2.1 Study area: Emaerete sub-catchment
The study site (Figure 1) is located in the Monduli Highland area, east
of the Northern Tanzanian Rift Valley, with an elevation ranging between
1746m and 2037m. The geology is from volcanic origin and the soils have
evolved to loamy clay andosols on the upper slopes, and to the typical
swelling clay vertisols in the lower topographic swales. The mean annual
rainfall (MAR) ranges from 800 mm in the lower areas to 860 mm for the
higher areas and was obtained from the global “CHELSA” dataset (Karger
et al., 2017). The area has a typical bimodal wet season, with a short
peak that occurs from November to December and a long peak between
February and May, and one long dry season from June to October (Prins &
Loth, 1988). Local and global climatic phenomena such as the El Nino
Southern Oscillation and the Indian Ocean Dipole interlink to create a
high interannual variation wherein the short rains can fail (droughts)
or connect to the long rains (wet) (Nicholson, 1996). The natural
vegetation is mostly an elevation-defined transition between savanna
bushland and afro-montane rainforest. The landscape in many areas is
characterized by severe surface denudation in open grazing land with
notable rill and gully erosion by overland flow (Figure 1b).
The communities are predominantly Maasai and have a long history of
assimilation and reciprocal influencing with other ethnic groups such as
the waArusha and waMeru. Livelihoods in these communities continue to
transition from nomadic pastoralism to sedentary agro-pastoralism driven
by factors such as population growth, social and environmental human
displacement. While traditional customs have gradually lost importance,
they still exist, sometimes assimilated within local governance
structures, or in parallel with formal governance. Much village land is
still set aside for communal grazing, however, during transition to
agro-pastoralism, large areas of land have been entrained into different
ownership processes, and used for mixed agriculture. The rights to these
lands mostly belong to the ‘original’ Maasai people although some of
these plots are also being leased to farmers from other regions in
Tanzania who pay for their tenure in crop-shares. Both processes have
resulted in a conversion of semi-natural grazing lands to cropland. The
dominant cropping system is intercropping of maize with common beans.
However, there are other crops grown in the area such as wheat and
horticultural products. These croplands areas are mostly located in the
upper slopes of the landscape, while the grazing lands are mostly
located in the lower areas and topographic swales.
<< Insert Figure 2 >>
Figure 2: Emaerete catchment (a) broad land cover and (b) topography
showing areas designated for agriculture (grey outline) where remainder
is open land utilized for common grazing. Note areas of severe gully
erosion and surface denudation.