In order to judge how much water a tree needs to survive after planting, I carried out a lot of research. Neither literature research, nor enquiries at arboreta could answer this question.
It may be clear that both the variety of the tree as well as specific parameters like temperature and humidity play an important role. As nurseries could only give an indication of the amount of water they are using per square meter, tests have been conducted at controlled circumstances.
As the Pinus is known for its ability to survive under harsh circumstances (they are presently used by the East Moroccan Water & Forest Authority to plant in the Sahara), it has been decided to use this tree for the test.
The tests have been conducted in an empty room with controlled temperature, behind glass. In this way the most extreme draught could be simulated, because capillary water, condensation and precipitation were unavailable. Measurements were carried out each morning shortly after eight. The room was in the sun until about 13:00. The temperature in the room varied between 12 and 33 degrees daily, in this way copying desert circumstances. The relative humidity varied from 49 to 75%.
Eleven little trees with a height of about ten centimetres were planted. Ten of them had a small pot mound of soil of 3 x 3 x 3 cm and one had no pot mound. The trees were numbered and the quantity of water to supply was set at 5, 4, 3 en 2 cc per day and 2 cc every second day. For each quantity two trees were used. The tree without the pot mound received 5cc.
The quantities were given with the aid of two hypodermics without needles with a clear partition in cc, bought at the local pharmacist. The first hypodermic has a partition from 1 – 10 cc; the second one from 1 – 30 cc. After planting, the trees were given a large amount of water, before letting the soil dry out almost completely.
Only then the watering was started. Quite soon the quantities mentioned turned out to be too low and after two weeks they were raised to 2, 4, 7 and 10 cc. With the arrival of hot weather, also these quantities turned out to be too low. The trees with 7 and 10 cc survived, but stopped growing. The trees receiving less water died or suffered badly. After five weeks the quantities were raised again; this time to 10, 15 and 20 cc. Both trees that received 10 cc and one receiving 15 cc of water per day died in the meantime. One receiving 15 cc and two trees receiving 20 cc are still alive.
We can conclude that a small Pinus can survive with 15-20 cc per day at a temperature of 25-35 degrees Celsius and a relative humidity of 50-70%. To grow, however, the tree needs more than that. In order to find out more of minimum needs, resistance to high temperatures and survival chances in deserts, further research is needed.
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