Phenology, cold injury and growth of American chestnut in a Range-Wide provenance test

The primary factor limiting the distribution and growth of American chestnut (Castanea dentata (Marsh.) Borkh.) in eastern North America is tolerance to chestnut blight that is caused by the introduced fungal pathogen Cryphonectria parasitica (Murr.) Barr. However, a better understanding of how genetics and the environment influence American chestnut physiology and growth will also be needed to guide restoration as blight-tolerant growing stock becomes available. Here we describe patterns of phenology, cold injury and radial growth for American chestnut from 13 seed sources that represent three temperature zones (warm, moderate and cold) grown together in a unique provenance test in Vermont, USA. Temperature zones were established using data on the mean minimum winter temperatures over 10–30 years for weather stations nearest seed source locations; these averages were −5 °C and above for the warm temperature zone, −5 to −10 °C for the moderate temperature zone, and below −10 °C for the cold temperature zone. There was a consistent trend for trees from the warm temperature zone to break bud and leaf out earlier, and experience greater spring leaf frost damage and shoot winter injury than trees from other temperature zones. After initial establishment, woody growth (approximately 6 years of ring counts) was robust and tended to be greatest among moderate temperature zone sources and lowest for cold zone sources. Especially for trees from the warm zone, earlier budbreak was associated with greater growth. Foliar frost injury was not associated with altered growth, whereas winter shoot damage was associated with lower growth – especially following significant shoot loss. Even though warm temperature zone sources experienced more winter injury than trees from cold temperature zones, the growth of cold temperature zone sources tended to underperform that for warm and moderate zone sources – this suggests that, at least for the limited time that we evaluated growth, greater protection from the cold may come at the cost of greater growth potential. Although American chestnut is considered to be a relatively drought-tolerant species and growth was assessed during a period of historically high precipitation, higher moisture availability the year before, and occasionally during, the year of ring formation was broadly associated with greater growth across the temperature zones. Despite the negative influences of winter shoot injury on growth, the overall productivity of trees was exceptional, even at the northern edge of the species’ range provided that moisture availability was adequate.