Book Reviews: Ecology

Seeds: Ecology, Biogeography, and Evolution of Dormancy and Germination Baskin, Carol C., and Jerry M. Baskin, 1998. ISBN 0-12080260-0 (cloth US$99.95) 666 pp. Academic Press, 525 B Street, Suite 1900, San Diego CA 92101-4495. - If you are interested in seeds, their germination ecology, or evolution of seed plants, and do not already own this book, I encourage you to buy it for yourself and also order a copy for your library..... perhaps even before perusing this review! Carol and Jerry Baskin bring many years of seed germination experience with a wide array of species to what is an inspiring work. They interweave their own studies of numerous temperate North American species with those done by others world wide. To provide some idea of scope, individual chapters contain hundreds of references, with two chapters each having more than a thousand. Data for individual species are summarized in tables for particular dormancy types; also often included is information about stratification (warm or cold treatment that breaks dormancy), optimal temperatures for germination, and / or responses to light. Despite a qualifying statement in the Preface regarding possible omissions, virtually all pertinent studies of which I am aware are included; some may only be noted in a table, but anyone interested in the germination behavior of a particular species or family can follow the leads provided.

Just as the number of studies presented is extensive, so too is the number of species. Nearly 6400 are listed in the taxonomic index! These species provide a substantive base for the concluding discussion of biogeographic and evolutionary aspects of seed dormancy and germination.

For students just beginning germination studies, there is much to inform experimental designs. A chapter on methodology provides guidelines for undertaking ecologically meaningful studies, even of seeds about which nothing is yet known. Elsewhere, discussions of dormancy and germination attributes of particular species provide insights about handling seeds and carrying out studies; in addition, throughout the authors raise pertinent questions that might be addressed. Both empirical studies and models suggest varying approaches to achieving a primary aim of the methods chapter which is to encourage studies that achieve understanding germination in nature. Toward this end, laboratory studies may be supplemented with those conducted in the field, slathouse, non heated greenhouse, or transplant garden. Another outcome should be increased comparability between studies.

Where needed, background information is provided. There are short understandable explanations, for example, of the effect of light on phytochrome, as well as descriptions of both modern and paleoclimates, of vegetation types, and of embryo types. There are many interesting examples; among those I noted were: (1) The type of germination paper (e.g., Whatman No. 2 vs. Nos. 4 and 5 filter paper) can influence germination percentage. (2) The geographic site of origin of Triticum aestivum (red wheat) seeds accounted for differences in yield in the second (but not third) generation. . (3) Seeds of Setaria faberi from both 2,4 D treated and control plants required cold stratification for germination; however, after overwintering in the field, seeds from 2,4 D treated plants germinated to significantly higher percentages. (4) Seeds from montane plants of Penstemon eatonii have physiological dormancy and require cold stratification; seeds from low elevation warm desert plants have nondormant seeds. (5) Ipomoea pestigridis from India has nine seed forms that differ in size, weight, color, and dormancy and germination characteristics. (6) From the background information about parasites, I also learned that there are no parasitic monocots and that the Rafflesiaceae exist as endophytes within the tissues of the host and break out of the tissues when flowering occurs.

Much attention is given to dormancy types because they are used to compare seed characteristics of various vegetation zones and ultimately as the basis for evolution of dormancy / germination characteristics. These dormancy types are: (1) Physiological: seeds are generally permeable to water but either warm or cold treatment permits radicle emergence. (2) Morphological: the seed is unable to germinate due to the undifferentiated nature of an embryo that is only a mass of cells or to an underdeveloped radicle or cotyledon(s). (3) Morphophysiological: seeds have both underdeveloped embryos and physiological dormancy (the embryo must reach a critical size and the physiological dormancy has to be broken). (4) Physical: the seed coat is not permeable to water. (5) Physical and physiological (chemicals are present in the pericarp). (6) Mechanical (fruit / seed structures prevent germination). These dormancy types are those proposed by Nikolaeva (1977); numbers 5 and 6 are generally considered as subsets of physiological and physical dormancy. Dormancy types are related to embryo type, which in turn, are plant family characteristics. Thus, by knowing the family and its embryo type, certain suggestions regarding dormancy characteristics for a given species may be entertained.

Following a thorough discussion of dormancy types, seed ecology is related to the fate of seeds in the soil and in aerial seed banks (in serotinous cones and fruits), to the influence of seed banks on populations and communities, and to the genetic basis and variation in dormancy and germination characteristics. Many examples are provided, including, e.g., the effect of mineral nutrients, position on the mother plant, and temperature during seed production on germination responses.

Seed size is also affected by many environmental factors, including position on the plant, seed number, habitat, day length, and temperature. Although seed size has many potential effects on plant biology, including recruitment, there are species whose large seeds germinate to higher percentages than small ones, others (fewer in number) whose small seeds germinate better, and still others (still fewer in number) for which germination is independent of seed size. In addition, the geographical distribution of dormancy types is considered for tropical and subtropical zones and temperate and arctic zones. For each zone there is discussion and summary in numerous tables of the available information regarding the impact of biotic and abiotic factors on the germination of tree, shrub, vine, herbaceous, and weed species. Depending on zone, special factors involving seed ecology, such as seed predation, fire, allelopathy, myrmecochory, and vivipary, are highlighted.

