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

Abstract:

In former studies, a linkage between stream water element exports and stream discharge was observed at the 8.6 ha microcatchment in the montane forest of Ecuador, which was attributed to different water flow paths and the accessibility of different element sources in soil. Climate models predict an increase in temperature and precipitation. This climate change will have an impact on the water flow paths in soil and therefore alter element exports. To estimate current and future element exports, the hydrological model WaSiM was applied to the study site in daily resolution and discharge was modelled for the period 1998 - 2013. Furthermore, weekly measurements of total organic carbon (TOC), NO3-N, NH4-N, dissolved organic nitrogen (DON), PO4-P, total dissolved phosphorus (TDP), S, Cl, K, Ca, Mg, Na, Zn, Al and Mn concentrations in stream water 1998-2012 were grouped into three flow classes (baseflow, intermediate and storm) representing the rate of modelled discharge at the time of stream water sampling. By multiplying the mean concentrations of elements per flow class by the average of the yearly discharge sums per flow class and subsequently summing up per element, fluxes for current element exports were calculated. To derive estimations for future element exports in stream water, discharge was modelled under the emission scenarios A1B and B1 for the decades 2050 - 2059 and 2090 - 2099 and grouped into the three flow classes (as per above). To derive the future element exports for each scenario, yearly sums of the predicted volumes of stream water per flow class were multiplied by the mean element concentrations per flow class and finally summed up per element. For the 1998 – 2013 period the resulting mean annual exports of TOC (57.56), NO3-N (1.21), NH4-N (1.82), DON (1.8), PO4-P (0.47), TDP (0.68), S (2.56), Cl (8.15), K (4.92), Ca (7.61), Mg (4.95), Na (37.41), Zn (0.12), Al (0.18), and Mn (0.01) in kilograms per hectare per year in 1998 - 2013 were in the same range as values from the literature, except for P compounds with higher export rates and Al with lower export rates. The number of days with high discharge rates (storm) was predicted to increase and low flow days (baseflow) to occur less often under both climate scenarios and decades. Furthermore, mean discharge rates were predicted to increase by between 7.5 and 21 % until the end of the 21st century. Whereas exports of TOC (+10-25 %), NO3-N (+11-27 %), NH4-N (+6-18 %), S (+4-13 %), Cl (+10-26 %), K (+6-16 %), Ca (+7-19 %), Mg (+7-20 %), Na (+4-15 %), Zn (+12-29 %), Al (+24-53 %), Mn (+10-28 %) were predicted to increase until 2090-2099, PO4-P (+4 to -1 %) and TDP (+3 to -2 %) exports were predicted to remain relatively constant. My results demonstrate, that alterations of the water flow paths through soil due to climate change could have a considerable influence on future element exports.

Abstract:

Saharan dust outbreaks occur regularly and huge amounts of this mineral dust are able to cross the Atlantic where it is then washed out over the humid Amazon Basin and hence provides the ecosystem with nutrients. Interannual elevation of base metal deposition (K, Mg and Ca) in an Amazonian montane rain forest in Ecuador was observed between 1998 and 2004 and strong evidence was shown that much of these base metals are deriving from the Sahara during La Niña events, when more days than usually with dry spells are given over the Amazon Basin. However, so far no direct proof for a Saharan dust input beyond the Amazon Basin has been obtained. Therefore, in this study data of trace elements, rare earth elements (REE) and Pb, Sr & Nd isotopes are presented from dust samples collected in a rain forest on the eastern Andean cordillera in south Ecuador in order to identify its provenance with a geochemical approach. In advance, periods of possible Saharan dust inputs were identified on basis of elevated base metal concentration in the rainfall samples, backward trajectories coming from the west and days with a dry spell over Brazil. The results of this study support the hypothesis that Saharan dust transport to the eastern Andean cordillera in south Ecuador occurs during la Niña events. During our study period Saharan dust inputs were identified with a high likelihood at least on two days. However, there are indications that Saharan dust inputs also occurred on several more days. Thus, Sahara dust fertilizes the tropical montane rain forest on the eastern cordillera of the Andes.

