Environmental changes in biodiversity hotspot ecosystems of
South Ecuador: RESPonse and feedback effECTs (FOR2730)

Abstract:

Ratios of stable oxygen isotopes in tree rings (δ18O) are a valuable proxy for reconstructing past climates. Such reconstructions allow us to gain better knowledge of climate dynamics under different (eg warmer) environmental conditions, which also forms the basis for effective risk management. The latter aspect is particularly relevant for our study site on the western flanks of the Andes in Southern Ecuador, since the region is frequently affected by droughts and heavy precipitation events during the rainy season (January to April), leading to enormous social and economic losses. In particular, we focus on precipitation amounts and moisture source regions as they are known to influence the δ18O signature of tree rings. Moisture source regions are based on 240 h backward trajectories that were calculated with the trajectory model LAGRANTO for the rainy seasons 2008 to 2017. A moisture source diagnostic was applied to the air parcel pathways. The resulting moisture source regions were analyzed by calculating composites based on precipitation amounts, season, and calendar year. The precipitation amounts were derived from data of a local Automatic Weather Station (AWS). The analysis confirms that our study site receives its moisture both, from the Atlantic and the Pacific Oceans. Heavy precipitation events are linked to higher moisture contributions from the Pacific, and local SST anomalies along the coast of Ecuador are of higher importance than those off the coast toward the central Pacific. Moreover, we identified increasing moisture contributions from the Pacific over the course of the rainy season. This change and also rain amount effects are detectable in preliminary data of δ18O variations in tree rings of Bursera graveolens. These signatures can be a starting point for investigating atmospheric and hydroclimatic processes, which trigger δ18O variations in tree rings, more extensively in future studies.

Abstract:

This paper focuses on the analysis of precipitation patterns, using a Local Area Weather Radar to collect information about the precipitation distribution in an Andean region of southern Ecuador (cities of Loja, Zamora and Catamayo). 54 representative events were selected to develop daily precipitation maps and to obtain their relevant characteristics, which were related to the topography and the season. The results showed that a strong correlation between the areas covered by precipitation (RA coefficient) and the season exists. In general, humid air masses come from the east (Amazon Basin), but during the main rainy season (December to April), humidity also frequently enters the study region from the west (Pacific Ocean). The rainy season is characterized by convective precipitation, associated with higher evaporation rates during austral summer. The relatively dry season is formed between May and November, but considerable precipitation amounts are registered, too, due to advective moisture transport from the Amazon Basin, a result of the predominant tropical easterlies carrying the humidity up the eastern escarpment of the Andes, generally following the natural course of the drainage systems.

Abstract:

Tropical forests and the trees as their principal components have been investigated in detail. However, due to its complexity, their interactions, adaptations and response to climate variations require much more research. In this study, dendrochronological techniques were applied to evaluate the potential of tree-rings from tropical tree species as climate records. Two ecosystems with very distinct climate scenarios were selected from a dry and humid forest in southern Ecuador. A comparative analysis between these two forest types was performed by applying three dendrochronological methods. First, Tree Ring Width (TRW) measurements from tree species with distinct ring boundaries were dated to develop ring-width chronologies. Second, stable carbon isotopes (?13C) were measured from whole-wood and alpha-cellulose of dated annual tree-rings. Finally, concentrations of more than 23 chemical elements were determined from individual dated tree-rings after dissolving the wooden material in HNO3. The results showed the high potential of tropical tree species as climate archives, Bursera graveolens and Maclura tinctoria for the dry forest and Cedrela montana for the humid forest. Radial growth variations in tree species from the dry forest revealed a strong and reliable precipitation signal. Then, for these tropical regions, the first ring-width based wet-season precipitation reconstruction over the past century was developed, and spatial correlations unraveled a strong connection to the climatic conditions of the central Pacific precipitation and temperature variability. Interseries correlations of the TRW from the trees of the humid forest revealed a weak common signal. Stable carbon isotopes evidenced higher climate sensitivity than TRW measurements in the humid forest. However, to infer a reliable climate reconstruction from stable carbon isotopes, more ?13C time series were needed. ?13C values from whole-wood and alpha-cellulose reflected local and regional signals of precipitation and humidity. Meanwhile, nutrient concentration in the wood was higher in the dry forest, but common patterns and trends of nutrients were more distinct in the humid forest. For both study sites, two groups of nutrients with opposite radial distribution were identified (Group 1: Ca, Sr, Ba, Ga; and Group 2: K, P, Rb). In conclusion, TRW of tree species from the dry forest have a high paleoclimate potential, especially to reconstruct precipitation amounts in arid zones of southern Ecuador. Stable carbon isotopes constitute a promising tool to perform climatic reconstructions in both ecosystems. Finally, the valuable historical information of nutrient concentration evidenced in tree-rings opens promising ways to study tree growth dynamics especially in the humid forest.

Abstract:

From 10 selected tree species, Bursera graveolens and Maclura tinctoria exhibited distinct annual and crossdatable tree-rings. It was possible to synchronize individual tree-ring series and to establish two tree-ring chronologies of 203 and 87 years length, respectively. The characteristic ENSO frequency band is reflected in wavelet power spectra of both chronologies. Both species showa strong correlation between ringwidth and precipitation of thewet season (January–May). Strong El Niño events (1972, 1983 and 1998) lead to strong growth responses in the tree-ring chronologies, whereas ‘normal’ ENSO events do not trigger long-lasting growth responses. The first ring-width based wet-season precipitation reconstruction for the past 103 years was developed. Statistical and spatial correlation analysis verified the skills of the reconstructed precipitation which captures a great part of the Rainfall Index over the land area of Ecuador and the equatorial Pacific. Furthermore, teleconnections with central Pacific precipitation and SST patterns were found.

Abstract:

Field studies have shown a wide array of responses of vascular epiphyte diversity to human disturbance-assem- blages of disturbed habitats range from largely unchanged to severely impoverished when compared with intact forest. This variability is not well understood. We explored the hypothesis that the relative impoverishment of disturbed-habitat epiphyte assemblages is a function of local climate, by analyzing the available literature on epiphyte diversity on isolated trees as a model system. We found that assemblages of moist and moderately seasonal areas experience considerably stronger impov- erishment than those of aseasonally wet or distinctly dry areas. We argue that the integrity of the vertical microclimatic gradient is more crucial for the maintenance of epiphyte diversity in moderately seasonal forests than in distinctly dry or aseasonally wet forests.

Abstract:

The Andes of Ecuador show an extreme heterogeneity of spatial and temporal distribution of precipitation. The existing operational network of the national weather service is not capable of reproducing these complex patterns. By using a cost-efficient rain radar and a network of high-resolution rain gauges, the real complexity of the rainfall distribution and the meteorological processes of rainfall formation can be assessed. A blendingmethod encompassing geostatistical tools allows to derive a comprehensive rainfall climatology for the study area. Precipitation is predominantly of the advective type, associated with humid air masses from the Amazon basin transported by the tropical easterlies. The typical form is light to heavy drizzle with long duration but lower rain rates. However, in contrast to former knowledge there is no single mechanism of rain formation for any given place. Several processes interact like small and large-scale convective cloud systems, local and regional valley/mountain breeze systems and terrain-lines of preferred moisture transport interact on various time scale. This leads to complex patterns of rainfall in space and time. Several types of characteristic weather situations are revealed by the study. They are characterized by specific combinations of local and regional atmospheric processes and interactions with the topographical configuration. They are modified by mesoscale and continental circulation patterns as the annual shift of pressure cells, the east Andean low-level Jet and katabatic flows.