The Distinctive Features of Conifers

By Mary Jane Busch, PA Forest Steward, Class of '22

I have needles, but no thread.
I have cones, but no ice cream.
I have bark, but no bite.
What am I?

Botanists classify trees into two groups—gymnosperms and angiosperms. The angiosperms are known as flowering plants and produce seeds enclosed in a fruit. Gymnosperms have no flowers and bear naked seeds.

Gymnosperms include four main phyla: conifers, cycads, gnetophytes, and gingko biloba. The latter used to be considered a conifer and has only recently been classified in its own group. In general, conifers are referred to as softwoods and angiosperms as hardwoods.

Conifers are the most abundant gymnosperms and include familiar species such as pines, firs, hemlocks, cedars, spruces, and junipers. Some, like the coastal redwoods, tower over 300 feet. Others, like blue-rug junipers, are prostrate shrubs. These softwoods sport many colors—red, bronze, yellow, blue, green—which are influenced by the changing temperatures of the seasons.

Not all conifers are evergreen, and not all evergreens are conifers. Of the 71 coniferous genera, 65 are referred to as evergreens because they do not lose their leaves (needles) in the fall.

Since wholesale, annual replacement of needles is a significant energy cost to a tree, deciduous conifers have adapted to this loss by reabsorbing nutrients before jettisoning their foliage. In Pennsylvania, native conifers which drop all of their leaves each autumn include the American larch (aka tamarack) and the bald cypress. Nonnative deciduous conifers that can be found in Pennsylvania include the European larch, the Japanese larch, and the dawn redwood, a species which was first identified in fossil records before being discovered in an isolated area in China.

In autumn, the Japanese larch turns from green to brilliant golden-yellow before dropping its needles. Credit: Mary Jane Busch

When it comes to needle replacement, all evergreens shed some of their older leaves annually. White pines replace all of their needles every two growing seasons, whereas bristlecone pines retain their needles for as long as 50 years. The longevity of needles depends on the species and the environmental conditions where the tree is rooted. Trees growing in stressful habitats retain needles longer than trees living in areas with abundant resources.

Shed needles decompose at variable rates from six weeks to seven years, determined by environmental conditions, particularly moisture. The slow rotting of needles is due to their resins and waxy cuticles, both natural protectants against microbial attack. Although the acidity of fresh needles ranges from 3.2-3.8 pH, microbial activity neutralizes the material. Conifers naturally flourish in low pH soils, but it is a myth that needles acidify soil. Instead of acidic allelopathic effects from fallen foliage, the sparse vegetation beneath conifers is better attributed to the tree’s year-round shading, shallow roots, and the long-lasting, thick duff layer on the forest floor.

Conifers monopolize the northern latitudes and higher altitudes of drier and colder climates. Surviving and excelling in dehydrating winters and freezing environments is possible because of five factors:

1. a waxy coating on the needles,
2. the tight closure of the stomata (openings in the needles) to reduce transpiration (water loss),
3. location of stomata in pits or grooves below the leaf surface,
4. fewer stomata in needles compared to deciduous leaves, and
5. the "antifreeze" effect of cryoprotectants which lowers the freezing point of water, protecting the cells from rupturing without inhibiting metabolism.

Larches are the most cold-tolerant of all trees. A few conifers can be found in temperate and tropical ecosystems, including shrublands, savannas, and swamps.

Evergreens have a photosynthesizing advantage over broad-leaved trees. Not only can needled trees turn on and off their food-making capacity during warmer winter spells (temperatures above 45ºF), but they can also begin photosynthesizing earlier than deciduous trees because cellular structure and nutrients are already present. Because of these physiological advantages, conifers are the climax forest type of the taiga (also known as the boreal forest). Located between 50º and 60º north latitude, the taiga is the largest terrestrial biome.

The all-weather, cold-hardy, needled cloak of conifers provides a winter oasis for fauna. Conifer branches that retain a coating of snow keep the forest floor clearer of snow, reduce wind chill, and create an insulated ceiling. These patches of evergreens are crucial habitat for nonmigrating birds. In winter, deer seek refuge in these havens which have been dubbed "deer yards."

