Management lessons from recent aspen declines and climate

Trembling aspen recently experienced extensive crown thinning, branch dieback, and mortality across North America. Most decline regions experienced exceptionally severe drought preceding these episodes. Decline tended to occur in marginally suitable habitat, and climatic suitability decreased markedly in the period leading up to decline in almost all decline regions. Other factors, notably multi-year defoliation by tent caterpillars and stem damage by fungi and insects, also play substantial roles in decline episodes. Many severely affected stands have poor regeneration potential, raising concerns that increasing aridity could ultimately lead to widespread loss of aspen forest cover. The analysis indicates that exceptional droughts were a major cause of the decline episodes, especially in the drier regions, and that aspen is sensitive to drought in much of its range. Models suggest that we should expect substantial loss of suitable habitat within the current distribution, especially in the USA and Mexico. Particularly in the interior western U.S., the results provide support for aspen management. Further, they suggest approaches for deciding where to invest in management under changing climates, taking advantage of the diversity offered by changes in elevation and aspect