Redwood Forest Ecology 

          The coastal redwood forest is known for its beauty and sheer impressive scale. Every year, hundreds of tourists flock to this cool sanctuary to enjoy the serenity that these giants provide. The redwood forest is named after the presence of Sequoia sempervirens, the coastal redwood tree. They are known for being the tallest trees in the world, as well as some of the most massive organisms ever to live on Earth (4).

 
          Coastal redwoods occur in an approximately fifty kilometer wide belt from 42°-36°N (3). This area is roughly known as central to northern California. There are several outlying groves, but redwoods are restricted by climate to a great extent (4). Redwood forests are known as temperate rainforests because they are particularly cool and moist all year round and the weather stays between forty and sixty degrees Fahrenheit for most of the year (8). Heavy winter rains provide much of the moisture, but redwoods are also characterized by large amounts of coastal fog during the summer months (3). This keeps the weather humid, like tropical rainforests, but their location on the globe means that these forests are cooler year round (8).

          The California coast is well known for its seismic activity. In fact, small seismic events occur every day and geologic unrest is well-documented. Upheaval along the fault line on the coast of California reveals rock formations common on the ocean floor, such as sandstone, shale, and siltstone. These rocks are softer, and easily eroded to form ravines and sloping hillsides, which are ideal for redwood trees (8). Redwood forests are very unique in their biogeography and climate. They are restricted to areas with the distinctive combination of the traits above. However, in the past, redwood forests had much greater diversity and range size (4).

Redwood History

Since the evolution of ancient redwoods, climate has been influencing range sizes and distributions have been shifting.  The current range of the coastal redwood is unlikely to stay as it is for any great length of time, especially with the current global climate change happening all over the world (4).

Ancient Redwoods

            Sequoia sempervirens is the only species of tree still alive from an ancient line of conifers within the family Taxodiaceae.  Many other genera within Taxodiaceae have gone extinct since the Cretaceous Period when they are first seen showing up in the fossil record.  These include Austrosequoia, Taxodium, and Sequoiadendron, also known as the modern giant sequoia.  In the beginning of the Cenozoic Era, many species of Sequoia existed in what would become the western United States.  Ranges included Wyoming, Nevada, California, Montana, Oregon, Idaho, and Colorado.  About 23 million years ago, during the Miocene Epoch, the climate became drier in these areas and the ranges of each of these species contracted.  During the Pliocene Epoch, geologic upheaval created the Cascade, Sierra, and coast mountain ranges, causing further constriction of Sequoias on the west coast.  Glacial cycles during the Pleistocene Epoch made redwood ranges expand and contract.  Redwood fossils from this time have been found further south of the current range in places such as Santa Barbara.  The end of the Pleistocene and beginning of the Holocene Epoch saw much drier and warmer climate changes and redwood trees were constricted to their current location by about 10,000 years ago (4).  Additionally, human influence is increased during this time because the entire coast of California was inhabited by Native Americans.  These people used redwood trees for creating boats and lodging and continued to do so until European settlement (8).

After European Settlement

            Many Europeans were drawn to northern California during the gold rush in the early nineteen century (4).  They came for the promise of riches buried in the hillside, but soon discovered that gold mining was not the quick way to make it rich that they had imagined.  Instead, many found that the booming logging industry was more lucrative.  Massive redwoods were felled and sent to the city of San Francisco to aid in its expansion.  In the beginning of this time period, old growth forests covered over two million acres of land on the California coast.  However, the huge influx of manpower, as well as continued improvement in logging technology, meant that these forests were soon in peril of being wiped out (8). 

Initially, most of the logging was done by sheer physical power, through hand axes and oxen pulling carts.  Due to redwood’s massive size, this was extremely difficult, dangerous, and time consuming work.  The invention of chainsaws and the later use of trains and automobiles to move the logs made the job much more manageable, and redwood forest felling went on at an accelerated rate.  The end of WWII and the consequent boom in the population made the need for timber even greater (10).  Tractor truck logging was more efficient and could access trees previously deemed too difficult to log (4).  Logging was mainly focused on the redwood trees within the forest, and not other species because of the greater biomass of redwoods compared to all others.  Selection logging of this kind led to forests with small proportions of redwood trees.  Technological advances within the logging industry, such as the invention of other wood materials like pulp and particleboard, meant that every tree was used.  Previously, down logs, snags, stumps, and unsuitable trees for timber were left behind.  Now everything was taken to be used in the mills, greatly decreasing biodiversity, habitat for animals, and the ability of the forest to regenerate itself (4).

