Volume and taper studies in Pinus patula and Cupressus lusitanica trees growing in Kenya forest plantations are discussed. The ultimate objective of the study was to find suitable models for estimating volumes and taper rates using two approaches for each parameter (i.e. volume and taper). These included producing volume models in the traditional way and by integrating taper models. Taper models derived from the best of the volume models were compared to the taper models produced from taper data in the traditional way to find out the efficiency of each approach. Data from the two species were used to fit a few popular volume and taper models. Trials were also made to develop new models. Of the popular volume models tested the logarithmic volume model was found to be giving very good estimates. Weighted models conditioned through the origin, by a technique proposed in the study, were also giving similar good estimates. Models weighted by current approach were, however, giving relatively poor estimates. Volume-based taper models were found to be giving biased diameter estimates along the tree profiles. However, when integrated for total volume, the volume estimates given seemed to be better than those given by the other taper models tested. Because of their bias in estimating the diameters and other points along the tree profile, volume-based taper models are not recommended for estimating volumes to any other points along the tree profiles. Other popular taper models were also giving biased diameter estimates. They lacked inflection points. When integrated for volumes, they were giving very poor estimates. Two fairly simple taper models have been proposed which have most of the characteristics needed in a taper model to give proper profile description. They have been recommended for constructing the inside volume tables and taper tables for the two species. They should also apply well in other conifers. One model describes profiles of trees with butt swell while the other describes trees with smooth stem forms. / Forestry, Faculty of / Graduate

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The recent trend in climate has shown that UK temperatures are increasing, summers are getting drier and winters are getting wetter. It is thought that this trend is set to continue for the foreseeable future and that this will have an impact on the growth and quality of timber in the UK. Sitka spruce (Picea sitchensis (Bong.) Carr) is one of the most widely planted and important commercial tree species in the UK but our knowledge of tree growth and wood properties is based on tree growth in the climate of the past 40 – 80 years. The rotation time for Sitka spruce is approximately 40 years so trees planted now will mature in the 2050s, when the climate could be different from today leading to impacts on the quality and quantity of the wood being produced. This project aims to predict the effect that changes in climate will have on Sitka spruce, by looking not only at growth but also at different properties of the wood and their susceptibility to any change in climate. This information could then be used to help make decisions as to whether Sitka spruce is the best tree to be planting now, at any specific site in the UK, to obtain the best quality wood in the future. The effect of seasonally changing weather on growth was measured at two sites by the use of LVDT point dendrometers to record changes in the radius of the tree stems. The data were compared to meteorological data collected from the site and from local weather stations, to determine how weather affected the growth of the trees. Data collection from the site at Griffin Forest near Aberfeldy was initiated in 2008 as part of a long term project at that site. Measurements taken during 2008 and 2009 were used as part of a previous PhD study and continued as part of the present study from 2010. The second site was newly established at Harwood Forest in Northumberland, northern England. At both sites the onset of growth at the beginning of the season was found to correspond to temperature >5°C. Deficit of soil moisture was found to decrease the growth rate during the peak growth period. Radial density, radial growth and the radial profile of longitudinal stiffness were investigated by analysing increment core samples taken from sites covering the full latitudinal range that Sitka spruce grows in Great Britain, with the aim of quantifying the effect of site factors such as latitude, longitude, initial spacing and elevation. The cores were measured from density and ring width using an ITRAX x-ray densitometer and analysed using Windendro software. Stiffness was investigated using acoustic velocity measurements taken directly on the increment cores using an ultrasonic scanner, modified to measure cores. A wide range of published radial growth models and a smaller number of radial density models were explored to see which were able to describe the data and compared to simpler linear segmented models. The sample population was found to be highly variable and the ability of the models to predict ring width or density from ring number alone was limited. Improved prediction of density was possible when ring width was included along with ring number as a predictor. The linear segmented models were found to be able to predict growth and density from ring number alone and this provides a useful and powerful tool. In practice ring width may not always be available and so there is a need for models which can predict density from ring number alone. Ring width was found to be negatively correlated with density, although the nature of the relationship was different between juvenile and mature wood. Most of the variation in both density and growth was between trees at the same site. Initial spacing was found to be the only significant effect on growth and then only by having a positive effect on the growth rate of the juvenile wood, which had a knock on effect on the size of the trees at the end of the juvenile phase. Both spacing and latitude were found to have significant effects on the mean density of the juvenile wood with spacing having a negative effect and latitude a positive effect. In the mature wood, cambial age was found to be the only significant effect on radial density.

