Organisms with disjunct range distributions fascinate me because they provide clues about past natural environments. Direct evidence of past landscapes is rare–over 99% of potential fossil evidence has vanished without being preserved in any way. The existence of extant species with odd distributions helps fill in gaps in our knowledge of natural history, though it requires some uncertain speculation. The sand myrtle is 1 of many species with an interesting disjunct range distribution. This member of the heath family (rhododendrons and blueberries) is found in the sandhills of southern New Jersey; the mountains of northeastern Georgia, eastern Tennessee, and western North Carolina; the sandhills of North Carolina’s coastal plain, and some isolated monadnocks in the upper South Carolina piedmont.
A sand myrtle in full bloom. They are a short plant, growing to just 20 inches in height. They can’t grow under tree canopies.
Range map of Kalmia buxifolia shaded in light green. The populations are more isolated than this map indicates.
One is left to wonder why the sand myrtle disappeared from or doesn’t occur in the areas between its disjunct populations. One hypothesis could be that it reached suitable habitat through seed transport via bird droppings. But the great distances between disjunct populations precludes this possibility. The seeds, if they even stayed viable within the bird’s digestive system, would be excreted long before they reached the other territories. Wind distribution is a more viable hypothesis. Winds carry insects, pollen, and light seeds great distances, and this light organic material eventually settles. Still, this seems an unlikely explanation because sand myrtle should occasionally be found growing in areas between their current distribution, even if the habitat is unsuitable. The most likely hypothesis requires a bit more complicated explanation. Sand myrtle may have existed throughout the entire region during the dry climatic phase of the late Pliocene/early Pleistocene. Today, sand myrtle favors open sunny conditions on poor rocky or sandy soils. Arid grasslands expanded when dry climates prevailed in the south. These dry prairie and scrub habitats were subjected to overgrazing by herds of megafauna, leading to bare soils, especially during droughts. Windy conditions stripped the top soil. Sand myrtle was able to grow on these poor soils with little competition from trees. When climatic conditions changed to a wetter cycle, deciduous forests expanded and outcompeted sand myrtle by shading them. Grassy savannahs were also unsuitable now because frequent lightning strikes led to more fires. Sand myrtle is both fire and shade intolerant and can only survive in communities with poor shallow soils where fire is infrequent. This probably explains why sand myrtle is currently found in rocky mountains and sand hills and nowhere else.
A Note on my Cod Liver Experiment
In my last blog entry I reported my visit to the Buford Highway Farmer’s Market. One of the products I purchased was cod liver in a can. I had a chance to try it yesterday. When I opened the can, I was surprised to find that most of the volume was filled with oil rendered down from cooking the liver in the can. I removed over half of the liver and squirted lemon juice on it. The first bites tasted like canned tuna, and maybe a little like oysters. But the texture was very soft. I started having a hard time accepting such a soft texture, so I ate the rest of this portion on buttered toast. This soft texture was not unlike that of scrambled eggs. I’m used to eating scrambled eggs, but I usually put lots of shredded cheddar cheese and smoked chipotle pepper in my eggs, and I also put them on buttered toast. Even with these additions, I still prefer eating my scrambled eggs with either salsa or brown mushroom gravy. Eggs are just so bland by themselves. I debated with myself whether to eat the rest of the cod liver for lunch today, but last night I fed it to the cat. Instead, I’m going to have a nice salami sandwich.