Abstract:

Aims: In acid tropical forest soils (pH <5.5)increased mobility of aluminum might limit aboveground productivity. Therefore, we evaluated Al phytotoxicity of three native tree species of tropical montane forests in southern Ecuador. Methods: An hydroponic dose-response experiment was conducted. Seedlings of Cedrela odorata L., Heliocarpus americanus L., and Tabebuia chrysantha(Jacq.) G. Nicholson were treated with 0, 300, 600, 1200, and 2400 ?M Al and an organic layer leachate. Dose-response curves were generated for root and shoot morphologic properties to determine effective concentrations (EC). Results: Shoot biomass and healthy leaf area decreased by 44 % to 83 % at 2400 ?M Al, root biomass did not respond (C. odorata), declined by 51 % (H. americanus), or was stimulated at low Al concentrations of 300 ?M (T. chrysantha). EC10 (i.e. reduction 10 %) values of Al for total biomass were 315 ?M (C. odorata), 219 ?M (H. americanus), and 368 ?M (T. chrysantha). Helicarpus americanus, a fast growing pioneer tree species, was most sensitive to Al toxicity. Negative effects were strongest if plants grew in organic layer leachate, indicating limitation of plant growth by nutrient scarcity rather than Al toxicity. Conclusions: Al toxicity occurred at Al concentrations far above those in native organic layer leachate.

Abstract:

Lowered temperatures may reduce the root water uptake of tropical trees at high elevations through several mechanisms; however, field studies to test their relevance are lacking. We measured sap flux density (J) in small-diameter tree roots across a 2000-m elevation transect in a tropical mountain forest for quantifying the effects of temperature, VPD and soil moisture on root water flow and uptake at different elevations. Recently developed miniature heat balance-sap flow gauges were applied to roots of about 10mm in diameter in mountain forest stands at 1050, 1890 and 3060m a.s.l. in the Ecuadorian Andes and the measured flow was related to anatomical properties of the root xylem. Between 1050 and 3060 m, mean J decreased to about a third. VPD was the most influential environmental factor controlling J at 1050 and 1890 m, while Ta was the key determinant at 3060 m. Large vessels were absent in the root xylem of high-elevation trees which resulted in a 10-fold decrease of theoretical hydraulic conductivity (kh theor) between 1050 and 3060 m. We conclude that both physical limitations (reduced VPD, increased viscosity of water) and biological constraints (large decrease of kh theor) result in a significantly reduced J and root water uptake of the trees in high-elevation tropical forests.

Abstract:

It is generally assumed that tree growth in tropical low-elevation forests is primarily limited by phosphorus while nitrogen limitation is more prominent in tropical montane forests where temperature is lower and the soils are poorly developed. We tested this hypothesis in mountain rainforests of South Ecuador by investigating the growth response of tree fine roots to N, P and K fertilization in ingrowth cores exposed at 1050 m (pre-montane) and 3060 m (upper montane) elevation. Root growth into unfertilized ingrowth cores (control treatment) was about 10 times slower at 3060 m than at 1050 m. At 1050 m, root growth was stimulated not only by P, but also by N and K. In contrast, N was the only element to promote root growth at 3060 m. The N concentration in fine root biomass dropped to nearly a third between 1050 and 3060 m, those of P, K, Ca and Mg decreased as well, but to a lesser degree. According to a 15NO3 15NH4 tracer study along the slope, tree fine roots accumulated nitrate and ammonium in root biomass at similar rates between 1050 and 3060 m, despite lower temperatures higher upslope.We conclude that the nature of nutrient limitation of tree fine root growth changes with elevation from an apparent co-limitation by P together with N and K at 1050 m to predominant N limitation at 3060 m, which is also reflected by low foliar N concentrations. Increasing N limitation may have caused the high fine root biomass and root/shoot ratio in the high elevation forest, while the capability of the roots to acquire mineral N apparently was not affected by lower temperatures at high elevations.

