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

Abstract

There is insufficient knowledge on theeffects of shifting cultivation on vegetationchange, especially in situations of land useintensification. This study investigated theeffects of shortening fallow length onrecovery of small (Dbh < 5 cm) and big(Dbh ≥ 5 cm) plant species richness,composition and height growth in a dryMiombo woodland in East Central Tanzania.Vegetation sampling was conducted on 40(10 m x10 m) plots and 80 (5 m x 5 m) subplotsfrom adjacent sites under fallow for 3,5, 7 and 15 years and a control secondaryforest. Results showed that shorteningfallow length to not less than 7 years did nothave a significant negative effect onrecovery of plant species richness and heightgrowth for both small and big sized plantspecies. However, there was a remarkableshift in composition of dominant specieswhen fallow length was less than 15 years.Results showed that big size Miombowoodland defining species such asBrachystegia bussei, B. boehmii, and B.spiciformis were deprived in fallowsyounger than 15 years but dominant insecondary forest. Non-Miombo woodlanddefining species such as Cassia burtii andDombeya shumpangae were insteaddominant in younger fallows. These resultsimply that if the fallow length is shortenedto 3 years as required by Village Land Useplans in Kilosa District, the sustainability ofthe shifting cultivation systems will bethreatened, affecting ecosystems servicesoffered by landscapes under shiftingcultivation. It is therefore recommended thatfallow length be prolonged to at least 7 yearsand that communities are encouraged toretain some of the Miombo woodlanddefining species in the fields undercultivation.