Mechanical Restoration of California Mixed‐Conifer Forests: Does it Matter Which Trees Are Cut?

Restoration Ecology (Impact Factor: 1.84). 10/2009; 17(6):784 - 795. DOI: 10.1111/j.1526-100X.2008.00414.x


The montane ecosystems of northern California have been subjected to repeated manipulation and active fire suppression for over a century, resulting in changes in community structure that contribute to increased wildfire hazard. Ecosystem restoration via reduction of stand density for wildfire hazard mitigation has received substantial attention in recent years; however, many ecological questions remain unanswered. This study compares belowground effects of two alternative forest thinning treatments designed to restore the large, old tree component of late-seral structure, one of which focuses on restoring Pinus ponderosa dominance (Pine-preference) and the other of which promotes development of large trees regardless of species (Size-preference). We evaluated forest floor and soil chemical and microbial parameters in six experimental thinning treatment units of 40 ha each in the Klamath National Forest of northern California 5–6 years after thinning. Inorganic N availability, soil organic C content, phenol oxidase activity, and forest floor C:N ratio were greater in the Size-preference treatment, whereas forest floor N and soil pH were greater in the Pine-preference treatment. Our results indicate that these two thinning strategies produce differences in the soil environment that has the potential to affect growth rates of trees that remain, as well as the growth and survivorship of newly established seedlings. Thus, which species/individuals are removed during structural restoration of these mixed-conifer forests matters both to the belowground components of the ecosystem today and the vegetation and productivity of the ecosystem in future decades.

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Available from: Jessica R. Miesel, Jun 12, 2014
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    • "Removal of small trees, often only possible where markets exist for low value forest biomass, reduces competition for soil nutrients and moisture (Evans & Finkral, 2009). For example, in a mixed conifer forest in the Klamath-Siskiyou region, the removal of small trees positively influenced available soil nutrients and hence tree growth (Miesel, Boerner, & Skinner, 2009). Uncharacteristically high tree densities commonly facilitate bark beetle, mistletoe, and root disease mortality (e.g.,Maloney & Rizzo, 2002). "
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    ABSTRACT: The expansion of forest biomass markets may affect California’s forests both positively and negatively. Existing research does not permit an exact assessment of biomass harvesting impact in each forest type, but policy decisions can still benefit from a synthesis of the available science. Biomass markets may permit the harvest and removal of trees that would previously have been left in the woods to die, so they may reduce the prevalence of key habitat elements such as snags and downed logs. Water quality, soils, and site productivity can also be affected by reductions in dead wood brought about by increased biomass harvesting. At the same time, new markets may allow for the restoration of forests that have become unnaturally dense because of fire exclusion (i.e., densities are outside the historic range of variability). Restoration can change fire behavior, and the removal of low value trees can benefit the remaining trees. However, the retention of large pieces of dead wood can limit the risk of biomass harvests, impinging on biodiversity, while keeping small pieces of dead wood and foliage on-site can benefit water quality, soils, and site productivity.
    Full-text · Article · Nov 2015 · Journal of Sustainable Forestry
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    • "This experimental design substitutes space for time (using data from control sites instead of pre-fire data), which is similar to other fire and restoration studies (LeDuc and Rothstein, 2007; Miesel et al., 2008), comparing treatments and reference controls within each year. Within each unit, ten modified Whittaker plots (50 m  20 m) were installed at randomly selected gridpoints for vegetation sampling (shown in Fig. 1 of Knapp et al., 2007). "
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    ABSTRACT: Restoring the natural fire regime to forested systems that have experienced fire exclusion throughout the past century can be a challenge due to the heavy fuel loading conditions. Fire is being re-introduced to mixed conifer forests in the Sierra Nevada through both early season and late season prescribed burns, even though most fires historically occurred in the late season. We assessed the impact of early and late season prescribed fires on soil biogeochemical and microbiological parameters that are important for ecosystem recovery. We found that the late season burns had more dramatic short-term effects on soil abiotic conditions (temperature, moisture and pH), mineral soil carbon levels, total inorganic nitrogen, and microbial activity than the early season burns, relative to unburned sites, suggesting a higher severity burn. However, the total soil nitrogen pools and fluxes and soil respiration rates were not differentially impacted by burn season. These burn season effects suggest that soil variables may be regulated more strongly by fire severity than by the season in which the prescribed fire is conducted.
    Full-text · Article · Jan 2008 · Forest Ecology and Management
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    ABSTRACT: Thinning and prescribed fire decrease the threat of catastrophic wildfire in western coniferous forests by reducing forest biomass available as fuel. Such treatments have been shown to alter foliar nitrogen (N) and phosphorus (P) concentrations, which may precede changes in stem diameter growth. However, the timing or duration of change in foliar nutrient concentrations of mature conifers is not well understood. I evaluated whether large-scale thinning and prescribed fire treatments impact nutrient characteristics and diameter growth of mature Pinus ponderosa (pine) and Abies concolor (fir) in a suite of experimental treatments (Size-preference Thin, Pine-preference Thin, Thin + Fire, and Fire) and a Control in the Klamath National Forest, CA. I analyzed pine needles to age 6 years and fir needles to age 10 years for N and P concentration and content. Vector analysis was used to simultaneously evaluate needle size, nutrient concentration and content to illustrate responses that may not be evident via analysis of nutrient concentration alone. There were no differences in foliar N or P concentration or content for pine or fir for any treatment relative to the Control. Nutrient resorption efficiency and proficiency were not affected by treatment for either species. The length of pine needles produced in 2001 was increased by all treatments that involved thinning, and the mass of needles produced in 2004 was increased by the combination of thinning and prescribed fire. There was no effect of treatment on fir needle length or mass for any cohort of needles. Vector diagrams indicated that pine needle N and P were diluted by treatments as needles increased in mass and total nutrient content while nutrient concentration decreased or remained constant. In contrast, fir needle nutrient concentrations increased or remained constant while dry mass and nutrient content decreased. Vector analysis indicated that the response in foliar characteristics of mature conifers differed between the historically dominant pine and the currently dominant, shade-tolerant fir in this northern California mixed-conifer forest, whereas traditional analysis of individual foliar characteristics generally did not detect differences among treatments. All treatments that involved thinning increased mean annual ring width index between pre- and post-treatment time periods for pine, whereas there was no effect for fir. These results suggest that restoration strategies may have negative or no effects on fir whereas the same treatments may favor pine, thereby facilitating re-establishment of a pine-dominated ecosystem that approximates historical conditions in California’s mixed-conifer forests.
    Full-text · Article · Nov 2012 · Forest Ecology and Management
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