Paper birch decline in the Niobrara River Valley, Nebraska: Weather, microclimate, and birch stand conditions

Abstract

of increased frequency of potentially injurious climatic events would make population recovery much more difficult now than from 1948 to 1977, when thaw/freeze conditions were less frequent. These conditions, combined with little evidence of recruitment of young birch and great geographic distances from potential immigrant sources, make the future persistence of birch in the Niobrara River Valley stands uncertain.

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

“…On a continental scale, one of the main threats to B. papyrifera has been increased climate variability, specifically temperature and precipitation. The species rarely occurs in areas where average July temperature exceeds 21°C (Stroh and Miller 2009). In comparison, the Niobrara River Valley July average temperature is approximately 23.8°C.…”

“…One of these ecotypes is located along the Niobrara River Valley in north-central Nebraska, where the species can be found in north-facing canyons and along riverbanks. The valley plays an important ecological role as an ecotone where grassland and forest species converge, supporting a diverse array of vegetation that is rarely found in close proximity elsewhere (Stroh and Miller 2009). Short grass species from the semi-arid grasslands of the surrounding Sandhills, as well as grasses representing the mixed and tall grass prairies, can be found alongside forest species representing the western coniferous, eastern deciduous, and boreal communities.…”

“…Scattered populations can be found in the Great Plains of Montana and North Dakota, the Black Hills of South Dakota, the Appalachian Mountains, and the Front Range of Colorado (Burns and Honkala 1990; map: http://nativeplantspnw.com/paper-birchbetula-papyrifera/). As a boreal species, B. papyrifera is adapted to the cold northern climate (Fowells 1965;Stroh and Miller 2009) and has been found to have mixed responses to temperature, especially during the growing season. Warming temperatures in the spring can result in an earlier bud burst, which can have positive impacts on growth due to increased cambial activity when water is available (Karlsson et al 2004;Hollesen et al 2015;Li et al 2016), but this comes with a risk of early season frost, which can damage and kill newly emerging buds and rootlets and may result in crown dieback (Pomerleau 1991).…”

“…After the Wisconsin Glaciation, remnant stands of B. papyrifera have persisted in the Great Plains but with declining presence (Wright 1970;Stroh and Miller 2009). One of these ecotypes is located along the Niobrara River Valley in north-central Nebraska, where the species can be found in north-facing canyons and along riverbanks.…”

“…In comparison, the Niobrara River Valley July average temperature is approximately 23.8°C. Stroh and Miller (2009) attributed the health of the Niobrara River Valley populations to a cooler localized microclimate and the close proximity to the riverbank. They reported dieback of B. papyrifera in recent years, which is thought to have started around the 1980s and is possibly attributed to temperature increase.…”