Tag Archives: Gleason

Community Development and Persistence in a Low Rocky Intertidal Zone. Jane Lubchenco and Bruce Menge (1978)

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Though I had to read through Community Development in a Low Rocky Intertidal Zone, in part or in full, several times before I feel I came to approach understanding, I feel the central idea is one of the more useful ones I’ve yet to read about for Ecological Thought and Practice. In the essay’s introduction the authors state that while communities have several characteristics, it is a mistake to study them as separate phenomena when in reality they are interconnected. In my notes, I wrote the following in order to clarify for myself what I was reading about: “Succession depends on competition (Connell) but also predation (Paine), dispersal rates and reproductive output (Gleason), life histories and persistence (Clements).

I think that due to their more holistic approach Lubchenco and Menge were able to add to ecological thought of the day by confirming and documenting the interactions among the ideas that their predecessors had proven. Though their results stated that “the role of consumers in determining the pattern followed during community development, or succession, seemed of overriding importance” which primarily confirms Paine’s 1966 essay, but predation, they found was largely inversely proportional to wave energy. They also documented, through denudation of patched of the rocks, the importance of dispersal and growth rates in determining which species became dominant, but because their study took place over several years, they were able to show the persistence of the communities and how quickly those patches returned to the state at which they had been before the experiment. This persistence supports Clements theory of a tendency toward climactic climax.

Today in class we were asked whether or not Connell and Paine’s studies contradicted one another, here Lubchenco and Menge showed that at least in some communities, the two ideas are both valid. I thought the reading was helpful in understanding other ideas we’ve already covered in class. The use of so many variables and controls including not only the exclusion of predators but the enclosure of predators were useful in illuminating the authors’ points.

The Individualistic Concept of the Plant Association. Henry Gleason (1926)

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Throughout The Individualistic Concept of the Plant Association, Gleason makes several arguments as to what the particular issues are with a term as broad as “association”. The essay states that previous descriptions of plant associations are mistaken due to their attempts to fit within existing frameworks which were developed when less information was available, and that, instead, as new information becomes available, new frameworks should be developed. Due to the use of what Gleason might have called antiquated frameworks ecologists were making undue reaches as to the conclusions implied by their research. Gleason suggests a new model based upon the individual plant.

A plant association is defined by Gleason as “an area of vegetation, having a measurable extent, in which each of which there is a high degree of uniformity throughout, so that any two small portions of one of them look reasonably alike.” One of the main issues with this definition is that there may be a continuous stretch of grassland from Illinois to Nebraska, but the easternmost and westernmost portions have vast differences. Is it to be considered one association due to the continuous stretch of grassland, or two associations due to the multitude of smaller differences in species? If it is to be considered two associations, where should that “measurable extent” extend to if each square mile is almost indistinguishable from the next and it is only at great distances that a difference can be quantified? For another example, Gleason speaks of woodlands. Without human interaction, a woodland’s advance or retreat into or from a particular grassland would be so slow as to make it impossible to define clearly a time-boundary on when the association began or ended in a particular locale. Additionally, Gleason states, that, particularly in growth after a fire, an association may be so brief that there is never a period of equilibrium. Gleason then calls an association effectively a coincidence.

To back up this claim, Gleason explains, in simple terms, how plant life comes to be in an area; “if I viable seed migrates to a suitable environment, it germinates.” No matter how far it has traveled, whether on the wind, in an animal’s digestive system or on its fur, by stream, or any other manner, if a seed comes to rest someplace that can provide the right amount of sun, nutrients, and water, it will grow. The majority of seeds land relatively nearby the parent plant, and fewer and fewer do in concentric rings traveling outward from that plant. Thereby, Gleason contends, every plant germinates wherever it is able and grows in proximity to other vegetation with similar environmental needs. Plant associations as popularly defined by ecologists of the time were an attempt at ascribing monolithic order to a system containing billions and billions of free agents in the form of each individual plant attempting to grow and spread.

My personal thoughts on this writing are that it was an interesting idea and helped me to understand not only Gleason’s ideas but also other ecologists’ definition of a plant association. I largely agree with Gleason’s concept, however understand the utility of grouping vegetation into associations for the sake of study. Aside from all that, I thought Gleason’s clarity of voice made reading this essay easy and enjoyable.