The Forest in Winter: Conifers
For most life, winter is a time of dormancy when little energy is expended. As autumn daylight wanes and gives way to winter, most plants shut down and cease many of their metabolic processes (e.g. photosynthesis). However, one of the more ancient lineages of plants, the conifers (Order Pinales), is composed primarily of evergreen plants that continue their regular activities over the winter, but at a reduced level.
Most people are familiar with these plants and recognize their seed bearing cones which give them their name. Black Rock Forest has ten conifer species: eastern hemlock (Tsuga canadensis), eastern white pine (Pinus strobus), pitch pine (Pinus rigida), tamarack (Larix laricina), eastern red cedar (Juniperus virginiana), northern white cedar (Thuja occidentalis), white spruce (Picea glauca), Norway spruce (Picea abies), red pine (Pinus resinosa) and jack pine (Pinus banksiana).
All of these conifers, with the exception of the tamarack, retain their needle-like leaves year round and can photosynthesize on warm winter days when soil waters are not frozen. The retention of needles also allows these plants to take advantage of years with early springs since they do not have to wait to develop new leaves before they can begin food production. This ability to produce carbohydrates during the colder months by retaining their leaves gives conifers a competitive advantage in many cold climates, which is one reason conifers are the dominant trees in northern boreal forests.
Our native conifers have many adaptations which they use to survive and thrive particularly in harsh environments. Their typical conical shape, which is the result of their branches, or boughs, pointing down, allows the trees to easily shed heavy snow in the winter time, preventing breakage after winter storms. Their boughs are often also much more flexible than their deciduous cousins. This again, helps them avoid branch breakage despite heavy snow and ice.
The needle leaves of conifers are also adapted to prevent excessive loss of moisture. The thin needles have significantly less surface area than the broad leaves of deciduous trees, and therefore have less area from which to lose precious water. In addition, their stomata, the openings where carbon dioxide is absorbed, are typically sunken in pits or grooves that minimize water lost loss. The needles are also covered in a waxy cuticle which helps further reduce water loss.
These adaptations have helped conifers persist on our planet for 300 million years. Their cold weather and water conserving adaptations have allowed them to colonize far northern latitudes, high altitudes and dry, rocky areas around the world. They no doubt will persist, but in a warming climate their ranges will likely change substantially over time.