During the last few decades Central Asia has experienced widespread changes in land cover and land use following the socio-economic and institutional transformations of the region catalyzed by the USSR collapse in 1991. The decade-long drought events and steadily increasing temperature regimes in the region came on top of these institutional transformations, affecting the long term and landscape scale vegetation responses. This research is based on the need to better understand the potential ecological and policy implications of climate variation and land use practices in the contexts of landscape-scale changes dynamics and variability patterns of land surface phenology responses in Central Asia. The land surface phenology responses - the spatio-temporal dynamics of terrestrial vegetation derived from the remotely sensed data - provide measurements linked to the timing of vegetation growth cycles (e.g., start of growing season) and total vegetation productivity over the growing season, which are used as a proxy for the assessment of effects of variations in environmental settings. Local and regional scale assessment of the before and after the USSR collapse vegetation response patterns in the natural and agricultural systems of the Central Asian drylands was conducted to characterize newly emerging links (since 1991) between coupled human and natural systems, e.g., socio-economic and policy drivers of altered land and water use and distribution patterns. Spatio-temporal patterns of bioclimatic responses were examined to determine how phenology is associated with temperature and precipitation in different land use types, including rainfed and irrigated agricultural types. Phenological models were developed to examine relationship between environmental drivers and effect of their altitudinal and latitudinal gradients on the broad-scale vegetation response patterns in non-cropland ecosystems of the desert, steppe, and mountainous regional landscapes of Central Asia.The study results demonstrated that the satellite derived measurements of temporal cycles of vegetation greenness and productivity data was a valuable bioclimatic integrator of climatic and land use variation in Central Asia. The synthesis of broad-scale phenological changes in Central Asia showed that linkages of natural and human systems vary across space and time comprising complex and tightly integrated patterns and processes that are not evident when studied separately.

Thesis (M. Environmental Science)--North-West University, Potchefstroom Campus, 2008.

Pollinator sharing in mixed species communities is expected to significantly contribute to mating patterns in contemporary populations but may also affect the evolutionary trajectory of traits associated with plant mating. In this thesis, I considered how the spring environment and pollinator sharing may contribute to the widespread convergence in traits among spring flowering species using comparative biology. The proposed correlation between a spring flowering phenology and white or light floral colour, fleshy fruits, woody growth forms and understory occupation is confirmed. In addition, I examined the effects of pollinator responses to community and population traits to determine the relative importance of inter- and intraspecific interactions in pollinator mediated reproductive success of a spring flowering species, Trillium grandiflorum. In this study, the reproductive success of T. grandiflorum was pollen limited. However, the magnitude of pollen limitation was influenced only by intraspecific density and varied independently of community diversity. The results of this thesis contribute significantly to our understanding of pollinator-mediated interactions in spring flowering communities but also highlight future avenues of investigation.

Thesis (M. Environmental Science)--North-West University, Potchefstroom Campus, 2008.

The definitive version is available at www.blackwell-synergy.com

Thesis (M.S.)--Oregon State University, 1988. / Typescript (photocopy). Includes bibliographical references (leaves 69-74). Also available on the World Wide Web.

Diss. (sammanfattning) Stockholm : Univ., 2005. / Härtill 4 uppsatser.

Thesis (M.A.)--West Virginia University, 1998. / Title from document title page. Document formatted into pages; contains viii, 51 p. : col. ill., col. map. Vita. Includes abstract. Includes bibliographical references (p. 32-34).

The timing of biological events in autumn, or autumn phenology, is an important factor in many ecosystem processes. Leaf senescence terminates the growing season, fruiting is important for seed dispersal and frugivorous wildlife, bird migration concludes the breeding season and is a high-mortality event, and insect diapause ends the active season for insects. Climate change and the spread of invasive species have the potential to shift autumn events and ecological processes. However, autumn has been neglected in the phenology literature, and there are many gaps in our knowledge of basic phenological patterns in this season, as well as how they are affected by anthropogenic changes. To address these gaps, I first synthesized the literature on how climate change affects autumn phenology. I found that shifts in autumn phenology can alter reproductive capacities, exacerbate invasions, increase disease transmission rates, reshuffle enemy-prey dynamics, and alter interactions between species. With a focus on autumn interactions between birds and fleshy-fruited plants, my colleagues and I then observed patterns of fruit phenology, using herbarium specimens of 55 species collected across New England, and over 400 species in the living collections of 5 international botanical gardens. Last, I monitored fleshy fruit phenology and abundance at Manomet, a migratory stopover site in coastal Massachusetts, and compared those patterns to seeds identified from landbird fecal samples collected across the autumn season. I found that the sequence of fruiting is moderately consistent from year to year and place to place, and has a significant phylogenetic signal. In wild plants, invasive species fruit, on average, nearly one month later than native species. Considering many landbirds are migrating through New England later over time and in warm years, this suggests birds are increasingly likely to encounter invasive fruits during late-autumn migration. However, bird diets do not reflect the increased availability of invasive fruits in late-autumn; rather, birds show a preference for native fleshy fruits throughout the autumn season. These findings add to our knowledge of how climate change and species invasions affect autumn synchrony, and highlight the importance of native, rather than invasive, fruits as a food source for migratory landbirds. / 2019-11-07T00:00:00Z

Phenological events in temperate forests, such as bud burst and senescence, exert strong control over seasonal fluxes of water, energy and carbon. The timing of these transitions is influenced primarily by air temperature and photoperiod, although the exact nature and magnitude of these controls is poorly understood. In this dissertation, I use in situ and remotely sensed observations of phenology in combination with surface meteorological data and measurements of biosphere-atmosphere carbon exchanges to improve understanding and develop models of canopy phenology in temperate forest ecosystems. In the first element of this research I use surface air temperatures and eddy covariance measurements of carbon dioxide fluxes to evaluate and refine widely used approaches for predicting the onset of photosynthesis in spring that account for geographic variation in thermal and photoperiod constraints on phenology. Results from this analysis show that the refined models predict the onset of spring photosynthetic activity with significantly higher accuracy than existing models. A key challenge in developing and testing these models, however, is lack of adequate data sets that characterize phenology over large areas at multi-decadal time scales. To address this need, I develop a new method for estimating long-term average and interannual dynamics in the phenology of temperate forests using time series of Landsat TM/ETM+ images. Results show that estimated spring and autumn transition dates agree closely with in-situ measurements and that Landsat-derived estimates for the start and end of the growing season in Southern New England varied by as much as 4 weeks over the 30-year record of Landsat images. In the final element of this dissertation, I use meteorological data, species composition maps, satellite remote sensing, and ground observations to develop models of springtime leaf onset in temperate deciduous forests that account for geographic differences in how forest communities respond to springtime climate forcing. Results demonstrate important differences in cumulative heating requirements and photoperiod cues among forest types and that regional differences in species composition explain substantial geographic variation in springtime phenology of temperate forests. Together, the results from this dissertation provide an improved basis for observing and modeling springtime phenology in temperate forests.