Thesis (MScFor)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Individual tree models, as opposed to stand models, have the potential to greatly improve sensitivity of forest growth models to changing conditions such as silvicultural amendments, irregular stand structures, etc. It was the purpose of this study to extend two sub-components of a European individual tree growth model to introduce individual tree growth modelling concepts in South Africa using Pinus elliottii as a study species. Two main objectives were established: Modelling the potential height of stands across different site qualities and modelling diameter increment using a potential modifier approach with a combination of competition indices that change in importance according to the edaphic conditions of the site. Potential height modelling used three steps in order to achieve this objective. The first was to compare site index models based on different model fitting techniques, namely nonlinear least squares, generalised nonlinear least squares and nonlinear mixed effects models. The nonlinear mixed effects model proved to be superior in terms of achieving the principles of regression assumptions and model fit for the data range observed. The second step was to fit potential height using nonlinear quantile regression on observed spacing trial height measurements. This proved to be a robust technique able to capture potentials according to the defined Chapman-Richards model structure. The final step was to use the predicted site index as a site classification variable in order to predict potential height. While some small deviation occurred, potential height seems to be well correlated to site index and validation on selected sites suggested that site index can be used to model potential height until a more sophisticated site classification model is used for future improvement of the model. Diameter increment modelling followed six major steps in order to apply the full parameterisation methodology of an age-independent diameter increment model dependent on tree diameter and competition. Diameter increment potentials were fit using site index as a predictor of the potential height curves. Multiple competition indices were tested on two sites to obtain a combination of two indices, which can capture overtopping and local crowding effects. Principle components analysis and variance inflation factors calculation were applied to test for collinearity between indices. Suitable combinations were tested resulting in a combination of the KKL and Local Basal Area competition indices. Changing importance of the two indices were observed on the two sites tested indicating a shift in the mode of competition according to a water gradient. These were combined in a deterministic potential modifier model, which mimicked competitive stages over age; however the validation showed a skewed distribution, which was not sensitive to stand density gradients. A stochastic model was constructed to model variance from observed residual plots using linear quantile regression to determine bounds for a truncated normal distribution which generates random deviates for a predicted increment. The stochastic element significantly improved the performance and sensitivity of the model, however the model was still not sensitive enough at very high and very low spacing densities. All in all two key models for an adaptation of an individual tree growth simulator to South African conditions were successfully demonstrated. The two main objectives were achieved; however some indicated improvements could be made, especially for the competition indices where the sensitivity of competition to changing resource limitation according to site and temporal scales needs to be further investigated. Furthermore, the full set of models for simulating individual tree growth still needs to be applied. Overall, as a methodological approach, the study outlined problems and future improvements, introduced new concepts and can serve as a guideline for future parameterisation of an individual tree growth model. / AFRIKAANSE OPSOMMING: In vergelyking met vakgroeimodelle, het individuele-boomgroeimodelle die potensiaal om die sensitiwiteit van plantasiegroeimodelle vir veranderende omstandighede soos aanpassings in boskultuur, onreëlmatige vakstrukture, ensovoorts, drasties te verbeter. Die doel van hierdie studie was om twee subkomponente