Patch Dynamics

Ecological Consequences of the 1988 Fires in the Greater Yellowstone Area

Final Report

The Greater Yellowstone Postfire Ecological Assessment Workshop

P.7

Wildfires rage even in areas of high tech fire suppression forces. Each approach brings it’s own environmental liabilities. No strategy is inherently right or wrong, but only becomes true according to the capacity of the receiving environment to accommodate it and of agencies charged with management of wilderness ecosystems to express it in operational terms.

P.9

The landscape embodies chance as well as mechanism; and there are those who would argue that chance is itself a value, that the unpredictable is the essence of the wilderness experience.

P.10

Our knowledge of the causes and consequences of natural processes such as fire is rudimentary, but we have learned enough to know that wilderness landscapes are not predestined to achieve some particular structure or configuration if we simply remove human influences.

- range of landscape configurations

- Yellowstone probably never looked the same twice

It was easy to promulgate objectives to protect and preserve a particular scene. Developing analogous objectives to preserve and protect particular natural processes has proven considerably more difficult.

-Park Service mission statement of preserve and protect may be counter-productive if idea is to achieve some kind of stasis

P.11

Idea of climax ecosystems: “....it was assumed that wilderness landscapes are predestined to assume a particular primeval configuration determined by relatively static environmental factors such as climate. These ecological precepts were consistent with management goals that focused on the preservation of particular community types and states, or management for specific objects or species.”

It is now accepted that the process of ecological change is far more complex than originally envisioned. Chance conditions soon after disturbance are now known to play a very important role in the process of successional change and contribute considerably to the natural heterogeneity that typifies most wilderness landscapes (Sousa 1984). Natural disturbances occurring on very large spatial scales were a prominent feature of many primeval landscapes. Furthermore, such disturbances appear to be necessary for long-term preservation of some ecosystem components. As important, it is now clear that ecosystem change does not occur against a backdrop of constant climate; the climatic conditions of today are likely different from those of a century or a millennium ago.

-ecosystem concept: not defined so much by the objects they contain as by the processes, energy flow and material cycling, that regulate them.

–Ecologists operationally define the boundaries of ecosystems so as to most easily measure inputs and outputs of energy and matter.

- forest patches at varying stages of succession

P. 12

The patch-dynamic model of landscapes (Pickett and White 1985) posits that each patch is constantly changing. If patch size is small relative to the total size of the landscape and if region-wide disturbance frequency remains constant through time, the relative abundance of patches in different successional stage classes should remain constant across the landscape. However, if patch sizes are highly variable and occasionally large relative to the size to the landscape, or if the rate of patch formation changes through time as a consequence of climatic shifts, then the frequency and distribution of patch types on the landscape will not be constant through time. (This provides a model for changing ecosystems at the end of the last ice age. Things didn’t stay the same and the patches started to change in response to shifting climate. Chris’ observation that plant communities just don’t migrate north and south as whole units.)

-landscape mosaic

- ...if natural disturbances are allowed to occur as they did the past, the landscape is not predestined to achieve some particular configuration. Within the realm of what is natural, a great number of configurations is possible.

P.13

....fire typically revisited grassland, shrub and savanna ecosystems of the Northern Range every 20 -100 years. However, return times of 200-400 years appear to be more typical of the forest ecosystems that dominate most of the GYA

Suppression of wildfires, whatever their origin, was a central feature of military, Forest Service, and National Park Service policy from 1886 to 1972. It is difficult to know the effectiveness of those activities and, therefore, the extent to which fires were actually suppressed because the inaccessibility of  much of the wilderness may have hampered effectiveness of this policy until the availability of airborne firefighting methods (ca. 1940). Thus, hand crews arriving at a fire two or three days following ignition may have been able to suppress a fire unless fire weather was severe or extreme. (So, saying that fire has been suppressed for over 100 years is not necessarily correct, as the earlier fire suppression may not have been very effective.)

P. 14

In most cases, however, fires were gradually extinguished only when weather conditions permitted.

-it’s windy on the Yellowstone plateau

The fires of 1988 demonstrated that, regardless of manpower and equipment, suppression of fires in heavy fuels may be impossible when the weather is severe. The large expanses of old-growth forests on the Yellowstone plateau (33% of the Park was vegetated by stands greater than 250 years old) certainly exacerbated the situation.

....although the 1988 fires cannot be considered wholly natural, their severity and magnitude may not have been unique in the long-term.

P. 17

Sediment yield from hillslopes increases in response to forest fire devegetation. In areas of moderate to light burn, lower erosion rates and sediment yields may be reduced by postfire needlecast on denuded surfaces.

-unburned needles cast off and provide protective carpet that breaks fall of raindrops and retards overland flow

These processes promote infiltration and trap fine sediment.

-needlecast influences ground temp. and inhibits frost heaving, a process which increases sediment availability