Potential for Fire History Reconstructions at Oak Woodland Sites of Texas State Parks

Potential for fire history reconstructions at oak woodland sites of Texas State Parks A report prepared for Texas Parks and Wildlife Department By Michael C. Stambaugh Introduction Natural community restoration and management commonly includes prescribed burning that attempts to mimic historic fire regime characteristics (e.g., frequency, severity, seasonality). Though it is generally agreed that fires were once a dominant disturbance agent of many different ecosystems of Texas, only a few studies have actually quantified fire regimes. All but one of these studies has been located outside of the Trans-Pecos Ecoregion (Stambaugh et al. 2011) – leaving nearly 90% of Texas with nearly no quantitative fire history information. The objectives of this work were to: 1) describe the potential to salvage fire history information in the Oak Woods and Prairies and Edwards Plateau Ecoregions and, 2) identify which state parks could be utilized for fire history studies. Why is fire history information important? Fire regimes are defined on broad spatial and temporal scales such as regions and centuries (Parisien and Moritz 2009). Over these scales fire characteristics are commonly measured by average conditions of fire frequency, severity, intensity, seasonality, size, and extent (Pyne et al. 1996, Knapp et al. 2009). In general, fire was historically a much more pervasive disturbance, particularly in temperate regions and subtropical biomes (Guyette et al. 2012). Fire was an important and complex driver of ecosystems evidenced by species assemblages and adaptations, fire effects, and carbon dynamics. Historically, ecosystems could be stratified by fire regimes that broadly reflected climate and on top of which regional variability was further controlled by finer-scale controls such as ignitions, topography, and fuels (Guyette et al. 2012). Major departures in fire during the 20th century have made characterization of historic fire regimes particularly difficult. Results of fire history studies provide a strong scientific basis for applied historic ecology – the use of historic information in modern day land management (Swetnam et al. 1999). An example of applied historic ecology is prescribed fire management aligned with historic fire regime characteristics. For these reasons fire history studies are important. Furthermore, important applications have been made such as guiding U.S. fire policy, assessing global change and climate change, and educating the public about the role and ecology of fire. Objectives The objective of this work was to survey and report on the potential for fire scar history research to be conducted at Texas state park units. The potential for fire history was assessed based on the presence of adequate numbers of old fire scarred trees within relatively small areas (e.g., 1 km2). The number of trees needed for a fire scar history study to be conducted depends on the number of fire scars per tree and longevity of pieces of wood, but typically forty to fifty trees (100+ scars) are needed for a post oak (Quercus stellata) fire history study spanning three centuries. Compared to other oaks, post oak has many characteristics that make it suitable developing fire scar history reconstructions (Guyette and Stambaugh 2004, Stambaugh et al. 2009). Methods I assessed the fire history potential at as many Texas State parks as possible over a nine day period in July 2011. Based on the experience of Texas State Parks’ staff the specific parks likely to have older trees and fire history potential were: Lake Mineral Wells, Possum Kingdom, Pedernales Falls, Colorado Bend, Enchanted Rock, and Bastrop State Parks. With the support of park personnel I surveyed forested and recently burned areas for existence of older tree (e.g., > 200 yrs; live and dead) with fire scars. At each park the ages and abundance of old trees were estimated and tallied. On fire scarred trees I estimated the numbers of scars, their ages, and decay. Limited coring and cutting of trees was done for the purpose of confirming estimates of tree ages and dating a limited number of fire scars. Cutting only included dead trees except for one young tree (~70 yrs old) from which a partial wedge was cut. Tree cross sections and cores were surfaced with 80-1200 grit sandpaper so that the cellular detail of rings was revealed. Tree-ring widths were measured in sequence to 0.01 mm precision. Ring-widths sequences were crossdated using standard dendrochronological techniques (Stokes and Smiley 1968). Post oaks were dated using existing master ring-width chronologies from Texas (Stahle et al. 1982, Stambaugh et al. 2011) and known regional frost ring dates (Stahle 1999). Fire scars on cross sections were identified by the presence of callus tissue, charcoal, barrier zones, and cambial injuries. Fire scar dates were assigned to the year of