get tall canopy with low rainfall?

I would like to (and I am sure that other people would like the same!):
- get some shade above (when the sun is up) -> a canopy higher than easy-to-harvest fruit trees.
+
- slow down wind
- get some mulch from leaves
- any use from food to forage through nitrogen fixing, wood, medicine...

Drought resistant trees are usually small apart from pines. My second shade-tree is almond... not very tall.
Which would be the highest?

Some ideas:

- leucaena esculenta: up to 15m
http://www.worldagroforestry.org/treedb2/speciesprofile.php?Spid=1747
"It can withstand up to seven months dry season and occasional light frost but it does not thrive above 2 000 m."
It seems the only safe edible for human and animals leucaena. (L. leucocephala seeds contain mimosine, toxic to nonruminant vertebrates.
I have not found the rainfall. Seeds neither...

- Pithecellobium dulce (guamuchil) :up to 10-15m or even 20m, and with a broad crown.
Very useful pods http://www.hort.purdue.edu/newcrop/duke_energy/Pithecellobium_dulce.html#Ecology
"Suitable for most dry regions, it is drought resistant, in low rainfall areas developing an extensive root system."
Can grow with even 5,5" if there is underground water/river.
Minimum annual temperature of 18°C (64°F)

- Azadirachta indica - neem: up to 30m
Needs 16" as a minimum.

So I have not found that many!
Who knows more?

I guess one constraint would be "fast growing". Seems like there are quite a few contenders if one has 50-100 years of patience to get them into the high canopy.....date palm, pistachio, several oaks, perhaps carob.
I'm trialing Casuarina, and intend to try Acacia melanoxylon. Internet research tells me both are naturally wetland/riparian/high to moderate rainfall species, but anecdotes, including from this very site, assure me that both, at least when established, can withstand some months of annual dry season......
If all else fails, there are always the eucalypts....but they are probably subject to the same critiques as are pines.....flammable, mulch is harsh/allelopathic, wood and browse of limited use, etc.....

I also have carob, and it will do for wind because it is bushy, but I do not expect any tall size, according to some old ones I know. And yes, one has to be patient, and more over you have to wait to know who is male who is female.

What varieties of oak give edible good acorns?

About eucalyptus:
I have decided to try one: E. citriodora.
- 600ml from east Australia = 24"
- Can grow very tall and straight and give a good wood.
- Easy from seed and fast grower (I have 4 at knee size, a few months old).
- They already have that great scent!
- The best against mosquito, and the oil is great for physical/muscle pains (anti-inflammatory).
- Can be coppiced for oil production, or let grow tall.
And yes you are right about fire-sensitivity... I have chosen a narrow place down the valley, where I want to cut wind + near prickly pears. I planted them very close.
I dunno if this one is allelopatic.

About "can withstand some drought when established", well, it also depends if you have a clear seasonality with a lot of rain when it rains. And the tree will also do better if its preferred summer or winter pattern is respected + preferred type of soil.

What "fails" at least leaves some roots in the earth!

Among the oaks, I am thrilled with our California natives blue oak (Q.dougasii) and valley oak (Q. lobata). The acorns are large.....a lot larger than any European oak....some are 4-5 cm. long! The trees are deciduous....a good thing for understory plants and once-yearly mulch deposition, and they are not prickly on the margins, like the holm oak and the various California live oaks. These two are both white oak group which means quick leaching...just a few hours really.. But where you will find seed of such things is anybody's guess. They need to germinate quite soon after falling, so they need to be shipped in a fresh state. CA and the USA in general can be very picky about IMPORTING seed and plants, but I don't know about the reverse!

Have you thought of vines? My best strategy for quick shade is to plant a fast growing vine and build a structure for it to climb, sisal twine and posts to hold it up. In my climate (high desert with freezing winters) I use hops and passion vines because they freeze to the ground each winter, giving me warming winter sun. In the spring they come exploding out of the ground, ready to grow 20 feet, and cover the arbor. I prefer these vines because they do not make a heavy load up high, and can be supported by comparatively light weight structures- as opposed to grapevines or kiwis or wisteria.

