Pinus halepensis, commonly known as the Aleppo Pine, is a pine native to the Mediterranean region. In dessert, water is limited for plants to grow up. Pinus halepensis has plans for water management. The leaves are very slender, 6–12 cm (2.4–4.7 in) long, distinctly yellowish green and produced in pairs (rarely a few in threes).1 The needle-shaped leaves exposed area minimizes the amount of moisture lost to breezes and the sunlight. The needle-shaped leaves are popular in dessert plants such as Alhagi sparsifolia. The observation raises the question that why trees grow in the deserts have small leaves. One hypothesis to that question is that they have needle-like leaves to prevent water loss by giving the sun a smaller area to evaporate water. Based on this hypothesis, it is reasonable to predict that if there are two leaves, one from ironwood and another one from a tree with bigger leaves, Pinus halepensis leaves should contain more water.
One way to test this hypothesis is getting same weight of we leaves from both tress and observe them under the microscope. If overall the Pinus halepensis needles also have much tighter stomata closure and stomata are the pores that allow air and water to pass in and out of the needle, then the hypothesis is proved correct. If there is no obvious difference between two kinds of leaf, then the small leaf may serve other functions.
Salisbury, Frank B. and C.W. Ross. 1978. Plant Physiology, second edition. Wadsworth Publishing Company, Belmont, CA. 422