Increase in technology was not the only thing affecting the health of the redwood forest at this time.  Government policy and forestry practices were making redwood resurgence even harder. Up until 1977, all standing timber was taxed on an individual’s property.  However, the law stated that no tax would be placed on timber that had been cleared of 70% of its biomass.  Because redwood trees have so much biomass, most land owners chose to selectively cut down the redwood trees on their property.  Additionally, forests that were reseeded after clear cutting were usually seeded with Douglas fir seeds, making it more difficult for redwoods to make a comeback (4).  Many environmentalists and concerned citizens began to see the massive decrease in redwood forests and joined together to form a coalition called the Save the Redwoods League in 1919.  This group was the first to propose and organize park reserves specifically for redwood forests (9).

Redwood National and State Parks

            During the 1920s, Save the Redwoods League started the first state parks.  The national park system began in 1968, by which time 90% of all redwoods had already been logged.  In fact, of the original two million acres of old growth forest, only five percent remain.  By 1994, the national and state parks had been merged to make cooperation and management easier between them.  Today the parks protect over 133,000 acres of land, 37 miles of coastline, and approximately 45% of the coastal redwoods still alive today.  They are all located on the north coast of California, within two counties, Humboldt and Del Norte (8). 

                                        Management of the parks focuses mainly on conservation of the redwoods that are left, as well as conserving and nurturing the most ecologically important groves.  These parks also play a large part in educating the public about the importance of these forests and exposing them to the innate beauty of these areas through ecotourism.  Programs such as the junior rangers create interest and excitement about conservation in future generations, and the strictly enforced rules of the park ensure that the forest is respected while it is being admired (8).  The mission statement of the Save the Redwoods League is, “to protect and restore redwood forests and connect people with their peace and beauty so these wonders of the natural world flourish” (9).  It seems that this mission has been successful, as conservation efforts and support from the public continue to increase the size and effectiveness of these reserves.  Human values on conservation and the innate value of the natural environment have changed dramatically since the early nineteenth century when the degradation of the redwood forests began.  Developed countries such as the United States have recognized this ecosystem as one of great importance and aim to preserve it as best as possible.  Today, the redwood forest has been proclaimed a World Heritage Site, as well as an International Biosphere Reserve (8).  It is undeniable that those that visit the redwood forest are struck by its intrinsic beauty, and support its conservation.  This has made conservation initiatives much easier to pass.

 Redwood Trees

            Redwood trees are commonly known as the tallest trees in the world.  They easily reach more than 92 meters and are unusual in that the tallest trees are not anomalies.  In most species, the tallest individual tree is much taller than any other individual tree of that species.  With redwoods, however, the tallest trees are all similar in height, with 47 known individuals measuring over 110 meters.  This shows that they naturally grow very tall, are not anomalous, and they truly are the tallest trees in the world (4).  Hyperion, 116 meters, is the tallest known tree at the moment.  Redwood trees are also nicknamed “living fossils” because of their extreme age.  They live an average of 500-700 years, but many are known to be over 2,000 years old (8).  However, extreme height and age are not the only things that make these organisms remarkable.

Resistance

             Redwood trees were targeted for logging because of their incredible resistance to many disturbance regimes.  Their wood is much higher in tannins than other trees, such as Douglas fir, which gives them a natural insect repellent and stops larger animals from feeding on the young chutes because they have a very bitter taste (8).  Additionally, the bark of a redwood tree can be an entire foot thick, making it resistant to disease, insect invasion, and especially fire (5).

            Redwood trees prefer full sunlight in order to maximize photosynthesis, but they are also very resistant to shade (2).  In fact, a redwood tree can survive for up to one hundred years in full shade; although its growth rate is much lower (8).

