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Wisconsin Natural Resources magazine

Wisconsin Natural Resources magazine

Female Norway spruce cones grow upright in early spring, and then tip over to release seeds in the fall. © Stephen L. Lang

December 2007

Coneucopia

Conifers adapt different strategies in the up and down world of seed dispersal.

Anita Carpenter


Female Norway spruce cones grow upright in early spring, and then tip over to release seeds in the fall.

© Stephen L. Lang

From my second story window, I have an intimate view of the Norway spruce which stands majestically tall just outside. This year I've watched blue jays build a stick nest, yellow-bellied sapsuckers drill holes, and migrating warblers, kinglets and ever-present chickadees glean for insects. Gray squirrels frequently scamper along its sturdy branches to nearby rooftops. A gray squirrel with its fluffy tail arched over its back is a common sight dining on a black walnut or shredding a spruce cone. This year I took tree watching to another level: I really focused on the development and maturation of its cones.

My curiosity about cones was piqued by the question: why do spruce tree cones hang down, while fir tree cones stick up? I was aware of these cone differences but the intriguing part of the question was "why." Realizing that the easiest reply for many of nature's questions is "because that's the way it is," I'll offer some observations nonetheless.

Ten groups of conifers grow in the United States: pines, spruces, firs, larches, yews, hemlocks, Douglas firs, junipers, arborvitae and false-cypress. Each group and even individual species within each group have their own characteristic ecology and "lifestyle" including needle structure (shape and length), number of needles per bundle, cones (size, shape and location on tree), pollination strategy, maturation time, seed dispersal, fire dependence and habitat requirements.

Firs differ from the other groups in that their cones sit permanently upright on the upper branches. However, if we look carefully, we find that early in the year, young unpollinated female seed cones of pines and some spruces also sit upright on the upper branches. Is there an advantage to this upright position? Perhaps the cones are more accessible to wind-carried pollen. It would be easier for pollen to settle down on open, upright cones than to somehow find its way up into down-hanging cones. After the pollen has settled in, the cone scales close up and seal, protecting the developing seeds from outside influences. The young cones, which up to this time have been red and small, about the size of red grapes, quickly turn green, begin to elongate and tip over. Do they tip over because of the weight of the cones or the flexibility of the supporting branches or from some other factor? I don't know, but they then hang down and ripen.

Fast forward to the cool of autumn and seed release time. Most cones ripen in the same year they sprouted, but pine cones require two years to mature. It seems as if almost overnight, the cones dry out, turn brown and harden. Recall how conifers seem to be green all summer even though they are heavy with cones because the green cones blend in with the green foliage. Then suddenly the tree tops are noticeably brown. In some years the cone crop is so huge that at first glance you might think something is damaging the trees. A closer look reveals it is just cones turning brown.

Downward-facing cones of spruces and pines can either drop to the ground with seeds inside or can open up while still on the tree and let the seeds fall out. Many species do both, but most cones open while still on the parent tree. Perhaps their seeds carried by winds disperse over a larger area. Sometimes fire is required to open cones. On these species, like jack pines, closed cones may remain on the trees for years.

So how do fir cones that mature in the upright position release their seeds? They could drop their cones but rarely do. Instead, in autumn, scales fall or flake off the mature cones starting at the cone top. As they do, seeds are released and drift to the ground. These disintegrating upright cones are absolute beacons to nuthatches and crossbills that dine on the easily-accessed seeds. When all the cone scales and seeds have fallen off, all that remain on the tree are the center stalks of the once seed-rich cones.

In my Norway spruce, the female seed cones appear in May as tiny red spheres on the tips of the uppermost branches. Male pollen cones are clusters of inch-long, spiral pasta-like strands. Wind disseminates the yellow pollen. Within days of pollination, female cones turn green, begin to elongate and tip over. Eventually they grow to become five-inch long cylindrical cones, hanging heavy on the branches. The cones turn brown in September and almost immediately begin to open, starting at the tip. A few seeds fall from these cones. Most are dispersed when gusty winds tug and shake the tough cones that hold fast to the tree until spring. Examining these fallen cones, I still find seeds tucked inside.

Cone-watching is something everyone can do. It doesn't require a great expenditure of energy but it does require patience. Perhaps from your observations you'll definitely answer the "why" question.

Anita Carpenter notices when the cones tip on walks near her Oshkosh home.