In your climate there may be other vines to consider, but vines do go up high and make shade.

good luck
Thekla

Alder, for importing seeds I never got any problem up to now, and American oak seems to be a good option...

Thekla, thanks for the idea of hops, as I thought they all needed loooots of water. I learned on wiki that some Humulus lupulus are American!
Which one do you have? Do you water a lot?
I guess the first one is the most water wise?
H. l. var. neomexicanus – western North America
H. l. var. pubescens – midwestern North America
H. l. var. lupuloides (syn. H. americanus) – eastern North America
I did use wisteria when I was in a wetter climate, and kiwi can grow in other places of the island (higher elevation, colder in winter and wetter), and would not do so good here. Wiser for me to barter them...

Passion vines do great! I also have some old wine-vines and I leave them.
I have no frosts, but I trim them when needed. More mulch...

I live in a large ravine, what is called here "barranco". I have planned to cover the bottom (as I have 2 walls facing each other) with vines, including cucurbitacea (some are perennials).
And breed hens etc beneath, in the shade!

The canopy is for wind protection and some shade from above where I do not plan a structure.

Cool! If you send me mailing information I could try to send you some acorns when they fall later in the summer. But if someone from further south in California sees this, I would guess seed from there would be even better since they have less frost and therefore even more similar a climate to yours. We regularly have temps of -5 to -7 C several times during a winter. The species Q. douglasii, the blue oak, at least, is found quite far south in the state, in climates a good deal warmer and drier than here....

Thanks! Yes I have one reason for looking for similar climates that is a more successful seed exchange. (not to speak of a wild canopy, we here have carrots seeds that are acclimated)
then also it can help see better the details of one's own weather, by comparison.
(please volunteer here! "dry subtropical Mediterranean climate: Who has one?"
https://permies.com/t/26215/permaculture/dry-subtropical-Mediterranean-climate

Just look at this mere tall trees talk... we just do not have a lot of choice when the weather is dry!

Look at this list: http://en.wikipedia.org/wiki/List_of_Quercus_species
and the valley oak: "growing in the hot interior valleys and foothills..."
great...
then "requires year-round access to groundwater..." sh**!!
That is why I prefer to go ahead slowly and inquire before.

Hi Xisca,

Interesting project. I looked at the photos of your ravine. I used to live in a dry mediterranean climate ( coastal valleys of central California-- less than 10 inches precipitation per year), so I am some what familiar with your constraints. I don't know what species of hops takes the least water. The ones I grow are the various named varieties used in beer making. In looking at your ravine, I see another possibility for you, which you may already be utilizing. You can channel the runoff in various ways to get more water in the places where you have the thirstier plants. See "swales", where ever you can find them discussed and explained. I heard of them through Hemenway's "Gaia's Garden", a great resource.

What I have lately discovered is the use of vetivert, a grass with deep roots and tall leaves that is non invasive. There is lots of info, maybe some here on Permies. I have no topsoil, well, less than an inch, and it will be perfect soil with the addition and incorporation of literally tons of carbon. (How handy that there is too much CO2 in the atmosphere, because that is where I plan to get all the carbon. Half the year I have irrigation water, and I am planning to plant vetivert in a cople of weeks, and at the beginning of each growing season. I'll have to dig and bring some in, propagate it as frozen ground kills it, but you would not have that problem. Take a look at the terracing that's being done with it all over the world. It would increase the organics in your soil, prevent any run off at all, allowing you to optimize what water you do receive from the sky. You could also capture any water coming down the ravine, and put that into your soil.

As you can tell I am pretty excited about the vetivert!

again, good luck in your endeavor

Thekla

A couple more ideas: eucalyptus of various species. Moringa

going slow is a good idea. I've been 6 growing seasons where I currently work and play in the soil and high desert climate.

