Impacts of invasive Australian acacias: implications for management and restoration

Abstract

Aim The biophysical impacts of invasive Australian acacias and their effects on ecosystem services are explored and used to develop a framework for improved restoration practices.Location South Africa, Portugal and Chile.Methods A conceptual model of ecosystem responses to the increasing severity (density and duration) of invasions was developed from the literature and our knowledge of how these impacts affect options for restoration. Case studies are used to identify similarities and differences between three regions severely affected by invasions of Australian acacias: Acacia dealbata in Chile, Acacia longifolia in Portugal and Acacia saligna in South Africa.Results Australian acacias have a wide range of impacts on ecosystems that increase with time and disturbance, transform ecosystems and alter and reduce ecosystem service delivery. A shared trait is the accumulation of massive seed banks, which enables them to become dominant after disturbances. Ecosystem trajectories and recovery potential suggest that there are important thresholds in ecosystem state and resilience. When these are crossed, options for restoration are radically altered; in many cases, autogenic (self-driven and self-sustaining) recovery to a pre-invasion condition is inhibited, necessitating active intervention to restore composition and function.Main conclusions The conceptual model demonstrates the degree, nature and reversibility of ecosystem degradation and identifies key actions needed to restore ecosystems to desired states. Control and restoration operations, particularly active restoration, require substantial short-to medium-term investments, which can reduce losses of biodiversity and ecosystem services, and the costs to society in the long term. Increasing restoration effectiveness will require further research into linkages between impacts and restoration. This research should involve scientists, practitioners and managers engaged in invasive plant control and restoration programmes, together with society as both the investors in, and beneficiaries of, more effective restoration.

Intensifying postfire weather and biological invasion drive species loss in a Mediterranean-type biodiversity hotspot

“…The impact was far more pronounced when viewed over the full study period, despite the near-complete eradication of woody alien species from the reserve before the 1996 survey (39), suggesting strong "legacy effects" (44) that have continued to impact diversity at our site 30 y after the removal of alien species. The dominant invasives were N-fixing Australian Acacia species that are known to have long-lasting effects on soil chemistry and to reduce indigenous seedbanks (40,41). The marginally positive response to aliens displayed by geophytes over the initial survey period may have been in response to greater N availability or increased light in the understorey after alien clearing.…”

“…The presence and density of serotinous overstorey shrub species at a site vary greatly between fires (37), and higher densities alter the composition and diversity of understorey species (36). Alien trees and shrubs from the genera Acacia and Pinus (38) are particularly problematic in Fynbos ecosystems, impacting diversity and ecosystem function by suppressing native vegetation, increasing biomass loads (and thus the intensity of fires), reducing soil moisture, and changing soil nutrient fluxes (16,(39)(40)(41). These species were introduced to our site >150 y ago to stabilize sand dunes and supplement the meager firewood provided by indigenous shrubs, but rapidly became invasive (42,43).…”

“…These species were introduced to our site >150 y ago to stabilize sand dunes and supplement the meager firewood provided by indigenous shrubs, but rapidly became invasive (42,43). Intensive clearing operations were started in the 1970s, and woody alien species were almost completely eradicated by the late 1980s (39), but we would anticipate a legacy of invasion history on diversity at our site (41,44).…”

Open-Source Processing and Analysis of Aerial Imagery Acquired with a Low-Cost Unmanned Aerial System to Support Invasive Plant Management

“…In regenerating forest invaded by A. mangium where the canopy closed in short time and biomass increased in a few years, dominance by the invasive species delayed colonization by native species and had an adverse impact on biodiversity (Le Maitre et al, 2011). Likewise, invasion by A. mangium in Mussununga formations is expected to accelerate biodiversity loss and alter plant communities.…”

“…We were able to map bare soil areas with high accuracy using simple semi-automatic classification. As mentioned before, disturbance increases opportunities for the spread of invasive plants (Lorenzo et al, 2010;Le Maitre et al, 2011) in open areas, on bare soil and other modified sites such as roadsides, trails, and degraded vegetation. These areas should, therefore, be a priority for preventative monitoring and early detection of invasive species followed by eradication or control.…”