Ecological Impacts of Mastication Fuel Treatments chaired by Mike Battaglia

Fuel Treatments by Mulching - A Synthesis of the Ecological Impacts

M. G. Ryan et al. — Tue, 23 Jun 2009 14:50:00 PDT

Concern over severe fire hazards has led to a novel, widespread management treatment in forests and woodlands in the American West. Tens of thousands of hectares have been treated by chipping or masticating (mulching) live trees, with the woody material deposited on the soil surface. This woody material differs from that added through natural processes: pieces are smaller, all of it is deposited at once, and the material forms a compact layer. Because of these differences, the state-of-knowledge on woody debris in forests provides little insight on the potential ecological effects of these mulching treatments for reducing fire hazard. We reviewed the literature to address the impacts of mulching treatments. Mulching fuel treatments tended to: (1) reduce the modeled risk of crown fire, (2) increase soil net nitrogen mineralization, soil carbon, and soil moisture; (3) decrease maximum soil temperature, herbaceous cover/biomass, and tree regeneration; and (4) not change plant nitrogen concentrations and soil compaction in the long-term. Mulching fuels treatments do not appear to decrease soil nitrogen availability, total soil nitrogen, or plant phosphorus concentrations. Few studies addressed questions important to the managers implementing these treatments. What is the optimal distribution and depth of the woody material? How long will it take to decompose? Will the treatments change species diversity, or impact rare or endangered species? What will happen to water yield? Will the treatments change the risk of insect outbreaks or disease? How long will the fuels treatments last? What are the effects of thinning compared to the effects of the added wood? How will ecosystem water and carbon balance change? The widespread application of these mulching treatments together with the lack of knowledge about ecological effects suggests research in this area should be a priority.

Surface Fuel Loadings in Mulching Treatments in Colorado Coniferous Forests

Mike Battaglia et al. — Tue, 23 Jun 2009 15:40:00 PDT

Recent large-scale, severe wildfires in the western United States have prompted extensive fuel treatment programs to reduce potential wildfire size and severity. Often, unmerchantable material is mechanically masticated because removing the material is cost-prohibitive. Mastication treatments involve shredding, chopping, or chipping small trees and/or shrubs into small chunks and leaving the material on site. While it is obvious that mechanical treatments will increase surface fuel loads, few studies have addressed how treatments alter fuel particle size and quantity. We examined how mastication treatments alter the distribution of woody material size by comparing paired masticated and untreated sites in lodgepole pine (Pinus contorta), ponderosa pine/Douglas-fir (Pinus ponderosa/Pseudotsuga menziesii), and 3) Pinyon pine (Pinus edulis) ecosystems 2-4 years after mechanical treatment. As expected, total woody fuel loadings increased in the treated areas of each ecosystem. However, the magnitude of the total increase differed among the ecosystems (lodgepole pine > ponderosa pine > pinyon-juniper). Average total woody fuel loads in the untreated areas ranged between 7 to 9 Mg/ha, but increased to 29 to 50 Mg/ha in treated areas. Large diameter fuels (>7.62 cm) represent about 33 to 65% of the total woody fuel load in the untreated areas, but only about 11% of the total fuel load in the treated areas. The majority of woody fuels in treated areas were <2.54 cm in diameter. Needle litter mass was similar among treatments, indicating that needles are still a component of the forest floor complex, but are mixed with other fuel types or buried. The increased surface woody fuel component in treated areas corresponds to a shift from a needle fuel bed to a compact woody/needle fuel bed. This change in the fuel bed composition and orientation will likely influence fire behavior and effects.

The Effects of Mulching Treatments on The Forest Herbaceous Layer of Colorado Coniferous Forests

M. Rocca et al. — Tue, 23 Jun 2009 16:00:00 PDT

Novel fire mitigation treatments that chip, shred, or masticate excess forest biomass and distribute it across the forest floor are increasingly prescribed to reduce the density of small diameter trees. We investigated the impacts of mechanical thinning and on-site fuel disposal on forest herbaceous layer productivity in four coniferous forest types (lodgepole pine, mixed-conifer, ponderosa pine, and pinyon juniper) across Colorado. Crews sampled the herbaceous layer in treated stands and in adjacent unthinned control stands across 18 study sites. Treated pinyon-juniper and ponderosa pine forests had twice the graminoid cover and forb cover of control stands. Lodgepole pine and mixed-conifer forests had similar covers of graminoids and forbs in treated and control stands. Within treated ponderosa and pinyon-juniper stands, herbaceous cover was negatively correlated with mulch depth, while in lodgepole and mixed-conifer forests, there was no relationship between mulch depth and herbaceous cover. Several factors may explain the differences observed between the ecosystems. Mulch depths tended to be higher in lodgepole (4.2 cm) and mixed-conifer (6.1 cm) treatments relative to ponderosa (3.7 cm) or pinyon-juniper (1.7 cm) treatments. Mulch depths in lodgepole and mixed-conifer may exceed the threshold where understory vegetation can grow, overriding the influence of increased light availability due to overstory thinning. Alternately, the overstory of lodgepole and mixed conifer are naturally dense compared to ponderosa and pinyon-juniper, and may lack sufficient understory flora to respond to canopy reduction. Consideration of the variability in treatment impacts (e.g., amount and distribution of mulch) combined with differences in overstory and understory species structure and composition are critical for design of “Best Management Practices” guidelines for mulching treatments in western US forests.

