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Natural Experiment
Kim: Foto
Before the eruption
After the eruption
What happened in Krakatau?
• Most of the island disappeared and islands in
the vicinity were stripped of their wildlife.
• In a few months, scientists arrived on the
island to investigate the effect of the
explosion. They discovered that not even one
species of plant or animal was found. The
island had been completely sterilized.
• The case of Krakatau, is an example of a
primary succession.
• Succession is the change in species composition
in an ecosystem over time.
• It may occur on bare ground where the process
begins from soil formation, or where no soil has
already formed.
This is primary succession.
Primary Succession
• If it occurs on an already established
community with developed soil, where
vegetation is suddenly destroyed, then it is
secondary succession.
Recovery in Krakatau
• To study how nature would recover, scientists
paid annual visits to Krakatau between 1883
and 1935.
• Eventually, life did appear on Krakatau
(Rakata) in May 1884, in the form of a small
• Then by September 1884, a few blades of
grass were growing
• After 3 years since the discovery of the spider, there
were “no fewer than fifteen flowering plants, and
shrubs – mostly beach plants (mosses, and ferns)”
implicating arrival by sea.
• According to scientists, by 1887, there were dense
fields of grasses of “Alang Alang” native of Java,
which is also usually the first to grow after a forest
Number of plant species found on Krakatau
1897 1924
Sea-dispersed flowering plants
Animal-dispersed flowering plants
Wind-dispersed flowering plants
Ferns (all wind dispersed)
• After about 40 years, the forest canopy closed, and
there was barely any open terrain remaining. It has
been debated whether there was a chance that some of
the species that first appeared on the island had already
existed in Krakatoa as survivors.
• But that theory is usually dismissed and primary
succession is more likely because Krakatau had been
blasted and bombed by searing heat, and then buried
under ash. The growth of new plants and species took
place in the absence of soil, on bare rock.
Anak Krakatau
• Due to recent volcanic eruptions, succession on the
Krakatau islands have been disrupted.
• For example, in the 1930s, new volcanic activity caused
the formation of the small island volcano known as the
Anak Krakatau (child of Krakatau)
Anak Krakatau
• Primary succession has occured on this particular island
• But frequent eruptions have cleared this island of
vegetation several times. (secondary succession)
Effects on Other Islands
• The eruptions of Anak Krakatau have also
disturbed succession occuring on the islands of
Sertung and Punjang.
• However, because of wind patterns, Krakatau
(Rakata) has not been affected by these volcanic
eruptions. For this reason the recovery from the
initial 1883 explosion is studied from there.
Current Situation
• The forest in Krakatau currently does look
dense and mature.
• But after 100 years after the 1883 eruption in
1983, a total of about 300 species of plants
had returned to the islands.
• This is quite small compared to the similar
areas on the nearby mainland which have
somewhere between 1200 and 1500 plant
species. WHY?
Future of Krakatau
• For the forests in Krakatau to reach a similar
biodiversity, scientists estimate it will take
more than 1000 years.