DEFENSIBLE SPACE‐EROSION PROTECTION TOOLS DEVELOPMENT (P055) PROJECT REPORT PREPARED BY: INTEGRATED ENVIRONMENTAL RESTORATION SERVICES, INC. SHELLY THOMSEN, LINDSAY DOWNING, KEVIN DRAKE, & MICHAEL HOGAN OCTOBER 17, 2012 This research was supported using funds provided by the Bureau of Land Management through the sale of public lands as authorized by the Southern Nevada Public Land Management Act (SNPLMA), and was funded in part through a grant from the USDA Forest Service Pacific Southwest Research Station. The views in this report are those of the authors and do not necessary reflect those of the USDA Forest Service Pacific Southwest Research Station or the Bureau of Land Management.
Defensible Space‐Erosion Protection Tools Development –Project Report PREFACE This project fills a critical information gap identified in the Lake Tahoe Environmental Improvement Program, discussed briefly in the Tahoe Total Maximum Daily Load (TMDL) Pollutant Load Opportunity Report and hinted at in nearly every defensible space directive– the need for practical residential defensible space practices that effectively reduce fire risk and while controlling erosion and reducing runoff. Unfortunately, current defensible space practices are tending toward the removal of protective soil cover, thus increasing erosion and water quality degradation risk. The following research identifies and quantifies defensible space practices around homes that are capable of reducing or eliminating fire risk (as per CA Public Resources Code 4291), while minimizing erosion, protecting water quality, infiltrating stomwater and snowmelt, reducing runoff and gaining acceptance from fire agencies and homeowners. This research is focused primarily on protecting water quality from poorly thought out defensible space strategies and perhaps improving water quality protection through implementation of defensible space practices. This project evaluates eight promising soil protection Best Management Practices (BMPs) for both flammability and erosion control parameters. The most mutually effective BMPs were showcased during a Conservation Landscape Tour and at Autumn Festival to showcase defensible space practices that achieve both fire protection and erosion control‐water quality objectives. The results from the study were also developed into an educational pamphlet geared for homeowners and were distributed throughout the Tahoe Basin. Page 3 Defensible Space‐Erosion Protection Tools Development –Project Report TABLE OF CONTENTS Preface ........................................................................................................................................................................... 3 Project Introduction ...................................................................................................................................................... 6 Project Background ....................................................................................................................................................... 7 Chapter 1. Monitoring Overview ................................................................................................................................... 9 Site Overview ................................................................................................................................................................. 9 Monitoring Methods ..................................................................................................................................................... 9 Penetrometer Depth to Refusal (DTR) .................................................................................................................... 10 Soil Moisture ........................................................................................................................................................... 10 Rainfall Simulation .................................................................................................................................................. 11 Burn Test Monitoring ............................................................................................................................................. 12 Treatment Methods .................................................................................................................................................... 13 Materials ................................................................................................................................................................. 13 Mulch and Amendment Application ....................................................................................................................... 15 Amendment Incorporation Methods ...................................................................................................................... 15 Plot Shape ............................................................................................................................................................... 16 Test Plot Reconstruction ......................................................................................................................................... 17 Chapter 2. Erosion Risk Assessment ............................................................................................................................ 18 Site Description ............................................................................................................................................................ 18 Treatments .................................................................................................................................................................. 18 Results and Discussion ................................................................................................................................................. 20 Statistical Analysis ................................................................................................................................................... 20 Sediment Yield and Infiltration Rate ....................................................................................................................... 20 Penetrometer Depth to Refusal (DTR) .................................................................................................................... 21 Soil Moisture ........................................................................................................................................................... 22 Mulch Cover ............................................................................................................................................................ 23 Summary and Discussion ........................................................................................................................................ 23 Results in Context ................................................................................................................................................... 24 Chapter 3 Fire Risk Assessment ................................................................................................................................... 25 Site Description ............................................................................................................................................................ 25 Treatments .................................................................................................................................................................. 25 Results and Discussion ................................................................................................................................................. 26 Summary ................................................................................................................................................................. 29 Chapter 4. Education and Outreach ............................................................................................................................ 30 Educational Brochure.............................................................................................................................................. 30 Conservation Landscape Tour ................................................................................................................................. 30 Autumn Festival ...................................................................................................................................................... 31 Educational Videos ................................................................................................................................................. 31 Conclusion and Recommendations ............................................................................................................................. 32 Conclusions .................................................................................................................................................................. 32 Management Recommendations ................................................................................................................................ 33 Literature Cited ............................................................................................................................................................ 34 Appendix A................................................................................................................................................................... 35 Appendix B ................................................................................................................................................................... 