Less rainfall better for rain forrests?

[The PIT]

Do I buy into this??

http://www.dailytech.com/Climate+Change+Ma...article9083.htm

Good point though about the K/T extinction at the end though.

[Devonian]

Do I buy into this??

http://www.dailytech.com/Climate+Change+Ma...article9083.htm

Good point though about the K/T extinction at the end though.

I think the point is that we could nuke the planet and some life would survive. But why would we want to be the cause of a 21st century KT event? Why? I simply can't get my head around it.

As to the rainforest. I think the discovery was that in drought the trees accessed deeper water than was previously thought. So, hey, no worries? Well, I'm not sure that kind of stress is 'better' for rain forests

Edited October 1, 2007 by Devonian

[saint]

????????? :huh: :wacko:

saint

[pottyprof]

I think the point is that we could nuke the planet and some life would survive. But why would we want to be the cause of a 21st century KT event? Why? I simply can't get my head around it.

As to the rainforest. I think the discovery was that in drought the trees accessed deeper water than was previously thought. So, hey, no worries? Well, I'm not sure that kind of stress is 'better' for rain forests

Any proof that this isn't the case then Dev??

[Devonian]

Any proof that this isn't the case then Dev??

Hey, easy, I only said I'm not sure that kind of stress is good for rainforest. Just my opinion.

[pottyprof]

Hey, easy, I only said I'm not sure that kind of stress is good for rainforest. Just my opinion.

Sorry Dev.. Only a question.. With what you were saying, I thought you had some info to share with us.

[jethro]

Speaking as someone who deals with trees day in, day out I'd have to say if rain levels reduced and sunlight levels increased and this resulted in a greater level of growth then the conditions which we consider to be normal in the Rain Forest, are not actually the optimum conditions for the trees to grow in. Sure they grow, it actually takes quite a lot to stress plants to the point of them dying, especially large species like trees. If conditions improve then they grow more, this is obviously the case here. Trees have vast root systems, some surface roots which absorb nutrients from the leaf litter, some anchorage roots which fan out to keep the tree upright and deep, deep roots which seek out moisture. If surface moisture is available they will utilise it, if it isn't they will seek it out lower down. The same can be said of plants in our own gardens, if planting a new border the plants will establish much better and require far less looking after, if the planting is done in the autumn; this gives plants a chance to develope a large root system in warm soil before the actual need to utilise it next spring for growth. Equally, if you water a garden little and often you actually create the need to continue doing so, the roots remain shallow as the most moisture available is from above, a damn good soaking when they are first planted followed by another GOOD soaking if and when they show signs of needing it, produces much stronger plants.

[pottyprof]

Speaking as someone who deals with trees day in, day out I'd have to say if rain levels reduced and sunlight levels increased and this resulted in a greater level of growth then the conditions which we consider to be normal in the Rain Forest, are not actually the optimum conditions for the trees to grow in. Sure they grow, it actually takes quite a lot to stress plants to the point of them dying, especially large species like trees. If conditions improve then they grow more, this is obviously the case here. Trees have vast root systems, some surface roots which absorb nutrients from the leaf litter, some anchorage roots which fan out to keep the tree upright and deep, deep roots which seek out moisture. If surface moisture is available they will utilise it, if it isn't they will seek it out lower down. The same can be said of plants in our own gardens, if planting a new border the plants will establish much better and require far less looking after, if the planting is done in the autumn; this gives plants a chance to develope a large root system in warm soil before the actual need to utilise it next spring for growth. Equally, if you water a garden little and often you actually create the need to continue doing so, the roots remain shallow as the most moisture available is from above, a damn good soaking when they are first planted followed by another GOOD soaking if and when they show signs of needing it, produces much stronger plants.

I suppose this sort of set up would produce ideal conditions for some of the tallest species of trees in the world then Dawn? Long downward roots and wide anchorage roots? Would seem to me that these conditions happen regularly to encourage growth/adaptation over several hundred years? We still don't understand the Amazon and lots of assumptions are made methinks but from what you say then some of these trees are used to tapping into these reserves?

