Quantifying invasion degree by alien plants species in Reunion Island

Abstract

The largest area of intact vegetation in the Mascarene's archipelago is found on Reunion Island, but the remaining natural areas are under threats. Biological invasions are one of the main threats to biodiversity loss on this island and globally worldwide. This study aimed to quantify invasion degree by alien plants species in Reunion Island. This work was possible thanks to a large partnership between researchers and managers. All existing spatial data on invasion pattern were combined and completed by expert knowledge to develop the first 250 x 250 m map of invasion degree at the island scale. To fill the gaps where no field survey data or expert knowledge was available, we used a Random Forest model using nine climatic, landscape and anthropogenic variables. This model also provides a preliminary assessment of drivers of invasion at Reunion Island. Results showed that 85% of the extant native vegetation was invaded in different proportions; 38% are slightly invaded, 26% moderately invaded and 22% very heavily invaded. Despite the high levels of invasion in some places, more than 50% of the extant vegetation is not invaded or slightly invaded. Most of the invaded areas are located in the lowland and in the leeward coast although alien plants invade all types of vegetation from the coast to the top of the island. These results highlight a clear increase in the distribution of alien species over time. This study constitutes a key first step for about the ongoing prioritisation of management interventions on Reunion Island.

Here be dragons: important spatial uncertainty driven by climate data in forecasted distribution of an endangered insular reptile

“…Other introduced species may also affect P. borbonica through predation and/or habitat alterations, including other reptiles ( Agama agama , Calotes versicolor , Furcifer pardalis ), rodents ( Rattus rattus , Mus musculus ), ants ( Solenopsis geminata ), birds ( Pycnonotus jocosus, Acridotheres tristis ) and plants ( Lantana camara ). The rate of invasion is increasing on Reunion Island (Fenouillas et al., 2021). Further studies will need to account for biotic interactions to better understand the key drivers of the distribution of P. borbonica and refine forecasted predictions.…”

“…In our study, we generate a set of SDMs for the two subspecies of the Reunion Island day gecko, Phelsuma borbonica borbonica and P. borbonica mater (subsequently referred to as P. borbonica ), quantify the sources of uncertainty related to the methods and the data and test potential differences in uncertainty assessments between two different approaches. Reunion Island is located in the western Indian Ocean and has faced a number of alterations over the last century related to agricultural practices (mostly sugarcane cultivation) and invasive species (Strasberg et al., 2005; Dubos, 2013; Fenouillas et al., 2021; Irl et al., 2021). Its herpetofauna has already been strongly modified after multiple local extinctions events and the arrival of allochthonous species (Cheke, 1987; Cheke & Hume, 2010; Sanchez & Probst, 2016).…”

High phosphorus availability and low light intensity resist the invasiveness of alien plant Chromolaena odorata on tropical coral islands

“…Biological invasion results in severe socioeconomic and environmental damage worldwide (Vilà et al 2011; Rani et al 2020). Despite being far from continental ecosystems and despite having clear oceanic boundaries, island ecosystems are still damaged by invasive plant species (Fenouillas et al 2021).…”

Warming and elevated nitrogen deposition accelerate the invasion process of Solidago canadensis L.

“…Invasion degree is a static term, referring to the status of invasion, which can be obtained by measuring the extent to which a community has already been invaded. This degree can be expressed as different numbers of exotic species or different ratios of invasive to native plants, for indicating the fractions of invaded species richness and biomass at the population or community level (Fenouillas et al 2021). However, existing studies of plant invasion have merely investigated three stages of invasion: (1) monoculture of a native species (i.e., no invasion); (2) native and invasive plants mixed in the habitat (usually at equal proportions); as well as (3) monoculture of an invasive species (i.e., invader monoculture) (Lazzaro et al 2014;Ren et al 2020a).…”

“…According to several recent studies, the effects of the invaders with different invasion degrees on plant taxonomic diversity and their performance traits vis-à-vis native species together plays an important role in the mechanisms of successful plant invasion (Fenouillas et al 2021;Wang et al 2019). Yet, few studies have linked the process of plant invasion to environmental change.…”