Ephedra dendrochronology

Trying to resolve the age of the Ephedra’s found on top Panoche Hills is super difficult. As with trees in arid environments, precipitation is the factor limiting secondary growth development. Thus, drought years can produce extremely small tree rings or “missing” rings altogether. Ephedra is additionally challenging being a shrub, which generally are tougher to date than “true” trees. Some key things I’ve learned from conducting a proper tree aging is:

1. Replication – Often it is important to compare multiple samples of the same individual as well as other members of the population. As with other sciences, more is always better.

2. Consider abiotic or limiting factors – temperature, precipitation, or snow melt can all strongly determine tree ring presence. This is also true for microscale topographical changes. For instance a tree or shrub growing on a slope will likely have a different ring structure than its counterpart growing on a flat/plateau.

3. Cross-validation – Besides comparing it to other individuals of the same species, it is often good practice to compare with an additional species found in the same area.

That being said! I’m going to give this dating thing a shot. From a sample individual collected at the Panoche Hill plateau, an area limited particularly by precipitation, I was able to count 42 growth rings in a core sample. Unfortunately the center is rotted (a trend in ephedra cores) which probably has a higher density of tree rings than the remaining sample. However, if I assume the same number of rings/cm as the not rotted wood, there would be approximately 58 total rings.

But!! Panoche Hills experiences drought events such as the last two years. From my time out there, Ephedra only produced seed in 2013 which I am going to assume is a “successful” growth year and would produce a growth ring. Years like 2014 and 2015 produced no seed, and were therefore likely to have a missing growth ring. On average, for the last 58 years, precipitation lower than the seed producing threshold represented %20 of the years.

What does this all mean? Not much actually… it seems than Ephedra at Panoche Hills, could be anywhere between 70-1000 years old. There are just so many considerations that it will definitely require the assistance of a professional. It is interesting to think though that Ephedra could have only colonized Panoche Hills, post-European arrival to North America.

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