This thesis presents data collected from a Sitka spruce plantation in Scotland, UK during May and July 2001. Data are presented that quantify the daily pattern of environmental variables and their effect on rates of key physiological processes monitored from branches, soils and entire canopies using each method. A method was also developed to measure the carbon isotope composition of CO₂ in air exchanged directly with branches. Daily patterns in instantaneous ¹³C discrimination (<i>D</i>_obs) and the <i>d</i>¹³C of respired CO₂ were combined with continuous environmental and gas exchange data to explore theoretical models describing photosynthetic discrimination, <i>D</i>. This study demonstrated fractionation factors associated with respiratory processes and mesophyll conductance (<i>g</i>_w) were important for explaining daily patterns in <i>D</i>_obs. Models were also developed and paramterised to predict daily cycles of instantaneous ¹³C discrimination and <i>d</i>¹³C of recently assimilated needle carbohydrates at the branch and canopy scale. This dynamically simulated the links between environmental conditions, canopy discrimination and the <i>d</i>¹³C branch respired CO₂, providing both a method and model to directly test hypotheses concerning the environmental regulation of autotrophic respiration measured aboveground and from soil surfaces, potentially leading to a clearer understanding of temporal variability in observed ecosystem <i>D</i> and <i>d</i>¹³C of ecosystem respired CO₂. Furthermore, these bottom-up estimates of canopy ¹³C discrimination provided a means of comparison with top-down estimates calculated from a recently developed approach incorporating the eddy covariance method and profiles of <i>d</i>¹³C and CO₂ mole fraction. At the forest scale daily patterns and estimates of <i>F</i>_A and <i>F</i>_{R<i> </i>}were determined using the three approaches described above. Daily patterns of <i>F</i>_A were comparable in magnitude and timing between methods and tightly coupled to environmental variables. Daily maximum uptake for <i>F</i>_A ranged from -20 to -30 μmol m² s^-1 and were similar to other published studies for Sitka spruce plantations.

Interception loss, throughfall and stemflow were measured in the unlogged and logged forest areas of Central Kalimantan, Indonesia for a period of 18 months. This involved 55 rainfall events in the unlogged forest and 99 rainfall events in the logged-over forest areas, each corresponding to a single storm or to several storms. The Gash's analytical model and the Ratter physically-based model were used to estimate the sensitivity of interception loss to canopy structure and climatic parameters. The cumulative rainfall interception loss were found to be 11% and 6% of gross precipitation in the unlogged and logged forest areas, respectively. The model performance, at this stage, could not be further elaborated, since they are still tested and adapted to our field data.

The aim of the study was to establish whether clones could be selected for single or multipurpose products by conducting studies involving the evaluation of phenotypic characteristics and their influence on biomass production using <I>Sesbania sesban</I> (L.) provenances and clones. The study initially examined the extent of genetic variation in phenotypic characteristics and biomass production in <I>S. sesban</I> provenances at Maseno, in Kenya. The study showed that significant differences existed between provenances and that it was possible to select of outstanding individual trees in the best provenances for testing on different sites as clones. Significant allometric relationships were established between dry mass, and tree dimensions for the different tree components. Stem diameter at 0.15 m provided a reliable estimation of biomass in the provenances. The provenance repeatabilities (0.31-0.41) and potential genetic gain (40%) highlight the expected returns due to selection. Plant growth analysis results helped in understanding the growth of young <I>S. sesban</I> clones in the field at Maseno, particularly the distribution of biomass into components. Clones performed similarly in the initial stages of growth and differences were only detected when competition set in. Clone net assimilation ratios were found to be sensitive to moisture stress. Leaf area was found to be the major determinant of clonal differences and was a good indicator of plant growth and productivity. The results from the genetic variation and productivity study of <I>S. sesban</I> clones grown at Maseno, Kisii and Machakos revealed a differential response of the clones to different environmental conditions. Although there was lack of genotype by environmental interaction among clones, biomass production was higher at Maseno and Kisii than Machakos. <I>S. sesban</I> clones differed greatly in absolute biomass but showed similar percentage distribution of dry mass among the different tree components with branches being a major preferred sink.