T

Hehe, I am already growing vetiver and I have posted about it!
It is a little harder than what they say, and I lost half of the 20 shoots I bought. Then last autumn I was not successful with my direct planting! They really need water for starting, and sun.
https://permies.com/t/26103/plants/Feedback-vetiver
If you lack top soil, then look at my "snake" pics in this topic as it works really great!

For swales, the problem is to not know where there is rock and fissures... I did not make my terraces and will not dig all to know how much soil there is on top of the rubble... I can just record what I see above ground and guess about the underground.
------------------
Another quite tall tree, but for over 20" of rain (or added watering...) : sclerocarya birea from south africa, the marula tree. 2,5m long tap root and extensive side roots (30m). Absolutely needs a dry season. Can tolerate down to 10" of annual rain if it gets at least 2"/month of rain during 3 months
It can reach from 9 to 18m.
Fruit and super nut! Need male and female... Is also tried in Israel and western Australia.

Yeah, the valley oak does prefer the moister niches....in fact I've learned to use it as an indicator when reading the broader landscape. It's quite green compared to the bluish of the blue oak. Even the runoff from the pavement can create a niche for it, or a gully where water pools for a while in the winter rain.....but the blue oak grows wherever.....up on hilltops, on the edges of ravines, etc. In a worse than normal drought, it can simply drop it's leaves early and wait....

Mulberry gets big, is a fast grower, leaves are great human & animal forage, makes great shade, easy to propagate buy cuttings or self-seeding, makes lots of useful & straight poles, drops leaves in winter to let the light in and, oh, makes fruit, too! Usually they say over 400mm/15.7inches rainfall, but they are grown in western China in areas with 100mm annual rainfall, as well as throughout the middle east. They grow big around here with 20in annual rainfall.

Great! This one for silk-worms? http://en.wikipedia.org/wiki/Morus_alba
In English it is 20m tall, 15m in Spanish and 30m in french!!!
I knew this one but did not think about it! I actually have one black mulberry, because it is known here for growing without watering when established.
I thought that the white one needed water, and yes, it loves it.
I found this:
http://www.fs.fed.us/database/feis/plants/tree/moralb/all.html
"White mulberry tolerates a wide range of annual precipitation, occurring in areas where reported average annual precipitation ranges from 11 inches (286 mm) in central Arizona to 60 inches (1,400 mm) in northern Alabama."
Seems to be liable to wind damage.

Great, I adopt it!

Glad the idea was helpful...hope it works out.

This winter I aim to diversify the varieties grafted onto my big old male tree. Right now I have 'Early White' and 'Lavender'. 'Pakistan White' graft didn't take.

Also planning to propagate by cuttings once the summer heat is finished.

I've tried eating the leaves, and the young ones are acceptable taste-wise, even raw. 25% protein. Hoping to come up with some recipes. Some places they stuff them like grape leaves.

White mulberry does pretty well in dry areas, we have lots here in the desert. Not much taller than other fruit trees on low water tho. Likes to start spreading at 3-4 meters on low water. Most people cut em back heavily there because of limb loading.

Morginga is the one to try to get growing...

your sight looks quite challanging to grow tall trees
quercus canariensis? honey locust,black locust,quercus ilex and suber
i agree about casurina
Alder there are probably better acacias for you egA victoria,a bayliana ,a dealbata if you want a timber species

Quercus canariensis does not grow around here!
I still would like to know which edible quercus would be the best adapted to my place with low winter rainfall... And does not NEED "all the time hot" summers. This year, our summer is still very "atlantic"!
The blue oak? Is there some other that would be better adapted?

Same question for acacias!
A victoria, a bayliana, a dealbata: aren't they for summer rainfall?

all those acacias are from winter dominant rainfall areas albeit higher rain than you
perhaps you can direct water onto your site from hard catchment areas .casurina cristata?

