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Open AccessArticle

Variability in Mixed Conifer Spatial Structure Changes Understory Light Environments

1
Colorado Forest Restoration Institute, Colorado State University, 1472 Campus Delivery, Fort Collins, CO 80526, USA
2
Department of Forest and Rangeland Stewardship, Colorado State University, 1472 Campus Delivery, Fort Collins, CO 80523, USA
3
USDA Forest Service, Rocky Mountain Research Station, 240 W. Prospect Road, Fort Collins, CO 80526, USA
*
Author to whom correspondence should be addressed.
Current affiliation: The Jones Center at Ichauway, 3988 Jones Center Drive, Newton, GA 39870, USA.
Forests 2019, 10(11), 1015; https://doi.org/10.3390/f10111015
Received: 3 September 2019 / Revised: 8 November 2019 / Accepted: 11 November 2019 / Published: 13 November 2019
(This article belongs to the Special Issue Impacts of Complex Forest Structures on Tree Regeneration)
In fire-adapted conifer forests of the Western U.S., changing land use has led to increased forest densities and fuel conditions partly responsible for increasing the extent of high-severity wildfires in the region. In response, land managers often use mechanical thinning treatments to reduce fuels and increase overstory structural complexity, which can help improve stand resilience and restore complex spatial patterns that once characterized these stands. The outcomes of these treatments can vary greatly, resulting in a large gradient in aggregation of residual overstory trees. However, there is limited information on how a range of spatial outcomes from restoration treatments can influence structural complexity and tree regeneration dynamics in mixed conifer stands. In this study, we model understory light levels across a range of forest density in a stem-mapped dry mixed conifer forest and apply this model to simulated stem maps that are similar in residual basal area yet vary in degree of spatial complexity. We found that light availability was best modeled by residual stand density index and that consideration of forest structure at multiple spatial scales is important for predicting light availability. Second, we found that restoration treatments differing in spatial pattern may differ markedly in their achievement of objectives such as density reduction, maintenance of horizontal and tree size complexity, and creation of microsite conditions favorable to shade-intolerant species, with several notable tradeoffs. These conditions in turn have cascading effects on regeneration dynamics, treatment longevity, fire behavior, and resilience to disturbances. In our study, treatments with high aggregation of residual trees best balanced multiple objectives typically used in ponderosa pine and dry mixed conifer forests. Simulation studies that consider a wide range of possible spatial patterns can complement field studies and provide predictions of the impacts of mechanical treatments on a large range of potential ecological effects. View Full-Text
Keywords: overstory spatial heterogeneity; light availability; overstory; restoration; Pinus ponderosa; Pseudotsuga menziesii overstory spatial heterogeneity; light availability; overstory; restoration; Pinus ponderosa; Pseudotsuga menziesii
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    Doi: 10.5281/zenodo.1490099
    Link: https://github.com/jbcannon/ICO_thinning_simulation
    Description: Animation of algorithm to simulate heterogeneous restoration treatments on stem maps to target basal area and target tree group size distributions
MDPI and ACS Style

Cannon, J.B.; Tinkham, W.T.; DeAngelis, R.K.; Hill, E.M.; Battaglia, M.A. Variability in Mixed Conifer Spatial Structure Changes Understory Light Environments. Forests 2019, 10, 1015.

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