Performing Department
(N/A)
Non Technical Summary
Fires have considerable impacts on the mortality and post-fire growth of many important timberspecies. However, the mechanistic causes of tree death remains uncertain and limited studieshave focused on how the timing of growth/dormancy season with fire seasonality impacts oaksurvival and post-fire growth following fires. We address these knowledge gaps through fourcentral hypotheses. The first seeks to assess how fire intensity impacts the probability of oak topkilland mortality. The second and third assess how seasonality of fires and growth/dormancyimpacts those responses. The fourth assesses whether fire induced mortality is due to xylem- orphloem-based mechanisms. The project has four supporting objectives: 1) Determine the fireintensity 'dose' to mortality and productivity 'responses' for the different oak species, 2)Determine how the relationships in (1) change by burning oaks at different dates associated withinteracting fire season and dormancy/growth season, 3) Assess mechanisms of fire-inducedmortality in saplings of selected oak species, and 4) Share data and results with forestproductivity and fire effects modeling teams. This project is directly aligned with the goals ofthe program as it assesses sapling growth, carbon assimilation, mechanisms of sapling responseto stress from fire, as well as how these responses are impacted by the interactions of fire andgrowing/dormancy seasons.
Animal Health Component
0%
Research Effort Categories
Basic
50%
Applied
50%
Developmental
(N/A)
Goals / Objectives
Our overall goal is to assess how the mortality, post-fire resprouting vigor, and growth of keyQuercus species are affected by varying fire intensity doses and how the timing of fire seasonversus growth season impacts these relationships. We will test our hypotheses through a series ofcontrolled nursery and combustion experiments. As stated above, our five objectives to achieveour long-term goal are:1. Determine the 'fire behavior dose to mortality and productivity responses' for thedifferent oak species at two different age groups (saplings and young trees). For eachof the selected species we will produce fire intensity dose to physiology and morphologyresponse curves as shown in Figure 1. Hypothesis 1A: Two fire intensity thresholds willexist: a lower threshold where top-kill occurs but subsequent resprouting occurs and anupper threshold where the tree exhibits complete fire-induced mortality.2. Determine how the relationships in (1) change by burning oaks at different datesassociated with both fire season and dormancy/growth season. Hypothesis 2A: Theprobability of top-kill and mortality at a given fire intensity dose decreases as thegrowing season moves from spring dormancy to the fall late growing season. We positthat as the growing season extends, the oaks will have a greater opportunity to store nonstructuralcarbohydrates that can be used to rebuild and recover following fires.3. Determine how the relationships in (1) change by burning young oak trees duringprescribed spring and fall fires. Hypothesis 3A: The form of the relationships (shapeof the dose-response curves) will remain the same, but we posit that higher fire intensitieswill be needed to produce comparable effects (i.e., the curves will 'shift' to the right).4. Assess mechanisms of fire-induced mortality in saplings of selected oak species.Hypothesis 4A: Fire induced mortality occurs due to emboli-induced xylem deformationand associated hydraulic failure. Hypothesis 4A-Alt: Fire induced mortality occurs dueto the inability of the phloem to transport sugars and starches to critical components.5. Share data and results with forest productivity and fire effects modeling teams. Asoutlined in more detail in our data management plan, we will widely share our data.
Project Methods
Sapling Selection: We have identified two key oak species native to the western United States and two key oak species native to the eastern United States. We will purchase 1.5- year-old plants (20 cubic inch plugs) and collect acorns as available. Given growing from native acorn supplies will leads to saplings only being ready for laboratory experiments during year 3 of the project, purchasing and conducting experiments on grown native plants enables us to generate prognostic data to guide year 3 verification experiments using the grown from acorns saplings. Experiments will be arranged as a completely randomized design.Heat Dose and Fire Line Intensity: We propose to assess three different fire intensity dosemetrics: Fire Radiative Energy (FRE, units: MJ m-2), maximum Fire Radiative Power (max FRP,units: MW m-2), and Fire Line Intensity (FLI, units: kW m-1s-1).Sapling Experiment Replicates, Treatments, and Controls: We will seek to characterize a 'dose-response curve' for each species and assess the post-fire ecophysiology responses. All saplings will be well-watered throughout the experiment. We will have four timing treatments: Early Spring-Dormant (ESD), Late Spring-Growing (LSG), Early Fall-Growing (EFG), Late Fall-Dormant (LFD). At each time treatment we will conduct the fire intensity (dose) to plant mortality/productivity (response) experiment, where 8 replicates (r=8) will be subjected to 5 fire intensity levels (L= 5, Unburned Control = 0MJ m-2, 0.4 MJ m-2, 0.8 MJ m-2, 1.2 MJ m-2 and 1.6 MJ m-2). These represent the range of radiative heat release observed in surface fires in multiple ecosystems (Smith et al. 2017). In year 3 of the project, we will use available grown from acorn saplings to conduct verification experiments on a sub-sample of these seasonality and fire intensity levels stratification doses. This will allow us to test the assumption that across species differences are greater than within species variation.Young Trees Experiment