Species with specialized life cycles and habitats are considered separately. Accordingly, parasites, saprophytes, orchids, carnivorous plants, aquatics, halophytes, and psammophytes (plants of sandy habitats) are discussed in light of their special requirements (e.g., the relationships between orchids and fungi, inundation and aquatic plants, and the depth of burial for psammophytes.

The final chapter, a major contribution of this book, examines seed dormancy in the context of biogeography and evolution of seed dormancy. It provides an important synthesis of embryo types, dormancy types, and how they relate to the evolution of dormancy. A relationship between paleoclimates and the evolution of plant families with their particular embryo and dormancy characteristics is discussed. Familial distribution of dormancy types across the phylogenetic tree of Takhtajan (1980), coupled with evolutionary origins of extant families, shows interesting trends. First appearance of extant angiosperm families with physiological and morphophysiological dormancy in the fossil record dates back to the Pliocene. Morphological and physical dormancy, which are more restricted, appeared much later in the fossil record. Also, in contrast to morphological and physical dormancy, nondormancy and physiological dormancy by family are widely distributed among the higher taxa of the phylogenetic tree. Unfortunately, there is little supporting evidence from the fossil embryo record for ideas presented about the origins and evolutionary relationships of the dormancy types. Embryo studies by paleobotanists could yield important supporting evidence.

The text is quite readable. There are very few typographical errors although a bothersome one occurs in the methodology chapter. (From careful reading, however, it would be obvious that the dark period often used for photoperiod studies is 12 hours long not 1). Oddly, all diacritical marks are missing from various non-English language citations. The book is well produced with the exception of a few figures, taken from other sources, where the illustrations are not as crisp as they might be, perhaps due to the poor quality of the originals.

The objectives, to provide people beginning seed germination studies with a comprehensive overview and active researchers with a sense of what is known and not known about seed biology, are fully accomplished. There were places where I would have liked a concluding "Therefore..." paragraph, but the text deserves the reader's own thought. As noted at the outset, I believe this book belongs on the desk of everyone interested in seed biology. We can each select defining books, like Sculthorpe's (1967) on aquatic plants or Harper's (1977) on population biology, that set the standard for many years to come. This on seed ecology and evolution, like those, will have "staying power", and fills an important niche, complementing other recent seed biology texts. We are indebted to the Baskins for their fine contribution, surely a labor of love, to the seed literature. - Mary A. Leck, Rider University, Lawrenceville NJ 08648

Literature Cited

The Ecology and Evolution of Clonal Plants de Kroon, Hans, and Jan van Groenendael, 1997. ISBN 90-73348-73-0(paperNLG120.00US$67.00) 456 pp. Backhuys Publishers, P.O. Box 321, 2300 AH Leiden, the Netherlands. - Both within and among chapters, this book is an impressive international collaboration. The book consists of 18 contributed papers by authors from 12 different countries. Two positive features that stood out to us are the following: First, the book is carefully organized to facilitate connections among different levels of questions (and among different contributed papers). The book moves from topics related to physiology and clonal integration to higher scales of populations, communities and ecosystems. Second, even in the initial chapters that cover mechanistic topics such as plant development and physiological integration of clones, authors strongly maintain both the ecological and evolutionary themes stated in the title the book. We were excited by all the opportunities presented to incorporate evolutionary questions into research on clonal plants.

In terms of what readers may gain from these papers, several benefits were apparent. Readers interested in broad ecological patterns associated with clonality will be most interested in the first chapter by Klimes and colleagues. This chapter tackles the difficult task of trying to assess the frequency of clonal plants in the flora of central Europe. Further, this chapter addresses the relationship between clonal traits and other factors (habitat, other characteristics of the species, etc.). We suspect this chapter will be cited in the introductions of many future papers on clonal plants. Subsequent chapters deal with specific areas of research within the clonal plant arena. Every chapter ends with suggestions for future research, and consequently, the book is a wealth of information and ideas for anyone developing projects on clonal plants. For readers looking for help with methods, the book includes a review of issues related to spatial modeling of plant populations and to the study of natural selection in situations where genets exist as multiple ramets. Those researchers interested in applied topics will find the last chapter by Pysek on plant invasions and clonality valuable.

We had a few minor complaints that are very biased by our own interests. Although the title of the book is "Ecology and Evolution of Clonal Plants", this book covers only clonal growth not clonal reproduction. The production, dispersal and establishment of clonal propagules are topics only briefly discussed. While we recognize that specialized clonal propagules are rare in most terrestrial vascular plants and are thus rarely studied, they are not uncommon in some aquatic vascular plants and, they are very common in bryophytes. We were pleased that bryophytes received attention in two chapters: one by van der Hoeven and During and another by Herben and Hara. However, after finishing the book, we felt that one suggestion for future research had been missed, and that is the opportunity to incorporate literature on bryophytes and seedless vascular plants into the strong vascular plant theory on clonal processes. More chapters could have included and referenced bryophyte and seedless plant literature since clonal processes are so important in many of these plants.

