This readme.txt file was generated on 2020-09-11 ------------------- GENERAL INFORMATION ------------------- 1. Title of Dataset Data supporting: Century-scale wood nitrogen isotope trajectories from an oak savanna with variable fire frequencies 2. Author Information Principal Investigator Contact Information Name: Trumper, Matthew L Institution: University of Minnesota Address: Department of Geography, Society, and Environment, University of Minnesota, Minneapolis, MN 55455, USA Email: trump022@umn.edu ORCID: https://orcid.org/0000-0002-9881-7742 Associate or Co-investigator Contact Information Name: Griffin, Daniel Institution: University of Minnesota Address: Department of Geography, Society, and Environment, University of Minnesota, Minneapolis, MN 55455, USA ORCID: https://orcid.org/0000-0002-1547-3615 Name: Hobbie, Sarah E Institution: University of Minnesota Address: Department of Ecology, Evolution, and Behavior, University of Minnesota, Saint Paul, MN 55108, USA ORCID: https://orcid.org/0000-0001-5159-031X Name: Howard, Ian M Institution: University of Arkansas Address: Department of Geosciences, University of Arkansas, Fayetteville, AR 72701, USA ORCID: https://orcid.org/0000-0002-8361-9575 Name: Nelson, David M Institution: University of Maryland Center for Environmental Science Address: Appalachian Laboratory, University of Maryland Center for Environmental Science, Frostburg, MD 21532, USA ORCID: https://orcid.org/0000-0003-2755-5535 Name: Reich, Peter B Institution: University of Minnesota Address: Department of Forest Resources, University of Minnesota, St Paul, MN 55108, USA Address: Hawkesbury Institute for the Environment, Western Sydney University, Penrith, New South Wales 2753, Australia ORCID: https://orcid.org/0000-0003-4424-662X Name: McLauchlan, Kendra K Institution: Kansas State University Address: Department of Geography and Geospatial Sciences, Kansas State University, Manhattan, KS 66506, USA ORCID: https://orcid.org/0000-0002-6612-1097 3. Date of data collection: 2018-03-07 to 2018-03-21 4. Geographic location of data collection: Cedar Creek Ecosystem Science Reserve, Bethel, Minnesota, USA 5. Information about funding sources that supported the collection of the data: National Science Foundation Division of Environmental Biology, Award: 0620652; National Science Foundation Division of Environmental Biology, Award: 1655144; National Science Foundation Division of Environmental Biology, Award: 1655148; National Science Foundation Division of Environmental Biology, Award: 1234162 -------------------------- SHARING/ACCESS INFORMATION -------------------------- 1. Licenses/restrictions placed on the data: Attribution-ShareAlike 3.0 United States, http://creativecommons.org/licenses/by-sa/3.0/us/ 2. Links to publications that cite or use the data: Trumper, M., Griffin, D., Hobbie, S. E., Howard, I., Nelson, D. M., Reich, P. B., and McLauchlan, K. K.: Century-scale wood nitrogen isotope trajectories from an oak savanna with variable fire frequencies, Biogeosciences, https://doi.org/10.5194/bg-2020-6, 2020. 3. Recommended citation for the data: Trumper, Matthew L; Griffin, Daniel; Hobbie, Sarah E; Howard, Ian M; Nelson, David M; Reich, Peter B; McLauchlan, Kendra K. (2020). Data supporting: Century-scale wood nitrogen isotope trajectories from an oak savanna with variable fire frequencies. Retrieved from the Data Repository for the University of Minnesota, https://doi.org/10.13020/428b-8h51. --------------------- DATA & FILE OVERVIEW --------------------- 1. File List A. Filename: CedarCreek_Wood_d15N_Data.txt Short description: Wood Nitrogen Data NA indicates data not available VARIABLE NAMES: Field 1 | Name: Sample_ID | Definition: Tree alphanumeric ID Field 2 | Name: Burn_Unit | Definition: Cedar Creek LTER Burn unit number Field 3 | Name: Burn_Freq | Definition: Burn frequency (burns/year) Field 4 | Name: Tree_Age | Definition: Tree age, based on 2017 sampling year and innermost ring date with no pith offset estimation Field 5 | Name: Tree_Inner_Date | Definition: Inner calendar date of the sampled tree Field 6 | Name: Year | Definition: Calendar year corresponding to wood sample Field 7 | Name: Biological_Age | Definition: Biological age of the tree corresponding to wood sample Field 8 | Name: d15N | Definition: d15N = {[(15Nsample/14Nsample)/(15NAir/14NAir)] - 1} * 1000 Field 9 | Name: Percent_N | Definition: Wood percent nitrogen Field 10 | Name: Heartwood_Sapwood | Definition: Sample from tree heartwood or tree sapwood Field 11 | Name: Years_In_Sample | Definition: Number of years contained in wood sample Field 12 | Name: Years_Contained | Definition: Calendar years contained in wood sample if > 1 Field 13 | Name: Amount(mg) | Definition: Weight of wood sample Field 14 | Name: Notes | Definition: Notes from the isotope lab technician DESCRIPTION: Details on the wood d15N data, wood percent nitrogen data, study site, and methods can be found in the reference listed above. This data file prepared by Matthew Trumper, 3 September 2020. ABSTRACT: Fire frequency exerts a fundamental control on productivity and nutrient cycling in savanna ecosystems. A single fire event often increases short-term nitrogen (N) availability to individual plants, but repeated burning causes ecosystem carbon and N losses and can ultimately decrease soil organic matter and N availability. However, these effects remain poorly understood due to limited long-term biogeochemical data. Here, we leveraged one of the longest running prescribed burn experiments (established in 1964) to evaluate how fire frequency and changing vegetation composition influenced wood stable N isotopes (δ15N) across space and time. We developed multiple δ15N records across a burn frequency gradient from precisely dated Quercus macrocarpa tree-rings in an oak savanna at Cedar Creek Ecosystem Science Reserve, Minnesota, USA. Sixteen trees were sampled across four treatment stands that varied in temporal onset of burning and burn frequency, but were consistent in overstory species representation, soil characteristics, and topography. Burn frequency ranged from an unburned control stand to a high fire-frequency stand that burned in four of every five years during the past 55 years. Because N stocks and net N mineralization rates are currently lowest in frequently burned stands, we hypothesized that wood δ15N trajectories would have declined over time in all burned stands, but at a rate proportional to fire frequency. We found that wood δ15N records within each stand were remarkably coherent in their mean state and trend through time. A gradual, temporally synchronous decline in wood δ15N occurred in the mid 20th century in the no-, low-, and medium-fire stands, whereas there was no trend in the high-fire stand. The decline in the three stands did not systematically coincide with the onset of prescribed burning. Thus, we found limited evidence for variation in wood δ15N that could be attributed directly to long-term fire frequency in this prescribed burn experiment in temperate oak savanna. Our wood δ15N results may instead reflect decadal-scale changes in vegetation composition and abundance due to early to mid 20th century fire suppression.