The Relative Importance of Abiotic and Biotic Factors for Seedling Establishment in the Colorado ...

113 Pages·2015·1.29 MB·English

The Relative Importance of Abiotic and Biotic Factors for Seedling Establishment in the
Colorado Desert, CA

DISSERTATION

Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy
in the Graduate School of The Ohio State University

By
Natasha Nicole Woods
Graduate Program in Evolution, Ecology and Organismal Biology

The Ohio State University
2015

Dissertation Committee:
Maria N. Miriti, Advisor
Peter S. Curtis
Kristin L. Mercer
Copyright by
Natasha Nicole Woods
2015
Abstract
Drought combined with warmer temperatures has caused extensive mortality in
US southwest desert ecosystems. Disproportional mortality among long-lived shrub
species can have dire consequences for community regeneration if novel recruitment is
dependent on facilitated establishment. However, regeneration niches can be under biotic
or abiotic control.
My dissertation research examines mechanisms that control juvenile recruitment
in the Colorado Desert, CA. Specifically I examine, seed and seedling responses to
resources by partitioning those resources that are under direct biotic control based on the
production and consumption patterns of standing vegetation, and those that are under
abiotic control due to the effects of temperature and precipitation. By examining the
relative importance of abiotic and biotic factors that affect plant recruitment, I can
anticipate community stability in the face of natural or anthropogenic disturbance and if
necessary offer strategies to mitigate species loss by identification of relevant variables to
promote recruitment of target species.
In chapter 1 I characterize the spatial and temporal distribution of nitrogen for
three years at a long-term study site in the Colorado Desert. In chapter 2, I examine the
capacity for dominant shrubs to serve as plant facilitators for seed establishment and use
a greenhouse experiment to identify the distinct roles of light and nitrogen on seed
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germination. In a third experiment, I examine the roles of neighboring species identity,
frequency and density on seedling performance when water and light are limiting.
I found that each focal species distinctly influenced nitrogen availability, which
is generally higher near plant canopies. I also found higher levels of nitrogen under
Ambrosia dumosa compared to the other focal species and the interspace. These results
were highly dependent upon season and year (Chapter 1). Adult shrubs did not uniquely
impact germination but beneficiary species identity was the main factor for germination.
In the greenhouse, differences in percent germination were strongest at full light, and
canopy light and nitrogen levels did not affect beneficiary germination (Chapter 2).
Using average rainfall, temperature and nitrogen concentrations from canopy
microhabitats of Ambrosia dumosa from 2011-2012, I found that competition influenced
early performance of A. dumosa, and Eriogonum fasciculatum, but not Larrea tridentata.
Reduced growth of L. tridentata seedlings was not attributable to competition (Chapter
3).
Given these results, seed germination is not strongly regulated by abiotic or biotic
factors; however, shrub canopies may be important for seedling growth and survival. If
seedling persistence responds to nitrogen resources, A. dumosa may be instrumental in
facilitating the establishment of perennial species. Nevertheless, all facilitators are
important for providing increased heterogeneity in the landscape, which may increase
regeneration niches for species not examined in my research. Nitrogen levels under
shrub control would diminish without shrubs and subsequently, regeneration niches
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would also decrease. However, relative competitive abilities can influence future
community composition at the study site.

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This document is dedicated to my brother, Lawrence C. Woods, my grandmothers, Mary
L. Terry and Edna Mae Yates, and my brother-in-law Anthony Hardy who are no longer
here to see me complete this goal.

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Acknowledgements
I would like to thank my advisor, Maria Miriti for her unfailing support since I
moved to Columbus. Maria has not only trained me in plant community ecology but has
supported me personally as well. Maria has always challenged me to think and read
broadly. She is my role model and I hope that I can invest in other students all that she
has invested in me.
I would like to thank my committee members Peter Curtis and Kristin Mercer. I
would like to thank Peter for allowing me to barge into his office without an appointment
to discuss my research projects and for providing useful feedback on my manuscript. I
would like to thank Kristin for inviting me to her lab meetings while Maria was on
sabbatical and helping me with some of the initial experimental design for my field work.
I also would like to thank Ralph Boerner for serving on my candidacy committee and
teaching me how to do soil nitrogen extractions.
I am grateful for the help of my lab mates, S. Rodriguez-Buriticá, C. Pieterson, T.
Ibrahim and R. McCarthy who faithfully read and provided useful feedback on all of my
chapters and/or supported me with my field work. I would also like to thank my work
study students and volunteers T. Catrett, E. Salcido, M. Perry, N. Kim, and C. Etiel, for
all of the work they helped me complete in the lab. I would especially, like to thank T.
Catrett for all of his assistance inputting data and helping me with an untold number of
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nitrogen extractions. I would also like to thank my fellow EEOB graduate students who
have helped me during the course of this research through loaning me necessary
equipment or by reading my manuscripts, C. Lin (Chia), H. Chang (Chi), A. Fotis, K.
Calinger-Yoak, R. Ricart, and K. Knight.
This dissertation would not have been possible without support and funding from
a number of different sources. This work was made possible by The Evolution, Ecology
and Organismal Biology Department at The Ohio State University, and grants from The
Desert Legacy Fund, (The Community Foundation Serving Riverside and San Bernardino
Counties), the Robert E. Lee Graduate Student Grant (Lee Family Foundation and Joshua
Tree National Park Association), Graduate Student Grant (Alumni Grants for Graduate
Research and Scholarship, The Ohio State University) and Professional
Development/Research Grant (Bells National Research Center, The Ohio State
University). I would also like to thank Dr. Valerie Lee, Dr. James Moore III, Dr. Samuel
Hodge, and Dr. Robert Bennett for all of their support during my dissertation.
I would like to thank M. Umbel, M. Gerring and E. Zehr for being GREAT
friends during my time in Columbus. I would also like to thank all of the members of
University Baptist Church for all of their support and care.
I would not have known that I could have a career in research had it not been for
my advisor from my Master’s Degree program, Dr. LaJoyce Debro. Dr. Debro has been
a friend and confidant for over ten years. I am grateful for her friendship.
I would not be here without the support of my family and friends from Alabama.
My dear family and friends, T. Christian, A. F. Christian, T. Toyer, K. Ward, G. Childs,
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J. Johnson, S. Smith, G. Webb, and J. Martin have supported me though this entire
process. I would also like to thank my nieces, J. Hardy, L. Hardy, M. Toyer (my adopted
niece), my nephew L. Hardy and my goddaughter (L. Ward). When the days got hard I
thought of you and pushed on. Thank you for your encouragement.
To my Mom and siblings, Frederica, Frederick and Lazarus, I am at a loss for
words when it comes to expressing my appreciation for all of the prayers, the emotional
and financial support you all have given me throughout my life. This is not just my
accomplishment, it is ours. I thank God for all of you and for allowing me to complete in
this awesome journey.

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Vita

1996………………………………………...Anniston High School
2001………………………………………...B.S. Biology, Jacksonville State University
2003………………………………………...M.S. Biology, Jacksonville State University
2003-2004…………………………………..Research Assistant, University of Alabama
at Birmingham
2004-2008…………………………………...Laboratory Educator, Spelman College
2008 to present ..............................................Graduate Teaching Associate, Evolution
Ecology and Organismal Biology, The Ohio
State University

Fields of Study

Major Field: Evolution, Ecology and Organismal Biology
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