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Tall Understorey Vegetation as a Factor in the Poor Development of Oak Seedlings Beneath Mature Stands
Craig G. Lorimer, Jonathan W. Chapman and William D. Lambert
Journal of Ecology
Vol. 82, No. 2 (Jun., 1994), pp. 227-237
Published by: British Ecological Society
Stable URL: http://www.jstor.org/stable/2261291
Page Count: 11
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1 Replacement of oaks (Quercus spp.) by other species after natural and human-caused disturbance is recognized as a common problem on average and productive sites in many parts of eastern North America. Oak seedlings are often numerous beneath mature stands, but seedlings are usually too small to compete effectively with tall saplings of other species. Reasons for the poor development of oak seedlings are not well understood. 2 An experiment was designed to evaluate the impact of tall and low understorey vegetation on oak seedling development beneath mature stands on two sites in south-western Wisconsin. Understorey stems taller than 1.5 m and scattered small canopy trees were removed on half of the main plots, with the other plots retained as controls. Half of the nested subplots within each main plot were also sprayed with foliar herbicide to reduce the density of vegetation shorter than 1.5 m. The development of planted Quercus rubra and natural Q. rubra and Q. alba seedlings was monitored for 5 years. 3 On undisturbed control plots, more than 70% of the planted oak seedlings died within 5 years, and survivors showed a net decrease in height. On plots with the tall understorey vegetation removed, more than 90% of the planted seedlings survived and average total height increased 50-96%. 4 Understorey removal plots had 10-140 times as many natural oak seedlings after 5 years as undisturbed plots. Height growth of natural oak seedlings under heavy partial shade (87% crown cover) was slow, however, averaging 4-6 cm/year. 5 Results suggest that tall understorey trees of Acer, Ostrya, Tilia, and other species are a major obstacle to the development of oak seedlings. Disturbances such as fire that reduce this understorey layer can probably improve the prospects that oak will be self-perpetuating, but development of competitive natural oak seedlings is a slow process that may take several decades.
Journal of Ecology © 1994 British Ecological Society