This picture, taken last fall along the PSE&G right of way that cuts through Hamilton Avenue in Glen Rock, shows what ecologists call a foliar flag. This vine–you know that it’s poison ivy, right?–turns brilliant red in early fall just when its berries ripen. And it doesn’t do it for our aesthetic enjoyment. It does it to advertise to the birds that its berries are ripe–that’s the flag. When the vine’s leaves are green it’s hard to see the plant among the tree leaves, so the vine has to do something special so the birds will eat its berries and scatter its seeds.
Here’s another picture of poison ivy doing its autumn thing taken a few days ago in the Thielke Arboretum.
Poison ivy does not hurt the trees it climbs, and it has especially nutritious berries that are devoured by many, many species of birds. Also, despite its scary name, many people are not allergic to it. Of course we need to remove it from places where children play, but we also need to remember that it plays an important ecological role and leave it along in natural areas. It is native and does not become invasive.
Another native vine that turns gorgeous fall colors is Virginia creeper (Pathenocissus quiniquefolia). Like poison ivy, it has nutritious berries that birds seek out and that ripen in early fall, so it too produces a foliar flag. also like poison ivy, it does not harm the trees or structures it climbs. If you have an ugly brick wall you would like to cover, consider this lovely plant.
Both these vines are very common in our area. They’re easy to tell apart: Virginia creeper has leaves made up of 5 leaflets. Poison ivy has three shiny leaves that are reddish in early spring, bright green in summer, and orange or red in fall.
Gorgeous, aren’t they?