            These trees are also very dependent on a moist, cool climate and grow at their peak when annual precipitation is 50-100 inches (11).  When flooding occurs, the root structure may be covered by layers of silt that usually smothers and kills trees (5).  Redwood trees have very shallow roots that only reach 4-6 feet into the soil, and no tap root.  These roots make up only 10 percent of the total biomass of the tree, which makes redwoods easier to uproot than some coniferous trees, but also makes them resistant to flooding (7).  When the silt is deposited over the root structure, the redwood’s shallow roots are capable of growing upward to reach the surface again (5).  Additionally, in times of drought, redwood trees suffer greatly from the lack of normal moisture and entire tree crowns may die.  However, redwood trees are capable of turning one of their branches into a second trunk, called a reiteration, and are thus fairly resistant to short drought periods (4).

            Lastly, redwoods are known for their incredible ability to re-sprout once cut down.  This is done through a biological structure known as a burl that is usually located somewhere near the base of the trunk.  This large, irregular outgrowth has three known purposes, all of which make the redwood one of the hardiest trees in the world.  First, burls can store large amounts of nutrients and carbohydrates for use by the tree after injury or during times of stress.  Second, burls are capable of growing roots to increase stability when on a slope or in high wind areas, and to increase the amount of nutrients gathered from the soil when damage occurs elsewhere.  Lastly, burls left at the base of a stump will rapidly sprout dozens of redwood chutes, and many adult redwoods may grow on top of the stump in this way.  This amazing ability has allowed the large expanses of redwood forest to grow again from the remnants of clear-cut forests.  Because redwoods are adapted to deal with so many types of stress, from insects to fires, they are able to out-compete other types of trees in the forest.  In fact, co-occurring species of trees such as western hemlock and Douglas fir are all more shade resistant than redwoods and would take over the forest if there were no disturbances.  Redwood is a persistent species that endures hardship and is highly adapted to its environment (4).

Redwood Growth

            Redwood trees are monoecious, meaning that one tree produces both pollen and seeds on separate branches.  The seeds become receptive to pollen from the months of November to March, which is the rainy season.  Pollen is thought to travel mostly by wind in between precipitation events.  It takes a redwood five to fifteen years to begin producing seeds, which are energetically costly.  Over the lifespan of the tree, viability increases with age until approximately 150 years, at which point viability will begin to decrease slowly each year.  Each seed is very small and winged.  Seeds are sensitive to fungal infections on the forest floor as well as sunlight exposure (4).  Most seeds grow from downed logs which provide nutrients and water (5).  Once established, a seed will germinate in only three to six weeks, at which time they are easily eaten by forest animals such as banana slugs, rabbits, and nematodes.  However, once a juvenile, redwood trees are not easily eaten by anything but bears, which strip off large pieces of bark and eat the layer of cambium just beneath. 

Redwood Limitations

            Adult redwood trees are limited in their range by several factors other than animal interactions.  Redwoods are thought to be intolerant of sea spray, and may suffer from salt burn.  This may be why they do not occur directly on the coastline.  In addition, redwoods grow best on mineral soils that are regularly exposed by fire (2).  Soils with too much calcium or that have already been established by other plants that have altered the soil to their own optimum, are difficult for redwoods to grow in.  Redwoods must also grow in areas with other tall trees because of their shallow root system.  Wind throw is one of the leading causes of natural redwood death (12).  When redwoods grow in large groves, they are capable of fusing themselves together to form a stable network that is harder to knock down (4).  Being in groups is also helpful for the collection of fog.  Lone trees are not as capable of capturing and holding fog as large groups.  Forest fragmentation from logging has made current redwood forests much more vulnerable to both wind throw and lack of moisture from fog (3).  

Forest Ecology

            The Redwood forest consists of several different kinds of ecosystems, the most obvious of which is forest.  There are also abundant seacoast, prairie, and river ecosystems.  All of these ecosystems contain plants and animals that interact with one another through different types of relationships, from mutualism to parasitism (8).

