Sweeney, B.W. and S.J. Czapka. 2004. Forest Ecology and Management 192:361–373.
Although restoration of riparian forests improves water and habitat quality of streams, it can be a slow and difficult process, particularly in landscapes where competition from non-native invasive plants and mammalian herbivores produces high seedling mortality. We experimentally evaluated the short-term (1 year) and long-term (5 years) effects on seedling survival and growth of measures to reduce both herbivory (tree shelters) and plant competition (herbicides, tree mats, and mowing) for five species of deciduous trees in two riparian sites in the coastal plain of eastern Maryland, USA. Study species included: Quercus palustris (pin oak), Quercus rubra (red oak), Quercus alba (white oak), Acer rubrum (red maple), and Liriodendron tulipifera (tulip poplar). Results show that: (1) seedlings protected by tree shelters exhibit on average about 39% higher survival and 300% greater growth after 5 years than seedlings without shelters; (2) tree shelters alter the relative growth relationships among species of seedlings; (3) controlling plant competition may be less important for increasing survival in optimal sites than in marginal sites and more effective when used in conjunction with other measures (e.g. tree shelters) for improving seedling survival and growth; (4) local herbivores preferred certain species of seedlings (tulip poplar and red maple) over others; (5) herbivory can mask the effects of other factors such as site-to-site differences in soil moisture and fertility. Based on these results, we conclude that most prescriptions for restoring a diverse and natural streamside forest need to include a proactive program to enhance the survival and growth of seedlings. This is because local site characteristics (soil moisture and fertility, light and temperature regime, etc.) will not be optimal for all species of seedlings, and herbivores and non-native invasive plants are at, and will continue to be at, historically unprecedented levels. Furthermore, if money and labor are limited, such a plan (especially in the mid-Atlantic region of North America) should give first priority to protecting seedlings from herbivory and assign protection from plant competition a lower priority.
NSF Award No. DEB-0096276. Title: LTREB: Stream ecosystem structure and function within a maturing deciduous forest. Duration: August 1998–July 2003.