Abstract
Tree productivity can be directly related to light interception by the canopy. To determine the effects of defoliation during mechanical harvesting on canopy light interception, we measured midday interception of direct light with a 16.3 m2 point grid system and of photosynthetically active radiation (PAR) with a ceptometer in mature 'Hamlin' and 'Valencia' sweet orange trees (Citrus sinensis). Light interception measurements were made near solar noon on trees before and after hand harvesting or trunk shaking harvesting with a lineartype trunk shaker in 2005 and 2006. Leaves removed during harvest were collected to estimate percentage defoliation. Canopy volume and leaf area the following year were estimated. Before harvest, well-developed citrus tree canopies intercepted 80% of the direct light and >88% of PAR per projected area of canopy. Although excessive trunk shaking can remove up to 15% of the leaf area compared to 2% by hand harvesting (Li et al., 2005), little change in canopy leaf area index (LAI) or midday light interception occurred after harvest using the trunk shaker. Canopy volume and total leaf area the following year were not correlated to previous harvest methods.
