Date of this Version
Evan Bumann (2017) Assessing Responses of Betula papyrifera (Paper Birch) to Climate Variability in a Remnant Population Along the Niobrara River in Nebraska Through Dendroecological and Remote Sensing Techniques. MS thesis, University of Nebraska-Lincoln.
Remnant populations of the boreal species Betula papyrifera, found along north-facing canyons and river banks of the Niobrara River Valley in north-central Nebraska, represent one of the southernmost distributions of the species in North America. Although, the species has persisted in the Great Plains after the Wisconsin Glaciation due to the local topography and microclimatic conditions, canopy dieback has been reported in recent years, which is believed to be attributed to temperature change. Therefore, the goals of this research are to: 1) use dendroecological techniques, or the study of tree rings to assess the responses B. papyrifera to intra- and inter-annual micro-environmental variability between 1950 and 2014, and identify the abiotic factor(s) which best describe the observed growth trends in this species; and 2) determine whether the use of satellite imagery from Landsat 5 TM (1985-2011) and MODIS (2000-2014) can serve as a proxy for assessing tree health by relating indices like the Normalized Difference Vegetation Index (NDVI) to tree rings characteristics.
Results showed that growing-season streamflow and precipitation were positively and significantly correlated with raw tree ring widths, basal area increment increase, and standardized ring widths (p < 0.05), while high late fall and spring precipitation and streamflow seemed to have a negative effects. The strongest predictor for standardized tree ring growth was the Palmer’s Drought Severity Index (PDSI), suggesting that B. papyrifera is highly responsive to a combination of temperature and water availability. GLMMs and Pearson R2 correlations indicated that increasing winter and spring temperatures were unfavorable for tree growth while increasing summer temperatures were favorable in the absence of drought.
Maximum and accumumlated NDVI derived from satellite imagery showed potential of these techniques to be used as a proxy for ex-situ monitoring B. papyrifera performance through high Pearson’s R2 values (≥0.76) at the pixel level. Landsat 5 TM derived max-value NDVI correlations identified adjacent rangeland of moderate bison grazing on rough landscape - similar to those occupied by B. papyrifera – as a likely reliable proxy for predicting seasonal growth and performance the species.
Results from this study have significant management implications and are critical to the development of biogeographical and ecophysiological predictive models aimed at forecasting the dynamics and performance of this species in the face of future climate variability, extremes, and change in both remnant populations and across its current habitat range in more northern latitudes.
Advisor: Tala Awada
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