Herbicide-free plantations of oaks and ashes along a gradient of open to forested mesic environments

Abstract

This study seeks to assess whether valuable hardwood species, red oak ( Quercus rubra L.), bur oak ( Quercus macrocarpa Michx.), white ash ( Fraxinus americana L.) and red ash ( Fraxinus pennsylvanica Marsh.), could be successfully underplanted in certain early successional vegetation types (alders, poplars, birch) in shelterwood systems, without the use of herbicides to control competing vegetation, as opposed to traditional plantations in abandoned fields. In the Eastern Townships region of southern Québec, six different plantation sites, occurring along a gradient from open to forested mesic environments, were selected for this study: (1) old-field sprayed with herbicide; (2) old-field without herbicide; (3) alder ( Alnus rugosa [Du Roi] Spreng.) stand; (4) aspen ( Populus tremuloides Michx.) stand; (5) red pine ( Pinus resinosa Ait.) plantation; (6) sugar maple (Acer saccharum Marsh.) forest. All of the forested sites were herbicide-free. After eight years of growth, results show that hardwood species can be successfully grown herbicide-free using shelterwood systems in mesic forested environments in southern Québec. Planted trees have shown equal and even greater growth gains in forested sites in comparison with the open environments during the last year of growth. Species showed clear differences in growth response between forested environments. In forested sites, bur oak and both ash species had superior growth gains in the alder stand, while red oak had the highest growth gain in all other forested environments. Maximum height growth gain in forested environments was obtained in the aspen stand by red oak. Deer ( Odocoileus virginianus) browsing has affected oak and ash species differently. Both ash species had unexpected reduced growth in the open environment with herbicide application, where conditions of resource availability are optimal. Although under heavy browsing pressure early on, red oak has had continuous growth gains in open environments. Both ash species and bur oak achieved better growth in the youngest stands (i.e. old-field and alder stand), whereas red oak achieved better growth in a relatively older stand (i.e. aspen stand) in our spectrum of the successional gradient. Past human activity has resulted in the disappearance of much of the hardwood forests in southern Québec. However, the resulting successional stands provide an exceptional management opportunity for the herbicide-free reintroduction of valuable hardwood tree species, using shelterwood cuts and an integrated plantation system.