Article: Canham et al. Windthrow…

** see below for some more tips on how to critique an article, using this one as an example

When you read a journal article (or write a lab report), you should be able to find the following information.

1.            What was the problem the authors addressed?

Relationship of storm severity and differential response of tree species had not been previously quantified.

Why is it important?

Knowing which trees withstand windthrow can help predict future forest development after storms, frequency and severity of storms could be changing with climate change.

2.     What are the objectives or hypotheses?

Develop a NEW IMPROVED method for distinguishing the effects of storm severity and species susceptibility, depending on the size of a tree.

Shade tolerant species should invest more in wood strength.

2.            What did the authors do, and where (methods)?

They measured windthrow in 43 plots in the Adirondacks, second growth and old growth.  They had a variety of degrees of disturbance.

4.            What did the authors find out (results)?

Intermediate sized trees: black cherry and red spruce showed highest rates of windthrow; yellow birch and sugar maple were low

Small trees: beech hemlock and sugar maple (shade tolerant trees) were less susceptible.  CONSISTENT WITH HYPOTHESIS

Big trees: Beech (very shade tolerant) was likely to break, maybe due to beech bark disease.  NOT CONSISTENT WITH HYPOTHESIS

Species composition affects amount of windthrow for same storm severity

5.            What are the conclusions?  Do they answer the original question?

Sure.

When you critique a journal article (which you will do later this semester), you will also address questions such as the following.

6.   What background information or ecological understanding is needed
       to understand the research?

Need to explain the equations that they use.

Disturbance, classification of wind disturbances, severity.

Shade tolerance, life history characteristics.

Previous methods, previous research results (suggesting relationship of shade tolerance to disturbance)

7.  What are the strengths of the study?  Do you have suggestions for
      improvement?

The problem is important, and the study design is broad (old-growth and secondary forest)  They provide a new method.  Conifers weren’t important in this study system.

The time at which measurements were taken could affect the results.

8.     Are the conclusions supported by the results?

Yes, there was a relationship between tree species and susceptibility.  They were able to address storm severity.

How far could the conclusions be extrapolated?

They only learned about the species that they studied.  Making a generalization about shade tolerance class means that hypotheses could be posed in other systems.

9.     What new research could be stimulated by the results of this study?

Apply this approach in other systems.

The difference between large and small stems could be further explored.  For example, is the difference due to dimensions or also to the material properties of the wood.

The time of year at which the storm occurred: compare lots of sites with storms at different times.

How long does it take for a forest to become wind-firm?  Simulation modeling might be one way to address this.

 

Critique of a journal article

 

Background

1.      Include background material beyond that in Intro of paper (full credit for papers not cited in your paper). 

2.      To describe this paper include info on: wind disturbance regimes in NE (known rates of severe or intermediate storms); other known work on windthrow in this region, or species composition in areas disturbed by wind, or other work done on the same research site.

3.      For those studying animals, tell us about the animal (habitat, etc).  Describe the ecosystem it is found in. Pictures help.

4.      End with why research is important (usually stated in their Intro):  understanding freq and susc of species to windthrow under differing severities could be important for modelling the change in forest composition under future climate conditions.

 

 

Strengths of presentation

1.      Intro- placed their problem in context of current knowledge ; makes it easier to understand why their study is important

2.      Methods- for those interested in statistics, they provide a thorough description of what they did to calculate MLE; this makes their methods repeatable

3.      Results- despite the difficult math, they describe the results clearly, relating it to species characteristics; this makes paper accessible to non-stats people

 

 

Suggestions for improved presentation

1.      Figure 3: hard to tell species apart by symbols; use more contrasting symbols

2.      Results: 2nd paragraph of Old vs young was confusing and seemed contradictory. They explained why windthrow RATE was higher in old stands, but they should also explain why SUSCEPTIBILITY was lower

 

 

Strengths of experimental design (why did authors choose this design?)

1.      Took a transect perpendicular to wind path; this is important because wind (and thus windthrow) probably decreases somewhat as it moves through the forest (parallel)

2.      They included a wide range of topographies (most likely to account for any variation associated with this feature)

3.      20 plots in both old and young stands seems like an ample sampling scheme

 

 

Suggestions for improved experimental design (or describe an alternate design?)

1.      Statistics- they say their predicted values shows an “excellent” fit to observed data, but they should use a goodness of fit test (chi-sq) to actually prove that their model  is accurate.

2.      Improvements to design (from conclusions after the study)- a) since species affects their storm severity index, they really need to find plots with similar species compositions (or put various compositions into different categories and evaluate separately), b) they conclude that height/diameter ratios are probably more important to susceptibility than diameter alone, so height info would have been useful

 

 

Are the conclusions supported by the results? Why or Why not?

1.      “Life history characteristics suggest that late successional species invest more in resistance to windthrow”:  their results only found a relationship between susceptibility and late successional (or shade-tolerant) species for smaller trees. It was somewhat true for intermediate sized trees (though I think that was more a function of height). Results for old trees were confounded by beech (BBD)

2.      “Height/diameter ratio explains differences in susceptibility in old vs. young stands… because trees in old growth have likely been suppressed and have denser wood”: it’s true that the older stands had smaller trees (they show a signif. diff. in dbh), but there is no data regarding suppression or wood density (I do think this is a valid SUGGESTION as a possible explanation though)

3.      “Our results suggest that distinctive abundance of yellow birch in old-growth… is due to its ability to survive the intermediate-scale disturbance events”: I thought this was kind of a stretch. What about the fact that the regeneration niche for YB is often on downed logs?

 

Recommendations

1.      windthrow susc. Of a conifer forest type

2.       Application/ incorporation of results into a model evaluating forest dynamics under climate change