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The conversion of UK even-aged conifer plantations to continuous cover forestry (CCF), a form of forest management that maintains forest cover over time and avoids clear-cutting, requires more frequent and spatially explicit monitoring of forest structure than traditional systems. Key aims of CCF management are to increase the spatial heterogeneity of forest stands and to make increased use of natural regeneration, but judging success in meeting these objectives and allowing an adaptive approach to management requires information on spatial structure at a within-stand scale. Airborne remote sensing provides an alternative approach to field survey and has potential to meet these monitoring needs over large areas. An integral part of CCF is the creation of canopy gaps, allowing regeneration by increasing understorey light levels. This study examined the use of airborne lidar and passive optical data for the identification and characterisation of canopy gaps within UK Sitka spruce (Picea sitchensis) plantations. The potential for using the distribution of canopy and gaps within a stand to quantify spatial heterogeneity and allow the detection of changes in spatial structure, between stands and over time, was assessed. Detailed field surveys of six study plots, located in three UK spruce plantations, allowed assessment of the accuracy of gap delineation from remotely sensed data. Airborne data (multispectral, hyperspectral and lidar) were acquired for all sites. A novel approach to the delineation of gaps from lidar data was developed, delineating gaps directly from the lidar point cloud, avoiding the interpolation errors (and associated under-estimation of gap area) resulting from conversion to a canopy height model. This method resulted in improved accuracy of delineation compared to past techniques (overall accuracy of 78% compared to field gap delineations), especially when applied to lidar data collected at relatively low point densities. However, lidar data can be costly to acquire and provides little information about the presence of natural regeneration or other understorey vegetation within gaps. For these reasons, the potential of passive optical (and in particular, hyperspectral) data for gap delineation was also considered. The use of spectral indices, based on shortwave infrared reflectance or hyperspectral characteristics of the red- edge and chlorophyll absorption well, were shown to enhance the discrimination of canopy and gap and reduce the influence of illumination conditions. An average overall accuracy of 71% was obtained using hyperspectral characteristics for gap delineation, suggesting the use of optical data compares reasonably to results from lidar. Methods based on shortwave infrared (SWIR) reflectance were shown to be sensitive to within gap vegetation type, with SWIR reflectance being lower in the presence of natural regeneration. Potential for using optical data to classify within gap vegetation type was also demonstrated. Methods of quantifying spatial structure through the use of indices describing variations in gap size, shape and distribution were found to allow the detection of structural differences between stands and changes over time. Gap distribution based indices were also found to be strongly related to alternative methods based on relative tree positions, suggesting significant potential for consistent monitoring of structural changes during conversion of plantations to CCF. Remotely sensed delineations of canopy gap distribution may also allow spatially explicit modelling of understorey light conditions and potential for regeneration, providing further information to aid the effective management of CCF forests.

This thesis investigates the influence of niche specialisation on floristic composition and species distributions of the family Dipterocarpaceae along topographic gradients at two contrasting lowland Mixed Dipterocarp Forest sites in Brunei Darussalam: Andulau (overlying nutrient-poor sandy soils) and Belalong (overlying nutrient-rich clay soils). Dipterocarp tree density, species richness and diversity were higher at Andulau than Belalong, and were also higher on ridges than in slopes and valleys. Randomisation tests detected significant dipterocarp species associations with site and tomography. Dipterocarp floristic composition was strongly correlated with various habitat variables at Belalong, even after accounting for distance between samples. In contrast, fewer habitat variables were correlated with dipterocarp floristic composition at Andulau, implying weaker habitat effects in this more topographically homogeneous site. In a field-based transplant experiment, <i>Dryobalanops aromatica </i>and <i>Dryobalanops rappa </i>seedlings consistently showed higher growth rates and survival in gaps than in understorey plots. Higher survival and leaf production of <i>D. aromatica </i>seedlings at Andulau than Belalong provide evidence of a habitat preference. Growth and survival of <i>D. rappa</i> seedlings were similar at the two sites, but <i>D. rappa</i> seedlings grew significantly faster in height than <i>D. aromatica </i>seedlings on slopes at both sites. In conclusion, local and landscape scale variations in edaphic and environmental resources influence dipterocarp species distributions and floristic composition, as well as dipterocarp seedling growth and survival. Thus, niche specialisation is an important mechanism in the maintenance of species coexistence at Andulau and Belalong.

The distribution of bacteria in Sitka spruce stumps between one and ten years old was investigated by dilution plating wood chips taken from seven sampling positions up to 55 mm from the stump surface. The same wood chips were used to determine the presence Basidiomycotina within the stump wood. The number of bacterial colony forming units in the wood samples decreased in stumps between one and five years old, reaching a minimum after six years, before increasing in stumps up to ten years old. There was also a decline in numbers of bacteria isolated with increasing distance from the stump surface and the stump edge. A similar trend was detected in the diversity of the bacterial community. The size of the bacterial population was also correlated with stump moisture content. The presence of Basidiomycotina was associated with the presence of bacteria within the sample. However, the number of bacteria isolated from samples containing Basidiomycotina did not differ from that where no Basidiomycotina were isolated. Interactions between wood-decay fungi, including Heterobasidion annosum, and bacterial isolates were studied in vitro. The growth medium, timing of inoculations, and bacterial and fungal species tested were fund to significantly affect the outcome of the interaction. Bacterial isolates degraded cellulose, pectin and starch, cellulolytic ability increased with increasing stump age. Siderophores and chitinase, potential antifungal compounds, were produced by 29% and 2% of isolates respectively, however, these isolates had no effect on the distribution of Basidiomycotina in the stumps. Four groups of bacteria were identified from cluster analysis of 13 phenotypic characteristics. Different groups of bacteria were found to dominate bacteria isolated from stumps of different ages indicating that bacterial successions occur in decaying Sitka spruce stumps.

