The effects of site conditions on variation in the floristic composition, physiognomy and hollow decay of the Mixed Dipterocarp Forest of Sarawak are investigated. Studies were concentrated on two series of pre-existing plots. The results from the set of larger plots show that there is considerable association between the distribution of floristically defined forest types and site conditions. The results from the smaller plots show that there issome association of site conditions with the distribution of individual species, and also with intraspecific variation in hollow decay. Site effects on the basal areas of individual species, and the basal area and the severity of hollow decay in the forest as a whole are less marked. Interpretation of the results is complicated by the clustered distributions of both series of plots. The relative importance of site properties as determinants of forest floristic variation depends partly on the range of rock, soil and forest types sampled. Over the full range, properties closely related to soil parent material appear to predominate. The results do not indicate any major immediate modifications to current procedures in forest inventory, soil survey or intersectorial land allocation, but they do emphasise the value of interdisciplinary exchanges of information. If regeneration in the forest is to be assisted by planting, the results should be useful in indicating probably viable species/site combinations.

Mahogany, Swietenia macrophylla (Meliaceae) is the most valuable hardwood species in Neotropics and is seriously threatened owing to over-exploitation and habitat destruction. The population genetic structure and mating system of S. macrophylla were studied in the Brazilian Amazon for conservation purposes. Ten highly polymorphic micro satellite markers were developed from an enriched genomic library of S. macrophylla and combined in three multiplexed fluorescence based genotyping systems. The number of alleles per locus ranged from 11 to 25 (mean = 15.8). The probability of genetic identity (7x10- 15) and the probability of paternity exclusion (0.999998) found over all loci indicate the high discriminating power of these markers. The genetic structure was investigated in seven populations 8- 2,103 km apart. High genetic diversity was detected within populations (mean He = 0.761, range 0.719-0.800) and a significant level of inbreeding was found (f = 0.046, P<0.0001, range 0.014-0.097) indicating nonrandom mating of individuals within populations. Genetic differentiation among populations was significant (A = 0.12 and p = 0.14, P<0.0001), but no clear pattern of isolation by distance was found. Conservation strategies for mahogany should take into account the existence of important genetic structuring of populations. S. macrophylla seems to have adaptations that preferentially produce outcrossed progeny but also allows for selfing. The high multilocus outcrossing rate (tm = 0.958) estimated for one population indicated that, although there was a prevalence of outcrossing, selfing was not negligible. Around 4-6% of seedlings in the population were likely to have resulted from self-fertilization and substantial biparental inbreeding was denoted by the significant difference between the multilocus and singlelocus estimates (tm - ts = 0.14). Owing to the species pre-adaptation to colonize newly open, disturbed habitats, many of the remaining trees in logged areas may persist as viable individuals which could be very important for population recovery and genetic conservation programmes.

No description available.

No description available.

Rates of loss of biodiversity caused by human action are on the increase worldwide. However implications of species loss on the natures' ability to provide ecosystem services and goods are still poorly understood. Despite providing an array of critical services and goods, mangrove ecosystems are under intense threat. In attempts to address the problem, several mangrove restoration initiatives have been formulated in many areas of the world with different objectives. Over the last two decades, experiments manipulating species diversity and measuring ecosystem functions have been conducted mainly using grassland ecosystems and have exhibited positive relationships. More recently, experiments investigating this relationship have emerged in longterm woody species i.e. trees; however these have concentrated on terrestrial forests. This study experimentally manipulated different mangrove species and measured a range of ecosystem functions including sapling survival, above and below ground biomass production and sediment C02 efflux. Enhanced sapling growth was positively correlated with plot height above datum, percentage silt and nitrates and negatively correlated with sediment salinity, ammonium and phosphates. Also high values of above and below ground biomass, root: shoot ratios, mean tree height, leaf area index as well as naturally recruited saplings were observed in mixed plots (particularly with Avicennia marina in the mixture) compared with monospecific plots. Species selection effect, particularly from the fast growing A. marina species was the mechanism behind a range of the observed ecosystem functions. However complementarily effects were observed particularly on above ground biomass. However sapling survival and sediment CO2 efflux was not influenced by species richness. We conclude that there is variation in the stages of plant development at which species richness effects manifest themselves, in addition the effects of environmental variables has a bearing on the nature and direction of the relationship between species richness and ecosystem function. We anticipate changes in the plots structure over time from A vicennia facilitative effects which are expected to lead to changes in sediment microclimate inducing changes in other species growth and promoting recruitment and development of wildlings.