I have Acacia mearnsii/decurrens and A. dealbata, but from what I see and read about them they aren't usually high canopy, so I didn't mention them. Perhaps it's just that every several years around here there's a freeze that kills them down? Two years ago it was -11 C one night....probably not common though. I was a bit surprised the big eucalypts around didn't seem to mind it. My newly planted citrus sure did ! (but the survivors sorted themselves out....meyer lemon, mandarin, kumquat)
I also have quite a few common "mimosa" (Albizzia julibrissin), which I'm planning to coppice and grow as nurse trees among new fruits and nuts; but left alone I've seen them reach a respectable size (10-15m)....larger than they do in the Southeast even though they are more invasive there. I think the rainy summers enable better recruitment there, and at the same time diseases take out the trees before they get too large. In any case the mature ones out here seem to survive without irrigation, too.
Blue oak has a wide range in CA, and some of that range is closer to the coast, with moderated summer temperatures, than here. So, once again, seed provenance may be crucial to getting some that will really fit your microclimate....

Yes I agree with the seed provenance, thus my looking for people that we can group according to climate similarities.

Yes again I wanted to stay in the tall canopy, and open a topic for quercus and one for acacia, in the tree forum.

Andrew, yes I work on collecting water in various ways. Tanks, but they will never be big enough (easier when it is raining in storms sometimes during the dry season like in the Mediterranean area). Earth: not easy when you cannot rebuilt the terraces that are full of stones and holes from the building.

So here my goal is to work also with some shade to keep water longer!

cannot; is a swear word here!
Gabions?
Olives?
artemesia?
Chenapodiam?(check spelling()
date palms?

I could but I "will not" uproot old trees for replacing stones for earth in the terraces then!
I think that planting trees for sending roots down there is a better choice!
By the way, I have started the other topic:
https://permies.com/t/26676/trees/acacias-edible-pods-climate-choice
-> all about acacia, whatever canopy they have.
You can list there what you have and grow in your place/climate...

Well... tall canopy for some shade and wind control, yes for date palm.
So obvious and you are the first one to think about it, but that is the use of a topic, gather ideas!
Here we have the Canary palm, with nearly nothing to eat around the pit. Some harvest the sap to make "miel de palmera", a sugar substitute like maple syrup.
The problem with date palms is that they hybridize and they don't like it here, not to loose the local palm.

Also, when you do not know where the water holes are in the soil, you cannot plant date palms that will not reach a water reserve.
I also had to cut a little palm that was planted 1m up a tall wall because the root is very damaging.

I guess that the palm trees here were growing where they sprouted (sure!), and then survived the ones that were lucky to be at the right place. Here they grow more in the east of the island.

Another tall thing I forgot till now, which might kill back for me but not in a situation with less frost, is Grevillea robusta. I don't know that it produces anything useful besides shade, mulch, and firewood though. Australians probably could say better....

http://www.winrock.org/fnrm/factnet/factpub/factsh/grevillea.htm

The natural distribution is in the warm humid to warm sub-humid climatic zones. However, the species has performed well when introduced to a much wider range of climates. In its native range mean annual precipitation is 700-2000 mm and mean annual temperature is 15-20°C.

Towards the hotter extremes of the tolerated temperature range, the dry season should be no longer than 4 months for good growth. Grevillea robusta performs poorly in lowland tropical environments where mean annual temperature exceeds 23°C, and very wet locations where annual rainfall exceeds 2000 mm.

Grevillea robusta has some resistance to frost. During the winter months in temperate latitudes, it can survive temperatures down to minus 8°C with little or no damage, but milder frosts of only minus 2°C or so will cause damage during the growing season. Low-intensity ground fires will kill seedlings and young trees. It cannot withstand severe gales or persistent strong winds without damage to the branches.

