Interpreting Botanical Progress
January-March 1999
Seed and Seedling Ecology of Piñon and Juniper Species in the
Pygmy Woodlands of Western North America
Jeanne C. Chambers, Stephen B. Vander Wall and Eugene W. Schupp.............1
Pollen Dispersal Models In Quaternary Plant Ecology: Assumptions,
Parameters and Prescriptions
Stephen T. Jackson and Mark E. Lyford .....................................39
A Brief History of the Lysigenous Gland Hypothesis
Glenn W. Turner............................................................76
Instructions to Contributors...................................................89
New Books Received.............................................................92
Order Form
Seed and Seedling Ecology of Piñon and Juniper Species in the Pygmy Woodlands of Western North America Jeanne C. Chambers USDA Forest Service Rocky Mountain Research Station 920 Valley Road Reno, NV 89512 Stephen B. Vander Wall Department of Biology and Ecology, Evolution, and Conservation Biology Program University of Nevada, Reno Reno, Nevada 89557 Eugene W. Schupp Department of Rangeland Resources and The Ecology Center Utah State University Logan, Utah 84322 I. Abstract/Resumen II. Introduction III. Woodland Description IV. Overview of Seed and Seedling Fates V. Seed Production VI. Seed Dispersal and Seed Predation A. Adaptations of Cones and Seeds for Dispersal B. Seed Dispersal Agents C. Seed Predators D. Differences in Disperser Effectiveness E. Effects of Seed Crop Size on Seed Dispersal and Predation VII. Post-Dispersal Seed Mortality VIII. Seed Germination IX. Seedling Establishment X. Implications A. Regional Migration and Local Expansion 1. Pre-historic and Historic Migration of the Woodlands 2. Short- and Long-distance Dispersal Events 3. The Role of Ecotones B. Natural and Anthropogenic Disturbance 1. Fire, Livestock Grazing, and Human Intervention 2. Species Life History Attributes and Disturbance Characteristics XI. Areas for Future Research XII. Acknowledgments XIII. Literature Cited
I. Abstract Knowledge of the seed and seedling ecology of the piñon and juniper woodlands of western North America is essential for understanding both the northward migration and expansion of the woodlands during the Holocene (< 11,500 BP), and the accelerated expansion of the woodlands since settlement of the West by Anglo- Americans around 200 years ago. We follow the fates of seeds and seedlings of the different piñon and juniper species within the woodlands from seed development to seedling establishment, and discuss the implications of this information for the past and present expansion of the woodlands. While seed development requires about two and one-half years in piñons, it is species-dependent in junipers and can take one, two or even three years. Substantial seed losses can occur during seed development due to developmental constraints, and before or after seed maturation as a result of insects, pathogens or animal predators. In piñon pines, the primary seed dispersers are scatter-hoarding birds (corvids) and rodents that harvest seeds from the trees or after seed fall and cache them in the soil. In contrast, most junipers appear to be dispersed primarily by frugivorous birds and mammals that ingest the seeds and defecate them onto the soil surface. We have recently documented that scatter-hoarding rodents also disperse juniper seeds. Disperser effectiveness, or the contribution a disperser makes to the future reproduction of a plant population, may vary among species of piñons and especially junipers. Piñon seeds are short-lived and exhibit little dormancy and they probably only germinate the spring following dispersal. Juniper seeds are long-lived and seed dispersal can occur over one or more years. Seed germination can be delayed for several years due to impermeable seed coats, embryo dormancy, or the presence of inhibitors. Seedling establishment of piñon pines is facilitated by nurse plants but, while junipers often establish beneath nurse plants, they are capable of establishing in open-environments. In the southwestern U.S. higher establishment of juniper occurs in open environments due to more favorable precipitation, and competition may be more important than facilitation in determining establishment. When considering the mechanisms involved in the past and present expansion of the woodlands, short-distance dispersal, local population growth, and long distance dispersal are all important. Different classes of dispersers, some of which appear to have coevolved with the tree species, appear to be responsible for local (short-distance) vs. long-distance dispersal in piñons and junipers. Because ecotones form the interface between the woodlands and adjacent communities, they can provide valuable information on both the seed dispersal and seedling establishment processes responsible for tree expansion. Disturbance regimes and, recently, the effects of humans on those regimes have major effects on the expansion and contraction of the woodlands. Before Anglo- American settlement, fires occurred as frequently as every 50-100 years throughout much of the woodlands. During this century, fire frequencies have been reduced due to the indirect effects of livestock grazing and the direct effects of removing Native Americans from the ecosystem and implementing active fire prevention programs. The result has been an increase in tree dominated successional stages at the expense of grass dominated stages. Various management techniques, including controlled burning and chaining, have been implemented to reduce tree dominance, but their effects depend largely on the life histories of the tree species and the disturbance characteristics. Several areas relating to the seed and seedling ecology of the piñon and juniper require additional research if we are to truly understand the dynamics of the woodlands. Click Here to Go to Back to Top
