Reproduction
One of the reasons the Coast Redwood has survived is its ability to reproduce in two different ways: seed or sprout
Seed Reproduction:
This is the primary means of reproduction in an old-growth forest, and it allows the genetic variation which is necessary for the long term survival of the species. If the tree is exposed to enough sunlight it can produce seeds at around 20 years of age. Seed production peaks at 250 – 1000 years. Redwoods have both male (pollen) and female (ovulate) cones, which grow on separate branches of the same tree. They form on the tips of high branches on mature redwoods in the fall. Pollen from the peppercorn-sized male cones is released in streams in the fall. It drifts and descends through the canopy to settle in the female cones. Fertilization will happen 4-8 weeks later.
Muir Woods - Coast Redwood Trees
Over the next year, the female cones mature into hard-sided cones from .5 to 1.5 inches in length. Protected by the hard scales are anywhere from 60 to 150 seeds. The seeds of the redwood are tiny, about the size of a small oatmeal flake. The will remain viable for up to a year. Some seeds are released from the cone while the cone is still on the tree, drifting down to the ground or blown by the wind. Most will settle within a few hundred feet of the tree. Other seeds remain until the cone falls to the forest floor, dries, and opens.
Less than 1% of these seeds will ever produce a tree. Many seeds cannot penetrate the leaf litter or duff to reach the soil. Some will land in water or on animals and will be carried away from the redwood forest. Many more will reach the soil but will be destroyed by fungal attack, bacteria, and insects. Many will be washed away by rain, and some will be eaten by animals. Probably fewer than one in a million seeds will ever become mature trees.
Seedlings will grow best under shady conditions, under the protection of larger trees. When larger trees fall, opening light gaps, seedlings will spring up to fill the void. They can grow roots of over an inch after just one day. Most seedlings will die within 3 months. Lack of moisture is the most likely cause, although many seedlings will also be washed away, eaten by animals or attacked by fungi. Their best chance of survival is after a fire, flood or fallen tree, when most of the competition is gone.
After a year the roots will be around 1 ft deep and the stem around 5 inches. After their first few years, redwoods can grow very rapidly, 2 to 3 feet in height and up to one inch in diameter a year. The trees can be 30ft (10m) at 20 years, 100ft (30m) at 50 years and fully grown at 200-300. After 300 years the tree will grow wider but not taller.
Sprout (burl) Reproduction:
Redwoods are one of a very few coniferous trees that can also reproduce by sprouting. As early as one year after beginning to grow, a redwood can begin to produce bud collars, most commonly referred to as ‘burls’. These dormant root buds will continuously form, sometimes creating large bulbous growth on the tree’s roots, base, or trunk. Hormones within the tree keep these burls from sprouting until the tree faces some form of stress. Fire, erosion, flooding, browsing, or other injury to the tree will trigger a release on the buds, causing them to begin to grow within a few weeks.
Redwood sprouts, or suckers, can grow rapidly, receiving their early nutrition from the roots on which they grow. They are genetically identical to their parent tree, often forming “family circles” around the parent tree. Under optimal conditions, sprouts may reach heights of 8-10 feet in their first year. Eventually the tree will grow its own root system and can survive even if the parent tree should fall. After a fire, trees will often sprout in such proliferation that many of the sprouts cannot compete and die back. Some day these sprouts will grow their own burls and produce their own sprouts. Most sprouting will occur when a tree is 200 – 400 years old.
