Restoring Fire Suppressed Texas Oak Woodlands to Historic Conditions Using Prescribed Fire

RESTORING FIRE SUPPRESSED TEXAS OAK WOODLANDS TO HISTORIC CONDITIONS USING PRESCRIBED FIRE Jeff C. Sparks, Michael C. Stambaugh, and Eric L. Keith Wildland Fire Program Manager (JCS), Texas Parks and Wildlife Dept., 12016 FM 848, Tyler, TX 75707; Research Assistant Professor (MCS), University of Missouri-Columbia; Project Manager (ELK), Raven Environmental. JCS is corresponding author: to contact call 903-566-0535 ext. 237 or email at [email protected]. Abstract.—Comparable to many oak ecosystems across the eastern United States, oak woodlands in Texas display characteristics of changing composition and structure due to altered fire regimes. Information describing historic fire regimes suggests woodlands underwent relatively frequent and repeated burning prior to major Euro-American influence in the early 19th century. Oak woodland management is a central goal of the Texas Parks and Wildlife Department natural community management; however many questions and challenges exist related to habitat loss and fragmentation, human populations, and prescribed fire implementation. In this paper we: 1) review information describing the historic fire regimes and community structures of Texas oak woodlands; and 2) detail fire prescriptions and challenges related to restoring long unburned sites. INTRODUCTION and chemical treatments be used initially followed by prescribed fire as a maintenance tool. These more A goal of many land management agencies is to intensive management efforts greatly increase the cost restore existing vegetation communities to resemble for restoring these invaded woodlands, thus limiting the vegetation composition and structure prior to the area that can potentially be restored. Based on industrialization or Euro-American settlement. The 13 years of experience, we have begun to develop timing of major landscape and fire regime changes prescriptions for effectively restoring these vegetation varied spatially but generally occurred in Texas communities to historic conditions by using fire as the during the mid-19th century or earlier. Restoring primary management tool. oak woodlands that have undergone decades of fire exclusion and become invaded by a dense understory and midstory can require intensive management and high cost inputs. CONDITIONS OF HISTORIC TEXAS OAK WOODS AND PRAIRIES Using prescribed fire with standard published Composition and Structure prescription parameters in these invaded oak Aside from anthropogenic features (roads, towns, woodlands often results in intermediate fire spread agricultural lands), the major difference between the and relatively low intensity fires, thus not meeting pre-Euro-American settlement vegetation and the objectives of reducing the stature of the invading current vegetation in Texas Oak Woods and Prairies understory and increasing the coverage of herbaceous (Fig. 1) is the increase in woody species biomass and species. It is often recommended that a combination resulting reduction in herbaceous species biomass of higher cost management tools such as mechanical (Diggs and others 2006). In the absence of fire (natural Proceedings of the 4th Fire in Eastern Oak Forests Conference GTR-NRS-P-102 127 Figure 1.—Map of Texas ecoregions within the Oak Woods and Prairies region. Place names relate to the descriptions given for historic descriptions of vegetation and fire history. 128 GTR-NRS-P-102 Proceedings of the 4th Fire in Eastern Oak Forests Conference and controlled), woody species have encroached into Olmstead (1857) described multiple community types post oak (Quercus stellata) dominated communities and structures including the presence of fires in this that were historically open and park-like (Diggs and description of Leon County: others 2006). The terms savanna and woodland do “During the first part of the day we went over not accurately portray the region’s current forest small, level, wet prairies, irregularly skirted by community structures, but according to early settler heavy timber, with occasional isolated clumps and explorer reports, they were accurate descriptors of and scattered bushes. Most of the prairies have pre-Euro-American settlement conditions (Diggs and been burned over. Both yesterday and to-day others 2006). we have been surrounded by the glare of fires at night. After a few miles began post-oak, which Olmsted (1857) described an area most likely near the changed to blackjack, and for the remainder Houston County–Leon County line: of the day the country was as forbidding as a “We came today upon the first prairie of any moor.” extent, and shortly after crossed the Trinity River. After having been shut in during so many Approximately 100 km to the south (Colorado days by dreary winter forests, we were quite