Portal de Periódicos da CAPES

Homage to Frederic E. Clements, Historian of Plant Succession Studies

2008; Ecological Society of America; Volume: 90; Issue: 1 Linguagem: Inglês

10.1890/0012-9623-90.1.43

2327-6096

Frank N. Egerton,

Botany, Ecology, and Taxonomy Studies

The study of plant succession has been a major focus for ecologists (McIntosh 1980, 1981, 1985, Holt et al. 1995, Cook et al. 2005). Frederic Edward Clements (1874–1945; Fig. 1, from Pool 1954:108) first summarized the history of the study of plant succession in a 24-page "General Historical Summary" in his huge monograph, Plant Succession 1916. In an earlier book, Research Methods in Ecology (1905:2–6, 1977), he had first sketched the history of ecology since Linnaeus, and his "Historical Summary" on studies of plant succession was the earliest attempted history of an aspect of ecology known to me. He also provided a historical summary in his Plant Indicators (1920; cited from Clements 1928:209–234). Therefore, it seems fitting to pay homage to Clements in this historical study. There is an extensive literature concerning the history of succession, and besides Clements' "Historical Summary," one can also consult two reprint collections published in 1977. Frank Golly compiled a volume, Ecological Succession, that encompasses animals as well as plants, with papers dated 1901 to 1973. With advice from Robert McIntosh, I compiled the other volume, Plant Ecology, 1897–1917, in which most papers are on plant succession. Only one paper appears in both volumes. There are also two previous articles on aspects of the history of succession studies (Spurr 1952, Drouin 1994). The earliest insights into plant succession came from studies of peat bogs (Fig. 2). These bogs (Fig. 3) interest modern plant ecologists, but in the 1500s and 1600s they seemed to be dreary (Fig. 4) obstacles to domesticating the land. John Leland (c. 1503–1552) was antiquary to Henry VIII, a position we would name historical geographer (Carley 2004). He traveled around England for six years and claimed to have visited "almost every bay, river, lake, mountain, valley, moor, heath, wood, city, castle, manor-house, monastery, and college in the land" (Lee 1921:893). His posthumous Itinerary of John Leland the Antiquary (nine volumes, 1710; edition 3, 1770) reported that farmers who dug peat commonly discovered buried tree trunks or roots, indicating that the vegetation changed over time. He reported two cases in which bogs had burst and flowed away, causing much damage. In one case, the landscape changed: "In the very toppe of Chate moore where the mosse was hyest and brake, is now a faire plaine valley, and a rill runneth in it, and peaces of small trees be founde in the bottom" (quoted in Gorham 1953:259). The earliest descriptions of Irish peat bogs come from Gerard Boate (born Gerrit Boot, 1604–1650), a Dutch physician who moved to London in 1630 and became physician to Charles I (Baigent 2004). The English colonized not just in America during the 1600s, but also in Ireland. During the Confederate War (1641), the Irish drove English landlords out of Ireland. Boate compiled Irelands Naturall History in 1645, without having been there (in 1649 he went with Oliver Cromwell's reconquest) as a guide for English imperialists and Dutch investors. (In 1983 another Dutchman, Matthijs Schouten, again appealed to his countrymen to buy Irish lands, this time to save three bogs [Foss and O'Connell 1997:194]). Boate's main source for the book was his brother Arnold Boate (1606–1653), also a physician, who lived in Ireland, 1636–1644, and who edited Gerard's text for posthumous publication in 1652 (Hinch 1928, Coughlan 1994, Boran 2004). The book was reliable on natural history (Prager 1949:52–53, Feehan and O'Donovan 1996:189), but receives low marks for objectivity toward the Irish (Barnard 1994, Coughlan 1994). Bogs were extensive enough to merit two chapters in Irelands Naturall History, and included the earliest known classification of bogs. Gerard Boate's Chapter 13, "Of the Heaths and Moores, or Bogs in Ireland," divided lands into three groups: boggy heaths, dry heaths, and wet bogs. Moory, or boggy heaths included red bogs with red soil and moss. Dry heaths occurred in the mountains, were grassy, and could be burned and turned into pasture. He discussed wet bogs (Fig. 5) in most detail and divided them into four classes: grassy, watery, muddy, and hassocky. His grassy bogs are now called blanket bogs (Gorham 1953:259–260). Chapter 14, "Originall