Tölgyesi Cs, M Zalatnai, L Erdős et al: Unexpected ecotone dynamics of a sand dune vegetation complex... (2016)

Tölgyesi Cs., Zalatnai M., Erdős L., Bátori Z., Hupp N., Körmöczi L.
2016
Unexpected ecotone dynamics of a sand dune vegetation complex following water table decline.
Journal of Plant Ecology 9: pp. 40–50.
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Aims
Central Hungarian inland dune ranges harbor heterogeneous grassland
vegetation with an extensive network of ecotones, arranged
perpendicular to topography-driven hydrologic gradients. The area
suffers from severe aridification due to climate change and local
anthropogenic factors, which have led to a dramatic decline of the
water table. As a result, groundwater is no longer reachable for lowlying
plant communities; thus, we expect they are bound to undergo
profound changes. This study investigates how the plant communities
respond to this changing environment over time by monitoring ecotones,
since they are frequently the hotspots of ecosystem change. We
monitored five ecotones along permanent belt transects for 15 years
to characterize their dynamic response, and to identify the internal
structural changes of the plant communities the ecotones delimit.
Methods
Ecotones were delineated with the split moving window technique.
The dynamics of two ecotone parameters, location and contrast,
were analyzed with linear regression models incorporating two
independent variables: study year as a measure of time since the
loss of groundwater, and precipitation as a possible driver of interannual
variations. The internal changes of the patches separated by
the ecotones were analyzed using plant functional groups.
Important Findings
Precipitation had no detectable effect on the ecotone descriptors,
but study year influenced ecotones in an unusual fashion.
The position of the ecotones appeared to be very stable in time;
their dynamics are stationary, not directional as we predicted.
The contrasts had clear tendencies; two ecotones disappeared,
one new one was formed and two ecotones showed no trend.
The internal changes of the patches over time were dramatic,
showing a shift toward more xeric and more open plant assemblages
in most stretches of the transects. Thus, the dynamic
response of the vegetation was not patch expansion vs. shrinking,
but fusion vs. division, which profoundly restructured the
vegetation pattern. Analysis of plant functional groups revealed
that the trends of the ecotone contrasts could be traced back to
internal changes of the patches and not to processes within ecotones.
Hence, in situations where stationary ecotone dynamics
prevail, ecotone position may be a poor indicator of the effects
of strong directional environmental changes. However, in this
study we show that ecotone contrast can serve as a sensitive tool
for monitoring landscape pattern transformations in these cases.
Also, this highlights the long-term nature of ecotone responses,
which can have implications in landscape planning and restoration
measures.