FENCEROWS, EDGES, AND IMPLICATIONS OF CHANGING CONNECTIVITY ILLUSTRATED BY 2 CONTIGUOUS OHIO LANDSCAPES

We evaluated the amounts and implications of changes in habitat connec tivity on rural landscapes by modeling the colonization success and su bsequent habitat colonization of a model edge organism within real lan dscapes. We first inventoried the changes in the fencerow and forest-e dge network of two contiguous Ohio (U.S.A.) landscapes, an agricultura lly dominated tillplain and a more diverse and dynamic moraine landsca pe, from 1940 to 1988. On the moraine the number of fencerows changed little from 1940 to 1971. The number increased by 86 during 1971-1988 as marginal farms were subdivided. The total length of fencerows on th e moraine increased 2.5-fold over 48 years. On the till plain the numb er and total length of fencerows remained relatively constant through the study period. The sum of fencerows and forest edges was used as a measure of total ecotonal edge. On the moraine total edge increased th rough the study period, whereas on the tillplain it decreased. We sele cted two levels of landscape connectivity low and high, to model anima l habitat colonization success. As connectivity increased the earliest successful colonists preempted an increasingly large proportion of th e total suitable habitat and the probability of successful colonizatio n by later-arriving individuals decreased. The changes in connectivity that resulted from changes in both the fencerow, network and the prop ortion of forested land have resulted in contiguous landscapes that pr esent very different colonization potentials to organisms with long-di stance dispersal capability. Given the current uncertainty of the effe cts of corri;dors on species-preservation efforts, we suggest that fur ther modeling of this type prior to field testing will add useful ins ights, especially if conducted using specific species and landscape ty pes.