Flora

            Although the redwood forest mainly consists of redwood trees, there are plenty of other trees, shrubs, and flowering plants that occur regularly within it.  Other commonly seen trees include the Douglas fir, Sitka spruce, evergreen hardwood tanoak, Pacific madrone, and red alder (8).  These trees become more commonly interspersed within the redwoods the farther south one travels down their range (4).  Shrubbery includes smaller plants that are adapted to shade such as huckleberry and blackberry.  These plants are important to the survival of animals within the forest because they provide food.  Ferns such as the sword fern are highly adapted to wet areas and cover most of the understory in the most northern regions of the forest.  Lastly, California rhododendron and azalea are flowers that are mostly seen within older regions of the forest (8).

           

Fauna

            The redwood forest is fairly typical in its fauna for a coniferous forest.  There are at least forty species of mammal present which includes black bear, puma, beaver, river otter, black-tailed deer, elk, red squirrel, and the big brown bat.  These mammals occur within all of the ecosystems of the forest, but many of them specialize, such as elk that spend much of their time in prairies.  There are over 400 bird species in the redwoods that include gulls, sandpipers, osprey, Stellar’s jay, and the great blue heron.  Once again, many of these birds specialize on the coastal ecosystem, others around rivers or within the forest.  Amphibians and reptiles are commonly found within the forest because it is so moist year round.  Some of these include the northern red-legged frog, rough-skinned newt, and pacific giant salamander.  As in almost all ecosystems, invertebrates are by far the most common animals within the redwood forest.  However, they are largely unstudied.  One of the most well-known and studied invertebrates is the banana slug, which can be said to be a sort of mascot for the redwood forest (8). 

While the redwood forest has many interesting flora and fauna, none of them are purely endemic.  Every animal can be found in another region, most of them neighboring ecosystems.  This means that the redwood forest can be an important site for preservation of animals, but it is not the only site that these animals can exist (4). 

Non-native Species

            Non-native species of Flora and Fauna also exist within the redwood forest, as with almost every other region in the world.  This is caused by human influence and disruption of the natural ecosystem.  While many of the 200 introduced species can be considered exotic, 30 are invasive, and ten are actual threats to the native ecosystem.  This number is actually fairly low compared to many other California ecosystems, but these species should still be studied and kept under control.  One of the ways that the state and national parks are attempting to get rid of invasive species of plants is by controlled burns within the reserves (8).  These invasive species are not as fire resistant as many of the local species, and redwood trees are actually positively affected by small fires because they clear the leaf litter and allows their seed to germinate more quickly (2).  At the moment, exotic species make up one forth of the total biomass of plants in the park (8). 

Rare and Endangered Species

            There are 57 species of rare or endangered plants in the redwood forest.  As stated above, none of these exist purely within the redwood forest, but the redwood forest preservation system may be the best chance they have of survival in the future (4).  The same holds true for the rare and endangered species of animals that exist in the forest.  The brown pelican lives along the coastline and is currently listed as endangered, while the bald eagle is threatened.  Chinook salmon that migrate upstream to breed are also threatened (8).  These fish are extremely important to the redwood forest because their deaths provide yearly nitrogen deposits at the base of the redwoods (4).  In order to save these species it is essential that we understand the interactions they have with other organisms within the forest, as well as what has caused them to become rare.

Ecological Interactions

            The redwood forest consists of a complex system of interactions between species.  The redwood trees themselves provide habitats for other plants and animals.  Downed logs provide shelter for small mammals and invertebrates, as well as nesting sites that are safe from the elements.  Many logs are used by other plants as germination sites because they act as a water reserve line by collecting and holding rainwater.  These downed logs with other plants taking root inside of them are known as “nurse logs” because they act as nurses, protecting and nurturing the seeds that grow on them.  Additionally, decomposers such as slugs and fungi break down these downed logs, releasing the nutrients and returning them to the soil for further use by living plants.  The breakdown of an entire redwood log can take up to five hundred years, making it an amazing slow-release fertilizer.  Some redwood trees that have died remain standing, and are called snags.  These tall bare trees can provide shelter and nest sites for animals such as the osprey or spotted owl (5).

