Flooding impact on tree health

[Gnarlyoak]

Had one of those "idle" thoughts pop in my head (as they do) recently with regards to the possible impact that all the recent flooding could have on the long term health of trees in the flooded areas. Of particular relevance is the duration that some tree roots have/or will have been consistently under water for weeks possible months, rather than days.

 

When roots remain under water for a period of time, they became unable to extract oxygen molecules from the soil, this naturally in time will cause problems for the health of the roots and tree ultimately with the possibility of leading to the untimely death of the tree.

 

So I did a bit of digging on the inter-web, and came across an article written by the University of Tennessee, which quotes from Diseases of Trees and Shrubs” by Sinclair, Lyon & Johnson, 1987 (see page two of attached pdf doc), that the impact is less severe on trees that are in dormancy.

 

However, I believe that due to the mildness (temperature wise) of this winter we may see an early spring, given that I have already begun to notice the first signs of leaf budding and even new leaves emerging on some shrub species (eg: buddlihea) in our more northern climes (Gtr.Manchester), and that the ground water levels will remain very high even after the surface flooding has receded. Would anyone with a better understanding of tree biology, than I can ever hope to attain, care to give their thoughts on what sort of impact we could likely see on the tree populations in some of the worst flood hit areas in the South West and South East.

 

http://www.utextension.utk.edu/mtnpi/handouts/Field%20Production/Crops_Tolerant_of_Moist_Sites.pdf

[se7enthdevil]

interesting question,

i know you can drown a tree or even a whole forest but i don know how long it takes or if its species dependent.

 

are they relatively protected at the moment because the sap hasn't risen and possibly not so affected by all the water??? not all species are dormant at the moment and as you say it's almost spring like as the winter didn't really arrive.

 

our garden has has one frost of note, that's it...

[Dave NE]

I was kind of wondering the same but more about the soil and all the bugs that live in it, for some farmers it must be heart breaking, it could have taken years to build up the soil fertility and then bang, thats it, all dead, or am i missing something, Dave

[sandspider]

I think the mud deposited by flooding is usually nice and fertile - which is why people used to plant crops rather than build houses on flood plains. So in the long run, the soil (and plants, insects etc.) should do better. Not sure about the shorter term though...

[Gnarlyoak]

Dave & Sandpiper. You both raise relevant points. Now I am absolutely no authority on this matter, but this is just some of the info that I have picked up whilst surfing the web simply to satisfy my own curiosity.

 

1) Long term flooding can be extremely detrimental to the fertility of soils. Not least because many of the micro organisms that are essential to maintain the health of soils are (just like the tree roots in relation to my OP) totally reliant on being able to take in the oxygen usually found in the 'gaps' between soil particles. The anaerobic conditions created by long term water logged soil will asphyxiate these micro organisms as well as the tree roots. So in the short to mid term, soil conditions will be very poor for anything growing in it.

 

2) Yes some silt deposition after flooding can be beneficial in bringing in additional nutrients for things growing in the soil. But again, oxygen is key. If roots and soil microbes have drowned, then there is little left to take up the newly deposited nutrients.

 

But the flooding can also remove as much if not more in the way of soils and nutrients there in, so it actually makes the soil poorer. Swiftly moving water, especially carrying lots of debris will have a 'scouring' effect. This may actually expose tree roots that are normally under ground, once exposed, these tree roots can dry out and die back, therefore rendering them unable to take up water and nutrients in the future, and that's before you consider the stability issues for the tree itself, which has had its roots undermined by having the ground around & underneath them washed away.

 

Other things to consider, is that an excessive build up of sediments, particularly around a tree, say. Can bury the trees root collar, and again this may kill the roots and lead to premature decline and/or death. Then there is the small matter of the stuff that is in the water. Pollutants of all kind, chemicals, effluents and other pathogens and fungal spores. These latter two in particular could arrive on a flood stressed tree, and in its weakened state become susceptible to infection which may go on to cause its decline.

