Tree Population Dynamics at a Desert Springs Complex: From Seed to Landscape
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Authors
Karam, Sarah L.
Issue Date
2013
Type
Dissertation
Language
Keywords
phreatophytic trees , plant distributions , seed dispersal , seedling establishment , soil salinity , water availability
Alternative Title
Abstract
The cumulative effects of the abiotic and biotic environment on plant distributions
are inherently complex due to spatio-temporal variation. The overall objective of this
dissertation was to examine the population processes and environmental conditions that
control tree distributions at a desert springs complex.
In chapter 1, I examined the efficacy and spatial pattern of coyote dispersal of
Prosopis seeds. Analyses showed that digested seeds remained viable and were deposited
in environments suitable for germination, but feces were not a suitable seed bed for
seedling emergence. Consequently, seed dispersal by coyotes may act as a demographic
bottleneck.
In chapter 2, I examined the effects of water availability and salinity on seed
germination, seedling emergence, and seedling survival using a series of controlled
laboratory and field experiments to identify the fundamental niches of three dominant
tree species. Experimental results showed that the effects of water availability and
salinity were strong, but varied among species, ontogenetic stages, and experimental
conditions. Physiological tolerances to these abiotic factors were lowest during early
seedling survival, suggesting another demographic bottleneck.
In chapter 3, I examined the effects of plant interactions along water and salinity
gradients on seedling establishment in the context of the stress gradient hypothesis.
Results of the field experiment showed that both herbaceous and woody vegetation
ameliorated environmental stress, but the net outcome of plant interactions depended on
species, ontogenetic stage, and the stress gradient. Facilitative effects were common during seedling emergence and early seedling survival, but net interactions shifted to
competition and became more consistent along stress gradients as seedlings aged.
In chapter 4, I examined spatial variation in the interactions between trees across
Ash Meadows. I developed a map of individual trees using object-based classification of
multispectral and LiDAR spatial data and examined spatial interactions between trees
using local point pattern analysis. Results provided strong evidence that the importance
of competition between trees varied spatially in association with water availability and
temporally over tree lifetime.
All together, this research illustrates the spatial and temporal complexity inherent
in plant-environment interactions depending on species, ontogenetic stage, and the abiotic
and biotic environment.
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In Copyright(All Rights Reserved)