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Posts Tagged: forest

Do California spotted owls prefer to nest near forest edges? SNAMP scientists say no.


Adult and juvenile California spotted owl

During a Sierra Nevada Adaptive Management Project (SNAMP) public meeting, a participant brought up the idea that California spotted owls preferred to nest near forest edges to be closer to foraging habitat and their prey. Principal investigator for the SNAMP Owl Team, Dr. Rocky Gutierrez, charged research fellow Casey Phillips and SNAMP Owl Team project leader Doug Tempel to research this question at SNAMP study sites in the Tahoe and Eldorado National Forests to see if this was true.

Owl researchers used field data that consisted of current vegetation maps derived from aerial photos and owl nest site location data gathered during their annual surveys. One nest tree site within a forest stand was randomly selected from each owl territory and one comparison location within those stands was randomly selected by a computer program. The distances between these two locations, relative to the nearest edge of the forest stand, were then compared statistically. A forest edge could be either a hard edge, such as an adjacent clear-cut; or a soft edge, such as a young, mixed-conifer forest. Elevation at each nest site was also considered because owls living at higher elevations prey on flying squirrels that typically inhabit forests with greater canopy cover. So, one might expect owl nest sites to be further from forest edges at higher elevations.

Researchers found no evidence that owls chose nest sites closer to forest edges than one would expect by chance, even though an edge location might bring them closer to a prey source. Results also showed that owls nested further from hard edges than expected. These results were consistent regardless of the elevation at a nest site.

It is possible that some timber harvest may have occurred after owls used a particular nest site, and before the vegetation maps were made. This scenario would have only lessened the distance to the nearest edge at these sites. This would also apply to the randomly selected points. Therefore, habitat alteration should not have affected the findings. Researchers speculate that limited availability of suitable nest trees within the stand may be as important of a determinant in the location of a nest site as any physical characteristics associated with its location.


Banded female California spotted owl

Where owls choose to nest has implications for forest managers and their management plans. This research suggests that creating forest edges would not enhance owl nest site choices and that other factors would likely influence owl nest site selection, such as the availability of large trees appropriate for nesting (i.e., those with cavities, broken tops, and mistletoe broom).

Information for this article comes from the following: Phillips, C.E., D.J. Tempel, and R.J. Gutierrez. 2010. Do California spotted owls select nest trees close to forest edges? Journal of Raptor Research 44:311-314.

Posted on Wednesday, February 23, 2011 at 8:04 AM

Study to examine giant sequoia groves

The giant sequoias of the Sierra Nevada are the biggest and among the oldest trees on the planet. Some are 2,000 to 3,000 years old. Forestry scientists from the University of California and Cal Poly, San Luis Obispo,  want to learn more about how disturbance factors affect the health of these aging behemoths.

Growth-response studies to date show that tree vigor can increase following moderate intensity disturbances such as prescribed fire or mechanical fire-hazard reduction treatments. Less certain, however, is how giant sequoias respond to lower and higher intensity disturbances. This information is of critical importance to identify the tradeoffs involved in fire prevention treatments or evaluating management options.

This summer scientists will visit native groves within Giant Sequoia National Monument, where high-intensity disturbances occurred 20 years ago. Harvests conducted at that time removed all trees except for large giant sequoia, creating a forest structure similar to what you’d expect after a high-intensity wildfire. Following the harvests, there was considerable public concern over the fate of the giant sequoias remaining. Mortality and growth in these areas has not been assessed until now.

The primary investigator on the project is Robert York, station manager of the UC Center for Forestry and an adjunct professor in the UC Berkeley Department of Environmental Science, Policy and Management. York is an expert in giant sequoia ecology.  His co-investigator on the project is Scott Sink, a professor in the Department of Natural Resources at Cal Poly, San Luis Obispo. He has investigated differences between old growth and secondary forests and developed expertise in measurements of tree ring growth. The researchers will partner with forest ecologist Steve Hanna of Giant Sequoia National Monument in Porterville.

The scientists will also study tree ring widths taken from 33 giant sequoias at the UC-Whitaker Forest, where light burns and small tree removal occurred in 1967. York previously conducted field work on growth response in a giant sequoia forest subjected to a moderate-intensity disturbance. In addition to publishing a journal article on this work, researchers will hold a field trip for managers of giant sequoia groves, involve UC and CSU students in field and laboratory work, and develop a lab module for coursework at UC Berkeley.

The project is funded by a $10,000 grant intended to foster collaboration in higher education in California on issues affecting agriculture, natural resources or human sciences. In their grant proposal, the researchers said: “We have a unique opportunity to measure growth response in giant sequoia to these different levels of disturbance intensity, and therefore improve our understanding of this species’ complex life-history strategy, while informing management within giant sequoia groves.”

Posted on Wednesday, February 16, 2011 at 8:30 AM
Tags: forest (12), giant sequoia (1), Sierra Nevada (8), wildfire (36)

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