of the Bogs in Ireland, and the manner of Draining them practiced there by the English inhabitants," explained that "very few of the Wet-bogs in Ireland are such by any naturall property, or primitive constitution, but through the superfluous moisture that in length of time hath been gathered therein." He thought some bogs accumulated "superfluous moisture" from springs, others from rainfall, and in both cases they lacked natural drainage. The discovery of trees buried in bogs by those who dug peat for fuel (Fig. 6) showed that bogs were not permanent. It blamed the existence of bogs on the unwillingness of the Irish to drain them. We now know that bogs were caused by glaciers having leveled hills and disrupted natural drainage patterns, and by a moist, cool climate. Even if drained, they often were unsuitable for agriculture unless fertilized (Feehan and O'Donovan 1996:39). Boate thought some kinds of bogs were unfit for drainage because of the difficulty of maintaining ditches, but grassy bogs were easily drained for pasture or crops. Clements began his historical survey with a substantial study by William King (1650–1729; Fig. 7 by John Faber, Jr. 1729), who "was a central figure in Irish intellectual life for four decades" (Connolly 2004). Although King wanted to turn bogs into productive land and discussed drainage, botanist Evil Gorham (1953:262) says King's "Of the Bogs and Loughs of Ireland" (King 1685) gave "a clear and definite statement of succession, beginning with the mineral soil, passing through grassy quaking bogs, and growing into turf bog." However, King believed that "the seed of this Bog-moss, when it falls on dry and parched ground begets the Heath" (1685:950). He observed (1685:950–951) that bogs are "generally higher than the land about them, and highest in the middle: the chief springs that cause them being commonly about the middle." Or a bog could develop where a tree fell across a slow stream. Whereas Boate had thought it impractical to drain red bogs, King thought it was practicable to drain them, with a deep surrounding trench (1685:955). In 1697 John Honohane reported to the Royal Society a dramatic change in a bog near Charleville, Limerick County, Ireland: it slid down a slope and covered a meadow, in some parts 16 feet deep. Heavy rains caused the slide. His report contained a diagram (Fig. 8) showing the direction in which it slid downhill, from south to north. This may be the earliest published diagram having ecological relevance. He could not have known that Leland had also reported two cases of bogs bursting and flowing away, since Honohane published before Leland's work appeared. These three authors—Boate, King, and Honohane—reported good general observations on bogs, without studying the species of bog plants. They knew that bogs arose when local moisture increased and trees on dry land were replaced by bog plants. Some European authors thought that peat bogs formed from decayed wood, and to refute this idea a Dutch physician, Johann Hartmann Degner (1687–1756), wrote a dissertation on peat (1729), in which he discussed plants that provided the substance of peat. Although his treatise was considered definitive for some 80 years, the idea that peat formed from decayed wood persisted. If one wishes to succeed in producing a forest, it is necessary to imitate nature, and to plant shrubs and bushes which can break the force of the wind, diminish that of frost, and moderate the inclemency of the seasons. These bushes are the shelter which guards the young trees, and protects them against heat and cold. An area more or less covered with broom or heath is a forest half made; it may be ten years in advance of a prepared area. The best shelter in wet soil is popular or aspen, and in dry soil Rhus, for the growth of oak. One need not fear that the sumac, aspen or popular can injure the oak or birch. After the latter have passed the first few years in the shade and shelter of the others, they quickly stretch up, and suppress all the surrounding plants. Buffon's rival, Carl Linnaeus (1707–1778), described plant succession in his most important ecological dissertation, Oeconomia naturae (1749, 1751). It was defended for a degree by Isaac J. Biberg. Clements seemed unaware of the scholarship showing that it was essentially by Linnaeus (Egerton 2007a:72) and cited Biberg as author. Since Clements (1916:10) cited only the Latin version, he may not have known Benjamin Stillingfleet's English version. Linnaeus (1775:78–80, 1977) described plant