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<p>Ecologists have long been interested in the relationships between climate change and forest biodiversity. For centuries, the scientific problems remain understanding the patterns of climate variation, forest geographic distribution, and demographic dynamics. Besides scientific merits, these questions will also help forest managers and policy makers to anticipate how forests respond to global change. This dissertation tackles these problems by using statistical modeling on climate and forest inventory data in the eastern United States.</p><p>In Chapter 1, we ask the question on the observed tree range distributions in response to contemporary climate change in the eastern United States. Tree species are expected to track warming climate by shifting their ranges to higher latitudes or elevations, but current evidence of latitudinal range shifts for suites of species is largely indirect. In response to global warming, offspring of trees are predicted to have ranges extend beyond adults at leading edges and the opposite relationship at trailing edges. Large-scale forest inventory data provides an opportunity to compare present latitudes of seedlings and adult trees at their range limits. Using the USDA Forest Service's Forest Inventory and Analysis data, we directly compared seedling and tree 5th and 95th percentile latitudes for 92 species in 30 longitudinal bands for 43,334 plots across the eastern United States. We further compared these latitudes with 20th century temperature and precipitation change and functional traits, including seed size and seed spread rate. Results suggest that 58.7% of the tree species examined show the pattern expected for a population undergoing range contraction, rather than expansion, at both northern and southern boundaries. Fewer species show a pattern consistent with a northward shift (20.7%) and fewer still with a southward shift (16.3%). Only 4.3% are consistent with expansion at both range limits. When compared with the 20th century climate changes that have occurred at the range boundaries themselves, there is no consistent evidence that population spread is greatest in areas where climate has changed most; nor are patterns related to seed size or dispersal characteristics. The fact that the majority of seedling extreme latitudes are less than those for adult trees may emphasize the lack of evidence for climate-mediated migration, and should increase concerns for the risks posed by climate change.</p><p>In Chapter 2, we ask the question on tree abundance within geographic range responding to climate variation in the eastern United States. Tree species are predicted to track future climate by shifting their geographic distributions, but climate-mediated migrations are not apparent in a recent continental-scale analysis (Chapter 1). To better understand the mechanisms of a possible migration lag, we analyzed relative recruitment patterns by comparing juvenile and adult tree abundances in climate space. One would expect relative recruitment to be higher in cold and dry climates as a result of tree migration with juveniles located further poleward than adults. Alternatively, relative recruitment could be higher in warm and wet climates as a result of higher tree population turnover with increased temperature and precipitation. Using the USDA Forest Service's Forest Inventory and Analysis data at regional scales, we jointly modeled juvenile and adult abundance distributions for 65 tree species in climate space of the eastern United States. We directly compared the optimal climate conditions for juveniles and adults, identified the climates where each species has high relative recruitment, and synthesized relative recruitment patterns across species. Results suggest that for 77% and 83% of the tree species, juveniles have higher optimal temperature and optimal precipitation, respectively, than adults. Across species, the relative recruitment pattern is dominated by relatively more abundant juveniles than adults in warm and wet climates. These different abundance-climate responses through life history are consistent with faster population turnover and inconsistent with the geographic trend of large-scale tree migration. Taken together, this juvenile-adult analysis suggests that tree species might respond to climate change by having faster turnover as dynamics accelerate with longer growing seasons and higher temperatures, before there is evidence of poleward migration at biogeographic scales.</p><p>In Chapter 3, we ask the question on the demographic dynamics of density dependence at the individual tree level in eastern US forests. Density dependence could maintain diversity in forests, but studies disagree on its importance. Part of the disagreement results from the fact that different studies evaluate different responses (per-seedling or per-adult survival or growth) of different stages (seeds, seedlings, or adults) to different inputs (density of seedlings, density or distance to adults). Most studies are conducted on a single site and thus are difficult to generalize. Using USDA Forest Service's Forest Inventory and Analysis data, we analyzed over a million seedling-to-sapling recruitment observations of 50 species for both per-tree (adult) and per-seedling recruitment rates, controlling for climate effects in eastern US forests. We focused on per-tree recruitment as it is most likely to promote diversity at the population level, and it is most likely to be identified in observational or experimental data. To understand the prevalence of density dependence, we quantified the proportion of species with significant positive or negative effects. To understand the strength of density dependence, we determined the magnitude of effects among conspecifics and heterospecifics, and how it changes with overall species abundance. We found that the majority of the 50 species have significant density dependence effects, mostly negative, on both per-tree and per-seedling recruitment. Per-tree recruitment is positively associated with conspecific seedlings, saplings, and heterospecific saplings, negatively associated with heterospecific seedlings, conspecific and heterospecific trees. Per-seedling recruitment is positively associated with conspecific and heterospecific saplings, but negatively associated with conspecific and heterospecific seedlings and trees. Furthermore, for both per-tree and per-seedling recruitment, density dependence effects are stronger for conspecific than heterospecific neighbors. However, the strength of these effects does not vary with species abundance. We conclude that density dependence is pervasive, especially for per-tree recruitment, and its strength among conspecifics and heterospecifics is consistent with the predictions of the Janzen-Connell hypothesis.</p> / Dissertation

