What counts as a conifer
Conifers are trees that bear their seeds in cones rather than in flowers and fruit. The group includes pines, spruces, firs, larches, hemlocks, cedars, cypresses, junipers and redwoods. Most have narrow, needle-like or scale-like leaves, and most are evergreen, keeping foliage through the year. Exceptions exist, notably larches, which shed their needles in fall.
Conifer forests cover enormous areas, especially in the cold north (the boreal belt) and on mountains. They also occur in warm, dry places, on sandy soils and in wet coastal regions. The common thread is that conifers often do well where conditions are hard for broadleaf trees: cold, short growing seasons, thin or acidic soil, or frequent drought.
Why needles work
A needle has a small surface area compared with a broad leaf. It also typically has a thick, waxy coating and sunken pores, which help limit water loss. That matters in winter, when frozen soil makes it difficult for roots to take up water, and in dry areas, where moisture is scarce.
Keeping needles for several years, as many spruces and firs do, has a second benefit. The tree does not have to rebuild a full set of leaves each spring, which is costly in nutrients and energy. On poor soils, where nutrients are scarce, holding onto what has already been built is an advantage. The needles can also begin photosynthesis whenever temperatures rise enough, even briefly in late winter or early spring, so the tree can use a short season more fully. The basic process is described in the article on tree photosynthesis.
The trade-off is that evergreen needles generally photosynthesize more slowly per unit of leaf than the thin leaves of broadleaf trees in good conditions. Where growing seasons are long and soils rich, broadleaf trees often outcompete conifers. The cold and poor sites are where conifers hold their advantage.
Shape and snow
Many conifers, especially spruces and firs from snowy regions, have a narrow, conical crown with flexible, downward-sweeping branches. The shape helps snow slide off rather than accumulate and break limbs. A narrow crown also catches light at low sun angles, which is useful at high latitudes where the sun stays low in the sky.
Conifers also tend to have a strong central trunk, which is why their wood is often straight and favored for construction and pulp. The distinction between softwood from conifers and hardwood from broadleaf trees is explained in the article on hardwood softwood, and the trade term does not always reflect actual wood hardness.
Cones and seeds
Cones protect developing seeds. Most conifers produce separate male and female cones. Wind carries pollen from the male cones to the female ones, a method that does not depend on insects, which can be sparse in cold or exposed places. Seeds usually take months to a couple of years to ripen, depending on the species, and details of this process appear under tree reproduction.
Cone strategies vary:
- Many species open their cones when ripe and release winged seeds that drift on the wind.
- Some pines have serotinous cones, sealed by resin until heat from a fire melts it. These species release seeds after fire, when the ground is open and ash-enriched.
- Some conifers rely on birds or squirrels, which harvest and bury seeds, and some of those seeds are forgotten and germinate.
Cone crops often vary from year to year, with abundant crops in some years and few in others, as described for broadleaf trees under mast seeding.
Resin and defense
Resin is a sticky, aromatic substance produced by many conifers. It flows into wounds, sealing them and trapping or deterring insects and fungi. This is one of the main tree defenses in the group. However, defenses can be overwhelmed. When drought stress weakens trees, bark beetles can attack in large numbers, and outbreaks have affected extensive conifer forests in several regions. The wider topic is covered under forest insect pests.
Soils and litter
Conifer litter, made of needles, twigs and cone scales, tends to decompose slowly and to be acidic. Over time it can build up a thick surface layer. Fungal activity dominates in these soils, and many conifers form close partnerships with mycorrhizal fungi that help them capture nutrients from poor ground. The slow turnover is part of why leaf litter in conifer stands behaves differently from that under broadleaf trees.
The resulting soils are often less fertile and more acidic, and plants growing beneath conifers tend to be adapted to those conditions, such as mosses, lichens, blueberries and other shrubs. Dense evergreen shade also limits light reaching the floor all year round, unlike in broadleaf woods where light arrives before the leaves open.
Fire
Many conifer forests burn from time to time. Some species have thick bark that protects them from ground fires, while others, as noted above, release seed after fire. In the boreal zone, large fires are a central part of the natural cycle, and in drier pine forests frequent low-intensity fires may keep the stand open. The wider story appears under fire ecology, and the role of deliberate burning in management is covered in prescribed burning.
Conifer plantations
Because conifers often grow fast and straight, they are widely planted for timber. Plantations of a single species can be productive, but they are often less varied in structure and wildlife than natural stands, and they can be more vulnerable to pests or storms. The strengths and drawbacks are discussed in the article on tree plantations, and the value of mixing species is examined under mixed stands.
A summary of the pattern
Conifers are not better or worse than broadleaf trees, simply suited to different conditions. Where winters are long, soils are thin or water is hard to get, needles, resin, flexible limbs and cones give them a durable and economical way of living. Where conditions are milder, they often share the forest with broadleaf trees or give way to them.