Concerns about changes in the quality of the maturing British spruce resource (principally stiffness) have raised doubts about maintaining strength grading pass-rates. Acoustic (or stress wave) instruments provide a non-destructive measurement of stiffness and are increasingly used to classify/segregate forests, trees and logs. A fundamental assumption in the use of acoustic instruments is that of constant density, yet there is little understanding of density variation within the British spruce resource. Understanding this variation is essential for understanding the accuracy of acoustic instruments, which can affect how and when they should be used. The extent of variation in density was determined experimentally from a range of sites with contrasting silviculture and environments, and trees within-site were chosen to reflect the extremes of growth rate. Variation within tree (important for log resonance measurement) was found to depend both on dominance class (i.e. relative diameter) and height within the tree. The density in the outer part of a tree (important for standing tree time of flight measurement) was found to vary with dominance class, distance in from the bark and season. Mean green density profiles of the outer part of the tree show that density ceases to be constant between dominance classes after 10 mm in from the bark. The effect of this variation could not be quantified because the propagation behaviour of the stress wave within a tree is not fully understood. An examination of wave propagation showed that it did not conform to behaviour as described in the literature and interaction with both density variation within the tree and with the tree's boundaries is likely to affect the accuracy of this technique. The utilisation of these instruments was also examined within a sawmill simulation study, to provide an alternative to simply diverting low stiffness logs to lower value, non-structural products. Exploiting the predictable within-tree stiffness variation and adjusting cutting patterns to avoid the lower stiffness core of lower stiffness logs allowed production of consistently higher stiffness battens. A reduction in twist and knot severity was also observed, but not at significant levels until the juvenile zone (first ten years) was completely excluded. All batten properties improved with increasing cambial age (number of growth rings from the pith). Alternative cutting patterns had no effect on the recoverable batten volume from within a log and showed considerable potential to improve value to sawmills.

The need for improved timber grading is key to improving Scottish forestry: the majority (80%) of the sustainable softwood population in Scotland is Sitka spruce of variable quality. Current visual assessment of strength and stiffness is inaccurate, and machine stress grading in sawmills is little better due to incorrect assumptions regarding consistency within softwood species and between trees of the same stand. The author develops and evaluates non-destructive test (NOT) methods for Scottish Sitka spruce based upon impact-e9ho testing across a range of scales from plank, to log, to standing tree. Correlations between harmonic wave propagation velocity and elastic modulus of 0.62 ::; R2 ::; 0.71 were possible in Sitka spruce under a range of conditions including: genotype progeny, variable height and radial position in stem, and variable knot content. In achieving this correlation, the research also investigated acoustic parameters such as: time of flight velocity, damping ratio, and resonant peak behaviour with regard to their influence on dynamically derived moduli of elasticity. Examination of variation in wood properties (including static elastic modulus, knot content, simulated decay, density, and grain alignment) on these acoustic parameters was conducted on semi-controlled specimens of differing homogeneities. The consequences of these results should influence the development of timber NOT tools. In addition to the development of an NOT method, the author has provided the first large-scale derivation of reference values for dynamic stiffness and other acoustic properties for 35 year old logs and beams of Sitka spruce in Scotland.

