Impacts of the 2011 Texas Drought on ForestsAugust 7, 2012

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“The date of the onset of the 2011 drought can be stated with remarkable precision: September 27, 2010. On that date a storm system bringing widespread rain to Texas left the state. Though it could not be known at the time, twelve of the next thirteen months would bring below-normal precipitation to Texas.”

John W. Nielsen-GammonTexas State ClimatologistThe 2011 Texas Drought

A Briefing Packet for the Texas LegislatureOctober 31, 2011

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Statewide62.4 million acres of forestland

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Pine plantation that is mostly green

Mixed natural forest with shades of brown and grey showing impacts of drought

Aerial photograph by Ron Billings near Nacogdoches, TX, August 26, 2011

Late Summer Observations

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Mortality on Forestland

• In December we conducted a preliminary analysis of drought-related mortality on forestland• Methodology• We surveyed foresters and asked them to identify

lower and upper bounds on tree mortality in their area• Survey information was combined with Forest

Inventory and Analysis (FIA) data on the number of trees

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Mortality on Forestland

• Results• 100 million to 500 million trees died as a result of the

drought• 2 to 10 percent of all trees on forestland in the state• Localized pockets of heavy mortality were reported for

many areas

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Google Earth

Sutton, Crockett, western Kimble and eastern Pecos counties saw extensive mortality among Ashe junipers

TFS Photo

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Pine mortality in Harris, Montgomery, Grimes, Madison and Leon Counties

TFS Photo

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Western Bastrop and eastern Caldwell counties, as well as surrounding areas, saw extensive mortality among cedars and post oaks

Photo: Ron Billings, TFS

Spring/Summer Assessment

• Objective: Estimate the number of dead trees on forestland in the state• Sample design

• Forestland map provided by FIA used as the population• Stratification• FIA units (7) to give regional estimates and for convenience in

administering the sample• NE TX, SE TX, and NC TX further split to hopefully give more

precision • NDVI change gradients east-west in SE and NE TX and reported

differences north-south in NC TX• 10 strata total 11

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Spring/Summer Assessment

• Two-stage unequal probability sample with replacement• 10 km x 10 km grid overlaid across state, defining

primary sample units (PSUs)• PSUs selected with probability proportional to the

amount of forestland• Random sample of seven secondary sample units

(SSUs)• 75-ft radius, fixed-area plot

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Field Data Sheet

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Status• Last day of field data collection was August 3• Data still coming in from the field

• Strata 1e, 1w, 2e, and 2w (East Texas) • 238 of 238 plots measured

• Strata 3n, 3s, 5s, and 6 (Central and North Texas)• Expecting 298 of 343 plots measured

• Strata 4 (South Texas)• Expecting 14 of 63 plots to be measured

• Strata 7 (Trans-Pecos)• Non-random sample of 51 plots split between readily accessible

areas of the Permian Basin, Chihuahuan Desert, and Davis Mountains 18

Analysis

• In East Texas, all plots measured and mortality numbers estimates currently being calculated• In Central and West Texas, working with Texas A&M

Department of Ecosystem Science and Management faculty (Drs. Moore and Washington-Allen) to combine plots with remote sensing observations (delta NDVI from ForWarn)• Report of drought impacts planned for late September

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Next Steps

• Looking beyond numbers of trees• Additional analyses of drought survey data

• Collaborator on NSF Division of Integrative Organismal Systems Core Program Proposal “Collaborative Research: The 2011 Texas Drought: An Autopsy of a Tree Mortality Event” by Dr. Georgianne Moore of Texas A&M and others.• Forest Inventory and Analysis• Comprehensive assessment of mortality• Assessing questions related to growth

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