The influence of conventional (stem only) and whole tree (all above ground biomass) harvesting on soil characteristics and second rotation Sitka spruce (<I>Pica sitchensis</I> (Bong.) Carr.) growth was investigated on a peaty soil in Kielder Forest, Northumberland. One site was intensively studied in the third and fourth years after restocking. The full factorial experiment (established by the Forestry Commission and the Macaulay Land Use Research Institute) included three treatments; retention of harvest residues (±R), herbicide application (± H) and fertiliser additions (± F), giving eight treatments which were replicated in three randomised blocks. Of the treatments, the effects of ±R, ±H and their interaction were observed. Confounding effects of soil compaction resulting from the passage of machinery were reduced by driving harvesters between treatment assessment plots. The total nutrient capital (N, P, K, Mg and Ca) and physical characteristics including bulk density, horizon depth and oven dried weight of the soil (LFH and upper O horizons) were determined annually. <I>In situ</I> mineralisation of inorganic nitrogen, fluctuations in soil moisture content, organic matter, and pH were recorded throughout the third growing season using capped corers. The vegetation (species type, biomass and nutrient content) was surveyed in August of the third growing season. Phenological and morphological characteristics measured in spruce included timing of bud flush, occurrence and length of lammas growth, duration and length of the leader extension and tree height. Foliar nutrient concentrations (N, P, K, Mg and Ca) were analysed throughout both growing seasons. At the end of the fourth growing season root depth and distribution were observed in relation to waterlogging and anaerobic soil depth. Treatments did not consistently alter soil nutrient capital or annually measured soil physical properties. Compared to - R plots, residue retention reduced seasonal fluctuations in mean soil temperatures and moisture content, especially in the litter layer. Differences were greatest in the summer when temperatures were warmer and precipitation low. Net ammonification (88 kg N ha<SUP>-1</SUP>) and total nitrogen mineralisation (90 kg N ha<SUP>-1</SUP>) during the third growing season were not significantly affected by treatment. However, significantly greater nitrate was released in the LFH horizon of + R and + RH plots (P < 0.039).

The response of Sitka spruce seedlings to inoculation with mycorrhizal fungi was studied over a range of root temperatures and available phosphorus. Fungi were isolated from roots of plantation Sitka spruce by surface sterilizing for short periods with dilute mercuric chloride. Four Basidiomycete isolates were selected in preliminary synthesis experiments. Multiple-seedling growth modules were constructed in which sterile conditions could be maintained, a specified nutrient regime could be imposed for up to 5 months and root temperature could be controlled independently of shoot temperature. Seedlings, with one of five fungal treatments, were grown at ten root temperatures from 3 to 35 °C. The isolates were capable of forming mycorrhizae but differed in their tolerance of high temperatures. All formed mycorrhizae at low temperatures. Average root length increased with temperature throughout the range but above 24°C total root length decreased. The number and length of mycorrhizal roots formed by three isolates was determined by the general effect of temperature on root growth but the infection rate of the fourth was positively related to temperature. This isolate stimulated root production at low temperatures. Growth of the four isolates in buffered pure culture media was broadly similar to their performance in association with the higher plant. Inoculation did not influence the distribution of nitrogen, phosphorus or potassium within phosphorus deficient seedlings. The degree of infection by the four isolates increased with available phosphorus from .002 to 10 mg./l. The benefits of the four isolates were influenced by phosphorus supply. It is suggested that host performance is related to root number and length irrespective of mycorrhizal status and where mycorrhizae are formed performance is related to the formation of mycelial strands and to a lesser extent the efficiency of uptake and use of absorbed phosphorus.

No description available.

The growth and acclimation response of wild dipterocarp seedlings to environmental change caused by logging disturbance was examined in lowland dipterocarp forest in Central Kalimantan (Indonesian Borneo). The seedling microclimate was characterised in logged and unlogged forest using automated equipment and hemispherical photography. A system of analysis of hemispherical photographs was developed and calibrated against direct measurements of daily PPFD (photosynthetic photon flux density). Predictions from photographs were linearly related to measured irradiance over the range 1 - 60 % of above canopy totals. Predictions were repeatable and accurate (R<SUP>2</SUP>>0.95). Errors were large relative to absolute totals below 5 % of above canopy totals. Hemispherical photography and direct measurements using a shade band were used to estimate the proportion of above canopy diffuse irradiance (pDif) as 0.53 ± 0.03 (n = 4), with good agreement between the two methods. Apart from the obvious effects of increased irradiance, the microclimate of undisturbed and logged forest was influenced more by season and topography than by canopy opening. Wind speed varied with site elevation and season and had a strong influence on the degree of coupling between above and below canopy conditions. Low wind speed was an important feature which will tend to decouple seedling leaves from ambient conditions. The most important effect of logging on the seedling microclimate will be the effects of increased exposure of seedling leaves to direct sunlight, rather than relatively small changes in air temperature and humidity. It was hypothesised that low boundary layer conductance and high leaf temperatures during periods of the direct sunlight would be an important limitations to dipterocarp seedling regeneration in logging gaps. Logging increased patchiness and removed dipterocarp regeneration from the most disturbed areas. Abundant dipterocarp regeneration occurred in logged forest, but was unevenly distributed and lacking in the gaps where it is most required.

