Photo by Steven D. Faccio
Red-backed salamanders like this one
are good indicators of forest health.
Fragmentation of forests is one of the biggest threats facing animal populations in the Northeast. Some forest animals, especially amphibians, are considered to be especially vulnerable to fragmentation because crossing patches of open habitat is often a lethal enterprise. Following fragmentation, animal populations end up being cut off from one another, and if the population in one patch dies out, chances of that territory being re-colonized with individuals from a neighboring patch are slim to none.
But one tiny forest denizen, the red-backed salamander, is found in surprisingly large numbers in fragmented forests. Researchers believe this salamander’s ability to move through open habitats could be helping to offset some of the negative effects of fragmentation. Other animals might also be able to move across fragmented landscapes in a similar manner, but very little is known about how they move because there are so many different kinds of fragmentation and responses to it. An animal that moves through forests with ease might hesitate to cross a field or refuse to cross a road, even if it is physically capable of doing so; or, it might change its behavior and become vulnerable to predation once in unfamiliar territory.
The Northeast is considered to be highly fragmented already. Between old fields, housing developments, forests in several stages of growth, and roads, the region is therefore a prime research area for David Marsh and his colleagues from Washington and Lee University in Virginia for quantifying salamander movements across open fields.
Terrestrial salamanders like the red-backed make great subjects for studying fragmentation because their habitat is restricted to forests, they have small home ranges and limited ability to disperse, and they easily dry out, making traverses of open areas especially difficult.
To find out how open areas affect red-backed salamanders, Marsh and his colleagues first moved salamanders equal distances into open areas and into the forest and compared the time it took both groups to return to the forest/field edge. Then they created artificial shelters of forest-like cover in the field and observed how quickly they were colonized over a year, as well as what size salamanders were colonizing the shelters.
In the first part of their experiment, the researchers found almost no difference in the time it took a salamander to return to the forest/field edge, whether it was released deep in the forest or an equal distance out into the field. However, the farther away from the forest edge salamanders were released, the fewer salamanders returned, suggesting to the scientists that the size (rather than the mere presence) of an opening in the forest might indeed be the most limiting factor in salamander dispersal.
The second part of the experiment revealed that almost all of the artificial forest shelters in the field were colonized by the fall of their first year in existence, mostly by young adult salamanders, though plots closer to the forest edge were colonized first. This suggests that the young adults, like some forest birds, disperse to new areas to find mates without competition from larger, territorial adults.
These experiments give some hope that minor fragmenting elements, like power lines, small house lots, and sparse roads, will not prevent red-backed salamanders from moving between forested areas, though they do emphasize that the larger a break is, the more of an impediment it will be to movement. However, effects of fragmentation on larger, more active animals with large territorial needs or on much more sensitive animals, like water-dependent amphibians, are not necessarily as benign.