Follow a shaded trail through a northern forest on a warm summer’s day, and the warm rich scent of fragrant conifer needles fills the air. Though we tend to refer to all conifers as pine trees, a closer look reveals a wide variety of cone-bearing species in our woods. Plants are classified by how they grow and reproduce, the type of flower they make, how the seeds are formed, and the structure in which the seeds are contained. Conifer is the scientific term for trees with seeds in cones and, generally, needle-like leaves. Conifer trees are part of a larger group, called gymnosperms, which includes plants with seeds considered naked, not enclosed in a fruit.
For most of our conifers, these seeds rest atop woody scales that spiral around a central stalk, making up the seed cones with which we are so familiar. However, there are two types of cones in each species of conifer. One is the pollen, or male, cone. These are quite small and not very substantial in structure, falling apart easily after releasing their pollen. The pollen cones do their job well, though, as anyone who has ever seen their car or a puddle or pond coated in yellow pollen dust can attest. Each pollen cone releases a mass of pollen grains which the wind transports, often great distances, to where some may encounter and stick to developing female seed cones of other trees of the same species. You’ll need to look up high in the tree to see these young cones located near the tips of branches.
When a pollen grain lands on a sticky female cone, the process of pollination has begun. It can take a year or more for the pollen grain to grow and the male cells to fuse with the female cells inside. Depending on the species, it can be another year or more before the seeds ripen and mature. During this time, the female cone slowly swells, as the scales enlarge and become woody and the seeds develop between these scales. The spiral arrangement of the scales allows the greatest number of seeds to be packed into the cones yet still be easily dispersed when mature. Usually two seeds rest on each scale, and most grow a tiny wing to aid in their dispersal by the wind.
The mature cones are specially designed so that they only open in dry weather, remaining closed when damp. Since most conifers are shade intolerant, it is important that the tree’s seeds are able to travel away from the parent tree. With cones only opening on dry days, the winged seeds are more likely to catch the wind and be carried to an open sunny spot rather than end in a soggy heap at the base of their parent tree.
Though most conifer seeds are designed for wind dispersal, many attract birds and other animals that pry open or strip off the scales to enjoy a tasty meal of seeds. Any that inadvertently fall to the ground or are carried away by birds or squirrels or other hungry animals may germinate in a new, and hopefully sunny, spot. Some cones are designed to open only after exposed to fire. These serotinous cones are sealed shut, and heat breaks down their resinous “glue.” After the fire, the cones open, the seeds fall out, and the fire-scorched barren landscape is perfect for these sun-loving species to germinate and grow.
Coniferous trees have needle- or scale-like leaves designed to conserve moisture. Their waxy coating keeps them from drying out in winter’s drought-like conditions. They can range in size from scales less than one-fifth of an inch long to needles sixteen inches long. They can be variously arranged on the stem, either singly, encircling the branch, in whorls, or in bundles. Needles are replaced gradually, with new growth replacing the oldest every year. Most needles last from two to four years, but some can remain on the tree and photosynthesize as long as ten years.
Conifers can be recognized by their striking silhouettes in the landscape: a single main trunk with branches radiating off it. Each of the seven main types of conifer has its own distinctive growth habit and form that can be used to identify it from a distance.
Pines are thought to have existed before the dinosaurs and have continued virtually unchanged, thanks to their great adaptability. A pine tree’s branches arise in very tight spirals, which appear as whorls encircling the tree. Pines usually add one whorl of branches per year. You can get a pretty accurate estimate of the tree’s age by counting the branch whorls, the remnants of lower branches that have died and broken off, and adding five (to account for the tiny scars of its earliest branches). Their waxy needles are grouped in bundles, or fascicles, with two, three, or five needles per bundle. Many animals use pines for nesting and cover as well as for food.
Spruce trees can be identified by their densely packed needles that attach individually and spiral around the branch. Their needles are four-sided, sharp, prickly, and uniformly green. Thanks to their dense foliage, spruce branches can hold a lot of snow, providing great cover for animals seeking shelter. The tree’s steeple shape helps it shed snow when the load is too great.
The boughs of balsam fir, with their rich resinous smell, have the fragrance of winter holidays. Thanks to their shade tolerance, firs keep many of their lower branches, creating perfectly shaped symmetrical silhouettes. They have long-lived, flattened needles encircling their branches, with faint white lines (stomata) on the undersides. Unlike the spiky spruce, the softer fir needles are considered “friendly” – an easy mnemonic to distinguish between these two trees with similar growth forms. A fir’s upright cones are purple when young, and, unlike other conifers, fall apart when the seeds ripen, leaving only spikes (called candles) to mark their former place on the branch. Fir seeds are winged, though birds or other animals often eat them before they get a chance to fly away.
Hemlocks are shade-loving trees that can create thick groves since only new hemlocks can germinate in such dense shade. Their needles are short with two prominent white lines underneath. They attach to just two sides of each branch by tiny stalks, creating a flattened surface. The branches, leaves and cones of hemlock provide food for wildlife.
Our only conifer to lose its needles each fall is the American larch, or tamarack. It looks like a typical “evergreen” until fall, when its needles turn a lovely yellow and drift to the ground along with the leaves of other deciduous trees. Tamarack needles grow in clusters out of stubby twigs that cover the branches. These give the tree a characteristic knobby look in winter when the needles are gone.
Instead of needles, short scale-like leaves form the spray-like branches of northern white cedar, or arborvitae. Though in the wild it prefers damp areas, it is widely planted as a hedgerow. Deer often browse the foliage, and its tiny cones, which are produced in large numbers every three to five years, provide food for birds.
Found in fields, red cedar, also called juniper, is a sun-loving tree with a columnar or pyramidal shape. It has two types of leaves. When young, it has sharp, pointed needles that become more flattened and scale-like with age. Its pollen and seed cones form on different trees. The seed cones start out with fleshy scales but never dry out to form the typical woody conifer cones. Instead, red cedar cones stay fleshy, looking rather like a blue-gray berry covered with a powdery bloom. Unlike the primarily wind-dispersed seeds of other conifers, red cedar seeds attract animals that eat them and pass the seeds along in their droppings.
All these different types of conifers can be found growing in the fields, forests, and wetlands across New England. Though they share some common characteristics, a closer look at the branches, needles, and cones of individual trees provides an opportunity to better know our evergreen neighbors. From the pointed spire of spruce to the spreading branches of white pine, the conifers of the northern woods grace the landscape with their varied shapes and many shades of green year-round.
Eastman, John. The Book of Forest and Thicket: Trees, Shrubs, and Wildflowers of Eastern North America. Harrisburg, PA: Stackpole Books, 1992.
Heinrich, Bernd. The Trees in My Forest. New York: HarperCollins, 1997.
Petrides, George A. A Field Guide to Eastern Trees (Peterson Field Guides). Boston: Houghton Mifflin, 1988.