Replicates, Treatments, and Controls: In the younger trees experiment,we are constrained by safe burning windows to the Early Spring-Dormant (ESD) and Late Fall-Dormant (LFD) time treatments. However, we contend that this subset will still provide valuableinformation to assess how relationships and potential impact of fire-induced mortalitymechanisms change as a function of tree age. At each time treatment, we will conduct the fireintensity (dose) to plant mortality/productivity (response) experiment. We will plant the largertrees in year 1 of the project in stands due to be burned in the proceeding 2 years. Given ourhypothesis that older trees will likely require higher fire intensity levels to cause the comparableimpacts observed in saplings, we will conduct a calibration experiment on 5 young trees of eachspecies in year 1 of the project. In this calibration experiment, we will subject the young trees toan expanded range of fire intensity levels to identify the approximate top-kill and mortalitythresholds.Pre-Fire Morphology Measurements: For both the laboratory and field experiments, we willmark the bole at the root collar to allow for consistent height and stem diameter measurementsfrom the same location. We will measure a series of plant morphological traits prior to eachexperiment for all plants in the different treatments. These will include tree height, height to firstlive branch, crown length, branch number and size, diameter at root collar, leaf mass and area,bark thickness, bud counts, and coarse and fine (<1 mm diameter) root mass.Pre-fire Ecophysiology Measurements: For both the laboratory and field experiments, we willmeasure plant water potential at midday to assess maximum daily water stress and during the predawn period to assess soil moisture availability. Leaf photochemical efficiency will beexpressed as leaf chlorophyll fluorescence (CF=Fv/Fm) and Light-saturated gas exchange measurements (photosynthetic rate, stomatal conductance) will be performed. Gas exchange, water potential, and CF will be measured one day prior to the burns.Laboratory Combustion Protocol: Prior to all the laboratory combustion experiments, fuels willbe oven dried at 105 °C for 48 hours to produce ~0% moisture content (Matthews 2010). A 10gsub-sample of fuel will be set aside in the burn lab following extraction from the oven, weighed,and reweighed at the start of the combustion experiment to measure any gains in moisturecontent; this moisture content will be used to adjust the estimate of FRE released in theexperiments (Smith et al. 2013).Landscape Fires Protocol: We will use an existing prescribed fire education program conductedannually by CoPD Keefe as part of experiential learning and fire ecology/forestry undergraduatecourses on the UIEF. The southeastern young tree experiment will be achieved through existing collaborations between PD Johnson and the Joseph Jones Ecological Research Center at Ichauway that regularly conducts prescribed fires with embedded research teams. In each case, sites will be selected with similar aspects and elevations. Prior to planting all large woody fuels removed from the sites. Each young tree will be planted in a grid at 10m spacing.Once the approximate lethal young tree fire intensity level is determined from the priorcalibration experiment, we will conduct the fire intensity (dose) to plant mortality/productivity(response) experiment, where 5 replicates (r=5) will be subjected to 5 fire intensity levelsIn each case, we will remove all fuels in a 5m radius circle around the base of each young tree and burn each tree individually using known quantities of oven dried fuel.Post-Fire Monitoring: All saplings will be returned to the greenhouses following the firetreatments, regularly irrigated, and monitored for post-fire growth and/or mortality weekly up to3 months post-fire or when shoot elongation begins following winter dormancy. After 3 months,50% of the saplings will be randomly selected and destructively sampled for xylem hydraulics,nonstructural carbohydrates, and nutrient analysis while the remaining 50% will be retained toassess the longer-term (1-2 years) impact of the treatments on post-fire vigor and resprouting.Post-Fire Morphology Measurements: For both the laboratory and field experiments,measurements will be taken daily during the first 7 days post-fire (Smith et al. 2016, 2017;Sparks et al. 2016; 2018; Steady et al. 2019). Afterwards, measurements will be taken weeklyand include the same measurements taken pre-fire. Additional post-treatment morphologymetrics will include percentage live crown, crown length scorched (fire treatment), and degree ofstem scorch (height and circumference in fire treatments). We will assess a series of standardanatomical features including the following on a per-ring basis: mean ring width, earlywoodwidth, latewood width, mean lumen area in the earlywood, mean radial cell wall thickness in thelatewood, maximum cell hydraulic diameter, and number of resin ducts (von Arx et al. 2016).Post-fire Ecophysiology and Nutrition Measurements: For both the laboratory and fieldexperiments, we will measure the same ecophysiology measurements daily for the first twoweeks, followed by measurements at one-month intervals until the end of the experiment. Inaddition to the measurements acquired pre-fire, a 25 cm section of the main stem from the 5saplings per species that were selected for the destructive sampling per FRE treatment will becollected. The hydraulic conductivity, knative and kmax, will be measured in all species. We will measure nonstructural carbohydrate (NSC) concentrations in needles, stems, and roots to assess effects on plant metabolism. Foliar and soil media samples will be collected during the postfiregrowth and dormant period following fire treatments using the above methods.