Ireland is one of the least forested countries in Europe. Until the end of the Middle Ages, the land was heavily forested with native trees such as oak, ash, hazel, birch, alder, willow, aspen, elm, rowan, yew and Scots pine. The growth of blanket bog and the extensive clearing of woodland for farming are believed to be the main causes of deforestation. Today, only about 10% of Ireland is woodland, most of which is non-native conifer plantations, and only 2% of which is native woodland. The average woodland cover in European countries is over 33%. According to ''Coillte'', a state owned forestry business, the country's climate gives Ireland one of the fastest growth rates for forests in Europe. Hedgerows, which are traditionally used to define land boundaries, are an important substitute for woodland habitat, providing refuge for native wild flora and a wide range of insect, bird and mammal species. It is home to two terrestrial ecoregions: Celtic broadleaf forests and North Atlantic moist mixed forests.