In this thesis, I have studied long shoot performance in the monoecious, deciduous tree Betula pubescens ssp. czerepanovii. In field studies and a common garden experiment, I have a) studied how environmental variations affect the performance of long shoots in mountain birch, and b) described the relationship between long shoot performance and characteristics of the parent long shoot. I have shown that difference in long shoot performance to some extent can be explained by environmental variables such as temperature, precipitation and global radiation the current and previous summer, annual soil and air temperatures, and the length of growing season. For example, a low summer temperature the previous summer had a negative effect on a majority of long shoot characteristics. Variation in shoot characteristics was of the same magnitude along the regional east-western gradient as along the local altitudinal gradient. Variation among individual trees was of the same magnitude as variation among years. Further, long shoot performance was affected by the parent shoot characteristics and reflects that primordia of different organs are formed in the previous summer. On several occasions, freezing damage to mountain birch has been observed on Mt Njulla in northernmost Sweden. Following such damage, fewer but larger leaves emerge. Damages were compensated for with increased number of buds on long shoots produced the same year and one year after damage. Moreover, there were more new long shoots born on short shoots among damaged trees. Dormant buds and short shoots fulfil important functions in a fluctuating environment and as an adaptation to recurring damages of different origin and severity. Differences in the performance among mountain birch saplings grown in a common-garden at Abisko could to a large degree be explained by their origin. Further, saplings from Sweden and from Iceland responded differently to defoliation, and fertilization did not alter the responses to defoliation.

Although there has been extensive research on the geomorphic and ecologic role of large woody debris (LWD) in streams, the dynamics of LWD in streams are poorly known due to various measurement difficulties during floods. In this thesis I present the results of two flume experiments on the dynamics of wood in streams. The first experiment examined the effects of piece interaction on wood transport, while the second evaluated a theoretical model predicting the threshold of movement, and factors controlling the deposition of individual logs. Flume experiments allow us to model the wood movement under a variety of piece geometries, piece concentrations, and hydraulic conditions. The first experiment showed that logs moved in three distinct transport regimes; congested, semi-congested, and uncongested transport. During congested transport the logs move as a single mass and occupy > 33 % of the channel area. Uncongested transport occurs when the logs are moving as individuals and occupy < 10 % of the channel area. Semi-congested transport is intermediate between these two transport regimes and occurs when wood moves in clumps of 2-3 logs. Transport regime was dependent upon the ration of the volumetric input rate of pieces to the flow, and to a lesser degree, the ratios of the piece length to channel width and piece diameter to channel depth. The transport regime was reflected in the deposit. Congested transport deposits have a higher portion of their pieces oriented parallel to flow than uncongested and semi-congested transport. We expect that congested transport will occur in low-order channels where input rates are high and channel geometry is small relative to piece size. Uncongested transport will dominate large channels where input rates are lower relative to flow and channel geometry is large relative to piece size. Our theoretical model and these experiments indicate that the entrainment of individual logs was dependent upon the angle of the piece, and the presence/absence of rootwads. Although previously noted as a first-order control on piece movement, piece length had little effect on the entrainment threshold, but did affect the distance transported. The distance transported decreased with increases in the ratios of the piece length to average channel width (L[subscript log]/w[subscript av]), the piece length to the radius of curvature (L[subscript log]/R[subscript c]), and the piece diameter relative to average depth (D[subscript log]/D[subscript av]). These three ratios comprise the debris roughness. Increased debris roughness caused a general decrease in distance transported. Pieces with high debris roughness can travel further than predicted if they have high momentum, and over 50 % of their channel area deeper than the depth at which the piece floats. These results indicate that flume experiments and theoretical models, tools that have been extensively used to study sediment dynamics, are a useful in examining wood dynamics. / Graduation date: 1998

Thesis (M.S.)--Ohio State University, 1943. / Includes bibliographical references (leaves 139-143). Available online via OhioLINK's ETD Center

Thesis (Ph.D.)--Brown University, 2008. / Advisor: Osvaldo E. Sala. Includes bibliographical references (leaves 111-117).

