California prescribed fire monitoring program: 2019–2024

1 California Prescribed Fire Monitoring Program Protocol I. Overview This field protocol is based on and modified from the US Forest Service Common Stand Exam protocol (USDA, 2015). While primarily utilizing the "intensive" measurement level, it excludes measurements of tree age or growth and employs a fixed-area plot design. A series of modifications were made over the years to improve efficiency and concentrate data collection on variables of interest to fire and fuels managers. The version of the protocol described here is current as of May 2025. II. Sampling design Within each delineated burn unit, a buffer zone of at least 35 meters from the burn unit boundary is incorporated into the sampling design, within which no plots are established to avoid edge effects. Additionally, a minimum distance of 50 meters is maintained between all plots. However, a greater separation of 100 meters, and occasionally up to 150 meters, is generally maintained between plots to ensure adequate coverage across larger burn units. The specific grid spacing, and thus inter-plot distance, is adjusted based on the size of the burn unit and the desired number of plots. The target sampling intensity aims for a minimum of 20 plots to be established within each burn unit, contingent upon the unit's spatial extent. The basis of where plots were installed was due to a burn unit identified by the partner on site (State Parks, Forest Service, etc.) as likely to be burned soon. Field data is collected at each plot during multiple sampling periods. Pre-fire data are gathered 1 to 6 months before the prescribed fires, while immediate post-fire data are collected 1 to 4 weeks afterward. Follow-up measurements take place 1 year later, with additional sampling conducted at some sites at 2, 4, 5, and 8 years after the fires. Permanent circular plots of 0.04 hectares (~0.1 acre) are established within each burn unit for vegetation monitoring. These main plots, also referred to as macroplots, have a default radius of 11.35 meters (405 sq m) for forested vegetation. A smaller subplot, termed a microplot, is established at the center of each macroplot for the tree regeneration protocol. These microplots are 60 sq m (0.006 ha or 0.015 ac), with a radius of 4.37 meters. (Figure 1) All data recordings are completed in datasheets designed for tablets. 2 Figure 1 Vegetation and Fuels Monitoring Plot Diagram. III. Data collection methods A. Plot installation To establish plots, locate the predetermined plot coordinates on the map generated in GIS (refer to maps for project area per site), utilizing either a GPS unit or Avenza Map application. Once positioned at the predetermined plot coordinates, permanently mark the plot locations with a 60-cm (2-ft) piece of 3/8” or 1/2” (1-cm or 1.25-cm) rebar and topped with a rubber/plastic orange rebar cap. Leave 10-15 cm of the rebar above ground. Use a permanent marker (Sharpie) to label the cap with plot ID and UC Davis. In instances where the pre-determined plot center is unsuitable for establishment (e.g., due to inability to install rebar due to rock or tree boles, presence of trails or roads within 35 m distance, proximity with the 35m burn unit boundary buffer, dissection by fences, or fewer than two live trees within the predetermined plot), move the plot center in a cardinal direction until the plot area meets sampling requirements. Discard the plots that remain unsuitable after these adjustments and make a note (which plot and why it was discarded) in the datasheet. For recurrent sampling events, generally after the treatments are conducted, relocate the established plot centers by identifying the permanent rebar. In cases where the rebar is absent, 3 GPS coordinates, in conjunction with witness tree measurements recorded during initial establishment, are used to relocate and re-establish the plot center. Plots should be permanently dropped from the study if new roads emerged within a 35 m proximity or intersected the plot, if the plot is directly impacted by mechanical treatments (e.g., bulldozing), or if the plot center could not be accurately relocated. B. Plot Description (macroplot) 1. Enter the plot ID, date, and all observers’ initials. 2. Enter the burn unit ID. If unknown enter “TBD”. 3. Identify the witness tree - this is the first live tree (≥ 7.6 cm Diameter at Breast Height, DBH, measured at 1.37m or 4.5 feet of height) tagged, clockwise from 0 degrees (true north). Where permitted, mark witness tree with pink or other highly visible flagging at approx. eyelevel. Record the distance (nearest 0.1m) from base of tree to plot center and the azimuth looking from the witness tree to center. Note tag number. If trees aren’t to be tagged, record tree species and DBH instead of tag number. 