A description of a case study forest is combined with computer-based simulation to develop a model of the dynamics of disturbed pine-oak forest in Southern Mexico. Contemporary ecological theory surrounding the problem of predicting forest dynamics is briefly reviewed. A conceptual framework for the study is presented based on a consideration of scale and a view of the forest as a whole system. Data provided by a forest inventory are used in a spatially explicit multivariate analysis that reveals both simple spatial patterns of species distribution and high local variability in forest structure and composition. Initial results of monitoring temporal change in permanent sample plots are analysed and an estimate of forest productivity produced. Slash and burn farming is proposed as the principal cause of the disturbance which has shaped the documented pattern. Mortality of trees caused by a recent forest fire is summarised using logistic regression models. The rates of recolonisation and the persistence of trees by resprouting following disturbance are documented. Multivariate analysis is used to reveal trends in species composition in abandoned slash and burn sites. Non parametric techniques for estimating species richness and species-area relationships are subjected to critical evaluation when applied to the problem of comparing the diversity of woody species in slash and burn sites and closed forest. The human decision making process associated with slash and burn clearance is described and modelled using Bayesian networks which synthesise indigenous knowledge of the system. A critical review of individual based forest models (IBMs) introduces a computer simulation approach to studying the dynamics of the disturbed forest. An IBM is programmed and parameterised using data obtained from the site. Measurements of tree growth rings and canopy light permeability are incorporated in the model. The model is validated against the inventory data.

The morphological and physiological responses of tree seedlings to water stress and the significance of the non-hydraulic influence of root on shoot behaviour of the effects of soil drying were investigated. The experiments were conducted in a glasshouse and growth chamber, using sycamore (<i>Acer pseudoplatanus</i> L.) seedlings rooted in a soil mixture with high water holding capacity. The prime objective of the project was to evaluate the morphological and physiological components of drought tolerance that could be useful for isolation of plants with seedling characteristics acceptable for afforestation in drought-prone environments. Effects of drought on water relations and root growth were studied using long soil columns. Drought resulted in active osmotic adjustment in leaves, with decreases in osmotic potential at full and zero turgor, and it increased bulk elastic modulus and leaf dry weight to turgid weight ratio. Stomatal conductance declined well before any observable change in bulk leaf water potential and was correlated with soil water status. Drought caused changes in the root distribution profile and it increased the root weight. The increase in root weight was mainly due to a substantial shift in assimilates allocated in favour of roots with total biomass being unaffected. Cyclic water stress treatment, induced major changes in sycamore seedlings, including osmotic adjustment, acclimation of photosynthesis and stomatal conductance to water stress, increased water use efficiency, and a substantial shift in biomass allocation pattern in favour of roots, with a consequent increase in root/shoot ratio. The acclimation of photosynthetic machinery was the major factor contributing to the acclimation of photosynthesis to water stress. These modifications were concluded to be important for improvement of seedling drought tolerance. Seedlings grown in soil columns and subjected to drought exhibited substantial reduction in stomatal conductance and a limitation in leaf expansion well in advance of any detectable change in shoot water relations. Root abscisic acid (ABA) concentration increased deeper in the soil profile in concert with the progressive soil drying, and it appeared to be a sensitive indicator of the soil water status around the roots.

This study was carried out at the Institute of Terrestrial Ecology (ITE), Bush Estate, Scotland, and at the Centre for Tropical Agricultural Research and Education (CATIE), Turrialba, Costa Rica, from December 1989 to September 1993. The work concentrated on two hardwood species native to Central America, <I>Albizia guachapele</I> (Kunth) Dug, and <I>Cordia alliodora</I> (Ruiz & Pavon) Oken. The main objectives of the study were to determine the effects of physiological factors on the rooting ability of both species and identify the optimal conditions for root initiation in leafy, stem cuttings using non-mist propagators. The study focused on some of the factors, both pre- and post-severance, generally accepted as having a crucial influence in determining the rooting ability of leafy cuttings. These included the stockplant growth environment, cutting origin, cutting foliar area, auxins, rooting media and propagation environment. Discussions are presented on the effects of these factors on cutting morphology and physiology, and their influence on the process of adventitious root formation. The practical implications for the propagation of both species and for further research are also discussed.

