Historical Range of Variability in Temperate Rain Forests
To what extent can or should landscape management practices learn from or seek to mimic "natural" ecosystem processes?
These are common questions in forestry, especially in the temperate rain forests of the Pacific Northwest. And this type of landscape-scale bio-mimicry informs ideas and practices of variable retention, silvicultural managment guided not only by the value of the timber removed, but also by the values retained: forest cover connectivity, soil stabilization and so on.
So I was intrigued to see the recent Ecology and Society paper: "Is There Potential for the Historical Range of Variability to Guide Conservation Given the Social Range of Variability?" by Jonathan Thompson, Sally Duncan and Norman Johnson.
The historical range of variability (HRV) is shorthand for the range of ecological conditions that occurred in the past, the conditions that supported the evolution of native species. The assumptions are that, although ecosystems changed over time, the magnitude of change was limited to a certain range, and that today’s native species are adapted to this range of conditions.
Thompson and coauthors examine how an understanding of HRV might continue to inform management, even as variability evolves with climate change and other factors into a future range of variability (FRV), and given that the capacity to implement HRV- or FRV-based management is constrained by the range of ecological conditions that society finds acceptable, the social range of variability (SRV).
The HRV of forest ecosystem composition, structure, and function is usually invoked for one of two reasons: landscape restoration ecology or emulating natural disturbance regimes with timber harvests. ... At least three attributes of natural disturbances can be emulated with forest management (Hunter 1993). First, the frequency of timber harvests can be matched to the expected disturbance interval. Second, silvicultural operations can be designed to leave a legacy stand structure and composition on the site to more closely emulate the forest condition in the aftermath of a disturbance. Third, harvest sizes and shapes can mimic the range of expected disturbances. ...
Even if the landscape were capable of supporting the HRV, there may not be social permission to do so. Most landscapes in the United States are well outside the HRV by many important measures. It follows, therefore, that there will need to be radical changes in management if an HRV approach is used. …
Findings from the social assessment suggest that the pace of both social and ecological change, combined with the increasing ability of humans to change their ecological environment, require that we continue to think through biodiversity conservation and make adjustments for the foreseeable future. It is not a one-time task. The development of the FRV will constitute an ongoing negotiation process.