Canopy gap age influences snow depth: Implications for gap-based silviculture on snowpack in the Sierra Nevada

Climate change is raising the elevation of rain-snow transition lines and accelerating spring snowmelt, posing increasing risks to California’s regional ecosystems and water infrastructure. Research has shown that snow accumulation and retention are shaped by complex interactions with forest structure. Open-canopy gaps tend to preserve snowpack better than closed-canopy forests. However, it is unclear how long these advantages persist as forests regenerate. This study examines how canopy gap age, defined as years since group selection harvest, affects snow depth across twenty-eight canopy gaps in the north-central Sierra Nevada. Multiple Linear regression models indicated that each additional year of canopy gap age corresponded to a 4.8% decline in March snow depth and a 0.3-day acceleration in snow disappearance, though these coefficients should be interpreted as indicative of direction and relative magnitude rather than precise predictions. Greater snow depth and later snow disappearance dates were both associated with younger canopy gaps, with these benefits declining approximately linearly over 30–40 years as regenerating cohorts grew and canopy closure progressed. Multivariate Autoregressive State-Space models showed that gap age was not a strong predictor of day-to-day snow depth; the time series was dominated by ablation periods during which snow depth loss was broadly similar across age classes. Combined with visual inspection of the season’s snow depth patterns, this suggests that gap age primarily influences end-of-season snow depth through differences established during accumulation events rather than during ablation periods. Gap age may serve as a practical proxy for structural forest characteristics that are difficult to measure yet critically influence end-of-season snow depth and presence, though replication is needed to assess the robustness and predictive utility of this relationship across multiple water years. From a forest management perspective, gap-based silviculture such as group selection harvesting is a promising starting point for maintaining greater snow depth as a co-benefit alongside other management objectives. Advancing this understanding will require multi-year observations, comprehensive snowpack measurements, and closer examination of how young regenerating vegetation influences snowpack.