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Krakatau 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 • 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 spider. • HOW DID THIS SPIDER REACH TO THE ISLAND? • 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 fire. Number of plant species found on Krakatau Year 1897 1924 1989 Sea-dispersed flowering plants 23 53 59 Animal-dispersed flowering plants 2 48 110 Wind-dispersed flowering plants 14 48 75 Ferns (all wind dispersed) 13 51 81 • 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 too. • 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.