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Rhabdocline pseudotsugae Syd., der Erreger der Rostigen Douglasienschütte, gehört zu den bedeutendsten pilzlichen Pathogenen der Douglasie (Pseudotsuga menziesii [Mirb.] Franco). Basierend auf makroskopischen und mikroskopischen Untersuchungen von Pilzfruchtkörpern, Ascosporen und infizierten Douglasiennadeln wurde der Erreger bisher als Nadelparasit beschrieben, dessen Ascosporen mit dem Wind verbreitet werden. Charakteristische Symptome der Erkrankung sind orangegelbe bis rostrote Fruchtkörper, die von Mai bis Juni auf der Unterseite befallener Douglasiennadeln entstehen, sowie ein vorzeitiger, oft massiver Nadelverlust, der bei wiederholtem Auftreten zu erheblichen Zuwachsverlusten und zum Absterben der Bäume führen kann. Ein erhebliches wirtschaftliches Risiko stellte R. pseudotsugae im 20. Jahrhundert für den Douglasienanbau dar, wobei insbesondere die massive Ausbreitung des Erregers eine Herausforderung für die Forstwirtschaft darstellte. Ziel der vorliegenden Arbeit war die Bearbeitung grundlegender Fragestellungen zur Infektions- und Verbreitungsstrategie von R. pseudotsugae, um neue Infektionsquellen zu identifizieren und die hohe Ausbreitungsdynamik des Erregers besser nachzuvollziehen. Vor dem Hintergrund der prognostizierten klimatischen Veränderungen sollen die Ergebnisse der Arbeit zu einem verbesserten Verständnis der Biologie von R. pseudotsugae beitragen und somit langfristig das Infektionsrisiko sowie die phytopathologische Gefährdung der Douglasie reduzieren. Die Arbeit umfasst im Wesentlichen drei Schwerpunkte, die als wissenschaftliche Publikationen zusammengefasst und in Zeitschriften mit Peer-Review-Verfahren veröffentlicht wurden. Im ersten Beitrag (Kapitel 4.1) wurde ein spezifisches Nested-PCR-Protokoll zum Nachweis geringster DNA-Mengen von R. pseudotsugae in Mischproben etabliert. Das Verfahren wurde zunächst mit nachweislich infizierten sowie phänotypisch gesunden Douglasien geprüft. Für eine detailliertere Untersuchung der Verbreitung des Erregers im Pflanzengewebe wurden anschließend Knospen und kambiales Gewebe infizierter Douglasien sowie Saatgut einer sächsischen Kreuzungsnachkommenschaft auf einen Befall mit R. pseudotsugae getestet. Der Erreger konnte mit dem etablierten Nachweisverfahren in Knospen, Kambium, Nadeln und Embryonen der Douglasie eindeutig nachgewiesen werden. Aufbauend auf den ersten Ergebnissen wurde im zweiten Beitrag (Kapitel 4.2) ein systematisches Saatgut-Screening durchgeführt. Zur Verfügung stand Saatgut der Küsten- (var. menziesii) und Inlands-Douglasie (var. glauca) aus fünf deutschen, dreizehn nordamerikanischen und zwei ukrainischen Provenienzen. Insgesamt wurde R. pseudotsugae in 19,3 % der getesteten Embryonen nachgewiesen, wobei alle fünf deutschen Provenienzen und sieben nordamerikanische Provenienzen betroffen waren. Im ukrainischen Saatgut konnte der Erreger dagegen nicht nachgewiesen werden. Im dritten Beitrag (Kapitel 4.3) stand erstmals die genetische Struktur von zwei R. pseudotsugae-Kollektiven im Fokus. Auf je einer Versuchsfläche in Sachsen und Nordrhein-Westfalen wurden 184 Apothecien des Erregers gesammelt und mittels BPS- und SCoT-Markern untersucht. Die R. pseudotsugae-Kollektive zeichneten sich insgesamt durch eine hohe genetische Vielfalt sowie eine hohe genetische Diversität aus. Innerhalb der jeweiligen Versuchsflächen konnte eine deutliche räumliche Differenzierung im R. pseudotsugae-Kollektiv nachgewiesen werden, wohingegen eine Differenzierung zwischen den Versuchsflächen nicht beobachtet wurde. Insgesamt konnte in der vorgestellten Arbeit nachgewiesen werden, dass Saatgut eine potenzielle Infektionsquelle für R. pseudotsugae darstellt und die Verbreitung über Ascosporen lokal begrenz ist. Die Auswahl von resistenten Provenienzen, die richtige Standortwahl sowie die konsequente Umsetzung geeigneter waldbaulicher Maßnahmen stellen nach wie vor die Basis für einen erfolgreichen Douglasienanbau dar. Ausgehend von den aktuellen