Timber is a local, sustainable and valuable building material, but it is highly variable compared to other building materials (e.g. concrete, steel). The quality of wood is its suitability for the end-user, in this case the construction industry (via timber processors). Douglas-fir is a tall conifer capable of producing high construction grade timber. Native to the north-western Pacific regions of America and Canada, Douglas-fir was introduced to the UK in 1827. After World War 1, the planting of conifers greatly increased due to the establishment of the Forestry Commission. Despite being a high value timber crop in North America, Douglas-fir was not highly utilised in Great Britain due to a perceived lack of suitable growing sites (requiring nutrient-rich soil) and a lack of knowledge on its qualities (mechanical). Consequently, it still to this day covers a relatively small amount of the total UK conifer plantation area, but under predicted climate change projections an increased range of sites will become more suitable for Douglasfir, thus investigation now is imperative. To investigate the quality of Douglas-fir timber and its biological variation, a variety of sites were sampled in Scotland and Wales. The variation in the physical and mechanical properties of UK-grown Douglas-fir were investigated to determine how strength and stiffness of Douglas-fir compares to other commercially important timber species in the UK (as well as compared to Douglas-fir grown in different countries). Standing and felled tree measurements relating to tree architecture and important for timber volume (e.g. size, height, branching habits and taper) were collected in the forest. This was followed by laboratory testing of wood samples obtained from those trees to determine important raw material properties. Ultimately this will enable some explanation and prediction of the variation in mechanical and physical properties in Douglas-fir. It was found that Douglas-fir is stronger, stiffer and denser than the UK's most planted conifer, Sitka spruce. Wood adjacent to the pith (middle of tree) termed as juvenile was weaker, less stiff and less dense. Within-tree variation accounted for most of the variation for the key properties of strength, stiffness and density. It was possible to build models for some of these properties based on cambial age (ring number from the pith). Considering branches, it was found that within-tree variation in size, frequency, angle and status (alive or dead) were highly variable but it was possible to build empirical models to describe branch architecture for a typical tree. It was possible to measure the rate of swelling in oven dry Douglas-fir in the radial and tangential dimensions, but swelling of the longitudinal dimension was below the limit of detection for the apparatus. Heartwood area can be successfully predicted from the diameter of tree at a given point. It is hoped the information in this study will detail some characteristic Douglas-fir traits that may be deemed beneficial for the timber construction industry and allow understanding of its variability plus provide important models to use in helping to describe Great Britain's forest resource.

Fast growing hybrids of Salix and Populus can be grown in a short rotation coppice (SRC) system to produce renewable energy. This PhD investigates the interactions between the environment and productivity, with a view to finding the key limiting factors to yield and the potential of these crops to fulfil UK renewable energy obligations, now and in the future. An empirical modelling technique, using partial least squares regression was developed to extrapolate actual field observations to a national scale. Genotype x age x environment interactions were studied to examine the key limiting factors to productivity. Modelled yields differed between genotypes, with mean annual aboveground biomass ranging from 4.9 to 10.7 oven dry tonnes (odt) per hectare for Populus trichocarpa x P. deltoides genotype ‘Beaupré’ and Salix triandra x S. viminalis genotype ‘Q83’, respectively. Variation in yield was primarily described by spring and summer precipitation, suggesting water availability is the key limiting factor to yield. Output from the model was up-scaled across the UK using a geographic information system (GIS), and scenarios were developed to better understand the role and impact of land use management and policy development on potential crop distribution. For example, to meet UK biomass and biofuel targets without compromising food security or ecosystem services, would require 5 % of grade 3 land, 56 % grade 4 land and 47 % of grade 5 land. This quantity of biomass would produce 7.5 M tonnes of biomass per annum and would theoretically generate 15.5 TWh yr-1 of electrical energy, displacing 3.3 M tonnes of oil – approximately 4% of current UK electricity demand. The South West and North West alone producing over a third of this figure (5.2 TWh yr-1). These results suggest that SRC has the potential to become a significant component of a mixed portfolio of renewables. Furthermore, climate change is predicted to have far reaching consequences on crop growth. Process-based models can help quantify these interactions and predict future productivity. Here we use ForestGrowth-SRC, a process-based model originally designed for high-forest species and parameterised for a coppice system. Climate change scenarios (UK Climate Projections) were run with the model to assess the impact of a changing climate on the growth and spatial distribution of SRC poplar. Results suggest ForestGrowth-SRC is capable of accurately simulating growth over a large spatial and temporal scale. However, pests and disease were found to significantly affect yield. In the absence of pests and disease, productivity could increase by 20 % nationwide by 2080 (under a medium emissions scenario), suggesting we will see a future increase in the value and production of these crops as feedstocks for heat, power and liquid transportation fuels

No description available.