4. Assess the fire severity class of any recent fire, based on Table 1. Table 1. Fire severity assessments (Welch et al., 2016). Fire Severity Class Description 0 Unburned 1 Light patchy burn pattern, very little overstory mortality, groups of surviving shrubs/saplings 2 Lightly burned, isolated overstory mortality, most shrubs/saplings dead 3 Moderately burned, mixed overstory mortality, understory mostly burned to ground 4 High burn severity, significant proportion (75-90%) of overstory killed, dead needles remaining on trees 1 year later 5 Very high burn severity, total/near total mortality of overstory, most needles consumed in fire 5. Enter the UTM zone and easting and northing measurements from the GPS unit. 6. Adjust the compass declination used for the project location. 7. Slope: using a clinometer, measure the slope to the nearest 1% from the highest point (topographically) along the outer edge of the plot, looking downslope. Alternatively, measure the slope from point center looking up slope and then down slope and average these two numbers. 8. Aspect: using a hand-held compass, measure and record the predominant aspect (averaged across the entire plot) to the nearest 1 degree. The aspect is the compass direction of the slope. This is also best done from the highest edge of the plot. 9. Vegetation Cover: Estimate percent cover (to nearest 1%) of total plot for the following classes, as viewed from above (airplane/satellite), while ignoring overlaps of the vegetation in each class; 4 a) Total Vegetation: is the total cover of all living vegetation as a percentage of the plot when viewed from above. This measure ignores overlaps among vegetation. This is the complement of the unvegetated area in the plot. b) Total Overstory Trees: is the total cover of live trees (≥ 1.37m height, DBH ≥ 7.6 cm) as a percentage of the plot when viewed from above. This measure ignores overlaps among trees. This is the complement of the plot area that is not covered by trees. c) Total Understory Layer: is the total cover of live saplings (= trees ≥ 1.37m tall and DBH < 7.6 cm) and seedlings (= trees <1.37m tall) and resprouts combined, measured as a percentage of the plot when viewed from above. d) Total live Shrub cover: is the total percent cover of live shrubs, ignoring overlap among shrub individuals, as viewed from above. e) Total Herb Layer: is the total percent cover of forbs and graminoids as seen from above, ignoring overlap. In addition, measurements of modal heights for graminoids and forbs are recorded. 10. Ground cover: Using the categories of bare soil, litter, rock , coarse woody debris (CWD), burn piles (if present) and basal vegetation (live and dead), estimate percent ground surface cover to the nearest 5%. Values must sum to 100%. For basal vegetation, think about what the plot would look like if you cut everything off right at ground level, capturing just the emerging stems/trunks of plants. It is rare to have basal vegetation that is more than 2-4% of the total plot area. Note: For both vegetation and ground cover measurements, take into account that: a) As a reference, in the macroplot, 4-m2 (or 2 m x 2 m) = 1% of the plot. For most people, arms held out at 90 degrees from each other roughly mark two sides of a 1-m2 area. b) If any above-ground cover types are present in the plot but make up less than 1%, record the percent cover as “tr” - this represents trace cover. 11. Photos: Plot photos are intended to (1) show the general aspect of the plot location and its fuels and vegetation; (2) facilitate relocation of the plot in the future recurrent sampling events; and (3) provides a visual comparison of the plot’s fuel and vegetation structure and composition pre and post burning. a) Take a photo of the labeled rebar cap, make sure the plot ID is visible. Alternatively, take a photo of a whiteboard with the plot ID written on it. b) Take one photo of the plot in each cardinal direction moving clockwise, starting with the north photo (the order in the camera should be N, E, S, W). i. Each photo is taken facing the cardinal direction indicated. That is, the N photo is taken from the south end of the N-S transect, and the E photo is taken from the west end of the E-W transect, etc. ii. Take the picture in a horizontal (landscape) direction with the horizon near the middle of the picture. Stand back from the end of the transect sufficiently that the flag marking the end of the transect is visible in the photo. Make sure the plot center is obvious, by stationing a person there or a backpack. 5 C. Trees (macroplot) Tree data: All live and dead trees with ≥7.6cm DBH and ≥1.37 m tall are individually measured. All live trees are tagged in clockwise order from plot center beginning at the North transect (0 degrees). If one tree is directly behind another, measure the closest one to plot center first. Should a qualified sprouting tree species have numerous individuals that are relatively similar in size within the plot, those individuals may be assessed together as group (i.e., modal height, diameter). In this case, each tree gets its own line, and live trees get their own tag, but the heights and diameters will be the same modal numbers. 