Ergebnissen müssen die bestehenden Behandlungskonzepte allerdings erweitert und vor allem die Saatgutgesundheit stärker berücksichtigt werden. Um das wirtschaftliche Risiko für die forstliche Pflanzenproduktion und den Anbau der Douglasie nachhaltig zu reduzieren, wird empfohlen Saatguterntebestände und Saatgut regelmäßig auf einen Befall zu prüfen. Die Erarbeitung von Grenzwerten für R. pseudotsugae würde darüber hinaus eine objektive Bewertung der Pathogenbelastung ermöglichen und zukünftig eine qualitätsorientierte Auswahl von Saatgut erlauben.:Abbildungsverzeichnis Tabellenverzeichnis Abkürzungen 1. Einleitung 2. Stand der Forschung 2.1 Rhabdocline pseudotsugae Sydow 2.1.1 Taxonomie 2.1.2 Wirt 2.1.3 Herkunft und Verbreitung 2.1.4 Infektion und Krankheitsverlauf 2.1.5 Forstwirtschaftliche Bedeutung und Management 2.2 Detektion und Identifikation von Pflanzenpathogenen 2.3 Untersuchung der genetischen Variation phytopathogener Pilze 3. Zielsetzung und Gliederung der Arbeit 4. Publikationen 4.1 Rhabdocline needle cast – Investigations on various Douglas fir tissue types 4.2 Rhabdocline needle cast – most recent findings of the occurrence of Rhabdocline pseudotsugae in Douglas fir seeds 4.3 Genetic variation between and within two populations of Rhabdocline pseudotsugae in Germany 5. Diskussion 5.1 Verbreitungsstrategien von Rhabdocline pseudotsugae 5.2 Konsequenzen für den Douglasienanbau 6. Ausblick 7. Zusammenfassung 8. Summary 9. Literaturverzeichnis / Rhabdocline pseudotsugae Syd., the causal agent of Rhabdocline needle cast, is one of the most important fungal pathogens of Douglas fir (Pseudotsuga menziesii [Mirb.] Franco). Based on macroscopic and microscopic investigations of fungal fruiting bodies, ascospores and infected Douglas fir needles, the pathogen has so far been described as a needle parasite with ascospores spread by the wind. Characteristic symptoms of the disease are orange-yellow to rust-red fruiting bodies, which appear on the underside of infected Douglas fir needles from May to June, as well as premature, often massive needle loss. If an infection occurs repeatedly, it can cause considerable growth losses and the death of the trees. R. pseudotsugae was a considerable economic risk for Douglas fir cultivation in the 20th century, with the massive spread of the pathogen in particular posing a challenge to forestry. The aim of the present work was to study fundamental questions on the infection and spreading strategy of R. pseudotsugae in order to identify new sources of infection and to better understand the high spread dynamics of the pathogen. In the context of predicted climatic changes, the results of the work should contribute to an improved understanding of the biology of R. pseudotsugae and thus reduce the risk of infection and the phytopathological threat to Douglas fir in the long term. The work essentially covers three main topics, which have been published as scientific papers in peer-reviewed journals. In the first publication (Chapter 4.1), a specific nested PCR protocol was established to detect extremely small quantities of DNA from R. pseudotsugae in mixed samples. The procedure was initially tested with confirmed infected as well as phenotypically healthy Douglas firs. For a more detailed study on the distribution of the pathogen in plant tissue, buds and cambial tissue of infected Douglas firs as well as seeds of a Saxon controlled cross-breeding population were subsequently tested for infestation with R. pseudotsugae. Using the previously established detection method, the pathogen could be clearly identified in buds, cambium, needles and embryos of the Douglas fir. Based on these results, a systematic seed screening was described in the second paper (chapter 4.2). Seeds of coastal (var. menziesii) and inland (var. glauca) varieties of Douglas fir from five German, thirteen North American, and two Ukrainian provenances were available for this study. Overall, R. pseudotsugae was detected in 19.3% of the embryos tested, with