succession from bare rock with lichens through a series of plant stages that culminated in a forest, followed by the death and decay of trees and the use of the decaying wood by fungi and beetles to create a revolving cycle of nutrients. Stillingfleet translated Lichens crustacei (Linnaeus 1751:27) as "crustaceous liverworts," whereas Clements correctly translated it as "crustose lichens." Linnaeus also discussed bog plants in a dozen publications, providing many new details about bog species (Du Rietz 1957:60–68 [in English]). However, he seems not to have discussed bogs in relation to plant succession. James Anderson (1739–1808; Fig. 9 by Samuel Freeman, 1809), studied chemistry in order to improve agriculture, and he received an honorary L.L.D. degree from the University of Aberdeen for his services to agriculture (Mullett 1968, Sweet 1972:407–410, Mitchison 2004). In 1794, he separated "moss" into quick, dead, and growing. His "quick moss" was peat; his "dead moss," the remains of plants, often 6–24 inches deep above quick moss; and his "growing moss," the live plants on top. Peat was usually dug, leaving potholes that filled with water, and eventually with peat. This provided an experimental situation for observing succession (Anderson 1794:40–42). potamogeton natans, is among the first that appears as springing from the bottom: this rises from the depth of two or three feet. On the surface, the duck weed, lemna, soon spreads over it, and forms a green scum; sometimes the ranunculus aquaticus appears, and various other aquatic plants…according as the seeds are near or at a distance. …when the broadleaves of the potamogeton, and the fibrous roots of the duck weed, are joined so as to form a kind of matting over the surface, the light moss earth is then supported by them, so as to form in time a kind of close surface, which often gives rise to some kinds of aquatic grasses, whose matted roots form a kind of hobling quag. While yet moist, there frequently grow out round the edges of these pots, large tufts of…sphagnum palustre… These observations seem to show Anderson as a modern scientific thinker, but he went on to argue (1794:49) that "peat moss, as we find it in the natural state is, of itself, a vegetable production, not a congeries of dead plants preserved by some mystical influence, as has been generally supposed, but actually alive…" That is, the peat itself is a giant plant. Anderson argued that it looked as much like a plant as do some fungi and sponges (both of which he considered to be plants). Because tree trunks and stumps were found in most peat bogs, he believed there was a causal relationship. He rejected the idea that decayed wood gave rise to peat by affecting the water. The relationship he accepted was that decaying wood was a nutritive substance for the seed of peat. Jean Deluc (1727–1817; Fig. 10), a Genevan living in London, was a very productive writer on geology, meteorology, and physics (Beckinsale 1971, Carozzi 1987:207–219). He discussed peat formation in two of his works from the early 1800s. Clements (1916:10) judged him to be "the keenest and most indefatigable of early students of peat-bogs… He was probably the first to…use… the term succession, and certainly the first to use it with full recognition of its developmental significance." Deluc used the term "succession" in relation to the invasion of vegetation into shallow lakes until the lakes were filled in with decayed vegetation (Rennie 1807–1810, I:137–141), and he reduced this succession to six stages of vegetation which Clements quoted in abbreviated form. Gorham (1953:266) summarized these six stages from Deluc's Geological Travels 1810. Robert Rennie's Essays on the Natural History and Origin of Peat Moss (two volumes, 1807–1810) publicized the ideas of Degner, Anderson, and Deluc and "gave the first comprehensive and detailed account of peat-bogs"(Clements 1916:12). The French poet and historian Adolphe Jules Dureau de la Malle (1777–1857) had an estate in Bocage Percheron, where he managed crops, meadows, and woodlands (Drouin 1994:149–150). He got the idea of plant succession not from Buffon, but from an English author, Arthur Young, writing on crop rotation. However, Dureau de la Malle reported on succession (1825; reprinted in Acot 1998, I:116–131) from his own experiences of harvesting timber and planting crops during 30 years. Clements (1916:13–14) summarized his article and translated this conclusion: The alternance or alternative succession in the reproduction of plants, especially