1. Vegetation cover by species was collected in 400 1m2 plots, 100 in each of four treatment sites: control, mechanical thinning, mastication, and fire. In addition, downed fuels and soil nutrients, moisture, and temperature were monitored at each site.
  2. Mastication sites had a greater quantity of downed woody debris as well as duff compared to control sites.
  3. Soil nutrient levels in mastication sites were no different than control sites; only the fire site showed different (higher) levels.
  4. The spatial structure of the understory was not greatly different than the control site, but was slightly more patchy.
  5. Composition on mastication site was different than control sites due to the dominance of certain species and an overall greater cover.
  6. The data do not suggest mastication has greater negative effects than other treatments.

Abstract: Mastication has become a common and cost-effective means for fuel reduction and restoration of open ponderosa pine forest, but mastication effects on the understory are still unknown. This study examined the spatial structure of fuels, soil and vegetation at Heil Valley Ranch in areas masticated and compared it to a control area and two other management techniques: thinning and fire (prescribed burn). The objectives were to determine to what extent mastication alters forest floor fuels, soil structure, and vegetation composition and diversity. Further, the spatial structure of these understory components were examined to help understand the impacts of mastication and influences on understory heterogeneity. Data were collected from a stratified random placement of 1m2 plots in each treatment type. Vegetation cover was collected from each plot. Soil cores were extracted within the top 20 cm of the soil surface from 15 plots in each site, and fuel data were collected from five locations within each site. Results show an increased level of available fuels in the mastication site when compared to thinning, but not when compared to the fire site, especially class 3 and class 4 woody biomass. Mastication also had greater levels of duff present at the site (>600g m2) while not significantly changing the soil composition, which could be due to the lack of time needed for proper decay and return of the nutrients to the soil. The fire site on the other hand had much greater levels of K, Ca, Mg. The mastication site did have slightly more spatial heterogeneity than the fire site and the control site, but less than the thinning site; however, the diversity within the fire site was much greater than that within the mastication site. Overall cover was also lower in the mastication site when compared to fire (>100% - due to abundance of species and overlap in shade cover), but slightly more compared to the thinning and control sites (<50% total cover). The data do not suggest major differences on fuel loads, soil chemistry, or spatial heterogeneity among the thinning treatments, but do elucidate an increase in cover and richness; thus, mastication may be just as effective of a technique for maintaining ponderosa pine ecosystems. The data further suggest that fire should not be excluded from management consideration.

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