Fire and High-Elevation, Five-Needle Pine (Pinus aristata & P. flexilis) Ecosystems in the Southern Rocky Mountains: What Do We Know?

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Rocky Mountain bristlecone pine (Pinus aristata Engelm) and limber pine (P. flexilis James) are high-elevation, five- needle pines of the southern Rocky Mountains. The pre-settlement role of fire in bristlecone and limber pine forests remains the sub- ject of considerable uncertainty; both species likely experienced a wide range of fire regimes across gradients of site productivity and connectivity of fuels and flammable landscapes. In dense stands and more continuous forests, stand history reconstructions provide evidence for infrequent, high-severity fires. Limber pine can be dispersed long distances by Clark’s nutcrackers (Nucifraga colum- biana), and in the high-elevation subalpine forests of the northern Colorado Front Range, it is an early colonist of extensive, high- severity burns. However, this relationship with fire may not be general to the southern Rockies. The degree to which high-severity fire was typical of bristlecone pine, and the spatial extent of such fires, is uncertain. Following fire, bristlecone pine regeneration tends to be constrained to burn edges or beneath surviving trees. In both five-needle pines, regeneration dynamics take decades to centuries. Where open stands border grassy openings both species frequently exhibit fire scars indicative of fairly frequent but low- intensity fire; because of the great ages attained by both species, they offer potentially very long fire history reconstructions in such settings. Whether or not fire suppression has led to declines in either species—through successional shifts to shade-tolerant com- petitors or by shifts to a stand replacing fire-regime—remains an open question that deserves further inquiry. In any case, re-estab- lishing pre-settlement fire regimes, whatever they were, may not be as important as determining appropriate disturbance regimes given current conditions and management objectives. Both species are highly susceptible to rapid declines caused by white pine blister rust (Cronartium ribicola) and mountain pine beetles (Dendroctonus ponderosae). In the face of these threats, and uncertain consequences of climate change, fire management (both prevention and applica- tion) can be a tool to promote resilient landscapes. Appropriate fire management may be used to conserve valuable stands, pro- mote regeneration and diversify age class structures, and/or alter the balance between these species and their competitors. Many of these themes and questions indicate the need for further basic and applied research.