Week 2: Gleason (1926) and Cannone et al. (2007) Blog Post
Kat Jordan
Foundations of Ecology Paper: The Individualistic Concept of Plant Association
Gleason, H. A. (1926). The Individualistic Concept of the Plant Association. In L. A. Real & J. H. Brown (Eds.), Foundations of Ecology: Classic Papers with Commentaries(pp. 98–117).
Companion Paper:Unexpected Impacts of Climate Change on Alpine Vegetation
Cannone, N., Sgorbati, S. and Guglielmin, M. (2007). Unexpected impacts of climate change on alpine vegetation.Frontiers in Ecology and the Environment, 5: 360-364. doi:10.1890/1540-9295(2007)5[360:UIOCCO]2.0.CO;2
Lead Paper and Author Background:
Gleason was a botanist who was a contemporary of Clements. He disagreed with Clements climax and organismic metaphor of plant communities. He argued that plant communities are much less uniform than previously thought and attempting to group plants into associations was a much too generalized approach. Instead, Gleason proposed plant communities should be studied as unique areas, some of which may be similar, but no two exactly the same. At the time, his “individualistic theory” was not taken seriously. Gleason ended up moving his area of focus into plant classification.
The lead author on the companion paper is Dr. Nicoletta Cannone. She is an associate professor at Insubria University and a researcher (in the past) at Ferrara University. Her research focuses on the affect of climate change on cold weather environments (high latitudes and high elevations).
Gleason paper:
· Summary of question:
Describe plant association by “…definition, fundamental nature, structure, and classification” (Gleason, 1926) by reevaluating what is known about them. Develop a better conclusion about plant communities to better the understanding of botany as a whole.
· Methods:
Gleason begins by briefly reviewing what has been done to describe plant communities, and the importance of attempting to detail plant associations. He proposes that, in the past, humans have made jumps in logic (i.e. “abstract extrapolations”) when trying to understand plant communities. To overcome this, Gleason suggests that the facts should be reevaluated.
· Summary of results (key ideas):
o Two similar areas of vegetation which look reasonably alike would potentially constitute a plant association. However, the degree of uniformity is not as exact as others in the past described. Though two areas may seem similar, no two areas will ever be exactly alike. What degree of difference is the key question? In other words, how much variation is generally permitted in a scientific context. This especially comes up since many studies had focused on northern latitude plant associations and not somewhere tropical were there are generally more species.
o Associations gradually blend into one another as you move through them. It is difficult to find the actual boundary. This makes it even more difficult to properly describe where one association begins and another ends.
o There are also “sporadic distributions” of plants within associations that are often disregarded because they do not fit within the context of what the association is supposed to be.
o There can be changes from year to year for vegetation depending on factors such as rainfall and temperature, where there may be increases or decreases in certain species annually.
o Succession means that plant communities will eventually be replaced over time. The duration of a plant community can be long or short depending on what factors are impacting it.
o It is difficult to come up with an average example of different types of associations because they do differ so much.
o There is a range of possibilities where different seeds can germinate. Does not have to necessarily be in one strict location. Most plants can withstand a range of different environments.
o Hard to predict change in an environment. Migrants (and succession) are always a possibility.
· Discussion/Interpretation (key ideas):
o Environments with similar climate and physiography may contain entirely different associations.
o The plants found in an area are dependent on the immigrants coming in and the changing of environmental conditions, which work independently.
o There are no reasons two areas on Earth will look exactly the same. Areas that look similar to each other are a matter of chance and this is subject to change.
o Plant associations, then, are when similar environments in the same region apply the same pressures to immigrants and residents, which can make areas look relatively the same. However, an exact, rigid definition of association is not possible since the similar environments can change rapidly and will never be exactly the same.
Cannone et al. (2007) paper
· Summary of question:
What has the change in vegetation been, if any, from the 1950s until the early 2000’s in the European Alps as the climate has become warmer.
· Methods:
The study focused on high elevation areas in the European Alps. A comparison of a phytosociological map from 1953 and 2003 was performed. Three measures (coverage, dynamics, and ecological series) were used to document vegetation changes (in area and elevation), and coverage was further divided into three categories (bare ground, discontinuous vegetation, and continuous vegetation). Dynamics were used to describe succession/ invasion of other plants from different altitudes. Ecological series were broken into seven habitat types. Precipitation and temperature records were also analyzed from two nearby stations and snow cover records were acquired from another local station from 1978 onwards.
