Annual tree ring formation and the impacts of cultural practices on citrus tree growth in Costa Rica seasonally dry tropical forests.
Abrams, Marc*,1, 1 Penn State University, University Park, PA, USA
ABSTRACT- Abstract Tree ring scientists have ignored the use of dendrochronological techniques to assess growth impacts of cultural treatments on important horticultural trees in plantations. In this study, we investigated differences in radial growth between orange (Citrus) trees growing in plantations in northern Costa Rica and southern Nicaragua that were either treated or untreated with the fungicide Benlate 50 DF (benomyl), which has potential phytotoxic effects. This region experiences prolonged and severe drought from January through April each year, during which an average of only 10% (about 260mm) of the annual rainfall occurs. Basal cross-sections taken from the citrus trees (a non-native, subtropical species) reveal distinct annual tree rings that closely match the ages of the tree. The rings are reasonable concentric and have good circuit uniformity. An analysis of 111 tree cores indicate that Benlate 50 DF treated trees had significantly slower radial growth during their first six years (averaging 4.54 mm/yr) than untreated trees (averaging 10.76-11.84 mm/yr). After year six, the treated trees had a similar growth rate (11.27 mm/yr) to the untreated trees. Four cores taken from each of ten citrus trees at cardinal directions around the stem reveal that the mean growth rate from any one aspect did not differ significantly from the mean growth per tree. Further analysis of these cores indicates that taking one or two random cores per tree produced a similar average growth calculation. The results of this study suggest that citrus trees produce distinct annual tree rings in a seasonally dry tropical environment, that trees treated with Benlate 50 DF had slower radial growth during their first six years, and that, with proper replication, taking one core per tree is adequate to assess radial growth. The approach in this study could be used to determine growth impacts following chemical application in a variety of horticultural woody plants worldwide.
SPANISH ABSTRACT- .
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