all five German provenances and seven North American provenances being affected. In contrast, the pathogen could not be detected in Ukrainian seeds. In the third paper (chapter 4.3), we focused on the genetic structure of two R. pseudotsugae collectives for the first time. On two experimental plots in Saxony and North Rhine-Westphalia, 184 apothecia of the pathogen were collected and examined using BPS and SCoT markers. In general, the R. pseudotsugae collectives were characterised by a high genetic variation as well as a high genetic diversity. A clear spatial differentiation in the R. pseudotsugae collective could be detected within the respective experimental plots, whereas no differentiation between the test areas was observed. In summary, the presented work has demonstrated that seeds are a potential source of infection for R. pseudotsugae and that dissemination via ascospores is locally limited. The selection of resistant provenances, the proper choice of site as well as the consistent implementation of suitable silvicultural measures still form the foundation for successful Douglas fir cultivation. Based on the latest results, existing treatment concepts need to be expanded, and the seed health has to receive more attention. In order to sustainably reduce the economic risk for forest plant production and the cultivation of Douglas fir, it is recommended to regularly check seed harvesting stands and seeds for infestation. The definition of threshold values for R. pseudotsugae would also allow an objective assessment of the pathogen load and a quality-oriented selection of seeds in the future.:Abbildungsverzeichnis Tabellenverzeichnis Abkürzungen 1. Einleitung 2. Stand der Forschung 2.1 Rhabdocline pseudotsugae Sydow 2.1.1 Taxonomie 2.1.2 Wirt 2.1.3 Herkunft und Verbreitung 2.1.4 Infektion und Krankheitsverlauf 2.1.5 Forstwirtschaftliche Bedeutung und Management 2.2 Detektion und Identifikation von Pflanzenpathogenen 2.3 Untersuchung der genetischen Variation phytopathogener Pilze 3. Zielsetzung und Gliederung der Arbeit 4. Publikationen 4.1 Rhabdocline needle cast – Investigations on various Douglas fir tissue types 4.2 Rhabdocline needle cast – most recent findings of the occurrence of Rhabdocline pseudotsugae in Douglas fir seeds 4.3 Genetic variation between and within two populations of Rhabdocline pseudotsugae in Germany 5. Diskussion 5.1 Verbreitungsstrategien von Rhabdocline pseudotsugae 5.2 Konsequenzen für den Douglasienanbau 6. Ausblick 7. Zusammenfassung 8. Summary 9. Literaturverzeichnis

Forest biomass burned for energy purposes does not need to be accounted for under IPCC rules. This has led to a number of countries considering tree stump harvesting as a source of forest biomass. However there are concerns that the soil disturbance that this may entail could have adverse environmental effects, including the loss of sequestered carbon from the soil. Published results differ in the degree and nature of stump harvesting soil disturbance. Two widely used measures employed in stump harvesting soil disturbance studies are visual assessment of disturbance extent and bulk density measures of the nature of disturbance. Each of these has limitations. This study seeks to extend the insight into both the nature and extent of soil disturbance resulting from stump harvesting by the application of additional techniques. In this way the physical effects of soil disturbance by stump harvesting will be compared with those of other forestry practices. To overcome the two-dimensional and subjective nature of visual assessment, a radiometric approach was adopted, utilising residual Chernobyl 137Cs fallout to determine the degree of soil mixing. To complement bulk density measurements, micromorphological analyses of soil thin sections taken from field samples were carried out to investigate the impact of compressive force on pore space. Low-cost tracer devices were deployed in the soil around stumps prior to extraction to permit the monitoring of the lateral