1. Enter tag #; live or dead status (L or D); and 6-letter species code. Dead trees are recorded but not tagged. Live trees that have died since previously tagged should retain their tags. 2. Measure trees at DBH (1.37m) from uphill side of slope with diameter increment tape measure (d-tape) for live and dead trees. Place tag and nail so that tag is facing the center of the plot. The nail should be placed at 1.37 m above ground. 3. For trees that have a burl, split or other anomaly that exaggerates their DBH, take the DBH measurement above or below the anomaly and add a remark in the notes column. 4. A tree on the edge of the plot counts as “in” if the center of the tree bole (pith) at the base is at or within 11.3 meters from the plot center (measure with rangefinder). Trees with base originating outside the plot but leaning into the plot are not counted. If only some stems on a multi-stemmed individual are in plot, only measure stems that are in the plot. 5. Measure each individual tree height with a range finder to the nearest decimal. If the tree bole is hidden behind leaves etc., use a reflector for higher accuracy. 6. Measure the Height to live crown base (HTLCB) to the nearest 0.1 m for live trees only. This is defined as the height to the lowest live foliage connected to the vertically continuous crown (Figure 2). 7. For standing dead trees (snags), enter decay class (1-5), see Table 2. 8. If you are in a recently burned area measure tree fire severity metrics (see post-fire sampling protocol below). 6 Figure 2 Height to Crown (branches in two quadrants) (USDA, 2015). Table 2. Snag decay classes and descriptions. 7 D. Regeneration (microplot) 1. Establish a microplot with a radius of 4.37 m (area = 60 m²). Use pin flags to mark four reference points around the perimeter, with each flag positioned 4.37 m away from the plot center (typically along transect tapes). See Figure 1 for reference. 2. Tree seedlings: a) Tally the number of tree seedlings (< 1.37 m in height) for each species (conifer and hardwood), categorized by age classes: 0 (first year) and 1+ (older than one year), within the microplot. Refer to Figure 3 for the dichotomous key of conifer seedlings species. b) Record the height for the tallest individual seedling within each species and age class. c) If the regeneration plot is covered with a homogeneous, extremely dense seedling population, count all seedlings in one quarter of the microplot and multiply by 4. 3. Tree saplings: Measure and record the DBH, height and species of each individual tree sapling (≥ 1.37 m tall but < 7.6 cm DBH) of each species (conifer and hardwood). Use a separate row for each individual entry. If groups of saplings form an obvious cohort, determine the modal DBH and height, and record the number of saplings in the cohort in the datasheet. 4. Tree resprouts: a) Tally the number of resprouts originating from each resprout clump of tree species (conifer and hardwood) and record the height of the tallest sprout. b) Consider hardwood resprout clumps as a group if they are similar in density and modal height. Tally the number of resprouts within a single clump and then multiply this count by the total number of clumps. Record the modal height of one of the clumps. c) Resprouts move to sapling category when they reach >1.37 m tall d) If there is no visible stump for origin of resprout, count stems as seedlings if height <1.37 m, not resprout. Figure 3. Dichotomous Key for conifer seedlings species 8 E. Species Cover (macroplot) 1. Record the species lifeform (tree, shrub, forb, graminoid, fern) and live/dead status. 2. Enter the layer class of the live and dead trees species (TOV = overstory tree; TSA = saplings; TSE = seedlings, TRE = tree resprouts). There may be multiple layer classes for each tree species. For example, most tree species will be in the TOV layer as well as the TSA/TSE layer. 3. Plant ID: a) Identify the plants to species level and record the 6 letter species code and percent cover to the nearest 1%. If the identified species is uncommon, add full scientific name in the notes column at least once. b) In case of inability to identify to species level, record “genus_sp”, “family_sp”, “lifeform_unknow” when identified to genus/family/lifeform level. c) To differentiate between different unidentified species on the same site, that are of the same genus, family, and lifeform, follow the following nomenclature: • Genus_sp_sitecode_year_pre/post_number or • Family_sp_sitecode_year_pre/post_number or • Lifeform_unknown_sitecode_year_pre/post_number d) If the phenology is not well-aligned with the sampling episode, species identification for forbs and graminoids might not be possible. If sampling occurs when herbaceous species have senesced for the season, they should still be noted as live. 4. Record the modal height of each shrub species to the nearest 0.1m. 5. Record resprouting shrubs as two entries: one row for the percentage that has been top killed with a dead status and another row for the percentage of live shrub that has resprouted, add “resprout” in notes. 