Summary

Based on the original report by Bertolino S., Lurz. P.W.W., Rushton S.P. 2006

DIVAPRA Entomology & Zoology, Via L. da Vinci 44, 10095 Grugliasco (TO), Italy

Italian IRES, School of Biology, Devonshire Building, University of Newcastle,    Newcastle upon Tyne, UK

1.  INTRODUCTION

American grey squirrels were first introduced to Italy in 1948.  There are now three colonies in the country, a large population in Piedmont near Turin and two smaller populations, one along the TicinoRiver (Lombardy) and another at Genoa Nervi (Liguria).    The introduction of the grey squirrel has caused the progressive disappearance of the native red squirrel and is causing damage to commercial tree and fruit plantations and cereal crops. 

The spread of the grey squirrel in northern Italy will have serious implications for red squirrel conservation throughout Europe.  Political concern about lack of action in Italy has been expressed by the Permanent Commission of the Bern Convention, who have produced a specific recommendation (December 2005) urging the authorities of the TicinoValley to eradicate grey squirrels. 

This modelling project predicts the: 

• Grey squirrel spread from Italy to France
• Grey squirrel spread from Italy into Switzerland
• Expansion and the distribution of grey squirrels in Italy
• Effect of the removal of the Ticino and Genoa populations would have on the spread of grey squirrels in Italy 

A spatially explicit population dynamics model (SEPM) was used to predict the spread of grey squirrels. This model was combined with habitat maps.   

Squirrel population dynamics are linked to the seed crop patterns and food availability.  This summary is based on the provision of average and good seed crop patterns. 

2.  THE PREDICTIONS     

2.1    Spread to France 

It is predicted that during the next 20 years grey squirrels will colonise the western Alps and the provinces of Turin and Cuneo and in approximately 30 years they will enter France.  By the end of the 100-year simulation the total population is estimated to exceed 2 million American grey squirrels in France.   

2.2    The Spread to Switzerland 

It is predicted that it will only take 20 years for the grey squirrel to colonise the area along the Ticino and Lake Maggiore with first populations in Switzerland in around 25-30 years. 

The spread of the grey squirrel in Switzerland will start in the Canton Ticino and around LakeLugano.  The model predicts over 3.5 million squirrels by the end of the century.   

2.3    Spread within Italy 

In Italy there will be a fast expansion of grey squirrels.  The eastern part of Liguria will be colonised within the next 35-40 years and in 50-60 years the colonisation of the Apennines between Emilia-Romagna and Tuscany will start.   

The Piedmontese region will be completely colonised as well as Liguria, parts of the Aosta valley, the western part of Lombardy and the northern part of the Apennines.  The total population size at the end of 100 years could reach 6 million animals. 

2.3    The Effects of the removal of the Ticino and Genoa Grey Squirrels  

2.4.1 Ticino 

The eradication of the Ticino population would delay the invasion ofSwitzerland by 100 years.  The Piedmontese population will eventually spread to the region; however it is only likely to reach this area and the end of the century. 

2.4.2 Genoa 

The effect of the removal of the Genoa population for France is more limited.  However, removing the population in Genoa would drastically reduce the spread in Italy in a south-easterly direction.  It would safeguard the two native species of red squirrel, S.v. italicus and S. v. meridionalis that are at present in the Apennines.   Without the Genoa population the grey squirrel will reach the very first part of the Apennines only at the end of the century. 

3.     CONCLUSION 

The results presented in this report leave no doubt that grey squirrels will colonise other European countries from Italy.  The only uncertainty is the likely speed of the spread.  The predicted population growth clearly indicates that the longer the spread is left unchecked the greater the impact this alien species will have on native wildlife, agriculture and forestry.   

The future of the grey squirrel in Italy and any decisions in regard to management should be considered in the context of the expected range expansion.  Large areas of Europe contain potentially good habitat for grey squirrels.  Grey squirrels do not recognised national boundaries and disperse where continuous woodland cover connects northern Italy with other European countries. 

The future spread of the grey squirrel into France, Switzerland and eventually other neighbouring countries would pose a significant future problem for commercial forestry, biodiversity and a threat to native wildlife such as the European red squirrel. 

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