Gaining i ground: The American chestnut in a new century Joshua L. Sloan and Douglass F. Jacobs Hardwood Tree Improvement and Regeneration Center Department of Forestry and Natural Resources Purdue University, West Lafayette, Indiana, USA 13 March 2010
Castanea dentata (Marsh.) Borkh. American chestnut Original range over 800,000 km 2 Common on wide variety of sites, mainly on dry mountain ridges Estimated that 1 in 4 trees in portion of Appalachian Range were chestnut!
Dominance in Appalachia
Extremely valuable to economic development in early Appalachia Timber plentiful Durable, rot- resistant wood was highly desired
Nuts valued for human and wildlife consumption Produced good seed crops nearly every year
Introduction and Expression of Chestnut Blight Fungus Introduction ti of the Asian diffuse canker disease, Cryphonectria parasitica, was devastating First discovered in New York City in 1904 Within 40 years, blight had spread throughout range and killed nearly every tree
Breeding for Blight Resistance
http://www.acf.org X Chinese Chestnut (Resistant) American Chestnut (Susceptible) X
American Chestnut Characteristics and Blight Resistance for Each Hybrid Generation in the Breeding Strategy American Degree of resistance (%) character Hybrid None Moderate Resistant (%) generation 50 F1* 0 100 0 75 BC1* 75 25 0 87.5 BC2 75 25 0 93.75 BC3 75 25 0 93.75+ BC3F2 43.75 50 6.25 93.75++ BC3F3 0 0 100 *F1 is the American x Chinese hybrid **BC refers to the backcross back to American
State chapters breeding for local adaptability BC3F3 seed first harvested in 2005 Widespread planting expected within 10-20 years
Ecology and Silvics of American Chestnut t Scientific research has focused nearly exclusively on breeding for resistance Due to early introduction and continued presence of blight, relatively little modern information available concerning ecology or silvics i
Natural Range Dominated upland habitats composed of non-calcareous, ~acidic, moist but well-drained sandy soils (Abrams and Ruffner Ruffner, 1995; Russell, 1987; Stephenson et al., 1991; McEwan et al., 2005) Thought to be ~uncommon in ravines or valleys, but represented 25-40% of basal area in pre-blight stands of sites sampled in riparian i zones (Vandermast and Van Lear, 2002) American chestnut is generalist
Response to Light Strong, positive response to high light (Boring et al., 1981; Griffin, 1989; Latham, 1992; King, 2003) However, has ability to survive for prolonged periods in shade (Paillet Paillet and Rutter, 1989; Latham, 1992; Tindall et al., 2004; McCament and McCarthy, 2005) and respond rapidly following release 2005) (Paillet and Rutter, 1989; Billo, 1998; Paillet, 2002; McEwan et al., 2006) Distinguishes American chestnut from oaks (Paillet Paillet, 2002) and other co-occurring occurring species
Response to Light American A i chestnut t is intermediate t shade tolerant (McCament and McCarthy 2005) or shade tolerant (Wang et al., 2006)
Growth and Competitiveness Reports from early 1900 s suggest American chestnut is highly competitive and fast growing during early growth Recent confirmation, with studies reporting annual diameter growth rates up to 10-1212 mm in plantation or natural stand settings (Paillet and Rutter, 1989; Jacobs and Severeid 2004; McEwan et al., 2006)
Typical American chestnut 8 yr following direct seeding: Over 6 m in height! Jacobs, D.F. and L.R. Severeid. 2004. Dominance of interplanted American chestnut (Castanea dentata) ) in southwestern Wisconsin, USA. Forest Ecology and Management 191:111-120. 120.
Strategies to Guide Restoration ti Plantings Recent recommendations for reforestation, including underplanting (Wang et al., 2006),, or thinning and burning (Wang et al., 2006) (McCament and McCarthy 2005) Limitations in reforestation sites suggests use of afforestation
In 70 yr, 9 planted trees provided sufficient regeneration to spread over 1 km from source For ~0.5 km from source, American chestnut comprised >25% of total canopy basal area and predominated among advanced saplings entering canopy (Paillet and Rutter 1989) Potential for dissemination into adjacent natural forests??
Pending Challenges to Restoration ti Public acceptance and policy issues Hybrid chestnut is not pure American chestnut Resistance to harvesting on public lands may limit potential for reforestation
Pending Challenges to Restoration ti Other exotic insects and pathogens Phytophthora cinnamomi - introduced soilborne oomycete may necessitate site selection and more resistance breeding Oriental gall wasp, Dryocosmus kuriphilus Gypsy moth, Lymantria dispar Ambrosia beetles, Xylosandrus crassiusulus and X. saxeseni
Pending Challenges to Restoration ti Deployment and Genetic Adaptability Scale of restoring nearly 4 million ha representing original American chestnut range (Ellison et al., 2005) Limits in BC3F3 seed quantities and cost Repeated testing needed to verify resistance and phenotype Long-term genetic adaptability and maintenance of genetic variation using ~narrow range of genotypes
Pending Challenges to Restoration ti Deployment and Genetic Adaptability Limiting hybrid chestnut plantings to original American chestnut range Central US may be heavily targeted for plantings, which is inconsistent with mission to restore chestnut to original species range Potential competitive dominance poses ecological considerations for introduction beyond natural range
Conclusions Largest forest restoration effort of its kind soon to be initiated Prioritization must shift toward guidelines for reintroduction based on ecology, management, and policy Recent research providing baseline ecological and silvicultural information, but must be expanded Increased use of hybrid material
Conclusions Continued obstacles: Social acceptance of hybrid chestnut tree Governmental policy limitations Logistics of commercialization and wide-scale dissemination Sustained threat of exotic insects and pathogens Likelihood of hybrid chestnut introduction and spread outside of natural range presents unique ecological uncertainties
Questions?