Adaptive management of rangelands
March 18, 2009
“Adaptive management” is a phrase applied more and more often to the management of natural resources, including rangelands. In an effort to better understand what others mean by adaptive management, I was exposed to a new phrase this week: Complex Adaptive Systems. The term is not new, so perhaps I was just paying closer attention this time around. It will take little to convince anyone who has grazed livestock on rangeland, dealing with the uncertainties of weather, plant response and animal behavior, that rangelands are appropriately described as complex. Even if the view is restricted to a single pasture, the list of variables is lengthy – current species composition, current use, past use, soil type, topographic position, aspect, current growing conditions, recent precipitation, soil moisture, etc. But what does it suggest to refer to rangelands as “adaptive?”
From a historical perspective, rangelands have been present in the Northern Great Plains for centuries. The response of vegetation following the “dust bowl” years of the 1930’s may illustrate how rangelands can be described as adaptive. Plant biologists described how, at the peak of the drought, the vegetation in areas that had once been dominated by productive, tall grasses had shifted to vegetation dominated by much shorter grasses. After the drought broke and precipitation returned to more normal patterns, the vegetation shifted again, back toward greater dominance of tall grasses. While many variables probably “adapted” to lower precipitation and moisture availability and then readjusted to more favorable conditions, the change in the stature of vegetation was conspicuous.
Similar adaptation to grazing has been demonstrated. Tall vegetation can be maintained with lower grazing demand; while prolonged, severe defoliation shifts vegetation to shorter stature grasses. This adaptive response of vegetation is possible because of the great biodiversity present on healthy rangelands.
Further documentation of the value of this biodiversity was provided in a recent research report in which the productivity of diverse prairie vegetation was compared to solid stands of introduced cool-season grasses – either Russian wildrye or crested wheatgrass. Production was followed for 12 or more years in Alberta. Conventional wisdom may be that introduced grasses can be more productive that native vegetation. In this research, crested wheatgrass did have a yield advantage for a few years after planting, but long-term performance found no advantage for either tame grass compared to the native. The diverse native vegetation is well designed to adapt to variable growing conditions and is generally efficient at converting available resources (water, sunlight and nutrients) into plant growth.
Part of the notion of “adaptive management” involves keeping track of how “the system” responds to management decisions. Native rangelands containing diverse vegetation (and other life forms) have the capacity to adapt to changing conditions. The challenge for the excellent manager, especially in times of accelerating and volatile change, is to be alert to the response of the Complex Adaptive System and to adjust management in order to maintain a positive trajectory of those system responses.