According to the BBC, the climate-linked mountain pine beetle epidemic in British Columbia is threatening to spread south and west, into the United States. Forests with a mixture of species and small regular fires would be more resilient, overall.
In addition to mentioning the importance of warm winters in aiding the spread of the insects, the article describes how past fire suppression policies have produced huge areas of mature lodgepole pine, which are especially susceptible to the beetles.
The continuing spread represents not only an economic and environmental cost linked to climate change, but also a potentially serious positive feedback effect. It is estimated that Canada’s boreal forests alone contain about 186 billion tonnes of carbon dioxide equivalent: an amount equivalent to about 25 years of global emissions at the present level.