6. If any cover types are present in the plot but make up less than 1%, record the percent cover as “tr” - this represents trace cover. F. Basal Area (plotless) 1. For a plotless measurement of stand basal area (BA), stand at the plot center and use a handheld basal area gauge (e.g., Cruzall or prism) to enumerate the trees that have a DBH that falls within or is less than the gauge's aperture at the selected Basal Area Factor (BAF). 2. Conduct an initial measurement of the BA with a BAF of 20 in most cases. Adjust the BAF if the initial count yields fewer than 6 trees (use a smaller BAF) or more than 9 trees (use a larger BAF). If a lower BAF does not increase the count, default to the largest BAF that results in 6-9 trees. Note that hardwood stands often require a BAF of 10. Record the BAF used. 3. Record the species, status, and count for the tree species enumerated through the gauge's aperture. Record live and dead counts for the same species on two different rows. G. Woody Fuels (macroplot) 1. Fuels data is collected from four Brown’s transects (Brown, 1974). These transects are laid out at the cardinal directions, coinciding with the plot axes, and stretch from the plot center to 11.3 m. The ends of the transects serve as the starting points for measurements, meaning 9 they are read starting from the edge of the plot and heading toward the center. See Figure 1 for reference. 2. Record the azimuth of each transect. Since transects are laid out in cardinal directions, record the azimuth as N, S, E, or W for the four different transects. If diverging from cardinal directions, record the azimuth in degrees. Four transects will share the same plot number. Record transect slope if it exceeds 20 percent. 3. Use a Go/No-Go gauge to tally and record the following fuel classes: a) 1-hr fuels (<0.64 cm) that intersect the transect between the last 2 meters of the transect line (11.3 m - 9.3 m). b) 10-hr fuels (0.64-2.54 cm) that intersect the transect between the last 2 meters of the transect line (11.3 m - 9.3 m). c) 100-hr fuels (2.54-7.62 cm) that intersect the transect between the last 4 meters of the transect line (11.3 m - 7.3 m) 4. Measure litter, duff, and fuel bed depth at the transect starting point (0 m, plot edge), and again at the 4 m mark from that starting point. These points are called duff and fuel pits. a) Litter is undecomposed or only partially decomposed organic material that can be readily identified (plant leaves, needles, twigs, etc.). b) The duff layer lies between the litter and mineral soil and comprises decomposing organic matter. This material is decomposed to the extent that it lacks clearly identifiable whole organic components, such as pine needles, leaves, or twigs, although larger decomposing tree branches may occasionally be present in the duff. c) Fuel bed depth is the vertical distance from the bottom of the litter layer (top of duff) to the highest dead fuel not originating from a rooted plant (e.g., branch, needle, or stick). 5. Cases requiring offset of a duff and fuel pit or an entire Brown's transect: a) If an obstruction (boulder, stump, etc.) is present at a measurement pit (litter, duff, or fuel bed depth), offset that single pit measurement perpendicularly to the transect, and not entire Brown’s transect. Record the offset direction and distance, keeping the offset distance minimal yet sufficient. b) If a burn pile is located on the 4 m Brown’s transect (4 m from the end of the transect), offset the entire Brown’s transect along the transect (towards the plot center) until the burn pile no longer intersects. Note the offset distance from the end of the transect. 6. Record diameter and the entire length (even if it extends outside of the plot perimeter) for every piece of coarse woody debris (CWD) that intersects the transects (see Figure 4) and meets the minimum criteria: 7. Asses the coarse woody debris (CWD) pieces that intersect the transects and meets the following minimum criteria: a) Central longitudinal axis of the CWD intersects the transect (refer to Figure 4) b) The diameter at the point of intersection is ≥ 7.6 cm. 8. For each qualifying piece of CWD, record: a) The species code of the CWD piece when possible. If unknown, use “unk” as the species code. b) The distance from the plot center (defined as 0 m) to the point where the CWD piece intersects the transect. c) The diameter of the CWD piece at the point of intersection.