How Plants Adapt to Rain Forest

Tropical Morphology

How Plants Adapt to Rain Forest

Leaf Structures

Presentation #6 – Extreme Adaptations

By Paul A. Thomas

Slide 1: Title Slide

Slide 2: About The Author

Slide 3: Learning Objectives

•  1. Be able to describe 3 ways tropical plants conserve water, and 3 ways plants manage extreme light levels found in the tropics

•  2. Be able to describe why plants that live in a rainforest region might have to conserve water, or manage very high light levels.

Slide 4: Tropical rainforests are tough places to live. In addition to high rainfall, high temperatures and extreme competition, there are also geologic differences that depend upon which side of the mountain, or valley, the plants reside it.

Slide 5: There are two basic environments: The wet, rainforest which usually faces the incoming ocean breezes, and the dry side of the mountain, that faces away from the incoming moist ocean air. Plants on the dry side of mountains face the heat, high light and sometimes very dry winds of the tropics without the benefit of frequent rains. To survive this, they must adapt. It is also true that the top portions of the rainforest canopy is hot, windy, and things dry out fast, so some of the modifications discussed here can be found on the rainy side, on plants way up in the canopy.

Slide6: One adaptation is how plants exposed to constant wind have adapted. A very large banana leaf will catch a great amount of wind force. If it didn’t flex properly, the leaf could be folded or broken off, or the entire banana could be toppled over. To reduce the wind force, banana’s possess a leaf-tear zone. If the leaf experiences high wind force, it tears rather than resist. The leaf is designed so that this tearing does not reduce photosynthesis and the vascular veins do not cross the tear zones. This every tear zone acts like a leaflet.

Slide 7. Palm trees use this method that allows large leaves but much less wind force effect by having hundreds of independent leaflets. Wind can pass easily through the Palm canopy, and exert very little force. This is how tropical palms can survive frequent tropical storms, Hurricanes and Cyclones.

Slide 8: The most obvious adaptation that one finds is very similar to what one would expect in a traditional desert. Very heavy waxy leaves and plants where the stem structure is designed store water when available. These plants, located on the rainy side of the Monteverde rain forest at the UGA Eco Lodge, show waxy leaves and the stringy-leafed plant. That stringy plant is actually an epiphytic cactus. Despite the rains, it can get dry ion the canopy.

Slide 9: On the dry side of the mountain just miles away, one can see traditional Yucca, Echeverria and true Cacti thriving on the slopes. Many cacti have very heavy waxy stem structures that are fluted and designed to expand and shrink, to store water when available, and to sustain the plants when it is not.

Slide 10: Agave, Yucca and other resident plants have extremely tough, waxy leaves that are almost impervious to dry winds and evaporation. Their stomates close during the day and open at night when heat and the dryness of the air is less. By doing so, they conserve much water. Notice the snail still clinging to the succulent early in the morning. Wonder how it survives?

Slide 11: Orchids have very heavy waxy leaves, stems and roots, and conserve water by storing it in their thickened stems, just like a cactus!

Slide 12: Another adaptation to high wind and light levels are trichomes. Trichomes are tiny hair-like appendages of plant epidermis. The trichome reduces the effects of wind at the leaf surface, and because they are grey or almost white, they reflect light and heat. The more trichomes, the more reflection. The trichomes can also hold in some heat if the dry slopes get cold, as can happen in some areas.

Slide 13: There are several other adaptations plants that live in the dry slopes use to survive. The first is having tiny, needle like leaves. The first image is nota pine tree seedling, it is a succulent shrub that has waxy needle-like leaves. Similar to pine trees, this leaf design conserves water by reducing exposed leaf surface area. The next image is a Cereus cacti growing among a Croton bush’s foliage. They both have waxy epidermin. The croton employs having cells with few pigments and little chlorophyll to cut down on light capture and hence heat load. Notice that interior leaves are darker. As the plant grows, the older leaves regain chlorophyll. The last plan is called the ribbon plant. It has no leaves, just modified stems that look like leaves. This, wiry and waxy, the plant displays all leaves straight upwards to reduce the angle the sun hits the leaves. This can reduce leaf temperature by 20-30 degrees farenheit.

Slide 14: The “String –o-pearls” plant represents extreme adaptation. Each leaf has been curled upon itself, eventuall developing into a round ball. There are few stomates, and very waxy coatings. The “pearl-like leaves hold water and photosynthesize with minimal water loss by storing CO2 taken up at night, and using it to make sugars during the day.

Slide15: Finally, the ultimate survivor. Many Opuntia cactus have waxy, upright facing leaves, that store water in their tissues and in the stem. They also have spines to ward off predators that might chew the leaves for moisture.

Slide 16: We have seen that there are three very distinct regions of land in Costa Rica. Plants in the rainforest areas adapt to high rainfall, plants on the dry side of the mountains adapt to hot dry conditions. These adaptations to dry, hot windy conditions include waxy cuticle, vertical facing leaves, leaves that store water, leaf designs that reduce wind force, and leaves that are so modified that they don’t look like leaves!

Slide17: Assessment Opportunity

Slide 18: Future Exploration