Estimates of bark beetle infestation expansion factors with adaptive cluster sampling

Abstract

Insects have infested over 37 million hectares of forested land, the most aggressive forest insect pest in North America is the mountain pine beetle that has attacked 14 million hectares. To determine infestation extent and spread rates, we examined mountain pine beetle damage at two sites over two consecutive years (2007–2008). High spatial resolution (20 cm) airborne digital imagery was acquired over a range of infestation intensities (High: site A; Low: site B). An adaptive cluster sampling approach assessed the extent and severity of damage from the imagery. In 2007, site A contained 5.22 infested trees per hectare (variance: 10.65) increasing in 2008 to 11.02 trees per hectare (variance: 24.83). In contrast, site B had 0.25 infested trees per hectare in 2007 (variance: 0.02), which increased in 2008 to 0.47 trees per hectare, with a variance of 0.08 trees per hectare. At both sites, infestations approximately doubled over a 1-year period. Adaptive cluster sampling applied to high spatial resolution airborne imagery can provide estimates of the severity of attack on the landscape.