[jethro]

They do tend to find their own equalibrium Paul, quite a lot will depend upon location rather than species; you can take the same species and plant them in completely different aspects/conditions and this will ultimately effect their growth patterns to a greater extent than their species genome. A prime but extreme example of this are Bonsai trees, trees capable of growing to vast proportions can be manipulated by growing conditions alone. Extra growth as reported in the Rain Forest indicates better growing conditions for the trees; it's not a last ditch, quick lets grow before the water runs out situation, they're not sentient beings. If a plant becomes stressed to the point of its' survival being threatened, they don't put on a growth spurt, they direct as much available energy as possible into reproducing themselves via seeds. We may not like seeing conditions change there, but the trees obviously do.

A tap root will seek out moisture, it keeps going until it's found it so long as the rest of the tree is alive to support it. If it doesn't find moisture and no moisture comes from above for the surface roots to utilise, then the tree will die. Even in such extreme circumstances as a prolonged, intense drought which dries up the bottom moisture, the tree will try to save its' self by loosing limbs, hence you get die back. Many other plants have the capability to grow very long tap roots if given the chance; parsnips, carrots etc normally have fairly short, stumpy ones but if you plant them in long containers full of well drained compost or even just sand they will continue to grow downwards - that's how folk grow those enormously long, prize winners. The wonders of Mother Nature eh?

Edited October 1, 2007 by jethro

[pottyprof]

Interesting stuff Dawn.

Has the Amazon basin dried up before though? Would the stronger root system encourage these giant trees, with huge canopies, to survive for longer and perhaps become these huge and very beautiful trees that we see? If the root system was shallow/anchor root, would they have reached the hight that they have? Or would they have just fallen over??

[jethro]

Interesting stuff Dawn.

Has the Amazon basin dried up before though? Would the stronger root system encourage these giant trees, with huge canopies, to survive for longer and perhaps become these huge and very beautiful trees that we see? If the root system was shallow/anchor root, would they have reached the hight that they have? Or would they have just fallen over??

I have no idea if the Amazon basin has dried up before but what I can tell you is, if left to their own devices, without our interference, plants will grow in the same way, the world over, regardless of type or species. Once germination has taken place the energy is focussed upon root growth, only when the plant has grown a big enough root system to support top growth will that top growth start. No roots, no top, poor roots, poor top, big root ball, bigger plant. This being the case, growth spurts can only happen with a supporting root system, without it they won't grow for the long periods needed to become mature trees so no, they wouldn't have reached such lofty heights, they would have died or fallen over. If I had to hazard a guess regarding the Rain Forest trees I'd say less moisture in the soil has enabled a greater concentration of oxygen which aids growth - water logged soil kills more tender plants in this country than cold as it excludes oxygen from the soil. Plus higher levels of sunlight have increased production of sugars through photosynthesis. Of course it could also be a reflection of the increased levels of Co2, it actually aids plant growth.

[Stratos Ferric]

Do I buy into this??

http://www.dailytech.com/Climate+Change+Ma...article9083.htm

Good point though about the K/T extinction at the end though.

I think it depends, and that analysis seems to assume a linear extrapolation of a short term response of the flora. One of the big problems where forests have been cleared is the change in weather from a very damp environment, often locked in by the multi-layer canopy in rain forest, to one where the soil can often dry and then be subject to deluge. Loss of soil where forests have been cleared is a huge problem. The other issue is that the soil, staying damp, will tend to maintain good nutrient balance, with leaf rot restoring nutrients. The problem with a wet-dry regime, particularly if a long dry season were to eventuate, might be the formation of surface pans.

Trees may well survive for a long while, but other grond cover may not fare so well, and I think the point with the rain forests is not just the trees, but the entire eco-system.

[jethro]

I think it depends, and that analysis seems to assume a linear extrapolation of a short term response of the flora. One of the big problems where forests have been cleared is the change in weather from a very damp environment, often locked in by the multi-layer canopy in rain forest, to one where the soil can often dry and then be subject to deluge. Loss of soil where forests have been cleared is a huge problem. The other issue is that the soil, staying damp, will tend to maintain good nutrient balance, with leaf rot restoring nutrients. The problem with a wet-dry regime, particularly if a long dry season were to eventuate, might be the formation of surface pans.

