The Inside Story
- The outer bark is the tree’s protection from the outside world. Continually renewed from within, it helps keep out moisture in the rain, and prevents the tree from losing moisture when the air is dry. It insulates against cold and heat and wards off insect enemies.
- The inner bark, or “phloem”, is pipeline through which food is passed to the rest of the tree. It lives for only a short time, then dies and turns to cork to become part of the protective outer bark.
- The cambium cell layer is the growing part of the trunk. It annually produces new bark and new wood in response to hormones that pass down through the phloem with food from the leaves. These hormones, called “auxins”, stimulate growth in cells. Auxins are produced by leaf buds at the ends of branches as soon as they start growing in spring.
- Sapwood is the tree’s pipeline for water moving up to the leaves. Sapwood is new wood. As newer rings of sapwood are laid down, inner cells lose their vitality and turn to heartwood.
- Heartwood is the central, supporting pillar of the tree. Although dead, it will not decay or lose strength while the outer layers are intact. A composite of hollow, needlelike cellulose fibers bound together by a chemical glue called lignin, it is in many ways as strong as steel. A piece 12″ long and 1″ by 2″ in cross section set vertically can support a weight of twenty tons!
Leaves Make Food for the Tree
And this tells us much about their shapes. For example, the narrow needles of a Douglas fir can expose as much as three acres of chlorophyll surface to the sun.
The lobes, leaflets and jagged edges of many broad leaves have their uses, too. They help evaporate the water used in food-building, reduce wind resistance—even provide “drip tips” to shed rain that, left standing, could decay the leaf.
California’s magnificent Coast Redwood is the world’s tallest known tree and one of the world’s oldest trees. Average mature trees, several hundred years old, stand from 200 to 240 feet tall and have diameters of 10 to 15 feet, and some trees have been measured at more than 360 feet. The tallest tree in the world, The Stratosphere Giant located at Humboldt Redwoods State Park, is just over 370 feet tall. In the most favorable parts of their range, Coast Redwoods can live more than two thousand years.
Redwoods are named for the color of their bark and heartwood. The high tannin content of the wood gives the trees remarkable resistance to fungus diseases and insect infestations. The thick, fibrous bark has an even higher tannin content, and insulates them from the periodic fires which have occurred naturally down through the centuries in the redwood region.
These immense trees have delicate foliage. Narrow, sharp-pointed needles only one-half to three-quarters of an inch long grow flat along their stems, forming feathery sprays. Redwood cones are about an inch long and each cone contains 14 to 24 tiny seeds; a pound of redwood seeds would number more than a hundred thousand. Redwood seedlings grow rapidly, more than a foot per year in good conditions. Young trees also sprout from their parents’ roots, taking advantage of the established root system.
Coast Redwoods form almost pure stands in some areas, especially on flat, silt-covered river and creek plains such as the Bull Creek Flats area and the Rockefeller Forest. Coast Redwoods are also found in mixed evergreen forest with the majestic Douglas fir, as well as western hemlock, grand fir, and Sitka spruce. On drier slopes tan oak, madrone, maple, and California bay laurel grow along with the evergreens. Rhododendrons and a variety of ferns are the most common under story plants. Other plants which flourish under the trees in the duff of fallen needles include poison oak, huckleberry, hazel, and many flowering herbs.
Mammals found in the redwood forest include the ubiquitous raccoons and skunks, black bears, Roosevelt elk, deer, squirrels, porcupines, weasels, mink, and the rare ringtails. Among the birds found would be the marbled murrelet or the northern spotted owl, both of which nest almost exclusively in old-growth redwood and Douglas-fir forest. Many visitors in the redwoods notice a common mollusk, the yellow banana slug.
It is generally believed that the last ice age limited the Coast Redwoods to their present range, a narrow 450-mile strip along the Pacific Ocean from central California to southern Oregon. In the redwood belt, temperatures are moderate year-round, and heavy winter rains and dense summer fog provide the trees with the water they need. This climate was far more common in earlier eras. Paleobotanists have discovered fossil redwoods throughout what is now the western United States and Canada, and along the coasts of Europe and Asia. Some of these fossils are as much as 160 million years old. Redwoods are relatively recent arrivals in their current region; the earliest fossil record in California is found in rocks less than 20 million years old.
A natural Coast Redwood forest is a perfect recycling system. The soil (like that in any high-rainfall climate) contains few nutrients; most of the substance necessary for life is in the trees themselves, living and dead, and in the other plants and animals of the forest. If trees are removed from the forest instead of being allowed to die and decay naturally, many nutrients are lost from the cycle.
Public Health and Social Benefits
Air Cleaning: Trees produce oxygen, intercept airborne particulates, and reduce smog, enhancing a community’s respiratory health. The urban canopy directly contributes to meeting a city’s regulatory clean air requirements.
Access to trees, green spaces, and parks promotes greater physical activity, and reduces stress, while improving the quality of life in our cities and towns.
- Urban landscaping, including trees, helps lower crime rates.
- Studies show that urban vegetation slows heartbeats, lowers blood pressure, and relaxes brain wave patterns.
- Girls with a view of nature and trees at home score higher on tests of self-discipline.
Climate change: Trees sequester carbon (CO2), reducing the overall concentration of greenhouse gases in the atmosphere. Read more about trees and climate change here.
- A tree is a natural air conditioner. The evaporation from a single tree can produce the cooling effect of ten room-sizes, residential air conditioners operating 20 hours a day.
- Acting as a natural air-conditioner, lush tree canopies ensure that summer temperatures are at least 6 to 8 degrees lower than in comparable neighborhoods without trees.
- Tree windbreaks can reduce residential heating costs 10-15%; while shading and evaporative cooling from trees can cut residential air-conditioning costs 20-50%.
Water filtration and retention: Urban forests promote beneficial water quality and reduce storm water management costs.
- Street and park trees can intercept 135 million gallons of rainwater. Trees capture and slow rainfall and their roots filter water and recharge the aquifer. Trees reduce storm water runoff, which reduces flooding, saves city storm water management costs and decreases the flow of polluted water into the Bay.
Wildlife habitat: Trees provide important habitats for numerous bird, insect and animal species.
Communities and business districts with healthy tree-cover attract new residents, industry, and commercial activity.
- Homes landscaped with trees sell more quickly and are worth 5% to 15% more than homes without trees.
- Where the entire street is tree-lined, homes may be worth 25% more.
- Trees enhance economic stability by attracting businesses; people linger and shop longer when trees are present.
- Where a canopy of trees exists, apartments and offices rent more quickly and have a higher occupancy rate; workers report more productivity and less absenteeism.
Tree Benefit “Fun Facts”:
- Trees provide inviting and cool areas for recreation and relaxation such as playgrounds and parks.
- Trees create a tapestry of color and interesting form that changes throughout the year.
- The color green is calming and relieves eye strain.
- Trees screen unattractive views and soften the harsh outline of masonry, metal, asphalt, steel and glass.
- People walk and jog more on shaded streets, which encourage interaction with neighbors and improve the sense of community.
- Trees absorb and block sound, reducing noise pollution by as much as 40 percent.