Removal or utilization? Testing alternative approaches to the management of an invasive woody legume in an arid Indian grassland

Abstract

Woody plant encroachment is a pervasive global driver impacting grassland structure and functioning, and we know very little about efficacies of management techniques for restoring woody plant-encroached tropical grasslands. In the Banni grasslands of India, which are extensively encroached by an invasive woody legume, Prosopis juliflora, we test the efficacies of two Prosopis management methods-mechanical removal and lopping-to restore native grasslands. Across eight sites in the Banni, using a randomized block design, we monitored herbaceous plant recovery in the two Prosopis management treatments, and an unmanipulated control for 4 years. We also sampled four reference grasslands. We found native herbaceous plant richness and cover to be threefold (mean = 6 species) and sixfold (mean = 18% cover) higher, respectively, in the mechanical-removal treatment compared to the control (mean richness = 2 species, cover = 3%), but found no significant differences between the lopping treatment (mean richness = 5 species, cover = 11%) and the control. While mechanical-removal increased plant diversity, neither management treatment changed the species composition, and both of these treatments were still missing perennial grasses that dominate the reference grasslands. Our data highlight the efficacy of mechanical removal over lopping in restoring native grasslands. However, mechanically removing Prosopis is costly, especially at larger scales. Apart from its detrimental impact on grasslands, Prosopis also has benefits varying with stakeholder groups, and its removal involves complex trade-offs. Until we fully understand the trade-offs involved, it may therefore be better to manage this social-ecological landscape as a mosaic of restored grassland and Prosopis-invaded patches.

Grassland conservation and restoration in India: a governance crisis

“…1). These landscapes are spatially distributed through the high-altitude grasslands in the Himalayas and Western Ghats (Arasumani et al 2018), to the semiarid and arid grasslands of the Thar Desert (Kher & Dutta 2021), from the floodplain grasslands of Indian Himalaya (Lahiri et al 2021) to the grasslands in peninsular India (Nerlekar et al 2022). Recent evidence suggests that many of India's so-called forests are in fact savannas (areas of mixed trees and C4 grasses "defined by fire tolerance and shade intolerance" with trees; Ratnam et al 2011, p. 653).…”

“…Many other programs—indirectly related to restoration goals—also contribute to the greening efforts. These include plantations for biofuel energy ( Jatrofa plantations) or plantations of Prosopis juliflora to tackle salt ingress and desertification in the grasslands of Banni (Gujarat) (which now occupy 50% of the total grasslands; Nerlekar et al 2022). Irrigation projects, such as the Indira Gandhi Canal, have also been pivotal in their efforts to “green” the deserts and scrublands of India, especially in the state of Rajasthan where policies aim to combat desertification, alleviate poverty, improve agricultural yield, and protect animal wealth.…”

“…NGOs and research institutions are also making efforts toward the scientific restoration of grasslands. Removal of invasive species is at the forefront of such activities, with examples from grasslands of Banni (Nerlekar et al 2022), and Shola grasslands of the Nilgiri hills (ERA n.d.; NCF & VCT 2006), wet grasslands of Manas Tiger Reserve, Assam (Sinha et al 2022). Grasslands outside PAs are also maintained by local or nomadic communities who depend on them mainly for pastoralism, grazing, grass collection for housing material, farming, and other livelihood activities.…”

“…Similarly, grassland habitats bear the brunt of neglect and ill-informed afforestation activities in Argentina Chaco grasslands (Grau et al 2015), and Brazilian Cerrado (Overbeck et al 2015). Indian grasslands harbor globally significant endemic biodiversity (Sankaran & Ratnam 2013;Nerlekar et al 2022) and carbon storage (Dad & Ahmad 2022). In some cases, BAD promotes planting trees in grasslands and savannas causing increased incidence(s) of megafires (Buisson et al 2019) and a decrease in long-term carbon storage (Hurteau et al 2008;Dass et al 2018).…”

Combining socioeconomic and biophysical data to identify people-centric restoration opportunities

“…While it may be simpler to facilitate agroforestry among individual land holders with clear land titles; restoring degraded common lands may facilitate broader benefits, particularly among the poorest people who often don't own land or have a strong culture of common (e.g., pastoralist communities in Gujarat and Rajasthan). However, restoration of the commons can be complex when the source of degradation (e.g., an invasive species), becomes a source of livelihood for a section of the local community 18 .…”