Trees...

[JRMcLeod]

I know this aint really an environment change topic but it is to do with the environment....the leaves on the trees here are changing, rapidly...especially on the Birch Trees, any ideas why thats happening so early??

[shuggee]

I would imagine it's the dry conditions forcing them to shut-down to survive? Just like grass does.

Even grass in Edinburgh has been patchy brown in the last fortnight...

Moving this into the nature section YBY

[Gray-Wolf]

As Shuggs says it a survival trick but it does have implications. As the water table recedes and ground water becomes unavailable the transpiration rates of trees must suffer. The cost to the tree of trying to maintain its leaves, whilst transpiring moisture from them all the while, must lead the tree to a 'do or die' point where the cost of the foliage to the tree outweighs the gain it gives to the tree so the tree sheds its leaves.

I believe that with tress the maxim 'as above so below' fits well (where's Mushyman when you need him!!) so the root structure has the same area of contact with the ground as the foliage has with the atmosphere. That is a lot of potential for sucking up rainfall. If the tree shuts down what happens if normal rainfall patterns re-establish themselves through August/September? If it continues dry then what about 'shrinkage' and cracking in clay based soils? What about the impact on the anchorage of a tree if the soil/sub-soil is weakened by shrinkage/cracking come the first blow of Autumn? It has me worried as we shouldn't be kicking up piles of dead leaves (Octoberesque) at the start of August surely?

Edited August 2, 2006 by Gray-Wolf

[Stratos Ferric]

I know this aint really an environment change topic but it is to do with the environment....the leaves on the trees here are changing, rapidly...especially on the Birch Trees, any ideas why thats happening so early??

The same thing happened to some extent in 1975 and 1995 I seem to recall. As others have said, it's a natural response to a shortage of available water, similar to your body closing down surface blood vessels if you're exposed to cold.

As Shuggs says it a survival trick but it does have implications. As the water table recedes and ground water becomes unavailable the transpiration rates of trees must suffer. The cost to the tree of trying to maintain its leaves, whilst transpiring moisture from them all the while, must lead the tree to a 'do or die' point where the cost of the foliage to the tree outweighs the gain it gives to the tree so the tree sheds its leaves.

I believe that with tress the maxim 'as above so below' fits well (where's Mushyman when you need him!!) so the root structure has the same area of contact with the ground as the foliage has with the atmosphere. That is a lot of potential for sucking up rainfall. If the tree shuts down what happens if normal rainfall patterns re-establish themselves through August/September? If it continues dry then what about 'shrinkage' and cracking in clay based soils? What about the impact on the anchorage of a tree if the soil/sub-soil is weakened by shrinkage/cracking come the first blow of Autumn? It has me worried as we shouldn't be kicking up piles of dead leaves (Octoberesque) at the start of August surely?

Not sure that, given the mass of the soil above the root system, any shrinkage would really impact the root system's ability to hold a tree upright, even if that soil were to break down just to dust (which it wouldn't). Your general points (made elsewhere) about prolonged drought and the impact on clay soils regarding built structures are, however, very valid. London has been suffering from the effects of falling and rising water tables for several decades now.

[mushymanrob]

(where's Mushyman when you need him!!)

here!...lol

birch trees are notoriously shallow rooted, so any prolonged period without rain will result in shallow rooted trees dropping older leaves.. its perfectly normal.

last year i was chuntering on about 'leaf fall' as several trees had started to 'colour up' in late july. after a period of sunny weather the second half of july last year was very dull...

interestingly, in this drier but sunnier july, those same leaves have not yet started to colour up, therefore last years event was probably due to the dull weather.

[Nick F]

If it continues dry then what about 'shrinkage' and cracking in clay based soils? What about the impact on the anchorage of a tree if the soil/sub-soil is weakened by shrinkage/cracking come the first blow of Autumn? It has me worried as we shouldn't be kicking up piles of dead leaves (Octoberesque) at the start of August surely?

Sustained periods of heavy rainfall leading to waterlogged soils is more likely IMO to contribute to trees being blown over more easily, October 1987 was a very wet month in the South and this was a major factor contributing to to trees being blown over more easily in the 'Great Storm', along with trees being in full leaf.

Dry soils, if I remember rightly from my horticultural study days, leads to many deciduous trees growing deeper tap roots to enable them to reach water as the water table lowers (though this can depend on how hard the bedrock is beneath) - so in theory one would assume the tree would gain better anchorage.

[Gray-Wolf]

Dry soils, if I remember rightly from my horticultural study days, leads to many deciduous trees growing deeper tap roots to enable them to reach water as the water table lowers (though this can depend on how hard the bedrock is beneath) - so in theory one would assume the tree would gain better anchorage.

Leading to greater mechanical erosion of the bedrock by the invasive roots.......... more stable ? (pure pedantry on my part of course!).