             Redwood foliage tends to collect at the base of large branches and reiterated trunks 45 meters and higher on tall redwood trees (8).  These traps for organic material are hydrated by precipitation and fog and break down to form a nutrient rich material known as canopy soil.  These soil collections are microhabitats in which many invertebrates breed and plants germinate.  In fact, many fern species can be found in the canopy of redwood trees such as sword fern and licorice fern, as well as some species of tree commonly found on the forest floor like Sitka spruce (4).  Invertebrates commonly found in canopy soil include worms, mollusks, and insects.  Even a species of salamander that lives on redwood trees, the clouded salamander, is known to breed in these soil mats.  Fungi are found in these mats which aid in the breakdown of organic materials and contribute to the amount of soil present (4).

            Fungi are found all over the cool, moist redwood forest.  Approximately twenty species of pathogenic fungus are currently known.  These pathogens can kill entire trees, and thus contribute to the structural diversity of the forest by creating downed logs and snags.  Fungus can also be eaten, and is a valuable source of nutrients and water for many forest animals.  Fungi known as endomycorrhizae are also found within the cells of redwood roots.  They have a mutualistic relationship with the trees in which the fungi provide nutrients and water from the soil and the redwoods provide a small amount of stored carbohydrates.  Saprobic fungi enhance the decomposition of forest leaf litter and ensure that nutrients from fallen leaves are recycled quickly into the soil (4).  Ecological interactions such as these are important for the overall health of the redwood forest and should continue to be studied to aid in conservation and knowledge of the important species within the forest.

The Current Situation 

            While much of the redwood forest is being conserved, there are still major issues that must be dealt with.  Global warming is causing the current range of the forest to shift northward over the Oregon border.  The most southern reaches of the range are gradually dying back from the unseasonably dry and hot weather (6).  Because the redwood range is also moving north, it may seem as if this range shift is not an issue; however, redwoods need a very specific array of conditions in order to survive.  Oregon may prove to be unsuitable; maybe the weather is too wet, the soil is too calcium rich or forest fires do not occur regularly enough.  The current range shift must be considered a serious matter.  The lack of redwoods in Oregon already indicates that this land is less suited for their habitation, and there are many factors besides climate that can affect the redwood’s migration north (12).  Several known climate refuges within California have been located, so it is imperative that future conservation efforts concentrate on preserving the forest in these areas (6).

The natural beauty of the forest has made it a very desirable place to live and retire.  Urbanization has created pollution in the streams and oceans near the forest, and has disrupted the wildlife to a great extent.  Additionally, when people build structures in the forest, they tend to keep many of the big redwood trees standing, but turn the rest of the forest floor into a manicured garden area.  This introduces exotic species and eliminates the natural habitats and home ranges of many wild animals.  Urbanization is also continuing the process that began with the logging industry, forest fragmentation.  Forest fragmentation occurs when a completely forested area is cut down or thinned, and several small patches of forest are separated by non-forested land such as cropland, pasture, or urban development.  Redwood forests are particularly vulnerable to forest fragmentation for two reasons, wind and fog (4).

           

Wind and Fog

            As stated above, high winds are the number one cause of redwood death aside from human interaction.  When forest fragmentation occurs, the surface area to volume ratio of the forest increases, and there are more trees exposed to high winds.  If forests become patchy and there are fewer large stands of trees with branch-trunk fusions between them, wind could become an issue for the survival of the species. 

Furthermore, fog is an extremely important abiotic factor within the redwood forest.  Summers in northern California tend to be dry, putting stress on the trees that need a cool, moist climate to survive.  Fog banks along the coast are essential during this time.  Fog can be collected as precipitation on the leaves and either taken up through the foliage itself, or dropped down to the root system to be taken up from the base.  In fact, redwood foliage has evolved to be a particular shape that is well adapted to precipitating water from the air (1).  Fog can also help to limit water loss during the summer months.  Redwood trees do not close their stomata, making them almost incapable of regulating their own water supply.  The presence of fog lowers the osmotic gradient of water between the air and the leaves, reducing transpiration (3).  Fog decreases when forests are logged because there are fewer trees to hold the moisture in along the coast (1).  Additionally, upwelling from the cold Pacific Ocean creates large amounts of fog rich in nitrogen.  As global warming begin to heat up the surface of the ocean, upwelling lessens and the nutrient-rich fog does not form.  It is important that there are many trees present along the coastline to capture what little fog is created as surface waters continue to warm (3). These factors illustrate why protecting large expanses of forest is imperative.  The forest survives as an entity, and must be conserved as such.