when one forces them to live in societies, is a general law of nature, a condition essential to their conservation and development. This law applies equally to trees, shrubs, and undershrubs, controls the vegetation of social plants, of artificial and natural prairies, of annual, biennial, or perennial species living socially or even isolated. The preeminent British geologist, Charles Lyell (1797–1875), was interested in the role of plants and animals in soil formation. His Principles of Geology (three volumes, 1830–1833) organized the science from the uniformitarian perspective (Wilson 1972, 1973, Oldroyd 2000, Rudwick 2004). He did not contribute any new data, but he drew upon Rennie's Natural History and Origin of Peat Moss and other works to provide a clear synthesis of the progress that had been made in understanding bogs and peat formation (Lyell 1830–1833, II:209–218). The next author whose discussion of plant succession seems notable was Japetus Steenstrup (1813–1897; Fig. 11), Denmark's greatest zoologist of the 1800s (Spärck 1932, Müller 1976a). He achieved fame for two scientific studies published in 1842. One earned him a professorship and lasting fame, on the alternation of generation among some invertebrates. The other study was of two forest bogs (moors) in northern Zeeland, The Netherlands, which he compared to several bogs in Denmark. Clements (1916:14–16) gave a lengthy summary of Steenstrup's bog study and reproduced diagrams (Fig. 12; "cosere" is Clements' term, meaning "a series of successions in the same spot") of vertical sections from the two Zeeland bogs (Vidnesdam and Lillemose). There are no known diagrams of ecological significance between Honohan's in 1697 and Steenstrup's two in 1842. The four forest vegetations, viz, aspen, pine, oak, and alder, found above each other in Vidnesdam and Lillemose, occur in all the forest moors of north Sjelland, and other evidence points to their former occurrence throughout Denmark. These four forests not only succeeded each other in the moors, but everything points to a synchronous succession on the uplands, so that one may speak of a pine period, for example, for the whole country. The final alder forest of the moor was succeeded by the beech forest which is now the dominant one. However, no trace of the beech has been found in the moors. Thus there seems no doubt that one vegetation succeeded another in such a way that the latter grew on the ruins of the former, and that the replacement of one by the other was the result of a slow natural cycle. In this cycle one organization develops and then gradually calls forth conditions which cause its disappearance and hasten the development of a new organization. Steenstrup founded paleoecology. Let us continue for a moment with other paleoecological studies mentioned by Clements. Steenstrup wrote before the theory of successive ice ages was established (Bolles 1999), but later studies came after it was established. The Swedish botanist Rutger Sernander (1866–1944) published two papers in German in 1891 and 1894 in which he traced the changing vegetation of peat bogs over time and related these changes to past ice ages. These two 1891 diagrams (Fig. 13; Clements 1916:381) owed nothing to Steenstrup. They were on different pages, but Clements ran them together to save space. They show spatial succession and suggest temporal succession. Sernander's 1894 paper was on Gotland, an island on the southeast coast. There is a tradition of placing the oldest strata at the bottom of a geological diagram, yet here (Fig. 14; Clements 1916:385) Sernander placed the oldest strata at the top and recent ones at the bottom. However, in the accompanying geological time chart the oldest period is at the bottom and recent at the top. Clements indicated that Sernander's diagram represents a "hydrosere," which is one of the many ecological terms that Clements coined. He provided a glossary of terms in his Research Methods in Ecology (1905:314–323, 1977)—borrowing some from Warming—but when he published Plant Succession 1916 he had coined more terms without providing a new glossary, though another one appeared posthumously (Clements 1949:279–289). Ecologists accepted some of his terms, but found others unnecessary. The English botanist Francis Lewis (1875–1955) studied peat bogs in Scottish highlands and on the Shetland Islands (1905–1911). In this diagram (Fig. 15; Lewis 1905) Lewis provided several kinds of information. It shows five different geologic profiles at different