Conifer growth

Jason Ashley

The growth pattern of conifers in general follow the same pattern of growth as found in broadleafed though there is the tendency to the conical form. What effects the growth pattern more than anything though is the proximity of other trees and available light. Assuming that wind is not a factor (as with isolated bristlecones), one can expect the tree to spend most of its energy as a juvenile growing toward the light source as quickly as possible. This means that in a dense wood the tree would sacrifice branch growth in favor of trunk growth until it reaches an acceptable light source when it would then begin to branch more laterally. To say that any one of these trees has a "pure form" would be incorrect as the tree will take advantage of its situation either as a single, isolated plant or as part of a dense wood.

Today we can see ornamental, non-hybridized conifers planted in isolation and given proper care will have a tendency to the conical (Christmas tree) form but this situation is uncharacteristic of their growth in the wild. The simple reason why lower branches are not present in most wild specimens is simply because there is not enough light at lower levels to warrant spending the energy to grow branches beneath the canopy level. Same is true in a rain forest. Trees which are singular (not in a stand) will not grow as tall as trees in a stand because there is no need to expend the energy to out-compete the smaller undergrowth or the rest of the woods in general. Fourth level forests (the most mature stage of forest growth) comprise trees of all kinds that sacrifice lateral for vertical growth.

The "ancient" trees we have left today are few, but telling. The umbrella pine, dawn redwood, and larch are all strongly conical when left in isolation from competition and truly they have very rigid forms but they are not known to have ever developed in the wild this way. The gingko is special because we know from Japanese records that the trees were selected over the eons for broader shape so that they would produce more thick branches and provide more wood for building houses (because gingkoes are very fire-resistant), however there is a strongly pyramidal variety that is less common then the broad-branched variety which is most popular for ornamental purposes. What each of these plants has most in common is the ability to throw sports of leaves along the trunk. In the days of the dinosaurs these trees were most likely only going to survive by growing as tall as possible and producing as few branches and leaves as possible until they reached above the reach of dinos looking for a tasty meal.

The umbrella pine grows excruciatingly slowly (6" in a good year) while the dawn redwood can grow exceedingly fast (6' in a good year). If speed is a factor in survival then why the big difference? The theory is simply that umbrella pines were not favored food and in any event are not known to grow very tall (80') today though they are exceedingly dense in needles. They, like the laughable monkey puzzle, probably used their needles as a defense to make them less palatable. Dawn redwoods had to use speed because the soft fronds are very palatable to animals even today so the effort to redirect energy into growing above edible level was an immediate need. What the dawn redwood does do, besides growing so fast, is to grow its lower branches higher than edible level as a form of defense. Lower branches of dawn redwoods grow "up" along the underside of the tree and once they have reached beyond the width of the tree leaf profusely. Leaves in the inner part die though there are always (this is important) sports along the trunk defended by dense branches with no leaves on them until the end of the tree. That's why dawn redwoods look like other conifers in that there are no leaves on the interior. But in the dawn redwood you get the sports on the trunk. So what's going on is the tree has prepared a "last defense". In case all the outer leaf bracts are eaten the tree still has leaves which are unreachable to all but the most determined predator. Left alone and totally de-leafed the tree still has a chance to gain photosynthesis from the sports along the trunk while it concentrates on re-leafing itself and growing taller. This kind of event is naturally disastrous to the tree but it works. Larches work the same way.

Gingkos are no different but you have to see them in the lesser-known conical form. An interesting note is that today nothing eats gingko leaves. Also, the tree knows no pests or disease of any kind (ask my deer, they eat everything else!).

You might guess what the "safe height" was in the case of all these ancient trees but particularly in the two oldest: the gingko (Cenozoic) and dawn redwood. If there were forests comprised of either trees you might guess how high sauropods could reach based on what natural height these trees would reach before branching out into a canopy in a forest environment. Unfortunately neither of these trees has ever been seen in such a state. Gingkoes can no longer propagate naturally without direct human intervention. Insects nor birds seem to do the trick. Gingkoes have not been planted in forest-like situations and it would probably take two or three hundred years to find out if they were planted in such a way now.

Dawn redwoods were found only so recently (1945) and then only from a small stand of trees which averaged about 60' and they were not densely packed together in a forest setting. The stand was isolated and on a mountain which could further explain the apparent slow-growth of the trees and the dwarfed stature of them. Soil was also poor and dry. This combination of factors may have caused their reason for survival, stunting growth and retarding aging. Today's oldest dawn redwoods grown from that stand are cultivated as specimens isolated from each other and thus we aren't able to judge how they would act in the wild (largest one I know of is now 160'). We would need a trial stand grown as a laboratory forest in order to determine how they would act in the wild left to their own devices. That might not be too much help either given that we do not know what kind of element they would have prospered in except that we do know they favor wet, loamy soils with a fairly shallow water table (6'-12'). Would there have been other plants growing nearby that formed a symbiotic relationship necessary for mutual survival? Certain organisms, insects, something we don't know? It's hard to say.

I've loved each of these trees and have grown and watched them with morbid curiosity since I planted them when I was 11 (my parents thought I was crazy asking for a tree for a birthday present), 12 (even more nuts), and 15 (certifiable), but I was lucky to live on a very large parcel of land and I thought, 'If I can't have dinosaurs, I could at least have their trees!'. A monkey puzzle will not live as far north as where I am, sad to say. The dawn redwood is my favorite because it is so genuinely beautiful. The fronds are airy and bright green while the wood is dark red. In autumn it is bronze and there is nothing like it. Pick one up! They grown fast near a stream and once the roots reach the water, POW! you get up to 6' a year. The deer will eat it but it defends itself and has faced more far, far, more dangerous predators...........