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Impacts of Invasive Shrubs

by Aimee Kemp

Winter 2010

Invasive species are transforming native ecosystems all over the world. In the northeast, the invasive shrub Japanese barberry (Berberis thunbergii) has spread from gardens into native forest ecosystems. Last summer, I looked at how both barberry and exotic earthworms are affecting salamander populations and leaf litter communities in deciduous forests.  I worked in the Forest under the guidance of Dr. Matthew Palmer in Columbia’s Department of Ecology, Evolution, and Environmental Biology. 

Salamanders are key components of forest ecosystems.  They are top-down regulators of arthropod and other leaf litter invertebrate populations and provide food for predators such as birds, snakes, raccoons, and bears. Declines in  salamander populations could have dramatic effects on native forest food webs. 

I compared sites dominated by native vegetation with sites dominated by barberry. I measured an array of environmental factors including soil pH, soil depth, soil organic content, and leaf litter depth. I measured arthropod abundance and diversity in leaf litter samples. I estimated earthworm abundance by pouring a dilute solution of dissolved mustard over a small patch of soil, which caused the earthworms to wriggle to the surface where I could count them.  I collected data on salamander abundance using a photographic record to identify individuals, measuring, photographing, and releasing them. Salamander searches took place after rain, when they are most active.

My results showed that barberry-dominated sites had higher soil pH, thinner leaf litter layers, shallower soils, and less organic content than sites dominated by native vegetation.  Barberry sites also had significantly lower abundances of salamanders, arthropods, and earthworms. 

I found 85 individual salamanders: 64 in sites dominated by native vegetation and 21 in sites dominated by barberry. The most frequently found species, the eastern red-back salamander (Plethodon cinereus), accounted for 54% of the total.  Red-back salamanders found in barberry sites were significantly smaller (average 18.9 mm) than those found in native sites (average 38.9 mm).

My results help us understand how invasives like Japanese barberry are affecting native ecosystems.  Getting a better sense of their extensive impacts  highlights the need to implement management plans. In slowing, or perhaps even stopping, the spread of barberry and other invasives, we will be better positioned to preserve native biodiversity in Black Rock Forest and the rest of the northeast.

Aimee Kemp is a senior majoring in environmental biology at Columbia.