El Niño southern oscillation and its effect on fog oases along the Peruvian and Chilean coastal deserts
Creators: name: Manrique Paredes, Rosa Soledad <1971>
Publisher: name: Alma Mater Studiorum - Università di Bologna
Year: 2011
Subjects: BIO/03 Botanica ambientale e applicata

description: Fog oases, locally named Lomas, are distributed in a fragmented way along the
western coast of Chile and Peru (South America) between ~6°S and 30°S following an
altitudinal gradient determined by a fog layer. This fragmentation has been attributed to the
hyper aridity of the desert. However, periodically climatic events influence the ‘normal
seasonality’ of this ecosystem through a higher than average water input that triggers plant
responses (e.g. primary productivity and phenology). The impact of the climatic oscillation
may vary according to the season (wet/dry). This thesis evaluates the potential effect of climate oscillations, such as El Niño Southern Oscillation (ENSO), through the analysis of vegetation of this ecosystem following different approaches:
Chapters two and three show the analysis of fog oasis along the Peruvian and Chilean
deserts. The objectives are: 1) to explain the floristic connection of fog oases analysing their
taxa composition differences and the phylogenetic affinities among them, 2) to explore the
climate variables related to ENSO which likely affect fog production, and the responses of
Lomas vegetation (composition, productivity, distribution) to climate patterns during ENSO
events. Chapters four and five describe a fog-oasis in southern Peru during the 2008-2010
period. The objectives are: 3) to describe and create a new vegetation map of the Lomas
vegetation using remote sensing analysis supported by field survey data, and 4) to identify
the vegetation change during the dry season.
The first part of our results show that: 1) there are three significantly different groups
of Lomas (Northern Peru, Southern Peru, and Chile) with a significant phylogenetic divergence among them. The species composition reveals a latitudinal gradient of plant
assemblages. The species origin, growth-forms typologies, and geographic position also
reinforce the differences among groups. 2) Contradictory results have emerged from studies
of low-cloud anomalies and the fog-collection during El Niño (EN). EN increases water
availability in fog oases when fog should be less frequent due to the reduction of low-clouds
amount and stratocumulus. Because a minor role of fog during EN is expected, it is likely that
measurements of fog-water collection during EN are considering drizzle and fog at the same
time. Although recent studies on fog oases have shown some relationship with the ENSO,
responses of vegetation have been largely based on descriptive data, the absence of large
temporal records limit the establishment of a direct relationship with climatic oscillations.
The second part of the results show that: 3) five different classes of different spectral
values correspond to the main land cover of Lomas using a Vegetation Index (VI). The study
case is characterised by shrubs and trees with variable cover (dense, semi-dense and open). A
secondary area is covered by small shrubs where the dominant tree species is not present. The
cacti area and the old terraces with open vegetation were not identified with the VI.
Agriculture is present in the area. Finally, 4) contrary to the dry season of 2008 and 2009
years, a higher VI was obtained during the dry season of 2010. The VI increased up to three
times their average value, showing a clear spectral signal change, which coincided with the
ENSO event of that period.