Colin Hoag
A transdisciplinary anthropologist and ecologist researching the histories of landscapes. I just published a book about water called, _The Fluvial Imagination: On Lesotho's Water-Export Economy_ (UC Press: https://www.ucpress.edu/book/9780520386341/the-fluvial-imagination). I'm now working on two new projects. One is about Sylvia Plath and plant conservatories. The other is about the biogeography of the cosmopolitan plant family, Asteraceae.
less
Related Authors
InterestsView All (33)
Uploads
Papers by Colin Hoag
Location: Motšerimeli Valley, Mokhotlong District, Lesotho
Methods: We created a geographic information system for a ~12km2 study area located in the upland cattle-post areas of the Lesotho highlands. Using a digital elevation model and knowledge of livestock movements, we modeled livestock grazing intensity for the study area based on the “piosphere” concept, which states that intensity diminishes with distance from heavily grazed sites such as water points. We used a point-intercept method to record vegetation in randomly generated plots on a 5m2 quadrat with a 0.5-m grid. At each plot, we measured soil organic matter, soil moisture, soil nutrients, soil depth, elevation, and slope. We then used regression to determine which variables explained variation in shrub density.
Results: Our analysis suggests that grazing intensity and soil resources are determinant of shrub density. Our model found that grazing intensity, soil moisture, and soil nutrients had significant explanatory power for shrub density, with grazing intensity and soil moisture explaining most variation. Assuming a linear response to changes in grazing regimes, our model results predict a 13% increase in shrub cover with a doubling of grazing intensity. With a halving of grazing intensity, shrub cover is predicted eventually to decrease by 4.5%.
Conclusions: In mesic grasslands with high interannual rainfall variability, control of livestock grazing intensity is a useful management tool for promoting grass dominance in pastures. However, shrub density is also determined by soil resources, suggesting that management decisions based on livestock numbers in isolation will not be likely to reverse trends of shrub encroachment and promote the productivity of grasses except where soil conditions permit it.
Theses by Colin Hoag
My dissertation, titled "Stability and Change in African Environments: An Historical Ecology of Rangelands in Lesotho" uses methods and theory from plant ecology, remote sensing, history, and anthropology to investigate environmental dynamics associated with livestock production in the Southern African country of Lesotho. Specifically, it describes land cover change by assessing historical records (oral histories, missionary and colonial accounts, and herbarium specimens) and by time-series classification of remotely sensed multispectral satellite images. In addition, it analyzes data produced through vegetation sampling in the highlands to examine the extent to which livestock grazing pressure is determinant of land cover, with a particular focus on shrub encroachment. Finally, in a review of literature on African environmental change from the Pleistocene to the Anthropocene, it situates the contemporary landscape dynamics of Lesotho in a continental and deep historical context.
Location: Motšerimeli Valley, Mokhotlong District, Lesotho
Methods: We created a geographic information system for a ~12km2 study area located in the upland cattle-post areas of the Lesotho highlands. Using a digital elevation model and knowledge of livestock movements, we modeled livestock grazing intensity for the study area based on the “piosphere” concept, which states that intensity diminishes with distance from heavily grazed sites such as water points. We used a point-intercept method to record vegetation in randomly generated plots on a 5m2 quadrat with a 0.5-m grid. At each plot, we measured soil organic matter, soil moisture, soil nutrients, soil depth, elevation, and slope. We then used regression to determine which variables explained variation in shrub density.
Results: Our analysis suggests that grazing intensity and soil resources are determinant of shrub density. Our model found that grazing intensity, soil moisture, and soil nutrients had significant explanatory power for shrub density, with grazing intensity and soil moisture explaining most variation. Assuming a linear response to changes in grazing regimes, our model results predict a 13% increase in shrub cover with a doubling of grazing intensity. With a halving of grazing intensity, shrub cover is predicted eventually to decrease by 4.5%.
Conclusions: In mesic grasslands with high interannual rainfall variability, control of livestock grazing intensity is a useful management tool for promoting grass dominance in pastures. However, shrub density is also determined by soil resources, suggesting that management decisions based on livestock numbers in isolation will not be likely to reverse trends of shrub encroachment and promote the productivity of grasses except where soil conditions permit it.
My dissertation, titled "Stability and Change in African Environments: An Historical Ecology of Rangelands in Lesotho" uses methods and theory from plant ecology, remote sensing, history, and anthropology to investigate environmental dynamics associated with livestock production in the Southern African country of Lesotho. Specifically, it describes land cover change by assessing historical records (oral histories, missionary and colonial accounts, and herbarium specimens) and by time-series classification of remotely sensed multispectral satellite images. In addition, it analyzes data produced through vegetation sampling in the highlands to examine the extent to which livestock grazing pressure is determinant of land cover, with a particular focus on shrub encroachment. Finally, in a review of literature on African environmental change from the Pleistocene to the Anthropocene, it situates the contemporary landscape dynamics of Lesotho in a continental and deep historical context.