Suzanne Boyden

Background/Question/Methods Forest management techniques that emulate natural disturbance regimes have become increasingly popular as a tool for increasing forest complexity and diversity, yet still remain largely untested. We lack information about how the spatial pattern of canopy trees will alter resource heterogeneity in the understory and therefore competitive interactions and productivity of regeneration. Species with different light and nutrient demands should respond very differently to the variation in competitive environments created with different patterns of tree retention after thinning. In this large scale and long-term experiment conducted in red pine forests in Minnesota, USA, we used a likelihood approach to model the growth of jack, red and white pine seedlings as a function of resource availability (light and nutrients) and competition from residual trees and understory shrubs in stands with different spatial patterns of canopy trees. We implemented a randomized-b...

ABSTRACT Variable retention harvesting is used to sustain structural and compositional complexity, along with various ecosystem functions, in harvested forests. A key component of variable retention harvest systems is determining the spatial pattern of residual overstory retention, which can range from dispersed to aggregate. Hypothesized responses to retention pattern depend on the attribute examined. For instance, growth of intolerant tree regeneration is likely to be higher, at the stand-scale, with aggregate retention, whereas growth of tolerant species should be higher with dispersed retention. Other ecosystem attributes such as songbird populations, plant resource availability, and mortality of residual trees should also vary depending on spatial pattern of retention. We report on early results of a large-scale retention experiment in Great Lakes red pine forests in northern Minnesota. The experiment includes four replicates of three overstory manipulations—dispersed retention, aggregate retention with small gaps, and aggregate retention with large gaps—and unharvested controls. Three years after harvest, avian abundance, richness, and diversity were all greater within treatment compared to controls, but no discernable differences among retention pattern were found. Tree seedling diameter growth after five years began to show differences among spatial patterns, with greater growth of intolerant pines with aggregate retention, but greater growth of tolerant pines with dispersed retention. Differences in resource availability among retention treatments are less discernable. Mortality of residuals trees does not appear to vary substantially with spatial pattern of retention and rates of mortality do not appear to be higher than those in the uncut controls, at least over the short-term.