It took two months, but I can now finally say that the entire batch of tree samples that Emily and I collected over spring break are now processed and ready for data analysis!
The final haul of samples, processed and ready for the next step in nitrogen analysis!
In the above picture, each stack represents one sampling location. For reference, the shortest stack in the front right/centerish is South Carolina, and is 5 trays. The tallest stack in the back is Texas (apparently, everything really is bigger there) and is 16 trays. Each tray holds ~80 rings. Some of the Alabama samples ended up in bags because I ran out of trays. In total, we have 13 sites, producing 124 usable cores, totaling ~9,000 rings. While we sampled 130 cores, a few are unusable due to sap stain fungus (see below), rings so faint or narrow as to make splitting unnecessarily difficult (this is why we sampled extra at each site), or ‘crumbly’ cores (which disintegrate after drying).
Individual rings of Juniperus virginiana. Each ring gets its own well in the tray. Notice the variation in color, even within a single ring.
For now, the rings are hanging out, each in their own little well. Some of them will be loaded for analysis (see ‘Next Steps’ section), and others will be archived for future research, or as a back-up if any of our isotope analyses go awry. The picture above is of Juniperus virginiana rings from Nebraska.
Summary of Sampling Locations
To the left, you can see the breakdown for sampled genera and chronology ages at each of the sampled sites. For example, in Alabama, we sampled individuals from Pinus, Quercus, and Tsuga. While all the pines were Pinus taeda (loblolly), and all the Tsuga were eastern hemlock (Tsuga canadensis), the oaks included Quercus alba (white oak) and Quercus montana (chestnut oak). Collectively, these trees ranged in age from 60 years old (a Tsuga individual) to 130 years old (also a Tsuga), with the pines and oaks somewhere in the middle.
As is common in dendro work, Pinus and Quercus are fairly ubiquitous, while other genera are less common – such as Juglans (walnut) and Liquidambar (sweetgum) which are each represented by a single individual.
The only real problems here are the sites that have short chronologies. South Carolina is the worst of these, with a maximum length of only 29 years. This stand contained good sized trees (diameters of 45-50 cm), but the rings were incredibly wide. Nice growing habitat for Pinus, bad sampling location for me. I’ve been in touch with our contact there in the hopes of finding an older stand and re-sampling.
Less severe, but still awfully short are Tennessee (max 40 years), Nebraska (max 57 years) and Arkansas (max 59 years). We set a (somewhat arbitrary) minimum for usable cores at 60 years. Since our goal is to get at long term ecosystem nitrogen cycling, the longer the core the better. Less than 30 years (like South Carolina) is virtually useless for our purposes (although could still be used for site or species mean values, just not temporal trends). Nebraska and Arkansas may be able to squeak by our cutoff. Tennessee is in a bit of a gray area. As with South Carolina, I will get in touch with our contacts and see if there are known stands of older trees. Again, each of these contained relatively large trees (in some cases pushing 70 cm diameters), but just had large growth rings, and therefore short temporal representation. This will make it difficult to identify older stands without coring a few trees there to see the rings.
It’s also worth noting the different types of cores you get, depending on how you drilled the corer into the tree. There are three ways coring can go:
1) You don’t get to the center of the tree. This can happen if the radius of the tree (distance from bark to pith) is longer than your corer, if the center of the tree is rotted out (as we ran into with many of the Quercus), or if the resistance of the wood to the corer is such that you can’t drill far enough in to reach it. This last can be common in hardwoods, particularly when you have my upper body strength (or lack thereof) and are coring 130 trees in a week….
When this happens, the resulting cores show little or no ring distortion and no central ring.
2) You get far enough into the tree to pass the center, but you don’t actually hit it. This usually happens because you have a long enough corer, and you have the muscular fortitude to get it in, but you cored a little off center. Trees are rarely perfect circles, so this is usually the most common occurrence. Generally speaking, passing the center is considered ‘hitting the center’. You may miss a few years (depending on how far off the mark you were), but you get the bulk of the chronology, and you have a close approximation of the age of the tree.
When this happens, the rings nearest the center show a strong distortion towards the center. You can easily see where the rings start to repeat.
3) You hit the true center, the once-was-a-little-baby-sapling heart of your mighty oak (or pine, you know, whatever).
This results in a core that not only has minimal ring distortion, but also contains the pith of the tree. Now you have undistorted ring width measurements, and the full chronology of the tree’s life, including it’s exact age.
Our sampling fell about equally into the first and second categories, but we did also get five direct center hits (three Juniperus from Nebraska, and two Pinus from South Dakota)! I was very proud of this, even though it involved no real skill on my part and was mostly due to random chance and the law of large numbers.
And now here are some other cool things from the samples:
1) Sap stain fungus on one of the Georgia oaks. It is pictured next to a healthy oak for comparison. Sap stain fungus (as the name implies) does not seem to permanently impair the tree, but the fungal spores stain the wood a lovely blue color.
Healthy oak (top), and oak infected with sap stain fungus (bottom). Both are Quercus phellos from Arkansas
2) I know that eastern redcedar (Juniperus virginiana) is wreaking all sorts of havoc as an invasive species throughout the midwest. But it sure does make for a beautiful core. Reminds me of raspberry-lemon sorbet (random, I know). It also smells wonderful. Despite not *actually* being a cedar, Juniperus virginiana is often used to make cedar chests. Growing up, we also used redcedar chips in our dog’s bedding to ward off fleas. My two favorite smells growing up were the cedar chips, and the Pine-Sol my Mom used in our laundry (I was a weird kid, ok?). Not surprisingly, I love the smell of the pine cores too.
Next Steps
Once we get a green light from the isotope lab, I’ll begin loading our 9,000 rings into tin capsules for isotope analysis. This will take some time, as will the actual analysis, so I’m hoping to get started on it right away.
We also still have samples from other sites that have been mailed to us. While I’m waiting to hear back from the isotope lab, I’ll continue splitting these samples, which are from Ohio, Alaska, and Wyoming.
Additionally, Emily and I are still working on filling in the remaining states. Emily will be sampling in Illinois at the end of the month, and I will be taking a road trip through the southwest and coming back with cores from New Mexico, Arizona, and (hopefully) Nevada. Permitting in Nevada is becoming a bit of a snafu, but hopefully will be worked out by the time I get there.
Check back here for more details as we work through the data and obtain new samples!
Laci M. Gerhart 