Holocene vegetation, fire and climate history of the Sawtooth Range, central Idaho, USA

Abstract

The paucity of low- and middle-elevation paleoecologic records in the Northern Rocky Mountains limits our ability to assess current environmental change in light of past conditions. A 10,500-yr-long vegetation, fire and climate history from Lower Decker Lake in the Sawtooth Range provides information from a new region. Initial forests dominated by pine and Douglas-fir were replaced by open Douglas-fir forest at 8420 cal yr BP, marking the onset of warmer conditions than present. Presence of closed Douglas-fir forest between 6000 and 2650 cal yr BP suggests heightened summer drought in the middle Holocene. Closed lodgepole pine forest developed at 2650 cal yr BP and fires became more frequent after 1450 cal yr BP. This shift from Douglas-fir to lodgepole pine forest was probably facilitated by a combination of cooler summers, cold winters, and more severe fires than before. Five drought episodes, including those at 8200 cal yr BP and during the Medieval Climate Anomaly, were registered by brief intervals of lodgepole pine decline, an increase in fire activity, and mistletoe infestation. The importance of a Holocene perspective when assessing the historical range of variability is illustrated by the striking difference between the modern forest and that which existed 3000 yr ago.

Holocene seasonal variability inferred from multiple proxy records from Crevice Lake, Yellowstone National Park, USA

“…Other paleoenvironmental data from the northern Rocky Mountain region suggest early-Holocene conditions that were warmer than at present, although effective moisture levels at this time were higher than in the middle Holocene (Whitlock and Brunelle, 2006;Power et al, 2011;Whitlock et al, 2011). For example, pollen records from high-elevation sites indicate an upslope expansion of low-elevation taxa in the northern Rocky Mountains (e.g., Pseudotsuga and Chenopodiaceae) in the early Holocene (Whitlock and Brunelle, 2006) and those from low-elevation sites show relatively open forest conditions (Power et al, 2011;Whitlock et al, 2011).…”

“…The transition to more open vegetation in Yellowstone after 8000 cal years broadly coincides with maximum aridity at many locations in the Rocky Mountains and mid-continent (e.g., see Bartlein and Whitlock, 1993;Whitlock and Brunelle, 2006;Williams et al, 2009;Shuman et al, 2010;Grimm et al, 2011). In the northern Rocky Mountains, well-developed grassland and open parkland, high fire activity, and low lake levels characterized low elevations (MacDonald, 1989;Brunelle et al, 2005;Stone and Fritz, 2006;Shuman et al, 2009;Power et al, 2011;Whitlock et al, 2011). The Rocky Mountain pattern is an interesting contrast to records from the Pacific Northwest, which register cooler effectively wetter conditions after 7000 cal yr BP (Whitlock and Brunelle, 2006;Barron and Anderson, 2011).…”

“…For example, pollen records from high-elevation sites indicate an upslope expansion of low-elevation taxa in the northern Rocky Mountains (e.g., Pseudotsuga and Chenopodiaceae) in the early Holocene (Whitlock and Brunelle, 2006) and those from low-elevation sites show relatively open forest conditions (Power et al, 2011;Whitlock et al, 2011). Warm humid summer conditions in the early Holocene are broadly registered throughout the Rockies and Great Plains (e.g., Fall, 1997;Shuman et al, 2010;Williams et al, 2010;Anderson, 2011;Grimm et al, 2011;Jiménez-Moreno et al, 2011;Minckley et al, 2011;Whitlock et al, 2011;Briles et al, 2012) and ascribed to higher-than-present summer insolation and its attendant effects on regional climate.…”

Potential influence of wildfire in modulating climate-induced forest redistribution in a central Rocky Mountain landscape

“…Historical fire regimes in the region can be broadly characterized as ranging from relatively infrequent, stand-replacing fire in high-elevation forests and some sagebrush communities, to relatively frequent low-to mixed-severity fire in lower elevation forests . However, variability in climate and periodic widespread mortality from forest pathogens also influenced forest conditions and fire regimes over time (Pierce et al 2004, Brunelle et al 2008, Baker 2009, Whitlock et al 2011.…”

Pollen-based reconstruction of Holocene vegetation and climate in southern Italy: the case of Lago Trifoglietti

“…As the development of pedogenesis under forest cover may have favoured a mineral magnetic increase in soils (de Jong et al, 1998), low MS recorded in sediments is to be expected during phases of stabilised vegetated slopes (Whitlock et al, 2011), while increased magnetic concentrations may be related to changes in sediment sources and to erosive processes of soils (Dearing et al, 1996;de Jong et al, 1998;Vannière et al, 2003;Cruise et al, 2009). Nevertheless, when ferrimagnetic mineral concentration is low (magnetite and maghaemite), the value of MS may be largely influenced by diamagnetic minerals (quartz, carbonates) (Thompson and Oldfield, 1986).…”