A recently discovered population of the North American grey squirrel (Sciurus carolinensis), introduced to Ticino Park, Lombardy (N Italy), is likely to spread into continuous prealpine broadleaf forests of Lombardy and the south of Switzerland. The replacement of red by grey squirrels that is taking place in Piedmont, northern Italy, does not only have serious implications for red squirrel conservation in Italy, but also for the whole of Europe.
We used Spatially Explicit Population Dynamics Models, successfully used to predict the spread of grey squirrels in England and Piedmont, Italy, to examine the effects of different control scenarios on grey squirrel expansion in a 20000 km2 area around Ticino Park, Lombardy.
All the runs started from the situation known in year 2001 and forecasted squirrel population dynamics for the following 40 years. Without control, grey squirrels will invade Switzerland within the next two decades, and, concomitantly, the size and distribution of local populations of native red squirrels will be reduced. Simulating different grey squirrel control or removal scenarios suggests that: (i) efficient control is possible and mainly determined by the spatial distribution and woodland size of the `target’ control areas; and (ii) immediate actions must be taken. Delay in grey squirrel control will result in the population growth and spread, which will make the problems of successful containment more difficult and eventually impossible.
The coupled use of SEPM and GIS proved to be a useful tool in conservation as it allowed us to test the effectiveness of different control strategies, including the no action option, providing wildlife managers with maps showing the consequences of each strategy. Control maps analysis allowed use to identify the best cost/effective action control plan to prevent the spread of the invasive grey squirrels. Those maps, theoretically, could already be used on the field to place traps.
However caution must be used, as model scenarios were based on surveys that may underestimate the real distribution range and current population size of grey squirrels. In addition no information was available about the presence of the species outside the park boundaries, and this will have to be addressed.
For all these reasons our predictions can be conservative and we suggest a combination of grey squirrel monitoring and public participation survey to map grey squirrel presence, which may also help increase public awareness. Moreover future surveys can be used to improve model performance and to test the reliability of our predictions. Successful containment of further grey squirrel spread will require local co-operation between Italian and Swiss authorities involved in wildlife management. Without control, grey squirrels will invade Switzerland within the next two decades, and, concomitantly, the size and distribution of local populations of native red squirrels will be reduced.
Istituto Oikos, ONG Vareses, Italy carried out the research for Parco Regionale della Valle del Ticino Lombardo. Guido Tosi was the Prof. in charge. fauna.dipbsf.uninsubria.it/