Abstract:

Rural households in agricultural economies are vulnerable to several environmental risks such as fires, floods, and droughts that may affect their productivity in whole or in part. These hazards are especially relevant in developing countries where farmers have few or no access to traditional risk-transfer techniques, such as insurance and finance, and where low governmental investments in rural infrastructure, risk assessment techniques, or early warning systems makes the aftermath of such hazards more expensive and results in slower recovery for those who are affected. In this paper, we use historical satellite data (Terra) of burned areas in South America to fit a semiparametric spatial model, based on kernel smoothing and on a nonlinear relationship between average time between events and damage, to assess the environmental hazard affecting the land’s productivity. The results were twofold: first, we were able to develop a spatial assessment of fire hazard, and second, we were able to evaluate how much a farmer may lose in terms of productivity per hectare due to the environmental hazard. The methodology may be easily adapted to other world regions; to different environmental hazards such as floods, windbreak, windthrow, or related land-use changes; or to integrate various environmental hazards simultaneously, as long as they can be monitored via remote sensing (e.g., satellite imagery, aerial photographs, etc).

Abstract:

The precise estimation of precipitation quantities in tropical mountain regions is in great demand by ecological and hydrological studies, due to the heterogeneity of the rainfall distribution and the lack of meteorological station data. This study uses radar images and ground station data to provide the required high-resolution precipitation maps. Also wind data are taken into account, due to its influence on the precipitation formation and to demonstrate the relation between synoptic wind, topography and the precipitation distribution inside small mountain valleys. The study analyses the rainfall distribution and amounts of 4 days inside the San Francisco Valley, a small catchment in the tropical Andes of southern Ecuador, representing different seasons and the typical atmospheric flows, which are correlated to the annual precipitation map. The results show that the rainfall distribution and amounts are generally defined by the wind direction and velocity, besides the topographic location in relation to the main barriers and pathways. The dominant wind direction causes a division of the catchment in a wetter eastern and a dryer western part. Moreover, the annual seasons are reversed; the main rainy season for the eastern part occurs between June and August, while the western part reaches the precipitation maximum between January and March. This may have influence on the species composition at the different slopes and the annual hydrological cycle inside the catchment.

Abstract:

Increased nitrogen (N) depositions expected in the future endanger the diversity and stability of ecosystems primarily limited by N, but also often co-limited by other nutrients like phosphorus (P). In this context a nutrient manipulation experiment (NUMEX) was set up in a tropical montane rainforest in southern Ecuador, an area identified as biodiversity hotspot. We examined impacts of elevated N and P availability on arbuscular mycorrhizal fungi (AMF), a group of obligate biotrophic plant symbionts with an important role in soil nutrient cycles. We tested the hypothesis that increased nutrient availability will reduce AMF abundance, reduce species richness and shift the AMF community toward lineages previously shown to be favored by fertilized conditions. NUMEX was designed as a full factorial randomized block design. Soil cores were taken after 2 years of nutrient additions in plots located at 2000 m above sea level. Roots were extracted and intraradical AMF abundance determined microscopically; the AMF community was analyzed by 454-pyrosequencing targeting the large subunit rDNA. We identified 74 operational taxonomic units (OTUs) with a large proportion of Diversisporales. N additions provoked a significant decrease in intraradical abundance, whereas AMF richness was reduced significantly by N and P additions, with the strongest effect in the combined treatment (39% fewer OTUs), mainly influencing rare species. We identified a differential effect on phylogenetic groups, with Diversisporales richness mainly reduced by N additions in contrast to Glomerales highly significantly affected solely by P. Regarding AMF community structure, we observed a compositional shift when analyzing presence/absence data following P additions. In conclusion, N and P additions in this ecosystem affect AMF abundance, but especially AMF species richness; these changes might influence plant community composition and productivity and by that various ecosystem processes.

