Introduction American chestnut (Castanea dentata (Marsh.) Borkh. once occurred over much of the eastern deciduous forests of North America (Russell, 1987), with a natural range exceeding 800,000 km 2 (Braun, 1950) (Figure 1). Castanea dentata was a dominant tree species throughout much of its range, comprising between 25-50% of the canopy (Braun, 1950; Foster et al., 2002; Russell, 1987; Stephenson, 1986). Particularly in the Appalachian region, C. dentata filled an important ecological niche (Ellison et al., 2005; Youngs, 2000). The wood of C. dentata has a straight grain, is strong and easy to saw or split, lacks the radial end grain found on many hardwoods and is extremely resistant to decay (Youngs, 2000). Historically, C. dentata wood served many specialty use purposes including telephone poles, posts, and railroad ties, as well as construction lumber, siding, and roofing (Smith, 2000; Youngs, 2000). Due to the high tannin content, both the wood and bark were used to produce tannin for leather production. The nuts, which are edible raw or roasted, were collected throughout the fall to provide a dietary supplement and were also used as a commodity for sale or trade on U.S. streets (Steer, 1948; Youngs, 2000). Figure 1: Original natural range of Castanea dentata in eastern North America, as adapted from Little (1977). Chestnut blight disease, caused by Cryphonectria parasitica (Murr.) Barr (= Endothia parasitica (Murr) Anderson and Anderson) (Anagnostakis, 1987), rapidly annihilated C. dentata throughout its range (Roane et al., 1986). The introduced pathogen is thought to have been 2
imported on Castanea spp. seedlings from Asia and was first discovered in 1904 on infected chestnut trees at the Bronx Zoological Park in New York City (Anderson and Rankin, 1914; Murrill, 1906; Roane et al., 1986). By 1950, the disease had spread throughout the range of C. dentata, and by 1960 had killed an estimated 4 billion trees; essentially extirpating the species from the canopy (Anagnostakis, 1987; Hepting, 1974; McCormick and Platt, 1980). Since the discovery of chestnut blight, many groups have worked to develop blight-resistant C. dentata through diverse strategies including biocontrol of the fungus, breeding and selection of large surviving C. dentata trees, inter-species backcross breeding with resistant Asian chestnut species, and genetic modification. Continuing and recent progress in these areas suggest a large-scale re-introduction program is imminent (Diskin et al., 2006; Jacobs, 2007). Because C. dentata disappeared decades before the development of modern principles of forest ecology (Paillet, 2002), our knowledge of basic biological and ecological characteristics of the species is rudimentary (Jacobs, 2007; Paillet, 2002). Much of our understanding regarding establishment and growth of C. dentata originates from historical observations or growth of stump sprouts (Paillet, 1982; 1984; 2002). With the successful advancement of C. dentata breeding programs leading to the verge of reintroduction, there has been increased prioritization for research examining C. dentata establishment and growth in planted and natural forests (Jacobs, 2007). This progress, combined with continued advances in genetic technologies for production of blight-resistant C. dentata trees for reintroduction, implicates the need for an updated critical synthesis to aid in further developing protocols for disease resistance breeding and subsequent germplasm deployment. Thus, the purpose of this technical review is to synthesize the current state of knowledge regarding 1) C. dentata biology and natural history 2) the development of blight-resistant C. dentata trees and 3) the ecology of C. dentata pertinent to pending restoration programs. These knowledge areas as well as understanding of their considerable overlap will contribute to the formulation of a viable restoration plan for the ecologically and socially important C. dentata (Figure 2).