I was reviewing the trees slated to be cut as part of a thinning project to improve forest habitat. Even if all the trees marked with blue paint were removed, there would still be too many Douglas fir trees shading out the native oaks and madrones. So we marked more trees with blue paint, leaving the biggest firs and all the Oregon white oaks and Pacific madrones.
When the thinning was finished, we had hundreds of tall firs, but they weren’t crowding out the sun-loving oaks and madrones.
Why did I think fewer trees would be better for the forest’s long-term health?
The forest I was walking through was young but my thoughts were focused on the forest 200 years in the future, when some of these trees would finally be old – most Pacific Northwest conifers can live for more than 500 years. As a restoration practitioner, I plan for the ecosystems of today and for the long-term health of our forests, wetlands and other habitats. That means planning restoration efforts that factor in our warming climate and the unprecedented challenges of climate change.
The common if imperfect analogy is to think of our forests as gardens. Garden plants grow in response to soil nutrients, water and sunlight. So do forests. The hotter, drier summers we are experiencing create extended periods of drought for our forests.
We cannot water them as we could our garden. But we can influence other growing conditions to make forests more resilient to environmental stresses while continuing to provide the benefits of a forest ecosystem.
Current science about keeping forests healthy as the climate changes suggests some simple actions. First, forest thinning creates more space for plants to grow and reduces competition for water. Trees experiencing water stress have fewer resources to resist insects and diseases. Indeed, this summer we saw the effects of drought in the wide-spread browning of needles and die-back of tree branches.
Maintaining and increasing plant diversity is another recommendation. Research suggests that some of our familiar plants might stop reproducing in the Willamette Valley. Other plants might expand their range. We have some information about the winners and losers in the plant world, but more research is needed. Maximizing plant diversity is a cautious approach. If one species fades out of the forest as the climate changes, others might survive.
Another recommendation is to control aggressive invasive species which allows native plants to survive, supporting the wildlife that depends on them.
At Metro natural areas such as Chehalem Ridge, along Johnson Creek and in the McCarthy Creek watershed, these are the practices Metro is implementing to create resilient forests.
For example, at McCarthy Creek Natural Area, we’ll thin some of the young Douglas fir forests at the former tree farm, keeping some firs but making room for willows, maples, and other hardwood trees to thrive. In the process, we’ll leave logs and branches on the ground to start replenishing the dead wood depleted by previous land management. The trees will grow larger and faster – providing better protection for water quality and improved wildlife habitat.
Climate change will affect all of our habitats. Metro’s restoration work, informed by science and designed to adapt to changing conditions, will help keep our forests and habitats healthy for our wildlife and for us.