Integrating knowledge of ecological succession into invasive alien plant management: A case study from Portugal

Prepared by Liliana Neto Duarte, Carlos Pinto Gomes, Hélia Marchante & Elizabete Marchante

Invasive alien species are one of the major threats to biodiversity worldwide, presenting a significant risk for homogenisation of ecosystems and landscapes, with several negative impacts at ecological, economic and ecosystem services level, and consequently to human well-being.

The main goal of controlling invasive alien species is to re-establish native species and/or restore ecosystem functions. Therefore, knowledge of the ecology of invasive alien plants (IAP) and plant community succession may increase the effectiveness of IAP management by selecting native plant species that are best adapted to outcompete IAPs in a particular habitat.

Plant communities occurring on a site and replacing one another along the natural succession (under homogeneous environmental conditions) may be grouped in vegetation series. Having a high level of dependence on climate, vegetation series are used to define ecologically homogeneous geographic space (biogeographic units) and can be identified by assessing the present-day natural vegetation remnants. The name of the series follows the mature stage association (i.e., climax plant community), which represents the potential natural vegetation.

Alien plants distribution depends on several factors such as the number of propagules or time since introduction. However, environmental conditions also play a major role as they do for native species.

In this study, several native plant indicators and nine selected IAPs were surveyed in 60 1-km² sampling plots in the South of Portugal in order to 1) demonstrate how IAP distribution varies within the territory and identify which are the most invaded and invasible vegetation series, and 2) analyse the potential native plant communities and the ecological conditions that favour (or hamper) IAP to propose native species for revegetation. Vegetation series where the selected IAPs occur (or not) were identified using persistent native plant species as indicators.

We found IAP in 51 (out of 60) plots, on average with two IAPs species per plot. A total of 139 records of a given vegetation series with one (or more) IAP (either presence, 70,5%, or absence, 29,5%) were identified. Silver wattle, Acacia dealbata, was the most common IAP and showed a broad ecological amplitude by invading riverbanks, dry sclerophyll, marcescent and deciduous oak woodlands. Giant reed, Arundo donax, was the most widespread IAP, mainly associated with riparian plant communities, such as ash woodlands and willow galleries. Littoral areas were more invaded, particularly those with sand dune habitats, which are highly dynamic and exposed to disturbance and, as such, are less resistant to invasion. Psammophilous cork oak vegetation series was always invaded, and the maritime turbinate juniper endemic series was mainly invaded by golden (Acacia longifolia) and Port Jackson wattles (Acacia saligna).

The approach used in this case study is a valuable tool for selection of native plants for revegetation that are likely to function as efficient natural barriers to (re)invasion, even when plant communities are highly degraded and successional stage identification relies on plant indicators. Furthermore, knowledge about IAP ecological requirements also help practitioners to predict areas more prone to invasion and establish management priorities.

This is a plain language summary for the paper of Duarte et al. published in Applied Vegetation Science (https://doi.org/10.1111/avsc.12488).