Hydrologic connectivity
and the management of biological reserves: A global perspective.
Abstract: Increasingly, biological reserves throughout the world are
threatened by cumulative alterations in hydrologic connectivity within
the greater landscape. Hydrologic connectivity is used here in an
ecological
sense to refer to water-mediated transfer of matter, energy and/or
organisms
within or between elements of the hydrologic cycle. Obvious human
influences
which alter this property include dams, associated flow regulation,
groundwater
extraction, and water diversion - all of which can result in a cascade
of events in both aquatic and terrestrial ecosystems. Even disturbances
well outside the boundaries of reserves can have profound effects on
the
biological integrity of these 'protected' areas. Factors such as
nutrient
and toxic pollution are perpetuated by hydrologic connectivity and
their
effects can be exacerbated by changes in this property. Hydrological
alterations
are now affecting reserves through increasingly broad feedback loops,
ranging
from overdrawn aquifers to atmospheric deposition and global climate
change.
Such alterations are often beyond the direct control of managers
because
they lie outside reserve boundaries and data on hydrologic connection
between
reserves and surrounding landscapes are scant. The subject of 'water'
has
also been typically excluded from the literature pertaining to both
theoretical
and practical aspects of reserve size, isolation, and design. This
results,
in part, from early management strategies developed when the landscape
matrix outside of reserves was not excessively fragmented and when
awareness
of hydrologic connectivity was in its infancy. The location of a given
reserve within a watershed, relative to regional aquifers wind and
precipitation
patterns, can play a key role in its response to human disturbance
transmitted
through the hydrologic cycle. To illustrate this point, I discuss
reserves
of varying sizes from diverse regions throughout the world. Reserves
located
in middle and lower watersheds often suffer direct hydrologic
alterations
which cause severe habitat modification and exacerbate effects of
pollution.
In contrast, reserves in upper watersheds may have intact physical
habitat
and contain important source populations of some native biota, yet
hydrologic
disturbances in lower watersheds may cause extirpation of migratory
species,
cascading trophic effects, and genetic isolation.
Pringle, C. M. 2001 . Hydrologic connectivity and the management of biological reserves: A global perspective. Ecological Applications 27(4): 981-998.
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