Morgan De Dapper

Object-oriented change detection for the city of Harare, Zimbabwe

Object building and the extraction of homogeneous landscape units on which spatial statistics can be applied is useful in assessing land use and land cover change. Object-oriented processing techniques are becoming more popular compared to traditional pixel-based image analysis. A hierarchical image segmentation approach was adopted to extract the objects from multi-temporal Landsat images over Zimbabwe. The spatial arrangement of t0 and t1 objects was independent as the segmentation process was independently applied, although object change of t1 was based on t0 boundaries. We applied a Standardized, Object Oriented, Automatic Classification (SOOAC) method based on fuzzy logic. The error matrix for the TM image had an overall accuracy of 95.6% and a KIA value of 94.7%, the ETM showed slightly lower overall accuracy. Various LULC changes were identified over the 13year period per object and also per class, mainly vegetation decrease. Object-oriented change information is necessary in decision support systems and uncertainty management strategies. This approach addresses some of the major issues in object-based GIS change analysis as it is based on stable object geometry.

Competitive interaction between aspen and birch moderated by invertebrate and vertebrate herbivores and climate warming

Background: Considerable changes in vegetation structure and distribution are predicted in high latitude ecosystems as a result of amplified climate change. However, some documented plant community changes do not follow model predictions. Aim: We compared the growth of and the responses to climate variation by the thermophilic aspen (Populus tremula) and its sub-Arctic competitor mountain birch (Betula pubescens ssp. czerepanovii) over the past 100 years. Methods: Repeat photography, high-resolution vegetation transects, dendro-ecological analysis, and local climate record archives were used to study changes in vitality and distributional range of the two tree species in response to climate variability. Results: Aspen grew 45% faster and had seven times higher recruitment numbers than birch. However, no aspen stand expansion was observed, most likely because of browsing by moose (Alces alces). Birch, on the other hand, suffered from cyclic outbreaks of the autumnal moth (Epirrita autumnata). One-hundred-year-old birch trees experienced on average 9.0 years of reduced growth due to moth herbivory compared to 1.4 years for aspen. Moreover, these moth outbreaks on birch stimulated recruitment of aspen in birch stands. Conclusions: As the sub-Arctic continues to become warmer, the dynamics between aspen and birch in forest ecosystems will likely depend on the number of vertebrate browsers relative to the number of aspen recruits, while major moth outbreaks on birch may facilitate the spread of aspen by reducing competition. Our results suggest that alternating episodes of apparent species range stabilities (homeostasis) and abrupt non-linear shifts may characterise species migration patterns in this ecosystem.

Range Expansion of Thermophilic Aspen (Populus tremula L.) in the Swedish Subarctic

Abstract In subarctic Sweden, recent decadal colonization and expansion of aspen (Populus tremula L.) were recorded. Over the past 100 years, aspen became c. 16 times more abundant, mainly as a result of increased sexual regeneration. Moreover, aspen now reach tree-size (>2 m) at the alpine treeline, an ecotone that has been dominated by mountain birch (Betula pubescens ssp. czerepanovii) for at least the past 4000 years. We found that sexual regeneration in aspen probably occurred seven times or more within the last century. Whereas sexual regeneration occurred during moist years following a year with an exceptionally high June–July temperature, asexual regeneration was favored by warm and dry summers. Disturbance to the birch forest by cyclic moth population outbreaks was critical in aspen establishment in the subalpine area. At the treeline, aspen colonization was less determined by these moth outbreaks, and was mainly restricted by summer temperature. If summer warming persists, aspen spread may continue in subarctic Sweden, particularly at the treeline. However, changing disturbance regimes, future herbivore population dynamics and the responses of aspens competitors birch and pine to a changing climate may result in different outcomes.

Neolithic occupation of an artesian spring: KS043 in the Kharga Oasis, Egypt

Abstract KS043 is a stratified site associated with a complex of artesian springs. The archaeological remains, as well as a series of radiocarbon determinations, date the site to between 4800 and 4200 b.c. Our study suggests a connection between Saharan pastoralists, forced to move into oasis areas by increasing aridification, and the first Predynastic cultures of the Nile Valley. The site is the only well dated stratified settlement attributed to the Late Neolithic in the eastern Sahara that is characterized by Tasian cultural traditions.