Ancient of Days

     The post title is a reference to the book of Daniel, which was likely written around the 100s B.C.E., or about 2100 years ago (1). This is about the time that currently living organisms I would like to investigate in this post might have gotten their start in the high, hostile crags of the Rocky Mountains. Some, although likely not many, of the lichens and trees that grow in the alpine and subalpine zones of the mountains are so ancient of days that they have endured since the times of the later Old Testament, demonstrating extreme longevity. The two long-lived organisms that I want to highlight are the map lichen,  Rhizocarpon geographicum, and the Rocky Mountain bristlecone pine, Pinus aristata. 

Rhizocarpon geographicum, Map Lichen  

R. geographicum (yellow-green) growing on an exposed rock face on Mount Evans at around 11,000 feet. 

The gray lichen at right is Rhizoplaca  melanophthalma, a common foliose lichen, and the brown 

and black lichen surrounding both the others is Lecidea atrobrunnea. 

    An unassuming, yellow-green lichen that seems to prefer high altitude exposed rock faces, R. geographicum is distinguished by both its extreme slow growth and extreme longevity. It has a yellow-green thallus, black apothecia, and oftentimes a black margin. R. geographicum derives its common and scientific names both from its similarity to a map or a landscape viewed from high above (2). For a review on lichen terminology, feel free to scan my previous post on lichens. I have not been able to find a source that specifies a preferred altitude range for R. geographicum in Colorado, but I have mostly noticed it starting at 8,000 feet and growing all the way up to 14,000 feet high. 

Splotches of R. geographicum sharing crumbling Pike's Peak granite with an unidentified moss. 

R. geographicum is frequently subtle until you're right on top of it: the thalli in this picture are about dime-sized.

     R. geographicum may owe its longevity to its decidedly unhurried growth rate. The growth rates of crustose lichens tend to be measured in yearly gains of the thallus' diameter, and R geographicum gains size very slowly. Smaller thalli (<10mm) cruise along at a relatively quick 0.8 mm/year, before slowly diminishing to around 0.64mm/year (± .24mm/yr) in larger thalli (>50mm)(3). At any rate this is what researchers discovered in Iceland; different studies have found similar results with small variations depending on the growth conditions with respect to substrate, climate, etc. Using understandings of growth rates such as these, researchers have dated R. geographicum thalli in the arctic to up to 8,600 years old(4). This kind of research is what allows for the performance of lichenometry, or using lichen growth (especially of R. geographicum) to make inferences about the age rock faces.

     I have been unable to locate any literature on R. geographicum growth rates in Colorado in particular, nor have I been able to locate any information that the particular lichen thalli present in the alpine tundra of Colorado are as old as their arctic counterparts. However, the alpine environment of Colorado does mimic the arctic effectively enough that other arctic species can be found here(5). It is reasonable to surmise that some of the larger splatters of R. geographicum seen at high altitudes in Colorado are at least several hundred if not thousand years old. Try taking a metric ruler with you next time you head to the tundra to see for yourself! 

Pinus aristata, Rocky Mountain Bristlecone Pine 

P. aristata growing on the flanks of Mount Evans. Note the straight and twisted habits in the wood, as well as the stripped, exposed wood on one side of the tree. Bristlecones can take on an assymetrical "flagpole" appearance due to consistent, powerful prevailing winds from the summits of the mountains they grow on.

Bristlecone wood can take on many hues as it weathers over centuries. Very old trees frequently have large tracts of exposed deadwood, despite the living parts being in good health.

     The Rocky Mountain Bristlecone tends to prefer the windswept altitudes near timberline at 8,000-11,000 feet(6). The harsh environment with the short growing season may actually be part of the reason for the bristlecone's extreme longevity, with maturity reached at approximately 200-250 years, and most trees living between 800 and 1,700 years. Some live beyond 2,000 years, however. 

A stand of  Rocky Mountain Bristlecone Pine, again on Mount Evans. The gnarled, tortured appearance of the trees is due to the harsh environment. The much younger saplings (bottom left and far right) have a much more normal, "Christmas-tree" appearance than their ancient counterparts. 

     P. aristata is easily identified as it often grows in pure stands near timberline(7). The habit of the trunk may be relatively straight or twisted, and whether the trunk twists or not appears to be determined by genetics rather than environmental factors(8). The environment is responsible for the partially stripped appearance of many of the trees, with exposed deadwood being the rule rather than exception on older trees. Only 10 inches of healthy bark is needed to sustain a large crown of needles(7). Deadwood in bristlecone forests decays extraordinarily slowly, and dead trees can remain in place for hundreds or thousands of years(10). The crown of the bristlecone is often spreading and unruly-looking, which can give the trees a top-heavy appearance. 