Most conifers are monoecious—each tree bears both male and female cones. Since pollination is by wind, and to prevent self-pollination, the male cones are usually located on the lower branches of the tree. Male cones are short-lived, soft, spongy, and smaller than the familiar, woody, female cones. A few conifers such as yews and junipers (typically) are dioecious—male cones and female cones are borne on separate trees—and only the trees with female cones will bear fruit.

An interesting deviation of the familiar woody cone is the blue berry of the Eastern red cedar (aka red cedar, Eastern juniper, red juniper). These berries (a misnomer) are modified cones and edible. The deciduous bald cypress also produces an odd-looking cone—a roughly 1-inch, wrinkled ball.

From left to right: Japanese larch cones are about 1-1.5 inches long with distinctive outward-curved scales; the Eastern red cedar's berries can be used in small quantities as a spice or in teas; bald cypress seed balls are a vital food source for wildlife, including squirrels, turkeys, and water birds. Credit: Mary Jane Busch

In pines, and in many other cone-bearers, it can take several years for the seeds to mature. The cones can remain on the tree for up to 10 years, and a tree can have different ages of cones on its branches. Because pines are the largest group of conifers, all cones are commonly referred to as pine cones; however, it is more correct to refer to other species’ cones as spruce cones, hemlock cones, fir cones, etc.

Cones are species-specific and vary in size, shape, color, and texture. The protective encasement closes its scales to shield the seeds from water, cold temperatures, and animal consumption. They open when the weather is conducive to seed dispersal and germination. In some conifers, seeds are protected from animal consumption by resins and spines.

In various species of pine, spruce, cypress, and sequoia, resin seals the seeds in their protective enclosures. These serotinous cones require a hot fire to melt the sealant. In Pennsylvania, the Table Mountain pine of dry, rocky, middle-southern regions requires fire or high temperatures for the release of its seeds.

Pine seeds (aka pine nuts) are an important food source for squirrels, chipmunks, mice, rats, raccoons, woodpeckers, crossbills, turkeys, finches, chickadees, nuthatches, and quail. Deer eat the seed-laden cones only when other preferred food is unavailable. Red squirrels usually cache whole pine cones in piles of vegetative debris. This cool, dark, moist pantry with its low oxygen environment keeps the seeds viable but dormant. There can be up to 14,000 pine cones in one storehouse!

Most pine seeds are winged and dispersed by wind. The winged nuts are called samaras and look like ash seeds. A few species such as the whitebark pine, the limber pine, and the pinyon pine produce wingless seeds which are comparatively large (pea-sized). These have mutualistic relationships with birds that can extract the seeds from the sealed cones, and the tree benefits by the distant dispersal of its seeds.

Clark's Nutcracker has a dagger-like bill to hammer into and remove pine nuts. After consuming their fill, the birds accumulate the extras in a gular pouch under their tongue and then bury them up to 20 miles away. Some of these tens of thousands of seeds will be winter food or fed to spring nestlings. If unrecovered, these seeds may sprout into trees and expand the forest—dubbing the "pine crow" a "natural forester."

Pine nuts are a good source of protein, fiber, unsaturated fatty acids, phosphorus, magnesium, vitamin E, vitamin K, and thiamine. Known also as pignoli, pine nuts are one of the most expensive nuts on the market due to the lengthy time for pine trees to mature, the labor-intensive harvesting, and the difficult extraction, drying, and processing of the nut kernels. Human consumption usually comes from sugar pines, western white pines, longleaf pines, red pines, and pitch pines; the latter two are found in Pennsylvania.

The role of conifers in the world is significant. They provide important wood products, food, habitat, and ecosystem services, and their evergreen foliage breaks the dull, gray landscape of winter. These softwoods with their "tightly-rolled leaves" fill a niche that most deciduous trees have fewer adaptations to endure.