Woody Mulch Effects on Soil Nitrogen Availability in Mechanical Fuel Reduction Treatments

C. Rhoades et al. — Tue, 23 Jun 2009 16:20:00 PDT

Extensive implementation of mechanical fuel reduction treatments represents a new, but poorly-understood manipulation of western forest ecosystems. The shredded woody residue created by fuel reduction operations forms a mulch layer upon the forest floor that can change the biogeochemical processes that regulate nutrient availability and ecosystem productivity. Mulch layers affect both soil microclimate and inputs of water, nutrient and carbon. Plant demand for soil resources and the consequences of mulch application likely differ between ecosystems and fuel reduction treatments. The objective of work reported here was to determine the relation between mulch depth and soil nitrogen fertility. We created 2 x 2 m residue beds of varying thickness (0, 7.5, 15 cm) in three conifer forest types at fourteen sites throughout Colorado. We used ion exchange resin (IER) bags installed beneath mulch beds to assay the movement of inorganic forms of nitrogen (ammonium and nitrate) in the upper 5 cm of mineral soil. Nitrate, a highly-mobile anion, comprises 50 to 90% of IER-N. In general, both ammonium and nitrate declined with mulching. IER-N was 50 to 63% lower in mulched compared to untreated plots regardless of mulch depth, though deeper layers reduced IER-N 36 to 95%, whereas the reduction beneath thinner layers was somewhat less (20 to 85%). When mulch treatments are assessed across forest landscapes, spatial variability of mulch deposition and variability in soil characteristics and plant populations complicate the biogeochemical signals created by mulch applied at the plot scale.

The Influence of Mastication on Soils and Fuels in Moist and Dry Forests of the Northern Rocky Mountains

Theresa Jain et al. — Tue, 23 Jun 2009 16:40:00 PDT

We evaluated the applicability of mastication as a fuel treatment alternative within Northern Rocky Mountain moist and dry forests to treat post-harvest activity slash (moist forest) and standing trees (dry forest). On the moist forest site, we compared four different slash treatments, mastication, machine grapple piling, lop and scatter, and a control within a wildland urban interface setting to determine the effects of these treatments on soil nutrition, forest floor depth, and woody debris distributions. We randomly assigned the slash treatments and controls to 12 one-acre plots. Nitrogen, soil carbon, and magnesium concentrations within the soil components were not significantly different among the slash treatments. Lopped and scattered sites had significantly here duff depths than duff depths within the other slash treatments and control. Two years after treatment the structure and character of the masticated fuels was such that these areas resembled the grapple piled sites. We established the dry forest site to treat excess standing non-commercial 80-year old ponderosa pine. We masticated 20 acres in the fall; six one-acre plots were randomly located within the masticated area. We applied prescribed fire the following spring to three of the plots the remaining three plots were post-masticated controls. During the prescribed fire, flame lengths were low (< 0.5 m), although combustion continued to occur from smoldering. The radiation and convection was of sufficient intensity that crown scorching raised canopy base heights by 3 to 5 m. A critical element of the prescription was that lower duff moistures had to be greater than 100 percent during burning, therefore, there was little to no consumption of the forest floor even with the smoldering fire. Based on these results, we recommend that when burning masticated material particular attention to lower duff moisture is critical to minimize the down ward heat pulse.

Overstory and Fuel Loading Changes Following Mechanical Mastication or Thinning of Southwestern Pinyon-Juniper Stands

G. Gottfried et al. — Wed, 24 Jun 2009 08:00:00 PDT

Mechanical mastication treatments are becoming common for treating fuels or for stand restoration in the western United States. Pinyon-juniper woodlands are a dominant vegetation type on lands administered by the U.S. Forest Service and USDI Bureau of Land Management at the Dolores Service Center of the San Juan National Forest in southwestern Colorado. The woodlands surround many rural and exurban housing developments and towns in the region. Mortality in these stands has been great during this decade because of drought, high stand densities, and the regional infestation of the bark beetle Ips confusus. The high mortality has contributed to increased standing and dead and down woody fuels. Managers are using mechanical mastication or traditional thinning-piling-burning treatments to reduce fuels and the risk of fire within the wildland-urban-interface (WUI). Mastication is used in more remote areas to restore more natural stand densities. The Dolores Service Center is planning to masticate 2,000 to 3,000 acres annually. Standard thinning treatments are used in WUI areas adjacent to recreation areas or developed areas where scenic considerations are important. Little information is available about the effects of mastication on the overstory, understory (including invasive species), fuel loadings, and soil resources. A study supported by the Joint Fire Science Program is comparing the effects of mastication, thinning, and no treatment on resources of pinyon-juniper stands in southwestern Colorado. This presentation will compare overstory and fuel loading changes in a stand dominated by pinyon (Pinus edulis) and Utah juniper (Juniperus osteosperma), with Rocky Mountain juniper (J. scopulorum). Overstory measurements were collected from plots within 36-acre representative treatment sites before and after treatments using woodland inventory procedures and fuel loading measurements were collected using the Brown technique. Results from the companion soil study are present in this session by S. Overby.

