Over 34,000 trees were identified, mapped, and tagged in one of the largest studies conducted to date 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 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.”
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 forested 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 learn 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.
“Working in the Yosemite forest is not just a nice trip,” Swanson continued. “Students who visit forests in other bioregions come back with a greater understanding of those in their own regions.”
Swanson said that he and his colleagues in the study planned to continue to study the plot in the future. The site is the largest fully mapped old-growth plot in North America, and one of the largest in the world.
Swanson said that the site and the data set created by the current study would set the stage for future studies of prescribed burning and other forest-management strategies, as well as serve as a case study for understanding the effects of climate change.
The study, led by University of Washington research scientist James Lutz, is co-authored by Swanson together with Andrew Larson of the University of Montana and James Freund of the UW. Their study was published today in PLoS ONE. The study was funded by the Smithsonian Center for Tropical Forest Science.