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How to find out if you can sustain your trees by rain alone

 
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Hello Permies!

I am currently researching the water needs of the trees I want to plant this year. I am trying to establish pioneer trees on rain water alone
I would like to share this with you and also hope to get some feedback on this.
I obviously left many factors out as it can become very complex, I am also not including the construction of swales or dams (although we will dig out some swales).
But I hope that I am was to catch a general feel of the challenges.

Here it goes:

I created a spreadsheet called Tree Satisfaction (you can view and copy it into your own library so you can use it for your own planning)

The example shows the data for Barcelona and we are going through the data based on the example. But don’t worry, I will also show you how to use it for your own location.

Prerequisites
We want to know if we can sustain a young tree through the means of catching rainwater only. To find out the answer, we need to consider a few things:

  • how much does it rain?
  • how frequently does it rain?
  • what is the area a tree can draw water from?
  • how much rainwater can be caught when it rains?
  • how much water does a tree consume?
  • how much water is lost through evaporation, transpiration or other means?


  • Please note that we will only take the area around the tree into account. Other means of catching rainwater such as dams, diversion channels or swales are not considered here.

    Let’s study Barcelona

    First, we need to get relevant historical data regarding precipitation – ncdc.noaa.gov offers free historical data from weather stations around the world. In our example, we will study the years 2015 to 2018.

    Equipped with this data, we can already print some useful graphs that can tell us something about the situation:

    Temperatures fluctuate between 2 and 37° throughout the year. Winters are cold but don’t go below 0° C.



    Minimum and maximum temperatures in Barcelona 2015 – 2018

    The precipitation shows us that 2015/16 were much dryer than 2017/18. Something interesting is going on here and we should look at the data on a much longer timescale. 4 years of data are not enough to jump to conclusions.


    Precipitation in Barcelona 2015 – 2018

    Especially interesting is the chart of days without rain. The red triangles, that are building up mostly peak between 20 – 25 days but in the Winter of 2015/16, we had a staggering 73 days without rain.


    Days without rain in Barcelona 2015 – 2018

    So many days without rain
    20 – 25 days without rain… It looks like we can’t rely on rain alone, right? Well, don’t underestimate how much water can be held in the soil.

    You know, when it rains, the soil can stay wet days after the rain occurred. Let’s have a deeper look.

    Regular soil can hold water up to a quarter of its volume. A cubic meter, therefore, can hold up to 250 liters.

    Water, once in the soil, can only disappear through 3 main ways:

    evaporation through sun and wind influences
    water flow within the soil to other areas
    evapotranspiration by the plants
    The more we are able to reduce these factors, the longer the soil can retain the water and make it available to our plants.

    Tree satisfaction

    In order to combine it all together, I will use the term tree satisfaction. It’s a metric that tells us how happy trees are based on how much water they have available in the soil.

    When they receive water, the satisfaction rises. When the soil is completely dry, the satisfaction is basically 0.

    Let’s assume a few things…

    Assumptions for tree satisfaction calculation

    A tree younger than 2 years usually requires around 80 liters a week, or 11 liters a day. We assume they can draw water from a 2 meters radius which gives us the area of rainwater a tree can collect (12.57 m²).

    As a starting point, we also assume that we can collect 100% of the rain and don’t lose any water. Let’s have a look at the following chart.


    Tree satisfaction in a perfect world

    A lot comes together in this chart, let me break it down for you.

    The green line is the tree satisfaction. In a perfect world, it is constantly rising until the soil cannot hold more water.

    The blue columns show the precipitation of the day. You can see that when it rains, tree satisfaction rises.

    The red triangles, in the beginning, are sad tree days. Those are the days when the tree has absolutely no more water to drink from. We want to avoid them.

    Finally, the orange line is the anticipated tree consumption. During winter the consumption is lower due to less direct sun. The calculation in the spreadsheets makes this assumption based on temperature.

    A more realistic example
    In reality, we cannot catch all the water and also lose water every day through the soil:

    Water loss/day 5%
    Catchment Coefficient 70%


    A more realistic example of tree satisfaction

    As you can immediately see, the sad tree days increased significantly and tree satisfaction stays low most of the time. There are 3 major periods ranging from 50 to 80 days. In a Mediterranean climate as we have in Barcelona, plants usually don’t go into dormancy as temperatures stay constantly above 0° C.

