For years now, the tree community that measures and documents coast redwoods have come across a huge conundrum that really boils down to "what is an individual tree?" and "how does one document clonal organisms like the coast redwood?" For the coast redwood, usually trees create large clones and fusions that are irregular. After talking with John Montague, Michael Taylor, and Yinghai Lu, we all decided that there has to be a way to better document and make fusions "fair" and their parameters definable for comparison with the large single stems.
Michael Taylor first got started thinking about how many of the "single-stemmed" redwood champions are really not single-stems but rather gigantic fusions. This is not uncommon, and appears to be the rule in many situations. Some examples of "single stems" that are almost certainly ancient fusions include Del Norte Titan, Iluvatar, El Viejo del Norte, ARCO Giant, and the newest "biggest single stem redwood find" you all have been hearing about over the past few years. When one has a clonal species that grows like a weed, certainly they gobble up new trunks. Then there are many large, notable doubles including the most famous Screaming Titans. Then we have trees that are more obviously fusions with smaller accessory trunks, such as Lost Monarch and Melkor. So again, we all posed the question: how do we measure these trees.
That got John Montague and me thinking of how to add more trunks to a tree without simply destroying the competition. Screaming Titans would be a massive redwood if all of the volume was counted. But is it fair for single stems? Well, yes and no. A single-stemmed tree versus a fusion would likely have a smaller ground footprint making both nutrients collected from the ground and structural integrity a bit harder to manage once a trunk gets big. For the coast redwood, from a stability standpoint and from a nutrient standpoint, fusions are an advantage. But this is not good for the notable single stems. Why should we discount large 30000 cubic foot trees like Howland Hill Giant, an undisputed single-stem redwood, by adding up all the volume of fusions? Another issue are disadvantages to fused trees as far as the ranking. Consider that plenty of sugars from one stem go to the other and vice versa. Just measuring the main stem and discounting smaller trees is not a fair assessment, as the large tree would likely be larger if it didn't have another "mouth" to feed. And what about fusions with two or three decent-sized trunks? They deserve a shot at being measured, categorized, and given a "ranking."
As human beings and scientists, we all strive to make things fit into a box, and clonal organisms break every box we try and put on them. Take the question "what is an individual plant?" When does a basal sprout become a tree and when is it simply just a "branch" of the parent tree. And what about genetics? Is an albino branch up in a tree its own individual? What about a 50-foot tall albino basal sprout? There's no easy answer. We look at identical human twins and what makes them different? Their physiological separation, of course. With redwood trees and many other clonal plants, physiology changes from communal to autonomous from a large fairy-ring being communal in the winter to the tree making even individual branches have to produce enough photosynthate to survive in the summer. And from a structural integrity standpoint, generally the limiting factor for size (not height) of any tree, obviously a redwood by itself is less stable than a clonal fusion. A huge fusion rarely can be "blown over," especially if its shape is fairly round. So knowing this, below is an attempt to "create a box," as our humanity desires, for the clonal redwoods.
This will be called the "functional volume (fV) equation" and I am hoping it will be heavily critiqued by you all so we can try and get some sanity as far as how to measure these things. It came from the premise (and discussion with John) about what we define as a "single-stem" redwood. We decided to call a single-stem redwood any redwood that does not split until at least 1/3 the height of the tree. This means for a 300' redwood, any split that is above 100' is an "undisputed single-stem redwood." But here's where it gets interesting. Taking the 300' tree example, a stem split at 50 feet is quite a bit different then a stem split at 20 feet or 10, so obviously the split has a lot to do with a tree's "singleness." From a physiologically-connected point of view, the lower the split, the more distance (and less likely) sugars will travel from one stem to the other.
As John and I were thinking about it, I thought "what if we just take the percentage of an accessory trunk based on our definition of 1/3 equaling a single-stem tree?" I created the below formula and we ran through a plethora of examples to determine how "fair" it was, and it seems quite fair. Below is a photo showing the formula in the easiest way. The idea is that we treat any fusion, that is any set of fused stems less than 1/3 the tallest tree's height, as separate stems that we selectively add together. The selectiveness depends on the height of the split compared to the 1/3 designation. Say we have a split at 50 feet, 1/6th of the total height or 1/2 of 1/3. Then we calculate the volume of the accessory trunk and add 1/2 of the calculated volume to the total volume of the main trunk. That is the essence of our model and it seems to be effective, though everything is "subjective" to a human-being's perspective as to "what is a bigger, more-impressive tree (single-stem, double, fusion, etc.)?"
- For the fused portion of stems, the volume is proportional to the area of the trunks at the split if they were cross-sectioned. If the area of the trunks is 2/3 to 1/3, then the larger trunk is 2/3rds the volume of the fused stem and the secondary trunk is 1/3 the volume of the fused stem. This idea was started by me and enhanced by Yinghai Lu.
- One can also add trunks accordingly, using the split height of the added trunk compared to the total height of the tallest/main trunk within the fusion.
- For big double-trunked trees like Screaming Titans, for example, either one can measure the trunks separately and say that Screaming Titans are two trees with ~15000 cubic feet each (making numbers up here), or one tree with 25000 cubic feet (again, making numbers up--I have not measured the size of Screaming Titans). It gives a measurer flexibility, either categorizing their find as one tree or two, but having both numbers or either categorization being a "fair" assessment.
The whole reason we decided to do this is so that the Lost Monarch can be fairly assessed just like any other trees that don't really fit into a box. Also, in case there's a misunderstanding, we've found a transitional series with fusions. Some fusions do not have a high split but we know others with an immensely high split that will eventually look like a single-stem in a few hundred years. And then we see those trees that were certainly fusions a few hundred years ago but are now considered single-stems. We have plenty of evidence supporting the fact that fused structures in redwoods are dynamic, changing from clearly fusion to clearly "single-stems," or trees that should have that distinction, anyways. Please vote on the poll.
We all look forward to hearing your comments!
Zane Moore (on behalf of John Montague, Michael Taylor, and Yinghai Lu)
Last edited by yofoghorn
on Sat Jul 04, 2015 12:29 am, edited 1 time in total.
Zane J. Moore
Plant Biology PhD Student
University of California, Davis