    The needles themselves are one of the bristlecone's most telling features. Needles grow in fascicles of five and are .75-1.5 inches long. The needles exude speckles of white resin (see photos below), the most important field mark to differentiate bristlecones from the limber pine, which is highly similar in having fascicles of five needles, having a similar habit, and growing in the same habitat(6). 

Needles and cones of P. aristata. Note the white granules of sap on the needles. The purple cone at top is an immature female cone with the eponymous bristles. At bottom are the pollen-bearing male cones.  

     P. aristata is monoecious, bearing both male and female cones on the same plant(9). The male cones are stubby, yellow nobs as seen above which distribute pollen to the wind. The mature female cones are 3-3.5 inches long, and bear characteristic hair-like bristles at the tips of each scale which are 0.5-0.75 inches long(6). This differentiates the cones of P. aristata from the cones of other species such as Pinus ponderosa, or Pinus contorta which have sharper, shorter, more thorn-like projections from the scales of their cones(6). 

     It is worth noting that the bristlecone most people associate with extreme longevity is actually a closely related but different species, Pinus longaeva. P. longaeva lives in the White Mountains in California and can boast individual trees which have been alive for nearly 5,000 years (7). The longest-lived P. longaeva specimens are those living in the harshest conditions, around 10-11,000 ft. This is presumably true for Colorado bristlecones as well, although I have not been able to find a source to verify it. 

Honerable Mention 

     At least two other species warrant mention for being long-lived, although not so much so as R. geographicum or P. aristata. One is the limber pine, P. flexilis, which can live up to 750 years(6). The other is the lichen Lecidea atrobrunnea, which can live to a venerable 1,500 years of age(11). 

Limber pine needles and male cones. Highly similar to a bristlecone in many regards, 

but without the resin spots. 

L. attrobrunnea growing on granite. It is easily recognizable with its brown thallus, 

gray to black margin, and chocolate chip-like black apothecia. 

     Thank you for reading about old species. I would like to end this post with a plea to pay heed to climate change warnings for the Rocky Mountains. This report  (not peer-reviewed, but does cite peer-reviewed literature) details many of the problems that are currently or soon shall beset the ecosystems of the Rocky Mountains due to anthropogenic climate change. Despite their extraordinary toughness, species such as map lichens and bristlecones are picky about their climatic conditions, and rapid change could wipe out huge populations. This means that P. aristata saplings growing today may die well before they reach their potential to witness the beginning date for the show Futurama in the year 3,000. Make sure to advocate for policies that slow the progression of climate change, and to get out and enjoy these ancient organisms while they are still in their full glory. Thanks for reading! 

References

1. Antiocus IV Epiphanes (n.d.). Retrieved from https://en.wikipedia.org/wiki/Antiochus_IV_Epiphanes
2. Corbridge, J. N., & Weber, W. A. (1998). A Colorado Lichen Primer. Niwot, CO: University Press of Colorado.  
3. Bradwell, T., & Armstrong, R. A. (2007). Growth rates of Rhizocarpon geographicum lichens; a review with new data from Iceland. JQS. Journal Of Quaternary Science, 22(4), 311-320. doi:10.1002/jqs.1058
4. Lichens (n.d.). Retrieved from http://www.nps.gov/glac/learn/nature/lichens.htm
5. Mammoser, D., & Tekiela, S. (2007). Wildflowers of Colorado. Cambridge, Minnesota: Adventure Publications, Inc.
6. Tekiela, S. (2007). Trees of Colorado. Cambridge, MN: Adventure Publications Inc.
7. Blue Planet Biomes (n.d.). Bristlecone Pine Retrieved from: http://www.blueplanetbiomes.org/bristlecone_pine.htm
8. Wing, M. R., Jones, A. K., Melbostad, S. R., & Knowles, A. J. (2014). Spiral grain in bristlecone pines (Pinus longaeva) exhibits no correlation with environmental factors [electronic resource]. Trees - Structure And Function, 28(2), 487-491.
9. Fryer, J. L. (2004). Pinus aristata. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Retrieved from http://www.fs.fed.us/database/feis/plants/tree/pinari/all.html  
10. Carrara, P. E., & McGeehin, J. P. (2015). Evidence of a higher late-Holocene treeline along the Continental Divide in central Colorado. Holocene, 25(11), 1829-1837. doi:10.1177/0959683615591353
11. Miller, C. D. (1973). Chronology of Neoglacial deposits in the northern Sawatch Range, Colorado. Arctic And Alpine Research, 5(4), 385-400.