Abstract:

Schwermetalle sind im Gegensatz zu Hauptnährelementen wie N, P oder S im Ökosystem gering angereichert, jedoch wirken diese schon bei kleinen Gehalten toxisch für Organismen wie Pflanzen und Tiere. Schwermetalle sind im Boden stabil und werden nicht abgebaut, nur die Verbindungen, die sie enthalten. Es kann auch zur Anreicherung von Schwermetallen in den Pflanzen, vor allem in Wurzeln und Blättern, kommen. Die Motivation der Bachelorarbeit besteht darin, sowohl die Flüsse der Schwermetalle in der Streu als auch deren Umsatzzeiten in der organischen Auflage des Waldbodens zu bestimmen. Es wurden Streuproben des Zeitraums Juli 2012 bis Februar 2013 aufgeschlossen und die Gehalte der Elemente As, Ba, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, V und Zn gemessen. Ausgewertet wurden jedoch die Messresultate der Proben von August 2011 bis Juli 2012. Die benötigten Daten zur Berechnung der Umsatzzeiten wurden von der Gruppe für Bodenkunde zur Verfügung gestellt. Die Schwermetallgehalte in der Streu dienten als Grundlage zur Berechnung der Monats- und Jahresflüsse sowie der Umsetzungsquotienten. Die Gehalte der Schwermetalle in der Streu zeigen kaum eine Variabilität über die Zeit. Die jährlich regelmässigen Schwankungen der Monatsflüsse sind auf die periodisch unterschiedlichen Streufallmengen zurückzuführen, die jeweils 2 Maxima und 1 Minimum aufweisen. Erstaunlich sind sowohl die hohen Kupfergehalte in der Streu als auch die hohen Umsetzungsquotienten für As, V und Fe. Die hohen Umsatzzeiten lassen sich durch Vermischung des Mineralbodenhorizonts mit der organischen Auflage erklären. Die Ursache der hohen Kupfereinträge konnte nicht abschliessend erläutert werden, jedoch wurden mögliche Lösungsansätze formuliert.

Abstract:

A digital soil mapping approach is applied to a complex, mountainous terrain in the Ecuadorian Andes. Relief features are derived from a digital elevation model and used as predictors for topsoil texture classes sand, silt, and clay. The performance of three statistical learning methods is compared: linear regression, random forest, and stochastic gradient boosting of regression trees. In linear regression, a stepwise backward variable selection procedure is applied and overfitting is controlled by minimizing Mallow’s Cp. For random forest and boosting, the effect of predictor selection and tuning procedures is assessed. 100-fold repetitions of a 5-fold cross-validation of the selected modelling procedures are employed for validation, uncertainty assessment, and method comparison. Absolute assessment of model performance is achieved by comparing the prediction error of the selected method and the mean. Boosting performs best, providing predictions that are reliably better than the mean. The median reduction of the root mean square error is around 5%. Elevation is the most important predictor. All models clearly distinguish ridges and slopes. The predicted texture patterns are interpreted as result of catena sequences (eluviation of fine particles on slope shoulders) and landslides (mixing up mineral soil horizons on slopes).

Abstract:

Systematic investigations of the upper forest line (UFL) primarily concentrate on mid and high latitudes of the Northern Hemisphere, whereas studies of Neotropical UFLs are still fragmentary. This article outlines the extraordinary high tree diversity at the UFL within the Andean Depression and unravels the links between the comparatively low position of the local UFL, high tree-species diversity, and climate. On the basis of Gentry?s rapid inventory methodology for the tropics, vegetation sampling was conducted at 12 UFL sites, and local climate (temperature, wind, precipitation, and soil moisture) was investigated at six sites. Monotypic forests dominated by Polylepis were only found at the higher located margins of the Andean Depression while the lower situated core areas were characterized by a species-rich forest, which lacked the elsewhere dominant tree-species Polylepis. In total, a remarkably high tree-species number of 255 tree species of 40 different plant families was found. Beta-diversity was also high with more than two complete species turnovers. A non-linear relationship between the floristic similarity of the investigated study sites and elevation was detected. Temperatures at the investigated study sites clearly exceeded 5.5°C, the postulated threshold value for the upper tree growth limit in the tropics. Instead, quasi-permanent trade winds, high precipitation amounts, and high soil water contents affect the local position of the UFL in a negative way. Interestingly, most of the above-mentioned factors are also contributing to the high species richness. The result is a combination of a clearly marked upper forest line depression combined with an extraordinary forest line complexity, which was an almost unknown paradox.

