Decades-past logging still threatens spotted owls in national forests
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Decades-past logging still threatens spotted
owls in national forests
6 December 2017, by Eric Hamilton
Compared to nearby national parks, which were
never extensively harvested, national forests in the
area were more extensively logged until the 1992
restrictions on harvesting large trees and logging
near owl habitat took effect. The new study shows
that spotted owl populations are stable in national
parks. But in the more recently logged national
forests, the researchers suggest historical logging
of the largest trees may be contributing to the
continued declines in owl populations they
observed.
While California spotted owls (left, adult; right, juvenile)
typically perch and roost in smaller trees like this incense
cedar, their nest trees are often several feet in diameter.
Credit: Danny Hofstadter
Logging of the largest trees in the Sierra Nevada's
national forests ended in the early 1990s after
agreements were struck to protect species' habitat.
Researchers in Zach Peery's lab track spotted owl
But new research reported Dec. 6 in the journal movements using mini-GPS tags fastened to a backpack
Diversity and Distributions by University of harness system. Here, Gavin Jones checks the fit of a
Wisconsin-Madison ecologists shows that spotted newly mounted tag. Credit: Sheila Whitmore
owls, one of the iconic species logging restrictions
were meant to protect, have continued to
experience population declines in the forests.
Diagnosing causes of decline is difficult, says
Department of Forest and Wildlife Ecology Peery, and factors responsible for owl declines are
graduate student Gavin Jones, Professor Zach likely complex. "Other factors we didn't measure
Peery, senior scientist R. J. Gutiérrez, and their could have contributed to declines too, including
colleagues say the owls in the area may still be contamination of owl prey from rodenticides used
paying an "extinction debt" that was created by as part of illegal marijuana cultivation," he adds,
historical logging of large trees. These large, old which has been recently observed in other species
trees the owls rely on are slow to grow back, in the region like the Pacific fisher, a weasel
meaning the owl population could still be showing relative. However, the researchers say owl declines
the effects of logging that ended decades ago. were consistent with observations expected in
forests with a deficit of large trees.
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The findings could indicate parallels among other requires a bit of performance from the researchers.
species and other habitats around the world. The
results also have the potential to inform policy "We wander through the woods at night hooting to
decisions about how to continue protecting ourselves," Jones says of the surveys they conduct,
sensitive habitats, since existing regulations may which attract owls with vocalizations. They can then
require more time to pay off in bolstering species' band individual owls they encounter to track them
populations. from season to season. Jones was only 4 years old
when the surveys began. "I'm the beneficiary of
"The spotted owls' habitat contains the most decades of work," he says. They also used satellite
economically valuable trees," says Jones, who is information to determine the area covered by trees
the lead author of the new study. He explains that and relied on a new set of data on the size of trees
the ideal spotted owl habitat includes trees that recorded by other scientists.
could be more than 6 feet wide and hundreds of
feet tall. These giants are often centuries old. While the habitat was stable in the once-logged
national forests as a result of habitat retention
Combined with the owls' long lifespan, the slow guidelines implemented by the U.S. Forest Service,
regrowth of very large trees means that population these areas are characterized by a large-tree
declines caused by habitat loss may both take time deficit. Jones and his colleagues found that the owl
to appear and last long after protections are put in populations in these areas had continued to
place. That lag between cause and effect is termed decline—evidence of an extinction debt. In contrast,
an "extinction debt." the nearby national parks hosted stable owl
populations, even though their habitat wasn't
actively improving. High-quality owl habitat was
about four times more common within owl sites in
the national parks as in the national forests.
"There is a shortage of very large, old trees that
support spotted owls that take decades to centuries
to regenerate," explains Jones. "Owl populations
could stabilize in their forests with a large-tree
deficit, but it will take time to regrow the trees they
rely on." He says spotted owls aren't unique in their
plight. "Any species can continue to experience
decline after you remove habitat," he says.
The takeaway, says Jones, is that stabilizing, and
even increasing, spotted owl populations might
California spotted owl nest sites are typically require more than just halting habitat loss. It likely
characterized by large trees and a closed canopy. Credit: requires restoring the large, ancient trees they rely
Danny Hofstadter on to the landscape—and patience.
Provided by University of Wisconsin-Madison
To determine whether spotted owls were paying off
this debt, Peery's group traveled to four sites that
included three national forests—which had been
logged—and two national parks, Kings Canyon and
Sequoia, which were left intact. Beginning in 1993,
after logging restrictions were established, they
surveyed the number of owls each season. That
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APA citation: Decades-past logging still threatens spotted owls in national forests (2017, December 6)
retrieved 13 November 2021 from https://phys.org/news/2017-12-decades-past-threatens-owls-national-
forests.html
This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no
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