After a long absence I am back. My first semester of full time teaching was quite a ride, but I work with a very cool group of people from whom I get more than a little help.
During the winter break I happened to be driving to a pet store with my friend (and our lab manager). He is one of the smartest people I know and his specialty is what I call “big biology”… point to a plant or animal and he probably knows the genus, species and its natural history. Being from the South, he also has an incredible grip on local natural history (something that I was just begining to get in San Diego). Anyhow, we were taking the long way to Conyers so he could show me all kinds of cool stuff and we passed a lone magnolia (M. grandiflora, I believe) when a question popped into my head.
“Why aren’t there forests of magnolia trees?”. I don’t think I have ever seen anything but solitary magnolias, or at the most a very few of them together. Unlike pines, which will form a somewhat dense stand of trees, magnolias seem somewhat aloof and off by themselves.
A pine tree will cast its seeds about and you soon have baby pines everywhere. Other local trees also seem pretty dense, or at least more dense than the magnolia. Given the number of flowers I see per tree, magnolia’s certainly seem to produce enough seeds for a population to spread (or not, see below); why don’t they fill in? I can think of several possible answers:
#1 – there are places where magnolias form dense stands and I am just an overexcited city mouse. I am definitely overexcited about many things and I am certainly ignorant when it comes to natural history of the South.
#2 – we are at the edge of M grandiflora’s range and some condition in the local environment isn’t “just right”. The range of this thing is pretty damn interesting, almost exclusively south of the Fall Line – there is a whole set of posts right there. I wonder if some aspect of late Cretaceous sedimentation is behind this (see this picture and look about where our campus is to see what I mean).
#3 – Magnolias are an ancient lineage of flowering plant, having split off from the other angiosperms (flowering plants) quite early. Paleobotanists don’t seem to agree on early evolution of flowering plants, but there seems to be strong support for the earliest being similar to magnolias (the “Woody Magnoliid Hypothesis”). Given that flowering plants only appeared on the world stage about 200-140 million years ago, its seems possible that magnolias could be more adapted for a different age. Perhaps they haven’t kept up with the times as much as pines.
#4 – (subset of #3) Perhaps magnolias do not progress to sexual maturity as quickly as pines or they don’t set as much seed as I assume they do or the seeds do not germinate as efficiently as pines do. A quick check of Wikipedia supports the slow maturity and inefficient germination of magnolia seeds, but their reference is a 197o USDA bulletin. Perhaps there are some experiments to be done germinating seeds hmmmmmmmmmmmmm?
#5 – (subset of #4) The seeds of magnolias are more tasty to some rodent or bird than those of pines.
Well, this has been absolutely fascinating, but my syllabi aren’t writing themselves.
Interspecies 