Báo cáo lâm nghiệp: Winter moisture content and frost-crack occurrence in oak trees (Quercus petraea Liebl. and Q. robur L.)

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Báo cáo lâm nghiệp: "Winter moisture content and frost-crack occurrence in oak trees (Quercus petraea Liebl. and Q. robur L.)"Winter moisture content and frost-crack occurrencein oak trees (Quercus petraea Liebl. and Q. robur L.)B. Cinotti Nancy, France la Qualite des Bois, INRA-CRF,Station de Recherches sur of differences in counteract the possible effectsIntroduction chosen. soil, were An increment borer was used to take diame-Our research investigates the relations tral cores in an approximate north-south direc- tion. Cores were then kept in plastic tubesbetween the frost-crack occurrence in whose diameters were just sufficient for theoaks and some physical and anatomical core to enter. This prevented water loss fromparameters of solid wood. The starting the cores.point of our interest in water in trees is the In the laboratory, the increment core of eachobservation that frost-cracks occur with a tree was divided into 6 pieces: central heart-higher frequency in trees growing on soils wood (rings from pith to the 15th), external heartwood (rings from the 16th ring up to thewith high winter moisture content (Schirp, and sapwood from sapwood-heartwood limit)1968). Also, severe stem contractions with both the northern and southern sides of thefreezing winter temperatures (greater than bole. Each piece was immediately weighedthose arising from summer droughts, but while wet and than dried in an oven at 103°Cequally dependent upon the moisture for at least one day. A second weighing gave the dry weight and, by subtraction, the initialcontent) have been commonly observed water weight. Moisture content (water weight(Hinckley et al., 1978). In this paper, we divided by the weight of dry wood) is expressedreport our observations of winter moisture percentage. as acontent variation in oak trees, using non-destructive sampling by increment cores,and relate it to frost-crack occurrence. Results Table I illustrates the variability of resultsMaterials and Methods from one forest to the other (even on cores bored at proximate dates), and forIncrement cores were taken from 90 oak trees the same plot and on the same trees fromfrom 3 different forests in central and eastern one month to the next. However, the fol-France. Paired trees of similar diameter, as in lowing general observations could beour previous study (Cinotti, 1987), one frost- content in oak made: 1) winter moisturecracked and one sound in close proximity totree boles is from 60% to total Discussion saturation,i.e., in the range where wood freezing more or less frost-expansion counteracts and KObler, 1968;shrinkage (Schirp Our results correspond to those of MillerKubler, 1983; Cinotti and Tahani, 1988); 2) (1987), which underlined the importancethe sapwood moisture content is always of site conditions on frost-crack spatialhigher than or equal to that of the middle distribution. Such differences could beheartwood, as was previously noted by site effect (either a climatic or seen as aHinckley et aL (1978). edaphic one). Roosen (1956), while an Table II shows that frost-cracked trees studying the winter water status ofalways have a moisture content signifi- poplars, stated that the environment wascantly higher than that of sound trees and likely to influence tree moisture content: the more water in the soil, the higher thethat north-south differences are only signi- moisture content. In our Bellary plot, forficant for Q. petraea Liebl.example, differences in the moisture Since a study of frost-shrinkage of small oakwood samples has shown that tangen-contents between sapwood, middle andcentral heartwoods and between north tial shrinkage (the main explanation ofand south are no longer significant in frost-crack formation) depends mostlyMarch; perhaps this is an effect of the upon moisture content exceeding aspring ascendant flow of sap which modi- thres ...