· Results (key ideas):
o Climate conditions in the Alps changed between 1953 and 2003, with average air temperatures rising especially after the 1980s.
o Precipitation levels fluctuated but generally increased after the 1980s.
o Permafrost degradation coincided with change in temperature.
o Vegetation increased in coverage, with low altitude plants increasing and the displacement of shrublands at high altitudes.
· Discussion (key ideas):
o Expansion of different shrubs increased competition at alpine elevations.
o There was also an upwards migration of some alpine grasses.
o More precipitation and earlier snow melt could mean more flooding and debris flow. This could mean more bare ground and vegetation rejuvenation.
o Permafrost degradation could lead to more landslides and debris flow, affecting the way plant communities can appear.
o The study confirmed that vegetation at lower and high altitudes responds quickly and flexibly to changes in climate (even smalls changes such as an increase of 1-2°C).
My thoughts:
I chose the Cannone et al. (2007) paper because I felt it captured the idea Gleason was trying to get across. Environmental changes, in this case climate change, have transformed plant communities in the European Alps. As seen in Gleason’s paper, changes in environment (and in the migration of species) have caused alpine areas and high latitude areas (nival areas) to change in composition. The Cannone et al. (2007) paper did not mention anything about the Alps appearing visually different from the past. This is probably because of the subjectivity of this idea and because it may be hard for a human to observe a change in 50 years (i.e. a person may not remember what the Alps used to look like). Regardless, observable differences (in maps) can show how plant communities in the Alps are becoming different than they once were. If climate change has continued to the affect the Alps since this paper was published nearly ten years ago, then even more changes can be observed now.
If the plant associations in the Alps were labelled in the way Clements had done (as we read last week), I am not entirely sure how the new appearance of these plant communities would be discussed. I prefer Gleason’s method of talking about plant communities, though he never concluded on how to describe an association. As a paleontologist, I want to conclude that, in my mind, associations are easier to categorize when looking backwards. This is to say that in hindsight, when looking at the fossil record for example, it may be easier to give an association a label. In a dynamic present, it may be more challenging to properly categorize something, only for it to change again.
I found the Gleason paper to be a very interesting contrast to the Clements paper from last week. Many of the same issues in some of Clements's lines of thinking that we raised in our discussion were similarly raised by Gleason in his own paper from over ninety years ago. Gleason provides far less rigid definitions and classifications of the associations and communities he viewed compared to Clements who believed in a stricter idea of succession toward an ultimate climax point.
ReplyDeleteAs such, modern papers such as Cannone's fit closer to a Gleasonian model of succession and community structure. Modern ecologists address the highly variable conditions faced by communities that may be caused through climate change, other human influence, or simply via natural disruptions. Modern studies of the effect of climate change over time are interested in looking at this dynamic structure of communities, and fit a modern interpretation of Gleason's general concepts in his species-individualistic model.
- Elizabeth
Both authors discussed about environmental changes as a driving factor of plant community composition changes. I was trying to find a definition of “association” though out Gleason’s paper but there does not seem to be one. Through the context, I think the “association” means some sort of “stable” or “static” community composition. Indeed, this paper talked about heterogeneity and the author addressed that there was no typical association. The author believed that many factors would influence association in a given place, including chance, seed mobility, and the environment. However, Gleason spent endeavors to find the “static association” and overlooked community dynamics. Also, the influence of small-scale environment and interactions within a community were not addressed.
ReplyDeleteCannone et al. studied the effects of climate change on alpine plant communities. This paper, compared with Gleason’s paper, discussed a lot about the dynamic itself, along the changing environment. I think 2 of the findings in this paper are really interesting and fill the gaps of Gleason’s paper: 1. plant communities respond to climate change quickly even in some environment that looks inert; 2. even small degree of environmental changes in a small geographic scale can shift competition and species survival.