    In this case, we have to step in and make sure that our trees receive the water they need.

    or we apply water harvesting and retention techniques
    There are many things, we can do to harvest more water and to retain it over longer periods of time. Let’s assume the following improvement:

    Water loss/day 2%
    Catchment Coefficient 90%


    Tree satisfaction when applying water harvesting techniques

    We can see that our trees most likely stay happier throughout the years. Granted, there are still 3 major periods of sad tree days, but they seem less scary.

    I think those periods can then be mitigated by installing swales and dams.
     
    pollinator
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    Far more research than I ever did. I just did my earthworks, planted everything and watched it die. lol

    Good luck!
     
    Posts: 606
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    Some very good information there - thanks Eric.

    When considering 'trees' are you referring to cropping ones that provide human food (fruit and nuts), trees for habitat, trees for wood production, or all the above?

    Typically, most cropping species will require a degree of frequent watering for good production, whereas most habitat/wood production species don't require much, if any, supplemental watering.

    We're in a similar climate, though with less rainfall. I would never provide any tree with 11 litres a day - it makes it seriously drought intolerant and susceptible to wind. I aim to force the tree to work hard for water - encouraging it to send its roots deep to get it.

    The choice of cultivar and species is critical - for indigenous habitat species, they get water for the first month after planting, then I reduce it to once a week for another month, then none thereafter. That gets them midway through our summer, which has recently got up to about 45 C this year. If they survive, and most do, they don't need anything but natural rainfall.

    It's important to only do deep watering at the drip line of the tree - where most of the feeder roots exist, but also to encourage it to send its roots out and down - just like a natural forest.

    Though, it is dependent on soil type, we mostly have heavy red and grey clays with a very thin overlay of friable soil and leaf litter. The cropping trees get sugar cane mulch and watered with fish/seaweed emulsion to increase soil biota and general tree health.

    Incorporating all the typical Permaculture devices will increase water holding and efficiency: Swales, talus garlands, keyline design, drip irrigation, grey water, etc.


     
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    If they get enough water the first year to get established you should be goo unless there is a drought. roots of healthy saplings will stretch out roots to seek water.
    I love Barcelona . Wish every city had a road such as La Rambla
     
    pioneer
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    I do not water my fruit trees and I go all summer and fall with no rain, so no rain for about 6 months.  Yes, I get lots of apples, plums and pears with this treatment.  And blackberries, but they are not trees.  I do carry water to them from time to time for the first season, and if I do it after the first season, for the 2nd and 3rd they grow faster, but the ones I didnt lived and eventually fruited. This was the first year for me to get fruit from the Lady William apple tree, just in time for christmas.  The rooststock used helps, I chose a rootstock that is deep and doesnt mind sandy soil, so for me my apple trees are on M111.  The pear is on...I forget.  The green gage plum and the japanese plums, not sure either, some times my labels fall off, even though they are metal.  

    SO, I kind of wonder about how one can realy generalize about water needs when there are so many variables ?  I mean, in answer to teh question, "how to find out if you can sustain your trees on rain alone" is often, try it and see !  Mulching in the early years is sure helpful, but I have an illness and let it go, and we sure were swimming in fruit this year.

    I DO have to water the citrus.  So, the citrus is up against the barn by the hose bib I use to fill the animals water buckets.  Right where I go by twice a day, so they dont get forgotten.  the apples and pears are far from a hose bib, by design.  
     
    Posts: 31
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    Wow, F Agricola...great post. (And great news, too - for the past ten minutes, I've been wondering how I was gonna supply all those extra liters...)

    "It's important to only do deep watering at the drip line of the tree (...) Though, it is dependent on soil type, we mostly have heavy red and grey clays with a very thin overlay of friable soil and leaf litter."

    Would this also be the recommendation for silty loams with moderate clay content? (Do you happen to know?)

    Many thanks
     
    F Agricola
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    Donner MacRae wrote:Wow, F Agricola...great post. (And great news, too - for the past ten minutes, I've been wondering how I was gonna supply all those extra liters...)

    "It's important to only do deep watering at the drip line of the tree (...) Though, it is dependent on soil type, we mostly have heavy red and grey clays with a very thin overlay of friable soil and leaf litter."

    Would this also be the recommendation for silty loams with moderate clay content? (Do you happen to know?)

    Many thanks



    Thanks Donner.

    If I'm guessing correctly, your silty loam would be like fine sand with organic matter holding it somewhat together?

