Forest Senescence and Rejuvenation

It's not hard to observe that often the older fruiting branches of a tree will have smaller leaves and  be less vigorous than the leaves of suckers sprouting from lower down on the trunk. This year I was observing Oak and Teposan (Buddleja cordata). The oak trees are quite old and have mostly been coppiced at least once. Most of them have 2 trunks or more and have reached maturity again. The large old toposan trees have very few leaves compared to the one tree that was blown down and resprouted with vigorous growth. I pointed it out to my children and I asked them which one of these trees is doing more photosynthesis per square meter of ground? The answer was obvious. We had been watching videos on syntropic agroforestry and they talk a lot about focusing on photosynthesis in order to boost fertility and mulch production. So I decided that what should happen to these old trees now is they should have their canopy reduced by cutting the side branches. This will cause the old trees to put on new growth and it will provide mulch and wood. It will also open up space and give light to smaller trees trying to start out underneath. I believe the smaller trees will have more vigorous growth and that they should replace the older trees gradually but in order to do so it seems like they need my help. The wide spreading canopy of oak leaves blocks much of the rainwater from ever-reaching the smaller saplings and many smaller saplings are dead standing between huge old trees. Opening the canopy will not only benefit the small trees it will also benefit grasses and make it possible to produce some crop species in the forest.

Most of what you wrote is over my head 😜 but I need to ask, what in the world is going on with that tree you posted a picture of?

The tree is not from my property I think it's a maple but it's a good example of a tree that doesn't really grow very much anymore.

I wonder, do the very old trees have some role to play with a grove or a forest that we do not understand?

I heard the pioneering tree canopy biologist Meg Lowman on the radio once describing how in the canopies of tropical trees there are some battered, faded leaves that are many years old and do not seem to be photosythsizing much, but they still hang on. She described them as “grandmother” leaves.  Also in Robin Wall Kimmerer’s book “Braiding Sweetgrass,” the author describes how some water plants rely on the pressure difference between old, drying leaves and new tender leaves to transport nutrient-filled fluids to the roots. If you cut off the old leaves, the plant might not survive.

Elderly oaks, usually have a very deep root system and trade it for sugar with the other oaks.
Parent oaks are also know to selflessly give sugar to their related off-spring/seedlings near their dripline

Surely old trees play a huge roll in accumulating nutrients and they provide habitat for bromiliads and lichens. The nutrition in the oak leaves will foster rapid regrowth after the pruning. Big wide trees kill corn by blocking the rain? Trees and things like corn can live together in a syntropic pruning system. In syntropic agroforestry consortiums of species work together for good. As humans our job is to maintain harmony in the system. We do this by pruning and mowing.

My assumption was that that tree was very old and has had a lot of damage done to it from weather or other causes.

What does Senescence mean?

It means dormant or not growing vigorously.
Senescence or biological aging is the gradual deterioration of functional characteristics in living organisms. The word senescence can refer to either cellular senescence or to senescence of the whole organism. Wikipedia

This interesting clip from Paul's latest YouTube video release may be of relevance to this discussion. Ernie and Erica Wisner talk about trees, plants and energy transactions within ecosystems.  This lecture is part of the online permaculture design course.



You can also see the full class here: https://permies.com/wiki/190538/Tree-ecology-energy

There are many scholarly studies of different aspects of the senescence of the ancient Platycladus orientalis trees at the famous Mausoleum of the Yellow Emporer in China. They've been replanted over time, but of the original planting there are 30,000 trees over 1,000 years old. Just search for "platycladus orientalis senescence" and you'll get a ton of articles.

In casual plant talk (latin), to be senescent means to have gotten past one's prime. Senescence is a big deal in farming, ie it's the point after which you've missed the optimal harvest. However in bonsai senescence is the objective, the older looking the better. In ecology senescence is just one quadrant of the circle of life.

When we lived in the Piney Woods of East Texas there was an abandoned orchard of very old trees that we passed quite often.

At some point do old fruit trees quit producing or no longer produce a viable crop?

Is it possible to rejuvenate the trees?

Pruning can rejuvenate trees. It doesn't always work, but it often does. If the tree is very old, cutting back won't make it young again unless you pretty much cut it down at the ground, but when cut higher up you will probably get at least some new fruiting wood. With the new vigorous leafy growth, those new shoots should be grafted onto new rootstock if you want to keep the variety going long term.

Some trees however can be kept alive indefinitely with regular pruning. Hazelnuts for example only live 100-150 years if left unmanaged, however if cut down to the ground at least once every century, they can live forever. In fact in Italy there are hazelnut trees planted by the ancient romans that have been continuously managed and are still producing today.

In syntropic ag, aggressive pruning is used to not only rejuvenate the tree that is trimmed, but also to invigorate the nearby plants. When trees and plants are cut they release a wide variety of chemical signals to nearby plants, more or less inducing them to grow by chemically shouting "WE'RE UNDER ATTACK! IF YOU WANT TO SURVIVE YOU NEED TO GROW GROW GROW!!" In syntropic ag, these chemical signals are widely referred to as hormones, but recent scientific studies have discovered that there are additional chemicals besides hormones that get expressed (terpenes, flavinoids, etc).

I'm personally of the opinion that every time a human thinks they can improve on nature, they mess it up.  I'm a very big fan of leaving as much land as possible alone to it's own devices.  I have 80 acres of land.  I'm developing a food forest on an acre or maybe a little more, and have another acre-ish split up into different gardens.  My house and other building may use an acre or so.  The rest I try very hard to leave alone.  I do cut downed trees for my wood stoves and I have walking paths around my property, but other than that, it is undisturbed.  When I walk around the land through the various seasons, I'm in awe of the way nature has handled the changes, the various microclimates, the different types of soil and vegetation.  I, in no way, think I could improve upon it.

My opinion is different regarding land that as already been ruined, or nearly so, by previous humans.  In that case, I believe everything that can be done to restore it, should be.

Another thing to note with older trees, which further speaks in favour of pruning rather than cutting them down, is that they are sort of communications hubs. Apparently, a tree has more mycorrhizal connections the older it gets, and the higher degree of connectivity probably makes a more resilient forest. Also, even if they might not photosynthesize as much, their root systems are far bigger and more developed, meaning that they might be able to access water and nutrients that are out of reach for the younger trees... and some of these resources get redistributed to the younger trees by the mycorrhizal networks that are "centered" around the old trees. And the old trees might get some sugar in return, to compensate for their low level of photosynthesis. Typing this I wonder if this might be part of the reason for those cases you read about when an old stump is kept alive for years without leaves, fed all its sugar needs by the surrounding trees through the mycorrhizae?