movement of soil during stump extraction. These methods were applied to a stump harvesting operation carried out under current UK guidance at a UPM Tilhill managed site in south west Scotland. The radiometric method demonstrated its capacity to recognise differing degrees of soil disturbance in an operational forest environment, including some disturbance that might escape visual assessment. Analysis of soil thin sections provided the evidence of a significant increase in the pore capacity of disturbed soil. The soil movement tracers developed for this project provided the capability to examine the various trajectories of soil during stump extraction as well as dimensioning the resulting disturbance crater. The study indicated that under current UK management and operational practice, stump harvesting generated a higher level of soil disturbance compared to ground preparation by trench mounding, with an estimated 1260 m3 ha-1 of soil disturbed by stump harvesting compared to 250 m3 ha-1 from trench mounding. Stump harvesting was found to generate a net reduction in soil bulk density in the affected areas, contrary to the findings of some other studies. This outcome is dependent on adhering to particular site management and operational procedures. The practice of raking over the site following stump harvesting is estimated to add a further 10% to the volume of soil disturbed, and is a questionable activity under soil sustainability guidance. This work was part-funded and actively supported by the UK Forestry Commission and UPM Tilhill.

This thesis presents the results of a study to examine long-term forest dynamics in the high-altitude mountains of West-Central Mexico. Vegetation dynamics on temporal scales ranging from 10² to 10³ years were reconstructed in order to provide essential information on the temporal variability of ecological patterns and processes in these forests; information that is of direct relevance for their current and future conservation and management strategies. Vegetation and palaeoecological methods undertaken included fossil and modern pollen analysis, vegetation surveys, microfossil charcoal analysis, magnetic susceptibility, inorganic and organic geochemistry, radiocarbon and ²¹⁰Pb dating. These were used to evaluate the long-term dynamics of three forest types; Pine Forest, Cloud Forest and Transitional Forest on timescales spanning the past 4260, 1340 and 1230 years respectively. The main drivers of change were climate and disturbance events induced by climate fluctuations, for example increased fire frequency. The reconstructed records indicate that the sequences from the Cloud Forest and the Transitional Forest spanned two wet and one dry climatic interval while the Pine Forest sequence spanned two dry and two wet periods. The impact of these climatic fluctuations was significant on all three forest types and resulted in variations in forest diversity, taxonomic turnover and successional change. The climate change episodes observed in these records seem to be the local manifestation of climatic events that were occurring throughout Mexico at these intervals in time. Human influences were evident in the three forests through the appearance of cultural taxa, particularly during the driest period (~ 1200 yr BP). There is little evidence from these records, however, to suggest a widespread clearance of the landscape for agriculture. Results from this study support the current conservation and management recommendations for Cloud Forest to exclude timber extraction, grazing and agricultural activities from this forest type. In the Pine Forest, human interventions such small-scale agriculture, prescribed burning and silvicultural actions are in agreement with the longterm pine ecology and as such, total exclusion of human activities is not necessary. For the Transitional Forest, results from this study suggest that there needs to be the establishment of adequate plans to reduce frequent fires to arrest the development of prone-to-fire taxa.