van ‘n Europese individuele-boomgroeimodel uit te brei om sodoende individuele-boomgroei modelleringskonsepte in Suid-Afrika bekend te stel. Pinus elliottii is gebruik as studiespesie. Twee hoofdoelstellings is bepaal. Eerstens, die modellering van hoogtegroei potensiaal van opstande oor verskeie vlakke van groeiplek kwaliteit. Tweedens, die modellering van deursnee-aanwas deur gebruik te maak van ‘n potensiaal matigingsbenadering “potential modifier approach“ met ‘n kombinasie van kompetisie-indekse waarvan die belangrikheid verander volgens die edafiese toestande van die groeiplek. Die hoogtepotensiaalmodellering bestaan uit drie stappe. Tydens die eerste stap word groeiplek bonniteitsmodelle vergelyk op grond van verskillende modelpassingstegnieke, naamlik nie-lineêre minimum kwadrate, algemene nie-lineêre minimum kwadrate en nie-lineêre gemengde effek modelle. Laasgenoemde het die beste gevaar in terme van die beginsels van regressiemodelle asook die mate waarin die model die waargeneemde data pas. Tweedens is hoogtegroei potensiaal gemodelleer deur nie-lineêre kwantielregressie op waargeneemde hoogtes van spasiëringseksperimente toe te pas. Die metode is robuust en in staat om potensiale volgens die gedefinieerde Chapman Richards modelstruktuur vas te vang. Laastens is die voorspelde bonniteits indeks as ‘n groeiplek klassifasie veranderlike gebruik om sodoende die hoogtegroei potensiaal te voorspel. Alhoewel klein afwykings voorgekom het, blyk hoogtegroei potensiaal goed gekorreleer te wees met bonniteits indeks. Uit validasie op geselekteerde groieplekke blyk dit dat bonniteits indeks gebruik kan word om hoogtegroei potensiaal te modelleer totdat ‘n meer gesofistikeerde groeiplek klassifikasiemodel beskikbaar is wat die model verder sal kan vebeter. Die volledige parametriseringsmetodiek van ‘n ouderdoms-onafhanklike deursnee-aanwas model wat afhanklik is van boomdeursnee en kompetisie bestaan uit ses hoof prosesse. Nie-lineêre kwantielregressie is gebruik om deursnee-aanwaspotensiale te pas vir verskeie groeiplekke. Dié is gekombineer met ‘n bonniteits indeks om ‘n nuwe model te vorm waarmee hoogtegroeipotensiaal kurwes voorpel kon word. Daar is met veelvuldige kompetisie-indekse op twee groeiplekke geëksperimenteer om ‘n kombinasie van slegs twee indekse te vind wat die effekte van oorskaduwing en plaaslike verdringing kan vasvang, te vind. Hoof komponent analise “Principle components analysis” en variansie inflasie faktore berekening “variance inflation factors calculation” is gebruik om vir kollineariteit tussen die indekse te toets. Gepaste indekskombinasies is getoets. ‘n Kombinasie van die KKL en plaaslike basale oppervlakte “Local Basal Area” kompetisie-indekse het die beste resultate gelewer. Die twee indekse is as volg geselekteer. Veranderings in die belangrikheid van elk van die indekse is waargeneem op die twee toetspersele. Dit dui op ‘n verskuiwing in die modus van kompetisie afhangend van ‘n watergradiënt. Die twee indekse is gekombineer in ‘n deterministiese potensiaal matigings model wat die kompeterende stadiums oor ouderdom naboots. Validasie het egter ‘n skewe verdeling wat nie sensitief vir opstandsdigtheidsgradiënte is nie, gewys. ‘n Stogastiese model is ontwikkel om variansie in die residuele grafieke te modelleer. Lineêre kwantielregressie is gebruik om grense vir ‘n afgestompte normaalverdeling wat ewekansige afwykings vir ‘n voorspelde aanwas te bepaal. Die stogastiese element het die prestasie van die deterministiese model merkbaar verbeter. Selfs met die stogastiese element, is die model egter steeds nie sensitief genoeg vir baie hoë en baie lae opstandsdigthede nie. Ter opsomming is twee modelle vir ‘n aanpassing van ‘n individuele-boomgroeisimuleerder vir Suid- Afrikaanse toestande suksesvol gedemonstreer. Die twee hoofdoelstellings is bereik. Daar is egter steeds ‘n paar aangeduide verbeterings wat aangebring kan word. Die sensitiwiteit van die kompetisie-indekse op hulpbronbeperkings wat verander op grond van die ruimtelike en temporale skale moet veral verder bestudeer word. Verder moet die volle stel modelle wat benodig word om individuele-boomgroei te modelleer nog toegepas word. As ‘n metodologiese benadering, het die studie probleme uitgewys en toekomstige verbeterings aangedui, nuwe konsepte bekendgestel en kan dus dien as ‘n riglyn vir toekomstige parametrisering van individuele-boomgroeimodelle.

