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Baby Got BACI: Changes in Forest Community Composition in Response to the Chatfield Reallocation Project
Purcell, Ashley
Ramey, Colette
Place of Publication:
Denver, CO
Metropolitan State University of Denver
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Conference Papers ( sobekcm )


Collected for Auraria Institutional Repository by the Self-Submittal tool. Submitted by Matthew Mariner.
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Faculty mentor: Erin Bissell
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Major: Environmental science

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Auraria Institutional Repository
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Auraria Library
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Introduction The Chatfield Storage Reallocation Project was implemented to increase the municipal water storage capacity of Chatfield Reservoir, Littleton, CO, during years of high water availability . The plan included removal of cottonwood trees from forests around the reservoir and its tributaries . The process began in Fall of 2017 , and most of the major modifications were completed by June 2019 . 1 We conducted a Before After Control Impact (BACI) study to monitor changes to vegetation composition resulting from the reallocation project at sites located along the Platte River upstream of the reservoir . These cottonwood forests occur in two distinct age categories : 1 ) younger stands in dense formation, and 2 ) more widely spaced older legacy trees . We collected two years of data from both stand and legacy forest sites before the modifications, one year of post modification data, and data from two control sites located outside of the park . Materials and methods To standardize data collection across multiple years, the BBIRD field protocol was modified for use in a riparian environment . 3 Focal tree or stand at each site was selected, identified and DBH Within a 5 m circle around focal tree, individual shrub, woody vine and sapling species were counted and Within a 11 . 3 m circle around focal tree, all tree species were counted and identified . Coarse woody debris and snags were also Nearest neighbor to focal tree shrub, tree and sapling species identified, measured : DBH, distance from focal tree and Canopy cover measured using a convex densiometer at each cardinal Results The post modification data shows several changes to the forest composition after the reallocation project. Histograms were used to confirm the data was non parametric so the signed rank test for paired data was used to analyze the results; V values (test statistic) and p values (significance) are reported in figure captions. Conclusions The Chatfield Reallocation Project, a human induced disruption of the ecosystem, is a one time discrete event, which triggered abrupt changes to the plant community and population structure . This, in turn, may result in changes to resource availability and soil parameters, such as moisture and microbial activity . This could create a habitat ripe for secondary succession of r selected species, which quickly colonize disturbed areas while tolerating harsh conditions and unpredictable environments . 2 An increase in the invasive Cirsium arvense (Canada thistle) is one example of an r selected species that has colonized the now open understory of the cottonwood forests around Chatfield Reservoir . Tree removal has likely enabled the growth of new plants, including invasive species, by opening up the canopy and allowing more light to penetrate to the understory . 2 While % forb coverage was initially measured, the species diversity was not . Post modification visual observations, however, showed an increase of forb species . As the process of succession continues, we expect the diversity of forbs, shrubs and woody vines to increase, possibly to significant levels in subsequent years . The stand forest type experienced the most change because thinning of the dense tree formation allowed for new vegetation growth . Development of new seedlings from the seed bank may also have been facilitated by reduced competition with trees or the transmission of invasive seeds by the activity of the project itself . While the number of species of adult trees was reduced, there was an observed uptick in new saplings which could increase the species counts and/or diversity in future years . Future research will include analysis of control data from outside Chatfield State Park . We expect this will also show the most change in the stand forest type due to the extensive clearing done in the study area . Native species diversity may continue to increase over several years . The time required for establishment of native species is greater than invasive species as the seed bank may produce stronger competitors . 2 Future studies will be needed to analyze this concept . Ashley Purcell 1 and Colette Ramey 2 , Faculty Advisor: Dr. Erin Bissell Earth and Atmospheric Sciences 1 , Biology Department 2 , MSU Denver . Contact for questions Ashley Purcell Colette Ramey Dr. Erin Bissell Fig.1S: V=15, p= 0.02895 Fig.2S: V=1, p= 0.0625 Fig. 4S: V=1, p= 0.05203 Fig. 3S: V=6, p= 0.08678 Fig. 5L: V=10, p= 0.0625 Fig. 5S: V=15, p= 0.03125 Fig. 3L: V=6, p= 0.4251 Fig. 4L: V=0, p= 0.5 Fig.2L: V=0, p= 0.0625 Fig.1L: V=9, p= 0.125 Modifications associated with the reallocation plan resulted in a reduction of canopy cover over sites in both forest types (Fig.5S & Fig.5L). Only the stand forest showed a significant decrease in canopy cover (Fig.5S), which likely contributed to the increase in understory vegetation. There was an observed reduction in the number of trees throughout the study area (Fig.1S & Fig.1L), but the only significant decline was found in the stand forest. (Fig.1S) Both forest types exhibited reduced species diversity of adult trees, but the differences were not significant. (Fig.3S & Fig.3L) Initial counts showed higher numbers of shrubs and woody vines in both the legacy and stand formations, but neither forest type confirmed a significant increase. (Fig. 2S & Fig.2L) The species count of shrubs and woody vines found in the post modification forests was higher than observed prior to plan implementation (Fig.4S & Fig.4L), but only the stand forest type showed a moderate significant change (Fig.4S). Chatfield Habitat 2017 Literature cited 1. ERO Resources Corporation and Tetra Tech EC. 2013. Chatfield reservoir compensatory mitigation plan prepared for the Army Cor ps of Engineers. 2. Gurevitch J, Scheiner SM, and Fox GA. 2006. The Ecology of Plants 2nd ed, c.12 p.283 304. Sinaur Associates, Inc., Sunderland, MA. 3. Martin TE, Paine C, Conway CJ, Hochachka WM, Allen P, and Jenkins W. 1997. BBIRD field protocol. Biological Resources Division, University of Montana Post modification Stand 2019