Flowers opening on sunny days result in the greatest number of berries. This can be problematic and deleterious, however, as coffee plants tend to produce too many berries; this can lead to an inferior harvest and even damage yield in the following years, as the plant will favor the ripening of berries to the detriment of its own health. On well-kept plantations, overflowering is prevented by pruning the tree. The flowers only last a few days, leaving behind only the thick, dark-green leaves. The berries then begin to appear. These are as dark green as the foliage until they begin to ripen, at first to yellow and then light red and finally darkening to a glossy, deep red. At this point, they are called "cherries", which fruit they then resemble, and are ready for picking. The berries are oblong and about 1 cm long. Inferior coffee results from picking them too early or too late, so many are picked by hand to be able to better select them, as they do not all ripen at the same time. They are sometimes shaken off the tree onto mats, which means ripe and unripe berries are collected together. The trees are difficult to cultivate and each tree can produce from of dried beans, depending on the tree's individual character and the climate that season. The most valuable part of this cash crop is the beans inside. Each berry holds two locules containing the beans. The coffee beans are actually two seeds within the fruit; sometimes, a third seed or one seed, a peaberry, grows in the fruit at the tips of the branches. These seeds are covered in two membranes; the outer one is called the "parchment coat" and the inner one is called the "silver skin". On Java, trees are planted at all times of the year and are harvested year-round. In parts of Brazil, however, the trees have a season and are harvested only in winter. The plants are vulnerable to damage in such poor growing conditions as cold or low pH soil, and they are also more vulnerable to pests than the C. robusta plant. It is expected that a medium-term depletion of indigenous populations of C. arabica may occur, due to projected global warming, based on IPCC modelling. Climate change—rising temperatures, longer droughts, and excessive rainfall—appears to threaten the sustainability of arabica coffee production, leading to attempts to