    In that case, incorporating LOTS of organic matter like compost, etc will make the soil more capable of holding moisture and nutrients. Otherwise, water and nutrients just drain out of it. The other issue with sandy/silty soils is they can easily become hydrophobic - water repellent. So, you may pump a lot of water on plants but they don't get any because it runs away elsewhere. The addition of organic matter into the soil (compost, fine wood chips, manure) and mulch (surface layer of whatever you can obtain: wood chips, hay/straw, sugar cane) will change the soil composition by breaking down the waxy residues on soil particles created by plants and fungi. Soils with a low clay content are susceptible to water repellency.

    Also, if you can get some clay soil, soak it in a bucket/wheel barrow until it becomes a thin soup and pour it over the soil - it will add clay content and therefore fix a range of issues, including some mineral deficiencies. Doing this repeatedly over time will add robustness to fragile soils.

    Have fun!






     
    Donner MacRae
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    "If I'm guessing correctly, your silty loam would be like fine sand with organic matter holding it somewhat together?"

    Texturally, this is a loamy soil with a high silt / low sand / moderate clay content. (It falls out at a ratio of roughly 70% silt - 10% sand - 20% clay.)
    Ksat (i.e. speed at which water is able to permeate the soil) is projected by our USDA to be low-moderate (no perc or permeameter testing done yet).
    Organic matter is roughly 3% within the top 12", but drops off quickly after that.

    I don't think it's a sandy soil, per se - that would imply that it's a faster draining soil, no? From what I can piece together, it's more like a slowly-draining, dense, silty soil that (barely) falls within the parameters of a loam.

    Building the organic matter (with as little disruption as possible) and improving drainage are two of my top priorities in the next few years. Down the road a piece, I'm hoping the irrigation guidelines you've posted for establishing & drought-hardening trees will prove applicable within my soil + climate situation.

    [Edited for clarity]
     
    Eric Lehmann
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    I really appreciate all your comments, it's exactly what I hoped for as for myself some things are also unclear as I am still a permaculture rookie.

    F Agricola wrote:When considering 'trees' are you referring to cropping ones that provide human food (fruit and nuts), trees for habitat, trees for wood production, or all the above?


    In my case, I did the research for mostly for pioneer species. My problem during my research was, that I couldn't find much information on how much a tree needs. I only found one source claiming that a young tree (1-2 years old) would need 80 liters a week to get properly established.

    I suppose, if one generally knows the water needs of their plants, one could change the number in "Daily tree consumption"

    F Agricola wrote:
    Typically, most cropping species will require a degree of frequent watering for good production, whereas most habitat/wood production species don't require much, if any, supplemental watering.



    This is what I am currently speculating on, in my case, I would look for signs if supplemental watering is needed during dry periods.

    F Agricola wrote:
    We're in a similar climate, though with less rainfall. I would never provide any tree with 11 litres a day - it makes it seriously drought intolerant and susceptible to wind. I aim to force the tree to work hard for water - encouraging it to send its roots deep to get it.
    It's important to only do deep watering at the drip line of the tree - where most of the feeder roots exist, but also to encourage it to send its roots out and down - just like a natural forest.


    I totally agree with you here. Maybe the assumption of "Daily Water consumption" is misleading then? Waiting for rainy days seems then the way to go, as trees in nature, not close to a water source, have to wait for rain anyway. That should make them work hard for water for sure :)

    Sue Reeves wrote:
    I do not water my fruit trees and I go all summer and fall with no rain, so no rain for about 6 months.  Yes, I get lots of apples, plums and pears with this treatment.  


    That's very encouraging for me!

    Sue Reeves wrote:
    SO, I kind of wonder about how one can realy generalize about water needs when there are so many variables ?  I mean, in answer to teh question, "how to find out if you can sustain your trees on rain alone" is often, try it and see !  Mulching in the early years is sure helpful, but I have an illness and let it go, and we sure were swimming in fruit this year.


    I will definitely try it! My goal with the research was to get a rough idea whether it might be feasible and how permaculture design increases success. For myself, I wanted to know whether I better install an irrigation system which I would like to avoid as this would mean for me to be dependent on those who provide the water. It also does not seem very reliable.
     
    They gave me pumpkin ice cream. It was not pumpkin pie ice cream. Wiping my tongue on this tiny ad:
    HARDY FRUIT TREES FOR ORGANIC AND PERMACULTURE
    https://permies.com/t/132540/HARDY-FRUIT-TREES-ORGANIC-PERMACULTURE
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