Fire and Vegetation Dynamics in the Serengeti-Mara Region

Principal Investigator:

Jan Dempewolf

This study investigates fire dynamics and woody cover changes in the Serengeti-Mara region (SMNR) in Kenya and Tanzania, East Africa. Savanna woody cover plays a critical role for ecosystem functioning. The woodland to grassland ratio defines savanna structure and habitat characteristics for grazers, browsers, predators, and birds. Wildebeest are the dominant grazing animal in SMNR, depend on abundant grass supply and prefer open savanna habitat with lower predation risk. Woody plants are a major food source for elephants and giraffes. Lions use shrubs as cover to stalk their prey. Vegetation structure is a causal factor for bird species distribution. The balance between woody and herbaceous plants in savannas is dynamic. Woody cover in SMNR has a documented history of change over the last 120 years. Important factors for woody cover changes include fire dynamics, climate, grazing and browsing pressure.

The objective of this study is to characterize the relation between fire dynamics and woody cover changes in the SMNR region and how it varies spatially under consideration of grazing and browsing pressure by wildebeest and elephants. Methodologies are developed and automated to determine gradual woody cover changes and map burned areas between 2000 and 2005 using a time series of Moderate-Resolution Imaging Spectroradiometer (MODIS) data. The MODIS woody cover change algorithm uses MODIS 16-day composites at 500 m resolution, field data, and high resolution imagery. The methodology is based on yearly metrics and a regression tree approach. Burned areas are mapped with high accuracy using an automated algorithm based on minimum near infrared composites generated from daily MODIS imagery at 250 m resolution. Burned area index thresholds are adjusted dynamically to the spectral characteristics of each composite. Results suggest spatial variations in fire dynamics as the driving force for woody cover changes. The relevance of fire is compounded by wildebeest and zebra grazing levels affecting fire fuel load and elephant numbers which have a direct destructive impact on woody plants.