Abstract:

Weekly samples from surface waters, springs, soil water and rainfall were collected in a 76.9 km² mountain rain forest catchment and its tributaries in southern Ecuador.Time series of the stable water isotopes (oxygen-18 and deuterium) were used to calculate mean transit times (MTTs) and the transit time distribution functions (TTDs) solving the convolution method for seven lumped-parameter models. For each model setup, the generalized likelihood uncertainty estimation (GLUE) methodology was applied to find the best predictions, behavioral solutions and parameter identifiability. For the study basin, TTDs based on model types such as the linear–piston flow for soil waters and the exponential–piston flow for surface waters and springs performed better than more versatile equations such as the gamma and the two parallel linear reservoirs. Notwithstanding both approaches yielded a better goodness of fit for most sites, but with considerable larger uncertainty shown by GLUE. Among the tested models, corresponding results were obtained for soil waters with short MTTs (ranging from 2 to 9 weeks). For waters with longer MTTs differences were found, suggesting that for those cases the MTT should be based at least on an intercomparison of several models. Under dominant baseflow conditions long MTTs for stream water ? 2 yr were detected, a phenomenon also observed for shallow springs. Short MTTs for water in the top soil layer indicate a rapid exchange of surface waters with deeper soil horizons. Differences in travel times between soils suggest that there is evidence of a land use effect on flow generation.

Abstract:

Quantification of nutrient stocks and their temporal changes are considered of prime importance in farm-ing systems of the humid tropics to answer the question of sustainable management. The research areain the Southern Ecuadorian Andes included forest, annual (0–5 years old) and different aged perennial(0–5, 6–10, 11–20, 21–30) and pasture (0–5, 6–10, 11–20, 21–30, >30) sites. Soil organic carbon (SOC),total and plant available soil nutrient stocks and nutrient balances were investigated to assess temporalsoil nutrient dynamics in relation to management activities. Forest conversion by slash-and-burn caused a decrease in SOC stocks in all three land-uses amounting between 14% and 19%. This was mainly due tothe absence of an organic layer and losses in the upper five cm of the mineral soil. Stocks of exchangeablebases and pH values increased in annuals which however, had the most negative nutrient balance of allland-uses amounting to ?128, ?25 and ?226 kg ha?1 a?1 for N, P and K, respectively. The abandonmentof annual sites after five years was linked to a shortage of available N and P due to low-external-input management which caused SOC stock decreases. Major soil nutrient changes in perennials and pasturesdid not occur directly but 6–20 years after forest conversion with increases in stocks for total N, P, S and exchangeable bases above forest level. SOC stocks of medium aged perennials and pastures increased above forest level in the mineral soil. Easily available inorganic N and P stocks remained low throughout the chronosequence in perennials and pastures, indicating a quick uptake by plant roots and microor-ganisms. Compared to medium aged sites, oldest perennials and pastures showed a strong decrease in SOC (?28% and ?16%) and soil nutrient stocks. Stocks for total N, P, S and exchangeable bases were up to50% below those of medium aged sites in oldest perennials and pastures.

Abstract:

A tropical smallholder cash crop farming system in a semi-arid Inter-Andean valley of Ecuador was investigated. Intensive irrigated agriculture with up to 400 kg of urea-N fertilization ha?1·a?1 prevails in colluvial sites whereas urea application in the steep eroded sites is lower. Farmers did recently introduce manure to partly replace urea fertilization. Knowledge about the effects of mineral and organic fertilizers on nitrogen and carbon cycling needs to be improved to maintain sustainable agriculture in the research area. Therefore, a laboratory incubation experiment was conducted to investigate effects of urea and guinea pig manure on microbial activity of colluvial foot slope and eroded upper slope soils. Soil samples were treated with 200 kg·N·ha?1 either applied as urea, guinea pig manure or a combination of both and compared to a control. Urea fertilizer was labeled with 15N to trace its fate. Microbial biomass and basal respiration were determined in different time intervals. Urea fertilization induced an acceleration of soil organic matter (SOM) mineralization (positive priming effect) in the first seven days of incubation. The combined fertilization served as a positive alternative to the present urea management since it increased the amount of microbial biomass and provided mineral nitrogen for immediate plant uptake. Moreover, low recovery rates suggested an immobilization of fertilized nitrogen into the microbial biomass inducing an efficient and sustained nutrient release throughout the entire growing season. SOM stocks in colluvial soils were 40% below those of eroded soils which was partly due to the positive priming effect after urea fertilization. Microbial activity and efficiency were not reduced by soil erosion.

