Accurate estimation of the responses of understory plants to natural and anthropogenic disturbance is essential for understanding efficacy and non-target effects of management and restoration activities. However, ability to assess changes in abundance of understory plants that result from disturbance may be hampered by inappropriate sampling methodologies. Conventional methods for sampling understory plants may be robust for common, well-distributed species, but may fail to adequately characterize the abundance of less-common species, which are often the taxa of management concern. I tested conventional and novel approaches to sampling understory plants to determine their efficacy (in terms of number of replicates and time required) for quantifying abundance of plants of varying frequency and spatial heterogeneity on three control and three thinned-and-burned treatment units located within the western Montana block of the Fire and Fire Surrogates Project (FFS) a large-scale investigation of the effects of fuel-hazard reduction treatments on a variety of ecosystem components. In each treatment unit, I used four sampling methods (modified Whittaker plots, Daubenmire transects, point line intercept transects, and strip adaptive cluster sampling) to estimate the cover of 24 understory species that vary in abundance. Compared to Daubenmire and point line intercept transects, modified Whittaker plots estimated cover with the lowest variances and, consequently, for the majority (67%) of species required the smallest sample sizes to accurately measure cover. However, this greater sampling efficiency was offset by increased time required to sample. For species grouped by growth-form and for common species, all three conventional sampling designs (i.e. Daubenmire transects, modified Whittaker plots, and point line intercept transects) were capable of estimating cover with a 50% relative margin of error with reasonable sample sizes (3-36 plots or transects for growth-form groups; 8-14 for common species); however, increasing the precision to 25% relative margin of error required sampling sizes that may be logistically infeasible (11-143 plots or transects for growth-form groups; 28-54 for common species). In addition, all three designs required enormous sample sizes to estimate cover of non-native species as a group (29-60 plots or transects) and of individual less-common species (62-118 plots or transects), even with 50% relative margin of error. Strip adaptive cluster sampling was the only method tested that efficiently sampled less-common species: for Cirsium arvense, an invasive non-native plant, adaptive sampling required five times fewer replicates than needed for modified Whittaker plots and 20 times less than for Daubenmire or point line intercept transects. My findings suggest that conventional designs may not be effective for accurately estimating the abundance of newly establishing, non-native plants as a group or of the majority of forest understory plants, which are characterized by low abundance and spatial aggregation. Novel methods such as strip adaptive cluster sampling should be considered in investigations for which cover of these species is a primary response variable.

Nitrogen (N) is a primary limiting nutrient in all ecosystems. Therefore, a thorough understanding of N cycling processes in forest ecosystems is required to minimize N losses to fire, harvesting, and other forms of land management. The influence of fire, fire exclusion and forest restoration treatments on non-symbiotic N-fixation in the forest ecosystem has been poorly studied. Over the past 100 years, fire has been greatly excluded from low elevation, fire maintained forests as a result of active fire suppression as well as land management activities that create discontinuities in landscape fire patterns. Previous studies have shown this activity to inhibit recolonization of sites by symbiotic N-fixing plant species. The lack of these important N fixing species may make non-symbiotic, free-living N fixing bacteria a more important source for N recovery in these forest ecosystems following disturbance. Recent studies also suggest that free-living N-fixing bacteria colonizing decomposing woody roots have the capacity to fix large amounts of N. The purpose of these studies was to investigate the effect of fire, fire exclusion, and forest restoration on the N contribution of non-symbiotic N-fixing bacteria (colonizing soil, woody roots, and soil crusts) to the forest ecosystem and how their contribution compares to symbiotic N-fixers in Western Montana. Studies were conducted in the laboratory and at numerous field sites throughout western Montana. In order to determine the N-fixation activity of organisms in these systems, we used the acetylene reduction technique. Neither time since fire, nor restoration treatment had any direct influence on free living N-fixation in soil or woody roots. Moisture and N availability were the potent drivers of free living N-fixation in western Montana. Nitrogen-fixation rates were low in decomposing woody roots in these ecosystems and woody roots do not contribute a significant amount of N to low elevation ponderosa pine/Douglas-fir forests in western Montana. Free-living N-fixing bacteria in soils were found to make a significant, yet modest N contribution to the forest ecosystem. Nitrogen demand by trees and shrubs are being maintained by residual soil organic N, symbiotic N fixation, and wet and dry N deposition in the Inland Northwest