Grevillea robusta prefers rather fertile soils such as those derived from river alluvia or basalts but will grow on shallower less fertile soils derived from sedimentary material. The pH range for good growth is around 4.5 to 7.5. Best growth is obtained on sandy loam, loam and clay loam textures. Heavy clay soils and prolonged waterlogging are not tolerated.

700 mm = It does not seem to match the driest mediteranean climate and comes from a wettest east Australia.
Sure great for wood and agro-forestry!

Grevillia Robusta is a great name for a tree
formally used to great use in AUS for windows ,doors ,cabinetmaking before we began importing lumber from aisian rainforest

silky oak Grevillia robusta is commonly grown in places less than 700 mm
sandlewood?

I noticed on a site describing trees on La Palma that they grow sweet chestnut (Castanea sativa). Would that be an option in your sunny ravine?

I second the vine arbor idea. Grapes give good shade, but you want then to be high, don't you? They would be difficult to prune and harvest without a tall sturdy ladder.

Yes there are tall trees of them at higher locations and more in the east and north.
The 2 sides of the only big tunnel between east and west are so different!!!
The vegetation (and the weather at the moment you enter and go out) are totally different.

I do have a chesnut, and 2 neighbours have... They give little nuts only.

Funny nobody has suggested anything that is native to desert climates. A good start would be mesquite. These grow fast, and require very little tending or watering. I have seen some as tall as 30 feet. When they are young they are very bushy, and as they grow they tend to rapidly climb skyward. With proper pruning they will become tall with a very large area of canopy. The tree's flowers provide a nectar source for bees to produce mesquite honey (monofloral honey), which has a characteristic flavor.

Mesquite is an extremely hardy, drought-tolerant plant because it can draw water from the water table through its long taproot (recorded at up to 58 m (190 ft) depth). It can also use water in the upper part of the ground, depending upon availability. The tree can easily and rapidly switch from using one water source to the other.

Mesquite trees grow quickly and furnish shade and wildlife habitat where other trees will not grow. Being a legume, it fixes nitrogen in the soil where it grows, improving soil fertility. Mesquite is a phreatophyte, which means it has deep roots and transpires efficiently. For this reason, one method of managing water loss in arid areas is the removal of mesquite. [ Not necessary if you are capturing runoff effectively, but you can remove these trees after your more favored hardwoods become well established being nurtured by the shade and biomass provided by the mesquite. ]

The bean pods of the mesquite can be dried and ground into flour, adding a sweet, nutty taste to breads, or used to make jelly or wine. When used in baking, the mesquite bean flour is used in combination with other flours – substitute ¼ cup-to-½ cup mesquite flour in each cup grain flour. Mesquite bean flour is used in breads, pancakes, muffins, cakes and even cookies. Mesquite powder is also high in calcium, magnesium, potassium, iron and zinc, and is rich in the amino acid lysine

Mesquite wood is hard, allowing it to be used for furniture and implements. Wood from Prosopis juliflora and Prosopis glandulosa is used for decorative woodworking and woodturning. It is highly desirable due to its dimensional stability after being fully cured. The hard, dense lumber is also sold as "Texas Ironwood" and is rather harsh on chain saws and other tools. As firewood, mesquite burns slowly and very hot. When used to barbecue, the smoke from the wood adds a distinct flavor to the food. This is common in the Southwest and Texas-style barbecue. Mesquite-wood roasting or grilling is used to smoke-flavor steaks, chicken, pork, and fish. Mesquite smoke flavoring can be added to vegetable stir-fries, scrambled eggs, soups, and even ice cream. Additionally he plant's bud regeneration zone can extend down to 6 in (150 mm) below ground level; the tree can regenerate from a piece of root left in the soil. meaning that you can potentially harvest the wood from the same plant for many years.

