Nyssa Sylvatica)

Articles Tales from the Blackgum, a Consummate Subordinate Tree MARC D. ABRAMS No species in the eastern United States better exemplifies a ubiquitous yet subordinate tree than does blackgum (Nyssa sylvatica). What enables blackgum to grow nearly everywhere, but almost always at very low densities? It is the longest-lived hardwood species in the eastern United States, with a maximum age that can exceed 650 years. It is inherently slow growing, which most likely explains its great longevity and high shade tolerance; it is also one of the few tree species that are fire resistant as well as shade tolerant. Blackgum can grow in bottomlands or at xeric sites, being tolerant of both flooding and drought. Despite these ecologically beneficial attributes—and the fact that early loggers systematically avoided blackgum because of its tendency to rot—this slow-growing tree is rarely dominant. Blackgum has so far simply persisted as a marginal species. The future of blackgum is uncertain, however, because of the opposing forces of global warming and increased competition from other tree species. This article synthesizes a broad range of ecological studies that relate to the unique behavior of blackgum as a consummate subordinate, something that is poorly understood for this and other similar species in the ecology literature. Keywords: Nyssa sylvatica, land-use history, witness trees, forest geography, ecophysiology n many respects, blackgum (Nyssa sylvatica) is temperate tree species in the ecological literature, of which Ienigmatic, and it is certainly unique among eastern US there are many, but none so ubiquitous as blackgum. I will ex- hardwood species. It has a large range and can grow on almost plore studies of paleoecology, land-use history, witness tree any type of site in the eastern forests (Burns and Honkala 1990, distribution from early land surveys, forest and physical Iverson et al. 1999). Despite its ecological breadth, blackgum geography, dendroecology, fire effects, and ecophysiology to almost never obtains overstory dominance, typically repre- investigate major ecological and environmental changes as they senting just 1% or 2% of the canopy trees. It is the longest- relate to the past and present distribution of blackgum in the lived hardwood species in the eastern United States, and eastern United States. I will also examine the potential of probably ranks among the longest-lived hardwoods any- blackgum in the current milieu of fire suppression, limited where in the world: The oldest known blackgum tree is 679 timber cutting, and global change processes. My main objective years old (Sperduto et al. 2000), and blackgum ages of 450 to is to address the following questions: 550 years are not unusual. Blackgum often grows in swamps and floodplains, but it also occupies extremely droughty sites • What were the distribution and frequency of blackgum (Barnes 1991). It grows best on nutrient-rich sites, but obtains in North American forests before European settlement, greater importance on nutrient-poor, xeric, and hydric sites. and what are they in present-day forests? Blackgum is one of the few tree species that combine shade tolerance, drought tolerance, and fire resistance (Harmon • What impact did early Euro-American land-use 1984, Burns and Honkala 1990). Moreover, it is late succes- practices have on the frequency and ecological sional but can invade disturbed areas such as old fields, dynamics of blackgum? burned areas, and mine spoils (Burns and Honkala 1990). If it does so many things so well, why doesn’t it dominate the • What are the ecophysiological, growth, and life vast majority of the eastern US forests? history attributes of blackgum as they relate to being The purpose of this article is to synthesize current scien- a consummate subordinate tree species? tific knowledge concerning the historical development, present distribution, stand dynamics, growth, and ecophysiological attributes of blackgum to explain why it is rel- Marc D. Abrams (e-mail: [email protected]) is Steimer Professor in the School of egated to a subordinate status in most forests. This is Forest Resources, Pennsylvania State University, University Park, PA 16802. something that is poorly understood for many marginal © 2007 American Institute of Biological Sciences. www.biosciencemag.org April 2007 / Vol. 57 No. 4 • BioScience 347 Articles Tales from the Blackgum, a Consummate Subordinate Tree MARC D. ABRAMS No species in the eastern United States better exemplifies a ubiquitous yet subordinate tree than does blackgum (Nyssa sylvatica). What enables blackgum to grow nearly everywhere, but almost always at very low densities? It is the longest-lived hardwood species in the eastern United States, with a maximum age that can exceed 650 years. It is inherently slow growing, which most likely explains its great longevity and high shade tolerance; it is also one of the few tree species that are fire resistant as well as shade tolerant. Blackgum can grow in bottomlands or at xeric sites, being tolerant of both flooding and drought. Despite these ecologically beneficial