plants. This garden is set in a mature oak, beech, and maple forest. The Eliot and Linda Paine Rhododendron Discovery Garden, opened in 2013 on 4.5 acres adjoining the Helen S. Layer Rhododendron Garden. The garden offers visitors a chance to learn more about the heath family, Ericaceae, the hybridizers from Northeast Ohio who introduced new rhododendron hybrids to the market, and how to successfully integrate rhododendrons into home landscapes. Leading to the garden is the R. Henry Norweb Tree Allée. The Hedge Collection, within the Display Garden, showcases 27 hedges ranging in size from 2 to 8 ft (0.5 to 2.5 m) in height. Some are evergreen, some deciduous, and some are barrier plants with thorns. The Conifer and Magnolia Collections contain over 135 magnolia plantings, and over 470 conifer plantings that represent pines, spruces, and firs. Other major collections of scientific value but not easily accessible to the casual visitor include Maple, Hawthorn, nut-bearing, and specimen trees (a diverse planting of deciduous trees). Natural areas The majority of land at The Holden Arboretum is maintained in a natural state. Even though it gives the appearance of being untouched, crucial management decisions are always being made to maintain the diversity and health of these areas. The goal of natural areas management is to maintain and ultimately increase species diversity of both flora and fauna. In order to preserve our native habitats, plant community surveys are conducted by Holden staff to inventory the composition of the existing flora. Wise management of unique areas such as Bole Woods, Pierson Creek Valley, Stebbins Gulch, and Little Mountain cannot begin until there is an understanding of the plant communities which comprise these areas. To limit damage, areas such as Stebbins Gulch and Little Mountain can only be accessed by visitors on guided tours. Diseases, pests and human threats have the potential to severely affect our natural areas. In order to reduce their impact these problems need to be monitored and researched. Current critical issues under study include: exploding gypsy moth and deer populations, beech bark disease, and water quality. Research The Holden Arboretum hosts a research program dedicated to ecological research. In 2009, the department received a National Science Foundation grant to examine the role soil organisms play in acquiring limiting nutrients from the soil for forest trees. In 2013, the Holden's research department, in partnership with Kent State University, earned a National