Disturbance & Forest Carbon

I. Fire

Ecological disturbances can strongly regulate material and energy flows often as a response to the reduction in biomass in terrestrial ecosystems. In recent decades there has been an increase in the size and/or severity of disturbances (e.g. wildfires, beetle outbreaks) in Colorado’s Front Range ecosystem. This trend is expected to continue, with longer wildfire seasons (Westerling et al. 2006) and an increase in fire likelihood (Moritz et al. 2012).

Fourmile Watershed 06/15Importantly, these disturbances can have consequences for carbon (C), nutrient, and water cycling within the ecosystems (McLauchlan et al. 2014). Given that forests cover approximately 4.17 Mha globally, contain 1,240 Pg C in biomass (Lal 2005), and fires impact approximately 383 million ha yr-1 releasing 2,078 Tg C yr-1 (Schultz et al. 2008), the recovery and resilience of forest C stocks to fire is particularly important to both regional and global C budgets.

During the summer of 2015, 3 CC undergrads (Kyra, Maggie & Theo) and 1 CC Alum (Kelsey) worked on this project with me. In addition, with support from NOVUS, Dr. Brian Buma (Univ of Alaska, Southeast) came down to CO to teach us about vegetation sampling and revisit some sites within the Routt National Forest.  Throughout the summer we worked to quantify the C stocks and fluxes within watersheds with different fire histories. Specifically we sampled soils and waters from watersheds draining forests impacted by the Hayman Fire (2002), Waldo Canyon Fire (2012), and Hinman fire (2002, in Routt National Forest) as well as adjacent (reference) watersheds that have not been impacted. Preliminary results were presented at the Fall AGU Meeting in San Francisco.

During the summer of 2016, Asheton & Kyra worked on this project with me. To follow up on results from 2015 we decided to sample 2 additional burn scars from 2002 (Big Fish Fire and Missionary Ridge Fire), as well as another hillslope within the Hayman Burn plus nearby reference sites for each fire. Each of these severe burns are along a precipitation gradient (Hayman < Missionary Ridge < Big Fish < Hinman) and represent both montane and sub alpine ecosystems. Read more about our 2016 work, including 2 new collaborative projects with Lynne Gratz (CC) & Kyle Whittinghill (Univ of Pittsburgh).

Sampling soils from the Schoonover Burn, Summer 2017

In 2017, two CC students Asheton and Kelsey built upon this work and focused on examining how organic matter is transformed as it moves through the hillslope and within the stream. Asheton performed a series of column experiments on intact soil cores from mesic montane hillslopes – simulating typical summer convective rainstorms. Kelsey sampled six streams draining the same montane landscapes Asheton sampled (three were severely burned in 2002, three unburned).

These interrelated projects are enabling me to answer four interrelated questions:

  1. How do wildfires affect the C pools within and exported from forested ecosystems?
  2. How do differences in the chemical composition of post-fire C pools impact the bioavailability and thus fate of C relative to reference (un-burned) ecosystems?
  3. How do the above changes in C pools impact the downstream export of dissolved and particulate organic C and inorganic C (e.g. CO2)?
  4. How does ecosystem type (i.e. montane vs. subalpine) affect soil C stock recovery and resilience? How do C stock recoveries relate to available moisture (precipitation)?

Conference Presentations & Theses:

Funding for this project provided by the Dean’s Segway fund (CC), Natural Science Divisional Fund (CC), Jackson Fellowship from the Hubert Center for Southwest Studies, and NOVUS. In addition, students were funded through a Faculty-Collaborative Summer Research Grants, the Grant Lyddon Foundation, and Mr. and Mrs. Dille. We are grateful for all the support!

II. Forest Migration

During the summer of 2016 I started a project in collaboration with Brian Buma (Univ of Alaska, Southeast now at CU-Denver) and Patrick Jurney (CC ’17) to examine how the northward migration of Yellow Cedar is changing forest carbon stocks in

www.fs.fed.us

www.fs.fed.us

Southeast Alaska. Trees and other above ground vegetation have already been mapped and thus we are focused on examining how the soil pool has (or has not) changed over the last 100+ years (Yellow Cedar decline began in the 1890s though it reached its peak in the 1980s and 90s; Hennon et al. 2012). This will allow us to compare the C and N stocks in recently colonized sites as compared to sites colonized decades ago and Western Hemlock dominated areas. The characterization of the soil pool includes isotopic analysis of the SOM (δ15N and δ13C), soil incubations to examine the relative bioavailability of SOM, as well as moisture content and bulk density. These measurements will help us understand the conditions needed for the Yellow Cedar survival as well as how the northward (and upward) migration is changing nitrogen availability and net ecosystem carbon balance. This work is the basis of Patrick’s Senior Thesis and funding was provided by the Grant Lyddon Foundation and Yale Institute for Biospheric Studies.

Theses:

References

  1. Lal R. 2005. Forest soils and carbon sequestration. Forest Ecology and Management 220: 242-258.
  2. McLauchlan KK, et al. 2014. Reconstructing Disturbances and Their Biogeochemical Consequences over Multiple Timescales. BioScience 64: 108-116.
  3. Moritz MA, Parisien MA, Batllori E, Krawchuk MA, Van Dorn J, Ganz DJ, Hayhoe K. 2012. Climate Change and disruptions in global fire activity. Ecosphere 3: art49.
  4. Schultz M, Heil A, Hoelzemann J, Spessa A, Thonicke K, Goldammer J, Held A, Pereira J, van her Bolscher M. 2008. Global wildland fire emissions from 1960 to 2000. Global Biogeochemical Cycles 22: 1-17.
  5. Westerling AL, Hidalgo HG, Cayan DR, Swetnam TW. 2006. Warming and earlier spring increase western U.S. forest wildfire activity. Science 313: 940-943.
  6. Hennon, P.E, D.V. D’Amore, P.G. Schaberg, D.T. Wittwer, & C.S. Shanley. 2012. Shifting Climate, Altered Niche, and a Dynamic Conservation Strategy for Yellow-Cedar in the North Pacific, BioScience, doi: 10.1525/bio.2012.62.2.8

 

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