36 Page 4 Defensible Space‐Erosion Protection Tools Development –Project Report Page 5 Defensible Space‐Erosion Protection Tools Development –Project Report PROJECT INTRODUCTION This project tested the effectiveness of eight different landscape treatments at reducing erosion and maintaining low fire risk. The aim is to develop (or support existing) field‐tested landscape practices that can satisfy two of the top land management objectives in the Tahoe Basin – defensible space and erosion protection. A steering committee made up of regulatory agency personnel, fire districts, and outreach and education specialists representing the fire protection and erosion protection communities was created to identify which landscape materials and treatments should be tested. The field monitoring used in the study includes rainfall simulation to test infiltration, runoff and erosion characteristics, and burn tests to assess the general flammability/burn characteristics of each landscape treatment. The results from the study were featured during two community gardening events and were incorporated into an educational pamphlet that was distributed throughout the Basin. What is the purpose of this project? The purpose of this project is to test the erosion reduction capacity and burn characteristics of a range of landscape materials and practices. The results of these tests are summarized into field‐tested recommendations for implementing residential‐scale landscaping treatments that achieve both erosion protection and defensible space goals. The findings from this project provide recommendations for homeowners, landscapers and agency staff that assist homeowners on defensible space and best management practices. In addition, this project has created a much‐needed dialog aimed at identifying common ground between those who promote and enforce defensible space practices with those who promote and enforce erosion control practices. What is the need for this project? This study begins to fill critical information gaps identified in the Emergency California‐Nevada Tahoe Basin Fire Commission Report (“Blue Ribbon Commission”), the Lake Tahoe Environmental Improvement Program, and the Lake Tahoe Total Maximum Daily Load (TMDL) Pollutant Load Opportunity Report– the need for practical residential landscaping practices that effectively reduce fire risk and while controlling erosion and reducing runoff. Who was involved in this project? This study worked directly with fire districts and residential Best Management Practice (BMP) implementers to develop and test fire and erosion safe BMPs. A steering team was formed to identify key surface mulches and practices to be tested. The team consisted of Tahoe Resource Conservation District (Tahoe RCD), Tahoe Regional Planning Agency (TRPA), Meeks Bay Fire Protection District, United State Forest Service‐Pacific Southwest Research Station, and Tahoe Fire and Fuels Team. Upon completion of the study, an educational brochure was developed to educate homeowners on fire resistant BMPs. Feedback on the brochure’s content and layout was provided by TRPA, Lahontan Regional Water Quality Control Board, Tahoe Douglas Fire Protection District, North Lake Tahoe Fire Protection District, Meeks Bay Fire Protection District, Cal Fire, and Tahoe RCD. Incorporating fire districts and residential BMP implementers into the project development and implementation allows the study’s findings to be adopted and promoted in a more efficient and effective manner. What does this report entail? This report summarizes the monitoring results, and management recommendations regarding defensible space and erosion control practices, and an overview of how the findings have been distributed to the public through education and outreach event Page 6 Defensible Space‐Erosion Protection Tools Development –Project Report PROJECT BACKGROUND Beginning in the mid 1900’s, fire suppression efforts in the Lake Tahoe Basin, and in the west in general, have resulted in overstocked forests that have reached either maturity or in many cases, decadence, overcrowding and suppressed growth forms. Such forests are prone to environmental stresses, related insect and disease attack that greatly increase an already high risk of catastrophic wildfire. Beginning in the 1960’s, the Tahoe Basin began its trajectory toward increasing urbanization. Urbanization within existing forest stands is highly prone to home‐
destroying wildfires. This is due to the fact that the Lake Tahoe Basin is dominated by a mixed conifer forest‐type ecosystem, which has coevolved with fire. While some forested areas were thinned or logged to accommodate residential development, most trees were left in place as part of the ambiance and perception of having a home or cabin “in the woods.” In 2007, the Angora Fire burned approximately 3100 acres (12.5 km2), destroying 254 residences, 67 commercial structures, and partially damaging 35 other homes. In August of 2007, the Washoe Fire on the northwest shore of Lake Tahoe near Tahoe City was contained at less than 20 acres (0.08 km2) and destroyed 5 homes. Both incidents brought immediate public attention and awareness to the very real potential of property damage and losses possible from wildfires burning near their homes due to existing forest conditions. Since that time, an increasing amount of attention and resources have been expended in planning and implementing forest vegetation management efforts aimed at changing forest stand structure. These efforts are likely to be intensified over the next several years. Those management activities are being implemented in order to minimize crown fires and fire transmissibility through forest stands. Additionally, fire districts, CalFire and the Emergency California‐Nevada Tahoe Basin Fire Commission Report (“Blue Ribbon Commission”) emphasize the removal of flammable materials around homes, suggesting and enforcing a 30 to 100 feet or larger “buffer” area around homes, leaving large areas of bare ground susceptible to accelerated erosion. Research by Grismer and Hogan (2004‐2005) as well as others, have shown that maintenance of a surface mulch layer and/or maximizing soil infiltration can be highly effective at reducing erosion and sediment loading while conserving soil moisture. However, little work has been done to apply these findings to home landscapes. Thus, what remains unknown is how such mulches and soil treatments might affect fire risk when adjacent to structures. This project addresses the lack of supporting data for fire and erosion management activities around homes. The other element is the ability to put that information and data directly into the hands of those who need it. This project addresses the general lack of direct connection between research, planners and end users of that research. Research science has been shown to, at times, be at odds with or at least be distanced from management actions (Gibbons et al. 2009). Research findings are left to agency staff, management professionals and others to interpret and apply to management activities, but in a relatively unstructured manner. Unfortunately, this approach has left managers with few understandable, accessible, scientifically‐validated tools to use to plan and implement water quality and fire safe BMPs, beyond the largely un‐calibrated erosion models. Further, managers have not always been able to adequately translate to researchers the questions or information gaps that need to be filled in order to help them make better, science‐based management decisions. With an increasing emphasis on application of fire‐safe practices around homes in the Basin, it is incumbent upon scientific investigators to work directly with fire and fuels managers to develop cost‐effective, quantifiable management strategies that reduce both fire danger and erosion potential. It is incumbent upon the scientific community to provide fire protection managers and residential BMP planners and implementers with scientifically‐
defensible, field‐verified management practices that achieve both important objectives. If we are not able to integrate these two management objectives, we will likely fail at both. . Intuition‐based solutions are unlikely to solve this problem. This project directly addresses the lack of integration between fire‐resistant and erosion‐
Page 7 Defensible Space‐Erosion Protection Tools Development –Project Report resistant landscapes, the lack of data needed to support an intelligent evaluation of management alternatives and the gap between scientific findings and management actions. Page 8 Defensible Space‐Erosion Protection Tools Development –Project Report CHAPTER 1. MONITORING OVERVIEW SITE OVERVIEW The burn and erosion test plots were constructed and the same treatment materials at two different sites (approximately 0.7 miles apart) on the Homewood Mountain Resort Property. Both sites are located at the bottom of ski runs at two different bases of the resort. The erosion tests were constructed at the north base and the burn tests were constructed at the south base. Overall site characteristics such as slope, aspect, existing vegetative cover, and soil conditions were similar between both areas and are described in detail later in the report. FIGURE 1. SATELLITE IMAGE OF PROJECT AREA LOCATION. TEST PLOTS WERE LOCATED AT THE NORTH AND SOUTH BASES OF HOMEWOOD MOUNTAIN RESORT IN HOMEWOOD, CALIFORNIA. MONITORING METHODS Monitoring methods for penetrometer depth to refusal and soil moisture were based on those described by Grismer, Schnurrenberger, Arst and Hogan (2009). Methods include penetrometer depth to refusal, soil moisture, rainfall simulation, and burn tests. Page 9 Defensible Space‐Erosion Protection Tools Development –Project Report PENETROMETER DEPTH TO REFUSAL (DTR) Penetrometer DTR measurements are used as a surrogate for soil density. A cone penetrometer with a ½ inch diameter tip is pushed straight down into the soil until a maximum pressure of 350 pounds per square inch is reached (See Figure 2 and Figure 3). The depth at which that pressure is reached is recorded as the depth to refusal (DTR). The depths are marked in 3 inch increments and can be read to the nearest inch. For the erosion test plots, penetrometer DTRs were measured at nine different points around each frame pre simulation and within each test plot rainfall frame post rainfall simulation. FIGURE 2. CONE PENETROMETER DIAL SHOWING PRESSURE APPLIED IN POUNDS/SQ IN. FIGURE 3. CONDUCTING CONE PENETROMETER READINGS WITHIN EROSION TEST PLOT FRAME POST RAINFALL SIMULATION, 2011. SOIL MOISTURE A hydrometer is used to measure volumetric soil moisture content adjacent to the penetrometer readings at a depth of 4.7 inches (Figure 4 and Figure 5). For the erosion test plots, soil moisture was measured at nine different points around each frame pre simulation and within each test plot rainfall frame post rainfall simulation. FIGURE 4. HYDROSENSE SOIL MOISTURE READER. FIGURE 5. CONDUCTING SOIL MOISTURE READINGS IN EROSION TEST PLOT POST RAINFALL SIMULATION, 2011. Page 10 Defensible Space‐Erosion Protection Tools Development –Project Report RAINFALL SIMULATION The rainfall simulator is a custom‐designed monitoring tool used to simulate rainfall events of a known intensity and directly measure infiltration, runoff, and erosion rates from disturbed, treated, and reference areas. The methods described below follow those established by Grismer and Hogan (2004) and have been used for hundreds of simulations since establishment (Grismer and Hogan 2005a, 2005b; Grismer, Ellis and Fristensky, 2008). For this study, one rainfall simulation was conducted in each plot for a total of 3 rainfall events for each treatment. FIGURE 6. RAINFALL SIMULATOR IN ACTION AT EROSION TEST PLOTS, 2011. FIGURE 7. COLLECTING RUNOFF SAMPLES FROM FRAME, 2011. The rainfall simulator “rains” on a square plot from a height of 3.3 feet (Figure 6). The rate of rainfall is controlled at 4.7 inches per hour and runoff is collected from a trough at the bottom of a 6.5 ft2 frame that has been pounded into the ground. The volume of water collected is measured (Figure 7), and then the volume of infiltration is calculated by subtracting the volume of runoff from the total volume of water applied to the plot. If runoff is not observed during the first 45 minutes, the simulation is stopped. The average steady state infiltration rate is calculated for each simulation and the collected runoff samples are then analyzed for steady state sediment yield and particle size distribution. Sediment yield is determined by filtering samples with Whatman #541 and 0.45‐
