As knowledge about forest ecosystems accumulates, it becomes important to develop an explicit description of the functional relationships between processes. These relationships include processes ranging from cell to leaf, tree and forest. Knowledge obtained at any one of these levels cannot provide much understanding or predictive power, because the overall behaviour is influenced by positive and negative feedback between levels. A hierarchical approach is applied for coupling processes at these levels. In this study, a hierarchical forest model FORDYN is developed, which can integrate knowledge at a biochemical or physiological level to make statements on tree growth and forest succession levels. This procedure is referred to as 'scaling up'. The model FORDYN consists of four levels of processes characterised by the time step or behaviour frequency. In level 1, a forest succession process is described by accounting the fate of spatially distributed individual trees in an annual time step. In level 2, each tree' growth is represented by a 'process-based' approach, whereby assimilation, assimilate allocation, nitrogen dynamics and water balance are accounted for in a daily time step during tree growth. In level 3, daily photosynthesis is accumulated by hourly value by a 3-point Gaussian scheme. In level 4, instantaneously CO<SUB>2</SUB> assimilation rate is calculated by a biochemical (mechanistic) photosynthesis model. To exploit fully the hierarchical feature of the model structure, FORDYN is designed to be used in different simulation modes to meet the demand of different purposes of users. FORDYN was tested against the common data set provided by the European Pine Modelling group, and sensitivity analysis of this model was compared with other published and validated European pines models. It was shown that FORDYN is robust and responsive. FORDYN has been used to analyse current problems of global change, such as the impact of CO<SUB>2</SUB> increase. It was shown that this model can provide new insights into ecosystem dynamics and environmental problems of wide concern. This is probably the first ecological model at can simulate long term forest development by scaling up biochemical processes, physiological processes, and tree growth processes. It is a contribution to the modelling methodology in forest modelling, also it provides a good example of unifying ecosystem science and population biology.

In theory, populations of agamospermous plants are genetically invariant and consequently hold little evolutionary potential. To test this hypothesis, molecular markers were used to examine evolutionary processes in the <i>Sorbus</i> microspecies <i>S. pseudofennica </i>and <i>S. arranensis</i>, which are endemic to the Isle of Arran, Scotland. The proposed hybrid origin of these microspecies was investigated using a variety of molecular markers. Two isozyme systems (AAT and 6PGD), a nuclear DNA marker and a chloroplast DNA marker all provided markers that were specific to the putative parental species, <i>S. aucuparia</i> and <i>S. rupicola. </i>These markers could not separate <i>S. rupicola</i> from <i>S. aria </i>(a potential parent), or fully distinguish between <i>S. arranensis</i> and <i>S. pseudofennica. </i>Individuals of both <i>S. arranensis</i> and <i>S. pseudofennica </i>were screened and results were compatible with these microspecies being derived from a cross between <i>S. aucuparia</i> and <i>S. rupicola/S. aria. </i>DNA sequences of the chloroplast trnL intron and trnL-trnF intergenic spacer for the Arran <i>Sorbus</i> microspecies were identical to those of <i>S. aucuparia. </i> In contrast, nucleotide substitutions were evident between the <i>Sorbus</i> microspecies and <i>S. rupicola</i> at three bases. Nuclear DNA markers (five microsatellites and a Rubisco intron primer pair) revealed variation among individuals within <i>S. arranensis </i>and <i>S. pseudofennica </i>microspecies. Only three <i>S. arranensis </i>clones were detected from a total of 179 individuals. In contrast eight clones were detected from a total of 140 <i>S. pseudofennica</i> individuals. Six families of <i>S. arranensis </i>and <i>S. pseudofennica</i> were screened with three nuclear DNA markers. No variation in banding pattern was found among any of the <i>S. arranensis </i>families. In contrast, segregation of molecular makes was found in three out of the six <i>S. pseudofennica</i> families.

No description available.