Natural communities of species embody complex interrelationships between the structure of the interspecific interaction network, dynamics of species' populations, and the stability of the system as a whole. Studying these interrelationships is crucial for understanding the survival of species in nature. In this context, studying the food web (the network of who-eats-whom) embedded in each interaction network is particularly important because trophic interactions are the main channels of energy flow in all ecosystems. Using a combination of mathematical modeling and empirical data analyses, this study explores the interrelationship between food web structure and multi-species coexistence in local communities. Chapter 1 of this thesis places the overall dissertation study in context of the history of research on species interaction networks and food webs. In Chapter 2, I use a population dynamical model to show how the requirements of stable multi-species coexistence results in the emergence of specific, nonrandom configurations of food web structure during community assembly. These structural "signatures" can be used to empirically gauge the importance of interaction-driven dynamical stability constraints in natural communities. In Chapter 3, I extend the model analyzed in Chapter 2 by imposing biologically feasible constraints on its parameters. This is made possible by the allometric scaling between individual metabolism and body size, and the constraints on interspecific trophic interactions due to body size differences between pairs of interacting species. I show that, using this approach, it is possible to interlink three aspects of local communities that have typically been studied in isolation: the species' body mass distribution, the distribution of ratios of body sizes of consumer and resource species (e.g., predator and prey), and certain food web structural features. Some of these features have previously lacked explanatory models. Finally in Chapter 4, using empirical data from nine communities across a range of habitats, I test some theoretical predictions of the previous chapter. The results provide strong evidence that the food web structure of natural communities do indeed exhibit signatures of dynamical stability constraints, and that the model developed in Chapters 2 and 3 is successfully able to predict a number of empirically observed food web structural features. / text

Deserts are the most abundant terrestrial biome on Earth, and microbial processes assume a major role since environmental stress severely limits higher plant and animal life. A major hurdle to developing an understanding of microbial ecology in deserts has been the lack of knowledge at the fundamental biodiversity level. This is due to lack of research focus and also the inherent bias in ‘traditional’ microbial diversity estimates based upon cultivation. In this thesis an evaluation of culture-independent approaches employing both DNA and RNA from environmental samples was made with comparison to more traditional cultivation techniques. These were then applied to soils from hot and cold deserts, and along stress gradients from semi-arid to hyper-arid. A literature review was first conducted to assess the extent of current knowledge and identify critical knowledge gaps. The scientific study was then carried out as follows. The second chapter presents an evaluation of fungal taxa using cultivation, DNA and RNA based techniques. The findings indicated major taxa are revealed in all approaches, yet differences in less abundant taxa occur. The third chapter describes fungal assemblages in the soils of the McMurdo Dry Valleys, a cold polar desert. In this study, RNA based approaches tracked active fungal assemblages, whilst DNA and cultivation revealed additional taxa. Chapter four analyzed microbial communities in the Thar Desert, a hot monsoon desert in India. This study revealed a diverse community that comprised known desiccation-tolerant taxa but also a phylogenetically broad range of bacteria, archaea and eukarya. Chapter 5 focuses on the delineation of total versus active microorganisms in environmental samples from the hot deserts. As with the initial experiments, this revealed that total and active assemblages track each other broadly in desert soils. A synthesis of the study revealed that certain common microbial phyla are likely well-adapted to xeric stress, although distinct hot and cold desert assemblages also develop. For such low-diversity systems it is likely that DNA-based approaches are reasonable tools for diversity analysis, and will be especially useful in arid systems when long periods of inactivity may confound attempts to estimate active populations. Broader significance of the study includes an increased appreciation of eukaryotic microbial presence in arid soils, and how latent soil microbiota may act as a reservoir for development of future microbial macro-structures (e.g. soil crust) that function in soil stabilization, and should therefore be included in conservation planning for deserts. / published_or_final_version / Biological Sciences / Doctoral / Doctor of Philosophy

Thesis (M.S. in Watershed Management)--University of Arizona, 1992. / Includes bibliographical references and index.

Thesis (M.S.)--Oregon State University, 1990. / Typescript (photocopy). Includes bibliographical references (leaves 97-102). Also available on the World Wide Web.

Thesis (Ph. D.)--Oregon State University, 2000. / Typescript (photocopy). Includes bibliographical references. Also available on the World Wide Web.

Thesis (M.S.)--Michigan State University. Interdepartmental Biological Sciences, 2008. / Title from PDF t.p. (viewed on July 29, 2009) Includes bibliographical references (leaves 97-98). Also issued in print.