micron filters. The sediment samples are oven‐dried at 221° F (105° C) and then combusted at 806° F (430° C) to determine organic matter content (Grismer et al., 2008). After rainfall simulation, the depth to wetting front is measured at nine locations within the frame to determine how deeply water has infiltrated into the soil column. Prior to conducting each rainfall simulation, plant cover and mulch cover is estimated by ocular estimates within each rainfall simulation frame. Page 11 Defensible Space‐Erosion Protection Tools Development –Project Report BURN TEST MONITORING Burn tests generally followed the methods used for tests conducted by University of Reno, Nevada (UNR) and University of California (UC) Cooperative Extension (Quarles and Smith, 2011). Each plot was ignited by a drip torch administered by a fire professional. Once flames had been established, a fan was turned to approximately ten miles per hour to mimic average wind conditions. Measurements and observations were recorded by several different personnel in attendance (Figure 9), including video documentation of each test. Observers included the Meeks Bay fire chief, RCD personnel and IERS monitoring technicians. Results were tallied and consolidated from these data forms. Table 1 describes the parameters and methodology used. Figure 10 illustrates the configuration of each burn test plot. FIGURE 8. DEFENSIBLE SPACE PLOT IGNITED BY A DRIP TORCH, 2011. FIGURE 9. CHECKING WIND SPEED AND RECORDING OBSERVATIONS AT A DEFENSIBLE SPACE PLOT, 2011. TABLE 1. BURN TEST PARAMETERS AND METHODOLOGY
Parameters Methodology
Burn test parameters Maximum burn temp Maximum flame height
3 heat‐sensitive paint chips at ground level in each plot (under the mulch) Graduated T‐stakes in the plot center marked in 15 cm increments
Average flame spread rate Placement of fire crackers under mulch surface at known distances
Flame and ember residence time Stop watch Ember production Observation (qualitative ranking)
Ease of ignition Material consumed % Time and/or # of attempts to carry flame after the fan is turned on (qualitative ranking) Ocular estimate measurement before/after burn Total burn time Stop watch
Wind speed Portable Anemometer
Total distance and area burned Measuring Tape
Ambient conditions Ambient air temp Portable Weather Station
Relative humidity Portable Weather Station
Wind speed Portable Anemometer
Page 12 Defensible Space‐Erosion Protection Tools Development –Project Report Center stake used to measure flame height Fire crackers used to measure flame speed
Air Flow from fan Paint chips used to estimate maximum temperature Location of ignition by drip torch
FIGURE 10. DIAGRAM OF IGNITION TEST DESIGN. PAINT CHIPS AND FIRE CRACKERS WERE PLACED AT SOIL SURFACE, UNDER THE MULCH TREATMENT METHODS MATERIALS The selection of materials and techniques were carefully considered to yield the most informative and useful results. The selection of the eight treatments ( Table 2) was made by the project steering committee. Each of the eight treatments were constructed and repeated in three different plots at the Erosion Control test plot area and once at the Defensible Space test plot area. Materials were selected based on availability, cost, and practicality of treatment materials. The eight treatments are grouped into two categories: surface mulch application only and tilling in of organic amendment. Mulch materials include pine needles, aged duff, Integrated Zero (composted woodchips) and landscape bark. Three of the treatment types were tilled with a standard Honda roto‐tiller rented from a local power equipment store. Mulch material was spread on the plot surface and then tilled into the soil using the roto‐
tiller. The materials tilled in included duff, woodchips, and Integrated Zero. The final treatment type was woodchips tilled into the soil using an excavator bucket. Page 13 Defensible Space‐Erosion Protection Tools Development –Project Report TABLE 2. AMENDMENT/MULCH MATERIALS USED Woodchips By‐product of Meeks Bay Defensible Space program. Material can be highly variable due to plant material processed and equipment used. “Integrated Zero” Composted Woodchip
Product purchased from Full Circle Compost in Minden, NV. Pine Needles Naturally occurring, collected from the West Shore of Lake Tahoe. Duff Naturally occurring, collected from within the Homewood Mountain Resort property boundary. Page 14 Defensible Space‐Erosion Protection Tools Development –Project Report Landscape Bark Purchased from local home and garden store. Note: Woodchips were selected over other commonly used woody material such as tub grinding. Woodchips are more readily available (and typically free) and in the short‐term, are likely to have similar effects on infiltration processes when incorporated into the soil. TABLE 3. SELECTED TREATMENTS FOR TESTING. Material Surface Application (2‐3" depth) 2” Amendment incorporated with roto‐tiller (3‐6” depth) 4” Amendment incorporated with mini excavator (12” depth) Woodchips X X “Integrated Zero” (Composted woodchips from Full Circle Compost) Pine needles Duff (partly decomposed pine needles) Landscape bark nuggets (not shredded) X X X X X X MULCH AND AMENDMENT APPLICATION For plots that were mulched only and not tilled, mulch was spread on the plot by hand and measured several times to reach the desired depth. For the plots that were tilled, amendment was spread on the plot by hand and measured several times to reach the desired depth. The amendment was then incorporated into the soil by either a roto‐tiller or mini excavator. After soil loosening was completed, any mulch remaining on the plot surface was measured. The difference between the mulch measurement and the original amendment measurement was recorded as the final amendment amount. In some cases, the use of the roto‐tiller created mulch as the tiller chopped up existing vegetation in the plot area. When measureable amounts of plant litter and root debris mulch was created, the depth was recorded as a second mulch type. AMENDMENT INCORPORATION METHODS Certain plots had amendment incorporated into the soil by either roto‐tiller or mini excavator. The (Figure 11) tilling depths typically reached approximately 4‐6 inches, while a mini‐excavator (Figure 13) or similar equipment can till to depths greater than 6 inches. Although tilling with a mini‐excavator is less practical for a homeowner than a using a roto‐tiller, it was used to evaluate the effects of the deeper tilling depths on infiltration capacity. BMPs are often installed by professional installers capable of achieving incorporation greater than 6 inches with a variety of equipment. The ability to understand the effects of deeper tilling on infiltration will guide determination Page 15 Defensible Space‐Erosion Protection Tools Development –Project Report of whether or not the additional cost is worth the effort, thus justifying the inclusion of the test plots with woodchips incorporated to 12‐14 inches with a mini‐excavator. FIGURE 12. ROTO TILLING A DEFENSIBLE SPACE TEST PLOT FIGURE 13. MINI EXCAVATOR TILLING AN EROSION CONTROL TEST PLOT PLOT SHAPE Plots constructed at the north base for erosion control testing measured 8 feet by 8 feet. The square shape allowed for the plots to fit together tightly in the space provided. Each treatment type was represented by 3 plots, equaling total of 24 plots. Plots constructed at the south base for defensible space testing were circular and measured 8 feet in diameter. Plots were round to allow for maximum flexibility in deciding what side of the plot to ignite the material during the burn monitoring. Ignition location was based on burn day conditions such as wind direction and fire safety consideration from fire personnel. FIGURE 14. DEFENSIBLE SPACE TEST PLOT (ROUND), HOMEWOOD 2011. FIGURE 15. EROSION TEST PLOT (SQUARE), HOMEWOOD 2011. Page 16 Defensible Space‐Erosion Protection Tools Development –Project Report TEST PLOT RECONSTRUCTION Test plots were constructed in summer 2010. However, frequent rain, cool temperatures and high humidity in September and October did not allow test plots to dry out as planned, resulting in unrepresentative conditions for the burn tests planned for October 2010. Additionally, initial rainfall simulation tests conducted in fall 2010 on a subset of the tilled plots produced very high intra‐plot variability in sediment yield results. This is due at least in part to the short period of time between soil loosening treatments and monitoring (approx. 1 month). Rainfall simulation and burn tests were rescheduled for summer 2011 in order to allow the test plots with soil physical treatments to equilibrate. This extension also allowed the plots to spend a winter under snow and to allow the mulch materials on the surface of all plots to dry out over the course of a summer. This change to the monitoring schedule was made in the interest of establishing more representative conditions for both the burn tests and erosion tests. Additional test plots were constructed in October 2010 to replace the plots that were disturbed by rainfall simulation in fall 2010. This was done to ensure that monitoring results in 2011 would not be influenced by soil disturbance associated with rainfall simulation monitoring in 2010. Page 17 Defensible Space‐Erosion Protection Tools Development –Project Report CHAPTER 2. EROSION RISK ASSESSMENT SITE DESCRIPTION In late summer of 2010, erosion control test plots were constructed on the bottom of the ski slope at the north base of Homewood Mountain Resort in Homewood, California. The test plots represent eight different erosion control treatments. The treatment type for each plot was selected at random within the test area. Each treatment was repeated three times, equaling a total of 24 plots (Figure 16 and Table 4). The site location is an open ski run covered primarily with wheatgrass. The area faces northeast and is moderately sloped at 8 to 11 degrees and has no canopy cover. The soil parent material is of volcanic origin. Soil was fairly dense (due to regular grooming throughout the winter) prior to any treatments being applied (penetrometer DTR averages around 4 inches). The site elevation is approximately 6,246 feet above sea level. Rainfall simulation monitoring was conducted in the first two weeks of July 2011. TREATMENTS FIGURE 16. MAP OF NORTH BASE EROSION CONTROL PLOTS, 2011. Page 18 Defensible Space‐Erosion Protection Tools Development –Project Report TABLE 4. EROSION TEST PLOT TREATMENTS FOR PLOTS 1A‐8C, CONSTRUCTED 2010.
