Light limitation creates patchy distribution of an invasive grass in eastern deciduous forests

  • Cole P
  • Weltzin J
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Abstract

Species interactions and their indirect effects on the availability
and distribution of resources have been considered strong determinants
of community structure in many different ecological systems. In deciduous
forests, the presence of overstory trees and shrubs creates a shifting
mosaic of resources for understory plants, with implications for
their distribution and abundance. Determination of the ultimate resource
constraints on understory vegetation may aid management of these
systems that have become increasingly susceptible to invasions by
non-native plants. Microstegium vimineum (Japanese grass) is an invasive
annual grass that has spread rapidly throughout the understory of
forests across the eastern United States since it was first observed
in Tennessee in 1919. M. vimineum occurs as extensive, dense patches
in the understory of eastern deciduous forests, yet these patches
often exhibit sharp boundaries and distinct gaps in cover. One example
of this distributional pattern was observed relative to the native
midstory tree Asimina triloba (pawpaw), whereby dense M. vimineum
cover stopped abruptly at the drip line of the A. triloba patch and
was absent beneath the A. triloba canopy. We conducted field and
greenhouse experiments to test several hypotheses regarding the causes
of this observed pattern of M. vimineum distribution, including allelopathy,
seed dispersal, light limitations, and soil moisture, texture, and
nutrient content. We concluded that light reduction by the A. triloba
canopy was the environmental constraint that prevented establishment
of M. vimineum beneath this tree. Whereas overstory tree canopy apparently
facilitates the establishment of this shade-tolerant grass, the interaction
of overstory canopy with midstory canopy interferes with M. vimineum
by reducing the availability of sunflecks at the ground layer. It
is likely that other midstory species influence the distribution
and abundance of other herb-layer species, with implications for
management of understory invasive plant species.

Author-supplied keywords

  • Asimina triloba
  • Japanese grass
  • Light
  • Microstegium vimineum
  • Non-native plants
  • Resource limitations
  • Species distribution and abundance

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Authors

  • Patrice G. Cole

  • Jake F. Weltzin

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