Impacts of heavy rainfalls in El Nino 1997/98 on the vegetation of SechuraDesert in Northern Peru (A preliminary report)

The Sechura desert in Northern Peru is characterized by open shrub and tree stands of a permanent community of Prosopis pallida and Capparis scabrida and an episodic occurrence of a sparse grass and herb coverage as an interi m vegetation. On three study sites that differ in their edaphic condition a t the coast near Paita and an additional one at Piura (Fig. 3-6) the follow ing life forms profit from extreme rainfalls caused by ENSO events (Fig. 2) : Therophytes react spontaneously, but only for a short time. Hemicryptophytes and chamaephytes show a medium-term profit for approximate ly one year. Phanerophytes indicate a long-term reaction with a still unpredictable incr ease of growth and a strong "regeneration push". In addition to the two tree species, the shrubby Acacia macracantha and Cor dia lutea appear within the periodic savannas further inland around Chuluca nas. Under "normal" circumstances, their development corresponds with the s cheme described above whereas after Nino events the following ephemeral com munities can occur in addition to the perennial ones (Fig. 7): An ENSO-community with progressive dynamics after heavy rainfalls. Post-ENSO-communities following disturbances by fire due to an extraordinar y fuel accumulation and with progressive dynamics in the consecutive rain s eason. Possibly a La Nina-community stimulating only a few species after cooler pe riods. Remarkable variations in the minimum and maximum number of species per samp le area as well as in the life form change exist depending on the climatic ecological and the geomorphologic position of the sites (Table 6). As a fut ure higher number of "Super-Ninos" can be expected (but not necessarily a f aster cycle!), the already important role of spontaneously reacting ruderal plants might increase even more.