Week 4 - 17 Sep. 2013 Disturbance and succession

We reviewed biomes and location of tropics  (between 23.5 N and 23.5 S)

Deciduous trees lose their leaves.

·         In the tropics this during the dry season.

·         In the temperate regions this is during winter.  Why?

o   Freezing temperatures would damage leaves.

o   Heavy snowfall would stick to leaves and break branches.

o   There is less light and less photosynthesis, the trees don’t need their leaves.

Disturbance = means just what it sounds like – the ecosystem is disturbed by something.

What causes disturbance in forests?

1.      Human

a.       Clearing – for agriculture

b.      Grazing – removes plants

c.       Burning – frequent fires will convert the tropical forest to a savannah.

                                                              i.      Edge of hot desserts, on the tropical side

                                                            ii.      Spiny shrubs, small trees loose leave during dry winter.  Where it is grazed by large animals we have savanna – grasses with scattered trees.  – AFRICA with giraffes, antelope, etc.

d.      Climate change

e.       Pollution – air and water

f.       Conclusion – humans have a huge impact on nature – enough to change it into a different biome.

2.      Natural

a.       Storms: heavy rains, hurricanes, wind

b.      Tree fall – creates gaps  = openings created in the forest that allow sunlight to penetrate to the forest floor.
See this article for more information about tree fall and gaps http://scf.rncan.gc.ca/pages/215

Leads to Succession 

Succession = an ecological process in which fast growing plants colonize an area that has been disturbed, to eventually be replaced by slower-growing species that remain indefinitely (until the next disturbance)

Primary succession – occurs where there are no plants – the rock breaks down into soil and slowly plants move in.  Requires 100s of year.

Secondary succession – what we see in tropical forest.  There is already a plant community, then it is disturbed and a 2^nd community comes along.

What we are talking about in this class is secondary succession.

1.      Disturbance

2.      Fast growing plants colonize the area

3.      Slow growing plants take over and remain

This also illustrates how long it takes for a forest to recover from human activities.

Pioneer species in tropical forest – the first to colonize previously disrupted or damaged ecosystems.

·         heliconia (Heliconiaceae),

·         piper (Piperaceae),

·         legumes (Fabaceae) – trees, shrubs, vines, herbs,

·         cercopia (Urticaceae)

 

Research paper:

Be more specific with your topics!

Use google scholar to search for articles: http://scholar.google.com/

You do not need to see the entire article – just use the abstract.

Outlines due on Oct. 1.