Woody species of the Brazilian Cerrado show morphological and functional adaptations to the soil water, soil nutrient and fire stresses of the Cerrado environment. This thesis considers these adaptations in relation to the growth and photosynthesis of Cerrado woody species, and in particular <I>Kielmeyera coriacea</I> Mart. (Guttiferae). Growth of <I>K. coriacea</I> and other Cerrado woody seedlings under field conditions is slow, but within the range seen for other late successional woody species. <I>K. coriacea</I> displays a limited growth rate plasticity in response to favourable conditions, with a maximum potential specific growth rate of 0.054 d<SUP>-1</SUP>. <I>K. coriacea</I> has relatively high unit leaf rates, but low leaf area ratios, due to an inherent low specific leaf area (SLA). Low SLA values are compounded by a rapid ontogenic decline in leaf weight ratio (LWR). Declining LWR is due to high biomass partitioning to root development. Within the root and shoot, partitioning is biphasic, with an initial 'establishment' phase of leaf and lateral root favoured development, and a secondary phase dominated by main root, <I>i.e.</I> xylopodium, development. The cotyledons have a maximum net photosynthetic rate of 11.0 μmol m<SUP>-2</SUP> s<SUP>-1</SUP> under favourable conditions, and provide the majority of photosynthate for the 'establisment' phase. Leaf emergence is episodic, or flushing, and individual leaf areas vary depending on their position within the flush. Leaf primordium production parallels leaf emergence, and maintains 4 unemerged primordia at the shoot apex. Adaptations, such as leaf scleromorphy and xylopodium formation, severely limit the growth potential of Cerrado woody species. Low growth rates under field conditions are primarily due to lower unit leaf rates (E), and are associated with slow leaf-area development.

This study examined the degree to which enhanced nitrogen inputs in a <i>Calluna</i>-dominated ecosystem can alter plant physiological responses, affect the response of soil respiration to environmental parameters by disturbing acclimatised soil microbial populations, influence the relationship between soil carbon fluxes and soil microbial populations, and change soil mineral nitrogen availability to the plants. A pilot study investigated the response of nitrogen deposition on <i>Calluna vulgaris</i> plants maintained in open-top chambers. Heathland monoliths were exposed to acid mist treatments of ammonium nitrate spanning across extreme values. Growth response to increasing fertiliser additions was detectable and high nitrogen fertiliser inputs significantly stimulated shoot growth. Fertiliser inputs were reflected in soil and tissue nitrogen concentrations with an increase in total nitrogen content within actively growing tissues while shoot phenolic concentration decreased in response to nitrogen additions in agreement with the carbon-nutrient hypothesis. A field study was conducted in experimental plots set up in a dense stand of mature heather at Castlelaw Hill, near to Edinburgh. A new, simple methodology is developed and operated to accurately measure soil respiration under controlled laboratory conditions using small soil microcosm with a gas analysis unit. Annual seasonal pattern of soil carbon dioxide effluxes and environmental parameters of soil temperature, moisture, pH, organic matter, microbial biomass and plant growth were measured. Soil temperature, pH, organic matter and microbial biomass were found to be important determinants of carbon dioxide fluxes from soil. In all the soil horizons, carbon dioxide efflux in response to temperature followed the expotential first order equation with an increase with increasing temperature but soil carbon dioxide fluxes decreased with depth. Nitrogen inputs significantly increased soil respiration and the results suggest that long-term effects of atmospheric N deposition, with accelerated mineralisation at higher temperatures, could disrupt the carbon balance of nutrient-poor ecosystems, as noted for heathlands.

No description available.