elevations, though in a geographic order that does not reflect elevation: the Merrick and Kells Mosses profile was at 800–1000 feet elevation, the Tweedsmier Mosses profile was at 1200 feet, and so on. Lewis did not merely name different strata; he also provided visual indications, including symbols for sphagnum peat, scirpus, and a scirpus and sphagnum mix. In 1905, Marie Stopes (1880–1958; Fig. 16) became the youngest doctor of science first lecturer in paleo-botany in Britain (Hall 1977:56, 2004:929). In 1910, she published in Ancient Plants a chart (Fig. 17) on the long-term evolution and succession of plants in relation to climatic changes. The oldest strata are at the left and most recent at the right. In 1915, Stopes began a second career, and achieved fame as a crusader for birth control, though she continued to study paleo-botany until 1920. After this paleo-ecological diversion, let's return to a chronological survey. Henry David Thoreau (1817–1862; Fig. 18, Daguerreotype, 1856) had a broad interest in subjects now called ecological (Egerton and Walls 1997). In the 1850s he began a large undertaking, "Notes on Fruits and Seeds," that remained unfinished at his death. However, a major portion of it, on the dispersal of seeds, is recently published (Thoreau 1993). A spin-off from it was a talk which he read in 1860 to the Middlesex Agricultural Society on "The Succession of Forest Trees," which he later published in that society's Transactions and also in a New York newspaper (Thoreau 1980). Clements never discovered this essay because he only searched scientific literature. Thoreau explained that when pine trees were logged, oak trees replaced them, and when oak trees were logged, pines replaced them. However, he explained, this only happened when the alternate forest was close enough to the logged forest to provide seed. He said that pines did not replace cut pines because oak seedlings were already growing there, and that pine seedlings did not grow in shade. Squirrels planted acorns in pine forests and never recovered as many as they had buried for winter food. Pine seeds annually blew into oak forests, and when oaks were cut, the seedlings flourished in the sunlight. Thoreau also observed that cherry trees grow in isolation over a wide area because their seeds are dispersed by birds that eat cherries and later expel the seeds in their droppings. Clements (1916:22) praised a paper that Finnish botanist Ragnar Hult (1857–1899; Fig. 19, Collander 1965:facing 80) published in 1885: "To Hult belongs the great credit of being the first to fully recognize the fundamental importance of development in vegetation, and to make a systematic study of a region upon this basis." The translated title of Hult's paper is "The Vegetation of Blekinge: A Contribution towards the Developmental History of Plant Communities." Clements thought that Hult's study of the vegetation of Blekinge, Finland was a "classic study." Hult did not use diagrams and Clements did not draw any to represent his verbal account. Hult concluded that there were seven different climax formations for different environments. Clements, who usually did not editorialize about papers he summarized, did comment in this case that "it seems obvious that the beech forest is the only real climatic climax" for the area (Clements 1916:23). Swedish botanist Ernst Hemmendorf (born 1866) in 1897 published a study on the vegetational succession of Oland, another large island east of mainland Sweden. Hemmendorf used this bottom-up diagram (Fig. 20; "hydrosere" is Clements' term) to indicate succession of species, which is otherwise similar to Sernander's chart for 1894. The Danish botanist Johannes Warming (1841–1924) in 1891 "was the first to give a consistent account of succession on sand-dunes"(Clements 1916:23), and in 1895 he published Plantesamfund, the first textbook on plant ecology (Müller 1976b, Coleman 1986). It had a brief discussion on plant succession (Warming 1909:358–365, 1977) that exerted a strong influence on the first generation of trained plant ecologists. Professor of Botany at the University of Chicago John Merle Coulter (1851–1928) had a graduate student, Henry Cowles (1869–1939; Fig. 21, Adams and Fuller 1940:39), write a synopsis of the German edition (1896) so that Coulter could review it for Botanical Gazette 1896. Both professor and student were impressed with Warming's work (Cassidy 2008:28–33), which led Cowles to write his doctoral dissertation on "The Ecological Relations of the Vegetation on the