal productivity. Once these char piles are planted, they are referred to as Char Gardens. This study examines the efficacy of Char Gardens as a technique to increase native plant dominance in the understory of rocky bald and upland woodland ecosystems in the San Juan Islands, Washington. Char Gardens were found to have a significantly higher proportion of native plants than the surrounding landscape, as measured from a Control plot adjacent and paired to each Char Garden surveyed in this study. Medians were calculated from the proportion of native vegetation of total biomass at each site - Cady Mountain, Mt. Grant LSR, and Turtleback LSR - for each monitoring period - April and June. On Cady during the April monitoring session, the medians were 85.74% and 24.34% Nativity for Burn Piles and Control plots respectively. In June, Cady medians were 80.36% and 38.97% respectively. At the Mt. Grant LSR site in April the medians were 81.24% and 23.36% for Burn Piles and Controls. In June the Mt. Grant medians were 82.33% and 29.07%. On Turtleback, the April medians were 66.58% and 3.56% for Burn Piles and Controls, and 75.02% and 11.52% in June. Shade levels, soil moisture, soil depth, and aspect were also compared between sites and treatments to determine their effect on plot nativity. Deep soil (>10cm) had the highest native cover (median = 23.5%) and species richness (median = 6). Optimal shade across all aspects was 50.34%, on warm aspects 58.23%, and on cool aspects 42.45%. Soil moisture showed a weak correlation with native cover (rho = 0.14, p-value = 0.03) and the proportion of nativity (rho = 0.13, p-value = 0.05). Fidelity and frequency of each species observed was also calculated. The species that showed high fidelity/high frequency to Char Gardens were Achillea millefolium (Yarrow), Eriophyllum lanatum (Wooly Sunflower), and Prunella vulgaris (Self-Heal). Some species included in the planting mix were more closely associated with Control plots - Brodiaea coronaria (Harvest Brodiaea), Toxicoscordion venenosum (Death Camas), Collinsia parviflora (Blue-eyed Mary), Fragaria vesca (Woodland Strawberry), Dodecatheon hendersonii (Shooting Star), Erythronium oreganum (Fawn Lily) - indicating that burning is either neutral or harmful to their populations and care must be taken to not harm their existing spread. This study indicates that Char Gardens are an effective method for increasing native plant presence in rocky bald ecosystems in the San Juans, and may have applicability in increasing nativity and species richness within the larger Pacific Northwest region and beyond.