Pollen Dispersal Models in Quaternary Plant Ecology: Assumptions,
Parameters, and Prescriptions
Stephen T. Jackson and Mark E. Lyford
Department of Botany
Aven Nelson Building
University of Wyoming
Laramie WY 82071 USA
I. Abstract
II. Introduction
III. Sutton's Equations and Prentice's Model
IV. Atmospheric Parameters and Their Consequences
A. Atmospheric Stability
B. Atmospheric Conditions During Pollen Release
C. Gustiness and the Paradox of Pollen Liberation
D. Parameter Specification for Sutton's Equations
E. Pollen Dispersal in Unstable Atmospheric Conditions
V. Depositional Parameters and Their Consequences
A. Deposition Velocity, Sedimentation Velocity, and Particle Size
B. Experimental Estimates of Pollen Sedimentation Velocity
C. Comparison With Theoretical Estimates of Sedimentation Velocity
D. Consequences of Measurement Uncertainty in Sedimentation Velocity
E. Impaction, Wind Speed, and Deposition Velocity
F. Effects of Wind Speed and Impaction on Pollen Dispersal
VI. Prescriptions for Model Application and Parameter Specification
VII. Prescriptions for Further Research on Pollen Dispersal
A. Physics of Pollen Entrainment
B. Sedimentation and Impaction in Vegetative Canopy
C. Vegetative Canopies: Particle Sinks or Transfer Stations?
D. Sedimentation of Pollen Grains
E. Source-Height Effects
F. Pollen Dispersal: Gaussian Plumes or Puffs?
VIII. Summary
IX. Acknowledgments
X. Literature Cited
XI. Appendix I: Measured Estimates of Pollen Sedimentation Velocity
XII. Appendix II: Measured Estimates of Pollen Size, Density, Mass, and Volume
I. ABSTRACT
Models of atmospheric dispersal of anemophilous pollen are important tools in Quaternary plant ecology for determining
pollen-source areas and for applying distance-weightings to vegetation data in formal pollen-vegetation calibrations.
The most widely applied model is Prentice's model, which uses a modified form of Sutton's equation for atmospheric
diffusion to predict pollen-source areas from size of the depositional basin and a set of depositional parameters
(deposition velocity of the pollen grains and mean wind speed) and atmospheric parameters (turbulence parameter,
vertical diffusion coefficient). We review the physical theory underlying Sutton's equation and Prentice's model, explore
the effects of different values of the depositional and atmospheric parameters on model predictions, and provide
prescriptions for model application, parameter specification, and further research on pollen dispersal. Most applications of
the models to pollen dispersal have assumed neutral atmospheric conditions. We argue that most pollen dispersal takes
place in unstable atmospheric conditions, and prescribe appropriate values for the atmospheric parameters for unstable
conditions. Our simulations using these parameters indicate more widespread pollen dispersal from a source than under
neutral conditions. We review available data sets for sedimentation velocity of pollen grains, and compare the measured
estimates with sedimentation velocities predicted from Stokes' Law to assess validity of the data. Substantial variability
exists among data sets, but several are suitable for application to pollen-dispersal models. Finally, we discuss aspects of
release, dispersal, and deposition of anemophilous pollen that are in need of further theoretical and empirical study. Such
studies will contribute not only to Quaternary plant ecology but also to understanding of pollination biology, population
genetics, and functional morphology of pollen grains and pollen-bearing organs. Click Here to Go to Back to Top
ZUSAMMENFASSUNG
Modelle für die atmosphärische Verteilung windverbreiteten Pollens sind wichtige Werkzeuge der Quartär-
Pflanzenökologie zur Bestimmung von Polleneinzugsgebieten und um bei der mathematischen Kalibrierung des
Zusammenhangs zwischen Pollen und Vegetation die Gewichtung von Entfernungen auf Vegetationsdaten anzuwenden.
Das am häufigsten angewendente Modell ist das von Prentice, das eine angepaßte Form von Suttons Gleichung für
atmosphärische Diffusion benutzt um Polleneinzugsgebiete auf Grundlage der Größe des Ablagerungsbeckens und einer
Reihe von Ablagerungsparametern (Sinkgeschwindigkeit, vertikaler Diffusionskoeffizient) vorauszusagen. Wir besprechen
die physikalische Theorie, die hinter Suttons und Prentices Modell steht, untersuchen, welchen Einfluß
Ablagerungsparameter unterschiedler Größe sowie die atmosphärischen Parameter auf die Modellvorhersagen haben und
geben Empfehlungen für die Anwendung der Modelle, Spezifizierung der Parameter und weiterführende Forschung zur
Pollenverbreitung. Die meisten Anwendungen von Modellen zur Pollenausbreitung gehen von neutraler thermischer
Schichtung aus. Wir erörtern, daßein Großteil der Pollenablagerung unter unstabilen Schichtungsverhältnissen stattfindet
und beschreiben angemessene Werte für die atmosphärischen Parameter unter unstabilen Schichtungsverhältnissen.
