PS 24-69
Tree spatial patterns in southwestern Oregon mixed conifer/hardwood forests: Spatial analyses to inform forest restoration at multiple scales
Across the west, changes in disturbance processes have shifted forests to be dominated by crowded, smaller trees of shade tolerant fire sensitive species resulting in more continuous tree cover, and a reduction in the number and size of gaps. Tree spatial patterns are often reported as a global statistic and gaps have typically been reported as a proportion of stand area. Understanding of the importance of gap requires an ecological rationale which ultimately allows quantification of gap size, shape, and function. Local statistics such as Plotkin’s clustering algorithm improve ecological context and help translate research to on-the-ground prescriptions comprehensible by managers and implementers. Our research compares historic and contemporary tree spatial patterns and gap sizes as a function of understory light availability and potential shade intolerant species regeneration. 8 three-hectare plots were measured on sites representative of dry Mediterranean mixed-conifer hardwood forests of southwest Oregon found across 800,000 hectares in the Rogue Basin. All live and dead stems greater than 25.4 cm diameter at breast height were mapped and reconstructed to the date of last wildfire. Spatially explicit light maps were generated with the forest simulation software SORTIE, and parameterized with tree allometry and species specific light transmittance data.
Results/Conclusions
We found that in 2011 there were few opportunities for shade intolerant species regeneration. Understory light availability was greatest in the reference condition with a greater range of gap sizes and a greater proportion of plot area in gap. Historic gaps with light environments favoring shade intolerant species regeneration infilled with shade tolerant species indicating that tradeoffs between tolerance to shade or fire may have exerted strong controls on species composition, and illustrates the interplay of top-down and bottom-up controls moderating forest structure and function. Historically forest structures contained a higher proportion of trees in small to intermediate clump sizes while contemporary forests are characterized by fewer larger clumps. Greater understanding of forest spatial patterning creates opportunities for implementation of treatments designed to provide diverse habitats that will sustain a range of species and thus promote healthy resilient forests.