Suitability of Acacia xanthophloea for dry climates and other points of interest

I am a farmer in Namaqualand and have a permanent tented camp on my farm (www.agamacamp.co.za). I would like to plant some trees in and around the camp and seriously consider planting Fever trees as it has all the properties I am looking for – indigenous, fast growing, edible, shade canopy, promoting bird life (I would love to have more owls at the camp) and attractive.
Our annual rainfall is however only approximately 320 mm per annum and can be as little as 220 mm in a bad year. To make matters worse, we get up to 90% of this from April to September as it is a winter rainfall area. From what I’ve read, this will not be enough water for the Fever trees to survive. I do however have ample bore hole water available to water the trees during the summer months, but the water is brackish. It is drinkable but you can definitely taste the salt in the water (makes great coffee though). Can you perhaps shed some light on how sensitive Fever trees are for brackish (salty) water? Amongst others, the Acacia Karoo seems to do just fine on this water.
We have well drained soil in this area. I therefore intend to excavate planting holes of about 2 m x 2 m and 3 meters deep for every tree. Do you think lining the sides with plastic and giving the hole a layer (250 mm or so) of clay at the bottom of each hole to retain moisture before filling the hole with compost enriched soil will create an acceptable patch to plant a Fever tree in or do you perhaps have a better suggestion? Should you agree, do you think 3 m depth is enough? I doubt if I will be able to go any deeper with the excavator at this site, even 3 m will be challenging at some spots.
I would also like to know about the pods produced by the Fever tree. I understand that it may be tasty and edible for sheep, cattle and game. Can you perhaps give me any idea of quantity of pods produced by a fever tree (in whatever measure or by means of comparison)? In Namaqualand we are always on the lookout for possible sources of feed for our animals. Pods usually are of high nutritional value to animals and it will be very interesting to know to what extent the Fever tree can be considered to be a source of animal feed.

I searched for other indigenous Acacias with pods that can be utilised for stock feed, that would tolerate the climatic conditions of arid to semi-arid areas. Acacia tortilis (Umbrella thorn) and Acacia erioloba (Camel thorn) were the clear winners and are used extensively across the arid areas of Africa for shade, and are valuable for stock feeding as they produce large quantities of nutritious pods. They are both highly suitable trees for your purposes. You can do a basic comparison of these three Acacias at the following sites:

• http://www.plantzafrica.com/frames/plantsfram.htm (This link will lead you to the main site, click [A], then scroll down for Acacia xanthophloea)
• http://www.plantzafrica.com/plantab/acaciatortilis.htm
• http://www.plantzafrica.com/plantab/acaciaeriol.htm

The method you are planning to use for planting your trees, as is the method I have described on my website, is now considered 'old style'. I can't go into the full explanation here but the bottom line is that trees that are planted in deep holes with plenty of compost do not develop strong root systems. With the presence of plentiful water, food and loose soil, the young roots do not venture out of this environment as there is no need to do so. The roots circle the prepared hole but do not venture out, eventually filling the entire hole with root matter – in other words the plant will become 'pot-bound' in its hole. Plastic and clay will only encourage this behaviour. Go to the following sites for excellent information on the new method planting trees for maximum growth and strong root systems:

• http://www.treesaregood.com/treecare/tree_planting.aspx
• http://www.treepeople.org/plant-right-way

Initially I was deeply suspicious of this radical change of planting method. I changed my mind after I had planted 30 trees using the 'old' method and watered them for two years. They were not watered after this. By the end of the third year only a third of the trees had survived, and except for one, the trees had not grown any bigger than they had done after two years. So far I have had better results using the 'new' method although it will take another year to make a more scientific comparison. Another point is that Acacias have enormously long tap roots so that they can reach deep underground water sources. (Acacia tortilis up to 60 meters down!) The last thing you want is to stunt the growth of this tap root as the trees will then need to be watered for as long as they survive.

A layer of compost covered with a thick layer of mulch (about 10 cm), stretching just past the drip area of the trees will go a long way to provide nutrients and preserve the moisture content in the soil surrounding the trees. Ensure that the area immediately around trunks of the trees is kept clear of the mulch and compost.