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Abstract Maximum stand density index (SDI_MAX) represents the carrying capacity of a forest stand based on the relationship between the number of trees and their size. Plot‐level inventory data provided through a collaborative network of federal, state, and private forest management groups were utilized to develop SDI_MAXmodels for important Pacific Northwest conifers of western Washington and Oregon, USA. The influence of site‐specific climatic and environmental variables was explored within an ensemble learning model. Future climate projections based on global circulation models under different representative CO₂concentration pathways (RCP 4.5 and RCP 8.5) and timeframes (2050s and 2080s) were utilized in a space‐for‐time substitution to understand potential shifts in modeled SDI_MAX. A majority of the region showed decreases in carrying capacity under future climate conditions. Modeled mean SDI_MAXdecreased 5.4% and 11.4% for Douglas‐fir (Pseudotsuga menziesii(Mirb.) Franco) dominated forests and decreased 6.6% and 8.9% for western hemlock (Tsuga heterophylla(Raf.) Sarg.) and Pacific silver fir (Abies amabilis), dominated forests under the RCP 4.5 in the 2050s and RCP 8.5 in the 2080s, respectively. Projected future conditions often fall outside the range of any contemporary climate profile, resulting in what may be referred to as extramural conditions. Within the study region, 45% and 46% of climate variables included in the final model were extramural for the Douglas‐fir and hemlock models, respectively, under RCP 8.5 in the 2080s. Although extrapolating beyond the range of input data is not appropriate and many unknowns remain regarding future climate projections, these results allow for general interpretations of the direction and magnitude of potential shifts in forest carrying capacity. 

Maximum stand density index (SDI MAX ) models were developed for important Pacific Northwest conifers of western Oregon and Washington, USA, based on site and species influences and interactions. Inventory and monitoring data from numerous federal, state, and private forest management groups were obtained throughout the region to ensure a wide coverage of site characteristics. These observations include information on tree size, number, and species composition. The effects and influence on the self-thinning frontier of plot-specific factors such as climate, topography, soils, and geology, as well as species composition, were evaluated based on geographic location using a multistep approach to analysis involving linear quantile mixed models, random forest, and stochastic frontier functions. The self-thinning slope of forest stands dominated by Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) was found to be –1.517 and that of stands dominated by western hemlock (Tsuga heterophylla (Raf.) Sarg.) was found to be –1.461, leading to regionwide modelled SDI MAX values at the 95th percentile of 1728 and 1952 trees per hectare, respectively. The regional model of site-specific SDI MAX will support forest managers in decision-making regarding density management and species selection to more efficiently utilize site resources toward healthy, productive forests. 

Abstract Soil physical and chemical properties play important roles in mass loss during soil–block tests but the relationship between soil properties and the decay caused by brown-rot and white-rot fungi remains unclear. The objective of this study was to investigate the soil effects on the decay resistance of pine (Pinus spp.) and poplar (Liriodendron tulipifera L.) blocks. The properties of soil from nine different sources (six from Idaho, one from Mississippi, one from Wisconsin, and one from Oregon) were characterized for soil texture, sieved bulk density, water-holding capacity, pH, organic matter, and carbon and nitrogen concentrations. The moisture content and mass loss of decayed wood samples after 8 weeks of fungal exposure were measured. At the end of the study, block moisture ranged from 30 to 200 percent and mass loss ranged from 20 to 60 percent. Despite using a range of soils, there were no direct correlations between soil properties and wood-block moisture content or mass loss. Moreover, among all the soil properties examined, no significant effect of a single soil property on wood-block moisture content and mass loss was measured. Instead, the combined effects of soil physical and chemical properties may interact to govern the decay of wood blocks in the laboratory soil–block test.