I am exploring how changes in the structure of riparian forests influence stream food webs, stream temperature, and ultimately the density, growth, and condition of stream fish in headwater ecosystems in western Oregon. This work has direct application to questions about whether, and in what way, timber management in the riparian zone that thins the forest or creates selective gaps would influence stream conditions and stream biota. Riparian zones are important features in the landscape and carry a number of restrictions in regard to timber management and land development. In most case the current harvest restrictions refer to regenerating forests as riparian zones were largely cut-over through the early and middle parts of the 20th century. Restrictions on harvest in the riparian zones have therefore led to the development of dense, largely uniform, closed-canopy forests adjacent to many streams in Oregon. But, the uniformly closed riparian canopies that dominate headwaters across Oregon are quite different from the historically dominant old-growth forests in this region, which are far from uniform in their canopy structure.

In a recent survey of light and forest canopy cover over streams in the HJ Andrews Experimental Forest (HJA), for example, we found that light availability was significantly higher in the streams with old-growth riparian forests than in the streams with younger closed canopy forests. Although young, closed-canopy forests keep streams cool in summer, they may also restrict stream production, which sets up and interesting contrast when considering forest management in the riparian zone. We know that lack of sunlight restricts primary production and associated algae biomass that contributes important resources to the base of stream food webs. But sunlight is also the primary factor in stream heat budgets, so increases in light also have the potential to increase the temperature of a stream.

I am exploring both current forest management and old growth forests to better understand how management in younger forests could be modified to mimic in at least some functional aspects the conditions of old-growth forests . Indeed, if thinning or selection harvest is implemented in such a way as to promote a complex canopy structure – and in particular the creation of canopy gaps – thinning may actually be able to recreate aspects of the historic light conditions of headwater streams. I have two overall goals for this work. First, I want to understand how changing forest structure and its associated influences on stream light affect stream ecosystems and ultimately stream light. I also hope to improve our understanding of how active management in the riparian zone that includes thinning in riparian forests may influence fish (positively or negatively) which will help forest managers guide responsible stewardship of fish habitat in headwater ecosystems.