Plot
Tilling
depth
(in)
Tilling
method
Amendment
type
Amendment
depth (in)
Mulch type 1
Mulch
depth
1 (in)
Mulch Mulch
type 2 depth
2 (in) 1A
7
Roto till
Woodchips
1
Woodchips
1
1B
1C
2A
2B
2C
3A
6
7
13
13
14
7
Roto till
Roto till
Excavator
Excavator
Excavator
Roto till
Woodchips
Woodchips
Woodchips
Woodchips
Woodchips
Coarse overs
1
1.8
3.5
3.8
3.5
0.5
Woodchips
Woodchips
Woodchips
Woodchips
Woodchips
Coarse overs
1
0.2
0.5
0.2
0.5
0.5
3B
3C
4A
7
5
7
Roto till
Roto till
Roto till
Coarse overs
Coarse overs
Duff
0.5
0.6
1.4
Coarse overs
Coarse overs
Duff
0.5
0.4
0.6
4B
4C
5A
5B
5C
6A
7
7
0
0
0
0
Roto till
Roto till
Duff
Duff
1.6
1.6
0.4
0.6
2
2
2
2
6B
0
2
6C
0
2
7A
7B
7C
8A
8B
8C
0
0
0
0
0
0
Duff
Duff
Pine needles
Pine needles
Pine needles
Landscape
bark
Landscape
bark
Landscape
bark
Coarse overs
Coarse overs
Coarse overs
Duff
Duff
Duff
Plant
litter Plant
litter Plant
litter 2
2
2
2
2
2
Page 19 1
0.5 0.8
Defensible Space‐Erosion Protection Tools Development –Project Report FIGURE 17. TEST PLOT AREA OVERVIEW, 2010. FIGURE 18. SAMPLE BOTTLES COLLECTED, 2011. FIGURE 19. RAINFALL SIMULATOR IN ACTION, 2011. FIGURE 20. COLLECTING RUNOFF SAMPLES, 2011. RESULTS AND DISCUSSION STATISTICAL ANALYSIS Rainfall data was tested using statistical methods such as z‐testing, ANOVA, and MANOVA statistical tests. Statistical results are presented in Appendix A. Analysis of this data indicates that there is no dependence of infiltration rate or sediment yield on factors such as soil density (Figure 21 and Figure 22). As a result of this finding, treatment methods were broken into the groups “Mulched Plots” and “Tilled Plots” for statistical analysis. The tilled plots category includes the roto‐tilled and excavator tilled plots. SEDIMENT YIELD AND INFILTRATION RATE Plots that were tilled had a higher average sediment yield (91.1‐196.5 lbs/acre/in) than those that had mulch application and no tilling (10.8‐ 41.6 lbs/acre/in), with the exception of roto‐tilled woodchips (37.9 lbs/acre/in, Figure 21). Page 20 Defensible Space‐Erosion Protection Tools Development –Project Report The sediment yield values for the mulched plots were lower than that of three out of four tilled plot treatments. The higher sediment yield in the tilled plots is likely a function of less surface mulch, since surface mulch was not applied after tilling. The mulch cover on the surface of the tilled plots was only what had remained after tilling, resulting in a thin non‐continuous mulch cover. The tilled plots had 20‐50% bare soil exposed on the surface compared to 0% (no bare soil exposed) in the mulch plots. When bare soil is exposed to erosive agents such as rainfall, soil particles are more easily detached and washed away in runoff water, and is quantified as sediment yield. See mulch section for a more detailed discussion on mulch. The infiltration rate was higher in the mulched plots (3.6 to 4.1 inches/hour) than the tilled plots (3.1 to 4.0 inches/hour), again, with exception of woodchips roto‐tilled (4.3 inches/hour, Figure 21). Within the tilled plots, the infiltration rates are not significantly different (too few points and too much variability). Similarly, the roto‐
tilled mean sediment yield is much smaller than that from the plots tilled with the excavator bucket, but not significantly so (because of variance and n). Average Sediment Yield Per Treatment
Sediment Yield
Infiltration Rate
4.5
4.3
200
4.1
3.9
150
3.7
3.5
3.3
100
3.1
2.9
50
Infiltration Rate (in/hr)
Sediment Yield (lbs/acre/in)
250
2.7
2.5
0
Integrated Zero Roto‐
tilled
Woodchips Excavator Tilled
Duff
Roto‐tilled
Landscape Bark Mulch
Woodchips Roto‐tilled
Pine Needle Mulch
Integrated Zero Mulch
Duff Mulch
FIGURE 21. INFILTRATION RATE AND SEDIMENT YIELD. SEDIMENT YIELDS TEND TO BE LOWER FOR PLOTS THAT WERE MULCHED ONLY THAN PLOTS THAT WERE TILLED WITH AMENDMENT, WITH EXCEPTION OF THE WOODCHIPS ROTO‐TILLED PLOTS. INFILTRATION RATE VARIED BETWEEN TREATMENT TYPES. PENETROMETER DEPTH TO REFUSAL (DTR) Average penetrometer readings before rainfall simulation for the mulch plots ranged from 3.5 to 5 inches based on 9 readings. The tilled plots ranged from 4.5 to 7.25 based on 9 readings. For the tilled plots, mean penetrometer depths are significantly different (99%) and can therefore be compared. The excavator tilled plots have the deepest DTR of any other treatments (7.25 inches, Figure 22) due to deeper soil loosening. Page 21 Defensible Space‐Erosion Protection Tools Development –Project Report Penetrometer DTR Per Treatment
Initial Penetrometer DTR (inches)
Integrated Zero Woodchips Roto‐tilled
Excavator Tilled
Duff
Roto‐tilled
Final Penetrometer DTR (inches)
Landscape Bark Mulch
Woodchips Roto‐tilled
Pine Needle Mulch
Integrated Zero Mulch
Duff Mulch
2.50
DTR (in)
4.50
6.50
8.50
10.50
FIGURE 22. PENETROMETER DTR AVERAGE FOR EACH TREATMENT TYPE. THE INITIAL PENETROMETER READINGS WERE TAKEN BEFORE RAINFALL SIMULATION AND THE FINAL WERE TAKEN IMMEDIATELY AFTER RAINFALL SIMULATION. THERE IS NO DEPENDENCE OF PENETROMETER DTR MEASUREMENTS ON INFILTRATION RATE OR SEDIMENT YIELD. SOIL MOISTURE Statistically, initial soil moisture of the plots before rainfall simulation was a more significant indicator of infiltration rate and sediment yield than penetrometer DTR. The initial soil moisture varied from plot to plot (Figure 23) due to several factors such as duration of the experiment, weather and possible influence from nearby irrigation. Initial soil moisture ranged from 4 to 9%. For plots that were mulched, there is a relationship between lower soil moisture and lower sediment yield, with exception of the pine needle mulch plots which had the lowest initial soil moisture and one of the higher sediment yields of the mulched plots (4.4% compared to 5.6 to 9.2% soil moisture and 36.9 compared to 10.8 to 41.6 lbs/acre/inch). For plots that were tilled, the relationship is opposite: higher initial soil moisture was associated with lower sediment yield. A somewhat surprising result given that increased soil moisture tends to be associated with increased penetrometer DTR with all other factors equal. Nonetheless, initial plot soil moisture readings have some merit and can be correlated as noted. Soil Moisture (%)
Average Initial Soil Moisture Per Treament
11
9
7
5
3
Integrated Woodchips Duff
Landscape Woodchips Pine Needle Integrated Duff Mulch
Zero Roto‐ Excavator Roto‐tilled Bark Mulch Roto‐tilled
Mulch Zero Mulch
tilled
Tilled
FIGURE 23. INITIAL SOIL MOISTURE AVERAGE FOR EACH TREATMENT TYPE. THE INITIAL PENETROMETER READINGS WERE TAKEN BEFORE RAINFALL SIMULATION WAS CONDUCTED. Page 22 Defensible Space‐Erosion Protection Tools Development –Project Report MULCH COVER The average mulch depth of plots that were mulched was four times deeper than the average of the tilled plots (2 to 0.5 inches, Figure 24). The tilled plots were not intentionally mulched as part of the restoration treatment. During the tilling process, any amendment that was not tilled into the soil and remained on the plot surface was counted as mulch. The mulch depths ranged from 0.45 to 0.67 inches for the tilled plots compared to the 1.48 to 2.48 for the mulched plots. As a result, the mulch cover on these plots was not consistent like the mulch‐only plots. This resulted in an increase of bare soil (20‐50% bare soil compared to 0% at the mulched plots). Mulch depth readings were taken in the exact location as the rainfall frame at the time of simulation. Mulch depth readings can vary from the treatment specifications because these readings are measuring a subset of the plot, whereas the treatment specifications were applied to the entire plot. When compared to the mulch plots, tilled plots had significantly greater sediment yields and exhibited a negative correlation between sediment yield and mulch depth. Mulch Depth Per Treatment 3.0