Trees may well survive for a long while, but other grond cover may not fare so well, and I think the point with the rain forests is not just the trees, but the entire eco-system.

Agree largely with what you're saying, except the surface panning. Eco systems are the complete working picture, take one thing out and it affects everything further down the line but this particular study wasn't taken from an area which had suffered interference or logging. It was a study of an un-touched area which has shown that "virgin" forest is responding positively to less rain/more sunshine.

[Devonian]

http://www.treehugger.com/files/2007/09/st...rue_drought.php

"The trees used the added sunlight and water siphoned from their deep roots to increase their rate of photosynthesis - allowing them to greatly up their productivity in the short term. That's not to say that persistent drought-like conditions, brought on by further global climate change, would bear no effect on the rainforest trees: "You take away enough water for a long enough time, the trees are going to die," said Saleska."

Trees 'want' to live. So, if there is a drought they try to survive. But, you can't have a rainforest in a desert.

Rainforest, despite the desire of it's life to live, need certain conditions to be met for their survival. It seems, on the evidence presented in the paper, that they may be tougher than we think, but lets not run away with the idea that persistent drought 'helps' rainforests.

Edited October 2, 2007 by Devonian

[Gray-Wolf]

The little I know about trees (from my attempts at Bonsai and my Geography) tells me that they are responsible for a great deal of Mechanical erosion. The 'forcing' of trees into ever deeper areas will inevitably lead to a rapid fragmentation of the lower soil horizons and a lessening of it's integrity. I would imagine that this would leave the forest 'fringes' open to collapse from winds that did not trouble them in the past. You could imagine a rapid decline of the Top Canopy were this to happen and a change to the ecosystem the forests could support.

Another thing I notice in nature, plants/trees seem to have a 'final flourish' if they are on the way out in an attempt to set seed and guarantee the next generation (how many times have your house plants put on a stunning display only to be stone dead within the month?).

[jethro]

Runaway drought won't help anything but this report deals with the here and now and currently the growing conditions in the Rain Forests are having a positive effect. As Dev and I both said, photosynthesis; more sunlight, more Co2=greater sugar production and therefore growth.

Any final flourish associated with the period prior to a plants' death is as I said earlier, related to reproduction - a drive to reproduce before dying, is directed into seeds, in order to set seed they need to flower; death throes don't stimulate leafy growth. Leafy growth is, if you like the plant being optimistic, it is confident that it is healthy enough and will continue to be so, long enough for that leafy growth to mature and in turn produce seed.

Not too sure I follow the Mechanical erosion and rapid fragmentation, can you explain again please so my sleep deprived brain can understand?

[Gray-Wolf]

Not too sure I follow the Mechanical erosion and rapid fragmentation, can you explain again please so my sleep deprived brain can understand?

Morning sleepy head!

The roots of plants and trees force their way into any cracks/fissures in the bedrock and ,as they grow and expand, they further break the rocks apart. The exposed surfaces of the rock then 'oxidise' and become more unstable (in the normal way of erosion) leading to further degradation of the underlying strata.

[jethro]

Morning sleepy head!

The roots of plants and trees force their way into any cracks/fissures in the bedrock and ,as they grow and expand, they further break the rocks apart. The exposed surfaces of the rock then 'oxidise' and become more unstable (in the normal way of erosion) leading to further degradation of the underlying strata.

Oh right, yes I get that but I still don't get the connection with the Rain Forest (but after only a couple of hours sleep, to be fair there's a lot which doesn't compute). Hang on, I've just read it again and yes, I guess that is a possibility but probably unlikely except for on long time scales. Moisture seeking roots go down so are unlikely to break apart surface rocks, associated with their growth would be surface root growth too which would tie the top layers together more; I suppose on the fringes it could happen but exposed ground would always generate new growth quickly so I think they cancel each other out. Any loss of trees over a large area would more likely lead to erosion though.

