A less restrictive technique for the estimation of understory light under variable weather conditions

Many techniques have been developed to estimate mean available light in forest understories. The standard methods estimate average seasonal PAR by recording it in situ with quantum sensors or through simulation using hemispherical image analysis (HIA). Other techniques have been developed to overcome some of the drawbacks of the standard methods, such as high cost, cumbersome equipment, user bias, and limited replication. The Overcast method allows rapid evaluation of average seasonal PAR in most situations by taking instantaneous measurements, but is restricted by the overcast sky conditions required. The present study proposes a new, less restrictive method (BF2), that uses a sensor array under a hemispherical dome to overcome the sky condition restrictions of the Overcast method, and tests it against the Overcast and HIA techniques. The study also evaluates the method's ability to predict seedling growth and morphology. The BF2 method provided rapid and precise estimations of %PAR under variable sky conditions, as well as good estimations of seedling's responses, and is suitable for multiple site or highly replicated designs. The methods were used under deciduous stands with contrasting structures. (C) 2007 Elsevier B.V. All rights reserved.