Inter- and intra-specific competitiveness of plantation-grown American chestnut (Castanea dentata).

摘要

The introduction of the fungal pathogen Cryphonectria parasitica (Murr.) Barr. decimated American chestnut (Castanea dentata (Marsh.) Borkh.) throughout its native range in North America. A blight-resistant backcross hybrid form of American chestnut has been developed, and these backcross trees are likely to be incorporated into restoration programs in the near future. To help guide future afforestation efforts, this study examined juvenile (five growing seasons) morphological and physiological competitive aspects of American chestnut grown in a plantation setting with northern red oak (Quercus rubra L.) and black cherry (Prunus serotina Ehrh.) in Indiana, USA. Species were grown in seven possible species combinations including both monospecific and polyspecific combinations at three densities (1x1 m, 2x2 m, and 3x3 m). Despite an initial advantage in height, American chestnut exhibited the lowest relative height growth in the 2x2 and 3x3 m spacings, resulting in less total height compared to the other two species 5 years after planting. Relative height growth, as well as final absolute heights, were comparable among species in the 1x1 m spacing. Black cherry exhibited 2-3 times greater relative ground-line diameter (GLD) growth compared to oak and chestnut at all spacings. Linear regressions showed that growth was generally proportional to net photosynthesis (A) for all species. Increases in A likely resulted from increases in leaf nitrogen concentration. Chestnut exhibited lower A than cherry and oak in years 2 and 3, but no differences occurred in year 4. Additionally, chestnut had significantly higher predawn leaf water potential (leaf Psi _pd) in year 4, reflecting greater drought stress in cherry and oak. While black cherry grew most aggressively, northern red oak and American chestnut performed acceptably, with high survival rates and moderate growth, especially in the 1x1 m spacing. American chestnut had the poorest stem form overall, but fared better in the 1x1 m spacing where the crown competition factor (CCF) was highest. Hence, an intermediate spacing between 1x1 and 2x2 m could optimize chestnut's growth and stem form. Mixture effects may be attributed mainly to individual species growth characteristics rather than inter-specific interactions during this juvenile developmental stage.