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In the savanna woodlands of Southern Africa, locally know as miombo, carbon cycling is poorly quantified and many of the key processes remain obscure. For example, seasonal constraints on productivity and leaf display are not well understood. Also, fire is known to be a key process, with around 50% of the annual global area burned occurring in Africa, but detailed understanding of its ecological effects is lacking. Land use change and woodland degradation are changing the structure and functioning of these tropical woodlands, which cover 2.7 million km2 of Southern Africa and provide ecosystem services which support the livelihoods of over 100 million people. In this thesis I quantify the major carbon stocks of the woodlands in Nhambita Regulado, Gorongosa District in Sofala Province, Mozambique. I also examine processes that affect these stocks, including fire and clearance for agriculture. Furthermore, I quantify the seasonal cycle of leaf display, and its relationship to climate. I conducted a series of experimental burns and found that fire intensity was strongly related to rates of top-kill and root stock mortality. Top-kill rates decreased as tree diameter increased up to 10 cm DBH. After this point increased size did not affect top-kill rates, possibly because of accumulated wounds and rottenness. I then extrapolated these results to long term predictions of tree populations and carbon stocks by modelling the interactions of fire, mortality and tree growth. The model was able to successfully predict woody vegetation structure at two sites with known fire regimes, including a 50-year fire experiment in Marondera, Zimbabwe. The results show that annual fires in miombo suppress all woody vegetation. Low intensity fires every 2.5 years are required to maintain observed stem biomass in Nhambita. High intensity fires lead to high top-kill rates (12%), even among large stems. Manipulating fire intensity rather than frequency seems to be the most practical approach to limiting degradation by fire in these ecosystems. Using a three year time series of hemispherical photographs of the tree canopy, combined with satellite data, I find that tree leaf phenology is not directly related to seasonal rainfall patterns, both in Nhambita and across Southern Africa. Pre-rain green-up is the dominant phenology, from the semi arid savannas of the south of the continent to the wet miombo of the Congo basin. Wet miombo woodlands have longer periods of green-up before rain onset (mean 60 days) compared with dry miombo (37 days). Green up-dates show little interannual variability but large spatial variability. The importance of pre-rain green-up in determining how these ecosystems will respond to changing rainfall patterns is unknown, but is an important area for future study. I quantified carbon stocks in the Nhambita woodlands in the soil (69% of total carbon stocks of 111 tC ha-1), tree stems (19%) and roots (8%) as well as other smaller pools. An allometric relationship between root and stem biomass and stem diameter was developed, and used to evaluate the uncertainties in stem carbon estimation at plot and landscape scale. We find that the uncertainty (95% confidence intervals) at plot scale can be quite large (60% of the mean) but this is reduced to around 25% at landscape scale. Strategies for effective inventories of miombo woodland are presented. Using a chronosequence of abandoned farmland, we estimate that stem biomass recovers from clearance after around 30 years of abandonment. Changes in soil carbon stocks are less well understood and need further work. This thesis concludes by outlining further work needed to model the carbon cycle of these woodlands, as well as discussing the implication of pre-rain green-up for satellite observations of land cover changes and biomass mapping.

This study investigates geographic patterns of genetic variation in aspen spring phenology to understanding how tree population adapts to climatically risk environments. These finding suggest rules to guide seed transfer between regions. I use a classical common garden experiment to reveal genetic differences among populations from western Canada and Minnesota, and present a novel method to seamlessly map the heatsum required for remotely sensed green-up. Both approaches reveal two major geographic patterns: northern and high elevation aspen populations break bud earlier than sources from the boreal plains, and late budbreak is strongly associated with the driest winter and spring environments. This suggests selection pressures for late budbreak due to both frost and drought risks in early spring, and we therefore caution against transfer of seed to drought regions of the boreal plains. Although such transfers have been shown to increase plantation productivity in short-term tests, non-local planting material may be susceptible to exceptional spring droughts. / Forest Biology and Management