Appreciation of how forest land can be managed in a sustainable way in arid and semi-arid zones (ASAZs) of centralized countries is limited. Accordingly, this thesis seeks to analyse the role of government and communities, including women, in the formulation and implementation of sustainable forest management (SFM) policy and practices in the semi-arid environment of Syria where such land is limited in extent (e.g. 3% forest and 57% rangeland) and yet where its high biodiversity value is of international significance. The thesis employs a variety of methods: a case study approach (Syria); a questionnaire (i.e. 142 respondents); face-to-face interviews (i.e. 26 interviewees); participant observation and secondary data. The SFM model was used to organise and analyse the influences of environmental, economic, social, cultural and political issues on the state of forest land in Syria. Three contrasting forest areas were selected for detailed analysis at local level: Al Foronloq had the Arab Institute of Forestry close by and the area had a high biodiversity value for landscape; Abo Kbeis contained key genetic resources and a number of women there had been trained in forest management and Abd Aziz Mountain was characterised by rangeland with traditional grazing plus a very arid environment. The main results obtained from census data confirmed that Syrian forest lands have diminished considerably since 1900 with regard to their geographical extent due to agricultural development, expansion of rural-urban settlements as well as of agricultural land onto Syrian forest land. On a more general level, the political issues in Syria (i.e. centralization and independency of the country) demand development of the internal resources of the country, such as agricultural production, in order to cover the needs of human maintenance. Scrutinising forest documentation and using results of face-to-face interviews, it was found that there were considerable changes in forest policies in terms of forest protection and plantation. In addition, there was a recent indication of adopting SFM principles in the case study area, largely as a result of action by agencies external to Syria at the national level, and the new role of NGOs in forest management at the local level. The increasing level of awareness of environmental problems; the capacity of institutions; community participation in natural resources management and achieving international agreements were also found to be paramount in any contracts between the Syrian government and other organisations. This thesis, at the local level, showed that respondents in the mountains (in the Abd Aziz Mountain (AAM) study area) seemed to be older, poorer, mostly with non-educated background, with more than three children, than in the Al Foronloq (AF) and Abo Kbeis (AK) study areas. Respondent groups in AAM were found to be more dependent upon forest resources than respondents in AF and AK; and they occupied land illegally because of their mission to develop agricultural activities, including grazing. The study confirmed that educated households in AF and AK use forest resources more than non-educated households. Conversely, non-educated households in AAM suffer from gaining a local income which may in turn affect their attitudes and behaviours in using forest resources; and as consequence, householders suffering from financial problems may be less aware of the importance of forest protection and try to solve their individual needs by increasing the pressures on the forest resources. The major constraints affecting the formulation and implementation of SFM policy are insufficient financial resources, inadequate management from national to regional and local levels; the limitations are also related to local communities’ attitudes and ignorance of the role of women in forest management. This thesis found that the contribution of women in the labour force at the local level was high in Lattakia (Al Foronloq study area) compared with other study areas (e.g. 32.9% in Lattakia against 13.4% in Hamah and 18.8% in Alhasake) (UNDP: Syrian Human development, 2005); although, there was a significant relationship between income level, family size and women’s contribution in forest management at the local level and no significant relationship with the educational level. On a more specific level, the role of religious faith in AK affects the contribution of women in the society and the workplace generally and in forest management in particular. Finally, the application of the SFM model in this study provided a flexible approach for analysis of complicated interactions between the government and communities. It also provided a comprehensive framework for different types of analytical purposes. Each of the three main components (issues, state and political decisionmakers) was divided into several sub-components which facilitate the explanation and identification of the complexities affecting the formulation of SFM policy and the implementation of such policy. It helped to provide a set of policy recommendations which may help to increase future community participation in forest management and reduce the influences of community pressures on forest resources in Syria.