[Andy Collins]

I am no expert either, but I have a sneaky suspicion Nature will cope far better than we can. Of course, some losses can be expected, just as we lose some in time of drought.

[Pumpy]

Some thoughts that don't really provide any answers, but may muddy the waters a bit more.

 

Some plants develop "water roots" (think hydroponics) I can think of a few trees growing right on the waters edge who have healthy root mass actually growing in the water, Willow and Oak spring to mind. So presumably nature has quipped them to cope to a lessor or greater degree depending on species.

 

Soil biota (bacteria/fungi) tend to go dormant when either temperature or O2 level is not ideal, high temps can kill them, low temps send them into a dormant state. For sure the ratios of soil biota will change, logically ratios will change with conditions, compaction will also be an issue.

[sandspider]

I suppose we'll find out how the flora and fauna cope! I hope that Andy is right - after all, nature must have gone through this kind of thing before.

 

We've finally had a day or two here with less rain (no rain!) and even some sun. Fingers crossed that will continue, and water levels will return to normal. I imagine that the quicker water levels return to normal, the less the long term effects on f&f will be...

[daltontrees]

Dave & Sandpiper. You both raise relevant points. Now I am absolutely no authority on this matter, but this is just some of the info that I have picked up whilst surfing the web simply to satisfy my own curiosity.

 

1) Long term flooding can be extremely detrimental to the fertility of soils. Not least because many of the micro organisms that are essential to maintain the health of soils are (just like the tree roots in relation to my OP) totally reliant on being able to take in the oxygen usually found in the 'gaps' between soil particles. The anaerobic conditions created by long term water logged soil will asphyxiate these micro organisms as well as the tree roots. So in the short to mid term, soil conditions will be very poor for anything growing in it.

 

2) Yes some silt deposition after flooding can be beneficial in bringing in additional nutrients for things growing in the soil. But again, oxygen is key. If roots and soil microbes have drowned, then there is little left to take up the newly deposited nutrients.

 

But the flooding can also remove as much if not more in the way of soils and nutrients there in, so it actually makes the soil poorer. Swiftly moving water, especially carrying lots of debris will have a 'scouring' effect. This may actually expose tree roots that are normally under ground, once exposed, these tree roots can dry out and die back, therefore rendering them unable to take up water and nutrients in the future, and that's before you consider the stability issues for the tree itself, which has had its roots undermined by having the ground around & underneath them washed away.

 

Other things to consider, is that an excessive build up of sediments, particularly around a tree, say. Can bury the trees root collar, and again this may kill the roots and lead to premature decline and/or death. Then there is the small matter of the stuff that is in the water. Pollutants of all kind, chemicals, effluents and other pathogens and fungal spores. These latter two in particular could arrive on a flood stressed tree, and in its weakened state become susceptible to infection which may go on to cause its decline.

 

Good post. And I wonder whether, deprived of oxygen at the roots, trees will be able to come into leaf anything like normally?

[Gnarlyoak]

Yes, I hope that Andy is right also, and nature will win out. But the water table is really high at the moment and it will need to be relatively dry for a long period of time before the water table falls depreciably even after the surface waters appear to have receded.

 

Some areas are likely to take weeks or months before the ground conditions are unsaturated IE: the Somerset levels. In the meantime of course Spring will have sprung, and in the most waterlogged areas could we potentially see acres of hedgerows in areas like Somerset be unable to recover in time, to prevent serious long term damage over a wide area?

 

Yes there maybe some trees & shrubs that are fairly tolerant to a prolonged period of submersion, and adapt to produce advantageous roots that are able to extract some o2 from the water. But I would imagine the vast majority may struggle, as high water levels persist especially during the transition from out of the Winter dormancy period into Spring.

 

Ecologically, many of the British countrysides fauna is critically dependant on their breeding period coinciding with the emergence of buds, leaves, and flowers of the flora at Springtime. I'm sure the short to mid term impact of these devastating floods will reverberate throughout the year!!!