Extended Abstract (1.2M)2B.8
Prescribed fire effects in the Ozarks of Missouri: the Chilton Creek project 1996–2001
George W. Hartman, Missouri Department of Conservation, Columbia, MO; and B. Heumann
The Chilton Creek basin is a 2500 acre forested area of the dissected breaks adjacent to the Current River, southeast Missouri Ozarks. Owned and managed by The Nature Conservancy, the basin has been under a frequent prescribed fire regime since 1998. In 1996, the Missouri Department of Conservation established 250 half acre permanent monitoring plots in the basin using stratified random placement of plots by slope, aspect, topographic position, and geologic substrate. Pre-treatment data was collected in 1996 and 1997 from 4000 1 m² herbaceous quadrats and on 50,607 woody stems in all size classes. Herbaceous vegetation was re-sampled in 1998 and 2001. Woody stems were re-sampled in 2001.
Pre-treatment data shows a well developed understory and mid-story as a result of a fifty year fire free interval of the mid to late 1900’s. Uneven-age timber harvests during this interval favored development of Black Oak (Quercus velutina) and Scarlet Oak (Q. coccinea) over previously more abundant Shortleaf Pine (Pinus echinata), White Oak (Q. alba) and Post Oak (Q. stellata). The 1996-97 ground layer was dominated by hardwood leaf litter with average vegetative cover of only fifteen percent. Of that vegetation, 46% were seedlings of trees and shrubs, 19% legumes, 16% broadleaf herbs, 9% grasses and sedges, 8% woody vines, and 2% ferns. Historic vegetation descriptions of Ozarks woodlands prior to twentieth century fire suppression described a ground layer dominated by grasses, sedges, and broadleaf herbs in areas with frequent fire. Despite the presence of over 500 non-woody species in the basin, only five non-woody species were in the top 20 Relative Importance Values from quadrat sampling. Two legumes (Desmodium nudiflorum and Amphicarpa bracteata) and one shrub (Sassafras albidum) dominated nearly 20% of the ground layer vegetation. Diversity was 11.5 species per quadrat with 465 species of vascular plants occurring in the entire 4000 m² sampled. Non-native taxa represented less than one percent of the flora sampled.
Data from 2001 sampling shows drastic reductions in understory and midstory woody stems, an increase in woody seedlings in the ground layer including copious basal sprouts, and an increase in herbaceous ground layer vegetation. Woody stems less than 1.5 meters tall were reduced from 13,002 in 1997 to 3,283 in 2001 (75%). Species considered fire tolerant and fire intolerant were both impacted. Shrubs and early successional woody species such as Redbud (Cercis canadensis), Persimmon (Diospyros virginiana), and Sassafras (Sassafras albidum) increased in number. Woody stems in the 1.5-4.5 dbh size class were reduced at a lesser rate from 18,032 to 12,967 (28%). White oaks in this category such as Q. alba and Q. stellata had mortality rates of 22% and 29 % respectively, while red oaks such as Q. coccininea and Q. marilandica were reduced 52% and 60% respectively. Mortality in overstory trees (dbh >4.5 inches) increased from 4% of the 1997 sample to 11% of the 2001 sample. The understory and midstory that developed in the absence of fire has been reduced. There appears to be adequate recruitment of small woody stems to maintain overstory trees. Tree species composition is still not representative of what would be expected on a fire managed landscape due to increased resistance of larger trees of all species to fire mortality. This composition is expected to change over time as repeated fires are applied.
The ground layer in 2001 was still dominated by hardwood leaf litter but average vegetative cover increased from 15% to 24%. Trees and shrubs in the ground layer decreased considerably from 46% to 33% and woody vines decreased slightly from 8% to 6%. Legumes increased from 19% to 30% and grasses and sedges increase modestly from 9% to 13%. The number of herbaceous species in the top 20 RIV increased from five to nine species with Bosc’s Panic Grass (Panicum boscii) and Woodland Sunflower (Helianthus hirsutus) increasing dramatically in frequency, and the two most common legumes (Amphicarpa bracteata and Desmodium nudiflorum) increasing fivefold in cover. Diversity increased slightly: from 11.5 to 12.2 species per quadrat, and from 465 to 482 species occurring in the 4000 m² sampled. Increase in ground layer vegetation has resulted from a flush of vegetative growth by already established perennial forbs, mostly legumes. An increase in the abundance of opportunistic native annuals such as Fireweed (Erechtites hieracifolia) occurred after initial fires but relative abundance of the annuals has decreased in subsequent seasons. Fires continue to stimulate flowering and seed production in perennial grasses, sedges, and forbs, and to create bare ground for seedling establishment. But herb seedling establishment in the rocky and excessively drained soils of this basin is slow. It is expected that ground layer change from a low diversity leaf litter and woody species dominated vegetation to a moderate diversity broadleaf herb and graminoid dominated vegetation may take decades of fire rather than a few years.
Session 2B, Fire Effects on Flora: Part 1 (TRACK II)
Tuesday, 18 November 2003, 8:00 AM-5:00 PM
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