Climatic changes associated with the El Niño Southern Oscillation (ENSO) can have a dramatic impact on terrestrial ecosystems worldwide, but especially on arid and semiarid systems, where productivity is strongly limited by precipitation. Nearly two decades of research, including both short‐term experiments and long‐term studies conducted on three continents, reveal that the initial, extraordinary increases in primary productivity percolate up through entire food webs, attenuating the relative importance of top‐down control by predators, providing key resources that are stored to fuel future production, and altering disturbance regimes for months or years after ENSO conditions have passed. Moreover, the ecological changes associated with ENSO events have important implications for agroecosystems, ecosystem restoration, wildlife conservation, and the spread of disease. Here we present the main ideas and results of a recent symposium on the effects of ENSO in dry ecosystems, which was convened as part of the First Alexander von Humboldt International Conference on the El Niño Phenomenon and its Global Impact (Guayaquil, Ecuador, 16–20 May 2005).

There is an exceptional group of alpine peatlands in the world situated in the arid grasslands of the central Andes. The peatlands in northern Chile occur in the most arid part of their range. Members of the Juncaceae are the primary peat-forming plant species. Fresh and mildly saline groundwaters originate from glaciers, snowmelt and rain are the water sources for the northern Chile peatlands. Paleoecological investigations suggest that some peatlands are recent features of the landscape having developed within the last three thousand years or less. These peatlands are unique, extremely fragile water features sensitive to climate changes and human disturbances such as regional mining activity. Much more work is required to develop scientifically based sound management and conservation programs for the rare plants and animals that live in them and to ensure the future livelihoods of the indigenous peoples who depend on them.

While climatic extremes are predicted to increase with global warming, we know little about the effect of climatic variability on biome distribution. Here, we show that rainy El Niñ o Southern Oscillation (ENSO) events can enhance tree recruitment in the arid and semiarid ecosystems of north-central Chile and northwest Peru. Tree-ring studies in natural populations revealed that rainy El Niñ o episodes have triggered forest regeneration in Peru. Field experiments indicate that tree seedling recruitment in Chile is much less successful than in Peru due mostly to larger mortality caused by herbivores. The dramatic impact of herbivores in Chile was derived from the combined result of slower plant growth and the presence of exotic herbivores (European rabbits and hares). The interplay of herbivory and climatic effects we demonstrated implies that rainy ENSO events may represent 'windows of opportunity' for forest recovery if herbivore pressure is minimized at the right moment.

1. The fast-slow plant economics spectrum predicts that because of evolutionary and biophysical constraints, different plant organs must be coordinated to converge in a unique ecological strategy within a continuum that shifts from fast to slow resource acquisition and conservation. Therefore, along a gradient of aridity, taxa with different strategies will be expected to be successful because selection pressures for slow resource acquisition become stronger as the environment becomes drier. In extremely arid and seasonal environments, however, a slow strategy may become disadvantageous because slow traits are costly to maintain.Additionally, as the availability of water decreases, selection pressures increase, reducing the variation in ecological strategies.2. Using shrub assemblages along an aridity gradient in the Atacama Desert, we test the hypothesis that selection pressures imposed by hyper-aridity act simultaneously on the variation and coordination of trait attributes, leading to an inverse pattern in the fast-slow plant economics spectrum, where strategies shift from slow to fast as the environment becomes drier.3. We established 20-22 plots at each of four sites along the gradient to estimate plant community structure and functional variation. For all species recorded, we quantified a set of leaf, stem, and root traits. 4. Results revealed an inverse pattern of the fast-slow economics spectrum for leaf and stem traits, but not for root traits; that is, as aridity further increased, aboveground traits exhibited a shift from a slow to a fast strategy with some level of coordination. Below-ground traits, however, did not shift accordingly with our prediction, rather they showed more complex pattern of shift and coordination with above-ground traits along the gradient. We also found that trait variation showed an idiosyncratic pattern of variation along the gradient, indicating that ecological strategies are driven by local processes within sites. 5. Synthesis. Our results increase our understanding of the fast-slow plant economics spectrum by showing that environmental gradients, as well as local process can K E Y W O R D S Additional supporting information may be found online in the Supporting Information section at the end of the article. How to cite this article: Carvajal DE, Loayza AP, Rios RS, Delpiano CA, Squeo FA. A hyper-arid environment shapes an inverse pattern of the fast-slow plant economics spectrum for above-, but not below-ground resource acquisition strategies. J