The Influence of Forest Management on Vulnerability to Severe Weather

Transcription

1 The Influence of Forest Management on Vulnerability to Severe Weather Presented by Robert Beach, RTI International Erin Sills and Tzu-Ming Liu, North Carolina State University Subhrendu Pattanayak, RTI International Presented at Advances in Threat Assessment and Their Application to Forest and Rangeland Management July 18-20, 2006, Boulder, Colorado 3040 Cornwallis Road P.O. Box Research Triangle Park, NC Phone Fax RTI International is a trade name of Research Triangle Institute

2 Outline Introduction Severe Weather and Forest Impacts Factors that Influence Vulnerability Alternatives for Managing Risk Management Implications Conclusions 2

3 Introduction Severe weather regularly causes major forest disturbances in many parts of the world High winds (hurricanes, tornadoes, thunderstorms) Ice storms Snow storms Significant impacts on: Forest stand dynamics and ecology Economic returns to landowners 3

4 Managing Risk Identify and characterize hazards Assess risk associated with hazards Identify options to mitigate risk Select optimal combination of options given management objectives Implement chosen strategy 4

5 Severe Weather: Hurricanes , average of about 1.6 hurricanes per year making landfall between Texas and Maine 0.6 major hurricanes per year (category 3 or above) Hurricanes causing greatest timber losses Hurricane of 1938 Camille (1969) Frederic (1979) Hugo (1989) Opal (1995) Fran (1996) Katrina and Rita (2005) 5

6 Projected Hurricane Winds: Southeast U.S. Southeast - 10 Year < 40 mph mph mph mph mph > 110 mph Source: FEMA HAZUS-MH model 6 Southeast - 50 Year < 40 mph mph mph mph mph > 110 mph

7 Tornadoes and Other High-Wind Events Important disturbance event in continental interior of North America Average almost 1,000 tornadoes per year in the U.S. $154 million annual damage (Dale et al, 2001) Other windstorms, thunderstorms, etc. July 4 th, 1999 windstorm 478,000 acres of MN forest, in a swath 12 miles by 30 miles, was leveled 7

8 Ice and Snow Storms Some locations in North America experience ice accumulation every 1-2 years, but most have return interval of 5 or more years Many events cause only minor damage or severe damage is concentrated in a small area, but also major events 1998 ice storm in southeastern Canada and northeastern U.S. damaged over 10 million ha 2000 ice storm damaged an estimated 40 percent of the 7.4 million ha in the state of Arkansas 2002 ice storm damaged almost 1 million ha in North Carolina 8

9 Forest Impacts Excessive loadings placed on trees due to these events can cause: Severe defoliation Bending Uprooting Branch loss Stem breakage July 4 th, 1999 Windstorm, MN Picture: NOAA Archives 9

10 Bending and Uprooting July 1999 windstorm, WI Picture: Steven Katovich, USDA Forest Service, Bending from weight of ice Picture: USDA Forest Service Archives, USDA Forest Service, 10

11 Breakage from Hurricane Katrina Pictures: Ricky Layson, Forest Resource Consultants, Inc., 11

12 Breakage: Tornado and Ice Storm Ice storm damage in Vermont Tornado damage Picture: Ronald F. Billlings, Texas Forest Service, 12

13 Secondary Damages Wildfires Additional fuel loading Disease Bark damage and other wounds increase susceptibility Insects Bark beetles and others can infest broken and uprooted trees Invasive plants Gaps and structural changes may create opportunities for invasive plants Increased vulnerability to future wind, ice, and snow storms 13

14 Factors that Influence Vulnerability Weather severity Wind speed and duration Ice and snow Accumulation Retention Site conditions Topography Affects local wind intensity Soil conditions 14

15 Wind Speeds Current Scenario: Historic; Name: FRAN Legend StormTrack - FRAN StormTrack - FRAN Wind Speeds - Peak Gust (mph) < > 200 Census Tract Census Tract Region Boundary Miles / Region Boundary (c) FEMA. 15

16 Factors that Influence Vulnerability (2) Tree characteristics Species Health Age Height, Diameter, H/D ratio Crown shape and canopy position Stand characteristics Density Thinning regime Edges and gaps 16

17 Empirical Literature Interactions between weather conditions and site, tree, and stand characteristics are very complex Spatial and temporal heterogeneity e.g., thinning may increase near-term risk, but reduce risk in the future and increase productivity/shorten rotation There are a number of characteristics for which empirical observations are mixed e.g., age and size; stand density Factors may have different implications for wind risk vs. ice and snow risk 17

18 Is Weather Risk Endogenous? Despite variation in empirical findings, studies generally find important effects related to: Site selection Species selection Silvicultural practices Stocking density Thinning/pruning Rotation length 18

19 Does it Matter for Management? Appropriate response depends on level of risk faced For low risk of occurrence and small expected damages, considering weather risk may result in minimal or no change in optimal management For high risk of occurrence and large expected damages, there may be no feasible strategy for reducing risk In the intermediate case, where risk is significant but there are cost-effective mitigation strategies, accounting for risk may alter optimal management 19

20 Management Implications Forest industry Select level of weather risk mitigation that maximizes expected profits (assuming risk-neutral) Example: thinning and rotation length Incorporating exogenous damage risk shortens optimal rotation Treating risk as endogenous still yields shorter optimal rotation than no risk, but longer than exogenous risk (Thorsen and Helles, 1998) Thin more often, less intensively Selectively thin high-risk trees where cost-effective 20

21 Management Implications Non-industrial private forest landowners Management decisions generally assumed to be more heterogeneous and complex than industry Select level of weather risk mitigation based on objectives for producing timber, recreation, aesthetics, wildlife Public lands Select level of weather risk mitigation based on multiple objectives for land management 21

22 Public Policy Potential role for public agencies to develop additional policies encouraging improved forest management practices Reduce weather damages Reduce secondary impacts (fire, beetle infestation) that may negatively impact neighbors Need to evaluate effectiveness New actions vs. crowding out private spending Study in Switzerland found varying strategies for public involvement in providing financial incentives for forest management had important distributional effects for forest owners and government spending, but not for forest health (Bisang and Zimmerman, 2006) 22

23 Conclusions Severe weather causes major disturbances to forests Factors that influence vulnerability have highly complex interactions Need for more empirical studies accounting for weather severity, interactions between multiple factors influencing damages Need for more careful and systematic evaluation of effectiveness of forest management in reducing weather impacts Endogenous Risk Management and Policy Implications 23