8 THE HISTORICAL ECOLOGY OF FIRE, CLIMATE, AND THE DECLINE OF SHORTLEAF PINE IN THE MISSOURI OZARKS Richard P. Guyette, Rose-Marie Muzika, and Steven L. Voelker 1 ABSTRACT.—We review studies that have shown reductions in the abundance of shortleaf pine (Pinus echinata Mill.) during the last century in the Ozark Highlands. These studies indicate that pine abundance is currently 15 to 53 percent of the pine abundance levels before major logging activity and fire suppression, activities dating from the mid- to late 19th century. Evidence of pine loss comes from General Land Office notes, the presence of pine remnants, and historical documentation that described pine forests. Selective removal of pine, followed by intense hardwood competition, reduced shortleaf pine abundance in the Ozarks over the past century. In addition, very short fire intervals (< 3 years) before and after logging reduced advanced pine regeneration. More recently (1940-2006), long fire intervals caused by fire suppression have contributed to a long-term decline in pine abundance. Under continuing fire suppression, vegetation dynamic models predict a decline in abundance that will stabilize in about 200 years. Additional, more recent threats to recruitment and maintenance of shortleaf pine populations may include global warming-induced insect outbreaks. 1 Research Professor (RPG), and Associate Professor (RMM), Department of Forestry, 203 ABNR, University of Missouri, Columbia, MO 65211, and Ph.D. Candidate (SLV), Department of Wood Science and Engineering, Oregon State University, Corvallis, Oregon 97339. RPG is the corresponding author: to contact call (573) 882-7741 or email guyetter@missouri.edu or muzika@ missouri.edu THE ABUNDANCE AND LOSS OF SHORTLEAF PINE Estimates of shortleaf pine occurrence and loss in Ozark forests come from several quantitative and qualitative sources, and are best presented in the context of the contemporary forest. Among the most recent studies, Voelker (2004) measured the diameter and age class distribution (Fig. 1) of oak and pine in the Current River Hill subsection of Missouri (Nigh and Shroeder 2002), and determined their current relative abundance. Shortleaf pine has a greater frequency in older age classes due to its greater maximum age relative to red oaks. The age class distribution of pine on these 1200 randomly chosen plots indicates that about 15 percent of the shortleaf pine in this region is over 90 years in age. Only two studies have evaluated the age structure of successional forests of the Ozarks left after the exploitation period, both of which were based in single stands in order to test silvicultural definitions of even-aged versus multi-aged forests (Loewenstein and others 2000; Shelton and Murphy 1990). It is common knowledge that many of the mature oak-pine stands are relatively even aged, but knowledge of the actual age distributions across the landscape is lacking. The most recent forest inventory data indicate that the shortleaf pine forest type occurs on approximately 72,000 hectares or 1 percent of the forested land in Missouri (Moser and others 2006). Historically, shortleaf pine was estimated to have covered 2.7 million hectares in Missouri (Fletcher and McDermott 1957). Using landuse-landcover maps and comparing these with General Land Office (GLO) survey notes, Hamilton’s (2003) analysis indicated that forests with a shortleaf pine component currently occupy about 36 percent of the landscape that was originally described as shortleaf pine forest in the Current and Eleven Point rivers region. An estimate by Cunningham and Hauser (1989) states that shortleaf pine forest types currently occur on approximately 162,000 hectares in Missouri. Despite considerable range in data describing current distribution, several studies have documented that the abundance of shortleaf pine in the Missouri Ozarks has diminished (Table 1). Batek and others (1999) quantified GLO note data in the Current River watershed of the Missouri Ozarks and identified 53 percent of the landscape as having supported a shortleaf pine component. Guyette and Dey (1997) documented the loss of pine by quantifying long-lasting pitch filled pine remnants such as stumps, snags and pine knots, and comparing that to current overstory composition. Additionally, Voelker (2004) found that the red oak group, primarily black oak (Quercus velutina) and scarlet oak (Q. coccinea) replaced the original shortleaf pine forest in the Ozark Highlands as evidenced by current distribution patterns of black and scarlet oak relative to occurrence of identifiable shortleaf pine remnants. The current diameter distribution of overstory shortleaf pines consists of a preponderance of small size classes, in contrast with the estimated historic distribution of shortleaf pine in the plots sampled in the Current River Hills Subsection (Fig. 2).