Diss. (sammanfattning) Umeå : Sveriges lantbruksuniv. / Härtill 4 uppsatser.

<p>In the Central Hardwood Region, the quantity and quality of hardwood timber critically depend on forest management decisions made by private landowners, since they hold the largest share of woodlands, some of which are plantations. These plantations are in a unique and critical position to provide much-needed hardwood resources. However, there is a lack of research and tools enabling rigorous assessments of profitability of long-term investments in hardwood plantations. Partially due to this, the majority of these privately held plantations remain unmanaged.</p> <p>This study aims at providing scientific evidence and tools to help promote forest management on hardwood plantations held by private landowners. To this end, I demonstrate in Chapter 1 an economic-modeling approach that minimizes establishment costs while ensuring free-to-grow status by year 5, and crown closure by year 10. Using temperate hardwoods such as black walnut and red oak as focal species, I find a black walnut plantation can attain crown closure in year six at the lowest cost ($4,540/ha) with 6 feet x 7 feet spacing, herbicide application for the first year, and fencing. For red oak, the minimum-cost option ($5,371/ ha) which achieves crown closure in year 10 requires a planting density of 6 feet x 7 feet, herbicide application for the first three years, and fencing. Modelling uncertainty in growth and mortality in a stochastic counterpart shifts optimal solutions to denser plantings for black walnut; planting more trees is, thus, risk mitigative. Based upon these research outcomes, I identify the tradeoffs between efficacy of treatments towards establishment success viz a viz their relative costs which serve as a solid foundation for the assessment of subsequent management strategies.</p> <p>Next, in chapter 2, I first calibrate growth, yield, and crown-width models for black walnut trees with existing and new tree measurements on selected Hardwood Tree Improvement and Regeneration Center (HTIRC) plots. Using spatial information on trees, I develop an individual tree level thinning model and simulate their post-thinning growth and yield. Significant predictors of annual diameter growth between years 10 to 18 include the initial tree DBH, forest edge effects, distance-dependent neighborhood competition, and tree age. Significant edge effects exist up to 3 rows and 3 trees from the non-forested edge. A tree on the perimeter rows grows 0.30 cm (0.12in.) in DBH more per year than the interior trees, between years 10 to 18. Next, I dovetail my results from the spatially explicit thinning model with the USFS Forest Vegetation Simulator (FVS) to understand the impacts of different scenarios of planting densities, site productivities, thinning treatments, and expected yields (as percentage of the total volume) of veneer sawlogs to quantify the growth and profitability from the mid-rotation until the final harvest. To support the attendant financial analyses, I incorporate risk into these projections by simulating stochastic windthrows based on certain assumptions. My projections suggest that, without the threat of windthrow damage, the net present day value (NPV) could exceed $4,900 per acre on the highest quality sites (SI =100) and high densities at planting (6 feet x 6 feet), assuming 10% or more of final volume was veneer and using a 3% discount rate. In contrast, under simulations of probable windthrow disturbances from mid-rotation to final harvest, the chances that standing timber value at harvest exceeds $5,000 per acre are 43.13% for a 96- and 90-year rotation and increase to 45.48% for 75 and further to 56.04% for 60.</p>

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.