 Britain's trees face environmental change at an "unprecedented scale", with the challenges and opportunities greater now than at any time in the past 100 years, according to a new report backed by 20 of Britain's leading forestry and wildlife bodies.  Organisations ranging from the Forest Stewardship Council to the Woodland Trust have joined together for the first time to highlight the state of British woodlands and are urging the Government to take action.  Threats to woods and forests include climate change, increasing pests and diseases, pollution, invasive species, overgrazing, and disappearing habitat.  Targets to maintain, restore and protect priority woodland habitats are generally not being met and in some cases, baseline information and monitoring is inadequate, says the report.  The most pressing issues include increasing woodland cover to help mitigate and adapt to climate change.