20-3 An Emerald Lining: the Potential of Dead Ash Trees to Supply Large Woody Debris in Riparian Corridors

Abstract:

Rivers are dynamic, interconnected systems that respond to driving forces inside and outside their watersheds. This study examines the potential effects of an invasive insect species, the emerald ash borer Agrilus planipennis, on river morphology by surveying the composition of dead trees in river corridors in New Jersey. The emerald ash borer is an invasive beetle in North America that is particularly adept at killing the deciduous ash tree. While this destruction of trees can have profound impacts on forest ecosystems and biodiversity, it is hypothesized that it may create a significant future supply of large woody debris if a large proportion of dead and dying ash trees are located near rivers. Large woody debris is an important component of river morphology, and is often lacking in modern streams in Eastern North America due to historic deforestation. Ash trees (including the black, white, and green species) are a common component of northern New Jersey forests, and can often occur in alluvial soils. However, the composition of dead trees in river corridors is unknown, so eight rivers across northern New Jersey were surveyed to determine the frequency and characterization of the dead trees in these areas. Tree height, breast height diameter, location, and genus (especially ash or not) were recorded for over 150 trees. Additionally, river bankfull width was measured to determine the relative height of the tree compared to the stream width. While ash trees only represent 5% or less of the trees in New Jersey, over 50% of the dead trees in or near rivers were ash. A large majority (~80%) of the dead trees were taller than bankfull width, suggesting their ability to become large woody debris once falling. Also, the majority of all dead trees were still standing (as opposed to falling or leaning) and represent a potential future supply of large woody debris to rivers. Future studies include monitoring the status of these trees to determine how many of them become large woody debris.

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