Quaking aspen (Populus tremuloides Michx.) at treeline: a century of change in the San Juan Mountains, Colorado, USA

Abstract

During a repeat photography study quaking aspen (Populus tremuloides Michx.) was observed invading conifer stands at treeline in the San Juan Mountains of south‐western Colorado. Aspen tree core samples were collected from nine plots ranging in elevation from 3192 to 3547 m, and estimated dates of establishment of aspen were grouped into 10‐year intervals for analysis. Estimated periods of establishment were compared with century‐long climate data records to derive any correlations with aspen invasion. Other disturbance agents, such as fire and livestock grazing were also considered. Quantitative analysis of climate variables suggests that decreased mean spring precipitation and increased mean summer maximum temperature provide optimal conditions for aspen establishment. Episodes of invasion were non‐synchronous, but all occurred after 1900, and are likely from seed germination, considered unusual in aspen. Different climate variables explain stand initiation from seed and subsequent peak establishment from vegetative reproduction. Long‐term climate records indicate a general warming since the beginning of the 20th century and explain the continued invasion and persistence of aspen at treeline, resulting from asexual reproduction. Short‐term climate records identify anomalously cool, moist years that explain rarely observed sexual reproduction in aspen.

Infestation and Hydraulic Consequences of Induced Carbon Starvation

“…The San Juan Mountains experience a summer rainy season that usually begins in July due to an influx of monsoonal air from the Gulf of Mexico and the Gulf of California (Keen, 1996). Previous studies suggested a mean annual temperature of 3.2°C and an average annual precipitation of 428 mm at high-elevation weather stations (2,660-2,710 m), although this varies considerably across elevation (Elliot and Baker, 2004). Aspen forests are found from around 2,350 to 3,250 m elevation in this region, co-occurring with ponderosa pine (Pinus ponderosa) forests at the lower end and Engelmann spruce (Picea engelmannii)/subalpine fir (Abies lasiocarpa) forests at the upper end (Worrall et al, 2008).…”

Simulation of Quaking Aspen Potential Fire Behavior in Northern Utah, USA

“…(hereafter aspen) stands are an important forest type in the intermountain region of the United States [1]. Recently, increased study of aspen stand dynamics, particularly "sudden aspen decline" [2] has led to a large body of literature suggesting aspen loss is due partly to a reduction of stand-replacing disturbances as the result of grazing, 20th century fire suppression, an extremely moist 20th century, and subsequent succession [3][4][5]. It is assumed that fire was an integral driving process in historic aspen stand dynamics [6]; however, the role of fire likely varies between seral and stable aspen stands.…”

Aspen Ecology in Rocky Mountain National Park: Age Distribution, Genetics, and the Effects of Elk Herbivory

“…For example, climate change and fire suppression may have influenced aspen stand regeneration (Romme and others, 1995;Elliott and Baker, 2004). The presence of rapidly growing Estes Park, located within the winter range, has provided forage (highly productive, fertilized lawns, golf courses, and ornamental shrubs) for an increased wintering population of elk in town since the late 1970s (R.J. Monello, T.L.…”