The effect of shortening fallow length on recovery of plant species richness, composition and growth in shifting cultivation landscapes of Kilosa district, Tanzania

Journal article

There is insufficient knowledge on the effects of shifting cultivation on vegetation change, especially in situations of land use intensification. This study investigated the effects of shortening fallow length on recovery of small (Dbh < 5 cm) and big (Dbh ≥ 5 cm) plant species richness, composition and height growth in a dry Miombo woodland in East Central Tanzania. Vegetation sampling was conducted on 40 (10 m x10 m) plots and 80 (5 m x 5 m) sub- plots from adjacent sites under fallow for 3, 5, 7 and 15 years and a control secondary forest. Results showed that shortening fallow length to not less than 7 years did not have a significant negative effect on recovery of plant species richness and height growth for both small and big sized plant species. However, there was a remarkable shift in composition of dominant species when fallow length was less than 15 years. Results showed that big size Miombo woodland defining species such as Brachystegia bussei, B. boehmii, and B. spiciformis were deprived in fallows younger than 15 years but dominant in secondary forest. Non-Miombo woodland defining species such as Cassia burtii and Dombeya shumpangae were instead dominant in younger fallows. These results imply that if the fallow length is shortened to 3 years as required by Village Land Use plans in Kilosa District, the sustainability of the shifting cultivation systems will be threatened, affecting ecosystems services offered by landscapes under shifting cultivation. It is therefore recommended that fallow length be prolonged to at least 7 years and that communities are encouraged to retain some of the Miombo woodland defining species in the fields under cultivation.