Nitrogen availability is limiting to the growth of certain tree species planted on oligotrophic peats in Britain and Ireland. Sitka spruce (<i>Picea sitchensis</i> (Bong.) Carr) requires repeated applications with fertilizer-N for the establishment of plantations on these sites. When spruce is planted in mixed stands with the pines or larches it can be grown successfully without fertilizer-N and with associated improvements in N status. Mixed stands accumulate greater biomass and nitrogen capitals than pure spruce plantations. Research indicates that greater N uptake in mixtures is derived from enhanced mineralization of the native peat organic matter. This thesis investigates whether certain tree species can access mineral-N from an oligotrophic peat substrate more readily than others and whether these trees have any influence on N release rates from peat. A large glasshouse experiment was planted with Sitka spruce, lodgepole pine (<i>Pinus contorta</i> Dougl.), Japanese larch (<i>Larix leptolepis</i> (Sieb and Zuc.)) and birch (<i>Betula</i> spp.). Trees were grown for two seasons in plots of <i>Sphagnum</i> peat, pH 3.1, fertilized with P, K at field rates. Treatments included plots with fertilizer-N and spruce in mixtures with the other species. There were no differences between the total N uptake for individual species or combinations of species in mixed plots (-N). In + N treatments the <i>rate</i> of N uptake by birch and larch was greater than for spruce and pine. In mixed plots birch was a more effective competitor for available N than spruce, larch was more effective in + N plots but not -N and pine was at a competitive disadvantage to spruce in all treatments. N use efficiency of biomass was similar for all species within the same N treatment and increased as N became limiting. Trees assimilated a mean of 220 μg N g^-1d.w. peat over two growing seasons. A 16 hr extraction with 2% acetic acid recovered less mineral-N than taken up by trees (130 μg N g<SUP>-1</SUP>d.w.). Approximately 40 percent of N uptake was derived from quantities of N which could only be extracted from peat after incubation for 6 weeks. Substrate N release rates during laboratory incubations did not show species-related differences. Planted peat N release rates were lower than for unplanted peats (40 vs 90 μgN g^-1 month^-1) but N release rates were considered to be a product of sample perturbation rather than an index of real N mineralization rates in-situ. Standing crops of fine roots were assessed in glasshouse plots (-N) during the second season. Root dry weight intensity reached a maximum of 1.3 mg cm^-3, equivalent to standing crops beneath forest stands. Birch had non-mycorrhizal roots, unlike other species, which rapidly exploited the whole plot volume. Root form for other species is described, with no change in morphology detected as a result of admixture. A separate glasshouse experiment confirmed that lodgepole pine roots were more tolerant of anerobic conditions in peat compared to Sitka spruce. However, the ability of pine roots to grow into an anaerobic peat substrate did not confer a significant advantage for N uptake. An experiment in 15 year old stands of lodgepole pine and Sitka spruce planted on a raised bog, investigated the response of fine roots to inorganic-N amendments to root ingrowth cores. Root production was not influenced by added N but production rates were different between stands. Trees fertilized with rock phosphate produced more root (782 kgha^-1yr^-1:pine, 913 kgha^-1yr^-1: spruce) than stands fertilized with superphosphate (524 kgha^-1yr^-1: pine, 374 kgha^-1yr^-1:spruce). Soil physical and chemical properties are described for each stand.

