The Influence of Forest Management on Vulnerability to Severe Weather

Robert H. Beach, Erin O. Sills, Tzu-Ming Liu, and Subhrendu K. Pattanayak

RTI International, North Carolina State University, North Carolina State University and RTI International respectively

Severe weather events that bring high winds and/or heavy precipitation (e.g., hurricanes and ice storms) regularly cause major disturbances to U.S. forests, significantly impacting both ecological conditions and economic returns to forest landowners. Forest landowners may suffer from the loss of merchantable timber; increased risk of wildlife, disease, and pests in damaged stands; and depressed timber prices in the immediate aftermath of events that cause widespread damage. These risks have a substantial impact on the expected economic returns to forestry as well as leading to distributional impacts among producers and between consumers and producers. This has led to considerable interest in identifying factors that influence damage levels as well as ways to mitigate damages. Anecdotally, many forest managers associate damage with silvicultural activities such as thinning. However, previous studies have focused almost exclusively on biophysical properties of forest plots or individual trees to explain differences in damages without explicitly examining the role of landowners’ forest management decisions. Overlooking the impacts of management decisions on the risk of weather damages may lead to inefficient decision-making by policy-makers and private landowners.

Timberland throughout the U.S. South has been affected by a number of major hurricanes over the past century (Lutz 2005). Hurricane strength winds can cause severe defoliation and can directly damage and kill trees through uprooting, breakage and loss of minor and major branches, as well as stem breakage. For example, Hurricane Hugo damaged over one-third of South Carolina’s timberland in 1989. The damaged volume of timber was estimated to be 1.3 billion cubic feet (Remion, 1990). Major ice storms may also result in substantial damages or death for affected trees due to branch and stem breakage. In January of 1998, an ice storm hit southeastern Canada and the northeastern U.S. and damaged over 10 million hectares of forestland (Irland, 1998; Miller-Weeks, Eager, and Peterson, 1999).

The immediate loss of timber is not the only risk imposed by weather events. The increased number of broken and uprooted trees raises the risk of wildfires as well as disease and pest outbreaks for the surviving trees. Forest landowners also may be affected by depressed timber prices, at least in the short run. Production risk has an unambiguous negative impact on optimal rotation length, expected returns to forestland, and land value, although the effects of price risk are ambiguous (Prestemon and Holmes, 2000; Prestemon, Pye, and Holmes, 2001).

In this paper, we review and synthesize the literature on the risk of forest damages from severe weather, the factors that influence risk, and alternatives for mitigating risk. Damage severity depends on the interaction of numerous factors related to biological, topographical, and stand characteristics. For instance, although wind speed is the most important factor contributing to timber losses due to high winds, topography and soil conditions also determine a stand’s resistance to wind loading. From the perspective of forest managers, a key question is what they can do to decrease the risk to a given tract of timberland. Forest management can change susceptibility to wind damage through effects on stand characteristics such as tree species, tree height, tree diameter, crown area, rooting depth and width, and stand density (Kerzenmacher and Gardiner, 1998; Peltola et al., 1999; Peltola et al., 2000; Dunham and Cameron, 2000). Stand age and forest structure may also contribute to vulnerability of forest to high winds (Everham and Brokaw, 1996; Francis, 2000; Mitchell, 1995; Ruel, 1995). Similar factors have been related to the degree of ice damage to forests (Bragg, Shelton, and Zeide 2003). Thus, we can identify options for mitigating weather risk, including choices about tree species, silvicultural practices such as bedding and fertilization, and thinning regimes (Persson, 1975; Lohmander and Helles, 1987; Zeng et al., 2004; and Olofsson and Blennow, 2005).

To illustrate findings from the literature, we examine the impacts of Hurricane Fran on forests in North Carolina. Using Forest Inventory and Analysis (FIA) data and a simulated wind field generated with the Federal Emergency Management Agency’s HAZUS-MH model, we estimate the influence of forest management decisions on the probability and magnitude of storm damages, controlling for other biophysical factors. This type of empirical analysis can inform forest management decisions and increase the efficiency of public policy that encourages timber stand management and compensates landowners for weather damages.

Air and Water Session - Thursday Afternoon

corresponding author:

Robert H. Beach
RTI International
3040 Cornwallis Road
Research Triangle Park, NC 27709-2194
919-485-5579
rbeach@rti.org