SUCCESSION Introduction by John Buck, Civil and Environmental Consultant   Illustration by James F. Thorne. Succession [L. Succedere, to follow after] is the orderly change in species composition in an area after a disturbance (often natural but sometimes human-caused as in the case of Nine Mile Run) which results in a more or less constant group of species that constitutes the climax community.   Changes that occur during succession: Soil building. Changes in the physical environment (light, moisture). New species of plants displace existing plants because their seedlings are more able to become established in the changed environment than the seedlings of existing species. Eventually a climax community that is more or less stable will become established and have the ability to reproduce itself. Disturbances will start the process of succession again. Rate and "success" of succession Presence of soil (an issue on slag): Primary succession starts with little or no soil present. Secondary succession starts after a disturbance of a previously vegetated area where the soil is left intact (or with the addition of soil amendments). Ability to retain water (an issue on slag): Depends on disturbed soil quantities. Increases with buildup of decaying vegetative matter. Can be amended with super-absorbents and organics. Mineral availability (an issue on slag): Depends on disturbed soil qualities. Can be amended with minerals and organics. Suitability of plants for the soil and environment: From existing underground plant roots. Existing seeds left in the soil and seeds of nearby plants. Existing Succession of Shrubs and Young Forest on Slag Slope on Nine Mile Run Trees Box-elder (Acer negundo) native Tree-of-heaven (Ailanthus altissima) introduced Catalpa (Catalpa sp.) introduced Ash (Fraxinus sp.) native White Mulberry (Morus alba) introduced and invasive Red Mulberry (Morus rubra) native Large-toothed aspen (Populus grandidentata) native Quaking aspen (Populus tremuloides) native Balm-of-Gilead (Populus balsamifera) introduced Sycamore (Platanus occidentalis) native Staghorn Sumac (Rhus typhina) native Black Locust (Robinia pseudoacacia) native Elms (Ulmus sp.) native Shrubs Butterfly Bush (Buddleja) introduced Forsythia introduced Wild Hydrangea (Hydrangea arborescens) native Privet (Ligustrum vulgare) invasive Honeysuckle family (Lonicera sp.) mostly introduced European Buckthorn (Rhamnus cathartica) introduced. Bristly Locust (Robinia hispida) introduced Annuals and Perennials Boneset (Eupatorium sp.) native Foxtail Barley (Hordeum jubatum) Butter-and-Eggs (Linaria vulgaris) introduced Sweet Clover (Melilotus sp.) introduced Japanese Knotweed (Polygonum cuspidatum) invasive Bouncing Bet (Saponaria officinalis) introduced Goldenrod (Solidago sp.) native Poison Ivy (Toxicodendron radicans) native Common Mullein (Verbascum thapsus) introduced Vines Japanese Honeysuckle (Lonicera japonica) invasive Virginia Creeper (Parthenocissus quinquefolia) native Multiflora Rose (Rosa multiflora) invasive Blackberry (Rubus allegheniensis) native Raspberry (Rubus occidentalis) native Grapes (Vitis sp.) some native but invasive There are many aspens (Populus sp.) on the slag heaps. Photo by Bob Bingham   Species of introduced honeysuckle (Lonicera spp.) are common at Nine Mile Run.   Staghorn sumac (Rhus typhina) typically grows along roads and in orld fields, habitats similar to the slag at Nine Mile Run.   The tree-of-heaven (Ailanthus altissima) is a common weedy tree in urban areas.   Black locust (Robinia pseudoacacia) commonly grows on slopes along Pennsylvania roads and in similar habitats at Nine Mile Run.