Documents associated with the old-growth refugia study:

Study Background

Coniferous forests within the Willapa Hills of Washington state are extremely productive, harboring rich biological communities and some of the most massive forest structures on earth. Over the last century, these forests have also been extensively managed for timber production; today, less than 1% of the original old-growth forests remain as scattered remnant patches across the landscape.  As exemplified by The Nature Conservancy's Ellsworth Creek project, recent conservation efforts in these lowland coniferous forests are focused on landscape scale forest restoration. A pivotal question for restoration, however, concerns the role old-growth forest remnants play in supporting biological diversity across the existing young-managed forest landscape. Do remnant old-growth forest patches serve as "lifeboats" for biological diversity? If so, how does the placement of these stands across the landscape affect recolonization and recovery of managed forests? In 2007, The Nature Conservancy (the Conservancy) initiated a study to characterize elements of biological diversity within remnant old-growth forest patches and second-growth young, managed forest stands on lands managed by the Conservancy, Weyerhaeuser, Willapa National Wildlife Refuge (WNWR), and Washington Department of Natural Resources (DNR) throughout the Willapa Hills.

The Willapa Hills are low-elevation ridges and valleys generally composed of uplifted marine sediments which contain some of the most productive managed forestlands in the world. Managed forests are composed of native tree species, primarily Douglas-fir and western hemlock. Forests are generally managed using a regeneration harvest system where forest stands are clearcut at ages ranging from 35-60 years of age. Washington's forest practice rules require no-cut forest buffers remain along all fish bearing streams, portions of non-fish bearing streams, and steep unstable slopes (e.g., inner gorge areas). Forest roads are often in high density, approaching 4 km/km² (6.5 miles/mile²), and are managed according to accepted road maintenance and abandonment plans which reduce sediment delivery to stream systems and minimize blockage of fish passage. While young-managed forests are known to provide habitat for many native species (see Ruggiero et al. 1991) there is still little understanding of the distribution and dynamics of many old-growth obligates, particularly within the Sitka spruce forest zone.     

In places such as Ellsworth Creek, where the Conservancy is working with the adjacent Willapa NWR to restore over 6,070 ha (15,000 acres) of young-managed forest, managers need better information about the range of conditions found in natural, unmanaged, old-growth remnant forest stands. Few old-growth remnant stands remain, and we know that there is a huge range of compositional and structural diversity amongst these stands - however, this diversity has never been documented in the Willapa Hills. A science panel working with the Conservancy on an experimental design for the Ellsworth Creek project (Rolph and Davis 2008) identified the following as a primary question for the study: "How do you define restoration goals without a solid understanding of historical conditions and processes or knowledge of future conditions and processes?" Clearly, before we can better define restoration goals managers need a much better understanding of the range of conditions found in unmanaged forest remnants in the Willapa Hills.

Study Objectives

The project aims to investigate three primary questions:

1. What is the diversity of vegetation characteristics (composition and structure) within natural, or unmanaged, remnant forest patches located within the Willapa Hills of Washington?
2. What is the diversity and abundance of forest plant communities, macrolichens, canopy arthropods, and forest floor arthropods within natural, or unmanaged, remnant old-growth forest patches located within the Willapa Hills of Washington?
3. How does the vegetation characteristics and the diversity and abundance of forest plant communities, macrolichens, canopy arthropods, and forest floor arthropods differ between 35 year or older second-growth, young, managed forest stands and remnant old-growth forest patches in the Willapa Hills of Washington?

In 2007, the Conservancy sampled arthropod composition and diversity of forest ground and canopy habitat within 4 old-growth forest patches and 4 young, second-growth forests (approximate age 35-65). Forest vegetation composition and structure and, and epiphytic macrolichen communities were sampled within 11 old-growth forest and 11 young second-growth patches in 2008.  

Data analysis and findings are outlined in the final report (see link at top of page).