Tree reproduction exploits wind, water, or animals as intermediaries to get pollen from one tree to another. A large animal-pollinated tree, however, faces distinct problems. It needs to produce enough edible reward—nectar and pollen—in its flowers to attract the pollinators to visit but runs the risk of producing so much within one canopy (the upper portion of the tree) that the pollinators linger rather than move to the next tree. Moreover, if all other individuals of species are in flower (which is needed for cross-pollination-the transfer of pollen from the flower of one plant to a genetically different plant) there may not be enough pollinators for the huge number of flowers produced.

One solution to these problems is to be in flower when other species are not, so that you have the pollinators to yourself. In temperate regions this is constrained by having to work around winter: nevertheless, flowering of insect-pollinated trees is indeed spread over a large part of the summer, but this still does not solve the problem of encouraging pollinators to leave the abundant food of one tree to go to another. Some large tropical trees get around this by having some parts of the tree in flower, others in bud and others in fruit, giving pollinators the impression of a series of small trees. A more extreme answer, used by other tropical trees, is to produce just a few flowers at a time over a long period, possibly all year. Hawkmoths, hummingbirds, bats, bees, and other pollinators exploit these extended-blooming trees by the equivalent of "trap-lining," where they fly over complex feeding routes, repeatedly visiting widely spread flowers, just like a trapper in the Arctic visiting his spread-out line of traps. Bees can travel more than 20 kilometers during these daily excursions.

At the other extreme, however, are mass-blooming trees producing huge numbers of flowers. This is especially seen in the aseasonal (no regular dry period) tropical evergreen forests of Borneo and Malaysia where the tallest canopy trees, mostly species of dipterocarp, may all flower and fruit simultaneously at intervals of two to ten years. Over a period lasting a few weeks to a few months, nearly all dipterocarps and up to 88 percent of all canopy species flower after years of little or no reproductive activity. The region over which such a mass-flowering event occurs can be as small as a single river valley or as large as northeastern Borneo or peninsular Malaysia. With individual dipterocarp trees presenting up to four million flowers, this mass flowering seems to ignore the above problems. But as is often the case, the solutions are subtle and not immediately obvious. Firstly, within the concentrated period during which all dipterocarp species flower, individual species flower sequentially, in the same order of species each time, thereby reducing competition for pollinators. Secondly, although an individual tree can flower over two to three weeks, individual flowers may last only a day. The main pollinators are small thrips, an insect attracted by the overpowering scent of the opening flower to spend the night moving around inside a flower eating it and the pollen. In the morning the flower falls, complete with its happy thrips, leaving the ovary on the tree to develop into a fruit. As the next wave of flowers opens the following evening the thrips fly up for their next feed, blown by even light winds to, hopefully, land in the flower of a different tree from the night before. Once there they deliver their load of pollen as they wander around feeding. This works only because, unlike most tropical trees, the dipterocarps tend to grow clumped together (the heavy winged seeds of dipterocarps spin like "helicopters" but do not go far). The thrips persist at low levels between mass flowerings and explode in numbers as the trees come into flower.

In general, mass-blooming trees use relatively unspecialized pollinators (pollinators that do not restrict themselves to certain tree types), and this gives them a greater number of pollinators to go around. Their strong visual image, created by mass flowering, can attract pollinators in large numbers from great distances. High rivalry among insects can benefit the tree if, in the battle for flowers, some insects end up being ejected and going to the next tree.