Fire is a natural part of most forest ecosystems in the western United States. Forest managers utilize fuel reduction projects to lessen fire severity, often without considering potential negative ecological consequences of non-native plant species introductions. The establishment and spread of non-native species following fire may significantly alter the ability of native plant communities to recover. Factors such as fire severity, resource distribution, and soil alterations all play a role in where and how non-native plant species may establish in burned areas. This doctoral dissertation research project addresses the invasion potential across the forest/grassland ecotone following low severity fire by studying microsite changes from pre- to post-burn conditions. The two research questions of the proposed study are: 1) Are there significant differences in the biotic (vegetation attributes) and abiotic (soil moisture, temperature, nutrients) microsite conditions across the ponderosa pine/grassland ecotone of the Colorado Front Range following low severity fire, which would make the site more invasible? 2) In the post-fire landscape, following low severity fire, how are non-native plant species colonization patterns affected by the microsite patterns? Data collected from several research sites along this forest/grassland ecotone over the course of several seasons prior to prescribed burning provide information on variation in soil moisture and temperature and vegetation structure during times of near normal conditions. Following prescribed burning, the changes in microsite patterns may vary across the ecotone and impact the availability of sites for native and non-native species colonization. Many of the studies of fire effects to date address this question at coarser scales. This research applies a more fine scale approach to determine the mechanisms involved in the spread of non-natives into the forested landscape from a grassland matrix.

This research will contribute to the understanding of the importance of microsite conditions and their effects on the potential for non-native plant species to move across ecotones after low severity fire. The use of this information will contribute not only to the overall understanding of the degree to which a recently burned area is susceptible to invasion by non-native species at the fine scale, but will also contribute to the integration of these fine scale mechanisms into landscape level responses to disturbance. This research will provide fundamental information that is necessary to support present and future forest management decisions in the western United States, in regards to prescribed fires and non-native species control. As a Doctoral Dissertation Research Improvement award, this award will provide support to enable a promising student to establish a strong independent research career.

Project Report

Normal 0 false false false EN-US X-NONE X-NONE Fine scale studies are rarely performed to address landscape level responses to climatic variability. The timing, distribution, and magnitude of soil temperature and moisture affects what species emerge each season and, in turn, their resilience to fluctuations in microclimate and disturbance. Studies done over several years can tease out the highly effective variations in microclimate versus other site characteristics that define species composition. For this dissertation research, I evaluated the response of vegetation change to climatic variability within two communities over a three year period (2009-2012) utilizing 25 meter transects at two locations along the Front Range of Colorado near Boulder and Golden respectively. To assess the variability of climate and soil conditions, correlation analyses were performed using both plant species abundance and cover; soil temperature; moisture; and various nutrients. The results from these correlations show that soil conditions and local climate may be important drivers of species distribution each season and add to current literature by directly examining the modifying effects of plant coverage type, fine scale soil property variation, micro and macro climate on the resistance and resilience of these sensitive communities to inevitable change. Initially, I demonstrate the use of autocorrelograms and variograms as tools to identify the degree of dependency of soil temperature and moisture on the distance and time between pairs of measurements and how to take advantage of this dependency along several line-transects that cross the forest-steppe ecotone. The magnitude of spatial and temporal variation of soil temperature, moisture, and several additional soil properties across a transition zone show variable autocorrelation depending on the season. The variability in soil temperature autocorrelation was the greatest in the summer and spring and fall had the highest (low variability) spatial and temporal autocorrelation. In an environment that is susceptible to lower precipitation/soil moisture values and higher heterogeneity in vegetation cover in the summer season it is intuitive that temporal and spatial variability of soil moisture would be more variable in this season. Spring and fall, being the wettest seasons in terms of moisture, have the highest autocorrelation values based on a steadier microclimate. Additionally, with this analysis I wanted to develop a technique to assess the optimum number of samples, sampling interval, and the distance between samples required to capture soil variation with fewer sample points required (lower cost). It was determined that a two meter interval would cover the spatial variability in this location while hourly measurements would need to continue throughout the summer season and decrease to three plus hours for the remainder of the year. Next, I used these in situ measurements of soil temperature, moisture, and several soil properties (pH, organic matter, texture, phosphorous, potassium, and nitrate) to determine the effects of changes in soil conditions on vegetation. I found that there are several plant groups in particular that are more sensitive to variations in temperature and moisture than others. Although there may be fall and winter precipitation events that play a role in the establishment or persistence of species, depending on annual or perennial, the month of utmost importance is March. When all seasons, locations, correlations, and regional climate are looked at this month stands out in terms of significance. Additionally, of all of the functional types represented at these two sites C4, C3, native, non-native, and forb species seem to be the most sensitive to fluctuations in soil temperature, moisture, and regional climate in the spring season. I wanted to take these observations of four years of climatic variability in this forest-steppe community along with the regional climate variability to assess ecosystem response to direct effects on grassland species. Through environmental sensor placements at each site, air temperatures have increased at both sites during the spring season while soil moisture has slowly declined. Even though soil temperatures have been preferable for increased growth the moisture has been insufficient for these species to take advantage of this. The steady decline in species size and abundance over the study period at both locations indicates that some species are unable to respond to continually higher temperatures and lower moisture availability, while other species more adapted to these semi-arid conditions may have an advantage in an ever changing climate. 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University of Colorado at Boulder
United States
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