For 25 years many forests in the western United States have been managed to protect habitat for endangered and threatened spotted owls.
Central to this has been ensuring that these forests maintain more than 70 percent tree canopy cover, as studies have shown spotted owls are more prevalent when this is the case.
The problem is that these dense levels of canopy cover also leave forests prone to fire and large tree mortality during droughts, meaning a conflict for forest management.
However, using remote sensing technology, researchers have found that it is not the extent of tall canopy cover that attracts owls, but the presence of tall trees, with owls seeming to avoid cover created by shorter stands of trees.
The lead author of the research, Malcolm North, a research forest ecologist with University of California Davis’ John Muir Institute of the Environment and the US Department of Agriculture Pacific Southwest Research Station, said the findings could resolve forest management conflicts by allowing for reducing density of small trees via fire and thinning.
“We’ve been losing the large trees, particularly in these extreme wildfire and high drought-mortality events. This is a way to protect larger tree habitat, which is what the owls want, in a way that makes the forest more resilient to these increasing stressors that are becoming more intense with climate change.”
The study examined height and distribution of tree foliage, and forest gaps, across 1.2 million acres of California’s Sierra Nevada forests using the relatively new technology of light detection and ranging imaging, or LiDAR. The tool uses laser pulses shot from an instrument mounted in an airplane to measure a forest’s canopy in detail.
The authors also used a data set collected by wildlife researchers spanning more than two decades that recorded the positions of 316 owl nests.
The researchers found owls seek out forests with unusually high concentrations of tall trees, but appear to be indifferent to areas with dense canopy cover from medium-height trees and avoided areas with high cover in short trees.
All this suggests a high density of small trees is not necessary to support spotted owls and that there is potential for more logging, as well as stronger forest management.
The study was led by the University of California, Davis, the USDA Forest Service Pacific Southwest Research Station and the University of Washington.
Image credit: John Keane, USDA Forest Service Pacific Southwest Research Station
Source: Science Daily
