Samniqueka J. Halsey | Search USGS

USGS2020

Visualizing the ecological importance of pre-Euro-American settlement fire across three Midwestern landscapes

Bearing-tree data were used to calculate an index, pyrophilic percentage, depicting the importance of fire before Euro-American settlement on three landscapes, two within the Prairie Peninsula and one outside the region. Based on functional traits, bearing trees were classified as either pyrophilic or pyrophobic, applied to Public Land Survey points, and the pyrophilic percentage was calculated for each point. Kriging was applied to this point database to create a continuous surface of pyrophilic percentages. Regression analysis was used to relate this surface to environmental factors. Regression models created separately for each study area explained 38 to 53% of the variation in pyrophilic percentage. A positive association between pyrophilic percentage and distance to water and summer potential evapotranspiration was consistent across all study sites. The consistently high values and spatial patterns of pyrophilic percentage revealed fire-dominated landscapes interspersed with patches of pyrophobic vegetation. The restriction of pyrophobic areas to the leeside (east) of waterbodies indicated these served as firebreaks in a fire-swept landscape. Lake Michigan must have had a profound effect on pre- Euro-American settlement fire environments, serving as a massive physical firebreak while casting a moist maritime climate eastward. In southern and southwestern Illinois, the Mississippi River and associated tributaries along with an increase in topographic complexity also served as firebreaks, with pyrophobic forests restricted to riparian zones which progressively graded to pyrophilic vegetation on surrounding uplands. Our analysis expands the use of Public Land Survey data by converting bearing trees into a meaningful fire ecology index. While much of the landscape included in our study area is now in agriculture or urbanized, pyrophilic percentage maps can help guide land managers in the application of fire for restoration, conservation, and forestry purposes.

Illinois, Indiana, Michigan, Wisconsin↗

USGS2016

Population-specific life histories contribute to metapopulation viability

Restoration efforts can be improved by understanding how variations in life-history traits occur within populations of the same species living in different environments. This can be done by first understanding the demographic responses of natural occurring populations. Population viability analysis continues to be useful to species management and conservation with sensitivity analysis aiding in the understanding of population dynamics. In this study, using life-table response experiments and elasticity analyses, we investigated how population-specific life-history demographic responses contributed to the metapopulation viability of the Federally threatened Pitcher's thistle ( Cirsium pitcheri ). Specifically, we tested the following hypotheses: (1) Subpopulations occupying different environments within a metapopulation have independent demographic responses and (2) advancing succession results in a shift from a demographic response focused on growth and fecundity to one dominated by stasis. Our results showed that reintroductions had a positive contribution to the metapopulation growth rate as compared to native populations which had a negative contribution. We found no difference in succession on the contribution to metapopulation viability. In addition, we identified distinct population-specific contributions to metapopulation viability and were able to associate specific life-history demographic responses. For example, the positive impact of Miller High Dunes population on the metapopulation growth rate resulted from high growth contributions, whereas increased time of plant in stasis for the State Park Big Blowout population resulted in negative contributions. A greater understanding of how separate populations respond in their corresponding environment may ultimately lead to more effective management strategies aimed at reducing extinction risk. We propose the continued use of sensitivity analyses to evaluate population-specific demographic influences on metapopulation viability. In understanding the underlying causes of the projected extinction probabilities of each population and identifying broad-scale contributions of different populations to the metapopulation, the process of pinpointing target populations is simplified. More detailed analyses can then be applied to the target populations to increase population viability and consequently metapopulation viability. Based on our research, we suggest that the best approach to improve the overall metapopulation viability is to manage the contributions to population growth for each population separately.

Ecosphere↗