| Steve Overby |
Gerald Gottfried |
Assisted with soil and plant analyses: |
Rocky Mountain Research
Station |
Rocky Mountain Research
Station |
Dana Erickson, Danielle Duncan and
Suzanne Owen (RMRS Chemist) |
Thinning of trees using a chainsaw. |
Thinning of trees using mechanical mastication. |
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RMRS soil scientist Dr. Steven Overby and RMRS research forester Dr. Gerald Gottfried collaborated on a project titled:
Effects of fuels/fire risk reduction treatments using hydro-mow or thinning on pinyon-juniper ecosystem components within the
wildland-urban-interface.
The specific objectives of this study were to:
1) measure vegetative response (composition, cover, frequency, regeneration) of both overstory and understory,
2) describe changes to fuel loadings, and
3) determine total carbon (C) and nitrogen (N) pool sizes and associated microbial population in the soil in Ips killed pinyon-juniper
woodlands of southwest Colorado region following mastication, thinning-piling-burning, and untreated plots. |
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| Control Plot |
Masticated Plot |
Thinned and Burned Plot |
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Three pinyon-juniper sites were selected for the study (Figure. 1 - Below):
1) School (BLM; NE of Egnar, Colorado; 2,318 ± 13 m; Sandstone Parent Material);
2) Summit (BLM; N of Mesa Verde National Park, Colorado; 2,115 ± 25 m, Mancos Shale, Sandstone Parent Materials); and
3) May Canyon (FS; N of Dolores, Colorado; 2,209 ± 14 m; Sandstone, Shale Parent Materials).
The San Juan National Forest and the Dolores Service Center prepared and administered the contracts and mastication and pile burn treatments. Variables measured included: overstory, dead and down material, herbaceous plant community and ground cover, shrub composition, canopy cover, C, and N, pH, in-situ available N and soil microbial structural assessments, including phospholipid fatty acids (PLFA). |
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| Figure 1. Map of the Three Sites: School, Summit and May Canyon in Colorado. |
Results:
Results showed that almost twice as much basal area and three times as much volume were removed by thinning relative to mastication. Sixty-one percent of the plots at School, the flattest area with slopes of 3 to 4%, were at least 50% masticated. The number dropped to 42% at Summit and 31% at May Canyon, with more than 40% of the plots at Summit and May Canyon either not treated or lightly treated. Neither mastication nor thinning-piling-burning altered the community of herbaceous plants significantly, but of concern was a significant increase in musk thistle and cheatgrass with thinning and burning.
Woody fuel loading in megagrams per ha fluctuated throughout the three years. The controls and thinning-piling-burning plots on all three sites indicate a decline between 2005 and 2006 and then a slight increase between 2006 and 2007. The mastication plots indicate, with the exception of Summit, an increase over time. Available N mineralized over the three years of post-treatment was not statistically significant, even though there is a trend toward lower N supply rates with mastication. Surface organic horizon C:N ratios significantly increased over time with mastication, but not in the mineral soil. Microbial populations were sensitive to treatments, both mastication and thinning-piling-burning. Both gram-negative and gram-positive bacteria increased in the masticated plots relative to controls, while fungi and actinobacter were not significantly altered by treatments. |
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Benefits of Mastication:
Mastication provides an effective low-cost, low-risk alternative for fuel treatments in pinyon-juniper woodlands. Mastication does not negatively impact the short-term regeneration of pinyon and juniper.
Shrub cover can be significantly reduced by mastication in the short-term, yet recovery by sprouting shrubs can be quit fast and may negatively impact tree regeneration in the long-term. Mastication favors stoloniferous plants, such as Canadian thistle, while thinning-piling-burning strongly favors cheatgrass and musk thistle. When non-native invasive plants are present prior to fuels treatment, mitigating the potential increase prior to treatment is preferable.
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| CLICK ON IMAGE TO ENLARGE |
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| Canadian Thistle and Gambel Oak |
Canadian Thistle |
Cheat Grass and Musk Thistle |
Cheat Grass and Musk Thistle |
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| Slow decomposition of masticated residues and increasing C:N ratios of these residues poses the potential to reduce nitrogen mineralization or begin to immobilize nitrogen in the mineral soil over the long-term. Bacteria are favored under masticated material due to attenuation of soil temperature and moisture extremes. Fungi are needed for decomposition of recalcitrant organic residues, yet it appears their potential to respond to additional inputs with wide C:N ratios is limited in pinyon-juniper woodlands. |
| Plant List for Study |
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