Biological invasions are a major driver of global change and cause deleterious impacts to socio-economies, environment and biodiversity. Woody plants are among the most invasive species and are increasing in importance worldwide. Invasive trees have a great influence on the environmental conditions due to their dominance, long life and impact on abiotic factors such as light regime, litter decomposition and water availability. Some trees are thereby referred to as transformers, namely those invasive plants that change the nature of ecosystems.
One such example is the black locust (Robinia pseudacacia L.), a pioneer tree belonging to the Fabaceae family. Since its introduction from North America to Europe as an ornamental tree, this plant has been used for a wide range of purposes and has widely spread, being now rated as a highly invasive species of severe concern. Due to its ability to fix atmospheric nitrogen, black locust can substantially alter the invaded habitats, shading out present vegetation and changing soil conditions and nutrient cycles.
Despite the large amount of research on invasive trees, there is a lack of experimental data on their impacts, and the studies carried out so far on black locust in particular have produced contrasting results.
The aim of this project is to test the hypothesis that the dominance of black locust in recent secondary stands plays a major role in shaping the diversity of the understory plant groups by altering the soil and light condition. By comparing black locust and native urban forest stands across different climatic regions in Italy, we aim to highlight the main changes that have occurred in plant species diversity and the overall effect of the dominance of R. pseudoacacia on the ecosystem. The project will provide new advances on the impact of one of the major invasive trees in Europe and crucial information for prioritization, risk analysis and the implementation of the EU Regulation on invasive alien species.
Despite scientific research on biological invasions has substantially intensified during the last years, we know surprisingly little about the environmental impacts that invasive species pose. Many studies have been carried out so far on key topics such as the taxonomy, biology and ecology of major invaders. Regional, national and global species databases have been gathered, making up the fundamental steps for further research. However, assessing the impacts of invasive alien species on ecosystems still remains a challenge. The importance of this issue has also been stressed by the EU Regulation 1143/2014 on invasive alien species, adopted in recent years by the European Union that addresses the threats posed by biological invasion and hence the importance to evaluate the negative impacts of major invasive taxa in order to prioritize management interventions.
Considerable progress has been made in recent years in Italy on vascular plant invasions. Several national projects on the non-native flora of Italy, coordinated by the proponent of the present project, have been carried out from 2005 to date. They have produced a comprehensive database of the alien vascular flora and provided an overall picture of plant invasion in Italy, identifying the major invasive species, patterns and threats (Celesti-Grapow et al. 2009; 2010). Ongoing projects are dealing with the invasive alien species of Union concern which are subject to restrictions and measures set out in the Regulation 1143/2014.
Following these important advances, it is now necessary to explore the relatively less investigated field of impacts and assess the effects of invasive species on the environment in the Italian territory and by means of experimental research.
This is particularly important for forests. Although they are generally acknowledged to be resistant to plant invasions, an increasing number of studies have questioned this assumption. One of the main reasons is that given the dominance of long-lived life forms among alien species such as trees, invasion in woodlands could be subject to time-lags and the level of invasion could increase in the future. Indeed, forests in Europe are expected to be increasingly affected by the threat of invasive species, and it is believed that with climate change invasion risks by this species will increase (Kleinbauer et al. 2010).
The black locust (Robinia pseudacacia L.) is the most widespread species in Italian forests (Rizzo, Gasperini 2011) and one of the most widespread and detrimental alien plant in Italy.
Several studies have been carried out on this species in Italy showing that the spread and dominance by black locust is favored by woodland clearing, coppicing, forest decline, fire and other disturbances (see e.g. Benesperi et al. 2012, Maringer et al. 2012, Radtke et al. 2013) but there is still a lack of experimental data and information on its impact on biodiversity, and some of the studies carried out so far on this subject have led to contradictory results.
In this view, our project is highly innovative because i) it deals with negative environmental impacts, a relatively little explored field of research so far; ii) it is based on experimental research and field surveys to analyze the effects of R. pseudoacacia on biodiversity of the invaded stands; iii) it analyses forests, which have generally been considered relatively resistant to alien plant invasions; iv) it will be carried out within a collaboration with the University of Padua, allowing the comparison with existing studies performed at different latitudes, climatic conditions and landscape patterns, hence delivering results at a broad spatial scale.
The results of this project will provide important information on impacts which will produce fundamental data to perform risk analysis and carry out restoration actions.
Benesperi R. et al. 2012. Forest plant diversity threatened by Robinia pseudoacacia (black-locust) invasion. Biodiversity & Conservation 21: 3555-3568
Celesti-Grapow L. et al. 2009. The inventory of the non-native flora of Italy. Plant Biosystems 143: 386-430
Celesti-Grapow L. et al. 2010. Non-native flora of Italy: Species distribution and threats. Plant Biosystems 144: 12-28
Kleinbauer I. et al. 2010. Climate change might drive the invasive tree Robinia pseudacacia into nature reserves and endangered habitats. Biological Conservation 143: 382-390
Maringer J. et al. 2012. Post-fire spread of alien plant species in a mixed broad-leaved forest of the Insubric region. Functional Ecology of Plants 207: 19-29
Radtke A. et al. 2013. Traditional coppice forest management drives the invasion of Ailanthus altissima and Robinia pseudoacacia into deciduous forests. Forest Ecology and Management 291: 308-317
Rizzo M., Gasparini P. 2011. Occurrence and distribution of alien invasive tree species in the
Italian forests. Forestry Ideas 17: 97-103