Project Objectives and Hypotheses
- Quantify surface and canopy fuel loads 7-15 years postfire across the full range of burn severities in five vegetation types.
- Survey plant cover, native species recovery, exotic species establishment, and seedling densities across the same sample sites as above as metrics of ecosystem recovery.
- Relate field plot measures to LandTrendr image products to assess landscape-level implications of large fires on fuel loads, effectiveness as fuel treatments, vegetation cover, and plant community composition as measures of ecosystem recovery across 15 wildfires and five vegetation types.
- Produce maps of estimate recovery rates for fuels and vegetation conditioned on recent fire history, vegetation type, burn severity and geographic location.
- Hold a workshop and webinars with fuels and fire managers regarding how the fuel and vegetation trajectories post-fire influence fuel and fire management options, focused on effectiveness in limiting fire extent and burn severity of subsequent fires and furthering vegetation management goals.
Our hypotheses are as follows:
1. Surface fuel accumulation will be highest and fuel treatment effectiveness lowest following moderate severity burns where most but not all of the overstory trees are killed and fine canopy fuels are not consumed.
2. Ecosystem recovery (e.g., plant species diversity) to pre-fire levels will be slowest in large, severe fire patches. 3. Considering recent wildfires as fuel treatments, conditioned on vegetation type and burn severity, can be formalized as a cost-effective fuel and fire management strategy.
4. Using ArcFuels software, fire atlas maps of past wildfires used as fuel treatment surrogates and LandTrendr-derived maps of vegetation recovery rates can be linked to FVS-ready stand attributes of interest to managers, to explore alternative fire management strategies.
5. Using Climate-FVS, and FVS-ready stand data, managers can explore implications of different fuel management strategies under alternative climate change scenarios, focusing on implications for extent and burn severity of future fires.
Sampling Design and Field Measurements
We focus on measuring the longer term fuel, vegetation cover, and plant species diversity responses to burn severity. High burn severity fires are the primary concern of land managers and are more extreme cases to test ecosystem resilience to fire. Insight into ecosystem resilience may be increased by comparing higher to lower severity conditions, as well as unburned areas. Some wildfires listed in Table 1 burned simultaneously and in close proximity in the same vegetation type (namely: Black Mountain 2 and Cooney Ridge; Robert and Wedge Canyon; Porcupine, Chicken and Wall Street), so each set will be considered as a single wildfire event to stratify for field sampling.
We measure fuel loads, vegetation cover, and plant species composition at the same field sites that we measured in 15 fires immediately after and one year after they burned. Nested plots within field sites were accurately geo-located with GPS and field plots were monumented with rebar in the event of a future re-measurement opportunity. Tree and sapling species, diameter at breast height, height, crown base height and condition are tallied in a 1/25-ha fixed-radius plot situated at the center of the field site. Seedlings are tallied along belt transects and distance to nearest seed trees measured, by species. Understory vegetation cover is ocularly estimated by plant species and functional type, within a 1 m x 1 m square subplot situated at the center of each field site and as well as four peripheral locations 30 m away in orthogonal directions oriented with the prevailing aspect. We measure coarse and fine surface fuel loads following the photoload sampling technique developed by Keane and Dickinson (2007). Ground cover fractions of surface materials (green and non-photosynthetic vegetation, litter, and mineral soil) are ocularly estimated in five 1-m2 nested plots per site; litter and duff depths, understory vegetation cover and composition, and overstory canopy closure composition will be measured at these same plots. Tree stem diameter measures will be converted to dry biomass using allometric equations.
To inform and complement the field data collection, we will quantify vegetation response rates to date across these wildfires using annual Landsat image time series. Vegetation and carbon recovery can be quantified via satellite monitoring. The field data we already collected, along with the proposed re-sampling field data, will be related empirically to the image data collected at nearly the same times. We will use LandTrendr to characterize vegetation response trajectories from annual Landsat images.