Abstract:

The first MRp|SE Newsletter offers research and knowledge transfer results: The test of models for small scale plant distributions shows the advantages of ensemble approaches. This result as well as a new method to analyze canopy evapotranspriation and leaf photosynthesis were awarded with poster prizes. A medical technique helps to study wood anatomy. In contrast to previous data the analysis of fertilized phosphorus revealed that it is not only retained in above-ground biomass and the organic layer but also enters the mineral soil. Mean transit times of water in the catchment and transit time distribution functions where modeled and can be related to land use effects. The Newsletter also explains the usefulness of digital soil maps and the prerequisites for developing local climate indicators. The designs of research plots and new research infrastructures are introduced and the characteristics of the second radar in the Radar Net Sur are summarized. Four of the SENESCYT Bundle Projects describe their research objectives. New in the Data Warehouse are a tool for control of funds consumption and a new booking tool. NCI already awaits researchers at the new Laipuna station.

Abstract:

Schwermetalle wirken schon in kleinen Mengen toxisch auf Pflanzen und Tiere und können sich negativ auf deren Wachstum und Entwicklung auswirken. Zudem sind viele Schwermetalle persistent, d.h. sie werden weder durch physikalische, chemische noch biologische Prozesse nachhaltig verändert. Atmosphärische Einträge von Schwermetallen können auf Dauer zu einer Anreicherung im Boden oder in der Biomasse führen. Das Ziel dieser Arbeit ist es, die atmosphärische Deposition von Schwermetallen in einem Ökosystem im ecuadorianischen Bergregenwald zu quantifizieren.Es wurden dazu Freilandniederschlagsproben und Bestandes-Niederschlagsproben vom Zeitraum Juni 2011 bis Mai 2012 gemessen und die Jahresflüsse der Schwermetalle Arsen (As), Barium (Ba), Cadmium (Cd), Cobalt (Co), Chrom (Cr), Kupfer (Cu), Eisen (Fe), Mangan (Mn), Nickel (Ni), Blei (Pb), Vanadium (V) und Zink (Zn) berechnet. Die Proben wurden wöchentlich entnommen, weshalb nebst den Jahresflüssen (Gesamtfluss) auch Wochenflüsse berechnet werden konnten.Weder bei den Niederschlägen noch bei den Wochenflüssen der Schwermetalle konnte eine deutliche zeitliche Variabilität beobachtet werden. Auffallend war der hohe Jahresfluss an Kupfer, welcher durch atmosphärische Deposition eingetragen wurde. Bis zu 68-mal höhere Werte (verglichen mit Ridame et. al, (1999)) als bei aktuellen Studien, wurden im Bergregenwald in Ecuador gemessen. Die Resultate zeigen, dass weder die Gesamtdeposition noch die Trockendeposition beim Eintrag in den Regenwald dominant ist. Eine eindeutige Erklärung für die hohen Kupfereinträge konnte nicht gefunden werden, lediglich einige mögliche Gründe wurden diskutiert.

Abstract:

Staub aus der Wüste Sahara wird mit Unterstützung geeigneter Windysteme über tausende von Kilometern bis nach Südamerika transportiert. Die mit dem Staub transportierten wichtigen Pflanzennährstoffe erreichen aber nicht nur die Amazonasregion, sondern gelangen bis in den ecuadorianischen Bergregenwald. Diese Regenwälder gelten als besonders artenreich. Es ist deshalb wichtig den Einfluss von Elementeinträgen auf diese Ökosysteme zu verstehen. Die Arbeit untersucht Windrichtung und Niederschlagsbedingungen über Brasilien und vergleicht diese mit in Ecuador gemessenen pHWerten des Regenwassers. Die Niederschlagsdaten stammen von 30 verschiedenen, meteorologischen Messstationen. Diese Daten werden in Sektoren zusammengefasst, die die tägliche Transportdistanz der Staubpartikel widerspiegeln. Die Dauer des Partikeltransports wird aus einer Trajektorienanalyse abgeleitet, die auch Informationen zu geeigneten Windbewegungen liefert. Ob Einträge stattfinden oder nicht zeigen pH-Werte im Regenwasser, die einen definierten Grenzwert erreichen bzw. nicht erreichen. Die Untersuchungsperiode dauert vom März bis Juli 2011. Die Annahme, dass erhöhte pHWerte gleichzeitig mit Trockenkorridoren und geeigneten Windrichtungen auftreten, die einen Saharastaubtransport ermöglichen, wurde teilweise bestätigt. Von den 4 Phasen mit pH-Werten über 6.5 korrelieren alle mit einem optimalen Luftpartikeltransport. 2 Zeitabschnitte verfügen ebenfalls über die seltenen Trockenkorridore (für 5-tägige Transportdauer: weniger oder gleich 10mm/d/Sektor). Für 2 Phasen mit erhöhten pH-Werten fehlen entsprechende Abschnitte mit geringem Niederschlag. Diese Schwankungen können durch Einträge von weiteren Staubquellen wie erhöhte Waldbrandaktivität oder vulkanische Ereignisse ausgelöst werden. Ein realistischeres Szenario ist jedoch von Staubeinträgen auszugehen, die aufgrund zu strenger Kriterien bei der Auswahl der Trajektorien oder der Bestimmung von Trockenkorridoren nicht detektiert werden. Zeitabschnitte mit Trockenkorridoren und geeigneten Windbewegungen, ohne Auswirkungen auf den pH, treten ebenfalls auf. Eine Erklärung wird in der reduzierten Staubproduktion des Tschadgebiets im Sommer und im möglichen Ausregnen des Staubes vor Erreichen des Brasilianischen Staatsgebiets gefunden.

Abstract:

The tropical montane forests of the E Andean cordillera in Ecuador receive episodic Sahara dust inputs particularly increasing Ca deposition. We added CaCl2 to isolate the effect of Ca deposition by Sahara dust to tropical montane forest from the simultaneously occurring pH effect. We examined components of the Ca cycle at four control plots and four plots with added Ca (2 × 5 kg ha–1 Ca annually as CaCl2) in a random arrangement. Between August 2007 and December 2009 (four applications of Ca), we determined Ca concentrations and fluxes in litter leachate, mineral soil solution (0.15 and 0.30 m depths), throughfall, and fine litterfall and Al concentrations and speciation in soil solutions. After 1 y of Ca addition, we assessed fine-root biomass, leaf area, and tree growth. Only < 3% of the applied Ca leached below the acid organic layer (pH 3.5–4.8). The added CaCl2 did not change electrical conductivity in the root zone after 2 y. In the second year of fertilization, Ca retention in the canopy of the Ca treatment tended to decrease relative to the control. After 2 y, 21% of the applied Ca was recycled to soil with throughfall and litterfall. One year after the first Ca addition, fine-root biomass had decreased significantly. Decreasing fine-root biomass might be attributed to a direct or an indirect beneficial effect of Ca on the soil decomposer community. Because of almost complete association of Al with dissolved organic matter and high free Ca2+ : Al3+ activity ratios in solution of all plots, Al toxicity was unlikely. We conclude that the added Ca was retained in the system and had beneficial effects on some plants.

