Albino Redwoods

If you are a very lucky person hiking in the redwood forests of California you may just be able to see a ghost. Not a "real" ghost of course, but pretty darn close. Scattered about these ancient forests are rare and peculiar albino redwood trees! Seeing one is seeing something very special indeed.

Redwoods (Sequoia sempervirens) are some of the largest and oldest organisms on the planet. They are famous worldwide for their grandeur. Aside from their obvious charismatic physical traits, redwoods are quite interesting genetically. These giant gymnosperms are genetically hexaploid, meaning they have 6 copies of their genetic code. What this means for redwoods is the ability to experiment with a wider array of mutations than a diploid organism like you and I. A mutation in one set of chromosomes still leaves 5 other copies to maintain normal genetic function. Whereas this can translate into massive benefits in defenses against pathogens, it also means there is a lot of room for error as well. 

The albino redwoods are an example of a seemingly dead end mutation. For a plant that relies of photosynthesis to survive, the loss of photosynthetic pigments should spell disaster. The question is why do albino redwoods exist at all? Well, the albinos become parasites on their photosynthetic parents. You see, albino redwoods are mutant offshoots of healthy trees. Something in a bud goes awry and the resultant shoot fails to develop chlorophyll. Sometimes chimeras arise which produce leaves that are half photosynthetic and half albino. Still, how do these mutations persist?

Researchers have found that the leaves of albino redwoods have twice the amount of stomata than do normal redwood leaves. This makes them quite susceptible to drought. During dry years, the trees quickly dehydrate and their host trees withdraw all support. The albinos will often die off but then re-sprout when conditions improve. This disappearing and reappearing act further lends to their mythos. However, this does not capture the full picture. The fact that photosynthetic redwoods tolerate the albinos on any level is quite curious. Even photosynthetic branches that don't produce enough energy are shed. What else could be going on?

Recent research might have found the answer. The albinos most frequently occur along the edge of the redwoods range where conditions just aren't that conducive. What's more, the soils around these albinos are often high in toxic metals such as nickle, cadmium, and copper. When researchers took a closer look at the chemical composition of the albinos, they found that they accumulate these toxic heavy metals at much higher rates.

In a healthy tree, these metals interfere with the photosynthetic machinery, making them quite toxic indeed. Because the albino redwoods are incapable of photosynthesis, this is not an issue. This has led to an interesting hypothesis. It could very well be that the photosynthetic redwoods tolerate their albino offshoots because the albinos accumulate the toxic heavy metals in their tissues and thus keep them away from healthy, photosynthetic tissues. This ideas is still in the hypothesis stage but work is being done to see if it plays out in the wild. 

There doesn't seem to be a solid consensus on how many albinos exist in the wild. I have seen numbers as low as 25 and as high as 400. Either way, they are a rare element of the coastal redwood community. With thousands of acres still to be explored, it is likely that more will turn up. While some exist in protected parks, many are under threat with increasing fragmentation of these ancient forests. Very little of the coastal redwood forests are under protection and we may be losing more than we will ever know. 

Photo Credit: Cole Shatto and George Bruder

Further Reading: [1] [2] [3]

 

 

The Dawn Redwood

The dawn redwood (Metasequoia glyptostroboides) is one of the first trees that I learned to identify as a young child. My grandfather had one growing in his backyard. I always thought it was a strange looking tree but its low slung branches made for some great climbing. I was really into paleontology back then so when he told me this tree was a "living fossil" I loved it even more. It would be many years before I would learn the story behind this interesting conifer.

Along with the coast redwood (Sequoia sempervirens) and giant sequoia (Sequoiadendron giganteum), the dawn redwood makes up the subfamily Sequoioideae. Compared to its cousins, the dawn redwood is the runt, however, with a max height of around 200 feet (60 meters), a mature dawn redwood is still an impressive sight.

Until 1944 the genus Metasequoia was only known from fossil evidence. As with the other redwood species, the dawn redwood once realized quite a wide distribution. It could be found throughout the northern regions of Asia and North America. In fact, the fossilized remains of these trees make up a significant proportion of the fossils found in the Badlands of North Dakota.

Fossil evidence dates from the late Cretaceous into the Miocene. The genus hit its widest distribution during a time when most of the world was warm and tropical. Evidence would suggest that the dawn redwood and its relatives were already deciduous by this time. Why would a tree living in tropical climates drop its leaves? Sun.

Regardless of climate, axial tilt nonetheless made it so that the northern hemisphere did not see much sun during the winter months. It is hypothesized that the genus Metasequoia evolved its deciduous nature to cope with the darkness. Despite its success, fossil evidence of this genus disappears after the Miocene. For this reason, Metasequoia was thought to be an extinct lineage.

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All of this changed in 1943 when a Chinese forestry official collected samples from a strange tree growing in Moudao, Hubei. Though the samples were quite peculiar, World War II restricted further investigations. In 1946, two professors looked over the samples and determined them to be quite unique indeed. They realized that these were from a living member of the genus Metasequoia.

Thanks to a collecting trip in 1948, seeds of this species were distributed to arboretums around the world. The dawn redwood would become quite the sensation. Everyone wanted to own this living fossil. Today we now know of a few more populations. However, most of these are quite small, consisting of around 30 trees. The largest population of this species can be found growing in Xiaohe Valley and consists of around 5,000 individuals. Despite its success as a landscape tree, the dawn redwood is still considered endangered in the wild. Demand for seeds has led to very little recruitment in the remaining populations.

Photo Credit: [1] [2] [3]

Further Reading: [1] [2]
 

 

Salamanders in the Trees

Redwoods are tall. Known scientifically as Sequoia sempervirens, this species is home to the tallest tree known to science. Even the branches of most redwoods would put all but the tallest trees to shame. It is no wonder then that the branches and crotches of these trees can sustain a lot of canopy debris. As debris builds up, it soon begins supporting entire floral communities of ferns, forbs, shrubs, and even other trees.

These epiphytic communities are hot spots of diversity among the redwood canopy. The sheer mass of these mats, with some weighing hundreds of kilograms, means they can hold a lot of water. Organisms that otherwise could not exist in such exposed areas find a safe haven free of desiccation. Everything from microbes to aquatic copepods call these places home. It is no wonder then that predators also haunt these microcosms.

It has been discovered that at least one species of salamander, the wandering salamander (Aneides vagrans) lives at least some of its life in redwood canopies. Though it is not solely a denizen of these trees, they have been found living among these mats during both the dry and wet seasons leading some researchers to believe that at least some individuals live out their entire lives up in the canopy. The mats hold so much water that the microclimates around them stay favorable for these amphibians year round. As roots decay within the mat, small interconnected tunnels form, offering even more protection in an otherwise chaotic environment.