Coastal redwoods (Sequoia sempervirens) are some of the most iconic trees in the world. They grow taller than any other living trees and more massive than all but a handful of others. They’ve shared our planet for millions of years, and over this time, they’ve played an important role in the ecosystems they’ve played a role in creating.
But these amazing trees are not able to grow just anywhere. In fact, the entire global population of naturally growing redwoods is restricted to a 450-mile-long strip, stretching from southern Oregon to Salmon Creek Canyon, near Monterey.
In total, redwoods have access to about 1.6 million acres of suitable habitat, although they are not the dominant tree species in much of this area. Redwoods represent more than half of the hardwood present in only about 640,000 of these acres. Redwoods occasionally grow at elevations of up to 3,000 feet, although most are found below 2,500 feet. Above these heights, redwoods fail to reach their characteristic size, and other trees begin replacing them in the landscape.
It actually appears that this range is shifting slightly to the north, probably in response to climate change. Fewer new redwoods are growing in the southern end of the trees’ range, while seedlings are popping up in previously uncolonized portions of the northern end of the range.
Climate and Weather
Redwood forests benefit from one of the most hospitable climates in the world. Mean annual temperatures vary between about 50 and 60 degrees Fahrenheit, and the temperatures rarely drop below 15 degrees Fahrenheit or climb above 100.
The forests literally drip with moisture. Most of the precipitation falls in the form of rain, although fog also contributes a substantial amount of moisture to the region. Like most of the Pacific Coast, the region receives most of its rainfall in the winter, with very little rain falling in the summer.
Redwoods were not always restricted to such a small geographic area. In fact, 100 million years ago, redwoods covered most of the northern hemisphere. However, about 20 million years ago, the climate began shifting, which allowed vast glaciers to extend farther south into North America and Asia than they previously had. Ultimately, this killed off mostthe redwoods alive at the time; only a relative handful were able to persist in small pockets of California and China.
But this range was reduced even further in the 19th and 20th centuries, as aggressive logging practices and habitat alteration removed thousands of redwoods from the gene pool. Currently, the redwood forest covers only about one-twentieth of the land that it did 150 years ago.
The Function of Fog
Redwoods reside near the Pacific Coast, penetrating inland as far as 35 miles in some places (although the forest contracts to about 5 miles wide in many areas). The primary limiting characteristic of this range is fog penetration. Fog is crucial to the health of redwoods. In fact, fog is more important than rainfall level in defining the coastal redwood forest type. While redwoods can be grown in areas without nearly constant fog, such as commercial orchards or residences, they do not do so naturally.
Nevertheless, these are still large trees with significant water needs. Large individuals may pull 500 gallons of water a day from the ground. Accordingly, while their habitat is restricted to only those areas that receive regular fog coverage, they do not grow equally well in all areas within these areas. The largest individuals and densest groves typically occur in riparian areas alongside major streams and in flat, low-lying areas – both of which have ample water stores. However, redwoods cannot grow in saturated soils, and soils carrying about two-thirds of their total water capacity are associated with the most productive portions of the forest.
The abundance of moisture in these forests (which are sometimes classified as super-humid) causes transpiration and evaporation rates to fall. Additionally, soil moisture levels remain higher throughout the year, further reducing the water stress that afflicts the trees growing in nearby but fog-free areas in the region.
The Neighbors of Redwoods
Redwoods are the dominant species in many of the forests they help create, although several other trees grow alongside them. Douglas firs (Pseudotsuga menziesii) are one of the most common species growing among the redwoods, but western hemlocks (Tsuga heterophylla) and Sitka spruce (Picea sitchensis) also occur with some regularity.
A litany of animal species live amid the towering redwoods. Small animals – including rodents, birds, reptiles, amphibians and invertebrates – represent the bulk of the local fauna, as occurs in most natural habitats. Rodents are particularly well-represented in the region, including two very large species: the porcupine and North American beaver. Nearly one-third of the country’s native bird species have been documented to occur in the redwood forest, including representatives of all major lineages, from flycatchers to owls.
However, large animals also live in the land of giant trees too. Black-tailed deer and Roosevelt elk – the largest of the United States’ native elk subspecies – browse vegetation amid redwood groves. Black bear, mountain lions and coyotes hunt through the forests, but their numbers are much lower than those of deer, elk and other herbivores, as is common in all habitats.
Frequent Fires Fuel Adaptation
Redwoods, like most other California natives, have a number of adaptations that allow them to survive the relatively frequent fires that occur in the state. Young trees – those less than about 20 years old – frequently die in these fires, but the stands rapidly regenerate in the form of clones, which sprout from the below-ground root systems. Older trees survive most fires, thanks in part to their 12-inch-thick bark. Most trees simply suffer bark damage, which is easily replaced over time.