Detailed TCAA data are presented from an 18 month period of intensive field sampling at two elevations (602 m and 325 m a.s.l.) in a remote upland Sitka spruce (<i>Picea</i> <i>sitchensis</i>) forest in southern Scotland. Concentrations of TCAA in different year classes of spruce needles and in air, rain water, cloud water, and forest soil were measured concurrently at sites with a wet deposition gradient to investigate the route of atmospheric input to forest. The observations of greater concentrations of TCAA in the needles at higher elevation (1998 year class mean concentration: 38 and 28 ng g^-1 dry weight to the upper and lower elevations, respectively, a trend towards accumulation of TCAA in older needles, and seasonal variations are all consistent with the hypothesis that the TCAA concentration may be controlled by metabolic processes in the needles. Higher concentrations of TCAA in cloud water (median: 0.94 ppb) than rain water (median: 0.87 ppb) with ratios as high as 7:1 at some times have been measured. No seasonal variation of TCAA in wet input to the forest has been observed. The sum of gaseous and particle-bound concentrations of TCAA in air is low (<100 pg m^-3). Concentrations of TCAA in forest soil are extremely variable (5 to 400 ng g^-1 fresh weight) with location and time, and the origin of some very high, but repeatable, measurements (>200 ng g^-1 fresh weight), which cannot be explained by atmospheric input only, has not been identified. The percentage of TCAA which can be extracted from the soil with water is shown to be <10%, suggesting that TCAA is adsorbed or bound to the soil matrix. No significant relationship between soil TCAA concentrations and total organic matter content, water content or pH has been observed. A zero-dimensional mass balance calculation based on measurements at the upper forested site has identified a net source of TCAA in the catchment, suggesting that a natural formation of TCAA in the soil is occurring. However, the nature of the formation process is not, at this stage, identified.

Agroforestry systems are currently being advocated for the uplands of the UK, consisting of widely spaced trees on grassland utilized by grazing sheep or cattle. One of the aims of agroforestry is to provide wind shelter which will benefit the animals and plants and lead to overall increases in productivity. Practical information on various aspects of the canopy microclimate, such as air flow, is needed to design the optimum agroforestry system. This thesis reports on a series of field experiments, wind tunnel experiments and numerical experiments which wereundertaken to examine and predict the properties of turbulent air flow through a forest of widely spaced trees. The field experiment was carried out at Cloich farm forest, 32 km south of Edinburgh, in three stands of 8 m tall Sitka spruce trees (<i>Picea sitchensis (Bong.) Carr</i>) at spacings of 4 m, 6 m and 8 m between tree centres. Turbulent statistics associated with the air flow were measured using a vertical array of 3-component propeller anemometers, at heights of between 0.25<i>h</i> to 1.25<i>h</i>, <i>h</i> being the mean tree height. Mean wind speed in the forest trunk space increased with increasing tree spacing, and was 46% (8 m), 29% (6 m) and 16% (4 m) of mean wind speed in an adjacent, open-paddock. Zero plane displacement, <i>d</i>, decreased with increasing tree spacing, and was 0.74<i>h</i> (8 m), 0.80<i>h</i> (6 m) and 0.87<i>h</i> (4 m) during daytime. Thermal stability acted to reduce turbulence velocities and momentum stresses at night by between 10% and 25%. Turbulence events within the widely spaced forest canopies were less extreme than reported elsewhere for closed forest stands. Slopes of the <i>u</i>-spectra in the trunk space were greater than -2/3 suggesting a bypass of the normal eddy cascade process. The wind tunnel experiment was carried out in an open jet wind tunnel at the Civil Engineering Department, Edinburgh University, using 1:75 scale model forest made from 20 cm tall bottle-brush elements at spacings of 1.3<i>h</i>, 1/2<i>h</i> and 2/3<i>h</i>, extending a distance of 10<i>h</i> and 20<i>h</i> in the downwind dimension. The area densities matched approximately those of the Cloich forest study. Turbulence statistics were mapped from extensive measurements obtained using a 3-hot-wire probe. The wind tunnel study was successful in stimulating many of the features of canopy flow identified in the field experiment. In addition, the experimental study resulted in a comprehensive set of measurements suitable for testing the predictions from the numerical experiment.

