Multiple invasions exert combined magnified effects on native plants, soil nutrients and alters the plant-herbivore interaction in dry tropical forest

While ecosystems worldwide are confronted with myriad of biological invasions, our understanding of their consolidated impacts and control remains restricted to a few species only. Any such assessment and management based on single invasions can be biased, leading to unintentional spread of new invasive species and resulting in pessimism around invasive species management. Tropical countries like India, with limited resources for invasion management and a plethora of invasive species, are amongst the most vulnerable to impacts of multiple invasions. We investigated the impacts of single and co-occurring invasive plants (Lantana camara and Pogostemon benghalensis) on native plants, soil nutrients, and herbivory in Kanha Tiger Reserve - a seasonally dry tropical forest of Central India. We systematically sampled 120 plots of 10 m X 10 m area and recorded plant richness, abundance, regeneration, edaphic characteristics, and mammalian herbivory. Ordination and linear models were used to understand the effects of single and co-occurring invasions. Results indicate a compositional change in the native plant assemblage, reduced richness and abundance of native plants, increased potassium content in the soil, and increased herbivory on native plants. These effects were more pronounced with co-occurring invasive plants, and larger than other key ecological determinants, indicating towards a homogenised alternate state of an ecosystem. Synthesis. Additive impacts of multiple invasions were greater than their individual impacts on native vegetation structure, composition, soil nutrients, and herbivory. We infer potential negative feedback, where plant invasions force higher herbivory on already declining native plants thereby exhausting the sustenance of native plants. It can cause a future decline of herbivores, which are an important food resource for charismatic carnivores in these ecosystems. Mitigating the impacts of multiple invasions is thus urgently required.

Automated summary

While our understanding of the impacts and control of biological invasions remains limited, this study found that multiple invasive plant species can have additive negative effects on native vegetation structure, composition, soil nutrients, and herbivory. The presence of co-occurring invasive plants led to compositional changes in native plant assemblage, reduced richness and abundance of native plants, increased potassium content in the soil, and increased herbivory on native plants. These impacts can potentially lead to a decline in herbivores, which are important food resources for carnivores in these ecosystems.