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Week 7 Discussion Questions — 7 Comments

  1. Hirota et al.
    How does temporal variation in rainfall complicate the model that Hirota et al. have laid out? Generally, how can temporal analyses be incorporated into this analysis?
    Why does low resilience based on precipitation levels correspond to high human pressures? Is this true in other places as well?
    “The patterns suggest a double hysteresis of tree cover in response to rainfall (Fig. 3).This can be inferred in a formal way from the data, assuming the distribution of states to result from the interplay between stochastic processes and the dynamics of an underlying deterministic system (16).” (234) What are alternative assumptions and how would this impact the model?
    Because tree cover can substantially enhance rainfall in some parts of the world (22, 27–30), an interactive vegetation-climate system may sometimes have alternative stable states even if vegetation by itself does not (8, 22, 29, 30). Because our analysis refers to current rainfall distributions, it will not reveal such hysteresis resulting from vegetation-climate coupling.” (235) What kind of analysis could you conduct to investigate vegetation-climate coupling and hysteresis?

    Allen et al.
    Delimiting spatial and temporal bounds of a system and selecting functional attributes to be examined seem like tasks with no ‘right’ answer, but also that would have significant impacts on the analysis of the system. How does one resolve this or at least address it?
    Allen et al. reference resilience despite species turnover. How is our definition of resilience affected by our imposed values and how does this influence the management of the system? I’m thinking here about the tension between, for example, managing endangered species vs. ecosystem services.
    Allen et al. set forth qualities of resilience: within-aggregation richness, evenness and diversity; and cross-scale redundancy. How does this integrate with or contradict Holling’s conceptualization of resilience?
    Allen et al. propose testing metrics by comparing collapsed systems and systems that have not collapsed unders similar perturbations. What are the advantages and disadvantages of this method? Would this test of metrics be translatable to other systems?
    “Can measuring body mass or city size or other variables assess overall system resilience or state? Animals, or city sizes, encompass a wide-range of scale. If these variables reflect cross-scale structure, and are entrained by key processes, the answer is yes.” (965) Do you agree?

    Holling
    I’m not clear on what the mechanisms are for the relationships between the phases Holling describes. (How) are the definitions of phases as such useful/relevant/real-world applicable?
    If, as Holling admits, there are different kinds of adaptive cycles, how is this analysis useful? What do we learn from this, or is it more of a starting hypothesis or way to think through possibilities?
    In Holling’s conceptualization, collapse can cascade between scales. How is a cascade up (to larger scales) different from a cascade down (to smaller scales)?

  2. Allen et al.

    in relation of the use of discontinuities to assess relative resilience: which is the role of the edge effect between two adjacent different ecosystems (e.g.: urban ecosystem and woodlands or urban landscapes and agricultural landscapes)in the resilience of both ecosystems?

    Hirota et al.

    the authors concluded that precipitation is related with the resilience of the three different attractors ( forest, savanna, and treeless). Could they have the same conclusion if they had analyzed soil fertility instead precipitation? which is the role of plant interactions (and other organism in the stable states?

    Holling

    clarification: which is the difference between panarchical connections and bifurcations?

  3. In Figure 2 of Hirota et al. 2011, rainfall in S. America and Africa is strongly bimodal (between about 1200 and 2200 mm mean annual rainfall), while in Australia there is no such signal. Is this pattern alone a sign of alternate stable states?
    (Hirota et al. 2011) How well does mean annual rainfall capture the driving influence of precipitation on forest structure in places like Australia, which are strongly influenced by interannual variability and ENSO?

    Holling 2001 defends his approach to complexity by arguing that “if you cannot explain or de- scribe the issue of concern using at least a handful of causes, then your understanding is too simple. If you require many more than a handful of causes, then your understanding is unnecessarily complex.” But how do you decide (who decides?) how big a ‘handful’ of explanations is in a given case? (This is partly a question about scale of analysis.)
    How does the panarchy view overlap and conflict with ideas of self-organized criticality we have explored to date?

  4. Week 7 Resilience discussion questions for 3/5/13

    1. A system can be identified as more resilient to random perturbations but perhaps more vulnerable to a targeted attack (Allen et al. 2005). Is this a common attribute of highly connected “resilient” networks? Might this beg the question “resilient against what?” when we talk about resiliency?

    2. Allen et al. (2005) say a lack of turnover at edges may simply indicate resistance, which may or may not correspond to resilience. How are these two things different? How can we tell if systems are strongly resistant to turnover at scale breaks and have little adaptive capacity before a transition occurs?

    3. Holling (2001) claims we are now in an era of transformation, in which ecosystem management must stop pursuing incremental gains in efficiencies and focus on building and maintaining ecological resilience. Some maladaptive systems can have high resilience. In the case of climate change and rising sea levels, for example, how can we judge our response as adaptive rather than maladaptive? When is it okay to let a type of collapse happen—e.g. let an area succumb to rising sea level instead of engineering a solution or building a higher flood barrier?

  5. 1. Can you further explain the correlation between tree cover and rainfall mentioned in Hirota?

    2. Again from Hirota, can you expand upon the alternate stable states observed in climate-vegetation patterns that are not observed in vegetation alone?

    3. Holling mentions that one of the defining characteristics of human systems is foresight and intentionality. Are there not animals who have learned to control aspects of their ecosystems, and prevent collapse?

    4. How are panarchies established?

    5. Allen et al. mention turnover as a good predictor of resilience, but note that turnover may or may not be correlated with collapse. How do you distinguish between turnover which leads to collapse vs. scale transitions?

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