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Conifer regeneration and fuels treatment longevity in dry mixed-conifer forests of the Colorado Front Range

Date

2018

Authors

Fialko, Katie, author
Ex, Seth, advisor
Fornwalt, Paula, committee member
Hoffman, Chad, committee member
Rocca, Monique, committee member

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Abstract

Throughout much of the western United States, wildfires have been increasing in size and severity. To prevent negative impacts to communities and ecosystems, costly fuels reduction treatments are being applied to dry, mixed-conifer forests in Colorado and throughout the southern Rockies. The objective of this project was to make inferences about treatment longevity by determining how site, treatment, and vegetation characteristics of treated areas influence the abundance and composition of conifer regeneration, which can serve as fuels to initiate a high severity wildfire. Thinning and mastication treatments ranging in age from 5-14 years old on north and south aspects were examined. Time since treatment and residual overstory density and composition, along with aspect, had the greatest influence on the abundance of Douglas-fir and ponderosa pine regeneration in fuels treatments. Conifer regeneration did not vary by mastication vs thinning treatment type. Although Douglas-fir advance regeneration abundance decreased over time since treatment, it comprised 50% of all regeneration observed. This is a concern because advance regeneration will reduce treatment longevity more than the gradual accumulation of post treatment seedlings, and because it has the potential to release. Post treatment Douglas-fir regeneration was positively related to Douglas-fir residual overstory density but had no relationship with time since treatment. Post treatment ponderosa pine regeneration, however, increased with time since treatment and was negatively related to total residual overstory density. These findings indicate that while Douglas-fir regeneration may belimited by the lack of residual Douglas-fir in the overstory to provide a seed source, treatments are effectively acting as shelterwood regeneration treatments to increase the abundance of ponderosa pine. Lastly, average abundance of all conifer regeneration was five times greater on north aspects than on south aspects. Forest managers implementing future fuels reduction treatments, or planning the re-treatment of existing units, should monitor advance regeneration for potential release, anticipate a greater post treatment regeneration response on north aspects, and possibly expect a shift in future stand composition towards ponderosa pine.

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