This study investigated the structure of, and carbon dioxide fluxes at, a 'primary' rain forest (PRF) in SW Amazonia, Brazil, and a distributed secondary rain forest (SRF) in SW Cameroon. The total above-ground biomass and leaf area index (LAI) at PRF were respectively 220 (±95% c.l. 48) Mg ha<SUP>-1</SUP> and 4.0 (±95% c.l. 0.7) m<SUP>2</SUP> m<SUP>-2</SUP>, and at SRF 90 (±95% c.l. 9.4) Mg ha<SUP>-1</SUP> and 4.4 (±95% c.l. 0.9) m<SUP>2</SUP> m<SUP>-2</SUP>. A novel method was devised to quantify the vertical profile in LAI: SRF was distinguished from PRF by a higher concentration of leaf area near the ground. Three methods were used to determine the flux of CO<SUB>2</SUB> from soil and gave overall agreement (static and dynamic chambers, and eddy covariance). The mean soil efflux in PRF and SRF was respectively 5.5 μmol m<SUP>-2</SUP> s<SUP>-1</SUP> (±95% c.l. 0.2; <I>n</I> = 42) and 4.5 μmol m<SUP>-2</SUP> s<SUP>-1</SUP> (±95% c.l. 0.2; <I>n</I> = 178) at 20 - 24 °C. The temperature response was higher in PRF than SRF (Q<SUB>10</SUB> = 2.3 <I>vs</I> 1.9). Soil efflux rates were also obtained from cerrado vegetation in central Brazil, where the efflux was 3.2 μmol m<SUP>-2</SUP> s<SUP>-1</SUP> (±95% c.l. 0.2; <I>n</I> = 10) the Q<SUB>10</SUB> 1.6, at 16 - 23 °C. Heterogeneity in emission was higher in SRF than in PRF and could be described by a non-linear model incorporating the variables: soil temperature, organic carbon and total nitrogen (r<SUP>2</SUP> = 0.82). Carbon was the most important variable determining respiration in SRF; soil moisture was not limiting. There was no observable effect of season on efflux rates in either rain forest, but a decline occurred in cerrado during the dry season. Effluxes of CO<SUB>2</SUB> were measured from stems and branches of diameter 0.002 m - 1.6 m in 24 species in PRF and 17 species in SRF; emission rates were 0.1 - 3.3 μmol m<SUP>-2</SUP> s <SUP>-1</SUP> with a Q<SUB>10</SUB> of 1.8 in PRF, and 0.2 - 5.2 μmol m<SUP>-2</SUP> s <SUP>-1</SUP> with a Q<SUB>10</SUB> of 1.6 in SRF. Maintenance respiration was 80% and construction respiration 20% of total woody tissue respiration (<I>R</I><SUB>t</SUB>) in SRF. A functional model described the relationship between <I>R</I><SUB>t</SUB> and diameter in SRF better than a purely empirical one (r<SUP>2</SUP> = 0.66). A novel method was devised in estimate sap CO<SUB>2</SUB> concentrations which in SRF were 1.2 - 11.0 nmol 1<SUP>-1</SUP> for <I>Distemonanthus benthamianus </I>and <I>Musanga cecropioides</I>. Sap CO<SUB>2</SUB> levels were highly sensitive to sap pH, and represented 1 - 30% of cuvette-measured leaf photosynthesis. Maintenance leaf respiration (<I>R</I><SUB>m</SUB>) was measured through the vertical profile during the night in PRF and SRF. <I>R</I><SUB>m </SUB>increased with height at both sites: ˜0.2 in PRF <I>vs</I> ˜0.3 in SRF at 1.5 m and ˜0.5 in PRF <I>vs</I> ˜0.9 in SRF at 26 m (values normalised to 22 °C, units: μmol m<SUP>-2</SUP> s<SUP>-1</SUP>). Leaf nitrogen and potassium concentrations (<I>N</I><SUB>leaf</SUB> and <I>P</I><SUB>leaf</SUB>) declined with height in the canopy. <I>P</I><SUB>leaf</SUB> concentrations were higher in SRF than PRF where <I>P</I><SUB>leaf</SUB> appeared to limit respiration. <I>R</I><SUB>m</SUB> was not significantly related.