Firstly, a database was constructed of tree anchorage measurements from almost 2000 trees of 12 conifer species. An analysis revealed that Sitka spruce had best anchorage on peat and poorest anchorage on gleyed mineral soils. Trees with root depths >80 cm had critical turning moments 10 to 15% larger than shallow rooted trees. There was better anchorage for grand fir and Douglas-fir than Sitka spruce with various soils and rooting depths. Lodgepole pine was less well anchored, as was shallow rooted (<40cm) Norway spruce on gleyed mineral soil and Corsican pine on medium depth (40-80cm) mineral soil. All other species had similar anchorage to Sitka spruce on equivalent soil. Secondly, as most tree pulling had been conducted on relatively horizontal sites, anchorage and root development of Sitka spruce was compared between a steep (30*) slope and an adjacent horizontal area with similar soil. No overall effect of terrain on anchorage was found, but trees pulled up-slope had significantly better anchorage than those pulled down-slope. Finally, the radial growth response of tree stems and structural roots to wind loading were examined in two experiments: 1. Growth ring chronologies from stems and structural roots of 46-year-old Sitka spruce trees grown on an exposed upland site, were compared with wind records. Wind speed was well correlated with growth of structural roots on the lee- and wind-ward side of the tree. 2. Wind movement, light and photosynthate supply were manipulated on 10-year-old Sitka spruce trees. Trees responded to reduced photosynthate supply (induced by branch girdling) with an immediate reduction in stem and root radial growth. Trees responded to a stand thinning treatment (increased light and wind movement), and to a thinning and guying treatment (increased light, reduced wind movement), with immediate increases in root radial growth, and increases in stem radial growth delayed by a year.

No description available.

This study investigated the physiological response to drought of a 41-year-old <I>Pinus</I> <I>sylvestris </I>stand in south central Scotland. The imposed drought (April-August) resulted in an approximate 15% reduction in the number of functional conduits but no adverse effects on the above ground hydraulic resistance were evident. This may be the result of 'spare capacity' in the amount of conducting tissue or may be indicative of refilling. Under water-stress a significant increase in xylem embolism was detected in 1-year-old shoots. Leaf-level conductance measurements established a strong reduction in conductance with increasing vapour pressure at the leaf surface and a reduction in transpiration and assimilation. Maximal levels of stomatal conductance, under ambient conditions, were 280 mmol m<SUP>-2</SUP> s<SUP>-1</SUP> in water-stressed trees and 315 mmol m<SUP>-2</SUP> s<SUP>-1</SUP> in control trees. Maximum net photosynthesis rates were approximately 4.5 μmol m<SUP>-2</SUP> s<SUP>-1</SUP> in both treatments. Stomatal control of transpiration prevented needle water potential from declining below -1.5 MPa. Strong restrictions on midday conductance at both the leaf and stand levels were apparent when soil volumetric water content declined below a threshold of 12%. The results show an immediate response of leaf conductance to the onset of drought and suggest a mechanism involving sensing of soil water status. There was an increase in ABA in the xylem sap to 600 μmol ml<SUP>-1</SUP> at the height of the drought, but the observed stomatal closure preceded any increase in ABA<SUB>xyl</SUB>. Calculations of ABA delivery times suggest it may take a chemical signal in excess of six weeks to travel from root to shoot, in a mature conifer, at the peak of the prolonged water-stress. It is therefore suggested that ABA signals from the roots are not the primary cause of stomatal closure in conifers.

The work seeks to elucidate the conditions for growth of seedlings in an Afromontane forest. The species studied were <I>Juniperus procera</I> Hochst, ex Endl. and <I>Afrocarpus gracilior</I> (Pilger) C.N. Page from the dry montane coniferous forests of Ethiopia. The main aim was to provide the necessary information for a silviculture based on natural regeneration. The understorey light climate was examined, particularly the photosynthetic photon flux (PPF) and Red:Far-red ratio. An empirical model was developed linking measured PPF to gap fraction as assessed from hemispherical photographs. Air temperatures and soil moisture contents were measured, and comparisons made with an 'open' site. The effects of burning and mechanical scarification on regeneration following clear felling and timber extraction were assessed. Finally, a programme of controlled environment experiments was carried in Edinburgh. The effects of seed pre-germination treatments and simulated forest canopy light on seed germination were tested, the responses of seedlings to simulated forest canopy light conditions and nutrient supply were measured, and the response of seedlings to Red:Far-red ratio was examined. The main findings were: (i) The forest is relatively 'open' with a mean photon flux density at the forest floor of 1.4 mol m<SUP>-2</SUP> d<SUP>-1</SUP> to 12.7 mol m<SUP>-2</SUP> d<SUP>-1</SUP>, and little annual variation. There is a mean Red:Far-red ratio in the range of 0.54 to 0.67 in the forest understorey. (ii) Clear cutting or manipulating the canopy alone did not result in the regeneration of both species, but regeneration and establishment of <I>Juniperus procera</I> could be enhanced by site preparation, particularly controlled burning, which exposes the mineral soil.