This would be a suitable cover for saplings which will outgrow the mesquite. I would suggest hickory. The Pecan tree. These trees have been farmed in Arizona for a long time, and can grow over 100ft tall. They generally get very tall and branch out creating a very broad canopy. The fruit from this tree is amazingly nutritious, and delicious as well. These trees grow slowly, but will be extremely productive for 300+ years.

https://en.wikipedia.org/wiki/Pecan

Do you have experience with mesquite to tell more? There is not only one type. Which one grows tall? as some are more bushy.
I have said in other posts that I look for seeds.

From wiki: "Pecan can be grown approximately from USDA hardiness zones 5 to 9, provided summers are also hot and humid."
Cannot find the minimum rainfall...
Would have loved to plant some, but they did not seem to suit my climate.

Of course, if they appear to be possible here with irrigation, I would give them a try!
(I say them because it is not possible to plant only one)
I mean if they need no more than macadamia...

Then, nurseries do not sell it here, and I do not remember any seed source.

Pecan is well documented:

https://docs.google.com/document/d/1Y_rwwdUi9h4fYNiq7SsEec0MGp9EXQ92f89U9peZXho/edit
Climate
Pecan tree can be grown successfully in areas which are free from severe frost in spring and excessive heat during summer. It requires a mean temperature of above 26.7o C. The tree can be grown successfully at elevations from 914 to 1,829 metres above sea level in the Himalayan region. It requires a moderate rainfall of about 75 to 100 cm and, therefore, heavy rainfall areas are not suitable for its cultivation.

http://www.daff.gov.za/docs/Infopaks/pecan.htm
"Low temperatures and even frost during winter are required for successful budding and flower formation"
Temperature:
The average monthly maximum temperature should be higher than 28 °C during summer and lower than 23 °C in winter.
The average monthly minimum temperature during the summer must rise above 16 °C, but drop below 8 °C in winter.

http://www.pecangrowers.org.au/pages/pecan_growing.html
Pecans require less than 400 chill units (hours less than 7 °C); 200-300 should be adequate.
Deep well-draining alluvial soils are considered to provide the best growing condition for trees, with at least 2 metres of soil depth. Although the tap roots may reach 7 metres, most of the tree’s feeder roots occur within the top metre of the soil. It is therefore essential that adequate water and nutrition are provided in this soil zone. Pecans can be grown on heavier soils with higher clay content than alluvial soils but growth may be restricted and care with irrigation to avoid water logging is critical. Pecans will not tolerate salt in soils, groundwater or irrigation water.

Planting pecans on slopes is generally not recommended due to lack of soil depth and the fact that the height of the tree (25 metres or more) makes tree management difficult and dangerous.

Prosopis glandulosa is the most common mesquite in north america, and as far as I know the largest. There are seven other varieties though, and as many as 20 world wide. It may take some looking to find the one you think will be most suitable.

The pecan may seem like a challenge, because it is. This is a tree that you will want to grow directly on a swale or beside a dam. Be careful. The large root system is only grown a meter or so under the soil, and will branch out and extended distance. As far as 50 feet in search of water. Most people grow them from saplings, or cuttings. It is apparently very hard to produce fertile seed. As I said though, they are very successfully farmed in Arizona through irrigation. Very low precipitation, and very few frosty winters here.

Here is some information on pecans that you may find useful. http://ag.arizona.edu/pubs/garden/az1400.pdf

I totally agree with Prosopis though they might find it not hot enough here...

I doubt Pecan for myself...
Actually, though I want all topics to be general enough to serve as many people as possible, appart from rainfall, there are other things one must take into account.

Arizona might have few frost, but I never have less than 8°C
So I have no chilling hours at all.

And I almost never pass 30-32°C in summer.
Some tree species might find it "cold"...!

For pecan.... They suit better flat deep grounds. I wander if they are not growing in the same kind of area as chesnut...
They might do well in the island at higher altitudes, with some cold + hotter summers. ... if they can stand some summer fog!
Here, no dam, no river, no wells, no underground water tab and no deep soil.
Impossible to know where are situated some natural rock holes underground.
Pines and others are sucking the water that stays under rocks.

