• Energy Research

Restoration of degraded drylands is urgently needed to mitigate climate change, reverse desertification and secure livelihoods for the two billion people who live in these areas. Bold global targets have been set for dryland restoration to restore millions of hectares of degraded land. These targets have been questioned as overly ambitious, but without a global evaluation of successes and failures it is impossible to gauge feasibility. Here we examine restoration seeding outcomes across 174 sites on six continents, encompassing 594,065 observations of 671 plant species. Our findings suggest reasons for optimism. Seeding had a positive impact on species presence: in almost a third of all treatments, 100% of species seeded were growing at first monitoring. However, dryland restoration is risky: 17% of projects failed, with no establishment of any seeded species, and consistent declines were found in seeded species as projects matured. Across projects, higher seeding rates and larger seed sizes resulted in a greater probability of recruitment, with further influences on species success including site aridity, taxonomic identity and species life form. Our findings suggest that investigations examining these predictive factors will yield more effective and informed restoration decision-making.

Nitrogen enrichment may play a role in successful invasion of indigenous South African mediterranean shrublands by alien invasive annual grasses. To test the hypothesis that an increase in nitrogen would result in a greater increase in biomass for an alien annual grass than for various indigenous plant functional groups, we conducted a field study in Western Cape Renosterveld shrubland fragments, surrounded by wheat or vinyards, to assess alien grass abundance in relation to soil nitrogen availability. Significant decreases in invasive annual grass Avena fatua cover and soil nitrogen were observed from the edges to the interior of Renosterveld habitat fragments and there was a significant positive relationship between Avena fatua cover and soil nitrogen. In addition, Avena fatua was grown in competition with three indigenous species of different functional types, an annual forb (Dimorphotheca pluvialis), a geophyte (Oxalis purpurea) and an indigenous perennial grass (Tribolium uniolae) at three concentrations of soil nitrogen in a pot experiment. Results revealed that the alien grass Avena fatua had significant increases in biomass when nitrogen was added, whereas the indigenous species did not. Alien grass competition significantly influenced performance of the annual forb and the indigenous grass but did not affect the geophyte. Results suggest the prioritization of hierarchical management options for the different functional groups in Renosterveld in response to invasive grasses. Nutrient enrichment through run off must be restricted to conserve remnant Renosterveld fragments.