UPDATED 2/8/05
Class Notes
Chap. 15 of Knight and Bates
Jan. 31/Feb. 2, 2005
Pickett and Ostfeld "The Shifting Paradigm in Ecology."
This is an important reading that links very closely to the second text and second half of the class.
Like the other chapters, this article offers a duality: the "traditional" vs. the "new" paradigm. But it also points out that neither are pure (ecologists and land managers have always been pragmatists who didn’t necessarily hold ecosystems to the theoretical models), nor are they necessarily mutually exclusive. But concepts and theories can affect how we perceive and manage ecosystems, so they are important.
1. Traditional paradigm:
(1) ecosystems as closed systems: their dynamics come from interactions of the elements within the system---i.e., interactions among the species. Although ecologists know that various factors cross any chosen boundary (like solar radiation), the notion of closedness is that you can analyze and capture an ecosystem’s main dynamics without having to deal with, for example, variations in solar radiation.
(2) ecosystems are self-regulating, tending toward equilibria defined theoretically as some average or persistent state (for vegetation this is the "climax" community; for animal species it is some measure of diversity, or various demographic measures like total population or density set by predator/prey interactions, carrying capacity, etc.). Disturbances are temporary set-backs on these equilibria. The carrying capacity of the environment, and the tolerance thresholds of the species, combine to define this equilibrium state.
(3) The concept of some "climax" or resting state is assumed to actually exist in nature, to be something more than a theoretical state. It could be defined as the climax state of the ecological community; the fixed carrying capacity; or the persistent species diversity. The idea of a climax community is applied to vegetation, but it entrains the notion, too, of the other species that come with vegetation communities.
(4) Change does occur, we all know that, but the models postulate change along fixed paths, given known inputs and controlling factors (like grazing pressure). So change is predictable: if you burn a forest or graze a grassland to bare soil, the ecosystem will start back up the successional pathway toward its climax state. Of course, if you continue to manage it, you can short-circuit those pathways to meet management goals.
(5) Human disturbance is almost always defined as external, something that perturbs the "natural" state. Ecologists worked hard to find ecosystems in pristine condition to do their research.
2. How it relates to resources management
Closedness meant that a management unit could be defined and managed as a separate entity.
Self-regulating meant, for exmaple, that the system could be left alone if wanted, an would relax to it equilibria state. Alternatively, it could be disturbed (e.g., grazed or logged) and would start to come back on its own.
Fixed carrying capacity essentially defined SY, and especially Maximum Sustained Yield (MSU)
You could expect a system to progress along a certain path, and since you knew the path you could intervene with management to hold it at some desirable state..
Disturbances like fire, blowdown, floods, harsh winters, etc. are seen as exceptional, emergency, not endemic events.
Humans were not considered part of the system, and thus they were not studied, modeled, or otherwise accounted for. They were seen as the managers and the consumers, not parts of the ecological action.
3. Balance of nature?
One broader idea that was enshrined in cultural thinking, and some environmentalism, was that nature tended toward some natural balance, especially if humans did not interfere. Some logic:
There are climax states; communities did recover after disturbance; there are natural limits on the growth and spread of ecosystems; so the idea of balance made some sense.
But if the idea is reified into paradigmatic expectations to which we manage, then we are in for surprises! Ecosystems are more changeable then these ideals allow----even if Europeans had not invaded North America, the continent’s ecosystems would be very different now than they were in 1400.
The authors of this chapter are suggesting that the notion that nature comes into balance in the absence of human disturbance is not very useful to ecosystems management.
4. New Paradigm: The Flux of nature
Most measures of ecosystems actually exhibit flux, and these can be of three types:
Systems are NEVER closed! Nor self-regulating—they are controlled by a variety of factors at a variety of scales, and many are external. They interact across scale and space (e.g., source vs sinks).
State states are relatively rare, but may exists in some, especially larger terrestrial ecosystems like rainforests. Still, that may be at a coarse scale, at the finer scales they may be in flux (so that the average age of a rainforest remains the same, but the locations of specific age stands moves around with disturbances).
Most successional stages are not deterministic, but result from specific histories and events, and factors like seed sources; migrations, etc.
Ecosystems are complex. And they can exhibit:
Scale matters a lot in the "new" paradigm.
We’ll take up the case of spatial scale:
coarse vs. fine-filter analysis and management
CASE: You are managing 10 sq miles of forest. Your job is to preserve it as a forest ecosystem with the suite of forest species. Disturbance occurs in all ecosystems, in forests it might be fire of blow-down. Both of these have characterisitic spatial and temporal patterns, that is, the disturbance regime has certain timing and size qualities. Say the average blow-down is a square mile, and each part of the forest averages a blow-down every 200 years. At any given time some sq mile patches of your forest are not forest at all, but open patches. Fine, you still have a forest overall.
NOEW: what if you only owned and managed 1 sq mile? And what if the blow-down hit you in year two of your management plan? Then you do not have a forest ecosystem anymore, and won’t for quite a while. Did your management fail?.
In terms of temporal scale, you can still claim that your patch of forest is a forest if you are thinking in terms of centuries---the trees are likely to come back, but the ecosystem just happens to be in an early successional stage right now and maybe for the next decade or two...
We’ll discuss this and other scenarios in class.
5. Management Strategies
need to pay attention to the whole system.
Must incorporate flux and disturbance into planning
Must be aware of "trans-boundary" effects, how what’s going on outside your defined ecosystem boundary can affect what’s going on inside.
"Adaptive management": prescriptions as hypotheses, management actions as experiments.
"Process management": plan and mange for
Caveat: "flux of nature" is not excuse for "anything goes." There are historical and natural limits; there are more or less desirable and sustainable states; evolutionary processes cannot fix all disturbances, nor overcome all human disturbance or induced limits.