Unsere Simulationen, die diese Parameter benutzen, deuten darauf hin, daß eine weitere Pollenausbreitung von der Quelle
aus stattfindet als bei neutraler Schichtung. Wir überprüfen verfügbare Datensätze zur Sinkgeschwindigkeit von
Pollenkörnern und vergleichen die gemessenen Werte mit den Fallgeschwindigkeiten, die von Stokes
Gesetz vorhergesagt werden, um die Richtigkeit der Daten zu beurteilen. Zwischen den Datensätzen bestehen
beträchtlichte Unterschiede, aber einige sind für die Anwendung auf Pollenausbreitungs-Modelle geignet. Scließlich
diskutieren wir die Aspekte der Freisetzung, Verbreitung und Ablagernug windverbreiteten Pollens, welche
weitergehender theoretischer und empirischer Untersuchung bedürfen. Solche Untersuchungen werden nicht nur zur
Quartär-Pflanzenökologie, sondern auch zum Verständnis von Bestäubungsbiologie, Populationsgenetik und funktioneller
Morphologie von Pollenkörnern und pollentragenden Organen beitragen. Click Here to Go to Back to Top
A Brief History of the Lysigenous Gland Hypothesis
Glenn W. Turner*
Section of Plant Biology
University of California
Davis, California 95616
* Present address: Institute of Biological Chemistry,
Washington State University, Pullman, Washington 99164-6340.
I. Abstract
II. Introduction
III. Origin of the Lysigenous Gland Hypothesis
IV. Early Objections to the Resorption Hypothesis
V. Reassertion of the Lysigenous Gland Hypothesis
VI. Additional Challenges to the Lysigenous Gland
Hypothesis
VII. The Possible Influence of Different Mounting Media
VIII. The Schizolysigeny Concept
IX. Recent History
X. Concluding Remarks
XI. Literature Cited
I. Abstract
This paper summarizes the early history of the lysigenous gland concept, traces
its evolution to recent times, and explores some possible causes of conflicting
reports of lysigeny and schizogeny. Secretory cavities and ducts are generally
thought to form either through the schizogenous separation of cells, or through
lysigeny (cell lysis). Gland lysigeny was first proposed by Karsten in 1857 who
believed that plant tissues represent solidifications of humoral fluids and that
plant secretions are formed by the resorption of previously solidified cells. The
lysigenous gland concept has modernized as our understanding of cytology has
improved, but it was established early, from Karsten's hypothesis, long before the
influence of artifacts of specimen preparation was appreciated. Different methods
of specimen preparation, including variations in the mounting media used to mount
freehand sections, may have caused some of the discrepancies between the findings
of lysigenists and schizogenists. Tschirch and Haberlandt promoted the
schizolysigeny concept, and believed that the conflicting reports resulted incomplete
observations of a developmental process that included both schizogenous separation
of cells, and cell lysis to form secretory cavities and ducts. Both lysigeny and
schizogeny have been reported in the recent literature, although most reports of
lysigeny have been opposed by conflicting observations of schizogeny, and lysigeny
may represent a false category of gland development caused by the misinterpretation
of artifacts. Click Here to Go to Back to Top
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Allen, A. 1977. Steps toward better scientific illustrations. Ed. 2. Allen Press, Lawrence,
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Alston, R. E. 1968. The genetics of phenolic compounds. Pages 171-204 in J. B. Harborne (ed.),
Biochemistry of phenolic compounds. Academic Press, New York.
CBE Style Manual Committee. 1983. CBE style manual: A guide for authors, editors, and
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Dahlgren, R. M. T., H. T. Clifford & F. F. Yeo. 1985. The families of monocotyledons:
structure, evolution, and taxonomy. Springer-Verlag, New York.
Funk, V. A. 1982. Systematics of Montanoa Cerv. (Compositae). Mem. New York Bot. Gard. 36:1-133.
_____& D. R. Brooks. 198 1. Advances in cladistics. The New York Botanical Garden, Bronx,
New York.
Gifford, E. M. & A. S. Foster. 1988. Morphology and evolution of vascular plants. Ed. 3.
W. H. Freeman, New York.
Takhtajan, A. 1980. Outline of the classification of flowering plants (Magnoliophyta). Bot.
Rev. 46:225-359.
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Chapman, W., V. A. Chapman, A.E. Bessette, A.R. Bessette, and D.R. Pens. 1998.
Wildflowers of New York In Color. ISBN: 0-8156-2746-7 (hardback), 0-8156-0470-X
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