I do wonder about the mechanics of 'species change' should Global warmings predictions prove real. Some of our species of tree are dependant upon our 'old' climate so I wonder how the chage would go. Would it purely be from reduced levels of 'new blood' entering the cycle as saplings die and seeds fail to grow or would existing stock die back at the same time? Obviuosly 'total drought' would do the job but intermittent stress (like this years June/July or 2003's August) may make things a little messier and I wonder how that mess would manifest and whether we are already witnessing some part of the picture.

Edited August 4, 2006 by Gray-Wolf

[Gray-Wolf]

In part answer to my own question it would seem that trees don't do awfully well in response to climate change. Recent genetic studies of white spruce in N. America has found that only by surviving in 'refuges' to the north of the ice sheets did the white spruce both survive and repopulate the area covered by ice(and not by sweeping back north as the ice retreated as was though). Recent rainforest studies also show that, as trees become isolated, their offspring become increasingly weak and their seeds less likely to germinate as the gene pool is reduced. Doesn't look good for our trees from where I'm viewing....

[The PIT]

Got to admit the trees are doing fairly well around here. Still green with no sign of wilting bar the weight of seeds etc. WEnt to Clumber park on Saturday and the trees looked very healthy there too.

Last year the trees didn't look at all happy although this was probably slightly later on. On the ring road to Sheffield University a lot of the had trees turned brown and shriveled up while the side facing away from the Sun stayed green. It also led to a very disappointing Autumn as there was little colour change.

[peterf]

As Shuggs says it a survival trick but it does have implications. As the water table recedes and ground water becomes unavailable the transpiration rates of trees must suffer. The cost to the tree of trying to maintain its leaves, whilst transpiring moisture from them all the while, must lead the tree to a 'do or die' point where the cost of the foliage to the tree outweighs the gain it gives to the tree so the tree sheds its leaves.

I believe that with tress the maxim 'as above so below' fits well (where's Mushyman when you need him!!) so the root structure has the same area of contact with the ground as the foliage has with the atmosphere. That is a lot of potential for sucking up rainfall. If the tree shuts down what happens if normal rainfall patterns re-establish themselves through August/September? If it continues dry then what about 'shrinkage' and cracking in clay based soils? What about the impact on the anchorage of a tree if the soil/sub-soil is weakened by shrinkage/cracking come the first blow of Autumn? It has me worried as we shouldn't be kicking up piles of dead leaves (Octoberesque) at the start of August surely?

good post this :lol: well worded for the layman :lol: (trans evaporation)

[Terminal Moraine]

If it continues dry then what about 'shrinkage' and cracking in clay based soils? What about the impact on the anchorage of a tree if the soil/sub-soil is weakened by shrinkage/cracking come the first blow of Autumn? It has me worried as we shouldn't be kicking up piles of dead leaves (Octoberesque) at the start of August surely?

As clay soils shrink and crack to due to drying they also become increasingly hard, rather like slowly baking a brick. With the root structure of a tree radiating through the surrounding clay in all directions it is more likely that the anchorage of the tree would be increased as the soil dried, in the same way that a post set in concrete is likely to stand more firmly than one set in soil.

Anyone who has done any amount of weeding will know that it's much harder to pull out a weed by the roots from a dried clay soil than it is from a wet one, similarly with a tree. The tree would be more likely to be de-stabilised in a very wet clay soil as individual clay particles are very fine and can hold a huge volume of water, the tree would therefore be standing in a medium which is more water than solid and would be relying more on the weight of what covered the roots rather than its binding properties.

Withe regard to the post about the possible progression of extinction of tree species if the climate were to undergo a long term change, it is likely that only shallow rooted species such as Birch and Beech would be affected initially.

I remember in 1976 seeing mature Beech die but these did tend to be trees that were approaching the end of their natural life, their demise being hastened by the increased stress.

Shallow rooted species growing in areas where there is intense competition, such as woodland, would also be the first to suffer. The weakest trees would be the first to go and only a sustained period of significantly decreased water supply, perhaps 5 years or more with little winter replenishment would cause otherwise healthy trees to begin dying.

Deep rooted species such as Oak, Elm and Ash would need a dramatic change in the rainfall regime to become threatened.

Whether or not such a change is likely is another matter entirely. It was widely suggested after the summers of 1975 and 1976, which followed dry years in 1971 and 1973, that the climate could be changing to a much drier and warmer pattern but this was soon forgotten in the remaining years of the 1970s and throughout the early and mid 1980s which were predominantly wet and cool.

25 years further on and who knows whether or not the current warming has altered things sufficiently to tip the balance toward sustained drier and warmer conditions. As always we need more time to know for sure, but at what point we know rather than suspect is a pertinent question.

T.M

Edited August 7, 2006 by Terminal Moraine

[Rustynailer]

That was a very good post T.M. :lol:

[The PIT]

Correction I've noticed the trees on the Dual Carriage way have died on the exactly the same side again this year.

Elsewhere the trees are looking healither and any paleness from distance seems to be related to seeds and fruit.