tailieunhanh - Báo cáo lâm nghiệp: "Ecophysiological factors contributing to the distributions of several Quercus species in the intermountain west"

Tuyển tập các báo cáo nghiên cứu về lâm nghiệp được đăng trên tạp chí lâm nghiệp quốc tế, đề tài:"Ecophysiological factors contributing to the distributions of several Quercus species in the intermountain west. | Ann Sci For 1996 53 291-302 Elsevier INRA 291 Short note Ecophysiological factors contributing to the distributions of several Quercus species in the intermountain west JR Ehleringer SL Phillips Department of Biology University of Utah Salt Lake City UT 84112 USA Received 1 March 1995 accepted 1 November 1995 Summary Aspects of the water relations of three oak species Quercus gambelii Q turbinella and Q macrocarpa and their hybrids Q gambelii X turbinella Q gambelii X macrocarpa were observed under common garden conditions in northern Utah USA. In the absence of summer moisture inputs Q macrocarpa and Q turbinella were unable to maintain active gas exchange through the day following an early morning peak leaf conductances to water vapor remained very low through the remainder of the day. In contrast Q gambeliiand the hybrids were able to maintain high leaf conductances throughout this period. Consistent with these observations Q gambelii is thought to have a root system penetrating to the deeper winter-recharged layers a feature apparently absent in both o macrocarpa or o turbinella. Based on current hybrid distributions both Q turbinella and o macrocarpa once extended into drier more northerly regions than they occupy at present. When these parents retreated they left behind hybrids with o gambelii which do not depend on monsoonal moisture input. Leaf size leaf longevity carbon isotope ratio and minimum winter temperatures appear not to be correlated with the absence of Q macrocarpa and Q turbinella from summer-dry habitats. Instead it appears that reliance on summer monsoon events is one of the critical factors influencing loss of these oaks from summer-dry sites in the intermountain west. leaf conductance monsoon I carbon isotope ratio I oak I Quercus Resume Facteurs écophysiologiques contribuant à la distribution de differentes espèces de chênes dans I Ouest américain. Les caractéristiques hydriques de trois espèces de chênes Quer-cus gambelii Q turbinella etQ