SETRES SETRES is major collaborative research effort to expand our fundamental understanding of relationships among forest productivity, genetics, and resource availability using loblolly pine as a model species. Collaborators include numerous scientists and graduate students from N.C. State University, the U.S. Forest Service’s Biological Foundations of Southern Forest Productivity and Sustainability Work Unit at Research Triangle Park, Duke University, and Virginia Tech. The first SETRES study was established in 1992 and includes a 2 x 2 factorial combination of nutrient (no addition and optimum nutrition) and water (no addition and well watered) treatments imposed on large plots within what was then a 7-year loblolly pine stand. The second study, established in 1995, includes five families from each of two extreme loblolly pine provenances (Atlantic Coastal Plain and Lost Pines of Texas provenances) grown under low (no nutrients added) and optimum (nutrients added every year) nutrition regimes. Numerous assessments have been made and are continuing on these two studies including photosynthesis, tissue growth and maintenance respiration, biomass production, leaf area, carbon allocation, soil respiration, net ecosystem productivity, tissue nutrient concentrations, soil carbon pools and fluxes, soil nutrient pools and fluxes, litterfall, forest floor development and decomposition, soil N mineralization, soil microbial communities, phenology of above and below-ground growth, wood quality, stem quality, crown development, intra-specific competition and stand development, tree water relations, hydrologic budgets, microclimatic conditions, and spectral reflectance to determine leaf area and foliar nutrition. The assessments are being integrated through the use of several physiologically based production models and have allowed us to scale from the tissue to the landscape level. To-date, over twenty graduate students have worked on thesis projects at the site and almost 70 papers and theses have been published. During the next few years, analysis and modeling efforts will focus on better understanding the long term of effects of elevated levels of resource availability on ecosystem productivity, nutrient cycling, intra-specific competition, and carrying capacity relationships. Key results to date include: Nutrient additions have increase biomass production by 2.5x this “dry” sand hill site. Irrigation has had little impact on production. Gains in production with increased nutrient availability have resulted from increases in leaf area and growth efficiency. Stemwood growth efficiency gains resulted from a strong shift in biomass allocation from fine roots to stemwood. On control plots fine roots accounted for 20% of production and only 8% on fertilized plots although the absolute production of fine roots remained nearly the same for the two treatments. Nutrient additions not only increased carbon gain but also dramatically reduced the period of time needed for site to regain positive net ecosystem productivity. Positive carbon gain responses of individual tress to elevated levels of C02 were limited by low nutrient availability. Increasing nutrient availability reduced within stand heterogeneity in tree size leading to slower stand differentiation into crown classes. This increased uniformity can be expected to impact future stand development, structure, and yield in ways for which current growth and yield models do not account. Ecosystem retention of added nitrogen was very high. Stand leaf area was easily and accurately estimated using Landsat imagery. Provenance and family effects have been highly significant but small compared to the nutrient effects. Few traits have shown any genetic x environmental interaction even though the range in genetic material and nutrient treatments represented extreme differences. In addition to serving as a base for considerable research, these studies also serve as very important education and demonstration sites. Over the past 15 years, the studies have been visited by several thousand forest managers, scientists, undergraduates, and graduate students from around the world.