Climatic and non‐climatic controls shaping early postglacial conifer history in the northern Greater Yellowstone Ecosystem, USA

Abstract

Mountain ecosystems are characterized by their complex vegetation responses to past climate variability because of the interplay between large‐scale climate changes and local‐scale biotic and abiotic conditions. This study reconstructs the early postglacial expansion of conifer populations in the northern Greater Yellowstone Ecosystem (GYE). The objective is to examine how climate change and non‐climatic factors, including species characteristics, edaphic conditions and disturbance, governed postglacial vegetation changes. Spruce populations expanded first at 13 300 cal a BP, concurrent with soil development and warming summers. Subalpine fir populations expanded after 12 300 cal a BP and probably lagged spruce expansion due to differences in climatic tolerances and/or its poorer seed dispersing capacity. Pine species expanded nearly synchronously after 11 300 cal a BP in response to elevated summer temperatures and increased fire activity. Douglas‐fir populations expanded last after 10 200 cal a BP during the early Holocene summer insolation maximum and cooler winters. The sequence and timing of conifer expansions in the northern GYE are consistent with the regional conifer history, indicating strong vegetation responses to millennial‐scale climate change associated with the seasonal cycle of insolation across spatial scales. Nonetheless, non‐climatic factors, including landscape stabilization and subsequent soil development, seed dispersing characteristics and fire, still shaped local‐scale patterns of conifer expansion.

Past vegetation dynamics in the Yellowstone region highlight the vulnerability of mountain systems to climate change

“…glauca were likely present, as evidenced by genetic studies that indicate the existence of hybrids in the modern GYE (Haselhorst & Buerkle, ). As the temperature increased and slopes stabilized after 13 ka BP (Krause & Whitlock, ), Picea expanded to higher elevations (>2,400 m elev) and became abundant above its current elevation of 2,900 m ( p > .73; Table ). Macrofossils at Fallback Lake, Emerald Lake, Divide Lake, Mariposa Lake and Buckbean Fen confirm local presence of the genus (Whitlock, ).…”

“…The absence or rarity of conifers at this time, however, does not rule out the possibility that small isolated populations grew near ice margins in undetected settings. These types of microrefugia seem likely given the rapid rates of conifer expansion into deglaciated areas after 16 ka bp (Krause & Whitlock, ).…”

“…SCDs = .02, .04 and .046; p = .01, .025 and .05 respectively) [Colour figure can be viewed at wileyonlinelibrary.com] in the spatial and temporal patterns of genera with similar climate tolerances (e.g. Picea and Abies) as well as the dominance of P. contorta in central Yellowstone region attest to the role of disturbance, soil fertility and competition in shaping vegetation at the local scale (Iglesias et al, 2015;Krause & Whitlock, 2017). & Hostetler, 2014).…”

“…The origins of the GYE, as we know it today, trace back 20,000 years ago, when the region was covered by a large glacial complex (Licciardi & Pierce, ). Ice recession and warming temperatures after 17 ka bp (ka bp = kilo annum before present) created vast new areas for biotic colonization and subsequent ecosystem development (Krause & Whitlock, ). As in most regions, our understanding of the ecological history of the GYE comes from pollen records obtained from sediment cores of natural lakes and wetlands that formed during deglaciation, and this history has been discussed in a series of papers dating back to the mid‐1970s (Baker, ; Huerta, Whitlock & Yale, ; Iglesias, Krause, & Whitlock, ; Krause & Whitlock, , ; Krause, Lu, Whitlock, Fritz, & Pierce, ; Millspaugh, Whitlock, & Bartlein, , ; Mumma, Whitlock, & Pierce, ; Waddington & Wright, ; Whitlock, ; Whitlock & Bartlein, ; Whitlock et al., ).…”

Post‐fire vegetation and climate dynamics in low‐elevation forests over the last three millennia in Yellowstone National Park

“…Research following recent stand-replacing fires in the Greater Yellowstone Area (GYA; Wyoming, Montana and Idaho, USA) has shed light on mechanisms by which forests respond to high-severity fire and traits that lead to success of species in particular settings (Turner et al 1997, Donato et al 2016, Harvey et al 2016). In the last few decades, considerable effort also has been directed towards understanding the long-term vegetation, fire and climate history of the GYA using a combination of pollen, charcoal and geochemical data from the sediments of lakes and wetlands (Whitlock 1993, Whitlock et al 2008, Krause and Whitlock 2017, Iglesias et al 2018. These records document vegetation dynamics since the last glaciation under a greater range of climate conditions than can be observed at present.…”