The aim of this thesis was to investigate the effects of elevated [CO<SUB>2</SUB>] and varying nutrient supply rates on the growth, phenology and physiology of Sitka spruce (<I>Picea sitchensis </I>(Bong.) Carr.).Two approaches were taken both using open top chamber facilities to fumigate seedling with either ambient (355 <I>μ</I>mol mol<SUP>-1</SUP> Co<SUB>2</SUB>) or elevated (700 <I>μ</I>mol mol<SUP>-1</SUP> CO<SUB>2</SUB>). Firstly, a long term study on the direct impact of elevated [CO<SUB>2</SUB>] was undertaken, this experiment ran for three consecutive years. Comparisons between responses obtained after one and three years exposure to elevated [CO<SUB>2</SUB>] were made. In addition, the impact of growing seedlings in OTCs <I>per se</I> was also investigated. Secondly, a study was conducted into the interaction between [CO<SUB>2</SUB>] and nutrient supply rate on growth, phenological and physiological responses. The effects of OTCs were also included in this experiment. Biomass accumulation was always enhanced by elevated [CO<SUB>2</SUB>] when nutrients were not limiting. Biomass stimulation as a result of elevated [CO<SUB>2</SUB>] was 16 and 37 % for seedlings with a foliar [N] of 1.9 and 2.4 % respectively. However, there was no enhancement at a foliar [N] of 0.9 %. A similar result was also observed in the long term study. There was no significant chamber effect on biomass but seedlings growing inside OTCs were 25 % taller. Biomass allocation was affected by [CO<SUB>2</SUB>], nutrient supply rate, growth inside OTCs and experimental duration. The amount of biomass allocated to roots was increased by elevated [CO<SUB>2</SUB>] and decreasing nutrient supply rates, with those seedlings receiving elevated [CO<SUB>2</SUB>] and low-N supply rates having the highest R/S ratios. Growth inside OTCs reduced the amount of biomass allocated to roots. Seedlings receiving elevated [CO<SUB>2</SUB>] and low nutrient supply rates had smaller amounts of biomass allocated to stems. Total leaf area and mass were both increased by elevated [CO<SUB>2</SUB>] and increasing nutrient supply rate but there was no significant effect of elevated [CO<SUB>2</SUB>] on specific leaf area, leaf area ratio or leaf mass ratio. Elevated [CO<SUB>2</SUB>] significantly affected bud phenology, delaying budburst and advancing budset, thereby reducing the growing season of seedlings with foliar [N] of 2.0 % or below. Increasing nutrient supply rates lengthened the growing season <I>per se</I>. Phenology of seedlings with a foliar [N] of 2.4% were not affected by elevated [CO<SUB>2</SUB>]. There was a large clonal variation in the phenological response to [CO<SUB>2</SUB>] and the effect of OTC was bigger than that of [CO<SUB>2</SUB>]. The effect of elevated [CO<SUB>2</SUB>] and climatic warming on spring frost damage was modelled and future risks of damage were predicted to decrease.

The nutrient regime of forest soils is one of the major abiotic influences on forest strand development. Its assessment is therefore essential to ecologically-appropriate silviculture. This is reflected in the new system of "Ecological Site Classification" being developed by the Forestry Commission. Soil nutrient regime will be one of the three main descriptors of site quality, alongside climate and soil moisture regime. A programme of simultaneous sampling for soil chemistry, humus type and ground vegetation species composition was carried out at 70 forest sites throughout mainland Great Britain. The intention was to derive a quantified definition of soil nutrient regime and to demonstrate that both ground vegetation species composition and humus type could aid its assessment in the field. Soil samples were subjected to laboratory analysis to measure the following nutrient parameters:- pH, loss-on-ignition, moisture content, total phosphorus and the availability of nitrogen, phosphorus, calcium, magnesium and potassium. Nitrogen was determined in the form of mineral components both before and after an aerobic incubation. Vegetation descriptions were treated by the assignment of indicator values to each species and the calculation of an abundance weighted site mean indicator value. Initially the R and N values proposed by Ellenberg were adopted. The data collected were analysed statistically using multivariate techniques. pH and nitrate-nitrogen availability emerged as the most important components of soil nutrient regime. Most other nutrients were positively correlated with these. A single composite gradient of soil nutrient regime, incorporating all parameters, was defined. It was shown that the weighted mean site Ellenberg R value was correlated with this gradient with r = 0.89. The correlation could be enhanced to r = 0.94 by the use of internally-generated species indicator values. Humus type [mor, moder, mull] was also found to be related to site position on this gradient. Both vegetation species composition and humus type were thus shown to be effective for the field assessment of soil nutrient regime as defined. A division of the gradient into five classes of soil nutrient regime was proposed.

No description available.