Photos courtesy of Mark Swanson, WSU
PULLMAN, Wash. More than 34,000 trees were identified, mapped and tagged in one of the largest studies ever conducted of the importance of big trees in temperate forests. Trees three feet in diameter and larger comprise nearly half the biomass accounted for at a Yosemite National Park site but represented only one percent of the trees in the research site.
“The take away message of the study is that big trees matter,” said Washington State University forestry scientist Mark Swanson. “We always suspected that large trees were important for forest structure and services like carbon storage. Now we’ve quantified that fact for Sierra Nevada mixed-conifer forests, and we can say how big trees contribute to the forest ecosystem.
“That is useful knowledge for logging operations and fire-suppression efforts, as we now know that we should retain at least a few large trees,” he said.
As important as the study’s scientific contribution to forest management is, Swanson said he was most gratified by working with the more than 50 undergraduate students who did much of the work of surveying, tagging and mapping the study area.
The Yosemite Forest Dynamics Plot site, located in the northwest section of Yosemite near Crane Flat, was visited every year by students from WSU, the University of Washington and the University of Montana.
“The teams of students participated in almost every aspect of the work, so they learned a lot of valuable research skills in this endeavor,” Swanson said. “They helped with surveying by gridding the 63-acre site into 20-meter squares. They helped map every tree with a diameter greater than 1 cm.
“This work requires the ability to identify tree species, shrubs, pests and pathogens and make diameter and height estimates in our effort to account for as much of the biomass in the plot as possible,” he said.
“Working in the Yosemite forest is not just a nice trip,” he said. “Students who visit forests in other bioregions come back with a greater understanding of those in their own regions.”
Swanson and his colleagues plan to continue to study the plot. The site is the largest fully mapped old-growth plot in North America and one of the largest in the world.
The site and the data set created by the study will set the stage for future studies of prescribed burning, other forest-management strategies and climate change, Swanson said.
The study, led by UW research scientist James Lutz, is co-authored by Swanson, Andrew Larson of UM and James Freund of UW. The study was published today (May 2) in PLoS ONE. The study was funded by the Smithsonian Center for Tropical Forest Science.