Assessing responses of Betula papyrifera to climate variability in a remnant population along the Niobrara River Valley in Nebraska, U.S.A., through dendroecological and remote-sensing techniques

Remnant populations of Betula papyrifera Marshall have persisted in the Great Plains after the Wisconsin Glaciation along the Niobrara River Valley, Nebraska. Population health has declined in recent years, which has been hypothesized to be due to climate change. We used dendrochronological techniques to assess the response of B. papyrifera to microclimate (1950-2014) and the normalized difference vegetation index (NDVI) derived from satellite imagery (Landsat 5 TM (1985-2011) and MODIS (2000-2014)) as a proxy for population health. Growing-season streamflow and precipitation were positively correlated with raw and standardized tree-ring widths and basal area increment increase. Increasing winter and spring temperatures were unfavorable for tree growth, while increasing summer temperatures were favorable in the absence of drought. The strongest predictor for standardized tree rings was the Palmer Drought Severity Index, suggesting that B. papyrifera is highly responsive to a combination of temperature and water availability. The NDVI from the vegetation community was positively correlated with standardized tree-ring growth, indicating the potential of these techniques to be used as a proxy for ex situ monitoring of B. papyrifera. These results aid in forecasting the dynamics of the species in the face of climate variability and change in both remnant populations and across its current distribution in northern latitudes of North America. Key words: paper birch, tree rings, riparian, MODIS, Landsat, NDVI, water, temperature, Nebraska Sandhills. Des populations reliques de Betula papyrifera Marshall ont persiste dans les grandes plaines apres la glaciation du Wisconsin le long de la vallee de la riviere Niobrara, au Nebraska. L'etat de sante des populations s'est deteriore au cours des recentes annees, vraisemblablement a cause des changements climatiques. Nous avons utilise les techniques dendrochronologiques pour evaluer la reaction de B. papyrifera au microclimat (1950-2014), ainsi que l'indice de vegetation NDVI derive de l'imagerie satellitaire (Landsat 5 TM (1985-2011) et MODIS (2000-2014)) en tant que substitut refletant l'etat de sante des populations. La precipitation et l'ecoulement fluvial durant la saison se croissance etaient positivement correles avec l'augmentation de l'accroissement de la surface terriere et la largeur brute et standardisee des cernes annuels. L'augmentation des temperatures hivernales et printanieres etait defavorable pour la croissance des arbres tandis que l'augmentation des temperatures estivales etait favorable en l'absence de secheresse. Le meilleur predicteur pour les cernes annuels standardises etait l'indice de severite de la secheresse de Palmer, ce qui indique que B. papyrifera est tres sensible aune combinaison de temperature et de disponibilite de l'eau. L'indice NDVI de la communaute vegetale etait positivement correle a la croissance des cernes annuels standardises, ce qui indique que ces techniques peuvent etre utilisees comme substitut pour le suivi ex situ de B. papyrifera. Ces resultats vont aider a predire la dynamique de cette espece face aux changements climatiques tant dans les populations reliques que partout dans son aire de repartition actuelle sous les latitudes septentrionales de l'Amerique du Nord. [Traduit par la Redaction] Mots-cles: bouleau blanc, cernes annuels, riverain, MODIS, Landsat, indice de vegetation NDVI, eau, temperature, dunes du Nebraska.
1. Introduction Paper birch (Betula papyrifera Marshall) is a widely distributed deciduous tree species across continental North America. It grows in the boreal forest from Newfoundland in eastern Canada all [...]