Graduation date: 1992

Climate change is shifting the seasonal timing of many biological events, and the possibility of non-parallel shifts in different taxa has raised concerns about phenological decoupling of interacting species. My thesis investigates interactions between climate, phenology, and pollination, using the plants and pollinators of Rocky Mountain meadows as a study system. Interannual variation in timing of snowmelt since the 1970s has been associated with changes in the assemblages of concurrently flowering species in these meadows, suggesting that plant species differ in their phenological responses to climate. Differences between plants and pollinators in responsiveness to changing climate could, in principle, cause early-flowering plants to flower too early in warm years, before pollinators are active. In fact, I found only transient evidence for pollinator deficits in one early-flowering species (Mertensia fusiformis), even in an early-snowmelt year. However, the assemblage of pollinators visiting M. fusiformis does change predictably over the season, with likely consequences for selection on floral morphology in years when pollen is limiting. Hence, early- and late-flowering populations may evolve in response to phenology of the pollinator community. Differences between plant and pollinator phenologies appear to be due to generally lower temperature thresholds for development in plants, combined with microclimate differences between the soil and the above-ground nests of some pollinators. Phenological decoupling between plants and pollinators seems possible but unlikely to be catastrophic, since many taxa possess adaptations to temporally variable environments. Nevertheless, for many species, adaptation to novel climates will entail evolutionary change, and species interactions can influence evolutionary trajectories. For species affected by increasing late-summer drought, earlier flowering may be advantageous. However, in laboratory experiments, bumble bees avoid rare, unfamiliar flower types, causing simulated plant populations to fail to adapt to changing conditions. Overall, my work emphasizes the importance of the interplay between species interactions and environmental change.

Climate change is shifting the seasonal timing of many biological events, and the possibility of non-parallel shifts in different taxa has raised concerns about phenological decoupling of interacting species. My thesis investigates interactions between climate, phenology, and pollination, using the plants and pollinators of Rocky Mountain meadows as a study system. Interannual variation in timing of snowmelt since the 1970s has been associated with changes in the assemblages of concurrently flowering species in these meadows, suggesting that plant species differ in their phenological responses to climate. Differences between plants and pollinators in responsiveness to changing climate could, in principle, cause early-flowering plants to flower too early in warm years, before pollinators are active. In fact, I found only transient evidence for pollinator deficits in one early-flowering species (Mertensia fusiformis), even in an early-snowmelt year. However, the assemblage of pollinators visiting M. fusiformis does change predictably over the season, with likely consequences for selection on floral morphology in years when pollen is limiting. Hence, early- and late-flowering populations may evolve in response to phenology of the pollinator community. Differences between plant and pollinator phenologies appear to be due to generally lower temperature thresholds for development in plants, combined with microclimate differences between the soil and the above-ground nests of some pollinators. Phenological decoupling between plants and pollinators seems possible but unlikely to be catastrophic, since many taxa possess adaptations to temporally variable environments. Nevertheless, for many species, adaptation to novel climates will entail evolutionary change, and species interactions can influence evolutionary trajectories. For species affected by increasing late-summer drought, earlier flowering may be advantageous. However, in laboratory experiments, bumble bees avoid rare, unfamiliar flower types, causing simulated plant populations to fail to adapt to changing conditions. Overall, my work emphasizes the importance of the interplay between species interactions and environmental change.

Climate change is rapidly altering natural ecosystems. Plastic and adaptive responses to climate change (i.e., range shifts and phenology) have been widely noted across taxa. However, the effects of climate change on evolutionary processes such as interspecific gene flow (hybridization) are less well known. In this study, we quantified hybridization rates in response to experimental manipulations of rainfall, an important dimension of global change. We used rain-out shelters in the field and quantified rates of hybridization between two congeners, Helianthus annuus (common sunflower) and H. petiolaris (prairie sunflower). We found that H. annuus maternal plants produced hybrid progeny more than H. petiolaris maternal plants, with a trend for decreased rates of hybridization with increased soil moisture (when rain-out shelters were absent). The relative number of open inflorescences of each species predicted hybridization rates. Thus, this study demonstrates how changing environmental conditions, specifically precipitation, could influence hybridization rates.

The mutualism between the dioecious Ficus tinctoria and its pollinators was studied at Hsitzewan, Kaohsiung. I investigated the phenology of F. tinctoria from December 2004 to May 2006. Wasps trapped in sticky boards were recorded from April 2005 to May 2006. The average diameter of receptive figs (B phase) of female F. tinctoria was significantly different from that of functional male trees (P < 0.01), but both with similar coloration. The durations of pre-receptive figs (A phase) through wasp- releasing figs (D phase) or mature figs (E phase) in F. tinctoria were slight longer in winter and spring (8.3-8.8 weeks) than in summer and autumn (6.8-7.0 weeks). The receptive figs were asynchronous both within-tree and among-trees. The receptive figs occurred in every month of 2005 and without seasonality. There were considerable overlaps (82.6%) in the receptive figs between functional male and female trees. The frequency of tender leaf phase of F. tinctoria was positively correlated with local rainfall and temperature, but the frequency of leaf falling phase was negatively correlated with them. The frequency of receptive figs of female trees was only positively correlated with rainfall, and the frequency of their interforal figs (C phase) were both negatively correlated with rainfall and temperature. Fig production of functional male F. tinctoria was not correlated with rainfall and temperature. There are five species of fig wasps, including one species of pollinator (Liporrh opalumgibbosae), one species of Sycoscapter, two species of Philotrypesis, and one species of Neosycophila. No significant difference was found in the average number of 4 species of fig wasps from D phase figs (6.3 pollinators, 8.8 Philotrypesis sp.1, 5.7 P. sp.2, and 5.7 Sycoscapter sp.1 per fig). In addition, one species of Sycophila (Eurytomidae) was also found inside figs of F. tinctoria. The coordination between D phase figs of male F. tinctoria to its B phase was iii 26.2%, which was similar to the coordination of it to B phase of female trees (29.5%). However, more pollinators arrived on male trees than that on female trees. The coordination between pollinators and B phase figs of male trees (43.0%) was higher than that of female trees (14.6%). Fig-pollinator mutualism in F. tinctoria is probably maintained by its asynchronous phenology, and aseasonal changes of the receptive figs. Seed production at female trees can be maintained by a small size of pollinator populations.