Conservation

            Several significant factors have already been discussed above, but it is important to answer one question.  What does “saving the redwoods” mean?  According to the Save the Redwood League, “it means protecting the forest ecosystem in its natural condition, wherever such opportunities still exist.  It means repairing damage that has been done by land uses that have disrupted natural processes and environments.  And it means managing the overall landscape in a sustainable way to proved commodities, recreational opportunities, beauty, and other values for humans” (4). 

It is important to note that the goal of saving the redwoods is not to shut it off to all human contact, but to be able to use and admire it in a long-term, sustainable way.  In order to do this, conservation must be approached from every angle.  There are two scales to forest conservation, which are within-site and among-site (4).  Continued scientific research on the past, present, and future of the redwood forest addresses both of these scales, but it is also important to get the community involved.  Initiatives such as Save the Redwood League’s “Redwood Watch” include the average citizen in both within and among-site analyses.  People interested in contributing to research and knowledge of the redwoods are encouraged to participate by taking pictures of the redwood trees within their community on their iphone and sending the picture and location to the foundation.  This increases excitement about conservation and helps people to feel involved in a worthy cause.  Ecotourism and community involvement are two extremely important means to keeping the redwoods strong.  If the average American cares about these magnificent organisms, the likelihood of their continued health and presence on this Earth is greatly improved (9).

Literature Cited:

1.  Dawson, T.E. "Fog in the California redwood forest: ecosystem inputs and use by plants." Oecologia. 117.4 (1998): 476-485. Web. 27 May. 2012. <http://www.springerlink.com/content/m0hhc22apyty1dxm/?MUD=MP>.

2.   "Fire Ecology - Vegetation Types: Coast Redwood Forests." Point Reyes National Seashore. National Park Service, 18 May 2012. Web. 23 May 2012. <http://www.nps.gov/pore/parkmgmt/firemanagement_fireecology_vegtypes_redwoods.htm>.

3.  Johnstone, J. A., & Dawson, T. E. (2010). Climatic context and ecological implications of summer fog decline in the coast redwood region. Proceedings of the National Academy of Sciences of the United States of America, 107(10), 4533-4538. doi:10.1073/pnas.0915062107.

4.  Noss, Reed. The Redwood Forest: History, Ecology, and Conservation of the Coast Redwoods. Covelo, CA: Island Press, 2000. 1-228. Print.

5.  "Redwood Forest Ecology." Humboldt Redwoods State Park. Humboldt Redwoods Interpretive Association, 18 May 2012. Web. 08 Oct 1996. <http://tracker777.tripod.com/ecology.html>.

6.  "Redwood Range Shifts." Data Basin. Kresge Foundation, 2012. Web. 22 May 2012. <http://databasin.org/climate-center/features/redwood-range-shifts>.

7.  "Redwood Questions and Answers." Redwood Technology. N.p., n.d. Web. 22 May 2012. <http://home.hiwaay.net/~redwood/rwqanda.html>.

8.  "Redwood National and State Parks." Wikipedia. Wikimedia Foundation, Inc., 09 May 2012. Web. 24 May 2012. <http://en.wikipedia.org/wiki/Redwood_National_and_State_Parks>.

9.  "Redwoods and Climate Change Initiative." Save the Redwoods League. Save the Redwoods League, 2012. Web. 22 May 2012. <http://rcci.savetheredwoods.org/>.

10.  "Redwoods National and State Parks: Area History."National Park Service. U.S. Department of the Interior, 17 May 2012. Web. 22 May 2012. <http://www.nps.gov/redw/historyculture/area-history.htm>.

11.  Wilson, Bert. "Coast Redwood Forest." Las Pilitas Nursery. N.p., 31 Jan 2012. Web. 27 May 2012. <http://www.laspilitas.com/nature-of-california/communities/redwood-forest>.

12.  Zinke, Paul. "Soils and Ecology of the Redwoods." Forestry Seminar Series. University of California, School of Forestry, Berkeley. Berkeley, CA, 1964. Lecture.