[Essan]

The DailyTech article referred to is disingenuous in it's criticism of model predictions (it's akin to saying that because it was wet this summer, model predictions for drier summers over the next few decades are wrong) and in its conclusion that a spurt of growth after a short drought is indicative of long term growth trends over decades.

If reduced rainfall encourages long term growth then the Sahara would still be a forest .....

Oh and

Consider the K/T extinction event. A 10 kilometer-wide asteroid struck the planet with a destructive force several thousand times as great as all nuclear weapons ever built. A massive tsunami several hundred feet high circled the entire planet. Firestorms raged, decimating most forests. Clouds of ash and dust obscured the sun for a decade, with near-constant rains of mud, saltwater, and dilute sulfuric acid. As catastrophic as this was, the fossil record indicates over half of all species survived ... and shortly afterwards, those survivors began thriving on the lack of competition, eventually differentiating into countless new species.

Is pure speculation. It's what happens when you believe the media and don't check out the science If the Chicxulub impact killed the dinosaurs, then it's speculated that such events must have happened because how else could the dinosaurs have died out? It basically a circular argument though. And falls down when we realise that bigger impacts didn't cause any extinctions at all .....

Although in any case it's disingenuous to say 'over half of all species' survived when whole genera disappeared. After all, if every mammal, reptile and bird on the planet because extinct, well over half of all animal species would survive (fish and insects etc) ....

[jethro]

You obviously read more into it than I did Essan, there are problems with the models, even those doyens of the IPCC say that, this is surely just another example of comparing theory with empirical? At the end of the day no climate model as far as I know predicts long term drought in the Rain Forests, concern there focusses upon logging. If there are no predictions for long term drought there, then a degree or two rise in temps with increased sunlight levels will promote growth; that's nature for you, resilient and opportunistic.

[Stratos Ferric]

Agree largely with what you're saying, except the surface panning. Eco systems are the complete working picture, take one thing out and it affects everything further down the line but this particular study wasn't taken from an area which had suffered interference or logging. It was a study of an un-touched area which has shown that "virgin" forest is responding positively to less rain/more sunshine.

Though presumably (and this is not to judge it, such is evolution) if certain species are thriving they will now outcompete others, probably lower down in the canopy.

[Essan]

You obviously read more into it than I did Essan, there are problems with the models, even those doyens of the IPCC say that, this is surely just another example of comparing theory with empirical? At the end of the day no climate model as far as I know predicts long term drought in the Rain Forests, concern there focusses upon logging. If there are no predictions for long term drought there, then a degree or two rise in temps with increased sunlight levels will promote growth; that's nature for you, resilient and opportunistic.

I thought the models concerned were climate models which expected a reduction in long term rainfall ?

And I believe they're likely to be based in part on studies on what happened in other parts of the world when rainfall patterns changed. Saudi Arabia wasn't always a desert .....

[Gray-Wolf]

I thought the models concerned were climate models which expected a reduction in long term rainfall ?

And I believe they're likely to be based in part on studies on what happened in other parts of the world when rainfall patterns changed. Saudi Arabia wasn't always a desert .....

Quite correct, it was once an shallow sea bed (where the dying critters laid down the basis for it's future wealth), so what? I'm struggling to find your point here Essan!

[Essan]

My point is that just because the Amazon didn't all die off during a one year drought doesn't mean it won't be unaffected by a prolonged decline in rainfall .....

North Africa, the Middle East, Arabia and NW India were all once covered in grass and trees. Until the ITCZ moved south, they lost their rainfall, and they turned to desert. The same could easily happen to the Amazon ....

And the Amazon used to be the bed of a shallow sea as well btw

Edited October 3, 2007 by Essan

[jethro]

I think the weather there this year has been a bit of a blip, not an expected turn around or prediction of things to come. I don't know if some sort of synoptical world wide pattern change in underway (akin to 1976) but there's been quite a few oddities or unexpected this year - our summer to name but one. Precipitation in that part of the world has been increasing and is expected to continue to do so.

http://www.sciencedaily.com/releases/2007/...70827174306.htm

http://www.nasa.gov/centers/goddard/news/t...ncrease_prt.htm