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Individual study: Early growth of swamp white oak Quercus bicolor seedlings in relation to initial acorn weight and size for seedlings produced by a containerized root production method, Illinois, USA

Published source details

Grossman B.C., Gold M.A. & Dey D.C. (2003) Restoration of hard mast species for wildlife in Missouri using precocious flowering oak in the Missouri River floodplain, USA. Agroforestry Systems, 59, 3-10


In parts of the Lower Missouri River floodplain of central-east USA, natural regeneration of oak Quercus species has been low following major floods. Increased planting of tree seedlings needs therefore to be considered. As a potential way of raising larger numbers of seedlings, an experiment was undertaken to assess early growth of swamp white oak Q.bicolor seedlings in relation to initial acorn weight and size for seedlings produced by a containerized root production method (RPMâ„¢).

A second experiment investigating seedling survival and acorn production over three years after outplanting was also undertaken, comparing RPMâ„¢ swamp white oak seedlings to nursery stock (for a summary please see:

Acorns were collected in autumn 1999 from Q.bicolor trees in Saline County, Illinois. In the normal RPMâ„¢ process, acorns are graded by weight and diameter; only the heaviest and largest are stratified (over the winter). In February, these are germinated in heated greenhouses in mesh-bottomed trays (to allow air pruning of the roots). After the first shoot flush, only the fastest growing seedling (approximately the tallest 50 %) are retained; these are transplanted into increasingly larger containers, before final potting and being placed outside for the remainder of the growing season. Typically seedlings grow to 1.5 m or taller after 210 days and develop dense, fibrous root systems.

For this study, acorns were grown by the RPMâ„¢ method regardless of size and all seedlings were retained regardless of speed of initial shoot growth. This resulted in eight treatments of all combinations of acorn weight (heavy or light), acorn size (large or small) and shoot growth (rapid or not).

At the end of the growing season, root collar diameter, height, root volume, root, shoot and total dry weight and number of shoot flushes were measured.

Acorn size had no discernable impact on first-year root or shoot size or growth (note, values given are approximate as read of graphs in original paper):

i) average root volume - heavy-small = 115; light-small = 142, light-large = 98, heavy-large = 132;

ii) average root dry weight - heavy-small = 47; light-small = 59, light-large = 40, heavy-large = 55);

iii) root collar diameters were similar between groups (range 11.9-13.3 mm);

iv) average seedling height (cm) - heavy-small = 102; light-small = 122, light-large = 97, heavy-large = 115;

v) average seedling dry weight (g) - heavy-small = 47; light-small = 49, light-large = 39, heavy-large = 54;

vi) the number of shoot flushes was similar for all groups (around 5).

These results are not consistent with most similar research which shows that acorn weight is positively correlated with early seedling growth.

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