There are upland forests scattered throughout the Upper and Lower Arb. All of these forests have been disturbed to some degree, and many are only a few decades old. During the early 20th century, the area of forest in the Arb was much less than today (see inset map). The most mature upland forest is Best Woods (K17) and the oldest upland forest restoration is Stork Forest (G4). Until recent changes in land use, the upland forests were highly fragmented and shaped in such a way that they were plagued by edge effects. The highest priorities for upland forest management have been to increase total forest area and to decrease the amount of edge habitat, thereby producing habitat for interior forest plants and animals.
A large block of upland forest is taking shape in the northeast portion of the Lower Arb, and eventually, there will be about 180 acres (73 hectares) of contiguous forest in that area alone. There will be an additional area of at least 50 acres (20 hectares) of upland forest in the southeast corner of the Upper Arb. Some of these forests will grow by means of natural colonization of abandoned agricultural fields by trees. However, the forest-building process can be significantly accelerated by hand planting of tree seedlings, and this is being done in select areas. Only offspring of trees from the local area are planted in the Arb, to maintain genetic similarity to nearby forests. In the Upper Arb, forest planting has been concentrated in the Alumni Field (H3-4, I3-4). This field was removed from agriculture in 1986, and trees have been planted here over several years starting in 1990. Alumni volunteers have done substantial amounts of the tree planting here. Many thousands of trees have been planted in old fields in the Lower Arb as well.
Trees planted into old fields suffer very high mortality without some further intervention. Competition with other plants, especially grasses, can be intense; this is prevented by placing black mats around the small trees to prevent growth of potential competitors. Browsing by deer (Odocoileus virginiana) and rodents (especially voles, Microtus spp.) can kill young trees, and some are now being protected by “sleeving” with plastic tubes until the trees are large enough to resist herbivores.