Climate and disturbance influence self‐sustaining stand dynamics of aspen near its range margin
This study sampled tree age and stand characteristics of isolated aspen forests in the arid Great Basin (USA) to determine if: (1) aspen communities are more fire‐dependent and seral or fire‐independent and stable; (2) ungulate browsing inhibits aspen stability; and (3) temporal patterns of vegetative reproduction (i.e., ramet establishment or “suckering”) are correlated with climate. Aspen size and age class densities strongly fit negative exponential distributions, whether grouped geographically or by functional type, suggesting landscape‐scale persistence. Continuous age distributions and high proportions of recruitment‐sized to overstory trees suggest stability at stand‐scales, with exceptions including stands with higher browsing pressure. Few stands had evidence of fire, and relationships between dead tree size and variability in live tree size suggest a lack of fire‐dependency. Several five‐year averaged climate variables and one sea surface temperature index were correlated with aspen ramet establishment densities over time, with strongest relationships occurring ~5 years prior to establishment year, often followed by inverse relationships ~1 year after. Indeed, aspen establishment density for a recent 41‐year period was reliably reconstructed using antecedent climate conditions derived from a single drought index. Temporally synchronized aspen ramet establishment across the study region may be due to climate‐driven storage of nonstructural carbohydrate reserves in clonal root systems later used for regeneration. Complex regeneration dynamics of these self‐sustaining aspen stands, especially sensitivity to climate variability, suggest they may serve as harbingers of ecological change in the arid Great Basin and in other aspen populations near their range margin.