The Effects of Environmental Heterogeneity
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Climate variability affects the germination strategies exhibited by arid land plants
This chapter examines the germination ecology of a subset of 10 Great Basin forb species common to the sagebrush steppe, asking how mean climate and climate variation at individual sites and across a species’ range affects the specialist-generalist spectrum of germination strategies exhibited by ten arid land forbs. We investigated these relationships using climate data for the western United States, occurrence records from herbaria, and germination trials with field-collected seeds. We found that nine out of ten species exhibited population-level variation in germination, and that more flexible strategies evolved in response to higher spatial variation in actual evapotranspiration at a local scale and in available water in the spring and annual precipitation at a range-wide scale.
Contrasting climate niches among
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Seed Bank Dynamics in Disturbed Areas
This chapter investigates seed bank dynamics in a Great Basin sagebrush steppe system, using sites that differ in their disturbance history. We used generalized linear models to test whether shrub cover, ground cover, climate, or disturbance history (fire and grazing) were predictive of the seed densities in the soil, the diversity of native and introduced species, the presence of rare species, and similarity between the above- and below-ground species composition. We found that common measures of fire and grazing disturbance may be overly coarse for predicting the effects of disturbance on seed bank dynamics. We also found that shrub cover was highly predictive of the seed bank dynamics in this system; more specifically, shrub cover of early seral shrub species was predictive of patterns consistent with moderate disturbance or recovery from disturbance within the above and below-ground plant community, while increasing cover of later seral species, such as Artemisia tridentata, produced patterns indicating a longer time since disturbance.
Find a copy of my dissertation by clicking the button below: Plant Responses to Environmental Heterogeneity in Great Basin Sagebrush Steppe |