Seeds & Growth of Rainforest Trees

Rainforest Tree Seeds and Seed Dispersal

• Broad-leaf, evergreen rainforest trees such as the ceiba or kapok grow in the top layer of the rainforest called the emergent layer. This tree has brown round seeds that grow in light green pods that are smooth and swing from the tree branches like pendulums. After the leaves of the tree fall, the pods burst open and the cotton-like filaments, like those found in pods of other emergent layer trees, disperse the seeds into the wind.

  Seventy to 90 percent of trees in the upper canopy, the layer immediately below the emergent layer, cannot depend on wind dispersal for their seeds so they turn to animals, especially birds, for seed distribution and processing.

  The understory of the canopy also contains trees such as the cecropia tree and the cacao tree. The cacao tree grows large pods out of its trunk and branches, which house small seeds that are used in making chocolate. These pods start out green as the seeds mature inside; over the next four to five months, they become orange, yellow, purple or red when ripe. Seeds remain fertile inside the ripe pod for to two or three weeks, which give small animals such as monkeys plenty of time to eat the pulp of the pod wall and disperse the seeds.

Germination

• Thousands of seeds from hundreds of tree species fall onto the rainforest floor. Those not eaten by the Peccary (little pig) or Agouti (tropical rodent about the size of a squirrel) germinate into seedlings in the rich loam and grow to about 2 feet tall.

Seedlings

• Once germinated, rainforest tree seedlings grow to about 6 inches and begin the search for sunlight, but these little trees usually spend most of the time in shade; some die from lack of sunshine. Short, intermittent shafts of light keep other seedlings alive, and some seedlings live for years waiting for enough light to continue growing. Those that are lucky enough to avoid falling branches progress to reach 3 feet tall, the perfect height for tapirs, (pig-like animals weighing up to 800 lbs. with short prehensile trunks like elephants) to consume up to half of them.

Saplings

• Those seedlings that reach 5 feet tall are referred to as "saplings" and finding life-sustaining sunlight is crucial. Lucky saplings survive after a large emergent tree falls to the rainforest floor, leaving a space called a "gap." Then the race is on to see which of them can grow quickly enough to fill the gap. Some trees grow rapidly but are not strong, while others grow strong but not quickly. When one or two trees reach the canopy of the rainforest, they spread their branches and leaves out to create umbrella-like formations that close the gap, thus shutting out the light to those trees below.