TALL UNDERSTOREY VEGETATION AS A FACTOR IN THE POOR DEVELOPMENT OF OAK SEEDLINGS BENEATH MATURE STANDS

Citation
Cg. Lorimer et al., TALL UNDERSTOREY VEGETATION AS A FACTOR IN THE POOR DEVELOPMENT OF OAK SEEDLINGS BENEATH MATURE STANDS, Journal of Ecology, 82(2), 1994, pp. 227-237
Citations number
71
Categorie Soggetti
Ecology
Journal title
ISSN journal
00220477
Volume
82
Issue
2
Year of publication
1994
Pages
227 - 237
Database
ISI
SICI code
0022-0477(1994)82:2<227:TUVAAF>2.0.ZU;2-V
Abstract
1 Replacement of oaks (Quercus spp.) by other species after natural an d human caused disturbance is recognized as a common problem on averag e and productive sites in many parts of eastern North America. Oak see dlings are often numerous beneath mature stands, but seedlings are usu ally too small to compete effectively with tall saplings of other spec ies. Reasons for the poor development of oak seedlings are not well un derstood. 2 An experiment was designed to evaluate the impact of tall and low understorey vegetation on oak seedling development beneath mat ure stands on two sites in southwestern Wisconsin. Understorey stems t aller 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 foli ar herbicide to reduce the density of vegetation shorter than 1.5 m. T he development of planted Quercus rubra and natural Q. rubra and Q. al ba 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 unde rstorey vegetation removed, more than 90% of the planted seedlings sur vived 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/y ear. 5 Results suggest that tall understorey trees of Acer, Ostrya, Ti lia, and other species are a major obstacle to the development of oak seedlings. Disturbances such as fire that reduce this understorey laye r can probably improve the prospects that oak will be self-perpetuatin g, but development of competitive natural oak seedlings is a slow proc ess that may take several decades.