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LTREB Renewal: Drivers of temperate forest carbon storage from canopy closure through successional time

Project Abstract: 
Forest disturbances, such as clear-cutting and fire, typically lead to large losses of carbon and nutrients from forests and their soils. Virtually all forests are recovering from such disturbances, whether natural or human-caused. But, it is not known how long it takes for forests to recover their carbon and nutrient stocks following disturbance, nor how re-growing vegetation, soil development and climate variation interactively regulate recoveries of carbon and nutrients as forests age. The long timescale of forest recovery makes it difficult to measure these changes, and limits the places where research like this can be conducted. This project uses long-term experimental plots at the University of Michigan Biological Station (a 110-year-old field station in northern Michigan) to investigate how changes in forest structure, nutrient cycling, and climate act together through time to influence tree growth, nutrient retention, and overall carbon capture and storage in forests. Researchers are regularly measuring tree species and biomass, forest structure (patterns of tree, leaf, and branch arrangement), soil carbon and nutrients, wood growth, leaf-fall and tree mortality in 6 forest plots (approx. 2 acres each) that were cut and burned in either 1936, 1948, 1954, 1980, 1998, or 2017. This cutting and burning treatment replicates a larger-scale cutting and burning that occurred, in the early 1900s, across the landscape (and the Great Lakes region) within which the experimental plots are nested. These plots thus range from 2 years (the 2017 burn) to 83 years (1936 burn) in age, and they are compared with plots that were cut in 1911, 1952, 1972, or 1987, but were not repeatedly and severely burned. By using nearby old forests (130- to >200-yr-old) that were not severely cut and burned as reference points, the team is linking disturbance, climate, soil, and vegetation controls to long-term patterns of C storage in forests that are representative of other forests across the northern U.S. and similar regions in Canada, Europe and Asia. This long-term (10-year) project began to answer globally significant questions in its productive first 5 years, and it involves students and forest managers in conducting research and applying findings to management plans. Globally, forests remove approximately ¼ of carbon emissions from fossil fuel combustion. Temperate forests like those studied here are responsible for almost half of that offset. However, it is uncertain whether forests will continue to partially offset human-derived carbon emissions as they age and mature following past large-scale disturbances. This project thus provides the data needed to predict the magnitude and duration of continued temperate forest carbon uptake, and the ability of forests to provide fiber, fuel, habitat, and their many other benefits to society. Importantly, it provides opportunities for students to help design and conduct research, as part of independent and guided studies, and class projects by students at this field station during summers. The research team also hosts outreach activities such as site visits and workshops, to professionals in government (state, federal, international) and non-profit forest conservation and management organizations, allowing a wide dissemination of the lessons learned from this long-term study.
Years Active: 
NSF supports the following activities necessary to bring our Decadal Research Plan to completion: 1) periodic census of trees and woody debris in our 32 intensive plots in the paired chronosequences and late-successional reference forests; 2) digitization of and derivation of long-term aboveground NPP from 500 tree cores; 3) quantification of soil heterotrophic respiration and subsequent derivation of NEP in all plots; 4) sustained measurement of key C fluxes across all 32 plots; 5) integration and synthesis of LTREB with other forest C cycle research at UMBS.
Funding agency: 
National Science Foundation