In natural settings, leaves, bud scales, twigs, fruits, and flakes of bark all accumulate on the ground to form a layer of debris. Encouraging “duff” helps you feed, shelter, and protect wildlife. You can call this wonderful stuff “plant dander” if you like, but naturalists have called it “duff–an adaptation of the Scottish words “dowf,” meaning decay, and “deaf,” describing unproductive soil–for the last 150 years.
Duff is prized for its ability to:
Inhibit plant growth by separating seedlings from the soil or from the sunlight.
Reduce the loss of soil moisture through evaporation by preventing sunlight from directly heating the soil.
Protect the soil by reducing the impact of rain and hail.
Prevent erosion by absorbing and deflecting both runoff water and wind.
Duff is nature’s mulch, although it doesn’t look much like the man – made stuff. In the garden, mulch presents a uniform appearance. It looks tidy, but natural duff appears unkempt, although this impression is deceiving. In fact, for wildlife gardeners, having a bit of duff in the garden is something to aspire to.
Wildlife emphatically prefer duff. Synthetic mulch, despite the convenience it brings to traditional gardens, can be hazardous to wildlife. For instance, some birds pull strips from exposed woven – plastic landscape fabric and then use them as building material. This can lead to them becoming entangled in their own nests; nest failure and death inevitably follow. (Orioles are particularly vulnerable due to their unique style of nest weaving.) In addition, mammals sometimes eat plastic mulches, though we don’t understand why or how; plastic fragments in coyote, fox, and raccoon droppings leave no doubt of this, however. Also, salamanders, toads, frogs, and snakes can become disoriented and trapped beneath plastic sheeting.
Duff, by contrast, figures into wildlife habitat as both food and cover. Duff stores raw materials much like a warehouse does, patiently holding them until they are ready to be processed back into the community. Dead leaves, for instance, contain phosphorus, which is an essential element in the building of plant cell membranes. A dead leaf becomes the food source for recharging the soil with phosphorus, and the soil in turn feeds new plants which become the food source for animals.
Robins scratch aside its leaves to find earthworms; towhees do the same to find crickets. Thrushes search the duff to find snails, and sparrows inspect the cover to find seeds. Each species has adapted to find some portion of its food by scratching through the duff. Grosbeaks and buntings select nesting material from the duff, and ovenbirds nest in it. Frogs and toads prowl here, while shrews hunt and nest and sleep in the duff, as well.
Usually a valuable commodity, duff can turn into a liability in certain situations.
Thick duff can become a fire hazard. Duff which accumulates in an oak forest of the Continental East or a lodgepole pine forest of the Mountain West, can become a fire hazard; we learned this in the 1988 Yellowstone National Park fires. Occasional light fires minimise duff in such places.
Duff can also teach us how to distinguish forests from woodlands. Forests, which are communities where trees grow close enough together that their crowns form canopies, produce expansive and thick duff. Thin and patchy duff characterises woodlands, which are communities where trees grow farther apart in a more scattered placement so that their crowns cannot form canopies. Wildflowers, butterflies, and birds all know these distinctions, and therefore the wildlife gardener should know them, too.
Duff, as a community within a community, serves wildlife whereas mulch serves the gardener. To use synthetic mulch is to take in the wildlife welcome mat; to let duff accumulate naturally in areas is to put that welcome mat back out.
As you clean your yard and garden this fall, think of duff as something to encourage among your shrubs and perennials. If you leave plant debris in place instead of raking the soil bare, your wildlife will thank you for it.