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Post-fire management affects species composition but not Douglas-fir regeneration in the Klamath Mountains

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Ensuring adequate conifer regeneration after high severity wildfires is a common objective for ecologists and forest managers. In the Klamath region of Oregon and California, a global hotspot of botanical biodiversity, concerns over regeneration have led to post-fire management on many sites, which involves salvage logging followed by site preparation, conifer planting, and manual shrub release. To quantify the impacts of post-fire management, we sampled 62 field sites that burned at high severity nearly 20 years ago in the Klamath-Siskiyou Mountain bioregion, stratifying by management and aspect. We measured cover of shrubs and trees and density and frequency of trees and used Nonmetric Multidimensional Scaling to compare community composition, plant community assemblage based on regenerative traits, and density of tree species between aspect and management. On average, shrub cover exceeded the cover of conifers, hardwoods or grasses, regardless of management history or aspect. The average number of species was lower and resprouting species were less abundant on south aspect sites; seed banking species were most abundant on north aspects. Post-fire management was associated with greater cover of seed banking and nitrogen-fixing species but it did not affect diversity. Management had no impact on Douglas-fir regeneration, the main species of concern in the region. Regeneration of ponderosa pine was higher on sites with post-fire management, but only on south slopes. The frequency of Douglas-fir was associated with aspect, while the frequency of ponderosa pine was associated with management. Overall, our study demonstrates the important role that aspect plays in determining the effectiveness of management after high severity wildfires. Indeed, the effect of aspect on site conditions often overwhelmed the ability of management to influence community composition (including different regenerative strategies), species diversity, and regeneration. Managed sites differed from unmanaged sites in several diverse ways with varied implications for longer-term forest development. Managed sites had taller dominant conifers, which suggests that post-fire management could hasten the period needed to achieve fire resistance. Managed sites were similar in plant community composition but had more homogeneous structure--e.g., managed sites had fewer snags, which are an important habitat feature for several bird species in the region. Finally, management was not associated with conifer regeneration success on north slopes, suggesting that interventions may not be needed uniformly across post-fire landscape. New policies of ecosystem-based management in the Klamath region should consider the important interactions between aspect and post-fire management, and tailor management practices based on specific objectives and landscape context.

M.J.Lopez Ortiz

Ortiz MJLopez. Post-fire management affects species composition but not Douglas-fir regeneration in the Klamath Mountains Marcey T. Forest Ecology and Management. 2019 ;432.