There has been little work done to investigate the importance of denitrification in forest soils. This has been caused by difficulties associated with measurement of the denitrification process and from the assumption that nitrification, and hence also denitrification, was insignificant in acid environments. Nitrification can, however, occur even in the acid conditions found in coniferous forest soils, and is especially important after clear-felling when levels of nitrate in soil and drainage waters are often observed to increase. A potential exists, therefore, for gaseous losses of N <i>via</i> denitrification from such soils. This thesis describes the establishment of a suitable method for measurement of denitrification using the acetylene block technique. This method was used to monitor denitrification losses of N, both as N<SUB>2</SUB> and N<SUB>2</SUB>O, from a peaty-gley soil at Kershope Forest. The total loss of N from the standing forest through denitrification was estimated to be 3.2 kg ha<SUP>-1</SUP> over the year studied. Of this loss, approximately 80% was produced as H<SUB>2</SUB>O. Gaseous loss of N through denitrification represents approximately the same order of magnitude as the N lost from the site <i>via</i> leaching. An adjacent site, clear-felled four years previously, was also monitored for denitrification losses. Although this site was denitrifying at only a slightly greater rate than the standing forest, examination of past records from the site revealed that an estimated 9-40 kg N ha<SUP>-1</SUP>y<SUP>-1</SUP> had been lost in the two years immediately after felling. To assess the factors which controlled denitrification in the field, sub-samples of the soils used for denitrification measurements were analysed for water content, extractable nitrate, and available carbon. None of these factors, however, were found to correlate clearly with the denitrification rate. Further experiments, using laboratory amendments of soil cores, indicated that nitrate concentrations had the greatest effect on denitrification rates, although both the availability of carbon and the aeration status of the soil also affected the rates measured.

A study of the fungal ecology of <I>Picea sitchensis </I>stumps on mineral soils on first rotation sites in Scotland was carried out to determine fungal colonization, succession and the mechanisms of fungal interaction. Fungal and bacterial colonization of stump and buttress roots of stumps 0, 7, 28 days, 12, 16 and 48/53 months old was assessed. <I>Melanotus proteus </I>was found in all 12 month old stumps; <I>Sistotrema brinkmanni</I> was recorded most frequently in 16 and 48/53 month old stumps. A series of <I>in vitro </I>experiments was carried out to identify interactions occurring between pairs of <I>P. sitchensis </I>fungi on Norkrans agar, <I>P. sitchensis </I>sawdust, root blocks and billets, to determine possible modes of interaction occurring <I>in vivo. </I>Fungi exhibiting antagonism toward <I>Heterobasidion annosum in vitro </I>were noted to determine possible <I>in vivo </I>applications as curative/preventative biological controls against <I>H. annosum. </I>Sitka spruce stumps were highly receptive to <I>H. annosum </I>basidiospore infection up to 24 hours after felling and showed a significant level of receptivity 7 days after felling. <I>M. proteus </I>infection was lower in live stumps, compared to dead or moribund stumps, and was reduced or inhibited in stumps inoculated with <I>Resinicium bicolor </I>sawdust inoculum. <I>In vitro </I>experiments indicated that 5% urea prevented <I>M. proteus </I>basidiospore germination and hyphal growth. Treating stumps or billets with a 20% urea solution, however, had no significant effect on <I>M. proteus </I>colonization. Antifungal metabolites were detectable in 85% of the 25 fungal species tested representing members of the Basidiomycotina, Deuteromycotina and Ascomycotina, when bioassayed with <I>Cladosporium cucumerinum. </I>The production of antifungal metabolites in Sitka spruce stumps by <I>H. annosum, R. bicolor, Stereum sanguinolentum, M. proteus </I>and <I>Hypholoma fasciculare </I>was demonstrated.

Due to forest degradation and loss, the use of ecological restoration techniques has become of particular interest in recent years. One such method is the Framework Species Approach (FSA), which was developed in Queensland, Australia. The Framework Species Approach involves a single planting (approximately 30 species) of both early and late successional species. Species planted must survive in the harsh conditions of an open site as well as fulfilling the functions of; (a) fast growth of a broad dense canopy to shade out weeds and reduce the chance of forest fire, (b) early production of flowers or fleshy fruits to attract seed dispersers and kick start animal-mediated seed distribution to the degraded site. The Framework Species Approach has recently been used as part of a restoration project in Doi Suthep-Pui National Park in northern Thailand by the Forest Restoration Research Unit (FORRU) of Chiang Mai University. FORRU have undertaken a number of trials on species performance in the nursery and the field to select appropriate species. However, this has been time-consuming and labourintensive. It has been suggested that the need for such trials may be reduced by the pre-selection of species using their functional traits as predictors of future performance. Here, seed, leaf and wood functional traits were analysed against predictions from ecological models such as the CSR Triangle and the pioneer concept to assess the extent to which such models described the ecological strategies exhibited by woody species in the seasonally-dry tropical forests of northern Thailand. It was found that seed storage behaviour (orthodox and recalcitrant) was strongly linked to other functional traits and that this was the basis of observed differences in performance based on seed size. There was evidence for the existence of a leaf economic spectrum in these forests and for differing positions of deciduous and evergreen species on this spectrum. It was further found that wood hydraulic capacity and safety was more strongly linked to leaf traits than wood mechanical strength; reflecting the importance of the seasonal drought in this type of forest. Selected functional traits were then used to predict the performance of species within the FORRU project. It was found that a combination of wood and leaf traits that encompassed mechanical strength, hydraulic capacity and water storage best described species growth rates in most years and that survival may be linked to a combination of both drought and pathogen load that differs by year due to environmental conditions. In conclusion, functional traits were found to be valuable indicators of performance in forest restoration projects.