Tropical montane cloud forests (TMCF) are one of the most fascinating, but least understood ecosystems in the world, and the interest in the carbon (C) cycle of TMCFs with regard to carbon sequestration and storage practices has increased rapidly in recent years. One feature that prevails in all TMCFs is a decrease in aboveground net primary productivity (ANPP) and standing biomass and leaf area index (LAI) with increasing altitude, together with the stunted growth form of the trees. This thesis focuses on the input part of the TMCF C-cycle, and investigates the controlling factors on photosynthesis on a leaf, canopy, and ecosystem level in the Kosñipata valley in south east Peru, on the eastern slope of the Andes (13º11’28’’S / 71º35’24’’W). Leaf traits are known to relate to foliar C-exchange, and compared with other altitudinal transect studies of TMCFs, the studied sites had similar altitudinal trends for foliar nitrogen (N) content (though not for phosphorus) and leaf mass per area (LMA), with N content decreasing and LMA increasing with altitude. N concentrations were relatively high and LMA values relatively low, but this observed relationship was consistent with those found in global leaf trait surveys. Examining plant stoichiometry (i.e. N:P ratios), the data suggests that unlike the general hypothesis, the Kosñipata forests are not N limited, except for the study site at 2990 m a.s.l. At the 2990 m a.s.l. site, which is the focal study site of the thesis, photosynthetic parameters Vcmax (the carboxylation efficiency of the Rubisco protein) and Jmax (the electron transport efficiency) proved to be similar to those found in lowland tropical rainforest leaves when expressed on an area basis and standardised to 25 °C (55.6 ± 2.6 and 106.5 ± 5.2 mmol m-2 s-1, for Vcmax and Jmax, respectively). However, when standardised to the mean ambient TMCF temperature of 12.5 °C, both photosynthetic parameters were much lower than ambient tropical rainforest Vcmax and Jmax values. The TMCF Jmax -Vcmax relationships were steeper than found in other tropical biomes, indicating a possible adaptation to the lower light availability in TMCFs because of frequent cloud cover, or a consequence of little atmospheric evaporative demand, which is also due to the humid conditions in this forest type. Although N-Vcmax relationships were significant (P<0.05), the fit was not very strong and the relationship between nitrogen use efficiency (NUE) and Vcmax indicates that TMCF species can be regarded as a different plant functional type compared with other tropical forest types. Diurnal measurements of net photosynthesis (A), stomatal conductance (gs) and leaf water potential (Yleaf) showed that different TMCF species experienced non-contrasting diurnal patterns of Yleaf and gs in the dry season. The observed patterns suggest that some TMCF species can be classified as isohydric species, while others behave anisohydrically. Additionally, in situ gs was not very responsive to these to the range of experienced photosynthetically active radiation (PAR), vapour pressure deficit (VPD) or soil water content (SWC), leading to the conclusion that in the studied TMCF, drought stress does not play a role in C-uptake. When using the measured photosynthetic parameters for up-scaling C-uptake to stand scale with a Soil-Plant-Atmosphere model, simulated annual gross primary productivity (GPP) was 16.24 ±1.6 T C ha-1 yr-1, which is about half the GPP observed in neotropical lowland rainforests. Analyses of the modelled results showed that GPP in this TMCF is mostly controlled by temperature, PAR and leaf area index (LAI) and when increasing these three factors to values found in tropical lowland forest, GPP increased up to 75%. In addition, the modelled results indicate that hydraulic limitations on TMCF C-uptake are very unlikely under current climatic conditions. The modelled results also showed that increases in radiation as a result of less cloud cover do not translate to straightforward increases of GPP. The cloudy conditions of TMCFs, which reduced incident PAR in TMCFs, should therefore not be regarded simply as a negative control on TMCF GPP. Instead, the increase in fraction of diffuse radiation partially offsets the decrease in GPP following the reduction in PAR. Overall, the results of this study show that leaves of Andean TMCF forests have similar C-uptake capacity to tropical lowland rainforests when standardized to similar temperatures, but that for in situ C-uptake temperature, radiation and LAI are the key controls.