Sand Dunes of Lake Michigan" (1899). The Indiana dunes Cowles studied ranged as high as 118 feet above lake level, and they were constantly changing under the influence of wind, rain, and vegetation. Thus, he studied changing vegetation in a changing topography. He documented his findings with photographs, not diagrams. He followed up on that study with two others published in 1901—"The Plant Societies of Chicago and Vicinity" and "The Influence of Underlying Rocks on the Character of the Vegetation"—and finally interpreted those three studies in "The Causes of Vegetational Cycles" in 1912 (all four papers reprinted in Cassidy 2008:100–240). In the last paper he identified four American climatic formations (in Cassidy 2008:221) In the eastern United States, the final formation is a mesophytic deciduous forest; farther to the north and in the Pacific states, the final formation is a coniferous forest; in the great belt from Texas to Saskatchewan, the final formation is a prairie; and in the arid southwest, it is a desert. In each area, "the ultimate plant formation is the most mesophytic which the climate is able to support." Cowles' four papers were an important contribution to the establishment of plant ecology in America, and additionally, he was an influential educator of other plant ecologists at the University of Chicago. In 1903 Canadian botanist William Francis Ganong (1864–1941; Fig. 22) published a lengthy ecological study, "The Vegetation of the Bay of Fundy Salt and Diked Marshes." For 38 years he was Professor of Botany at Smith College in Massachusetts and returned to St. John, New Brunswick, every summer to conduct research (Bell and Whiteford 1979, Cittadino 1997b). He studied marshes and bogs at the north end of Cumberland Basin, along the boundary between (Fig. 23) Nova Scotia and New Brunswick. The Bay of Fundy has the greatest tidal fluctuation in the world—over 40 feet in some places (Zahl 1957). Ganong discussed spatial succession, but indicated the same pattern applied over time as very moist environments became progressively drier. This (Fig. 24a) is his longitudinal section of a typical marsh at the mouth of a river, from the basin at the left, to a saltwater marsh, to a floating freshwater bog, to a solid raised bog. This (Fig. 24b) is an aerial view of the same, and (Fig. 25a) this is a cross-section of the previous view. This diagram (Fig. 25b) shows the principal associations of the marsh land in relation to one another, and this one (Fig. 25c) shows the same associations with indication of the species within each association, and their tolerance of water and salt. Danish botanist Helgi Jonsson, in 1905, studied succession on a laval field in Iceland. Clements' caption of his version of Jonsson's diagram (Fig. 26) shows another Clementsian term, "lithosere." This photo which I found of succession from a lava field in Iceland (Fig. 27; volcanic eruption was 1973; photos, Grove, May 1977:691, 701) does not illustrate the succession that Jonsson indicated. One can either conclude that the pattern of succession changed in the 72 years between publication of his diagram and publication of the photo, or conclude that he diagrammed the predominant pattern of succession and that there are isolated exceptions. Henry Gleason (1882–1975; Fig. 28a) was from Illinois and developed an interest in botany in high school (Nicolson 1990:95). He attended the University of Illinois, where he studied under the animal ecologist Stephen Forbes (McIntosh 1975). He was also strongly influenced by the published work of Cowles. Clements cited six of Gleason's papers in Plant Succession and reproduced this diagram (Fig. 28b) from Gleason's "Botanical Survey of the Illinois River Valley Sand Region"(1907), in which Gleason hypothesized two climax possibilities in an upland forest and one in a swamp. Clements labeled it a "psammosere," meaning "originating on sand." After Clements published Plant Succession 1916, Gleason became a critic of Clements' theory of a definite climatic climax for every region. William Cooper (1884–1978; Fig. 29), from Detroit, was one of Cowles' students. In 1908 he published a study on plant succession at Long's Peak (Fig. 30, photo, FNE, August 1959), now in Rocky Mountain National Park (established 1915). Cooper found (Fig. 31) two patterns of succession on exposed slopes and two other patterns within canyons. His diagrams progress from top down. In 1912–1913 he traced succession at Isle Royale (Fig. 32a), now also a National Park (established 