Jeremy S. Wilson

A quantitative technique for the identification of canopy stratification in tropical and temperate forests

Canopy stratification is one of the oldest concepts in tropical forest ecology. However, there has been considerable debate over the existence and identification of strata. Much of the confusion arises from the differing definitions of strata (i.e. vertical stratification of phytomass, individual crowns, or species) and the methods used to evaluate them (e.g. profile diagrams). In this paper, a quantitative technique for identifying stratification of individual tree crowns in the forest canopy is presented. Strata are identified by comparing sorted tree heights to a moving average of height at the base of the live crown. Height and crown measurements were obtained from 21 published profile diagrams of forests, representing many biogeographic regions and covering a wide variety of forest types. The technique provides an objective measure of canopy strata allowing for a valid comparison of stratification between the different profile diagrams. Neither the original authors estimates of strata nor the number of strata detected by the quantitative technique support the premise that tropical forests have more strata than temperate forests. With the sole exception of a mono-layered European Douglas-fir plantation, all forests in this study had two or three layers.

Flexibility in forest management : managing uncertainty in Douglas-fir forests of the Pacific Northwest

Abstract Long planning horizons generate substantial uncertainty in forest management, making management flexibility, the ability to choose between multiple options or opportunities, a desirable attribute of managed forests. Flexibility in forest management reflects both the relative rigidity of intervention requirements and the potential range of development pathways for a stand. The wind stability of Pacific Northwest Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco) plantations is used to demonstrate the concept of management flexibility. Dense Douglas-fir plantations develop high height to diameter ratios (H/D same units) in the dominant trees making them unstable and prone to wind damage. The management of these plantations is inflexible, because without early and timely thinning, the stands do not contain stable trees that could be expected to survive long rotations or late thinnings. A combination of reduced planting densities and site-specific management reduces both the necessity and rigidity of intervention requirements (e.g., thinning) and expands the number of potential developmental pathways for these stands. The cost of greater management flexibility is reduced efficiency of wood volume production; however, greater adaptability to changing markets, labor conditions, and management objectives may be more important for many forest owners. While this approach to management is complex, it frees owners and managers from rigid management requirements and allows for a wider range of future stand conditions.

Agent-Based Modeling of Harvest Decisions by Small Scale Forest Landowners in Maine, USA

Small-scale forests are an excellent example of coupled social-ecological systems, which involve human and biophysical subsystems with complex two-way feedback interactions. The multifaceted nature of landowner decisions drives a significant need to better understand decision-making processes, reactions to policy, and combined impacts on ecosystems in a comprehensive manner. Small-scale forests require an integrated approach to modeling the social and biophysical components comprehensively. Agent-based modeling involves modeling individualistic behavior and interpreting patterns that emerge. The interaction between agents and their environments makes this a valuable tool to assess repeated decisions of individual landowners responding to changing environmental conditions. Agent-based models can be used to determine potential ecological, economic, and social outcomes of landowner decisions and reactions to changing conditions. A forest landowner agent-based model experiment was developed to model timber harvesting in Maine, USA. We present baseline simulation results and compare the effect of a social change (an increased tax rate) and a biophysical change (a pest outbreak resulting in increased tree mortality) on the system. These three scenarios were analyzed using ANOVA and MANOVA tests on harvested hectares and landowner goal scores to assess landowner behavior and priorities by action. We conclude by reviewing implications for future modeling efforts.

Economic Aspects of Invasive Forest Pest Management

The past decade has evidenced growing concern with the causes and consequences of biological invasions, many of which are economic in nature (Perrings et al. 2002). The risk of a new pest introduction is positively correlated with world trade flows (Costello and McAusland 2003, Margolis et al. 2005) and new invasions threaten the productivity and biological diversity of native ecosystems (Mack et al. 2000). A recent study reports that roughly 50,000 exotic species are established in the United States and annual domestic costs and annual losses from invasive species (forest and non-forest) may exceed

Plant ecology (communication arising): Coexistence of tropical tree species

120 billion (Pimentel et al. 2005). The passage of Executive Order 13112 (Clinton 1999), which enhances federal coordination and response to invasive species, and the creation of the National Invasive Species Council (NISC 2001, NISC 2005), are evidence of the federal government’s substantial concerns with these emerging threats to terrestrial and aquatic ecosystems. Forests provide suitable habitat for an assortment of invading organisms (Liebhold et al. 1995) and invasive species have been ranked as one of the four critical threats to our Nation’s forest ecosystems by the Chief of the U.S. Forest Service (USDA Forest Service 2004). Although most people might argue that it is laudable to counter threats to the structure and functioning of forest ecosystems, relatively few exotic organisms become a major pest (Williamson 1996). It is the main thesis of this chapter that decisions regarding budget allocations and the targeting of forest protection efforts would benefit from a clear understanding of the costs and benefits of invasive forest pest management. Interventions designed to mitigate damages from exotic forest pests are costly—the Forest Service spent

Chronicling Landscape Transformation

95.1 million dollars for the management of invasive forest pests in fiscal year 2005 (USDA Forest Service 2005, p. 14-55). However, very little is known about the magnitude of economic damages caused by exotic forest pests, or the efficacy of the money spent on pest control. This lack of knowledge impedes economic analyses of pest management programs and it

Coexistence of tropical tree species: Plant ecology (communication arising)

For decades, ecologists have struggled to explain how so many tropical tree species can coexist. Kelly and Bowler propose that differences in recruitment fluctuation and competitive abilities among closely related tree species could promote coexistence, and data from a tropical deciduous forest in western Mexico seem to confirm their predictions. We argue, however, that the tests of their models predictions make fundamentally flawed assumptions about both size–age relationships in trees and the factors that influence population size structures. As such, their results are potentially misleading and lack the necessary rigour to “reject all other theories of coexistence”.

Stability and density management in Douglas-fir plantations.

Kilgo, John C., and John I. Blake, editors. Ecology and management of a forested landscape: fifty years on the Savannah River Site. Island Press, Washington D.C. xxii + 479 p.

Changes in landscape composition and stand structure from 19452002 on an industrial forest in New Brunswick, Canada

79.95 (cloth), ISBN: 1-59726-010-X (alk. paper);

Effects of intensive forest management on stand and landscape characteristics in northern New Brunswick, Canada (1945-2027)

44.95 (paper), ISBN: 1-59726-011-8 (alk. paper).