A simplified process-based model simulating growth and water use in forest plantations was utilised to predict the growth of Pinus elliottii in South African forest plantations. The model is called 3-PG (Physiological Principles in Predicting Growth) and predicted the growth of trees by simulating physiological processes that determine growth and water use, and the way trees are affected by the physical conditions to which they are subjected, and with which they react. Pinus elliottii growth data recorded in 301 sample stands around South Africa were sourced from forestry companies. A selection procedure reduced the number of stands to 44, where 32 were used to parameterise 3-PG and 12 were reserved for testing the final model parameters. This was accomplished by matching model output to observed data. All stand simulations were initialised at age four years and continued to the maximum age of recorded growth. A provisional set of parameter values provided a good fit to most stands and minor adjustments of the specific leaf area (σ), which was assigned a value of 5 m2.kg-1, were made, bringing about an improved fit. The predictions of mean DBH, Height, and TPH were relatively good, achieving R2 of 0.8036, 0.8975, and 0.661 respectively, while predictions of stem volumes were worse (R2 =0.5922, n=32). The 3-PG model over-predicted DBH in 20 stands, while modelled volume predictions improved substantially in thinned stands (R2 =0.8582, n=14) compared to unthinned stands (R2 =0.3456, n=18). The height predictions were generally good producing an R2 =0.8975. The final set of 3-PG parameter values was then validated against growth data from the 12 independent stands. The predictions of mean DBH, Height, and TPH were relatively good, achieving R2 of 0.8467, 0.7649, and 0.9916 respectively, while predictions of stem volumes were worse (R2 =0.5766, n=12). The results of this study demonstrated the potential for 3-PG to respond to many growth factors and to predict growth and water use by trees with encouraging realism. Patterns of changing leaf area index (L) over time, responses to drought, and annual evaporation patterns all look realistic. Consequently, 3-PG is judged to have potential as a strategic forestry tool. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2011.

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I evaluated effects of 5 intensive pine plantation establishment regimes during years 1 – 5 post-establishment on vegetation communities, loblolly pine (Pinus taeda) growth, nutritional carrying capacity for white-tailed deer (Odocoileus virginianus), habitat values for northern bobwhite (Colinus virginianus), and projected financial viability in the Lower Coastal Plain of Mississippi. Treatments were combinations of mechanical site preparation (MSP), chemical site preparation (CSP), and herbaceous weed control (HWC) designed to reflect the range of operational intensities on industrial forest lands in the southeastern U.S. Results should inform plantation management decisions throughout the region. Pine growth increased with greater treatment intensity. At age 5, trees in the most intensively managed treatment were 1.5 m taller than those in the least intensive treatment. Mechanical site preparation improved growth by alleviating soil physical problems. Growth and yield projections indicated that increased fiber yield may not justify investment in more intensive regimes; financial analysis favored the least expensive treatment, though all regimes produced potential internal rates of return > 9% when managed to financial maturity. Use of MSP with banded HWC yielded abundant low-quality deer forage sufficient for body maintenance; nutritional needs for lactating does were better served by CSP with banded HWC. Broadcast HWC reduced biomass of high-quality forbs. In this region of limited soil nutrients and abundant low-quality forages, the optimal combination of maintenance-level and lactation-level nutrition was provided by CSP or CSP and MSP combined with banded HWC. I evaluated vegetation communities for nesting, loafing, brood-rearing, and fall and winter food suitability for northern bobwhite. No treatment provided brood-rearing habitat due to combined lack of bare ground and forb coverage. Fall and winter feeding, nesting, and loafing cover were best produced by MSP and CSP combined with banded HWC. However, lack of brood-rearing cover may reduce or eliminate usable space in all treatments. Differences between vegetation communities were caused by use of CSP, which eliminated many residual woody and vine species, and by differences in broadcast versus banded HWC. Herbicide use decreased plant diversity and species richness, and impacted successional trajectory. Community differences persisted through year 5.