Florian Ulm, Cristina Cruz and Cristina Máguas
Faculdade de Ciencias da Universidade de Lisboa, cE3c – Centre for Ecology, Evolution and Environmental Changes, Campo Grande, C2, 1749-016 Lisbon, Portugal
Mediterranean basin ecosystems are under increasing pressure from invasive species and especially ecosystem-engineers, such as woody legumes, are a major threat to ecosystem functioning and biodiversity, as they can profoundly alter soil nutrient cycles. As many Mediterranean soils are highly oligotrophic and nutrient limited, alterations in these cycles can be detrimental for the native vegetation, which is adapted to low nutrient input and exhibits low growth rates. On the contrary, invasive woody legumes, such as Acacia spp., which are highly invasive in Portuguese dunes and adjacent agricultural landscapes, grow rapidly, increase soil organic matter (SOM) levels, change soil nutrient cycles and create monospecific stands that fully replace the native vegetation.
However, the alterations have also been shown to be initially beneficial for nearby plants by increasing available N, SOM and soil microbial activities in general. This leads to increased foliar N and plant growth rates in nearby native plants and is a positive effect that is juxtaposed with the negative consequences of competition for other nutrients. Not only the native vegetation, but also agricultural fields, are under pressure from invasion and exhibit similarly low SOM levels. This creates a vicious cycle, as one of the consequences of low SOM is increased nutrient leaching, benefitting Acacia plants in adjacent strips of unused land.
Here, we propose a potential win-win situation in which we present the feasibility of using Acacia derived biomass as soil amendments in an agricultural setting, thus making use of its extraordinary biomass accumulation capacity. We close local nutrient cycles by modelling existing biomass using field based and remote sensing technology, compost the biomass to remove the seed bank, and successfully use the resulting amendment for food production. Also, we show how this applied work can help to deepen the understanding of invasion impacts on soil level.