Establishment in Treeshelters II: Effect of shelter color on gas exchange and hardiness

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American Society for Horticultural Science

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We investigated the microclimate, gas exchange, and growth of field-grown Norway maple (Acer platanoides L.) and green ash (Fraxinus pennsylvanica Marsh) trees nonsheltered, and in brown and white shelters. Shelter microclimate—air temperature (Ta), vapor pressure deficit (VPD), and radiation—and tree leaf area, growth in diameter, stomatal conductance (gs), and photosynthesis were measured during the first growing season after bare-root transplanting. Bark temperatures in midwinter were also measured. Treeshelter microclimate was greenhouse-like compared to ambient conditions, as shortwave radiation was lower, and midday Ta and relative humidity were higher. Although trees in shelters had greater shoot elongation and higher gs than trees grown without shelters, photosynthesis was not different. White shelters allowed 25% more shortwave radiation penetration and increased Ta by 2 to 4 °C and VPD by 0.5-1 kPa over brown shelters. However, tree growth and gas exchange generally were not affected by shelter color. Winter injury was increased for trees in shelters and varied with species and shelter color. Both species exhibited shoot dieback in shelters the spring following a winter where bark temperatures varied 40 to 50 °C diurnally. More new growth died on maple, particularly in white shelters where several trees were killed. These data suggest that supraoptimal summer and winter temperatures may reduce vigor and interfere with cold tolerance of some species grown in shelters.

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