Are trees regenerating following high severity fire in ponderosa pine-dominated forests of the Colorado Front Range?

Background/Question/Methods

Wildfire is an important disturbance in ponderosa pine - dominated forests of the Colorado Front Range and the West, but the past two decades have witnessed fires of increased size and severity. The ability of ponderosa pine and other co-occurring conifers (such as Douglas-fir) to regenerate in the large, high severity burn patches created by such fires is unclear, as seeds of these species must typically disperse into severely burned areas from surviving trees, and seed production is typically episodic. We quantified post-fire tree regeneration in five 11 to 18 year-old Colorado Front Range fires to examine whether high severity burn patches are regenerating, and to examine how regeneration in these patches is governed by abiotic and biotic factors such as distance from seed source, aspect, and elevation.  Within the fires, we collected post-fire tree regeneration and other data in 100 m² plots that were distributed every 25 to 50 m along transects; transects were anchored 50 m inside live forest edges and extended out into the high severity burn areas up to 250 m.

Results/Conclusions

Our preliminary results indicate that ponderosa pine and other conifers are regenerating in high severity burn areas, but at low densities (less than 100 conifer stems ha^-1).  This contrasts with conifer regeneration in unburned and lightly to moderately burned areas, where regeneration averaged approximately 1000 and 500 conifer stems ha^-1, respectively. Our preliminary results also illustrate that as distance from seed source increases, tree recruitment decreases, with most regeneration occurring within 100 m of the live forest edge.   Transects averaged approximately 170 regenerating conifer stems ha^-1 within 50 m of the forest edge, but averaged fewer than 50 stems ha^-1 150 m from the forest edge, and only approximately 10 stems ha^-1 250 m from the forest edge.  Future analyses will further investigate how other abiotic and biotic conditions will influence conifer recruitment.  Results of this study will provide managers with information about conifer recruitment dynamics that will aid in post-fire restoration efforts.