The Heat is On: Texas Tree Response to Fires and Drought. Joseph D. White Professor of Biology Department of Biology Baylor University

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1 The Heat is On: Texas Tree Response to Fires and Drought Joseph D. White Professor of Biology Department of Biology Baylor University

2 Drying from West to East (approximately less 5 ) Average Precipitation Average Precipitation 2050

3 Heating from Northwest to Southeast (approximately 10 F) Average Temperature Average Temperature 2050 Low precipitation + Higher temperature = Low humidity

4 Area of conversion from woodland to savanna Waco Water Forest Woodland Savanna Shrub/grassland Barren Cloud Unsupervised Classification of MODIS data Tree Mortality Drought induced die back Disease susceptibility Sapling failure And then there is fire

5 2011 Drought Impacts % of Travis Co. woodlands Acres (100x)

6 2011: Satellite Detection of Global Fires Fires follow drought. Woodlands can go extinct with long term drought.

7 Fire Effects on Urban Trees Part I Fire in the Texas landscape Direct Effects Indirect Effects Part II Fire adaptation in the wildland urban interface Fire sensitive arboriculture

8 Arborists and Fire Wildfire Prescribed Burning Building Site Preparation

9 The Fire Triangle and Trees Fuel Temperature Oxygen Fuels Dead branches Downed branches and dead vegetation litter near the bole base Vines Insolation or exposure increases temperature of the tree environment Wind and loosely packed fuels and/or litter increase aeration

10 Bole Damage due to Fire Fire scars Interior rot Surface fires generally burn hottest on the opposite of the tree from the direction of the fire Chimney effect This super heating is lethal to cambial tissue at specific locations Living cells surrounding the wound grow around dead tissue resulting in catface scars Bole wounding due to fire may result in long term heart rot Texas red oak collected at the Balcones Canyonlands National Wildlife Refuge near Austin, Texas

11 Bark Thickness, Bole Diameter, and Fire Survivorship Data redrawn from Harmon, Ecology, 65:

12 Canopy Scorch Surface fires will also consume lower foliage either due to direct fire contact or from the thermal radiation from the fire Scorch height is predicted from the intensity of the fire (as an indirect measure of the fuel), temperature, and wind speed Scorch model from Van Wagner, Canadian Journal of Forest Research, 3:

13 Indirect, Post Fire Effects Low intensity fires Reduce understory vegetation and increase mature tree vigor by reducing competition Release nutrients from litter and downed woody materials Induce resprouting from root stock of basal sprouting species (fire as a signal?) Produce charcoal, 10% of which will be incorporated into the soil with improvements in soil water holding capacity and nutrient recycling

14 Woodlands, Fire, and People Fire return intervals range from 5 20 years across Texas landscapes The wildland urban interface (WUI) is an expanding front of housing development from cities and towns which are facing increasing influence from wildland fires Increased personal wealth and the desire to live near or in a woodland setting are positively correlated

15 US Forest Service Predicted Fire Return Intervals

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17 Mandate for Fire Adapted Communities Community wildfire protection plans (CWPP) may become mandatory for the near future as insurance losses associated as houses destroyed by fires in the WUI increase with time CWPP may use Firewise protocols that mandate clearing trees from within 30 from homes In addition, tree species (and other landscape plants) may need to be more fire resistant both as part of a Firewise plan with houses fire adapted

18 Defensible Space Within the 30 space Trees >10 (no overhang) Tree and woody vegetation spacing 15 Prune trees minimum 6 and remove understory vegetation Keep landscape wellwatered

19 Firewise: An Arborists To Do List Removing trees close to housing structures Safe pruning of lower limbs that act as ladder fuel for potential wildfires Prudent disease management Selection of low fire hazard tree species Consideration of trees that survive various types of fire events

20 What is a Low Hazard Tree? Low volatile oil composition in foliage High water content of leaves during drought Low energy content of wood Definition: hazard condition that increases the chance of loss

21 Volatile Oils Terpenoid compounds produced by tree to protect the leaves from high temperature stress in open sunlight In a distilled, pure form, the average flash temperature of plant secreted oils is 95 F! Fortunately most oils are in low concentration and diffuse in the canopy

22 Tree Leaf Oil Content and Ignitability HIGH Bald cypress Juniper Acacia Persimmon Magnolia Loblolly Pine MEDIUM Hornbeam Maple/Boxelder Sweetgum Elm Walnut Dogwood Pecan Chinaberry Cottonwood Beech Oak Ash Cherry LOW Locust Willow Hackberry Tulip tree Sassafras Derived from: Geron, et al Atmospheric Environment, 34:

23 Tree Leaf Water Sensitivity to Drought HIGH Hackberry Dogwood Maple Bald cypress Willow MEDIUM Oak Elm Sassafras Ash Pecan Loblolly pine Sweetgum LOW Juniper Cottonwood Cherry Magnolia Acacia Derived from: Abrams et al., Ecology,75: Bazzaz, Annual Review of Ecology and Systematics, 10: Petaki et al., Tree Physiology, 18: Yordanov, et al., Photosynthetica, 38:

24 Tree Wood Energy Content HIGH Pine Juniper Dogwood Oak Osage orange MEDIUM Maple/Boxelder Cottonwood Hornbeam Locust Beech Cherry Elm Ash LOW Walnut Catalpa Hackberry Basswood Hickory Sycamore Tulip tree Sassafras Derived from: California Energy Commission,

25 Potential High Fire Hazard Fire Trees? Low Leaf Water Wood Energy Dogwood Bald cypress Juniper Oil

26 Some Candidates for Low Fire Hazard Species? Tulip tree (Liriodendron sp.) Oil (L), Wood Energy (L) Sassafras (Sassafras sp.) Oil (L), Wood Energy (L) Locust (Robinia sp.) Oil (L), Wood Energy (M) Cherry (Prunus sp.) Drought (L), Wood Energy (M) Cottonwood (Populus sp.) Oil (M), Drought (L), Wood Energy (M) Walnut (Juglans sp.) Oil (M), Wood Energy (M)

27 Crown Bulk Density: Another Element of Fire Hazard of Trees Mass of leaves per unit volume of canopy Measure of packing density of live fuels Species/canopies with higher density will have lower rates of fire spread in canopies

28 Influence of Species on Crown Bulk Density Ashe s juniper Plateau live oak Shin oak Texas red oak CBD (g/m 3 ) Maximum CBD (g/m 3 ) worse Fire Hazard better However! Pruning within a species reduces hazard due to total fuel load reduction (e.g. dead branches)

29 Summary Long term future drought will continue woodland die back in Central Texas Fire follows drought Damage from fire: Dependent on bark thickness Windspeed and temperature during fire May induce heartwood disease Arboriculture in the WUI is an ongoing and expanding future concern Will include selective tree harvesting, pruning, and canopy modification Some species less hazardous than others based on leaf oil, response to drought, and wood energy (need research!)