The Earth Story

Of strings and cooler climes

Everyone has heard of the fabled tones of the musical instruments created in the late 17th and early 18th century CE by Antonius Stradivarius, and many attempts have been made over the centuries since to build instruments that replicate his sound and find the fabled 'secret ingredient' of the Cremona instrument makers, whether in the wood curing or the varnish. The task may well be impossible; it turns out that his 600 or so surviving instruments (violins, guitars, violas, and cellos) are unique because of the climate of that terrible century, that fell in the middle of the period known as the little ice age (see Little ice age http://on.fb.me/1j3khlF).

While the cause is still being debated (options include fluctuations in solar output, characterised by a period with few or no sunspots known as the Maunder Minimum and reductions in atmospheric CO2 due to the depopulation of the Americas by disease in the previous century), the tree rings in the wood he used to build his instruments show a characteristic pattern due to the unique climatic conditions of the time.

Trees produce narrower annual growth rings in these cooler conditions. They usually vary in width along with the annual climate variations, and have been used as proxies in many climate studies, recording everything from drought cycles in the American west to the Warm medieval Period in Europe. The prolonged cold during the 17th century resulted in a long succession of narrow dense rings with little variation due to the poor growing conditions (with long winters and cool summers), making for unusually dense wood with exceptional acoustic qualities, resulting in the deep resonances in his unique sound. Such conditions have not recurred since, making these pieces irreproducible.

Loz

Image credit, a violin at the Royal Palace, Madrid: Σπάρτακος, frost fair on the Thames: Thomas Wyke http://bit.ly/1NERBeZ http://bit.ly/1jMV2UW http://spaceplace.nasa.gov/violins/en/ http://bbc.in/1QdLEbo

The long gone forests of the icy wastes

Dinosaurs were not the only life forms to make their home in the cold dark regions surrounding the world's southern pole (see http://on.fb.me/1VXMHdt). They were preceded by warm climate forests in the early Triassic some 250 million years ago. While the globe was warmer than today, scientists have been curious to understand what adaptations allowed the plants (some of which resemble modern tropical trees) to survive the long months of darkness during the Antarctic's long night.

The trees, found near Mt Achernar, would have to photosynthesise intensely during the short growing season, laying in reserves of stored sugar to last through the dark months of the year. The team turned to the fossils, including the leaves and tree rings, which we know quite well how to read as environmental and climate proxies from modern studies of dendrochronology. The trees seem to have been deciduous, shedding their leaves every autumn into carpets that have been preserved. This makes sense as a survival strategy since the tree can resorb energetically expensive to make chemicals such as chlorophyll (why leaves turn colourful in autumn as first green and then red pigments are removed), and store it over the winter, dumping the dead husk to the elements.

The cells in the rings informed us about how the trees grew. There are two kinds of wood, early, made as it grew in spring, and late, laid down as the tree prepares to hibernate. Late wood is denser as it is used as an energy store, and has thicker cell walls. It is also possible to ascertain from the rings whether the trees were deciduous or evergreen, which led to a surprise. The leaves suggested deciduous, the cells evergreen, as did a more detailed analysis of carbon molecules, compounding the mystery. The trees seem to have had characteristics of both that are no longer around in any species alive today. The rings also suggested tropical trees, of a type that goes dormant for a short while to rest in lands without seasons.

Loz

Image credit: Patricia E. Ryberg

http://bit.ly/1LzRSPw http://bit.ly/1OALeea http://bit.ly/1OALSsh

What are tree rings?

When you look at a fresh cut piece of wood, you see concentric rings. One can count these rings in order to deduce the age of the tree. In fact, an entire branch of study known as dendrochronology pursues answers to questions about past climate simply by analyzing variations in tree rings. So what exactly are tree rings?

The answer to this question lies in the physiology of wood formation. Trees are most photosynthetically active during a period referred to as the “growing season”, when the sun is strong and resources are abundant. For most of the US, the growing season is April – September (give or take a month or two). For the first portion of the growing season, trees put on new growth in the form of “earlywood”. Earlywood is less dense (thinner cell walls, and wider lumen [cell wall opening]) with wider vessel elements. At some point during the growing season trees begin putting on new growth in the form of “latewood”. Latewood is denser (thicker cell walls, narrow lumen), with narrower vessels, and is visually darker in color. The point in which a tree transitions from earlywood to latewood production throughout the growing season varies both within and between species. This transition point is particularly important to scientists because the percentage of latewood is the most important factor controlling the density of wood (averaged across a tree), the mechanical strength and structure of the wood, as well as the yield and quality of paper pulp.

Trends in wood formation are fairly well studied. Between the ages of one to about 10-15 years of age, a tree is putting on a large percentage of earlywood each year (with percent latewood increasing each year). This portion of the tree is known as the “juvenile core”. Once the tree transitions to the “mature core”, the percentage of latewood produced each year stabilizes. Mature wood of trees is structurally superior to the juvenile wood since it contains the highest percentage of latewood.

So when you look at a fresh cut piece of wood and begin counting the rings to deduce the age; remember, you are not simply counting rings, but macroscopic differences in the physiology of earlywood and latewood!

-Greg Aegis

Further Reading http://wapo.st/1fKleym http://bit.ly/1I3Birk http://1.usa.gov/1I3Bnv7 Previous posts: http://bit.ly/1OgHvPO http://bit.ly/1LcDnlq

Image http://bit.ly/1RA8qve