Re: secondary hemiepiphytes

From: SelbyHort at aol.com on 2000.05.19 at 18:55:08(4597) In response to Alan's questions: Plants have adapted to epiphytism primarily to get up in the canopy where there is more light, less competition from other plants, increased pollinator activity and possibly for protection from ground herbivores. The tropical forest floor is extremely dark except in forest gaps. Plants that have developed either hemi or true epiphyte strategy are often rewarded with greater or more efficient pollinator activity, more light, better seed dispersal, additional nutrient from cloud and other advantages. Many of these hemiepiphytes are from high rainfall areas that are wet rather constantly year round, so they can get a lot of water either on the ground or up, so electing to stay at ground level provides few if any advantages. True epiphytes have a different root structure that allows them to very efficiently absorb and hold even trace amounts of moisture very quickly. They can grab moisture and nutrients from the rainforest clouds as they pass through the canopy. Other epiphyes in the canopy, such as the bryophytes, release nutrient into the cloud water as the cloud passes through, and plants nearby can absorb this nutrient readily as the nutrient saturated cloud passes over them. The cloud also picks up nutrients from other plant matter in the canopy and transfers it to other areas, sometimes far away. There have been a number of studies about canopy nutrient cycling in recent years that describe this process. All of this activity serves to provide suffient levels of nutrient to epiphyte colonies that sometimes attain massive ecosystems high above the forest floor. Hemiepipytes want to get up there to tap into this richness and to join the party! Hemiepiphytes may also develop other similar root strategies as found in epiphytes once they leave the ground behind. Leaves, stems and roots of some species in seasonally dry areas may develop to become very succulent for storing water. Some of the bird's nest type anthurium may trap debris that helps to hold moisture and provide extra nutrient. The canopy life is not so easy however, and can be harsh, much hotter than on the ground. Even in the rainest areas of the world, epiphytes must endure brief scorching dry periods more intense than anything encountered on the canopy floor. Many climbing and/or hemiepiphytic aroids will not flower unless they can scramble to great heights. Hemiephytes have developed flowering strategies to utilize different pollinators or seed dispersers that reside high in the canopy. These agents are perhaps not found on the ground, or the canopy residents may be more efficient at their tasks than ground dwellers, so the hemiepiphtye wants to get their flowers up to them. Whatever the case, there may be a number of compelling reasons why a plant might evolve into a hemiepiphte rather than stay on the ground where there it can survive more easily with a steady water supply. Major driving forces for change are those that promote success in pollination and seed dispersal. Donna Atwood Selby Gardens +More << (1) I'm wondering whether anyone has any other examples of this in the aroid family. (2) Is there any evidence or explanation as to why any plant would elect to dispense with a ready supply of water by doing this? Is there some energy consideration involved (eg., too expensive to maintain connections to the ground)? >>

Note: this is a very old post, so no reply function is available.