The DEMO experiment is complete randomized block design consisting of six treatments (each, 13 ha in area), replicated at six locations (blocks) in western Washington and Oregon. Treatments represent strong contrasts in retention level (15 to 100% of original basal area) and pattern (trees dispersed vs. aggregated in 1-ha patches) in mature coniferous forests dominated by Douglas-fir (Pseudotsuga menziesii).
The six experimental blocks were selected to represent a diversity of physical environments and forest types at low to moderate elevations (210–1700 m). In Washington, three are in the western Cascade Range (Gifford Pinchot National Forest) and one is in the Black Hills (Capitol State Forest, Washington DNR). In Oregon, two are in the western Cascade Range (Umpqua National Forest). Blocks represent different forest zones (characterized by different late-seral/climax tree species), but Douglas-fir (P. menziesii) is the dominant tree species throughout (see Maguire et al. 2007). All are upland sites supporting relatively homogeneous, mature forests (~65 to 170 years of age). Among blocks, the topography varies from gentle to steep (4–66%). Past management activities varied among blocks: three had no previous activity, one was salvage-logged, one was thinned, and one regenerated naturally after clearcut logging ~65 years earlier.
The experimental treatments are defined as follows: (1) 100%, unharvested control - a reference for assessing responses to harvest and natural temporal variation. (2) 75%A, 75% aggregated retention - all merchantable trees (>18 cm dbh) were harvested from three 1-ha circular gaps (56.4 m radius; 25% of the treatment unit). (3) 40%D, 40% dispersed retention - dominant and co-dominant trees were retained in an even distribution throughout the treatment unit. Within in each block, the basal area retained was equal to that retained in the corresponding 40%A treatment. (4) 40%A, 40% aggregated retention - five circular 1-ha aggregates were retained (40% of the treatment unit). All merchantable trees in the surrounding matrix (cleared areas) were harvested. (5) 15%D, 15% dispersed retention - dominant and co-dominant trees were retained in an even distribution throughout the treatment unit. Within in each block, the basal area retained was equal to that retained in the corresponding 15%A treatment. (6) 15%A, 15% aggregated retention - two circular 1-ha aggregates were retained (15% of the treatment unit). All merchantable trees in the surrounding matrix were harvested.
A permanent grid (8 × 8 or 7 × 9; 40-m spacing) was established within each experimental unit to facilitate systematic sampling of most response variables. Details on the history of vegetation sampling are available in “Related Materials: DEMO sampling history.”
Scans of all field sheets (pre- and post-treatment) are available as PDFs, on request. See “Related Materials: Original field sheet list” for a complete listing of field sheets by data type, experimental unit, and sampling date.
Repeat photographs of permanent plots (representative examples of treatments within each block), listed under Entity 20, are available as JPG files, on request.
Aubry, K. B., and C. B. Halpern. 2020. The Demonstration of Ecosystem Management Options (DEMO) Study, a long-term experiment in variable-retention harvests: rationale, experimental and sampling designs, treatment Implementation, response variables, and data accessibility. USDA Forest Service General Technical Report PNW-GTR-978. https://www.fs.usda.gov/treesearch/pubs/59269.
Halpern, C. B., J. Halaj, S. A. Evans, and M. Dovciak. 2012. Level and pattern of overstory retention interact to shape long-term responses of understories to timber harvest. Ecological Applications 22:2049-2064.
Aubry, K. B., C. B. Halpern, and C. E. Peterson. 2009. Variable-retention harvests in the Pacific Northwest: A review of short-term findings from the DEMO study. Forest Ecology and Management 258:398-408.
Halpern, C. B., D. McKenzie, S. A. Evans, and D. A. Maguire. 2005. Initial responses of forest understories to varying levels and patterns of green-tree retention. Ecological Applications 15:175-195.
Halpern, C. B., and D. McKenzie. 2001. Disturbance and post-harvest ground conditions in a structural retention experiment. Forest Ecology and Management 154:215-225.
Aubry, K. B., M. P. Amaranthus, C. B. Halpern, J. D. White, B. L. Woodard, C. E. Peterson, C. A. Lagoudakis, and A. J. Horton. 1999. Experimental design of the DEMO project: A study of varying levels and patterns of green-tree retention in harvest units in Oregon and Washington. Northwest Science 73 (Special Issue):12-26.
Detailed descriptions of sampling methods/protocols can be found in the post-treatment field manuals available under “Related Materials” and in the publications listed below (https://andlter.forestry.oregonstate.edu/data/abstract.aspx?dbcode=TP108).
Halpern, C. B., A. K. Rossman, and J. C. Hagar. 2022. Level and pattern of overstory retention shape the abundance and long-term dynamics of natural and created snags. Forest Ecology and Management 526:120575. https://doi.org/10.1016/j.foreco.2022.120575.
Halpern, C. B., and L. S. Urgenson. 2021. Level and spatial pattern of overstory retention impose tradeoffs for regenerating and retained trees. Ecological Applications 31:e302296.
Halpern, C. B., M. Dovciak, L. S. Urgenson, and S. A. Evans. 2014. Substrates mediate responses of forest bryophytes to a gradient in overstory retention. Canadian Journal of Forest Research 44:855-866.
Urgenson, L. S., C. B. Halpern, and P. D. Anderson. 2013. Twelve-year responses of planted and naturally regenerating conifers to variable-retention harvest in the Pacific Northwest, USA. Canadian Journal of Forest Research 43:46-55.
Urgenson, L. S., C. B. Halpern, and P. D. Anderson. 2013. Level and pattern of overstory retention influence rates and forms of tree mortality in mature, coniferous forests of the Pacific Northwest, U.S.A. Forest Ecology and Management 308:116–127.
Evans, S. A., C. B. Halpern, and D. McKenzie. 2012. The contributions of forest structure and substrate to bryophyte diversity and abundance in mature coniferous forests of the Pacific Northwest. The Bryologist 115:278-294.
Maguire, D. A., C. B. Halpern, and D. L. Phillips. 2007. Changes in forest structure following variable-retention harvests: target and non-target effects. Forest Ecology and Management 242:708-726.
Dovciak, M., C. B. Halpern, J. F. Saracco, S. A. Evans, and D. A. Liguori. 2006. Persistence of ground-layer bryophytes in a structural retention experiment: initial effects of level and pattern of retention. Canadian Journal of Forest Research 36:3039-3052.
Maguire, D. A., D. B. Mainwaring, and C. B. Halpern. 2006. Stand dynamics after variable-retention harvesting in mature Douglas-fir forests of western North America. Allgemeine Forst und Jagdzeitung 177:120-131.
Halpern, C. B., S. A. Evans, C. R. Nelson, D. McKenzie, D. A. Liguori, D. E. Hibbs, and M. G. Halaj. 1999. Response of forest vegetation to varying levels and patterns of green-tree retention: An overview of a long-term experiment. Northwest Science 73 (Special Issue):27-44.
