Structure, dynamics, and climate sensitivity of range-margin jack pine forests in central Minnesota

Abstract

Species' ranges are expected to shift in response to changes in climate and disturbance regimes. Individuals and populations along the edge of their range are expected to be most affected because of their proximity to climatically limiting factors and the unique dynamics relative to non-marginal portions of their range. However, limited empirical knowledge exists concerning the historic range of ecological variability in range-margin populations and systems.Jack pine (Pinus banksiana) reaches its southwestern range limit in central Minnesota where it displays traits, including low-levels of cone serotiny, that differ from other portions of its range. However, the stand dynamics (establishment, age structures, and disturbance regimes) and linkages with climate have never been documented for these populations. Our aim was to quantify the natural range of variability of stand dynamics and climate relationships to establish reference conditions for monitoring future climate impacts, informing refinement of forest ecosystem models, and assisting in the development of management decisions for conservation.Our results indicate that jack pine stands in this region are structurally complex even and un-even aged systems that follow a variety of developmental pathways. These patterns are attributed to the non-serotinous cones of jack pine in this region, which allow for both episodic and extended recruitment patterns over time. Annual growth and recruitment were both significantly sensitive to moisture and temperature variables, especially during the winter-to-spring transition, yet the directionality of associations displayed much seasonal variation. Our results suggest that management and modeling practices should be broadened to account for the variety of structural conditions and developmental pathways that historically characterized these range-margin jack pine forests. Such changes will help to conserve jack pine forests for the short-term while promoting the propensity for long-term resilience and adaptability.