weeping willow data

Discussion in 'Woody Plants' started by Mike Roberts, Jan 2, 2008.

  1. Mike Roberts

    Mike Roberts Member

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    Hello, I live close to a small lake in the South Okanagan that is surrounded by 53 willows, of an average 40 feet high, and 2 and a half feet in diameter at the trunk base. There is local concern about the amount of the limited water supply that the willows may be slurping up, and the amout of organic material entering the lake. So, here are my two questions. Can anyone realistically estimate, based on observed similar data, how many gallons per day each tree may absorb through the roots, and what weight or volume of foliage is dropped per tree per season? I have approached many other sources unsuccessfully, so here is an opportunity for a knowledgeable person to go to the top of the class, or to refer me to another site of expertise! Thanks. Mike
     
  2. Daniel Mosquin

    Daniel Mosquin Paragon of Plants UBC Botanical Garden Forums Administrator Forums Moderator 10 Years

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    Yes, someone should be able to estimate the number of gallons used / day, but I'm not that someone!

    I've searched for willow evapotranspiration, and did find a number of studies on the topic, but I didn't find anything that was generic enough to apply as a "rule-of-thumb". Of course, evapotranspiration is going to vary season to season, week to week, and day to day - it almost calls for its own study in your specific instance.

    Regarding mass of foliage dropped / yr - it'd be a relatively simple thing to measure, but it'd take a year, of course. I didn't find anything on this topic, but I perhaps don't know the right keywords to look for.
     
  3. Michael F

    Michael F Paragon of Plants Forums Moderator 10 Years

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    To look for research results, 'litres' (or 'liters') would be a much better search word than 'gallons'.
     
  4. jimmyq

    jimmyq Well-Known Member 10 Years

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    I would think it to be variable depending on air temp, relative humidity, time of year and wind.
    Being a relatively fast growing species with relatively soft leaves and known to be a lover of moisture it would likely be a high water user vs other species that have the opposite characteristics.

    Can a few trees drain a lake? wow, maybe, given the right climate for long enough.

    To see how much the trees are evaporating to the atmosphere, wrap one in clear plastic and provide a trough for the collected transpirate to collect, you should be able to get a rough idea of moisture exchange based on that. Of course it may be skewed by relative humidity within the enclosure increasing with the rising temps.

    Good question but I don't know if there is a real answer of any merit.
     
  5. Daniel Mosquin

    Daniel Mosquin Paragon of Plants UBC Botanical Garden Forums Administrator Forums Moderator 10 Years

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    It seemed like a few researchers were using an instrument that is inserted into the tree trunk and measures sap flow as a way to measure evapotranspiration, instead of the "plastic bag" suggestion. I suspect the latter method is only used for smaller plants. Though, a 15m plastic bag covered willow would make for an intriguing point of discussion...
     
  6. jimmyq

    jimmyq Well-Known Member 10 Years

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    ha, I guess maybe my suggestion was a bit preposterous? :P
     
  7. Mike Roberts

    Mike Roberts Member

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    Thanks for the several replies. Apparently the answer to my questions is not known or readily found. I will continue searching and check back regularly with the hope of a surprise response. MIKE
     
  8. Daniel Mosquin

    Daniel Mosquin Paragon of Plants UBC Botanical Garden Forums Administrator Forums Moderator 10 Years

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    Mike, if you have email notifications turned on, you should get a notifier when someone replies instead of having to check in from time-to-time.
     
  9. KarinL

    KarinL Well-Known Member 10 Years

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    As far as water uptake I think it must be somewhat relative to supply. My two willows grow in fairly arid conditions (in summer) and they survive, but if any water does happen to be poured onto the soil I am pretty sure they suck it up. I think given the variability in what the trees may be drinking, it would be the lake you should be observing, not the trees. After all, that's the organism you're more concerned about, right?

    As for organic debris, sigh. I can tell you how many times I fill my yard waste container per year from the willows, approximately, but due to wind distributing the largesse far and wide, and the fact that some debris stays on the ground and rots, it's an estimate, no more. But again I don't think that knowledge of what the tree produces is going to answer your question, which is whether the lake can take it.

    It seems to me you need some objective parameters to measure the status of the lake, not the behaviour of the trees. And if you have excess water loss or excess organic material, and you have FIFTY THREE willows, it doesn't seem like rocket science to recognize that (a) the willows are likely contributing a good bit to the problem, and (b) they aren't going to stop drinking out of consideration for the lake (and they aren't shrinking either).

    To assess how much of a contribution they make, you could always cut down about 5 trees (10% of your population) and see how much change you get in your lake parameters.
     

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