Current and potential distribution for Acacia Mill. species (Fabaceae) on Madeira Island and impacts on plant diversity after invasion

Abstract

The most common species of Acacia Miller on Madeira Island were introduced during the 19th and 20th century, usually as ornamental or on afforestation processes, and became invaders. This article aims to i) assess current distribution of Acacia’s species at Madeira Island, ii) evaluate the impacts on plant diversity after invasion, comparing phytosociological relevées from Acacia communities to native climax communities; iii) model their potential distribution, supported on species distribution modelling, based on a correlative approach; and iv) confirm the invasiveness of Acacia mearnsii, assessing the historical evolution using RLPT (Repeat Landscape Photography Technique). Data collection for current distribution was based on field survey, and guided by a systematic and stratified sampling approach, set to ensure that the entire environmental gradient of the island was sampled. As results, the communities of Acacia are characterized by very low species diversity, are usually monospecific at the tree layer, and present a scarce abundance of native and endemic taxa. In terms of potential distribution, just the higher altitudes of the island are predicted as unsuitable to A. melanoxylon and A. mearnsii. But some precaution must be taken on reading such results, once current species’ absence may not be connected to ecological determinants, but related to its recent introduction. Besides, the landscape historical evolution assessment puts on evidence the invasiveness of Acacia mearnsii, mainly because of its current presence on areas were deliberate introduction is not plausible. According to the results, namely the extensive suitable areas and extremely poor communities in terms of plant diversity, the species under focus can be considered as very problematic invaders.

https://doi.org/10.14195/0871-1623_35_6