Potential Site Productivity Influences the Rate of Forest Structural Development

Development and maintenance of structurally complex forests in landscapes formerly managed for timber production is an increasingly common management objective. It has been postulated that the rate of forest structural development increases with site productivity. We tested this hypothesis for Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) forests using a network of permanent study plots established following complete timber harvest of the original old-growth forests. Forest structural development was assessed by comparing empirical measures of live tree structure to published values for Douglas-fir forests spanning a range of ages and structural conditions. The rate of forest structural development—resilience—exhibited a positive relationship with site index, a measure of potential site productivity. Density of shade-intolerant conifers declined in all study stands from an initial range of 336–4068 trees/ha to a range of 168–642 trees/ha at the most recent measurement. Angiosperm tree species declined from an initial range of 40–371 trees/ha to zero in seven of the nine plots in which they were present. Trends in shade-tolerant tree density were complex: density ranged from 0 to 575 trees/ha at the first measurement and was still highly variable (25–389 trees/ha) at the most recent measurement. Multivariate analysis identified the abundance of hardwood tree species as the strongest compositional trend apparent over the study period. However, structural variables showed a strong positive association with increasing shade-tolerant basal area and little or no association with abundance of hardwood species. Thus, while tree species succession and forest structural development occur contemporaneously, they are not equivalent processes, and their respective rates are not necessarily linearly related. The results of this study support the idea that silvicultural treatments to accelerate forest structural development should be concentrated on lower productivity sites when the management objective is reserve-wide coverage of structurally complex forests. Alternatively, high-productivity sites should be prioritized for restoration treatments when the management objective is to develop structurally complex forests on a portion of the landscape

Grass Mountain research natural area: Guidebook supplement 32

This guidebook describes the Grass Mountain Research Natural Area, a 377-ha (931-ac) tract in the Oregon Coast Range. The area supports a grass bald complex surrounded by stands dominated by noble fir (Abies procera) and/or Douglas-fir (Pseudotsuga menziesii) in the overstory, and western hemlock (Tsuga heterophylla) in the understory. The area also contains a small rock garden plant community along high-elevation ridges, and young Douglas-fir forest that originated from a wildfire. Headwaters of high-elevation, Oregon Coast Range streams are surrounded by noble fir forest and add to the..

Postglacial Transient Dynamics of Olympic Peninsula Forests: Comparing Predictions and Observations

Interpreting particular climatic drivers of local and regional vegetation change from paleoecological records is complex. I explicitly simulated vegetation change from the late-Glacial period to the present on the Olympic Peninsula, WA and made formal comparisons to pollen records. A temporally continuous paleoclimate scenario drove the process-based vegetation model, LPJ-GUESS. Nine tree species and a grass type were parameterized, with special attention to species requirements for establishment as limited by snowpack. Simulations produced realistic present-day species composition in five forest zones and captured late-Glacial to late Holocene transitions in forest communities. Early Holocene fire-adapted communities were not simulated well by LPJ-GUESS. Scenarios with varying amounts of snow relative to rain showed the influence of snowpack on key bioclimatic variables and on species composition at a subalpine location. This study affirms the importance of exploring climate change with methods that consider species interactions, transient dynamics, and functional components of the climate

Modeling the effect of neighborhood competition on tree diameter growth in the Pacific Northwest Coast Range

Trees compete for various resources such as sunlight, water, and nutrients, which can be expressed as numerical terms, called competition indices (CI). Competition between individual trees is correlated with their growth and mortality. Therefore, CIs are used as independent variables to develop, improve and modify growth and yield models. This study was conducted to test the effect of neighborhood competition on tree diameter growth among Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), western hemlock (Tsuga heterophylla (Raf.) Sarg) and red alder (Alnus rubra Bong.), in the Pacific Northwest Coast Range, USA. After testing seven distance-independent CIs and three distance-dependent CIs, only the distance-independent CIs were found to significantly affect the diameter growth model. Among them, CIs with basal area and diameter information were the most impactful. As a result, a simple CI was very effective in a model that accounts for the basal area information of different tree species