Shelters Affect Tree Seedling Establishment Under Grass Competition

We investigated growth and water relations of tree seedlings grown in treeshelters surrounded by competing grass. Treeshelters were placed over one-year-old gambel oak (Quercus gambellii) and bigtooth maple (Acer grandidentatum) planted in field soil, and crested wheatgrass {Agrypyron cristatum x A. repens) was planted around half of the trees. Trees were irrigated only the first year. Surviving plants were counted over two years, and above-ground growth, root growth, and leaf water potential were measured the second year. Without shelters, all maples and most oaks under grass competition died within two years, while about half or more of those in shelters survived. Sheltered trees with competition had more height growth, and thus were able to extend foliage above the competing grass, and were under less water stress. Without competition, maple outgrew oak both above and below ground, but sheltered maple grew less than unsheltered maple, while the reverse was true for oak. Shelters reduced water stress in both species across all treatments. Shelters have the potential to increase seedling survival and growth when herbaceous competition is present, and increase drought tolerance, but the response will depend on the species.