The chapters of this book are not unwieldy in length and the book is very readable. Again, the careful organization and the communication that appears to have occurred between authors makes it worthwhile to read the chapters in order, even from cover to cover. The book has a number of useful figures and tables and also contains a handy glossary and two indices (a taxonomic and subject).

Our overall assessment is that this is a terrific resource for anyone interested in clonal growth and that this book will be a jumping board for many future studies. - Mary Puterbaugh, Natural Sciences, University of Pittsburgh-Bradford, Bradford PA 16701 and Nicholas McLetchie, Morgan School of Biology, University of Kentucky, Lexington KY 40506-0225

Plant Invasions: Studies from North America and Europe. J. H. Brock. M. Wade, P. Pysek and D. Green. 1997. ISBN 90-73348-23-4 (paper US$52.75) 223 pp. Backhuys Publishers, P.O. Box 321, 2300 AH Leiden, The Netherlands. - Studies of invasions of non-indigenous plants and animals are in vogue, but given the magnitude of the problems created by invasive species it is about time. This book adds to the accumulating literature on invasive plants and is a compilation of papers developed from a workshop held at Arizona State University in 1995.

As the subtitle suggests the book is arranged into two sections one focusing on America and the other on Europe: each section has nine papers. These are prefaced by the excellent paper by Wade, who discusses the steps of exotic plant invasions, predicting which species will become invasive and how both of these knowledge bases can be used to develop an invasive plant surveillance system. Since the establishment phase is followed by a lag phase before a species becomes invasive, he concentrates on these two early periods for surveillance as an early warning system before a species becomes a big management problem. In the preface, Brock tells us the book focuses on species' characteristics that can be used to provide an early warning system for invasive plants. As Wade points out however, we cannot adequately predict which species characteristics will determine invasibility. To be more accurate, many of the papers identify habitats that may be more prone to invasion by exotics in general or by particular species, which is very helpful in exotic plant management. The editors leave the synthesis of the papers to the reader.

The book could have been organized by the particular approach taken by the authors. There are three kinds of papers (with some overlap across types): 1) literature reviews about problem species, 2) phytosociological or distribution/abundance papers and 3) experimental studies or those that address particular hypotheses. Species covered by the literature reviews include Lepidium latifolium (Young et al.), Schinus terebinthifolius (Jones and Doren), Fallopia japonica (Sieger),Arundodonax (Bell), andprunus serotina (Starfinger). The phytosociological studies document exotic species abundance in novel habitats (Brock and Farkus), along an urban-rural riparian gradient (Green and Baker), across riparian disturbance and soil moisture gradients (Stromberg et al.), and among particular areas or regions or habitats in space and time (Wade et al., Keil, Andersen, Pysek and Manddk, and Child and de Waal). These papers show how habitat preferences or distribution data can be used in predicting future distributions and developing control strategies.

My favorite papers were the experimental studies which reveals my bias; however, this is by no means an attempt to denigrate the other papers. Bastl et al. elegantly introduced exotic plant seed into two disturbed habitats across three ages to examine habitat invasibility. They found clear patterns in only one habitat and generally found establishment was highest in mid-successional habitats (10 year old). Blank and Young documented the spatial components of Lepidium latifolium invasion, quantified the ways this species modifies soil characteristics, and experimentally showed that soil nutrient status and plant density influences the its growth and competitive ability with Bromus tectorum. Tiley and Philp discuss the ecology and morphology of Heracleum mantegazzianum and present results of experiments to examine how cutting height, shade, and population density affect the flower and fruit production. Other papers were interesting for different reasons. Wade et al. documented the invasion of H. mantegazzianum and discussed control strategies in the context of human culture and health; this species grows in riverine systems where recreation is common and physical contact with this plant produces a severe phytophotodermic reaction. Through ground water monitoring Duncan showed how the removal of Tamarix ramosissma, a species that one study showed transpires 0.3 to 1 cm per day, restored the surface water to a desert lake. Pysek and Manddk in a repeated sample study showed a dramatic increase in exotic plants in Czech villages over a 15 year timespan.

The book is well produced and largely error free. I found three errors. On page 39, the sentence on the eighth line should read 'Average shrub height [not 'density'] was 1.8 m.' The second to last sentence in the second paragraph on page 41 should have 'of' between 'levels' and 'urbanization'. On page 196, Table 3, the word 'dicot' is misspelled. The semi-gloss paper is thin so occasionally a dark photo or figure shows through to the text on the other side. I found that cross citations among papers, where relevant, were not always present. Species binomials are given first with common names in parentheses which is a benefit for the intended international audience. There is good information here for ecologists, botanists, and managers on both sides of the Atlantic and the book is a must read for those actively studying invasive plants. For students, the book is a good introduction to breadth of invasive plant research and the literature. - Noel B. Pavlovic, Lake Michigan Ecological Research Station, Great Lakes Science Center, U.S.G.S, Biological Resources Division, Porter, Indiana.

Return to: | Table of Contents || Book Reviews Home Page || Next Review