Monday, December 7, 2020

Time and the Botanist

Time is funny stuff. I live one day at a time. and somehow I've lived more than 26,645 of them. No doubt my memories of the past are filtered, but it doesn't seem that way to me. I easily remember things before other people were born. Weird. As I wrote about bamboos last week (link), I imagined a bamboo telling me about things that happened before I was born. More seriously, if more than 20 years elapses between the times when bamboos flower (true for many bamboos), a botanist can get only one replication of flowering into a career, that is, only see them flower twice. For species that flower less often, none of us get to see them flower more than once. 

clump of bamboo
Bamboo grove. When will it flower?

The first plant I studied demographically, to see how long they lived and where in the life cycle the greatest mortality was, lived an average of two years. and no individual lived more than seven. I marked individuals (aluminum tag on a nail beside the plant) and, after eight years, when I wrote up the study I had seen the complete life of every plant. Very satisfying. Although, as I write this, eight years sounds like a lot of time to devote to a little wildflower. (That was stickleaf, Mentzelia nuda (stickleaf family, Loasaceae) in western Nebraska, reference below. Blog post link).

stickleaf, Mentzelia nuda
stickleaf, Mentzelia nuda

But the second plant I studied, although not taller than my knee, has a lifespan of decades. There were really big plants of the bush morning glory (Ipomoea leptophylla, morning glory family Convolvulaceae, reference below, blog about the plant link) that I followed for 10 years, and they were still really big plants when I went on to another project. The site is no longer available to researchers, but I'm pretty sure I could lead you to those same plants now, 40 something years later. Lifespans like that aren't a surprise for trees, but many small species have long lifespans as well, it is just less evident. 

bush morning glory, Ipomoea leptophylla
Bush morning glory, Ipomoea leptophylla.
This plant is certainly more than 50 years old. 

Time is one thing you can't have back, can't speed up or slow down. We will struggle to study long-lived plants because, by comparison, we are short-lived--and careers are shorter. 

The same applies to long-lived animals. This week I am summarizing a study of western harvester ant colonies (Pogonomymex occidentalis, Hymenoptera: Formicidae) that I conducted in western Nebraska between 1977 and 2019. In 1977, there were almost no records of how long ant colonies lived. Harvester ants set up big conspicuous colonies, so, like marking trees, I figured I could easily come back until they were all gone. 

nest of western harvester ant, Pogonomyrmex occidentalis
The dark circle is the bare zone (disc) cleared by nest
of western harvester ants, Pogonomyrmex occidentalis

In a way, I'm doing a happy dance, having completed this long-term study. But it is not that simple. In 1977 when I set it up, I was a very green new professor. I chose a good experimental design based on what I knew then, but it is weak by 21st century standards. And most years it was a side project, so I'd make notes and shove them in a file. The next year I'd organize them enough to be useful looking for the ant colonies. I thought at the time I was doing a good job of record keeping. Going through the notes this year, I find I didn't always write what year it was on every page of the field notes, so I'm guessing from the choice of paper and ink what year some of the notes were made. Of course it was obvious at the time. I find myself critiquing younger self, which is quite uncomfortable.

nest of western harvester ant, Pogonomyrmex occidentalis
Nest of western harvester ant, Pogonomyrmex occidentalis

Which brings me back to the role of time. There's no way to do it over. For two reasons. First, who has 42 years to watch ants? Not likely to be a good use of someone's time. Second, though, is that the climate is changing, rather rapidly. 

Of the things that changed during my working lifetime in plant ecology, perhaps the most important were changes in paradigms--in our overview of how nature works. In 1977 the climate was seen as stable; I was studying harvester ant colonies as if the conditions they experienced, apart from the occasional drought, were eternal. But that's not how we see it today. The average temperatures have risen, and will continue to rise, taking us into the unknown. The study isn't repeatable because we could only start another such study today, beginning in conditions we know to be different from 1977, and expect to go on changing.  Paleontologists and historians have always been conscious that things don't repeat, but ecologists used to think of the climate as a given, in which studies could be repeated to work out ambiguities. Not anymore. Not if they last 40 years.

So the study is unique and unsatisfying both at once. I am searching through the frustration for lessons. I might  advise people setting up long-term studies that time will change the context of the study, but I see no way to know how it will change it. All one can do is the best you know how at the time--advice so familiar as to be unimpressive. I would also suggest: know your limits. Even a study that only takes a weekend can be difficult to sustain for decades. I wish now I had a bigger, better-replicated project, but that might have lapsed years ago due to time conflicts. Another lesson is to keep records as if someone else is going to write it up, because memories of how it was done blur; "obvious" in 1985 is not obvious in 2020. Finally, pay attention to how you store the data. The computer programs I used one by one became obsolete and, appalling but true, I found it easier to work with paper notes than try to recreate the software. Things change!

Long-term studies can be hugely frustrating because you can't hurry them and when completing them, there are all those issues of the end being in quite a different time than the beginning, but long-term studies reveal things we couldn't know otherwise. I see time as one of the last frontiers: hard to study but critically important. 

hoary puccoon, Lithospermum caroliniense
hoary puccoon, Lithospermum caroliniense, another small
plant that lives longer than humans 

And, because of all that, any long term observations you make will become invaluable. Back yard rainfall? The day you saw the first robin each year? Earliest frost? Anything that catches your eye. (And, if your camera has a date stamp, you can simply take a photo as your record.) Forty years ago, I'd've recommended keeping such records to document nature, because there are so many things we don't know. Now, you can expect changes. Rainfall next decade is likely to be different--where I live, less. The robins will move north earlier. First frosts will be later. When you look at the notes in 10 years, you'll be surprised by how much has changed, because without notes, gradual changes are hard to notice. 

As I said at the beginning, time is funny stuff. 

Comments and corrections welcome.

Technical papers on the organisms mentioned. The final paper on the harvester ant colonies is not done yet. 

Keeler, K.H. 1987. Survivorship and fecundity of the polycarpic perennial Mentzelia nuda (Loasaceae) in Nebraska sandhills prairie. American Journal of Botany 74 (6): 785-791.

Keeler, K.H. 1991.  Survivorship and recruitment in a long-lived perennial, Ipomoea leptophylla (Convolvulaceae).  American Midland Naturalist 126: 44-60.

Keeler, K.H. 1993.  Fifteen years of colony survivorship in the western harvester ant Pogonomyrmex occidentalis.  The Southwestern Naturalist. 38: 286-289.

Weller, S. G., K. H. Keeler, and B. A. Thomson. 2000. Clonal growth of Lithospermum caroliniense  (Boraginaceae) in contrasting sand dune habitats. American Journal of Botany. 87: 237-242.

Kathy Keeler, A Wandering Botanist
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1 comment:

  1. I realize that for really long term studies on ant colonies, it helps if there are previous studies done on the same colony. Kinda in the sense of stepping on the shoulders of previous work to mitigate our short lived nature. In one case, I looked at a unicolonial colony of Pheidole megacephala 30 years after it was discovered in a botanical garden. It was still there after decades!