<p> Pine species (genus <i>Pinus</i>) have been introduced across the Southern Hemisphere for forestry and several species have invaded surrounding ecosystems. Pine introduction across biogeographic regions sets up an ideal natural experiment to test underlying theories and assumptions of invasion biology. We studied the factors determining patterns of <i> Pinus contorta</i> invasion across nine sites in both the native and introduced ranges to understand how the invasion drivers change across sites and invasion stages. We found that propagule pressure is the most important factor in explaining invasion density in young invasions, but that biotic factors play an important role at later invasion stages. Additionally, we found higher invasion densities in the introduced than native range which may be explained by faster growth and earlier and more prolific reproduction in the introduced range. </p><p> We examined the impacts of ^{P. contorta} invasions on plant biodiversity across sites and found that species richness and native plant cover decline with increasing ^{P. contorta} cover across sites in both the native and introduced range. There were more significant changes in species composition and individual species cover at grassland and shrubland sites in the introduced range than in the native range or a native forest site in the introduced range. </p><p> Finally, there is concern that invasive pines, which are fire adapted, will alter fire regimes in a way that promotes a new fire-prone state further increasing their success over native plants. We examined the potential for ^{P. contorta} to form a positive feedback with fire by quantifying fuel loads and fire effects across an invasive gradient. We also examined ^{P. contorta} and native plant recovery following fire across an invasion density gradient. We found that fuel loads and simulated soil heating increased with older ^{P. contorta} invasions. Following fire, ^{P. contorta} dominated communities only when the pre-fire density was high. Therefore, we expect that a positive feedback between ^{P. contorta} invasion and fire will form only above an invasion threshold. Our invasion-fire simulation model suggested that fire in older invasions will increase invasion rates, but that fires in young invasions will not affect the invasion rate.</p>

<p> Silvopasture, the sustainable integration of livestock and trees on the same unit of land, may have the potential to contribute to agricultural productivity in the Northeastern United States and concurrently encourage the ecosystems services which trees provide. Extremely little is known regarding the ecological characteristics of silvopastures being utilized, their social and economic drivers, or their agricultural productivity. Silvopasture characteristics, management, and reasons for use were documented through a purposeful sample of silvopasture practitioners in New York and New England. Results document the functional role of silvopastures on regional farms. This research also investigated the ecological and production dynamics of silvopastures in the Northeastern United States, their management, and the reasons for their use. Forest conversion to silvopasture, open pasture, and heavily thinned forests were utilized to investigate the ecological and production dynamics during the establishment phase of forest conversion to pasture. Results suggest the potential for silvopasture as a competitive management option for forestland. This dissertation establishes a baseline for future investigations into the management of silvopastures in the Northeastern United States.</p>

<p> The introduction of lake trout <i>Salvelinus namaycush</i> into Yellowstone Lake preceded the collapse of the native Yellowstone cutthroat trout <i>Oncorhynchus clarkii bouvieri</i> population. As a system with a simple fish assemblage and several long-term data sets, Yellowstone Lake provided a unique opportunity to evaluate the ecology of a native salmonid in the presence of a non-native salmonid population undergoing suppression in a large natural lake. Diet data for Yellowstone cutthroat trout and lake trout were evaluated at varying densities to determine the effects of density on diet composition. Temporal diet shifts from 1996-1999 to 2011-2013 were likely caused by limitation of prey fish for lake trout. Diets, stable isotopes, and depth-related patterns in CPUE indicated lake trout > 300 mm consumed primarily amphipods, making them trophically similar to Yellowstone cutthroat trout from during 2011-2013. A lake trout removal program was initiated during 1995 to reduce predation on Yellowstone cutthroat trout. Abundance and fishing mortality were estimated for lake trout from 1998 through 2013 and Yellowstone cutthroat trout from 1986 through 2013. Density-dependence was evaluated by examining individual growth, weight, maturity, and pre-recruit survival as a function of abundance. In addition, a simulation model was developed for the lake trout-Yellowstone cutthroat trout system to determine the probability of Yellowstone cutthroat trout abundance persisting at performance metrics given potential reductions in lake trout abundance. Estimates of Yellowstone cutthroat trout abundance varied 5-fold and lake trout abundance varied 6-fold. Yellowstone cutthroat trout weight and pre-recruit survival decreased with increasing Yellowstone cutthroat trout abundance; however, individual growth and maturity were not related to abundance. Lake trout population metrics did not vary with lake trout abundance. Simulation model results were variable because of uncertainty in lake trout pre-recruit survival. Conservative estimates for required lake trout reductions were > 97% of 2013 abundance for a > 70% probability of Yellowstone cutthroat trout persistence at the performance metrics outlined in the Native Fish Conservation Plan. Lake trout removal will likely reduce lake trout abundance and result in Yellowstone cutthroat trout recovery if the amount of fishing effort exerted in 2013 is maintained for at least 15 years.</p>

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