Event Title

Aspen Forest Dynamics Associated with Conifer Encroachment at Lassen Volcanic National Park, California

Event Website

http://www.nafew2009.org/

Start Date

23-6-2009 1:50 PM

End Date

23-6-2009 2:10 PM

Description

In coniferous forested landscapes, quaking aspen (Populus tremuloides Michaux.) contribute disproportionately to ecosystem services and functions by supporting habitat heterogeneity and biodiversity, accelerating nutrient cycling rates, and increasing water yields. However, aspen are an early successional, clonal species with a relatively short stem lifespan, and aspen stands depend on regular disturbance for successful vegetative recruitment and establishment of replacement cohorts. Land managers are concerned that aspen stands in the western United States may be transitioning to a conifer dominated canopy as a result of disruptions to natural fire regimes and browse pressure on vegetative sprouting. As forest structure shifts in many locations towards overmature aspen and dense, even-aged stands of shade tolerant conifer species, the services and functions contributed by aspen may be at risk of loss. To evaluate the impact of increasing conifer cover, we measured forest structure factors (e.g., species canopy cover and density) that potentially influence the understory (e.g., species richness and diversity) and soil surface (e.g., litter depth, level of soil OM decomposition) in 30 aspen stands at Lassen Volcanic National Park. The stands represent a gradient of current conifer cover values ranging from 3 to 77%. For the same stands, photo interpretation of a time series of aerial photos (1952 - 2002) quantified the direction and rate of conifer cover change over the past fifty years. Conifer cover increased in 60% of sampled stands and decreased in one stand over the studied time period, with a mean increase in conifer cover of 38%, and a maximum increase of 85%. Regression modeling showed that aspen cover, vegetative sprouting, and understory species richness decreased with increasing levels of current conifer cover, and that leaf litter depth increased (p<0.1). We conclude that declines in characteristic aspen stand values are associated with increases in conifer cover.

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Jun 23rd, 1:50 PM Jun 23rd, 2:10 PM

Aspen Forest Dynamics Associated with Conifer Encroachment at Lassen Volcanic National Park, California

In coniferous forested landscapes, quaking aspen (Populus tremuloides Michaux.) contribute disproportionately to ecosystem services and functions by supporting habitat heterogeneity and biodiversity, accelerating nutrient cycling rates, and increasing water yields. However, aspen are an early successional, clonal species with a relatively short stem lifespan, and aspen stands depend on regular disturbance for successful vegetative recruitment and establishment of replacement cohorts. Land managers are concerned that aspen stands in the western United States may be transitioning to a conifer dominated canopy as a result of disruptions to natural fire regimes and browse pressure on vegetative sprouting. As forest structure shifts in many locations towards overmature aspen and dense, even-aged stands of shade tolerant conifer species, the services and functions contributed by aspen may be at risk of loss. To evaluate the impact of increasing conifer cover, we measured forest structure factors (e.g., species canopy cover and density) that potentially influence the understory (e.g., species richness and diversity) and soil surface (e.g., litter depth, level of soil OM decomposition) in 30 aspen stands at Lassen Volcanic National Park. The stands represent a gradient of current conifer cover values ranging from 3 to 77%. For the same stands, photo interpretation of a time series of aerial photos (1952 - 2002) quantified the direction and rate of conifer cover change over the past fifty years. Conifer cover increased in 60% of sampled stands and decreased in one stand over the studied time period, with a mean increase in conifer cover of 38%, and a maximum increase of 85%. Regression modeling showed that aspen cover, vegetative sprouting, and understory species richness decreased with increasing levels of current conifer cover, and that leaf litter depth increased (p<0.1). We conclude that declines in characteristic aspen stand values are associated with increases in conifer cover.

http://digitalcommons.usu.edu/nafecology/sessions/aspen/1