Functional attributes of conifers expanding into temperate semi-arid grasslands modulate carbon and nitrogen fluxes in response to prescribed fire
Data files
Aug 19, 2024 version files 35.41 KB
Abstract
Fire exclusion is a key factor driving conifer expansion into temperate semi-arid grasslands. However, it remains unclear how reintroducing fire affects the aboveground storage of carbon (C) and nitrogen (N) in the encroaching tree species and belowground in soils. To assess the impacts of fire reintroduction C and N pools and fluxes in areas of conifer expansion we targeted a region of the Northern Great Plains that has experienced extensive woody plant expansion (WPE) of two species: ponderosa pine (Pinus ponderosa) and juniper (Juniperus spp). We quantified tree mortality of both species to estimate the amount of dead biomass C and N produced by a recent prescribed fire, in addition to changes in soil C, pyrogenic C (PyC), and N concentrations across a woody-cover gradient using a before/after/control experimental design. Post-fire soil chemical analysis revealed a 2-year increase in mineral soil C, PyC and N, suggesting the return of fire led to the transfer of partially combusted plant organic matter back to the soil. Further, we found that functional trait differences between the two species influenced the distribution of living conifer biomass-N prior to fire. Despite junipers having 41% less total aboveground biomass than ponderosa, they contained two times more aboveground N. Prescribed fire resulted in 88% mortality of all mature juniper stems and increased fire severity correlated with greater pre-fire juniper cover. Ponderosa mortality varied by size class, with >40 cm stem diameter class having only 28% mortality. High mortality and greater aboveground N storage in juniper biomass, compared to ponderosa, led to 77% of the total conifer biomass N lost. Consequently, the functional attributes of expanding trees differentially contribute to fluxes of C and N after the return of fire, with junipers acting as conduits for N movement due to their relatively higher N content in less fire-resistant tissues and ponderosa serving as important and more stable storage pools for C. Together, these findings highlight the importance of considering species-specific traits when planning WPE management strategies at landscape-scales, particularly when goals include C storage or soil nutrient status.
README: Functional attributes of conifers expanding into temperate semi-arid grasslands modulate carbon and nitrogen fluxes in response to prescribed fire
https://doi.org/10.5061/dryad.v9s4mw756
Description of the data and file structure
Data include
- pre and post soil chemistry concentrations and area scaled pools (0-10 cm soil depth)
- biophysical plot characteristics
- individual pinus ponderosa stem measurements
- needle leaf and bole chemistry for pinus ponderosa and juniperus scopulorum
All NA's indicate missing or unmeasured values
See associated manuscript for detailed information on collection, processing, and analysis.
Files and variables
File: fire_soil_chemistry.csv
Description: Soil chemistry at a 0-10 cm soil depth pre and post fire treatment
Variables
- Plot: Plot identifer
- Label: month and day of sample collection
- Month: month of collection
- Year: year of collection
- Treatment: fire treatment (pre, post, burned, and unburned controls)
- C_conc: soil C concentration (%)
- N_conc: soil C concentration (%)
- C_N: soil C:N
- Bulk_density: soil bulk density in g cm^3
- SOC_pool: area scaled soil carbon pool Mg C ha^-1
- TN_pool: area scaled soil nitrogen pool Mg N ha^-1
- PyC: pyrogenic carbon concentration (%)
- PyC_pool: area scaled soil pyrogenic carbon pool Mg PyC ha^-1
- PyC_C: Ratio of PyC:C
File: DIN.csv
Description: Inorganic nitrogen concentrations via KCl field moist extractions (2M) at 0-10 cm soil depth, pre and post fire treatment
Variables
- Plot: plot identifier
- Month: month of sample collection
- Year: year of sample collection
- DIN: dissolved inorganic nitrogen concentration ug g^-1 dry soil (KCl extractable)
- Type: Identifier for NO3-N or NH4-N
- Fire: Treatment (pre, post, burned, and unburned controls)
File: wood_leaf_chem.csv
Description: Woody and foliar biomass chemistry
Variables
- Field id: Tree species and tissue type
- Sample ID: Unique identifier
- Species: Tree species
- Tissue: tissue type (bole wood or needle leaf)
- N: Nitrogen concentration in % of mass
- P: Phosphorus concentration in % of mass
- S: Sulfur concentration in % of mass
- Ca: Calcium concentration in % mass
- Mg: Magnesium concentration in % of mass
- Na: Sodium concentration in % of mass
- Zn: Zinc concentration in % of mass
- Fe: Iron concentration in % of mass
- Mn: Manganese concentration in % of mass
- Cu: Copper concentration in % of mass
- B: Boron concentration in % of mass
- C: Carbon concentration in % of mass
File: plot_characteristics.csv
Description: biophysical plot characteristics
Variables
- plot: plot identifier
- longitude: in decimal degrees
- latitude: in decimal degrees
- elevation: in meters above sea level
- aspect: primary aspect in a cardinal direction (N,E,S,W)
- sin_asp:
- cos_asp:
- ph: soil ph 0-10 cm depth
- slope: slope angle in degrees
- bulk_density: soil bulk density in g cm ^3
- mature_stem_density: mature tree (ponderosa and juniper) stems per 0.04 ha
- Max_age: max tree age (ponderosa and juniper) in the plot
- Pondo_cover: ponderosa over per plot (%)
- June_cover: juniper cover per plot (%)
- Woody_cover: total woody cover of plot (%)
- juniper_mortality: % of junipers that were classified as dead after the fire via > 70% crown scorch
- ponderosa_mortality: % of junipers that were classified as dead after the fire via > 70% crown scorch
File: tree_measurements.csv
Description: Individual tree measurements on just ponderosa pine stems
Variables
- Year: year of measurement
- Plot: plot tree is located in
- Tree: unique identifier for each mature ponderosa in the plot
- TreeBurnSeverity: burn classification (0 = no evidence of burn, 1 = light evidence of burning, 2= moderate evidence of burning, 3 = extensive evidence of burning)
- DBH: Diameter at breast height (cm)
- Height: Tree height in meters
- BA: Basal area
Code/software
All analysis was conducted in R.
Methods
The data from this study was collected over multiple field seasons and includes soil chemistry, bole and foliar biomass chemistry for pinus ponderosa and juniperus scopulorum, individual ponderosa stem measurements and biophsyical data for field plot characterization.