Gleason’s paper on the diversity of species and the dynamic changes within “associations” is a stark contrast to the communities in Clements’ paper that were classified by their unity and stability. Gleason embraced the idea that science is not a static body of knowledge and that scientific “ideas are subject to modification and change as additional facts accumulate,” and because of this viewpoint, he was critical of the science of his time period. He mentioned that other ecologists have theories that are “prone to surpass by far the extent warranted by observation,” which is one of the criticisms of Clements’ work that that we discussed last week. Clements provided speculation about scientific theories without much data-driven evidence to support his claims. Although Kat stated in her blog that Gleason’s theories “were not taken seriously,” at the time, the ideas presented in this paper seem to hold up to scrutiny in a much more favorable light when compared to Clements’ work.
ReplyDeleteThe Cannone paper is a nice complement to Gleason because it also has a contradictory spirit. Similar to how Gleason provided anecdotal evidence to contradict the scientific ideas of his time, Cannone’s “unexpected” results challenged the current understanding of the migration of alpine and nival species in response to climate change. Cannone’s results are an example of the “additional facts” that accumulate to change our ideas of how ecological communities are affected by climate change.
I really enjoyed reading Gleason’s paper. He did a great job of explaining the issues with discrete classifications of plant communities and the problems of scale when attempting to delimit communities in time or across space. Gleason identified how two processes, selection and dispersal, can be used to explain patterns. From a modern perspective, Gleason was describing two of the four processes that form a “logically complete set of process categories” that can be used to explain community composition and diversity (Vellend 2010).
ReplyDeletePerhaps this is because I am unfamiliar with plant community ecology, but I don’t think the Cannone et al. study convincingly demonstrated that the changes in alpine plant communities were driven by climate. They claim the observed increase in plant coverage and shift in communities towards later successional forms is driven by changes in precipitation and temperature. Why can’t some or all the observed changes in vegetation have been caused by “normal” successional changes in plant communities over time? Imagine that climate had remained stationary over the past 50 years, would they be surprised to find that plant coverage increased and that communities shifted towards later successional forms? Again, this could be my lack of knowledge about these systems, but I just don’t understand why this pattern couldn’t be explained by alternative explanations, e.g., the plant communities were not at equilibrium when measured 50 years ago, and are now approaching/at an equilibrium?
- David
Overall, I was very intrigued while reading the Gleason paper and found his approach very much in contrast to Clements’ need to categorize everything. The comment in the footnotes about ecologists (specifically, Pavillard in Europe) being generally skeptical of “the statistical method” in characterizing ecosystem-level vegetative communities stood out to me in that it is so different from how plant ecologists approach defining plant communities today. While observational studies, thorough data collection, and field experiments are still invaluable, we now frequently use these data to develop models that aim to quantify larger-scale dynamics (nutrient flow, carbon/water cycling, primary production, etc.) and predict future changes in community composition. The “abstract extrapolations of the ecologist’s mind” that Gleason alludes to in the introduction have largely been replaced by modeling and statistical inference, with the exception of studies that are exploratory and for which results require a fair amount of interpretation in terms of how the findings could hypothetically be applied/used to guide future work. I think his argument that vegetative communities are generally defined by their species composition/patterns of species immigration and environment, but that there are fine-scale gradients of species associations across a given environment that make it difficult to narrowly describe which species are truly characteristic, still applies to our thinking on the topic today. Gleason does acknowledge annual variations in climatic variables, and I think the “reactionary effects” of plants that he mentions are undoubtedly much more extreme and pronounced today, given how extreme moisture and temperature conditions have been from year to year in recent decades (and that these “climatic changes are [no longer] slow”).
ReplyDeleteI really enjoyed the structure and approach of the Cannone et al. paper. While their scope and framework for designing the study and the primary questions they hoped to address were largely driven by the need to quantify how alpine vegetative communities are likely to adapt (or not) in the context of human-driven climate change, many of the relationships they discuss follow the same principles as Gleason’s theory in the foundational paper. Though the approach the authors used to characterize the climate-plant growth/coverage dynamics was fairly simple, I think they still were able to capture the influence of many of the salient variables that drive changes in community structure within a given belt. The only thing I thought was lacking was more discussion on the potential positive/negative effects of shifts in distributions of the vegetational types (both coverage and dynamics). They provided a lot of numbers on how the communities have shifted over time and changes in relative abundance, but did not talk about the associated consequences (for other taxa), e.g., with increases in shrub coverage and decreases in grasslands at lower elevations, or sharp increases in bare ground at the highest elevation range.
