Trees that retain their foliage year-round and thus have color throughout the seasons are known as evergreen trees. Unlike deciduous trees that shed their leaves annually, evergreen trees maintain their green leaves throughout the year. This allows them to continue photosynthesis and food production even during winter when deciduous trees go dormant.
Common Evergreen Trees
There are many different species of evergreen trees found around the world. Some of the most common evergreen trees include:
- Pine – There are over 100 species of pine trees, including Eastern white pine, Scotch pine, and Austrian pine. Pine trees have needle-like leaves and produce pine cones.
- Fir – Fir trees like Douglas fir, Noble fir, and Fraser fir are pyramidal in shape and have flat, needle-like leaves. They are popular Christmas trees.
- Spruce – With prickly needles and distinctive cones, spruce trees include Norway spruce, Blue spruce, and White spruce.
- Hemlock – Eastern hemlock and Western hemlock thrive in shady, cool climates and also have needle-like leaves.
- Redwood – Coast redwood and giant sequoia are massive evergreen trees, growing over 300 feet tall with thick, fibrous bark.
- Juniper – Ranging from low, spreading shrubs to tall trees, junipers have scalelike, often prickly leaves and bluish cones.
- Cedar – There are many different types of cedar trees including Western red cedar, Atlas cedar, and Deodar cedar with aromatic wood.
- Cypress – Bald cypress and Pond cypress trees with feathery, needle-like leaves thrive in wetlands.
- Yew – Yew trees and shrubs have flat, dark green needles and red berries. Many are cultivated for ornamental purposes.
These common evergreens come from the conifer family of trees. The needle or scale-like leaves and cones are key identifying features of evergreen conifers. They thrive in many different climates from the cold boreal forests to tropical regions.
How Evergreen Trees Stay Green
Evergreen trees have special features that allow them to retain their green foliage throughout the year, even during harsh winters. These include:
- Needle-like leaves – The narrow, waxy needles found on pines, firs, and other evergreens have a smaller surface area. This reduces water loss during photosynthesis so the leaves stay hydrated.
- Thick cuticle – The tough, waxy cuticle on evergreen leaves also minimizes water loss by providing an added protective barrier.
- Cold tolerance – Evergreens produce natural antifreeze chemicals like sugars, salts, and alcohols to keep cells from freezing in cold weather.
- Resin seals – Resin seals over wounds on evergreen trees prevent damage from environmental stresses like winter desiccation.
- Cooler locations – Evergreens often orient their leaves away from the sun in winter or grow in cooler high altitude and northern regions to reduce water loss.
With these adaptations, evergreen trees can photosynthesize even during freezing winters and harsh environments. This allows them to outcompete deciduous trees in certain habitats.
Advantages of Being Evergreen
The fact that evergreen trees retain their foliage year-round gives them key advantages over deciduous trees in many situations:
- Extended growing season – Evergreens can photosynthesize whenever conditions permit because their leaves are always ready to capture sunlight.
- Early spring growth – In spring, evergreens can begin growing immediately while deciduous trees must produce new leaves first.
- Greater drought tolerance – The waxy cuticles and needle leaves of evergreen trees minimize water loss for better drought tolerance.
- Avoids leaf loss nutrients – Evergreen trees retain nutrients in their leaves rather than losing them each autumn like deciduous trees.
- Snow and ice tolerance – The conical shape and flexible branches of evergreens allow them to withstand heavy snow and ice better than broadleaf deciduous trees.
These advantages make evergreens well suited to cold regions and infertile soils where resources are limited. Evergreen forests are common in taiga and boreal habitats.
Popular Evergreen Landscaping Trees
Evergreens like pine, fir, spruce, and juniper trees make popular additions to landscaping because they provide green color throughout winter when deciduous trees are bare. Some top choices include:
- White pine – White pine is a towering pine tree that grows well in many different soil conditions and climates.
- Balsam fir – With a classic Christmas tree shape, balsam fir gives off a pleasant fragrance and retains needles well.
- Norway spruce – Adaptable and fast-growing, Norway spruce works well as screens, windbreaks, and as ornamental specimen trees.
- Eastern redcedar – Redcedar is an attractive cedar tree with dark green foliage and interesting twisted trunks when mature.
- Arborvitae – Arborvitaes are dense, pyramidal evergreens good for screens, hedges, and privacy boundaries.
The key to growing evergreens is choosing species well-suited to the site’s soil, sunlight, drainage, and hardiness zone. Proper planting, fertilization, pruning, and pest control will keep landscaping evergreens healthy and vibrant throughout the year.
Interesting Facts About Evergreen Trees
- Evergreen trees evolved during the Cretaceous period, allowing dinosaurs to have fresh greens year-round.
- The Wollemi pine is one of the oldest and rarest evergreens, dating back to the time of the dinosaurs.
- Giant sequoia trees are the most massive evergreen trees in the world, growing over 300 feet tall and 30 feet in diameter.
- Evergreens like spruce and fir are popular Christmas trees because they hold their needles much longer than deciduous trees.
- Evergreen trees can live for thousands of years, with the oldest bristlecone pines dated over 5,000 years old.
- Highly flammable eucalyptus, palm, and slash pine trees are adapted to regular forest fire conditions.
- The bald cypress is a deciduous conifer, meaning it sheds its needle-like leaves in fall like a hardwood tree.
- Ancient European cultures considered evergreens like pine, holly, and ivy sacred symbols of enduring life.
- Evergreen boughs and wreaths have been used to celebrate winter solstice holidays for thousands of years.
- Yew trees are toxic but have compounds used in cancer medications like paclitaxel (Taxol).
Threats Facing Evergreen Trees
While evergreen trees have adapted to survive harsh winters, they now face new threats from human activity and climate change:
- Deforestation – Clearing of evergreen forests for development, agriculture, and timber harvests is shrinking native evergreen habitat.
- Invasive pests – Nonnative insects like hemlock woolly adelgid, balsam woolly adelgid, and pine beetles have devastated some evergreen forests.
- Wildfires – Hotter, drier summers are increasing the frequency and intensity of wildfires in evergreen groves not adapted to frequent burning.
- Climate extremes – Hotter droughts and milder winters are stressful for evergreens adapted to historical climate patterns.
- Ozone damage – Ground-level ozone pollution is damaging the sensitive needles of evergreens like ponderosa pine.
- Acid rain – Air pollutants dissolve in rainwater creating corrosive acid rain that damages evergreen tree health.
Protecting evergreen habitats from logging and fragmentation while reducing fossil fuel emissions and invasive pests will help conserve these iconic trees into the future.
Conclusion
Evergreen trees provide year-round color and survival advantages that have allowed them to persist and thrive through changing climates. Their waxy, needle-like leaves specially adapt them to withstand freezing winters and long periods of drought when deciduous trees cannot. Much beloved evergreens like stately pines, full firs, aromatic cedars and handsome spruces will hopefully continue gracing our landscapes and forests for centuries to come.