The Caledonian pinewoods are a habitat of crucial environmental and cultural importance, and the sole home of many rare species. However, they have seen steady decline in recent centuries, through the establishment of hunting estates and forestry plantations. A recent trend in management is the attempted transformation of existing plantations (dense communities with a regular spatial structure and low variance in size and age) towards a state mimicking the perceived natural condition, which has a lower density, irregular spatial pattern, high variance in size and age. This presents a problem for traditional forestry practices, which were conceived primarily with “even-aged” plantation populations in mind. The shift towards management of an uneven-aged structure requires a more in-depth consideration of individual trees’ lifecycles and their effect upon long-term population dynamics. In recent years, great advances in computational and mathematical models for spatially interacting populations have been made. However, certain complications have prevented them from being utilised to their full potential for the purposes of forest management. Forest communities are not only spatially structured; the size of each tree plays a role in its ability to acquire resources for growth and survival. Existing models of population dynamics are discussed, and their extension to incorporate both size- and spatially- structured interactions is presented. The key aspects of populations’ structural development are studied. Data from both plantation and semi-natural Scots Pine stands in Scotland allow parameterisation of a stochastic individual-based model, which in turn provides insights into the behaviour of real populations, and the importance of spatial effects and heterogeneity in individuals. A partial differential equation (moment) approximation to the stochastic model is presented. While this is analytically intractable, numerical integration and heuristic analysis of the equations enable clearer identification of the drivers of population structure. Many results are concordant with existing models of both qualitative forest stand development and theoretical dynamics of spatially-structured populations, while others are specific to joint size-space structure. This deeper understanding of the population dynamics allows robust recommendations for diverse uneven-aged stand management objectives to be made. Approaches to accelerating the transformation of plantation stands towards a “natural” state (using two key operations: thinning – removal of trees, and planting) are investigated. Finally, approaches to so-called “continuous cover forestry” – the practice of maintaining a quasi-natural state while also obtaining economic value from a forest – are also considered. In both cases, the model’s simplicity enables clearer conclusions than would be possible using other approaches.

Within the field of ecosystem science, substantial progress has been made towards our knowledge of the factors which shape the global distribution of vegetation. However, factors which control the biogeography of belowground vegetation structure and function remain less understood than their aboveground counterpart. Vegetation types can differ substantially in terms of belowground processes such as root growth, root turnover, and resulting vertical root distributions. Fine roots provide an exchange surface, allowing transport of water and nutrients to the leaves. On the other hand they also represent a significant sink for photosynthetically fixed carbon to the soil in terms of maintenance and growth. Overall, root processes have a major influence on fluxes of water, carbon and nutrients within ecosystems. In this thesis, an electrical impedance method was used to determine the area of ‘active’ root in contact with the soil for the purpose of absorption. These measurements were compared to the leaf area of the trees, for the first time allowing the aboveground and the belowground resource exchange areas of plant to be contrasted. This approach was first developed to compare the exchange surface areas of leaves and roots within a Sitka spruce (Picea sitchensis) managed forest, making measurements in adjacent stands of differing tree density, but identical in age. Stem density was found to significantly influence the proportion of absorbing root area relative to leaves. Following the successful test of the method, it was used to compare the resource exchange areas of eight stands of forest and savanna vegetation in central Brazil. Across a broad gradient of vegetation structure, the results showed progressively more investment in fine root area relative to leaf area across the transition from dense forest to open savanna. However, a contrasting result showed that the forests had a higher absorbing root area to leaf area ratio than savannas. Furthermore, these measured ratios were strongly correlated with tree height across the eight structurally contrasting stands. It appears that absorbing root area index provides a physiologically meaningful way of characterising belowground water uptake ability, it is possible that excessive investment in fine root area, relative to leaf area, may reflect differences in the requirement for nutrient uptake in poor soils. Complementary to the analysis of root absorbing area, measurements of root activity and belowground carbon cycling were made by focussing on two of the eight tropical study sites. Here, the carbon costs of root growth and respiration were quantified to develop a belowground carbon budget for two structurally contrasting Brazilian savannas, using soil respiration measurements and a root presence/absence manipulation experiment. Annual estimates showed that at least 60% of the total CO2 efflux from the soil was contributed by autotrophic processes, with this value rising to 80% during the dry season. Seasonal fluctuations of soil respiration were strongly correlated with soil moisture for both the autotrophic (R2=0.79, pvalue< 0.05) and heterotrophic (R2=0.90, p-value<0.05) components, with maximum flux rates corresponding with 16.4 and 17.7% soil moisture content respectively. Furthermore, autotrophic respiration was found to varied with phonological patterns of fine root growth (R2=0.80, p-value<0.05). It follows that, the way in which phenological processes respond to a changing climate is of potential importance within seasonally dry regions. Diurnal fluctuations of heterotrophic CO2 efflux were correlated with soil temperature (R2=0.74, p-value<0.05), demonstrating a Q10 value of 1.6 across both sites. In contrast, total soil CO2 efflux was not correlated with temperature (p-value=0.31), suggesting that autotrophic respiration is predominantly limited by substrate supply.