2.5
2.0
1.5
1.0
0.5
0.0
Integrated Zero Roto‐tilled
Woodchips Excavator Tilled
Duff
Roto‐tilled
Landscape Bark Woodchips Roto‐
Mulch
tilled
Pine Needle Mulch
Integrated Zero Mulch
Duff Mulch
Mulch Depth (inches)
FIGURE 24. MULCH DEPTH AVERAGE FOR EACH TREATMENT TYPE. PLOTS THAT WERE MULCHED HAD AN AVERAGE OF 4 TIMES DEEPER COVER BY MULCH THAN PLOTS THAT WERE TILLED (.5 INCHES TO 2 INCHES). SUMMARY AND DISCUSSION For the plots that were mulched, lower soil moisture was the dependent factor on lower infiltration rates and sediment yield. Curiously the opposite was true with the plots that were tilled. When looking at the two treatment categories separately (mulched vs. tilled) soil moisture can be used as an indicator of sediment yield and infiltration rate. However, the conflicting effects of soil moisture on sediment yield and infiltration rate as found here make sole use of this parameter an unreliable predictor of sediment yield alone. Although tilled plots had significantly deeper initial penetrometer DTR readings than the mulch‐only plots, these treatments had greater sediment yields. The higher sediment yields from the tilled plots are likely more a function of mulch cover/depth than soil physical conditions. As described above, mulch cover was minimal on the tilled plots (covering 50‐70% of the plot at 0.45 to 0.67 inches deep, averaged by treatment type) because no additional surface mulch was added following tilling. Whatever mulch remained on the surface following tilling was left in Page 23 Defensible Space‐Erosion Protection Tools Development –Project Report place in order to test this low‐cost, one‐step treatment process, whereas mulch was applied to an even cover/depth (covering 100% of the plot at 1.48 to 2.48 inches deep, averaged by treatment type) on the mulch only (no‐till) plots. In this study, mulch cover was shown to be negatively correlated with sediment yield, which is consistent with previous research (described below). Additionally, soil loosening of the tilled plots 10 months prior to monitoring broke up well‐established vegetation in the test area (primarily grasses) whereas this existing vegetation was mowed and left in place for the mulch‐only test plots. These distinct differences in site (soil and vegetation) conditions makes it difficult to compare erosion/runoff characteristics and erosion resistance between the tilled and mulch‐only treatment categories, especially in the short‐term (less than 1 year following tilling). Overall the greatest sediment yields from this experiment came from the tilled plots with the exception of the wood chips roto‐tilled plot. The lowest sediment yields came from the duff mulch treatment type. The treatment type with the highest infiltration rate combined with the lowest sediment yield was the wood chips roto‐tilled plots. RESULTS IN CONTEXT Previous rainfall simulation research by Grismer and Hogan (2005) at 120 test plots in the Tahoe Basin shows that 25mm (~1 inch) of pine needle mulch results in nearly an order of magnitude reduction in sediment yield compared to bare soil conditions. Related research by Grismer and Hogan (2009) indicates that tilling compacted soils to at least 12 inches is associated with higher cover by native perennial bunchgrasses, higher infiltration rates and lower sediment yields than non‐tilled plots. Many treatments that included both tilling and amendment incorporation produced no runoff at all, even at rainfall rates of 4.7 in/hr (Grismer and Hogan 2005). In recent rainfall simulation research conducted by IERS at Homewood, sediment yield data was collected from other existing disturbed ski runs and inactive dirt roads on the property. These disturbed areas had similar slope and compacted soil. The average sediment yield from rainfall simulation at these sites was 5.6 times higher than the average sediment yield from the tilled plots in this experiment (685.91 lbs/acre/inch compared to 121.91 lbs/acre/inch). Previous research at Homewood and a large body of research throughout the Tahoe Basin indicates that soil loosening, incorporation of woody material and surface mulching (0.5 ‐ 1”) can reduce sediment yield, and substantially improve erosion resistance compared to compacted, partially vegetated areas with little to no mulch cover. Page 24 Defensible Space‐Erosion Protection Tools Development –Project Report CHAPTER 3 FIRE RISK ASSESSMENT SITE DESCRIPTION Burn test plots were constructed in September 2010 to represent different defensible space treatments. The plots were constructed at the bottom of a ski run at the south base of Homewood Mountain Resort (Figure 25. map of south base defensible space test plots, 2011. The ski run is an open run covered primarily with wheatgrass. The area faces northeast and is sloped at 11 degrees. The site elevation is approximately 6,303 feet above sea level. The closest forested area is about 50 meters away and is dominated by firs and cedars with some pines and large shrubs. Burn test monitoring occurred on September 28, 2011. On the day of the tests, temperature ranged from 66 to 77 degrees Fahrenheit and relative humidity was between 37‐ 50%. The day was considered a moderate day to burn in terms of air quality. Burn testing on a red flag day was desired but not possible because of the logistics with assembling fire crews to be on hand. Only seven plots were tested in 2011. The Integrated Zero roto‐tilled plot was not tested because of its location and potential fire hazard to surrounding areas at Homewood identified on the day of the burn. TREATMENTS The seven treatments are grouped into two categories: surface mulch application only and tilling in of organic amendment. Materials used as mulch included pine needles, aged duff, Integrated Zero (composted woodchips) and landscape bark. Two plots were tilled using a standard Honda roto‐tiller rented from a local power equipment store. One plot was tilled using an excavator, and the remaining four plots were not tilled at all. For the three tilled plots, mulch material was spread on the plot surface and then tilled into the soil. The materials tilled in included duff and woodchips. See Table 5 for more detailed treatment types. TABLE 5. DEFENSIBLE SPACE TEST PLOT TREATMENTS, 2010. TABLE IS IN ORDER OF THE PHYSICAL PLOT LAYOUT FROM LEFT TO RIGHT (SEE MAP FIGURE 25). Plot 1
5
7
2
8
6
4
Tilling
depth (in) 4
0
0
12
0
0
4
Tilling method Roto till
Amendment
type Woodchips
Amendment
depth (in) 1.7
Excavator
Woodchips
3.8
Roto till
Duff
1.7
Page 25 Mulch type Woodchips
Pine needles
Coarse overs
Woodchips
Duff
