Abandoned Pastoral Bomas as Long-Lived Fertility Hotspots in Savannas
A 2009 study by A. N. Muchiru, D. Western and R. S. Reid examined abandoned traditional pastoral settlements in the Amboseli ecosystem of southern Kenya. By comparing conditions inside former boma fences with the surrounding savanna, the researchers traced changes in herbaceous biomass, plant richness, species composition and soil nutrients across a succession extending to approximately a century.
What the study did and found
The researchers sampled plants and soils on and around abandoned bomas across a succession extending to roughly a century. “Onsite” referred to the area inside the former settlement fence, while “offsite” referred to surrounding savanna extending up to 200 metres beyond the fence. This design allowed the authors to examine how long the ecological legacy of pastoral settlement remained localized and distinct from background conditions.
Herbaceous standing biomass onsite rose during succession and reached approximately twice offsite levels within two decades. It remained elevated for about six decades before moving toward background levels later in succession. Plant species richness also increased rapidly and then stabilized on older bomas, while species composition continued to change. Soil carbon, nitrogen, magnesium and phosphorus were strongly elevated, and potassium, phosphorus and magnesium remained at about twice offsite levels for more than a century.
Why it is cited
The paper is useful as an example of how localized pastoral land use can leave ecological effects that persist far longer than the settlement itself. Former bomas did not simply return immediately to surrounding savanna conditions; instead, they developed distinctive trajectories in biomass, plant diversity, community composition and soil chemistry.
The study is especially notable for showing that different ecological variables recover at different rates. Some vegetation measures moved toward background conditions within decades, while particular soil nutrients remained strongly enriched for more than a century. This makes abandoned bomas useful examples of long-lived landscape heterogeneity created by historical land use.
The findings apply to abandoned traditional pastoral settlements sampled in the Amboseli ecosystem of southern Kenya. They demonstrate long-lasting local differences between former bomas and the surrounding savanna within that study system. The results do not establish that every pastoral settlement in every African savanna will follow the same timetable or reach the same nutrient concentrations. The study also shows that ecological recovery cannot be represented by a single endpoint. Herbaceous biomass, plant richness, species composition and individual soil nutrients followed different trajectories. The strongest long-term signal reported was persistent enrichment of potassium, phosphorus and magnesium, while other measures changed on shorter or different timescales. |
The topic today
The study illustrates a broader ecological principle: historical land use can remain embedded in present-day vegetation and soil patterns. A site that appears to be ordinary savanna may still reflect past concentrations of livestock, people and nutrients, creating small fertility islands within the wider landscape.
For interpreting savanna succession, the paper highlights the importance of combining vegetation and soil measurements rather than relying on a single indicator of recovery. Its long-term perspective also shows why past settlement patterns can matter when explaining current spatial variation in plant productivity, diversity and nutrient availability.