The goal of quantifying the woody cover and biomass of tropical savannas, woodlands and forests using satellite data is becoming increasingly important, but limitations in current scientific understanding reduce the utility of the considerable quantity of satellite data currently being collected. The work contained in this thesis reduces this knowledgegap, using new field data and analysis methods to quantify changes using optical, radar and LiDAR data. The first paper shows that high-resolution optical data (Landsat & ASTER) can be used to track changes in woody vegetation in the Mbam Djerem National Park in Cameroon. The method correlates a satellite-derived vegetation index with field-measured canopy cover, and the paper concludes that forest encroached rapidly into savanna in the region from 1986-2006. Using the same study area, but with radar remote sensing data from 1996 and 2007 (ALOS PALSAR & JERS-1), the second paper shows that radar backscatter correlates well with field-measured aboveground biomass (AGB). This dataset confirms the woody encroachment within the park; however, in a larger area around the park, deforestation dominates. The AGB-radar relationships described above are expanded in the next paper to include field plots from Budongo Forest (Uganda), the Niassa Reserve (north Mozambique), and the Nhambita Community Project (central Mozambique). A consistent AGB-radar relationship is found in the combined dataset, with the RMSE for predicted AGB values for a site increasing by <30 %, compared with a site-specific equation, when using an AGB-radar equation derived from the three other sites. The study of the Nhambita site is extended in the following paper to assess the ability of radar to detect change over short time periods in this environment, as will be needed for REDD (Reducing Emissions from Deforestation and Degradation). Using radar mosaics from 2007 and 2009, areas known (from detailed ground data) to have been degraded decreased in AGB in the radar change detection, whereas areas of agroforestry and forest protection showed small increases.

Heartwood is the dead, inner layers of wood in the tree which no longer transport water. It is usually dark in colour and has increased decay-resistance compared to the sapwood. Heartwood forms in the transition zone when the ray cells die and deposit chemical extractives in the surrounding xylem. These chemicals convey natural durability which is of value to the forest and timber industry. Despite its value the formation of heartwood is poorly understood. The objective of this PhD is to improve our understanding of heartwood formation in Sitka spruce and Scots pine, the most widely planted species in Britain. Separating heartwood and sapwood at the sawmill can increase timber value due to differences in wood properties. The amount of heartwood varies both with height within, and between trees. Empirical models were developed to describe heartwood and sapwood distribution by diameter, area and ring number 1) within any wood disc 2) with height in the standing tree using taper functions, and 3) its variation between trees. Models will be incorporated into wood quality models to optimise heartwood utilisation. According to pipe theory a certain area of sapwood sustains a volume of canopy, with redundant sapwood converted to heartwood. Sap flux was examined across the sapwood and transition zone in Sitka spruce to understand water transport in relation to heartwood formation and identify seasonal change in transport in the transition zone. Results suggest that the transition zone ceases water transport around dormancy and the amount of heartwood formed may be driven by new wood formation, maintaining sapwood depth. Heartwood formation is a seasonal process, however this has not been confirmed in Sitka spruce or Scots pine, or under UK climatic conditions. Seasonal variation in carbon dioxide and ethylene production by the transition zone were measured to identify the time of heartwood formation, which was late summer through dormancy, consistent with published literature. The role of ethylene in heartwood formation is confirmed. Heartwood formation is an active developmental process, a form of programmed cell death, and as such must be carefully regulated temporally and spatially. Regulation by phytohormones has been proposed but not confirmed. Screening for a broad range of phytohormones during the proposed season of heartwood formation identified an increase in abscisic acid and a decrease in auxin concentration in the transition zone. Abscisic acid, auxin and ethylene also regulate xylogenesis, therefore the same signals that initiate cambial dormancy may also provide the temporal regulation of heartwood formation. The results of this PhD will optimise the use of heartwood in Sitka spruce and Scots pine in the UK and contribute towards selective tree breeding for increased heartwood volume worldwide.