Landscape bark
Duff
Mulch
depth (in) 0.3
2.6
2.3
0.2
2.1
2.0
0.3
Defensible Space‐Erosion Protection Tools Development –Project Report FIGURE 25. MAP OF SOUTH BASE DEFENSIBLE SPACE TEST PLOTS, 2011. RESULTS AND DISCUSSION Of the eight different treatment types, only seven were tested. The one that was not ignited, Integrated Zero roto‐
tilled, was not tested due to its physical location in the test plot area and concerns over increased fire risk if the plot burned out of control on burn day. Although this plot was not tested, it is assumed that it would have behaved similarly to the other tilled plots due to how uniform those plots behaved. Of the seven plots that were ignited (or attempted to ignite) that day, only three were able to maintain and carry a flame. Therefore, the burn data presented only represents the mulch types that actually burned. The plots that failed to ignite include: •
•
•
•
Woodchips roto‐tilled Woodchips excavator tilled Duff roto‐tilled Duff Mulch Page 26 Defensible Space‐Erosion Protection Tools Development –Project Report FIGURE 26. DUFF ROTO TILLED TEST IGNITION ATTEMPT, 2011. FIGURE 27. DUFF ROTO‐TILLED TEST AFTER SEVERAL FAILED ATTEMPTS TO IGNITE, 2011. The depth and percent cover (by ocular estimate) of mulch cover on the plots the day of the burn is presented in the table below (Table 6). TABLE 6. MULCH DEPTH AND PERCENT COVER ON THE DAY OF THE IGNITION TESTS. PLOT MULCH
DEPTH (INCHES) MULCH
COVER (% OF
PLOT) WOODCHIPS
ROTOTILLED .25 WOODCHIPS
EXCAVATOR
TILLED .25 DUFF
ROTOTILLED
.25
PINE
NEEDLE
MULCH
.75
LANDSCAPE
BARK
MULCH
1
INTEGRATED
ZERO
MULCH 1 DUFF
MULCH 30% 20% 20%
100%
100%
100% 100%
0.6
The maximum temperature observed by paint chips imbedded in the Integrated zero mulch was the lowest of the three mulches that were able to maintain flames (Table 7). The true temperature of the landscape bark and pine needles is unknown. Both mulches burned at a temperature that erased the highest rated temperature paint on the paint chips (Figure 28, Figure 29 and Figure 30). From observation, the landscape bark test plot had the highest radiant heat of the three mulches, and was the only mulch that was extinguished by fire personnel immediately after the burn test due to fire safety concerns (Figure 32). This plot produced the most smoke and consumed the most fuel of the three mulches that burned. Although the temperature reached by the landscape bark was similar to the pine needle mulch, the behavior of the fire differed. TABLE 7. RESULTS FROM THE PLOTS CARRIED FLAME. MULCH
TYPE RATE OF
SPREAD
(FT/MIN) TEMPERATURE
REACHED ON PAINT
CHIPS (DEGREES C) PINE
NEEDLE
MULCH
LANDSCAPE
BARK
MULCH
INTEGRATED
ZERO
MULCH
2.6 315+ AVERAGE
FLAME
HEIGHT
(CM)
20
0.6 315+ 30
SURFACE ONLY,
APPROX. 33% OF
MULCH DEPTH
100%
0.7 200-260 20
25%
% OF MATERIAL
THAT BURNED Page 27 Defensible Space‐Erosion Protection Tools Development –Project Report FIGURE 28. PAINT CHIP BEFORE BEING EXPOSED TO HEAT. EACH STRIPE WILL IGNITE AT A DIFFERENT TEMPERATURE FROM 90C (LIGHT PINK STRIPE) TO 315C RED STRIPE. FIGURE 29. PAINT CHIP RECOVERED FROM PINE NEEDLE BURN PLOT. TEMPERATURES REACHED AT LEAST 315 C AS EVIDENT BY THE FADED COLOR OF THE RED STRIPE FIGURE 30. PAINT CHIP RECOVERED FROM LANDSCAPE BARK BURN PLOT. TEMPERATURES REACHED AT LEAST 315 C AS EVIDENT BY THE FADED COLOR OF THE RED STRIPE The mulches that burned are classified as class one and class two fuels. Class one fuels are defined as grass, litter, duff, pine needles or other vegetative material that is less than 0.25 inch diameter. These fuels are thin, tend to dry out faster and therefore are more susceptible to igniting on fire than thicker fuels. The pine needle mulch was quick to catch on fire, quick to heat up and quick to spread. During the test, a fan was used to simulate wind conditions commonly found on red flag fire warning days. The pine needle mulch that was consumed by the flames was on the surface of the mulch only. The wind speed was an influence in the flame speed and is possibly the reason that only the mulch layer surface burned. The material that burned was primarily in the path of the fan and self extinguished once the surface material had been consumed (Figure 31). Pine needles demonstrated that they can carry a flame quickly when windy, yet can also self extinguish in certain conditions. Both landscape bark and Integrated Zero mulch are class two fuels (0.25‐1 inches in diameter). Twigs and small stems are included in this category as well. The burn characteristics of these two mulches differed in the temperature reached and percent of material consumed. Spread rate and flame height were similar. Both of these fuels demonstrated that they can carry flame and can continue to smolder and spread without the wind. All of the material of the landscape bark was consumed by fire, including material not in the path of the fan. All material was consumed within 24 minutes. The integrated zero mulch behaved differently. Material was consumed in the path of the fan and continued to smolder up to an hour after the fan was turned off (the plot was mopped up after an hour). 75% of material was consumed in total of the Integrated Zero mulch. The flame height between the three mulches was estimated visually and ranged from 20 to 30 cm. The highest flames were too similar to compare accurately. Page 28 Defensible Space‐Erosion Protection Tools Development –Project Report Location of ignition by drip torch Direction of wind from the fan FIGURE 31. PINE NEEDLE TEST PLOT POST BURN. NOTE THE MATERIAL ONLY BURNED IN THE PATH OF THE FAN. FIGURE 32. LANDSCAPE BARK MULCH TEST PLOT 6 MID‐BURN, 2011. THIS MULCH TYPE PRODUCED THE MOST SMOKE AND WAS THE ONLY TEST WHERE ALL MATERIAL BURNED. SUMMARY Out of the 7 defensible space plot treatments tested, only 3 were able to stay ignited once the drip torch fuel was consumed. The high presence of mineral soil and less available material are contributing factors to why several of the treatments were not able to sustain a flame. Weather conditions on the day of the burn tests had medium relative humidity (37‐50%) which may have influenced the burn characteristics of the materials tested. Conditions with low humidity are more conducive for fires to ignite and burn. The commonality between the three treatments that were able to carry fire is that they were all mulches that were applied to the surface as opposed to the plots where the mulches were tilled into the soil. The general characteristics of the pine needle mulch are that it burns hot and can spread fire rapidly. This mulch was the only mulch out of the three to self extinguish. The burn characteristics of the landscape bark is that its flame spreads slowly compared to pine needles, yet burns just as hot and is able to ignite other material that is not directly in the path of the flame. The characteristics of the Integrated Zero mulch are that it spreads at a similar rate as the landscape bark, yet does not burn as hot. It continued to smolder and burn in areas that the flames did not pass over, but at a much slower rate than the landscape bark. Page 29 Defensible Space‐Erosion Protection Tools Development –Project Report CHAPTER 4. EDUCATION AND OUTREACH