1931). His studies there were along shore at Rock Harbor (Fig. 32b, S. Stefanoff, National Geographic Society) or on islands in Rock Harbor (Fig. 33; Richard Frear). His 1912 paper is on moss succession. He identified 90 species and provided two succession diagrams of original design. In Fig. 34a, he traced succession of 23 species in three different environments that all led to a climax forest with moss ground cover. In Fig. 34b, he traced succession of 23 species also, though there were a few different from the previous 23 species. Succession is from sedge mat to bog to climax forest. This vegetation map of Raspberry Island (Fig. 35a) is in his 1913 paper, though it is equally relevant for his 1912 paper. This section diagram for the bog on Raspberry Island (Fig. 35b) shows spatial succession but is also relevant to temporal succession. Cooper had two diagrams on the species composition of the climax forest, Fig. 36a showing frequency and size of species and Fig. 36b showing frequency and age composition of each species. Cooper's last diagram of forest succession on Isle Royale (Fig. 37) is a bottom-up one, faithfully reproduced here by Clements (1905:209) in type easier to read than in Cooper's original. Frank Gates (1887–1955) was from Illinois. In "The vegetation of the beach area in northeast Illinois and southeast Wisconsin" (1912) he provided this faint and very complex top-down diagram (Fig. 38) that Clements split into two diagrams, labeled respectively "xerosere" (Fig. 39) and "hydrosere" (Fig. 40), meaning succession from a dry and from a wet environment, both leading to climatic climax forests. Clements' two diagrams are slightly simplified from Gates' original diagram. Edgar Transeau (1875–1960; Fig. 41) was from Pennsylvania and studied under Cowles (Sears 1960). In 1913 he published a study of plant succession at Cold Spring Harbor, Long Island (Fig. 42). His diagram (Fig. 43) represents a study of oceanic beach succession that Clements labeled "halosere," meaning saltwater succession. In 1915 Transeau went to Ohio State University, where he remained. Although Clements included many of the diagrams I have reproduced here in Plant Succession, only one of the diagrams he reproduced was his own (Fig. 44; Clements 1916:376), showing changes caused by the waxing and waning of glaciers. Accompanying it is a map of North American glaciation, which he borrowed from another paper by Transeau. In a textbook which Clements coauthored with animal ecologist Victor Shelford (1877–1968), Bio-ecology (1939:230), there is only one diagram on succession (Fig. 45), which resembles none of those in his 1916 book. It is neither a top-down nor a bottom-up diagram, but shows five different communities of plants and animals that converged over time to form a beech–maple red-backed salamander climax formation. What did Clements contribute to the advancement of understanding succession beyond synthesis of data from over two centuries? He used that data to support a theory of diverse successions toward a single climatic climax for vast regions, and Plant Succession became a paradigm for subsequent studies, despite criticisms from Gleason and others (Tansley 1946, Sears 1973, Worster 1977, Tobey 1981, Cittadino 1997a, Hagen 1999). His theory of succession has not survived, but it stimulated many investigations. His historical research was not controversial and was a positive contribution. If we compare this survey on the history of plant succession studies with my previous one on the history of studies on food chains and webs, one sees that the use of diagrams to illustrate plant succession began two decades before they were used for food chains and webs. However, once diagrams were used for food chains and webs, they became steadily more sophisticated as more and more information was represented in the diagrams. There was less innovation in the use of successional diagrams than in food chains and webs, and successional diagrams mostly just showed the sequence of species replacements. When there was innovation in design of diagrams, they were usually not adopted by later plant ecologists. This is an revised version of a talk given at the ESA Annual Meeting in August 2008 in Milwaukee, Wisconsin. I thank for their assistance Professors Michael O'Connell (for Figs. 2–6, and 8) and Michael Mitchell, Department of Botany, National University of Ireland, Galway, and Professor Emeritus Robert P. McIntosh, Department of Biology, University of Notre Dame, Notre Dame, Indiana (now in Florida).