The aims of this research were to investigate the breeding system, seed set, Ploidy levels and the extent and arrangement of genetic variation (detected as both neutral and adaptive traits) among British populations of <i>P. australis.</i> Significant differences in seedset and germination rates were found amongst populations. Seedset was reduced by the presence of <i>Claviceps purpurea </i>infection and was positively associated with mean maximum October temperature (when seed maturation occurs) and site size (possibly a proxy measure of genotypic diversity). All populations, apart from two northerly populations, had > 50% germination rate and germination rate was found to increase with increasing seedset. Microsatellite analysis was used to estimate clone structure, genetic variability within and among populations and the outcrossing rate. Substantial genetic differences in morphology were found among but not within natural British populations of <i>P. australis</i>. Shoot height and number of shoots showed consistent variation among populations. Under nutrient-stressed conditions, northern populations produced longer shoots than southern ones whilst the opposite was true in full-nutrient conditions. Application of synthetic sewage resulted in a marginal significant decrease in the number of shoots produced per population and an increase in below ground biomass compared to populations not receiving treatment. A further aim of this study was to assess the intraspecific variation in the effectiveness of <i>P. australis</i> in nutrient removal from constructed wetland systems (CWSs). Mini-CWS (~ 70 | volume) were created using five British <i>P. australis</i> populations and their efficacy in removing NH_4-N, NO₃-N, P and BOD over a one-year period was compared. There were significant and substantial differences in NH₄-N removal between populations in the CWSs: a difference of 40% was found between the highest and lowest removal rates. This was most likely attributed to genetic differences among populations. From the results of this research, the main recommendations for reedbed establishment and conservation were that seeds should be collected from large reedbeds with high clonal diversity. To prevent the loss of genetic diversity over time in established reedbeds, anthropogenic disturbance should be encouraged to promote sexual recruitment. Where populations are monoclonal, and seedset is depauperate, seedlings would need to be planted from an external source. The source of <i>P. australis</i> could be important for CWS performance, particularly in the removal of NH₄-N, suggesting that source of <i>P. australis</i> should be taken account of in CWS design and construction.

The corpus of available vegetation knowledge is characterised by its fragmented form and by the way in which relationships between different ecological quantities tend to be expressed non-quantitatively. Much of the corpus is only held informally and composed of deterministic factual or conditional statements. Despite its form, this thesis demonstrates that available ecological knowledge can be usefully employed for predictive modelling of vegetation dynamics under different conditions. The thesis concentrates on modelling Mediterranean vegetation dynamics. Using a mixture of concepts and techniques from deterministic state transition and functional attributes modelling. Qualitative Reasoning and knowledge-based systems, three ontological distinct modelling systems are developed to demonstrate the utility of available knowledge for modelling vegetation dynamics. All three systems use declarative, rule-based approaches based on first-order logic and are composed of a set of representational constructs along with a separate system for reasoning with these constructs to make predictions. A method for reasoning about change in non-quantitative model variables is developed based upon time and direction of change. This ‘temporal reasoning system’ provides a solution to the state variable problem and may offer a general way of modelling with non-quantitative knowledge. To illustrate, a different model of Mediterranean vegetation dynamics is developed and run under different conditions for each system. The capabilities and possible problems of each system in terms of ecological validity, knowledge representation and reasoning are discussed. The general utility of rule-based approaches to modelling vegetation dynamics are also discussed along with the implications of the modelling systems developed for the activities of decision-support and ecological theory development.

Measurements of leaf and ecosystems scale CO<SUB>2 </SUB>flux were made at the millet, fallow and tiger bush sites at the HAPEX-Sahel Southern supersite. These were analysed in relation to biological and environmental variables. In the five species studied, leaf scale photosynthesis was strongly influenced by photosynthetic photon flux density (<I>Q</I>) and stomatal conductance, and was well described by the non-rectangular hyperbola model of Jarvis, Miranda and Muetzelfeldt (1985). Stem respiration was measured in two species, and increased exponentially with temperature. Stem respiration rates were higher in the wet season than in the dry season and this difference was used to separate growth and maintenance respiration. Effects of <I>Q</I> and sap flow on stem CO<SUB>2</SUB> efflux were observed. A small number of soil respiration measurements were also made. Direct measurements of leaf area index, biomass and canopy structure were made at the millet and fallow sites. Two indirect methods of estimating leaf area index, from hemispherical photographs and measurements of transmitted <I>Q</I>, were used to all three sites. Together with measurements of canopy structure at each site, the measurements of leaf photosynthesis, stomatal conductance and stem soil respiration were used to parameterise two models which predict ecosystem net CO<SUB>2</SUB> flux: a simple one-dimensional "big leaf" model and a complex three-dimensional model "MAESTRO". Model predictions were compared with independent ecosystem flux measurements made by eddy covariance. Generally, both models agreed well with measurements at all three sites. Differences between measurements and predictions were very small in millet and largest in tiger bush, and were attributed to the effect of canopy heterogeneity on eddy covariance measurements and the accuracy with which canopy structure parameters could be estimated.