While Clements argued that there is little to no change to plant community makeup once a climax state is reached, Gleason proposed that plant communities are dynamic and unique. I thought Cannone et al was an excellent companion for Gleason's paper, as the study in the alps provided evidence for Gleason's paper from a modern perspective. Although Cannone's paper showed that communities may not be as stable as Clements described, the paper did provide support for a key part of Clements' paper. He argued that humans can cause the stable climax communities which Clements described to become disturbed and altered, and the altered community structures described in the alps were linked to by Cannone et al to climate change, a human-driven phenomenon. However, I agree with David's comment that there is little evidence that the plant distribution changes in the alps were necessarily due to climate change as opposed to "natural" shifts over time. Regardless of the cause of the observed changes, the Cannone paper shows that Gleason is correct in his claims that plant communities are much less static than Clements described.
ReplyDeleteI found Gleason's much more enjoyable to read than Clements.I found his logic easier to follow. His lack of citations was also very interesting. He states that climax represents a stable state, but it is not permanent and may give way to new secession. This is in stark contrast to Clements, who argued that climax states were much more stable and permanent, and is more inline with how we view ecosystems today. One facet of Gleason's paper I found most insightful was the idea of how important immigrants are in determining which species are in a community. History has proven him right with the countless number of invasive species that exist today.
ReplyDeleteThe Cannone paper supports Gleason's well.They show how a what might be consider a climax state changes gradually throughout the decades due to a changing climate. They also support Gleason's individualist community idea by showing that different species within a community are responding differently.
-Miranda
Gleason's (1926) description of associations at first glance seems to more accurately describe reality than Clements' paper on climax because it takes into account some degree of variation as well as the dynamicism of plant communities. Though he makes a good point (and his association concept is more in line with current perspectives), I would argue that his definition of an association is too vague. He justifies this ambiguity by basically arguing that each plant will do what it wants irrespective of the broad terms and classifications we assign to each group. Again, I can see his point because a dynamic system by definition keeps changing and species have obvious differences which preceded the decision to classify them as such. However, a vague concept is of no practical use to anyone, so for me, these ideas really needed to be brought back to a more applicable conclusion (e.g., management implications, trophic cascades). Otherwise, why do we care? Maybe this is an artifact of the difference in culture and practices between current and past scientific papers, where a century ago ecologists could just write down their thoughts and impressions but now we are urged to make the applications of our research clear. Apart from those criticisms, I do think some of the ideas in this paper were necessary to bridge the gap between the climax concept and current community assembly theory. The paper made me curious to find another string of papers that lead to current practices.
ReplyDeleteCannone et al. (2007) applied the association concept to their work fairly successfully, so either I was overly critical of Gleason (1926) above or this concept has evolved to have more specific applications over time (my guess is the latter). I think the powerful computational tools we now have compared to Gleason's time makes it easier to incorporate more of that fine-scale variation and change that may have been more ambiguous to classify in the past. Cannone et al. (2007) exemplifies the need to revisit systems to investigate mechanisms for short- and long-term changes and the effects of those changes on the state of the system.
-Annie
The Gleason and Cannone papers are a fascinating compliment to each other and to Clements' paper. Both of this week's papers underline a central tension and a central difficulty in ecology: how do you decide what is pattern and what is noise in the context of a given question? Are the idiosyncrasies of systems evidence of fascinating underlying dynamics, or just stochastic processes obscuring a question of theoretical or applied importance? The answers to this question likely depend on the question, system, and even investigators in question, posing difficulties not only for advancing Ecology as a field, but also for knowing when and how much we have advanced.
ReplyDeleteAdditionally, as David pointed out, it will always be difficult to attribute causation in field-based observational studies. The nature of observational studies, even natural experiments as was featured in the Cannone study, often preclude controls and replication. It is therefore difficult to conclusively prove relationships, much less make reliable predictions based on observational inferences. This tension, between signal and noise, and observation and causation, drives one of my own major interests in developing models that can be used for ecological forecasting and prediction.
-Lyndsie