2.3.3 Ecosystems

Tropical rainforest:

Vegetation grows in distinct layers.

• Emergent layer: tall trees up to 50m. Few lower branches. Grow above others to get full sunlight.
• Main canopy: trees 30-40m forming a continuous canopy. Few lower branches.
• Under canopy: trees 20m high (& young trees) – less dense can survive in less sunlight.
• Shrub layer: low shrubs & saplings. Shade plants.

Forest floor: little grows except fungi – too little light.

• Since the trees grow so tall they have large buttress roots to give them support.
• Lianas use the large trees as a support in order to reach the sunlight.
• Epiphytes grow on trees to get light & have hanging roots that collect rainwater.
• Leaves shed the water easily having drip tips & “channels” to direct the water.

Tropical desert:

Plants such as cacti:

• have thick, waxy cuticles to reduce transpiration;
• fleshy stems to store water;
• leaves reduced to spines to reduce surface area for transpiration & prevent animals eating them & sunken stomata.

Shrubs have:

§  small, waxy leaves & like cacti long tap roots to reach down to the water table and/or shallow roots to collect any moisture before it evaporates.

• Seeds can lie dormant for years. After rain they germinate quickly, flower & produce seeds within 2-3 weeks.