This project successfully identified landscape materials that were effective at minimizing the fire risk and soil erosion. The next step includes disseminating the information to homeowners to incorporate into their landscapes. To do this, an educational pamphlet was developed and distributed, and treatments were displayed during a community garden tour and gardening event. EDUCATIONAL BROCHURE The two study findings were compiled into an educational brochure with homeowners as the target audience. To ensure buy‐in from erosion control and fire entities, a workshop was hosted to review the brochure’s content. Input was provided by Tahoe Regional Planning Agency (TRPA), Lahontan Regional Water Quality Control Board, Tahoe Douglas Fire Protection District, North Lake Tahoe Fire Protection District, Meeks Bay Fire Protection District, Cal Fire, and Tahoe Resource Conservation District (Tahoe RCD), with the final product aligning with all agency regulations and fire recommendations. Over one thousand copies of the brochure were printed and distributed to local fire protection agencies, TRPA, and Tahoe RCD for distribution. Additionally, an electronic copy of the brochure was posted to the website of fire districts, TRPA, Tahoe RCD, South Tahoe PUD and Integrated Environmental. FIGURE 33. EDUCATIONAL BROCHURE,
AVAILABLE AT WWW.IERSTAHOE.COM
CONSERVATION LANDSCAPE TOUR Using the motto ‘seeing is believing,’ the landscape treatments recommended in the educational brochure were featured in the Conservation Landscape Tour in Tahoma, California on August 19, 2012. Tahoe Resource Conservation District has hosted the Conservation Landscape Tour annually for the last five years. The tour has traditionally featured gardens that incorporate defensible space, Best Management Practices (BMPs), water wise landscaping, and native/adapted plants. An educational component was added to the nine gardens on the tour this year, which included highlighting the study’s recommended treatments with signage and providing a demonstration on how to install the treatments. The educational brochure was also distributed to tour participants. The tour attracted more than 150 people and provided an ideal venue for educating homeowners on the study’s findings. FIGURE 34. INTEGRATED ENVIRONMENTAL’S STAFF EXPLAINING FIGURE 35. CONSERVATION LANDSCAPE TOUR PARTICIPANTS NOTICE MOSAIC LANDSCAPING RECOMMENDATIONS DURING THE TOUR. A PLANTER BED WITH TILLED IN WOODCHIPS. Page 30 Defensible Space‐Erosion Protection Tools Development –Project Report AUTUMN FESTIVAL Tahoe Resource Conservation District and Integrated Environmental Restoration Services, Inc. worked together to distribute the educational pamphlet and educate community members on the various study findings at Autumn Festival on September 16, 2012. Autumn Festival is an annual community gardening event held at the Lake Tahoe Community College Demonstration Garden. The free festival hosted by Tahoe Resource Conservation District attracted over 300 community members. The event featured talks on backyard conservation landscaping and educational booths. FIGURE 36. COMMUNITY TRAINING AT AUTUMN FESTIVAL. EDUCATIONAL VIDEOS Many homeowners had specific questions on how to install the various surface mulch recommendations after reviewing the educational brochure at the Conservation Landscape Tour and the Autumn Festival. . Examples of questions ranged from ‘how to design a mosaic landscape; to ‘how and where to till in woodchips.’ To address these questions and reach a wider audience of homeowners, the study findings were incorporated into short educational videos that will soon be posted on Integrated Environmental and Tahoe Resource Conservation District’s website. The video subject matter covers appropriate mulching options to include in a mosaic landscaping and provides a step by step demonstration of how to incorporate tilled in woodchips into a landscape. The videos allow homeowners to watch a simple demonstration right before incorporating the recommendations into their landscape. Page 31 Defensible Space‐Erosion Protection Tools Development –Project Report CONCLUSION AND RECOMMENDATIONS CONCLUSIONS This research project was undertaken to assess and identify fire‐safe erosion control treatments that can be implemented on a residential home landscape scale. The results of this study have identified common ground between defensible space and water quality protection goals. These results represent an important step forward toward developing the data and knowledge necessary to provide practical and effective landscaping guidance to homeowners and small landowners. Key conclusions from this study: ‐
‐
‐
‐
‐
‐
‐
Mulch cover is highly effective and important in preventing erosion. However, pine needles and landscape bark nuggets posed the highest fire risk of all the mulches tested. All mulches that were tilled into the soil (leaving limited mulch on the soil surface) were not able to be ignited with a drip torch. Further, tilled in wood chips had the highest infiltration rate and the lowest runoff rate. Pine needles had the fastest flame spread rate in this study. Duff mulch had the lowest erosion results of all mulches tested and failed to ignite. Distinct flammability differences were observed between fresh pine needles and duff (partially decomposed pine needles): o Pine needles were easily ignited and readily carried flame, whereas duff (partially decomposed pine needles) was not able to be ignited with a drip torch, and had the lowest sediment yield of all treatments. It is difficult to compare erosion resistance between tilled and mulch‐only plots in this study due to distinct differences in mulch cover/thickness and well‐vegetated baseline conditions. However, a large body of previous research at Homewood and throughout the Tahoe Basin indicates that loosening and incorporation of woody material into the soil can reduce sediment yield compared to compacted soil conditions when adequate mulch cover is in place to protect the soil from raindrop detachment. The following graphic was produced to rank the fire risk versus erosion risk of the different treatments tested for this project (Figure 37, Appendix B includes matrices used to decipher rank). This graphic represents data from this study only, and does not include data from other similar research. Page 32 Defensible Space‐Erosion Protection Tools Development –Project Report Fire Risk & Erosion Risk of Landscape Mulches
Higher Risk
5
4.5
Landscape Bark Mulch
Pine Needle
Mulch
4
Fire Risk
3.5
3
2.5
Integrated Zero Mulch
2
Lower Risk
1.5
1
Woodchips
Roto‐tilled
0.5
Duff Mulch
Duff Roto‐tilled
Woodchips
Excavator Tilled
Integrated Zero Roto‐tilled
0
0
1
2
3
Erosion Risk
Lower Risk
4
5
6
Higher Risk
FIGURE 37. FIRE RISK VS EROSION RISK. NOTE‐ PINE NEEDLE MULCH AND LANDSCAPE BARK MULCH RANK THE SAME IN TERMS OF FIRE RISK ALTHOUGH EACH MULCH HAS DIFFERENT IGNITION CHARACTERISTICS. Notes: During the ignition tests the tilled treatments and the duff mulch treatment would not ignite and therefore are considered
zero fire risk. **These treatments did not ignite under specific conditions, and have been known to ignite in other circumstances.
