Biochar Rescues Native Trees in the Biodiversity Hotspot of Mauritius

Background/Question/Methods

Mauritius is part of the globally important Mascarene biodiversity hotspot, where the endemic flora is most threatened by the invasion of strawberry guava. Current efforts to control the spread of invasive species are insufficient. Strawberry guava has allelopathic effects that contribute to its success in native plant communities. Biochar (pyrolyzed biomass) can sorb allelochemicals produced by invasive plants such as strawberry guava, potentially reducing their inhibitory effects on native species.In this study, we ask how strawberry guava removal and biochar additions affect the performance of native trees and the regeneration of strawberry guava. We answer these questions by conducting a 30-month field experiment in areas invaded by strawberry guava within Mauritius’ largest national park. Biochar was locally produced from readily available coconut husks. We measured the growth and survivorship of native trees, strawberry guava regeneration and overall tree species diversity in plots subjected to four treatments: non-weeded, weeded, weeded + 25 t/ha biochar, and weeded + 50 t/ha biochar. We estimated total aboveground plant biomass using diameter2 x height as a proxy. We used structural equation modelling with the R package piecewiseSEM to examine drivers of native tree growth and survivorship, strawberry guava density, and tree species diversity.

Results/Conclusions

Strawberry guava strongly suppressed the growth and survivorship of native trees after 6 months and 30 months since establishment. Strawberry guava removal had a positive effect on native tree survivorship but no effect on tree growth. Biochar additions significantly alleviated the negative effects of strawberry guava on native tree growth, survivorship and species diversity, while suppressing strawberry guava regeneration, consistent with growth-promoting properties and sorption of allelochemicals produced by strawberry guava.We conclude that biochars, including “sustainable biochars” produced from local sources of biomass using low-tech pyrolysis systems, have considerable potential to reduce the inhibitory effects of allelopathic invaders and promote the regeneration of native plant species in tropical island ecosystems. Biochar can not only be applied to large areas of forests due to the low cost of production, but it can also reduce the frequency of weeding by suppressing the regeneration of strawberry guava. In Mauritius, weeded strawberry guava stems are an obvious feedstock option, although further research is needed to test the effects of strawberry guava biochar.