Response of two field-grown maple (Acer) species to reduced irrigation in a high vapor pressure, semi-arid climate

Urban forests provide many benefits for those living and working in urban areas. However, urban trees face many challenges (e.g., poor soil, drought, high vapor pressure deficits). Therefore, finding tree species adapted to urban climates is essential to maintain a healthy urban forest. In a semi-arid climate, field-grown 'Autumn Blaze' (Acer × freemanii 'Autumn Blaze') and shantung (A. truncatum) maple trees were subjected to three reference evapotranspiration (ETo) based irrigation regimes (100%, 66%, and 33% ETo) over a three-year establishment period (2003-2005). During this time, weather data, tree water relations, gas exchange, and growth data were measured. Growing-season maximum air temperature was 40.1°C, and maximum vapor pressure deficit was 6.8 kPa. Pre-dawn leaf water potential was more negative for 'Autumn Blaze' trees, and trees receiving the least amount of irrigation. However, midday stomatal conductance was similar for trees receiving 100% and 66% ETo based irrigation regimes. In addition, stomatal conductance was greatest for 'Autumn Blaze' trees. Growth data were influenced by species and irrigation regime. However, despite differing irrigation volumes, greatest growth was not necessarily associated with trees receiving the greatest irrigation volume. Regardless of irrigation volume, these maple species maintained adequate growth and appearance when grown in an adverse, semiarid climate. Despite reduced irrigation, each species appears to be adapted to harsh climates associated with urban environments.