The fire risk for Integrated Zero composted woodchips roto-tilled into the soil was assumed based on the trend of the other tilled
mulches failing to ignite. This treatment was not burned due to the physical location of the plot and fire concerns from fire
personnel in charge of safety on the test day. MANAGEMENT RECOMMENDATIONS ‐
‐
‐
‐
‐
Add or maintain mulch cover wherever possible – highly effective and important for erosion control. Manage duff : maintain 1‐3” of native duff where it already exists in your yard by lightly raking only the top layer of dry pine needles without scraping down to bare soil. Fire districts recommend raking annually by May 1st and leaving pine needles that fall throughout the rest of the season. Roto‐tilling amendments 4‐12 inches into the soil (leaving only small amount on surface) substantially reduces fire risk and can help prevent runoff and erosion by increasing infiltration. Combination of tilling and mulching is the most effective defense against erosion. Tilling, mulching, managing native duff, and keeping a mosaic landscape in mind is the best combination for a fire‐safe, erosion‐resistant landscape. Page 33 Defensible Space‐Erosion Protection Tools Development –Project Report LITERATURE CITED Grismer, M. E., Ellis, A.L., & Fristensky, A. (2008). Runoff sediment particle sizes associated with soil erosion in the Lake Tahoe Basin, USA. Land Degradation & Development, 19(3),331–50. Grismer, M.E., C. Schnurrenberger, R. Arst & M.P. Hogan. 2009. Integrated monitoring and assessment of soil restoration treatments in the Lake Tahoe Basin. Environmental Monitoring & Assessment 150, 1‐3: 365‐ 383 Grismer, M. E., & Hogan, M. P. (2004). Simulated rainfall evaluation of revegetation/mulch erosion control in the Lake Tahoe Basin: 1. Method assessment. Land Degradation & Development, 15(6): 573‐588. Grismer, M. E., & Hogan, M. P. (2005). Simulated rainfall evaluation of revegetation/mulch erosion control in the Lake Tahoe Basin: 3. Soil treatment effects. Land Degradation & Development, 16(5), 489‐501. Quarles, S., & Smith, E. (2011). The combustibility of landscape mulches [pamphlet]. Carson City, NV: University of Nevada Cooperative Extension. Page 34 Defensible Space‐Erosion Protection Tools Development –Project Report APPENDIX A TABLE 8. STATISTICS TABLES FOR RAINFALL SIMULATION DATA. Stats Summary Roto‐tilled frames ‐ outliers and no‐data pts removed leaving n=8
Significant (95%) linear regressions from ANOVA
Conflicting factors limit ability to form reasonable MANOVA model Slope
R2
F
F significant SY vs Inf (runoff) rate ‐0.0105
0.44
0.629812
0.463405
SY vs SM ‐0.0744
0.237
1.862387
0.221311
SC vs SM ‐0.1257
0.289
2.43558
0.169631
Inf rate vs CP ‐10.54
0.23
1.459549
0.28102
Inf rate vs SM 3.9 0.33
2.492947
0.175191
Runoff OM vs inf rate ‐0.775
0.754
18.38705
0.00516
Runoff OM vs SM ‐3.018
0.265
2.166341
0.191477
Adding Excavated frames to the roto‐tilled data so n=11
Slope
R2
F
F significant SY vs Inf (runoff) rate ‐0.0083
0.129
1.332961
0.278013
SY vs mulch depth ‐0.746
0.203
2.291729
0.164362
SY vs SM ‐0.0732
0.1414 1.482287
0.254375
SC vs SM ‐0.1158
0.1561 1.66454
0.229152
0.12 1.223512 0.297361 Inf rate vs CP 4.344 Inf rate vs SM 5.1 0.365
5.163887
0.049168
Runoff OM vs inf rate ‐0.532
0.582
12.53595
0.006308
Runoff OM vs SM ‐3.296
0.3131 4.101662
0.073496
Mulch cover frames ‐ F
F significant n Slope
R2
SY vs CP (6& 7)
6 ‐
0.27
1.48019
0.290622 0.0497 SY vs SM (6& 7) 6 0.036
0.54
4.689486
0.096292 SC vs SM (6 & 7) 6 0.085
0.6935
9.05267
0.039598 Runoff OM vs SM (6 6 3.784
0.5863
5.668644
0.075916 & 7) SY vs mulch depth (6, 7 & 9
0.03
0.2554
2.058067
0.201402 8) Inf rate vs SM (6,7 & 9 ‐4.44
0.7356
16.69023
0.006463 8) Abbreviations: SY‐ sediment yield, Inf rate‐ infiltration rate, SM‐ soil moisture, CP‐ cone penetrometer, Runoff OM‐ runoff organic matter. Page 35 Defensible Space‐Erosion Protection Tools Development –Project Report APPENDIX B Tables showing the relative ranking of treatments for erosion risk and fire risk. TABLE 9. RANK OF TREATMENTS BASED ON EROSIVE FACTORS Treatments Duff mulch Sediment yield rank Infiltration rate rank average Pine needle mulch Landscape bark mulch Integrated Zero mulch Integrated Zero roto tilled Woodchips Woodchips roto tilled excavator tilled 1
Duff mulch roto tilled
3
1 1 2 5
1 5
2 2 3 3
3
5
1 2
1.5 1.5 2.5 2
3
5
1 3.5
TABLE 10. RANK OF TREATMENTS BASED ON COMBUSTION CHARACTERISTICS. NOTE‐ INTEGRATED ZERO ROTO‐TILLED WAS NOT TESTED DUE TO SAFETY CONCERNS ON THE DAY OF THE IGNITION TESTS. Treatments Duff mulch Pine needle mulch Landscape bark mulch Integrated Zero mulch Rank of maximum burn temperature Ranks of spread rate Rank of % of depth of material burned average 0 5
5 0 5
0 0 Integrated Zero roto tilled Woodchips Woodchips roto tilled excavator tilled 4
Duff mulch roto tilled
0
0
0 0
2 2
0
0
0 0
2
5 2
0
0
0 0
4
4 2.7
0
0
0 0
Page 36 Defensible Space‐Erosion Protection Tools Development –Project Report TABLE 11. MATRIX OF RANKING OF EROSION CHARACTERISTICS Sediment Yield Sediment yield 0‐39 lbs/acre/in Sediment yield 40‐79 lbs/acre/in Sediment yield 80‐119 lbs/acre/in Sediment yield 120‐159 lbs/acre/in Sediment yield 160‐200 lbs/acre/in Rank
1
2
3
4
5
Infiltration Rate
Infiltration Rate 4.20‐4.50 in/hr Infiltration Rate 3.90‐4.19 in/hr Infiltration Rate 3.60‐3.89 in/hr Infiltration Rate 3.30‐3.59 in/hr Infiltration Rate 3.00‐3.29 in/hr Rank
1
2
3
4
5
TABLE 12. MATRIX OF RANKING OF COMBUSTION CHARACTERISTICS Maximum Burn Temperature Did not ignite 1‐64C 65‐129C 129‐194C 195‐259C 260‐325 Rank Rate of Spread
Rank
0 1 2 3 4 5 0
1
2
3
4
5
Did not ignite
0.01‐0.54 ft/min
0.55‐1.09 ft/min
1.10‐1.64 ft/min
1.65‐2.19 ft/min
2.20‐2.75 ft/min
Percent of average depth of mulch burned to depth that did not burn Did not ignite
0‐19%
20‐39%
40‐59%
60‐79%
80‐100%
Page 37 Rank
0
1
2
3
4
5