Arboriculture & Urban Forestry 35(6): November 2009 Calvez (1976) observed that single-occasion pruning of oil palm, Elaeis guineensis, to retain 17 youngest leaves signifi- cantly reduced the length of new leaves produced in the ensu- ing months. Plants treated thus took two years to fully recover normal leaf size. Tajudin and Yeoh (1987) measured the length, area, and weight of leaves during experimental pruning treat- ments of oil palm carried out over four years and recorded no changes, except in the third year of the most severe treatment (retaining 24 leaves), in which case new leaves came out signifi- cantly shorter in length. Treatment consisted of selectively re- moving a certain number of leaves from each whorl of the crown. Mendoza et al. (1987) tried one-time pruning of the for- est understory palm Astrocaryum mexicanum at three levels (one-third, two-thirds, and full defoliation) and measured sub- sequent new leaf production and plant survival. Completely- defoliated juvenile and immature palms produced fewer new leaves than controls. Mature specimens experienced a 30% in- crease in leaf production after treatments removing one-third and two-thirds of the oldest leaves. Defoliation was also found to decrease abscission of retained and newly-produced leaves in all age categories except seedlings. Abscission generally de- creased proportionately to increased amounts of pruning, es- pecially where older rather than younger leaves were removed. Oyama and Mendoza (1990) examined the effects of prun- ing on Chamaedorea tepejilote, an understory palm of neotro- pical forests. Leaflets were removed at 25%, 50%, and 100% levels on one occasion only. For a 6-month period following treatment, the rate of new leaf production nearly doubled for male palms defoliated at 25% and 50% and nearly tripled for those defoliated 100%. Size of new leaves was not measured. Endress et al. (2004) studied the effects of leaf harvesting on the small forest palm, Chamaedorea radicalis, and found that pruned palms produced leaves at a slightly faster rate but that the leaves were shorter in length. After two years of treatment, new leaves were so much shorter that 48%, 54%, and 68% reductions in overall foliar yield was recorded for treatments consisting of removal of all mar- ketable leaves once, twice, and four times per year, respectively. Jimenez (2004) found that pruning of pygmy date palm (Phoenix roebelenii) increased production rate but also de- creased the length of new leaves. Pruning of all but the five topmost mature leaves was maintained for nine months. Pruned specimens produced an average of 8.3 new leaves per month compared to 5.4 leaves for those left unpruned. Aver- age length of new leaves was 60.9 cm (24 in) for pruned plants, and 76.7 cm (30.2 in) for controls. Leaf length averages were reported differently in the abstract than in the data charts. EFFECTS ON LEAF NUTRIENT COMPOSITION Canja et al. (2003) carried out pruning of coconut palm from leaf #19 (maintaining 18 youngest leaves in the crown) on fer- tilized specimens over several years and measured changes in foliar nutrient concentrations. Differences between pruned and unpruned palms were insignificant, although percentages of N, P, K, Cl, S, and B were slightly higher in pruned palms while percentages of Ca, Mg, and Na were slightly lower. Tajudin and Yeoh (1987) found that leaf nutrient concentrations of N and K increased with leaf pruning of oil palm, while Mg con- centrations decreased. They pointed out that the higher N and K con- centrations in more heavily-pruned palms may have resulted from 295 these elements becoming more readily available due to decreases in fruit bunch production that also resulted from treatments. Pruning methods consisted of selective leaf removal at all levels of the crown. Palms recycle mobile nutrients such as potassium (K) from old, dying leaves to new, developing ones. In cases where palms are deficient in K or other mobile nutrients, removal of old leaves has been shown to increase deficiency symptoms and accelerate decline of the plant (Hartley 1988; Broschat 1994b). EFFECTS ON STRUCTURAL INTEGRITY OF PLANT Pfalzgraf (2000) wrote, “Research tells us the following: juve- nile leaves are dependent on mature leaves for structural support (Tomlinson 1990)…The individual leaves work well in unison… In removing large portions of mature crown mass, we promote wind failure of juvenile leaves via exposure.” James et al. (2006) demonstrated that the canopy of leaves of the palm Washingto- nia robusta provided some damping of the harmonic sway ef- fect that can potentially lead to stem failure in strong winds. Chan and Duckett (1978) wrote that lower leaves of oil palm gave structural support to the crown through a “bracing ef- fect” in strong winds. They recorded that crown fracture from strong winds only occurred among trees with leaves missing and not among those with a full crown. Calvez (1976) found the highest incidence of weather-induced crown fracture to oc- cur among oil palm specimens with the highest level of pruning. Many arborists and horticulturists believe that reduction of stem/trunk diameter results from too much pruning of palm leaves (Bailey 2002; Bezona 2004; Gabel 2004). Broschat and Meerow (2000, p. 220) wrote, “Overtrimming reduces the food- manufacturing efficiency of the living palm and may result in suboptimum caliper development at the point in the crown where diameter increase is currently taking place.” Although casual observations of this effect are widely reported, no con- trolled studies could be found to have formally tested the theory. EFFECTS ON FRUIT PRODUCTION AND YIELD Since pruning reduces the photosynthetic capacity of plants, reduction in fruit yield may be an indication that a palm is be- ing forced to cope with a dwindling supply of carbohydrates by “cutting back” on production. Farmers have been interested in coconut leaf pruning (CLP) for the purposes of increasing light transmission to undercrops and for harvesting of leaves for thatching and other uses. CLP studies have also been carried out to simulate the effects of leaf-feeding insects on fruit yield. Marar and Padmanabhan (1970) measured the effects of CLP for a period of four years. In one treatment, palms were kept trimmed of their oldest leaves whose accompanying coconut bunches had already been harvested. In the other group, all opened leaves on one side of the tree were removed additionally. No significant change in fruit production was recorded with the first group, but the second group showed a significant decline in average production (45.6 coconuts per year compared to 68.6 before treatment). Another study observed no change in yield after removal of the bottom-most leaves of Cocos nucifera, conducted by Sudhakara et al. (1989), in which 3 to 10 of the oldest leaves were removed during the 5-month dry season of each year over a period of five years. Bailey et al. (1977) recorded major declines in coconut yield due to increased premature fruit shedding following pruning ©2009 International Society of Arboriculture
November 2009
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