Evaporation vs. Transpiration in arid lands

I'm assuming I should be aiming for no bare soil in order to cut evaporation. But a cover crop and/or trees can potentially lose soil moisture faster than bare soil due to transpiration from leaves. So what cover plants can guarantee soil water retention, should I be going for succulents or particular types of shrub/tree?

How arid are we talking? Great basin, prairie or Sonoran desert? (You might update your profile with your location.) I take clues from what the native plants were before grazing, where I can get any info.

personally, as someone that lives in a arid region - i am more worried about evaporation that i am about transpiration for one reason:

it is almost ALWAYS sunny here, but it isnt always windy.


i also 2nd Ann comment about adding your location. you will be much better answers (imo) that way.

Have updated profile as suggested to show location.

It's rocky desert, a couple of hundred miles West of the border between Morocco & Western Sahara. Trade winds blow strong much of the time. Humidity rarely goes below 65%. 400mm of rain in a wet year. No rain for 6 mths in summer.

Current approach is small check dams to stop runoff, planting native trees in natural cracks in the rock and putting in prickly pairs and aloe versa at the upwind boundary and working more of them in downwind as time allows. Got the usual suspects of drought tolerant nitrogen fixer trees growing from seed in nursery ready to be planted before winter rain possibility window starts end of Oct. Salt Cedars and Canary Islands Cedar are growing native without irrigation (but don't get very big), so bringing some of those in from wetter parts of the island.

Steve - if you look at the boxes on the left of each post our location info is visible there. I'm not sure what you altered in your profile, but it isn't displaying alongside your posts.

Steve Farmer wrote:I'm assuming I should be aiming for no bare soil in order to cut evaporation. But a cover crop and/or trees can potentially lose soil moisture faster than bare soil due to transpiration from leaves. So what cover plants can guarantee soil water retention, should I be going for succulents or particular types of shrub/tree?

I think that you need to worry about both; but one you can control (evaporation) much better than the other (transportaiton), unless you don't want vegatation to grow. I look at this way. Evaporation is a 100% loss of benefit. Transpiration at least it makes it through the plant that fights evaporation for one cycle. If you can recapture some of that transpiration you have some recovery as well. By recovery, if the canopy is multistory, you may get some of that back through humidity or vapor back into the soil. Lawton claims "up to 80% recovery" is possible. I don't know how he came to that figure, though. Whatever the loss/recovery rate, you have benefited from the use of the moisture by growing a plant that slows further evaporation by shading and protecting the soil. It is a war of attrition...

Wind evaporation would concern me a lot more than transpiration with those humidity levels. Mulch, planting in depressions, wind breaks and keeping the soil covered with ground covers. What herbs grow wild in the drier side of the Mediterranean islands, like Greece. Rosemary, oregano maybe, thymes for sure. They may need a bit of help to get started. Also a bunch of plants from South Africa are becoming available here.

One site that comes to mind for research (doubt they would ship even if you wanted to pay full premium price) is High Country Gardens. They specialize in drought tolerant plants and introduce a lot of new options to the western US market. They aren't big in edibles, but it might give you some ideas for analogues.

If at all possible I would attempt to use cover crops that use and transpire the least water.
And then there's mulch.

hau, Steve, In your locale, the canary islands, I would lay down mulches and plant low growing succulents for my ground covers.
Anywhere on the planet you should strive for no bare ground since those areas are most likely to erode and that is what we don't want.
Arid land means you need to minimize moisture loss and the easiest method to do that is mulch and ground covers. succulents are great for this since they hold onto moisture with thick skins.
Trees and shrubs with waxy leaves are also good for arid lands since that waxy coating keeps transpiration to the least amount possible.

Thanks for comments & suggestions. I'm putting in succulents - mainly aloe veras and prickly pears, as these are what I can get hold of free of charge basically in unlimited supply. The constraint is time to plant, most of the surface area has NO soil due to the frequent 30mph+ wind. So I am starting upwind and working my way down. Some of the plants can go in natural cracks in the rock, but mostly I am using a hammer drill to make small craters for planting, running via an inverter off my Landcruiser. The drill takes approx twice as much power as the alternator gives so I do 3 mins on and 6 mins off to not kill the battery. I've done a few with the pickaxe but it's much much slower that way.

Steve, if you can get it, wood chips would be a great way to get planting ground.

If you lay down a really thick (10-20 cm) layer you might not loose it to the winds and so be able to plant directly into the woodchips.
from there, every addition of compost will filter down into the chips and as the chips break down you will end up with great soil that should stay put.
This method also works great for building raised beds.

If you have a rental place nearby, you could see how much a jack hammer set up would cost for a day or two, that would let you bust out some really nice holes or trenches fast.
The compressor for those is normally gas powered and here you rent the hammer and compressor for around 80 dollars US for a day.