The expansion of invasive acacias has been consolidated as a serious threat to the Atlantic forests of the Iberian Peninsula. A study by teams from the Universities of Vigo and Coimbra, led by researcher Raquel Juan Ovejero, provides recent evidence that raises the level of concern due to its ecological scope.
The analysis, carried out in the Serra da Lousã (central Portugal), explores a highly fragmented forest landscape where introduced conifers, oak groves, chestnut groves and Mediterranean scrub coexist. There the effect of acacia dealbata (mimosa) and acacia melanoxylon (black locust) on vegetation, soil chemistry and litter, as well as on understory fauna, with a special focus on springtails, key invertebrates for nutrient recycling.
Ecological impact and ecosystem changes
When the coverage of these exotic species increases, the abundance of herbaceous plants is falling and the floral richness is reduced, a trend that leads to significant biodiversity losses. This is not a one-off effect, but rather a consistent pattern at the stand level.
The study also identifies changes in the quality of the soil and litter: a lower C/N ratio in the foliage and an increase in organic carbon, variables that alter nutrient availability and decomposition rates. These biochemical changes reconfigure essential processes in the functioning of the ecosystem.
The effects do not remain in the plants. edaphic fauna, and springtails in particular, respond unevenly to these disturbances, revealing subtle but significant imbalances in soil dynamics. Different responses were observed between functional groups, indicating cascading impacts on the underground food web.
The invasion advances driven by traits that give advantage to the Australian acacias: fix nitrogen, form dense masses and displace native vegetation. Added to this are anthropogenic factors such as rural abandonment and fragmentation, which exacerbates the situation. Portugal has the largest number of invasive acacias in the Mediterranean, and Galicia is following a similar trend.
Management, monitoring and restoration
The authors of the work agree: act early Working on small areas is more effective, less costly, and reduces environmental risks. Stopping the spread before large masses consolidate makes a difference in results and budget.
- Elimination manual or mechanical of seedlings and incipient stands.
- Ringing or debarking of specimens to exhaust reserves and avoid regrowth.
- Herbicide injection in isolated trees when other techniques are not viable.
- Basal cut in large masses, always combined with complementary treatments.
For control to be effective, it is recommended repeated cuts before regrowth exceeds approximately 1 meter, targeted application of herbicide to the regrowth when feasible and direct chemical treatment of the stump in those scenarios where its use is justified.
In all cases it is essential to have a continued monitoring: both A. dealbata and A. melanoxylon possess persistent seed banks and show a great capacity to regrow after being cut or even after fire. Without sustained control over time, the risk of reinvasion remains high.
As a complement, the restoration of native habitats It promotes ecosystem recovery and helps stabilize local plant communities, reducing the likelihood of acacia re-entry. Strengthening the native canopy and closing gaps in the landscape improves the resilience of forests and shrublands.
The evidence gathered by the Vigo and Coimbra team, led by Raquel Juan Ovejero, reinforces a clear message: The invasion of acacias is not a minor problem and requires early intervention, adaptive control, and restoration. Understanding changes in understory vegetation, soil, and fauna allows for more precise and effective management decisions. Galicia, Portugal and other areas with increasing risk.