Does Mastication Residue Alter Soil Nitrogen Dynamics in Woodlands Of Southwest Colorado?

S. Overby et al. — Wed, 24 Jun 2009 08:20:00 PDT

Large wildfires were historically uncommon in the woodland ecosystems of southwest Colorado, yet between 1996 and 2003 six large wildfires occurred. The potential for large wildfires in these woodlands has been exacerbated by the fuel buildups related to extended drought and infestation of pinyon ips (Ips confuses) that have killed millions of trees in this region, along with Euro-American settlement impacts that has altered the fire regime. Wildfire mitigation treatments are few, but one promising technique in woodland ecosystems is mastication of both live and dead standing fuels to alter wildfire behavior. Mastication of woody material has raised concerns that a shift in the carbon: nitrogen (C:N) ratio due to the residual plant material left on the soil surface may slow decomposition rates and limit plant available N needed for long-term site productivity. We compared net N mineralization in the upper 15 cm of mineral soil from thinned and burned, masticated, and untreated plots at three sites dispersed over a large area of southwest Colorado. Net N mineralization was measured using plant root simulator probes (WesternAg, Inc.) continuously for over two years following treatment. Preliminary data on microbial biomass and community structure, measured using phospholipid fatty acids, will also be presented. This technique allows us to determine if there has been a structural shift of microbial communities with emphasis on changes to the fungal:bacterial (F:B) ratios in organic and soil horizons. The plant residue additions to the soil surface should increase C:N ratios and total surface biomass following mastication. Does this alteration also influence the mineral soil C:N ratios by reallocating N from the upper mineral soil and immobilizing it in the mastication residue by fungal decomposers, thus decreasing N availability for a plant growth?

Mechanical Mastication Showed Fewer Negative Above-and Belowground Impacts Than Slash Pile Burning

Suzanne Neal et al. — Wed, 24 Jun 2009 08:40:00 PDT

Management designed to reduce wildfire risk must consider both above- and belowground factors in order to promote native plant growth and reduce soil erosion. This goal is challenging because current methods, such as tree thinning and burning the resulting slash, can create soil disturbances that favor exotic plants. We compared mechanical mastication to slash pile burning (both 6-months and 2.5-years post treatment) and untreated controls in pinyon-juniper (Pinus edulis-Juniperus osteosperma) woodland and measured soil properties, arbuscular mycorrhizal fungi (AMF) and understory plant composition. Our results showed slash pile burns had severely degraded soil properties, low plant and AMF abundance and richness and a dominance of exotic plant species compared to untreated or mastication plots. Only two variables differed between mastication and untreated plots 6-months post treatment: mastication had lower soil temperature and higher soil moisture. Mastication plots 2.5-years post treatment had more plant cover and richness than untreated plots or pile burns, although exotic plant richness and Bromus tectorum cover were also greater and AMF spore biovolume and richness were lower than untreated plots. In the short term, mastication is a preferable method as it creates fewer disturbances than pile burning, however long-term impacts of mastication need further study as they could affect native communities. Our results showed the manner in which woody debris is treated has an important influence on sustaining soil stability and native biodiversity.

An Integrated Study Investigating Masticated Fuel Treatments in the Rocky Mountains

Robert Keane et al. — Wed, 24 Jun 2009 09:00:00 PDT

Many coniferous forests in the western US once supported frequent, low intensity fires, but due to a century of fire exclusion and other factors, severe wildfires have now become common. With the goal of lowering fire intensities and severities, one possible fuel treatment that is currently gaining favor in with many land managers is mastication which breaks, shreds, or grinds canopy (seedlings, saplings and pole trees) and surface fuel (fine and coarse woody material) into smaller sizes and deposits the treated fuel on the ground. However, very little is known concerning the effects of this treatment on the resulting fire behavior, vegetation community, and ecosystem responses. Managers need to be aware of the beneficial and adverse effects of mastication to more effectively manage ecosystems. The goal of this study is to investigate the effects of masticated fuels on various ecosystem processes and characteristics with the following objectives • Describe the characteristics and properties of masticated fuelbeds • Develop a sampling protocol to estimate the loading of masticated fuelbed • Describe fire behavior in burning masticated fuelbeds • Evaluate the effects of masticated fuelbed on the ecosystem We have established study sites on the Valles Caldera National Preserve, New Mexico; San Juan National Forest, Colorado; and Kootenai National Forest, Montana. Each site contains control, masticate, masticate and burn, and burn only units. As of fall 2008, all sites had received the mastication treatment but none had been prescribed burned. We found that a cover-depth sampling protocol was the best option for quantifying masticated fuel loadings and mastication reduced canopy fuels by approximately 30-50 percent.