Helicopters used to spot sick larch

Media playback is unsupported on your device
Media captionBBC Wales environment correspondent Iolo ap Dafydd was shown some of the areas affected

Helicopters are being used to track the spread of a disease affecting larch trees across forests in Wales.

The aerial surveys conducted by Natural Resources Wales (NRW) suggest the disease may not have spread as much as in previous years.

This year 10 sites containing 40,000 trees are under further investigation. In 2013, NRW found around 3m trees over 3,000 hectares were affected.

Wet weather in 2012 could have helped phytophthora ramorum spores to spread.

Conversely the dry summer of 2013 may have had the opposite effect.

The aerial surveys will be followed by surveying and sampling work on the ground.

Since the disease was first identified in 2010 in Wales, more than 6,000 hectares (14,500 acres) of woodland containing approximately 6m trees have been affected.

More than 2m larches on the Welsh government woodland estate have been felled.

NRW has planted 750,000 replacement trees using a variety of native species.

More on this story