first cambial response to injury. Fire scars dates were not meant to be used to describe fire frequency (i.e., more trees are required), but were used to positively identify the existence of fire scars and potential ranges of future fire scar history chronologies. Results Bastrop and Buescher State Parks Excellent potential for fire history from post oaks exists. Often these areas consisted of oak dominated uplands such as along Harmon Road. Large areas of older oaks were observed in northern portions of the park. Areas of older post oaks occurred where loblolly pines were absent. Older post oak communities may be associated with the Jedd gravel series. Some external evidence of fire scarring existed on post oak trees. Conversely, no loblolly pines (Pinus taeda) were observed having fire scars. One very large loblolly that was cut had an approximate age of 130 years. At Bastrop five dead post oak trees were cut to determine potential tree ages and degree of scarring. Inner ring years on these trees were 1730, 1737, 1742, 1859, and 1880. One tree had three possible fire scars. Other trees had 0 to 2 fire scars. Only limited surveying occurred at Buescher S.P., however, based on its proximity and similarity to Bastrop, it is likely that equal fire history research opportunities exist. Lake Summerville State Park A high abundance of 150-200 year old post oaks were observed throughout the park. Older trees exist in the park, but seemed to be much less abundant (Figure 1, 2). There likely exist sufficient amounts of dead solid post oaks to construct a well-replicated fire history study. No external evidence of fire scars was observed on trees in the park suggesting that it has been a long period (e.g., 50+ yrs) since the last fire. Few large hollow trees were found. Of the two trees sampled only fire scars in the early 20th century were captured. In comparison, little to no fire scarring was observed at Purtis Creek despite the areas excellent fire history record. Within the park small topographic changes may be associated with older post oak trees. Post oaks were prevalent throughout the park and above the floodplain. Enchanted Rock State Park Little potential for fire history exists due the dominance of tree species that are not well-suited for multi-century fire scar records (mesquite (Prosopis glandulosa), cedar elm (Ulmus crassifolia), and live oak (Quercus virginiana). Most trees in the park appeared to be <150 years old. This was supported by the ages of three of the oldest (dead) trees cut. Their inner ring dates were 1824 (Figure 3), 1850 and 1854. Only one of these trees exhibited fire scarring. Though we covered large portions of the park only 2-4 trees showed external evidence of fire scarring. Furthermore, few dead trees currently occur in the park compared to those at Bastrop and Lake Summerville. Dead trees within prescribed burn units are generally <100 years old and dominated by mesquite and live oak. Pedernales Falls State Park Post oaks offer the only potential for obtaining a fire scar history at Pedernales Falls. However, older trees are rare occurring along rocky drainages in uplands. The oldest trees observed were likely <200 years old and no older trees of other species were observed. Though cores were taken of two older post oaks, these trees were hollow. The outer 3 inches of these trees had up to 50 rings. Limited fire scarring on trees was observed in drainage to the southwest of the road leading to the water treatment facility. Older live oaks exist next to the park manager residence; however cores taken from these trees had indistinguishable rings. A few older Ashe junipers (Juniperus asheii) were observed on the upper portions of Bee Creek where small limestone cliffs occurred, however these trees likely do not exceed 150 years. Because very little potential for fire history existed I spent my remaining daylight at the park coring trees of interest and, though not central to this report, they do contribute ecological information concerning the park and therefore are reported here. In Bee Creek a core from a small shin oak (Quercus sinuate) with a diameter of 12.9 cm was 93 years old. Potential ages for shin oak are not well known. Two cores were taken from baldcypress (Taxodium distichum) trees growing on the south side of the Pedernales River at Trammel Crossing. One baldcypress with a diameter at breast height (dbh) of 79.7 cm showed very fast growth and estimated to be about 70 years (58 years on the core and center of tree was missed). Another baldcypress had a dbh of 47.7 years and was estimated to be 120 years old (105 rings on the core and center of tree was missed). “Skeletons” of long-dead baldcypress currently exist on the northern bank near Trammel Crossing. A subfossil oak tree was found on the southern bank of the Pedernales River approximately 50 meters downstream of Trammel Crossing.

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