County), Roemer (1849) described the structure of exhilarated at coming out upon an open country post oak forests: and a distant view. During the whole day’s ride “These forests …have a remarkable resemblance the soil improved, and the country grew more in winter to the cultivated German oak forests…. attractive. Small prairies alternated agreeably In other forests of North America many varieties with post-oak woods. The post-oak…forms a of trees are usually found, but in the post-oak very prominent feature in Texas scenery and forests all are excluded with the exception of a impressions. It is a somewhat small broad- few walnuts. Underbrush is also lacking. The leaved oak of symmetrical shape, and appears soil upon which the post-oaks grow is usually wherever the soil is light and sandy, in a very of average fertility, but also often sterile and regular open forest growth. It stands in islands in unproductive…. [There] is a wide zone where the large prairies or frequently borders an open deposits of gravel and sand are found, and where prairie through a large tract.” farming cannot be carried on successfully. Here the land is covered with post-oaks.” More densely forested areas would have occurred in association with natural fire breaks or in areas with In summary, the Texas Oak Woods and Prairies region lessened fire severities such as in rough terrain or low was likely a complex mosaic varying from prairies and productivity sites. Roemer (1849) provides evidence open savannas to forests with closed canopies (Diggs for this vegetation patterning in his descriptions of an and others 2006; Keith 2008, 2009d, 2010a, 2010b; area between Gonzales and La Grange as “a sandy, Keith and Leavitt 2008). hilly country, covered almost entirely with post oak forests.” Fire Regimes Since Euro-American settlement, fire regimes in Texas Captain Domingo Ramón in 1716 described forests in and throughout North America have been highly what is probably present-day Burleson County as so altered. Although fire is regarded as a principal historic dense that “there were not enough hatchets and knives disturbance to most of Texas’ ecoregions (McNab and to open a passage” (Foster 1995). Avers 1994), relatively little work has been done to Proceedings of the 4th Fire in Eastern Oak Forests Conference GTR-NRS-P-102 129 describe how fire regimes of Texas Oak Woods and Timbers as the mechanism for grassy understories and Prairies varied spatially and temporally (Courtwright branch formations of the trees. A survey conducted in 2007, Diamond and others 1995). Here we describe the Trinity River watershed by the U.S. Department fire regimes relevant to Texas Oak Woods and Prairies of Agriculture in 1942 used fire scars to show that (Fig. 1). periodic fires were still occurring through the mid-20th century (Dyksterhuis 1948). Oak Woodlands Very little information is available describing the Recently, several fire scar history studies in more historic fire regime in the Oak Woodlands (Fig. 1). northerly Cross Timbers have contributed to Many of the relict oak woodlands have experienced characterizing the fire regime (Allen and Palmer 2011, infill of woody vegetation suggesting that the Clark and others 2007, DeSantis and others 2010, disturbance regime (fire and/or grazing) has been Stambaugh and others 2009). Common among these altered. A recent fire scar history study developed in a studies are pre-Euro-American settlement period relict sand post oak (Quercus margaretta) woodland mean fire intervals of 3 to 6 years, a preponderance in Van Zandt County provides one example of what of dormant season fire events, and evidence for the fire regime may have been (Stambaugh and others anthropogenic burning. These studies have had little to 2011). Here, the mean fire return interval for the 325 bear on the range of fire severity, however all sites had years from 1681-2005 was 6.9 years. Prior to 1850 trees >200 years in age, suggesting no stand replacing (approx. timing of major Euro-American influence), events had occurred during at least the previous two fire intervals ranged from 2 to 16 years, with a mean centuries. Based on observations of fire scar heights fire interval of 5.9 years. Based on the presence in Cross Timbers post oaks, many of these sites likely and recruitment of trees, there was no evidence of experienced low- to moderate-severity fires. However, stand replacing fire events, however two relatively fires have the potential to be very high severity (e.g., severe fires occurred prior to 1850. During the Civil stand-replacing) and widespread (>100,000 acres), War era, fire frequency decreased and coincided particularly during drought conditions. In April 2011, with establishment of an oak cohort. Nearly all fires wildfires burning through the western

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