How does a tree die?

[technetium]

Hi forum,

I curious as to how a tree (or plant in general I guess) dies? There is a magnificent Ghost Gum Eucalyptus down the road which goats completely ring barked a few months ago but now in the height of summer is still going strong.

Nearby are other eucalypts, perhaps a few years old & protected from goats, that have wilted and died apparently due to lack of water, while next to them are trees that have been cut to ground level and are resprouting.

Now in most animals we could say that the loss of heart or brain function will eventually cause death (or even defines death), but is there an equivalent for trees. Why can some sprout from seemingly dead stumps? There is no central nervous system coordinating the trees parts (I assume) so when is the tree actually dead?

 

[Spud Emperor]

Good question with a range of answers I suspect. I've killed enough plants/trees to have a bit of an idea. I've grown some absolute rippers which are still growing strong.

Lack of water will do it obviously but also fungal diseases or other systemic complaints.
Fire certainly doesn't kill most eucs or proteaceous plants and neither does cutting them off at the base, they have a lignotuber which can reshoot without the need for photosynthesis. Tough buggers the Aussie natives.

I don't know the point at which their life expires but I have seen plenty come back from the dead and others turn up their toes at the drop of a hat.
Looking forward to an answer from Fraggle Rocker.

 

[draqon]

every cell of a plant undergoes apoptosis and will die of inefficient mechanisms in the end...that is before it dries of from water, gets chopped down by people, destroyed by wind, chewed by insects...and etc.

 

[Fraggle Rocker]

Looking forward to an answer from Fraggle Rocker.

Well geeze dude, we raise dogs and parrots, not trees; I'm more of a zoologist than a botanist. Nonetheless we do live out among the redwoods, one of the longest-living species of trees, so the question comes up in casual conversation.

After a brief web search, the consensus of what I've found is the following:

Obviously one class of plants is annuals and they are programmed to produce seeds only once and then die. But plants that do not die after one year have no programmed lifespan. Under ideal conditions they could, theoretically, live forever. Animal metabolism is much more complex, and this plus our mobility causes damage to tissues at an astronomically faster rate than it happens in a lucky plant. Therefore we have repair systems that plants did not need to evolve, and these systems themselves slowly degrade so they can't quite keep up with essential repairs. This is why we sleep less as we grow older: Our bodies run out of repairs they can make overnight with the tools that are still working so we wake up earlier but a little less healthy than the day before.

The failure mode of a tree usually starts with external trauma: breakage. Wind, fire, drought, earthquake, parasites, or the bad luck of having part of another tree fall on them causes a rupture in their tissue. This creates an entry point for pathogens. The pathogens weaken the tree so the next breakage comes more quickly, and eventually the pathogens overwhelm the tree's ability to nourish itself.

There are several reasons redwood trees live so long. In addition to root-feeding they extract moisture from the air, like the plants on Dune, so even in a drought they don't dry out. They secrete acid into the soil, creating a hostile environment for underbrush, so redwood forests virtually never support a raging fire. And apparently few parasites have evolved that can attack them.

The oldest tree in the world is a bristlecone pine in Nevada, 5,000 years. You have to go down the list to #9 to find a redwood at 3,000.

However, certain species of plants reproduce asexually by cloning themselves from their own roots and grow into a colony of genetically identical individuals, which are sometimes connected by a common root system. It's a matter of semantics to decide whether the individual trees "die," since their roots never die and there is no discontinuity of metabolism. It can also be a matter of semantics to decide whether one of these colonies is a single organism.

The oldest clonal plant colony is a quaking aspen colony in Utah that covers more than 100 acres, has almost 50,000 stems, and is the heaviest known organism at 6,000 tons. It is somewhere between 800,000 and one million years old.

 

[iceaura]

Most trees die from sustained lack of water to the photosynthesing cells - like most humans die from sustained loss of oxygen to the brain neurons.

The water is picked up by osmosis into intake cells in the roots, piped up through special cells in the trunk, and delivered on demand (pulled in by stomatal loss creating tensile forces in the water column) into the spongy layers of the midleaf.

A variety of things can cut off the water - pathogen invasion and clogging, physical disruption of some kind, wilting collapse of the channel cells, repeated removal of the leaves, damage to the water intake cells or other prevention of water uptake at the root level, - - -