The earth surface is monitored periodically by numerous satellite sensors which have different spectral response functions, image acquisition heights, atmosphere correction schemes, overpass times, and sun/view angle geometries. Temporal and spatial variations of land surface properties, such as vegetation index, Leaf Area Index (LAI), land surface temperature, and soil moisture, have been provided by long-term time series of various remote sensing datasets. Inter-sensor translation equations are required to build long-term time series by the combination of multiple sensors from historical to advanced and new satellite datasets. In the first chapter, inter-sensor translation equations of band reflectances and two vegetation indices (e.g. Normalized Difference Vegetation Index (NDVI) and Enhanced Vegetation Index (EVI)) were derived using linear regression equations relative to Moderate Resolution Imaging Spectroradiometer (MODIS) values. The consistency and validation of inter-sensor transforms were investigated through statistical student's t-test and the root mean square error (RMSE).In the second chapter, cross-sensor extension of EVI and a 2-band EVI (without the blue band; EVI2) were investigated based on the continuity of both EVI's. Sensor specific red-blue coherencies were examined for the possibility of the EVI and EVI2 extension from MODIS sensor. The EVI continuity to MODIS was particularly problematic for the Visible Infrared Imager / Radiometer Suite (VIIRS) and the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) that have dissimilar blue bands from that of MODIS. The cross-sensor extension and compatibility of EVI2 were improved and provided the possibility to be lengthened to the Advanced Very High Resolution Radiometer (AVHRR) using its translation equation.Finally, we evaluated the use of sensor-specific EVI and NDVI data sets, using a time sequence of Hyperion images over Amazon rainforest in Tapajos National Forest, Brazil for the 2001 and 2002 dry seasons. We computed NDVI, EVI, and EVI2 with the convolution data of different global monitoring and high temporal resolution sensor systems (AVHRR, MODIS, VIIRS, SPOT-VGT, and SeaWiFS) from Hyperion, and evaluated their spectral deviations and continuity in the characterization of tropical forest phenology. Our analyses show that EVI2 maintains the desirable properties of increased sensitivity in high biomass forests across all sensor systems evaluated.

Migratory birds face the distinct challenge of travelling between widely separated and environmentally distinct areas for their breeding and non-breeding periods. They may be faced with different pressures at different points in their life cycle, and a solid understanding of the drivers of individual fitness and population demography is crucial to understanding the ecological and evolutionary trajectories of their populations. In this thesis, I combine long-term data and experimental manipulations to study migratory patterns and arrival dynamics, density dependence, and reproductive behaviour in a long-distance migratory bird, the American redstart. First, I show that non-breeding season weather is associated with redstart phenology on the breeding grounds. Greater winter rainfall corresponds to earlier arrival and egg-laying dates at both the population and individual level, indicating that individual birds may be able to adjust their phenology in response to conditions in winter. Furthermore, I demonstrate these associations independently at two breeding populations at opposite sides of the redstart breeding range and their corresponding putative non-breeding areas: greater rainfall in Jamaica and Mexico was associated with advanced redstart phenology in Ontario and Alberta, respectively. Second, I performed a manipulation experiment to delay the arrival of male redstarts to the breeding grounds. I show that delayed males suffer reduced fledging success in comparison to early-arriving males that bred early or late, but equivalent success in comparison to males that arrived and bred late. These results provide evidence against the importance of either timing or individual quality, but instead suggest that other aspects of quality, namely mate and territory quality, may be important factors driving the success of early-arriving males. Third, I examine the consequences of density dependence for reproductive success and mating behaviour in a population of redstarts for which I showed density-dependent population growth over a period of 11 years. Greater breeding density, both at an annual scale and at a local scale, was associated with reduced success and greater paternity loss. Overall, my findings contribute to a broader understanding of the selective pressures and regulatory mechanisms acting on migratory birds, from the individual up to the population level. / Thesis (Ph.D, Biology) -- Queen's University, 2012-09-25 13:17:33.172