As shown in this document ( http://naldc.nal.usda.gov/download/IND43968576/PDF ) Pecan does not have a particularly deep tap root. Usually only 10 feet in poor soil, in good soil it will be shorter. The pecan root system spreads horizontally across the ground. This allows it to grow in relatively shallow soil as long as it gets enough moisture and nutrients there should not be a problem. A well irrigated flat area of at least 35 feet across will be best. Pecans tend to prefer soils with a sandy loam texture and a clay subsoil. Most pecan roots are concentrated in the top 6 to 18 inch soil layer and are most dense near branch tips. Also this species is sensitive to salt, and your location near the ocean will require that you use only rain water for the irrigation. Well water will likely be too salty. These limiting factors will make pecan growth very difficult in your location. I only suggest it because it happens to be a very large hardy tree with good fruit with high production (around 50-100 lbs of fruit per tree depending on age).

Here is a document which may help you find your Prosopis selection. This is specifically about the main verities found in south america. Specifically Brazil and Peru. The interesting thing is that these trees formation is more a matter of the conditions they are grown in rather than their genus. Page 54/98 in this document will illustrate this. ( http://www.arch.cam.ac.uk/dgb27/chapter-3.pdf ) Also found in this document is information about the importance of pruning. (Page 49/93).

I have to agree with this quotation from the document. There is hardly any soil, if it is not habitually damp, in which the mesquite cannot grow; no hill too rocky or broken, no flat too sandy or saline, no dune too shifting...to entirely exclude it.

Well, thanks!
For pecan, then it can be difficult to obtain cuttings too!
If I could get some, I would find someone to plant them!
Actually I know someone in an adequate place, well except if the pecan is wind sensitive, because some storm produce whirling winds that uproot trees. Well, there is a very big chestnut there...

Apart from spring water that is good, my main water is from pumping deep deep deep, so it can be salty (well it tastes ok!).

For mesquite.... the only drawback is "Mesquite is a phreatophyte, which means it has deep roots and transpires efficiently. For this reason, one method of managing water loss in arid areas is the removal of mesquite."

I would just chose some rocky place far from the orchard!

And let's see how it does in the rock cracks... because there is no deep water table here.

Have you considered Paulownia? They are not quite "tall canopy" but they will grow to 40-50 feet, are very quick growing, and provide ample shade. Maybe they could serve as nurse trees that could allow you to get some taller canopy trees started.

They are known to spread aggressively, so don't let them get out of control.

Known here... http://www.xerics.com/paulownias.html
http://www.agrodesierto.com/paulownia.html
el desarrollo de las Paulownias es espectacular en las zonas más apropiadas.
En el Archipiélago Canario el coste de la madera es el más caro de Europa y el 98% del consumo local es importado.

They are just not very "low rainfall trees"... but suitable here with irrigation.

Agree. The mesquite will be best suited as your zone 5 edge tree, to provide lots of biomass and shade for your top most swale. I would not worry about the mesquite finding water. The roots will travel as far as needed to find it. If you look at some of the illustrations from the document I linked to earlier you will find that the root system will travel along the rocks until it finds the cracks or holes to allow it to place down a deep taproot. In one that was dug out of a sand dune directly over hard stone the taproot traveled horizontally over 20 meters to find an opening to continue its downward growth. They should also be able to take full advantage of the moisture from these dense fogs you have talked about. They will have some roots near the surface likely turned upward to just mm below the surface in some cases just for this purpose because it will adapt it root growth strategy in order to seek out as much moisture as possible.

I don't see hardly any Paulownia here, not even planted. The somewhat similar American Catalpa by contrast grows pretty well.
Pecan will definitely need regular irrigation I think....In the wild it is in fact a riparian or floodplain tree. Other related trees....the hickories....are probably more drought hardy, but not completely so (they are mostly native to the summer-rainfall eastern half of North America), and the nuts are much harder-shelled than the pecan.