Gully mitigation and rehabilitation measures have varying effects on soil macrofauna abundance and diversity in semi-arid lands

Abstract

One of the most features of land degradation is soil erosion, which at its extreme, causes formation of gullies. Nonetheless, there is limited understanding on how such gullies, their management or rehabilitation measures inuence soil macrofauna, despite being a critical component of soil ecosystems. Thus, this study evaluated the inuence of gully erosion mitigation and rehabilitation measures on soil macrofauna abundance, diversity and species richness in semi-arid lands with severe degradation and where restoration efforts are being put in place. Soil macrofauna were sampled across two categories of lands under mitigation (terracing) and rehabilitation (sand-damming) efforts in croplands and pasturelands. These were compared with lands where no mitigation or rehabilitative measures were taken up. Therefore, the combinations were as follows: (i) terraced croplands, (ii) unterraced croplands, (iii) terraced pasturelands, (iv) unterraced pasturelands, (v) sand dams, and (vi) degraded lands. Soil samples were also collected in these lands for chemical analysis. Results showed degraded lands to be characterized by low organic C, available P and total N (less than 9.9 g kg−1, 4.7 mg kg−1 and 2.8 g kg−1, respectively) indicative of chemical degradation. Land degradation signicantly reduced total earthworm abundance by more than 80 % when compared with pastureland and croplands. Specic genera were also affected negatively, with abundance of Lumbricus sp. reducing by up to 6 times in degraded lands compared with terraced croplands which had 65 individuals m−2, and by more than 9 times compared with that of terraced pasturelands that had 97 individuals m−2. Beetles also showed similar differences to that of earthworms, with greater abundance in pasturelands than in degraded lands. On the contrary, termites were more abundant in the degraded lands, with an average of 306 individuals m−2 which was more than four times the abundance reported in sand dams and close to 50 % more than that reported in pasturelands. Terracing and sand-damming increased soil macrofauna diversity by more than 21 %, to more than 1.3 units compared with that of degraded lands with 0.99 units. In summary, our study shows that gully mitigation and rehabilitation measures positively affects the most sensitive soil macrofauna groups (earthworms and beetles), which are often used as bioindicators of soil health. Thus, installation of these measures can be a starting point towards restoration and increasing the resilience of these fragile ecosystems