The Framework Questions

In planning this volume we decided to focus on a set of questions that emphasize the dynamic nature of climate variability and ecosystem response. An important consideration was the need for generalization. Within the LTER program, modeling is a fertile method for generalization. Whereas the material we deal with does not lend itself to cross-site modeling per se, we decided to ask questions that will lead to a modeling framework. With this in mind, we next discuss the questions that were used at the outset.

The first framework question is, What kind of climate variability is being investigated? We must first recognize that there are several types of climate variability. The principal types according to Karl (1985) are as follows: (1) a trend is a smooth monotonic increase or decrease; (2) a fluctuation is two changes of mean whereby two maxima (minima) and one minimum (maximum) are evident; (3) a discontinuity is a single abrupt change in the mean; (4) a vacillation is a series of climate fluctuations but with mean values drifting about two or more average values; (5) an oscillation is a gradual transition between a maximum and minimum value that tends to repeat itself in the time series; (6) an oscillation in which the interval between the maximum and minimum values is approximately equal is called a periodicity, particularly where the maximum and minimum values are more or less equal over the period of interest. Even at the outset, we recognize that one or more of these types of climatic variability may operate simultaneously at any one LTER site. In addition, the distinction between the different types of climatic variability is not always clear, as is pointed out by McHugh and Goodin (chapter 11).

The next part of the framework consists of a series of questions.

1. Are there any preexisting conditions that will affect the impact of the climatic event or episode? For example, the effect of an intense rainstorm will be different, depending on whether the soil is already saturated.

2. Is the climate effect direct or does it go into a cascade? If a cascade is entered, how many levels does it have and is the interaction between each level linear or nonlinear? A cascade system is generally regarded as one that exhibits flow of material, energy, or information (Chorley and Kennedy 1971; Strahler 1980; Thomas and Huggett 1980). This is one of the more important questions. In introducing the framework questions, we note that the question about the existence of cascades, or a cascading set of events, lays the groundwork for systems analysis and modeling approaches. During this cascade identification, or modeling process, the parts of the cascade about which little is known are sometimes highlighted, thus establishing a potential agenda for further research needs.

3. Is the primary ecological effect completed by the time of the next climatic event or episode (or part thereof) or not? If the effect is complete, we may consider the next part of the cascade (if any). If the primary ecological effect is not complete (i.e., reaches a new constant level), is it still of sufficient magnitude to have an effect on the rest of the ecosystem? If so, we should pass the effect along the cascade.

4. Does the climatic event or episode or the ecological response have an identifiable upper or lower limit? If a limit exists, we can stop the consideration if necessary at the limit but keep the cascade going until it reaches limits that may exist in later parts of the cascade.

5. Does the climatic event or episode or ecosystem response reverse to some original state? If so, what timescales are involved? Does the climate state go back to the original position or beyond? Do cascades reverse? Can we identify the timing of these events?

6. After the climatic event or episode has occurred, do the values of the climatic or ecosystem variables return along their outward path or is there hysteresis or some other trajectory in operation? If the latter, how does this affect the cascade?

All of these questions relate to a deterministic, nonchaotic system. We may also ask whether the system is chaotic or random. If the system is random, no further explanation is possible, except that in some cases it may be possible to proceed using probability theory. If the system is chaotic, we must compute, or otherwise find, the parameters of the chaos such as its attractors and Lyapunov exponents.

This initial framework is summarized for convenience in a schematic in figure 1.3. A complete answer to these questions would place investigators in a good position to develop a model of the important climate variability and ecosystem re-

Figure 1.3 Schematic of the original framework questions used in the book.

sponse factors for the LTER site in question. Possibly more important, the aim of the questions is to ensure that the topic is treated in a systematic and thorough manner. The questions were "field tested" in conference presentation and in print (Greenland 1999) and found to be quite useful. Once more we recognize the limitations of this "one size fits all" approach, but we believe the need for focus and the quest for generality surpass the inherent limitations of any particular set of questions. The authors of the chapters in this book were presented with an early version of these questions and asked to address at least one or more of them in the preparation of their chapter. They were free to choose whether to deal with the question implicitly or explicitly.

After all the individual investigations that form the chapters of this book were complete, we reexamined the framework questions. We found that some changes in the ordering of the questions was necessary and that some questions are more fruitful than others. In retrospect, the framework questions fall into two categories (fig-

CLIMATE VARIABILITY & ECOSYSTEM RESPONSE

Questions of Dynamics of CVER

What preexisting conditions will affect impact of climatic event or episode?

Is effect direct or cascading?

s effect completed by time of next event or episode?

Does event or episode return to original state?

Nature and Characteristics of CVER

Nature and Characteristics of CVER

Identify climate variability.

Does event or episode have an upper or lower limit?

Does the climate and/or ecosystem exhibit chaos?

Figure 1.4 Schematic of the revised framework questions used in the book.

ure 1.4). The first category deals with the dynamics of climate variability and ecosystem response and assumes an underlying temporal sequence. The questions that fall most naturally into this category are those dealing with the preexisting conditions, the cascade of effects, whether the effects are completed by the time of the next climatic event or episode, and whether the event or episode and/or the ecosystem return to some original state. The second category of questions deals with the nature and characteristics of climate variability and ecosystem response. The questions of this type include the identification of the climate variability, whether the event or episode and/or the ecosystem response have an upper or lower limit, and whether the climate and/or ecosystem exhibit chaos. The discussion in the final chapter of the book (chapter 21) resequences the framework questions to better match the distinction between these two categories of questions.

Most of the questions that refer to the ecosystem are dependent on the scale of the particular ecosystem under consideration. On the other hand, the climate variability usually crosses multiple timescales and often has its root causes in other, larger, spatial scales. Both climate variability and ecosystem response, and the questions relating to them, cross multiple temporal scales. Beyond the scope of this book is the probability that the ecosystem effects may also be large spatial-scale effects and that the ecosystem effects may ultimately feed back on to the climate system at multiple scales.

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