Arboriculture & Urban Forestry 35(6): November 2009 mens, so studies of the effects of pruning on leaf size are of interest. The experimental data summarized above generally show that pruning causes an increase in new leaf production coupled with a decrease in length of new leaves, particularly under more severe pruning treatments. Even though Jimenez (2004) was the only study to apply pruning in a way that com- pares to practices in the ornamental environment, results were still similar in studies using other pruning methods. It appears that palms try to compensate for lost photosynthetic surface area by producing new leaves more quickly, but fewer carbo- hydrates are invested or available to make these leaves as large as they would otherwise be. Trials employing methods identical to those currently used on ornamental palms would be useful. Broschat and Meerow’s (2000) explanation of how the re- moval of green leaves in palms may lead to reduction of stem/ trunk diameter makes logical scientific sense, but experimental data are lacking. Trials must be carried out to show a conclusive link between pruning and stem tapering. Meanwhile, it is clearly observable throughout the island of Oahu, Hawaii that mature co- conut palms frequently experience severe stem tapering follow- ing transplantation, but this could be due to a number of possible stress factors among which severe leaf pruning is only but one. Both Calvez (1976) and Chan and Duckett (1978) observed that severe palm pruning weakens the structural integrity of the crown under the force of storm winds and increases the likelihood of crown fracture. Research and modeling show that trees’ canopies limit the sway and potential failure of their trunks by counterbalancing and dispersing the forces of wind. Although palms have a small relative canopy size, the leaves still function to dampen sway (Tomlinson 1990; James et al. 2006). Ironically, commercial properties and hotels that keep their palms severely pruned often do so at least in part because they are concerned about leaves breaking off in windy conditions. Anyone can walk around after a night of strong winds in Hawaii and see large sections of green palm leaves lying on the ground which have broken off from a fracture point along the rachis. Trials should be carried out to count the number of green leaves with broken or damaged raches after severe weather for palms pruned at various levels com- pared to controls. If pruning were found to have a relation- ship to rachis failure of retained leaves, it could have im- portant implications for public safety and liability concerns. Many studies have looked at how coconut leaf pruning af- fects fruit production and yield. Insofar as fruit production and yield can be seen as indicative of overall health, these studies indicate that routine leaf removal is potentially harmful to the plant. Research in the Philippines suggested that it is neces- sary to retain at least 18 youngest leaves in order to maintain the productivity of coconut palm. Palms in tourist areas and commercial properties in Hawaii and Florida are often not al- lowed to retain that many leaves. On the other hand, removal of inflorescences and fruit bunches should free up more resources for the plant and may thereby offset the negative consequences of leaf pruning, at least to some extent. Studies that are more specifically addressed to ornamental palms must be undertaken. Sudhakara et al.’s (1989) results support Sampson’s (1923) claim that the bottom 6 to 8 leaves are past their prime and of little value to the coconut palm. Workers servicing coco- nut palms on a bi-annual or more frequent basis may be able 297 to remove this number of the very lowest green leaves from a full-headed palm and accomplish the goal of preventing leaf senescence before the next trimming cycle without com- promising tree health. One complicating factor here is that removal of lower leaves could conceivably result in an ac- celerated rate of descent and senescence for retained leaves, even though Mendoza et al. (1987) suggests otherwise. Test- ing this hypothesis would be both simple and worthwhile. Many palm species are planted in areas close to the edge of their range for cold tolerance. Cocos nucifera is native to the deep tropics, and overnight temperatures dur- ing the cool season in both Hawaii and southern Florida can be lower than ideal for the species (Sampson 1923). Con- sidering this, and in light of Broschat and Meerow’s (2000) observation of Sabal palmetto after freezing temperatures in Florida, it may be wise to avoid pruning of Cocos and other tropical species between November and March in these states. Acknowledgments. The author sincerely thanks Hugh Harries (Research Associate, Herbarium, Royal Botanic Gardens, England), Timothy K. Broschat (Professor, University of Florida), Henry Donselman (Palm consultant, California), and Steve Nimz (Consulting arborist, Hawaii) for guidance, assistance, information, and feedback. LITERATURE CITED Aldaba, V.C. 1931. A study of condition of coconut trees in the leaf- miner infested area. Philippine Journal of Agriculture 2:51–65. Aterrado, E.D., and R.G. Abad. 1998. Response of coconut to simulated injury levels caused by leaf-feeding pests. Philippine Journal of Crop Science 23(Supplement 1):39. Bailey, C.C. 2002. Palm pruning: why palms should not be scalped. The Palmateer 9:10–11. Bailey, P., D. O’Sullivan, and C. Perry. 1977. Effect of artificial defolia- tion on coconut yields in Papua, New Guinea. Papua, New Guinea Agricultural Journal 28(2, 3, and 4):39–45. Bezona, N. (2004, June 13). Hurricane season is here—trim those trees. West Hawaii Today. http://www.westhawaiitoday.com/archive/2004/06/13/ LocalNews/233564.html (accessed 8/6/04). Broschat, T.K. 1991. Effects of leaf removal on survival of transplanted sabal palms. Journal of Arboriculture 17(2):32–33. Broschat, T.K. 1994a. Effects of leaf removal, leaf tying, and overhead irrigation on transplanted pygmy date palms. Journal of Arboriculture 20(4):210–213. Broschat, T.K. 1994b. Removing potassium-deficient leaves accelerates rate of decline in Phoenix roebelenii O’brien. HortScience 29(7):823. Broschat, T.K., and A.W. Meerow. 2000. Ornamental Palm Horticulture. University Press of Florida, Gainsville. Calvez, C. 1976. Influences on oil palm yield of pruning at different levels. Oleagineux 1(2):57–58. Canja, L.H., S.S. Magat, and R.Z. Margate. 2003. Long-term coconut leaf pruning (CLP) effects on CBFS: coconut-coffee agroecosystem. C.O.R.D. XIX(2):39–55 Chan, S.K., and J.E. Duckett. 1978. Crown fracture and palm type–initial findings. Planter, Kuala Lumpur 54:142–148. ©2009 International Society of Arboriculture
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