attributes—and the fact that early loggers systematically avoided blackgum because of its tendency to rot—this slow-growing tree is rarely dominant. Blackgum has so far simply persisted as a marginal species. The future of blackgum is uncertain, however, because of the opposing forces of global warming and increased competition from other tree species. This article synthesizes a broad range of ecological studies that relate to the unique behavior of blackgum as a consummate subordinate, something that is poorly understood for this and other similar species in the ecology literature. Keywords: Nyssa sylvatica, land-use history, witness trees, forest geography, ecophysiology n many respects, blackgum (Nyssa sylvatica) is temperate tree species in the ecological literature, of which Ienigmatic, and it is certainly unique among eastern US there are many, but none so ubiquitous as blackgum. I will ex- hardwood species. It has a large range and can grow on almost plore studies of paleoecology, land-use history, witness tree any type of site in the eastern forests (Burns and Honkala 1990, distribution from early land surveys, forest and physical Iverson et al. 1999). Despite its ecological breadth, blackgum geography, dendroecology, fire effects, and ecophysiology to almost never obtains overstory dominance, typically repre- investigate major ecological and environmental changes as they senting just 1% or 2% of the canopy trees. It is the longest- relate to the past and present distribution of blackgum in the lived hardwood species in the eastern United States, and eastern United States. I will also examine the potential of probably ranks among the longest-lived hardwoods any- blackgum in the current milieu of fire suppression, limited where in the world: The oldest known blackgum tree is 679 timber cutting, and global change processes. My main objective years old (Sperduto et al. 2000), and blackgum ages of 450 to is to address the following questions: 550 years are not unusual. Blackgum often grows in swamps and floodplains, but it also occupies extremely droughty sites • What were the distribution and frequency of blackgum (Barnes 1991). It grows best on nutrient-rich sites, but obtains in North American forests before European settlement, greater importance on nutrient-poor, xeric, and hydric sites. and what are they in present-day forests? Blackgum is one of the few tree species that combine shade tolerance, drought tolerance, and fire resistance (Harmon • What impact did early Euro-American land-use 1984, Burns and Honkala 1990). Moreover, it is late succes- practices have on the frequency and ecological sional but can invade disturbed areas such as old fields, dynamics of blackgum? burned areas, and mine spoils (Burns and Honkala 1990). If it does so many things so well, why doesn’t it dominate the • What are the ecophysiological, growth, and life vast majority of the eastern US forests? history attributes of blackgum as they relate to being The purpose of this article is to synthesize current scien- a consummate subordinate tree species? tific knowledge concerning the historical development, present distribution, stand dynamics, growth, and ecophysiological attributes of blackgum to explain why it is rel- Marc D. Abrams (e-mail: [email protected]) is Steimer Professor in the School of egated to a subordinate status in most forests. This is Forest Resources, Pennsylvania State University, University Park, PA 16802. something that is poorly understood for many marginal © 2007 American Institute of Biological Sciences. www.biosciencemag.org April 2007 / Vol. 57 No. 4 • BioScience 347 Articles • What impacts will current and future environmental plain swamps in the Southeast. N. sylvatica var. sylvatica is conditions and management practices have on black- found in swamps of the Northeast, extending into wetlands gum dominance and distribution in eastern forests? of the upper South. However, recent literature recognizes two distinct species (N. sylvatica and Nyssa biflora) among Blackgum classification and distribution these three varieties, and they will be treated as such for the Blackgum is widely distributed in the forests of the eastern purposes of this review (Burckhalter 1992). N. sylvatica com- United States, with a range bounded by southeastern Maine, bines the varieties sylvatica and carolinina, whereas the vari- southeastern Wisconsin, eastern Texas, and Florida (figure 1; ety biflora is now the species N. biflora. Little 1971). Blackgum ranks 15th among 80 common tree Blackgum (N. sylvatica) is widely distributed in upland sites species in the eastern United States in the amount of forest across its entire range and in bottomland sites in the North- area occupied, according to the USDA (US Department of east and upper South, whereas swamp tupelo (N. biflora) Agriculture) Forest Inventory Analysis (Iverson et al. 1999). grows mainly in swamps and estuaries of the coastal plain in Fernald (1950) recognized three principal varieties within the the mid-Atlantic and southern states. Swamp tupelo also species N.

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