Ecology meets practice: The case of uneven-aged silviculture and 'emulation' of gap-phase dynamics

Background/Question/Methods

Uneven-aged or selection silviculture (SS) is the predominant forest management practice in Northern hardwood forests of eastern North America, and is increasingly practiced in other forest systems from the boreal to the tropics.  SS is of particular ecological interest in that it is designed to “emulate” gap-phase dynamics as occurs in unmanaged forests.  I outline salient details of SS as practiced in the Canadian province of Ontario (the jurisdiction with the largest area of forest is managed under SS) and examine how ecological theory has informed these practices.  I also present novel data comparing unmanaged (“old-growth”) forests to SS forests at Haliburton Forest in Central Ontario, with a specific focus on: (1) tree species composition, (2) stem size and age distributions, (3) gap dimensions, (4) leaf area index, (5) understory light conditions, and (6) stand-level carbon flux.

Results/Conclusions

Empirical data are consistent with prior studies in finding that SS management results in pronounced shifts in tree species composition, favoring certain shade-tolerant trees and reducing mid-tolerant species and overall tree species diversity.  Stem size distributions in SS stands show a reduced abundance of large old trees compared to unmanaged stands that largely account for reduced basal area and volume in SS stands.  Gap dimensions in SS stands are similar to those in unmanaged stands, but on average leaf area index is higher, and understory light levels lower in SS stands than in unmanaged stands.  Carbon flux data based on eddy covariance measurements over 4 years indicate a greater C sink in most years in an SS stand compared to a comparable unmanaged stand in northern Wisconsin, but in one exceptional year the SS stand was a large C source.

The case is made that in general there has been very little input of ecological theory on evolving forestry practice related to SS, and conversely that SS provides a set of important patterns and problems that remain largely unaddressed by theory.  For ecological theory to have greater relevance, ecologists must understand both the details of management practices to find "windows of opportunity" that make applications possible, as well as the policy framework(s) within which management regulations and guidelines can be implemented.