ENSO Effects on Biota
ENSO has a strong impact on the distribution and abundance of organisms in a landscape setting. For instance, ENSO can affect the abundance of plants that are tolerant to great variations in precipitation. Extinctions of species have been witnessed due to the impact of a strong ENSO event.
When the warm water of an El Niño reaches the coastal areas of Peru and Ecuador it stops the deep upwelling of cold water from the ocean depths. This upwelling of water contains phosphorus, a key limiting nutrient in marine ecosystems. Without the nutrients of the cold water upwellings, marine ecosystems can crash.
For example, Barber and Chavez (1983 Science, 222i, I-203) detected a huge outmigration of frigate birds on Easter Island soon after the beginning an ENSO event. Before the ENSO event started they counted over 100,000 frigate birds. Within the period of one month, all except 200 frigate birds had left Easter Island. The reason is because the warm water of El Niño caused a massive die-off and migration of fish which the frigate birds consume. In the Galapagos Islands, Barber and Chavez noted that sea lions failed to reproduce immediately following an ENSO event.
When a major ENSO occurs, it can have catastrophic impacts on those who depend on harvesting natural resources for their well-being. A hundred years ago the major concern about El Niño was its impacts on Peruvian guano production (Glantz, et. al., Teleconnections Linking Worldwide Climate Anomalies, 1991). Guano, produced by sea birds on the rock islands along the coast of Peru, is a valuable fertilzer. The El Niño resulted in a sharp increase in bird mortality within bird colonies. The anchoveta population, the staple food of many sea birds, had crashed and caused a powerful reaction up the food chain. Thus, Peruvian guano production and guano exports declined.
The impact of ENSO and Indian monsoon droughts and floods on grain yields has been analyzed statistically by using world-wide grain yield data (Garnetter, et.al. The Impact of Large-Scale Atmoshperic Circulations and Anomalies on Indian Monsoon Droughts and Floods and on World Grain Yields Agricultural and Forest Meteorology, v.61, 113-128, 1992). Scientists found that an ENSO event is generally associated with drought in the Indian Monsoon followed by low grain yield over south Asia and Australia and high grain yields over the North-American prairies.
ENSO also affects landscapes in higher latitudes, such as in the southwest of North America. Armstrong, et. al., has observed through dendrochronology data (tree rings) that ENSO increases snowpack which in turn creates a colder environment with less nutrients available for tree growth. Swetnam and Betancourt (Fire-Southern Oscillation relations in the Southwestern United States. Science, 249:, 1017-1020, 1990) also have observed that fire rings in Southwest's ponderosa pines forests are correlated with climate records that indicate the presence of La Niña events. Thus, ENSO events could be important mechanisms that sychronize fuel production, moisture content, and fire occurrence at large spatial scales.
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