Mike Turner

Zelkova serrata

Cordyline fruticosa

This is the time of year when you can easily visually see the effect that slavery has had on the species composition of our local forests.  Flowering dogwood is in bloom.  This understory tree, which is very common in most parts of its range, is few and far between in this part of upstate SC (Greenwood).  As you go north of Greenville or south into the coastal plain, it becomes common again, but around here you can only spot an occasional solitary specimen or a small group of 2 to 4 and you can drive for miles through the woods without spotting one.  By far, most of the flowering dogwoods around here are found growing in people’s yards.

When I first moved down here, noticed that the local forests were highly deficient in trees bearing fleshy fruit that are primarily distributed by birds (dogwood, magnolia, holly, black gum, black cherry, mistletoe).  Most of the trees had either wind distributed seeds (maple, elm, tulip poplar, sweetgum, ash, redbud, pine), large seeds distributed by squirrels, (beech, oak, hickory, walnut), fleshy fruit that are eaten by birds, but is often distributed by wild mammals or livestock (persimmon, plum, honey locust, grape, blackberry, elderberry, red cedar).

The reasons behind this goes back to the history of this region.  The virgin forests were clear cut to create cotton fields, then after 5 to 10 years when the soils had been depleted, the eroded land was abandoned to grow back up into forest.  So the plants had to go through this bottleneck of getting their seeds from existing virgin forests across acres of cotton fields to the abandoned fields to start anew.  Wind, squirrel, and mammal distributed seed had no problem doing this, but bird distributed seed had great difficulty making the jump.

In the plantations on the coastal plains, rivers, ponds, swamps, and marshes were common and most plantations were located along navigable rivers for ease in shipping their product.  So the slaves could easily use their free time to find a body of water and go fishing to add high protein food to their diet to augment the bland grain diet provided by the slave owner.  But when they were relocated to a plantation in the upstate where no ponds, swamps, or marshes existed and with the only a few rivers spaced far apart, a slave would be lucky to find a small creek to try to fish, so for most slaves, fish was unavailable.  So they turned to another form of high protein food that could be easily caught using low tech methods, namely small birds using birdlime to trap them.  Birdlime is a sticky substance that can be easily made using local materials that has been traditionally used by primitive societies throughout the world to catch small birds.  The sticky birdlime is smeared on branches where small birds would alight, trapping them until they could be collected for the pot.  Squirrels are hard to catch without shooting them and slaves wouldn’t be allowed to have a gun.  The slave owners would be more likely to hunt larger game such as deer and turkey rather than the lowly squirrel, so squirrel populations would have remained healthy.  So as the small bird population got thinned out by trapping, bird distributed seed wasn’t able to make the leap and get established in the newly established forests.  

Today, small birds have made their comeback and are busily distributing seeds, but it will take some time for bird distributed plants to regain their normal populations in our local forests.

If you have problems with squirrels  or other mammals eating your chicken feed, mix some gravel in with the feed.  Chickens can peck around the gravel to get at the feed, whereas the larger mouthed mammals have great difficulty eating the feed because the gravel gets in the way.

Growing bamboo is a great way to provide cover for birds.  It makes a great place for birds to roost overnight.  The dense evergreen foliage hides them from predators and reduces their heat loss in cold weather.  The flexible canes and branches with slick stems make it hard for land predators to climb up to them and the jiggling stems gives them plenty of warning that the predator is trying to reach them.

 I have 100's to 1000's of blackbirds and grackles that overnight in my bamboo groves providing an aerial display every evening as they fly in at dusk (complete with red shouldered hawks and merlins working to intercept them on their way in) and the guano they leave behind fertilizes the bamboo groves and the surrounding land.  During the day, cardinals and English sparrows use the groves as places to hang out.

There are a number of trees whose wood is so dense that it sinks in water.  Many of these trees have a common name of "ironwood".  In the southeast USA, Carpinus caroliniana (Carolina ironwood) holds this honor.  Any wood that weighs more than 62 lbs per square foot will sink in water.

Since few seem to want to speculate on this, here are my thoughts on the matter.  In the the lower latitudes during the day, the sun spends most of its time high in the sky so the light is coming from above most of the time.  The best tree shape under these conditions is broad and relatively flat topped (think mimosa tree shape) with only enough height to keep above the tree competition.  Conversely at the high latitudes where the sun spends most of its time near the horizon so the light is coming from the side all of the time, the best tree shape is tall and narrow (columnar), which is the shape seen in trees of the taiga forests.   In the mid-latitudes the optimum tree shape is intermediate between these two.

Our temperate trees weren't always growing where we find them growing today.  From the time that angiosperms first evolved over 100 million years ago during the Cretacious until about 8 million years ago, temperate trees were growing up near the arctic circle as part of the polar deciduous forest (the conifer and ginkgo lineage in that location goes back even further).  Then, starting 8 million years ago, as the climate cooled down into the Ice Ages, these trees were pushed south into the mid-latitudes. As they moved south, their shape evolved away from the columnar shape most efficient at the high latitudes into the broader shape that works best at their new home in the mid-latitudes.  But those ancient genes for a columnar shape are still there and it is relatively easy to pick them out of the mix when selecting for new cultivars.  

There are also narrower cultivars of tropical and subtropical trees such as avocado and Virgnia live oak.  These aren't columnar, but are narrower than their typically broad wild type shapes and are are typical for the shape of mid-latitude trees, ancient genes going back to when these trees were growing in the mid-latitudes over 8 million years ago.  But tropical trees have never grown in a high latitude location where a columnar shape would be optimum and so have never evolved the genetics for it, hence the dearth of columnar tropical trees.

Interesting, while researching this, I came across papers about fossil dendrochronology showing that the trees  growing in the polar forests during the Cretacious were about twice as productive as their modern taiga equivalents, no doubt due to a combination of warmer temperatures, longer growing season, and higher co2 levels at that time.

Mike Jay wrote:

Mike Turner wrote:Anyone care to speculate?

Maybe there's more of a demand for columnar temperate trees?  Maybe the biology makes it harder to create a columnar tropical troee?

I can't see why there wouldn't be a demand for columnars in tropical landscaping and orchards.  Columnar fruit trees makes it possible to shoehorn a bunch of different fruit trees into a small garden.  Columnar trees are very useful in formal garden design.

What aspects of tropical tree biology would make the columnar shape difficult to select for when compared to temperate tree biology?  I'm just trying to figure out why there is this disparity.  There are literally 100's of columnar cultivars of temperate tree, but almost none for tropical trees.

So why is it that columnar cultivars are "dime a dozen" among temperate zone dicot trees and conifers, while being practically nonexistent among trees from the tropics?  Among the tropicals, I could only find a single cultivar of Erythrina (Erythrina variegata 'Tropic Coral') that was columnar.  In hibiscus, the temperate Hibiscus syriacus (rose of Sharon) has several columnar cultivars, whereas the tropical Hibiscus rosa-sinensis, the common tropical hibiscus, which has 100's of cultivars, has none.  Anyone care to speculate?

Should have been more specific.   I'm asking about dicot trees, not monocots or plant growth types that have no temperate zone equivalent (palms, papayas, etc.).