BackgroundIn the Peruvian Coastal Desert, an archipelago of fog oases, locally called lomas, are centers of biodiversity and of past human activity. Fog interception by a tree canopy, dominated by the legume tree tara (Caesalpinia spinosa), enables the occurrence in the Atiquipa lomas (southern Peru) of an environmental island with a diverse flora and high productivity. Although this forest provides essential services to the local population, it has suffered 90% anthropogenic reduction in area. Restoration efforts are now getting under way, including discussion as to the most appropriate reference ecosystem to use.Methodology/Principal FindingsGenetic diversity of tara was studied in the Atiquipa population and over a wide geographical and ecological range. Neither exclusive plastid haplotypes to loma formations nor clear geographical structuring of the genetic diversity was found. Photosynthetic performance and growth of seedlings naturally recruited in remnant patches of loma forest were compared with those of seedlings recruited or planted in the adjacent deforested area. Despite the greater water and nitrogen availability under tree canopy, growth of forest seedlings did not differ from that of those recruited into the deforested area, and was lower than that of planted seedlings. Tara seedlings exhibited tight stomatal control of photosynthesis, and a structural photoprotection by leaflet closure. These drought-avoiding mechanisms did not optimize seedling performance under the conditions produced by forest interception of fog moisture.Conclusions/SignificanceBoth weak geographic partitioning of genetic variation and lack of physiological specialization of seedlings to the forest water regime strongly suggest that tara was introduced to lomas by humans. Therefore, the most diverse fragment of lomas is the result of landscape management and resource use by pre-Columbian cultures. We argue that an appropriate reference ecosystem for ecological restoration of lomas should include sustainable agroforestry practices that emulate the outcomes of ancient uses.

RESUMENSe evaluó los cambios en la vegetación de las lomas de Mejía -Arequipa y se registró automáticamente temperatura, radiación solar global y neta, temperatura y contenido de agua en el suelo, y precipitación en la Estación Meteorológica Campbell, ubicada en las lomas de Mejía, Distrito de Mejía, Provincia de Islay, Departamento de Arequipa, Perú, a 750 msnm, entre 17 Q 03' LS y 71 2 50' LW; ubicada ecológicamente en la zona de vida Matorral desértico -Templado cálido. Durante el ENOS 1997-98 (agosto 97 -marzo 98): la temperatura ambiental promedio osciló entre 14,1 Y 19,1ºC, la precipitación tuvo dos máximos que se alcanzaron en los meses de setiembre con 189,4 mm y 173,6 mm en febrero, teniéndose un acumulado de 715,4 mm y la evaporación acumulada fue de 271 ,8 mm. En la evaluación de la vegetación, resultante de estas condiciones climáticas, se tiene que: antes de "El Niño" se registró 89 especies de plantas, y debido al incremento en abundancia de la precipitación y del contenido hídrico en el suelo se tuvo 170 especies, es decir un aumento del 91 %. before "El Niño", 89 species of plants were recorded; and because an increase in abundance 01 the species and hydric soil content were obtained 170 species of plants, that is an increase of 91%.

Myrcianthes ferreyrae is an endemic, endangered species, with a small number of individuals located only in hyperarid, fog-oases known as lomas along the Peruvian desert in southern Peru, where fog is the main source of water. Following centuries of severe deforestation, reforestation with this native species was conducted in the Atiquipa lomas, Arequipa-Perú. On five slopes, five 2-year-old seedlings were irrigated monthly with water trapped by raschel-mesh fog collectors, supplementing natural rainfall with 0, 20, 40, 60 and 80 mm month(-1) from February to August 2008. We measured plant growth, increment in basal diameter, height and five leaf traits: leaf mass area (LMA), leaf carbon isotope composition (δ(13)C), nitrogen per leaf area, total leaf carbon and stomatal density; which are indicative of the physiological changes resulting from increased water supply. Plant growth rates, estimated from the variation of either shoot basal diameter or maximum height, were highly correlated with total biomass. Only LMA and δ(13)C were higher in irrigated than in control plants, but we found no further differences among irrigation treatments. This threshold response suggests an on-off strategy fitted to exploit pulses of fog water, which are always limited in magnitude in comparison with natural rain. The absence of a differential response to increased water supply is in agreement with the low phenotypic plasticity expected in plants from very stressful environments. Our results have practical implications for reforestation projects, since irrigating with 20 mm per month is sufficient to achieve the full growth capacity of this species.

RESUMENEste trabajo presentó la evaluación del comportamiento fenológico de la vegetación arbórea con el fin de determinar su probable utilización como indicadores biológicos de la ocurrencia de eventos "El Niño". Los árboles evaluados fueron Caesalpinea spínosa, Duranta armata, Caríca candícans y Citharexylum flexuosum. Los resultados indican una alta variación en las respuestas fenológicas. C. spinosa por ejemplo en 1995 y 1996 inició la floración antes que el brote; en 1997 inicio mucho antes, pero tuvo una corta duración, yen 1998, se ha presentado en forma tardía y breve, mientras que la cubierta foliar se ha mantenido en forma constante. En el caso de D. armata y C. flexuosum la floración se presenta posterior al brote, pero en ambos casos durante la ocurrencia del evento en 1998 no presentaron floración; y C. candícans presenta floración antes que el brote, pero con alta variabilidad en el tamaño de la floración. ABSTRACTThis work present the evaluatíon of phenologic behave of the arboreal vegetation in order lo determine its possible use as biological indicator of "El Niño" events. The evaluated trees were Caesalpinia spinosa, Duranta armata, Carica candícans, and Cítharexylum f1exuosum. The resulls showed a high variation in phenologic answer. C. spínosa for example began flowering befo re shoot in 1995 and 1996; in 1997 began before, but had a short duration, and in 1998 it had presented in a late and brief period, while the foliage covering had been maintaíned constant. In the case of D. armata and C. f1exuosum the f10wering occurred after the shoot. but both cases during 1998 did not present flowering; and C. candicans presented Iloweríng before the shoot, bul wilh hígh variability in flowering size.