The largest area of commercial timber plantations in southern Africa is situated along the Eastern Transvaal Drakensberg Escarpment north of Nelspruit. The site requirements of tree species in this area are poorly understood. The purpose of this study was to examine site-tree relationships in the region and the implications of such relationships for the science of forestry. Pinus patula Schiede & Deppe in Schlecht. & Cham. was selected for the study as it is the most widely planted species in the region. In Chapter 1 the geology, geomorphology, climate, soils and vegetation of the study area are described. A geological map was compiled. Soil descriptions were based on 439 soil pits distributed so as to cover the range of site conditions in the area. The regression techniques used to identify key environmental factors and to model their relationships with tree parameters are described in Chapter 2, in which site-growth relationships specifically are investigated. In mature stands of P. patula 159 plots were established in such a way as to cover the widest variation in both site conditions and tree growth. The relationship between site index (mean top height at 20 years) and 100 site plus 10 stand parameters recorded at each plot was modelled by means of best-subsets, multiple and ridge regression. Several candidate models were compared on the basis of coefficient of determination and validation using independent data. The best model predicted the site index of the validation plots within 60 cm of the measured site index. The possible roles of the site variables identified by the models are discussed. In Chapter 3 site-foliar nutrient relationships are described. A close relationship was found between foliar and soil nutrient levels for the six major geological substrates. Site index was more accurately predicted from concentrations of individual foliar nutrients than from ratios of these nutrients. The Diagnosis and Recommendation Integrated System (DRIS), however, appeared to have greater potential for nutrient diagnosis. Provisional ORIS norms for P. patula were computed. In Chapter 4 the excessive accumulation of litter in P. patula stands was examined. Undecomposed litter layers were greater than 15 cm in thickness on nearly 25% of the 159 sites studied. Average litter layers contained greater amounts of nutrients than the underlying topsoil. Due to the colonization of the litter by tree roots, the degree of immobilization of nutrients in litter is not known. Environmental factors associated with variation in litter thickness were identified by models which explained up to 73% of the total variation. These factors are considered to act indirectly by promoting or retarding decay organisms. The possible implications of litter accumulation for the maintenance of site productivity are discussed. In Chapter 5 relationships between site and some wood properties are described. Although between-tree variation was larger than between-site variation, some important relationships with site were identified. 10% of all trees on the 159 plots had severe stem bumps. Most of the variables in a model to predict the severity of bumps could be interpreted as being associated with stem stability or exposure. The conclusion was that wind is probably the major cause of this defect. The findings of the study are summarized in Chapter 6. Particular attention is given to a synthesis of the possible roles of site factors in their relationships with the tree parameters investigated. There were strong relationships between tree parameters and mainly rainfall, altitude, soil wetness, exchangeable bases, effective rooting depth, slope position and geology. The single most deficient nutrient element appeared to be calcium. The implications for both research and management are outlined. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1990.

In recent years research has shown that exposing seed to smoke or smoke solutions results in increased germination of some, but not all the species tested. Tests showed that exposing seeds of some commercial crops to smoke increased early plant growth. The stimulatory effects of smoke were shown to benefit the germination of species regardless of whether or not fire played a part of the species ecological cycle. In commercial forest nurseries any method of increasing the recovery rate of seed presents opportunities for realising savings of related production costs. Greater recovery rates of genetically improved seed present opportunities for capturing more related growth in field operations. Improving efficiencies of seed recovery at an early point in the production chain have multiplied effects further on down the chain. Two species of pine, namely Pinus taeda and Pinus elliottii that do not generally present high rates of germination were selected to test if applications of smoke solution could increase germination or emergence rates by more than 5%. As seed of both species are known to respond positively to existing seed pre-treatments the effects of smoke needed to be tested in combination, and apart from the pre-treatments. A secondary aim of the study was to examine the effect of smoke on early plant growth. Attempts to optimizes the concentration of the smoke solution were not undertaken as part of this study, as a rinsing treatment, included in the trials, is known to remove any inhibitory effects of a high concentration of the smoke solution. Tests to determine the variability of the seedlots was carried out for statistical purposes. The interaction between smoke application and pre-treatments were tested, firstly in Petri dishes under controlled environmental conditions, and then in nursery trays under standard commercial nursery conditions for both species. The inclusion of smoke in combination with the target moisture stratification (TMS and rinse pre treatment) had a significantly positive effect on P. taeda in a controlled environment. The same combination did not yield a positive results when tested under nursery conditions. Recommendations are made regarding future tests to see if the beneficial combination found in the controlled environment could be replicated under nursery conditions. Further motivation for conducting the tests exists in that the particular combination set gave significantly better early plant growth under nursery conditions. No other combinations tested yielded positive results. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2008.

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.