Emerging Concepts and Principles of Climate Variability and Ecosystem Response

In this synthesis, the following recurrent principles begin to emerge:

Issues of time and space scale are pervasive throughout the field of climate variability and ecosystem response. It is not always possible to separate the effects on ecosystems of climate events and episodes of different timescales.

At each LTER site climate events and episodes operate at different timescales. Consequently, these scales cannot be viewed in complete isolation.

Some timescales, like that on which the ENSO operates, show patterns with a broad spatiotemporal coherence that therefore encompass responses across a wide range of ecosystems.

Most LTER sites show evidence on their landscape of some past climate event or episode.

Timescales of climate variability and ecosystem response determine, in large part, whether the response is complete by the time of the next climate episode or event.

Some ecosystems return to an original state following climate disturbance, whereas others do not. When ecosystems return to an original state, sometimes the return is linear and sometimes it is nonlinear.

For a climate event or episode to be effective, there must be some identifiable, usually physiologically related, link to the flora and/or fauna of the ecosystem. Some proportion of climate variability will not have an effect on the ecosystem.

In some cases, for a climate event or episode to be effective it may involve a nonlinear amplification in forcing that later has an impact on the ecosystem.

Most ecosystem responses to climate events and episodes are not simple, single-cause, single-effect responses. Rather, the response takes the form of a cascade of effects.

The response cascades may be short or long, intuitively obvious or not, and linear or nonlinear or both. The nature of the cascade often depends on the complexity of the ecosystem. The LTER network includes some relatively simple ecosystems such as MCM and some very complex ecosystems such as LUQ.

Response cascades may take place both in time and space. Shaver et al. (2000) point out the need for improved models of the temporal sequence of ecosystem response because long-term responses may be very different from initial responses and responses will not be uniform in space.

Cascades that result from climatic impact in ecosystems often take time to manifest themselves and can result in legacies within ecosystems that condition subsequent climate impacts. Because cascading climate-driven impacts within ecosystems are often lagged in time, efforts to identify fixed time correlations are sometimes ineffective.

An initial climate driver may cause parallel cascades acting through several different climate variables.

There may be many parallel cascades, sometimes interacting with each other and sometimes not interacting.

Many of our studies focus on a single process. A focus on cascades leads us to concentrate more on the sequential linkage of one process to the next.

Whether upper and lower limits of the values of climate events and episodes and resulting ecosystem responses can be identified depends on both the degree of our knowledge of the relevant biophysical processes and the amount of empirical data available.

Cascades or parts of cascades in the atmosphere and ecosystem may act as gateways, filters, and catalysts to additional ecosystem response.

There seem to be at least three broad classes of interaction between ecosystems and climate:

1. The ecosystem buffers climate variability.

2. The ecosystem system simply responds to individual climate events and episodes that exceed some threshold for response. This threshold is often crossed or triggered by a nonlinear process.

3. We hypothesize that the ecosystem can move into resonance with the climate variability with positive and negative feedbacks that produce strong ecosystem response.

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