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Edge-mediated succession and drought response in a plant community
Elise M. Tulloss and Scott J. Meiners
Department of Biological Sciences, Eastern Illinois University
Introduction
Edges are important in determining community structure but their
impact on community dynamics is relatively unknown. Edges can mediate
succession by buffering communities on either side through changes in climatic
factors across edges. We examined patterns of vegetation dynamics along an
edge gradient in 1996 and 2001, a time period that included a severe drought in
1999.
Objectives
Determine possible vegetation patterns across an edge in response
to succession and a severe drought.
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Methods |
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Study Site: Hutcheson Memorial Forest, New Jersey. A grid was
stretched across the forest-field edge and divided into 1m2
plots. The site consisted of a mid-successional system with a
young forest and fourteen-year-old field. |
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Sampling:
Ten transects run across the forest edge with plots placed at ten
meter intervals from the edge. Each transect went
thirty meters into the forest and sixty meters into the field
(Figure 1).
Percent ground cover of each understory plant species was recorded
in each plot. |
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Figure 1. Sample area transects. |
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Analysis: Measures of community and
population level attributes were analyzed with regression and ANOVA
to determine possible edge-mediated succession and drought response
patterns. |
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Results
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Cover,
diversity, richness and evenness were lowest in the forest, higher
at the edge and highest in the field (Figures
2,
3, 4 and
5). The pattern was consistent
between years.
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Figures 2, 3, 4 and 5. Cover, diversity, richness and
evenness across the sample area, respectively. |
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Grasses (Figure 6) and exotic species
(Figure 7) showed an increase in
cover in the field between 1996 and 2001. This indicated an
unexpected pattern of successional reversal. Some of the
species that greatly increased in cover in the field included
Achillea millefolium, Agrostis hymenalis, Hieracium
pratense and Bromus racemosus. |
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Figure 6. Grass cover across the sample area. |
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Figure 7. Exotic cover change across the sample
area. |
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Species turnover
(Figure 8)
increased from the forest to the field from 1996 to 2001, showing an
increasing replacement in the field following the drought. |
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Figure 8. Species turnover in the sample area. |
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Conclusions
The pattern of successional reversal in grasses was likely due to
effects of the 1999 drought. Drought would have created many gaps that would
have been filled by early successional species such as grasses. This was
especially important in the field where open conditions are more at risk from
drought than the forest interior.
The increase in species turnover with distance from the edge reflects increasing
replacement by grass species in the field following drought.
Increasing cover of exotic species in the field suggests area returned to an
earlier stage of old field succession following the drought.
Results suggest that the observed pattern is more related to the drought than to
the process of succession. Edges serve primarily as buffers from drought
stress. Areas further from the edge experienced greater community change.
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