Abstract:

Water-bound nitrogen (N) cycling in temperate terrestrial ecosystems of the Northern Hemisphere is today mainly inorganic because of anthropogenic release of reactive N to the environment. In little-industrialized and remote areas, in contrast, a larger part of N cycling occurs as dissolved organic N (DON). In a north Andean tropical montane forest in Ecuador, the N cycle changed markedly during 1998–2010 along with increasing N deposition and reduced soil moisture. The DON concentrations and the fractional contribution of DON to total N significantly decreased in rainfall, throughfall, and soil solutions. This inorganic turn of the N cycle was most pronounced in rainfall and became weaker along the flow path of water through the system until it disappeared in stream water. Decreasing organic contributions to N cycling were caused not only by increasing inorganic N input but also by reduced DON production and/or enhanced DON decomposition. Accelerated DON decomposition might be attributable to less waterlogging and higher nutrient availability. Significantly increasing NO3-N concentrations and NO3-N/NH4-N concentration ratios in throughfall and litter leachate below the thick organic layers indicated increasing nitrification. In mineral soil solutions, in contrast, NH4-N concentrations increased and NO3-N/NH4-N concentration ratios decreased significantly, suggesting increasing net ammonification. Our results demonstrate that the remote tropical montane forests on the rim of the Amazon basin experienced a pronounced change of the N cycle in only one decade. This change likely parallels a similar change which followed industrialization in the temperate zone of the Northern Hemisphere more than a century ago.

Abstract:

The sloping mire landscape of the investigation area, in the southern Andes of Ecuador, is dominated by stagnic soils with thick organic layers. The recursive partitioning algorithm Random Forest was used to predict the spatial water stagnation pattern and the thickness of the organic layer from terrain attributes. Terrain smoothing from 10 to 30m raster resolution was applied in order to obtain the best possible model. For the same purpose, several model tuning parameters were tested and a prepredictor selection with the R-package Boruta was applied. Model versions were evaluated and compared by 100 repetitions of the calculation of the residual mean square error of a five-fold cross-validation. Position specific density functions of the predicted soil parameters were then used to display prediction uncertainty. Prepredictor selection and tuning of the Random Forest algorithm in some cases resulted in an improved model performance.We therefore recommend testing prepredictor selection and tuning to make sure that the best possible model is chosen.This needs particular emphasis in complex tropical mountain soil-landscapes which provide a real challenge to any soil mapping approach but where Random Forest has proven to be successful due to the testing of model tuning and prepredictor selection.

Abstract:

Species diversity of geometrid moths (Lepidoptera, Geometridae) has previously been shown to be extremely and constantly high along a continuously forested elevational gradient in the Andes of southern Ecuador. We analysed samples taken from 32 sites between 1999 and 2011 in northern Podocarpus National Park and adjacent areas from 1020 to 2916 m a.s.l. We conjecture that high elevation habitats were historically mostly colonised by species from lower elevations, and that environmental filtering (e.g. through host plant specificity or temperature tolerance) constrained colonisation from lower elevations, which would yield a pattern of elevationally decreasing phylogenetic diversity. We analysed elevational phylogenetic patterns by means of: 1) the nearest-taxon index (NTI), 2) DNA barcode-based terminal branch lengths (TBLs) from maximum-likelihood phylogeny, 3) the subfamily composition of the local assemblages, and 4), the rarefied number of morphologically defined genera per site. We counted a total of 1445 species. NTI values significantly increased with elevation, both in a conventional and a rarefaction approach. TBLs decreased significantly with elevation. Subfamily composition profoundly changed with elevation, particularly expressed as an increased proportion of the subfamily Larentiinae and decreased fractions of Sterrhinae and Geometrinae. The number of genera in equally rarefied species resamples significantly decreased with elevation. We conclude that environmental filtering indeed contributed to an altitudinal decrease in moth phylodiversity, but these constraints prevented only relatively few clades from colonising high elevation habitats.

Abstract:

Approaches to reconciling food production with climatic and environmental protection often require agricultural intensification. The production of more food per unit of agricultural land through "sustainable intensification" is intended to enable the protection of natural ecosystems elsewhere (land sparing). However, there are problems associated with agricultural intensification; such as soil erosion, eutrophication or pollution of water bodies with chemicals, landscape homogenization and loss of biodiversity; for which solutions have not yet been found. Reuse of abandoned agricultural lands – which are abundant throughout the world – to address the rising demand for food is a potentially important alternative, which up to now has been widely ignored. To test the power of this alternative, equilibrium economic land allocation to various land-use practices by risk-avoiding tropical farmers in Ecuador was simulated. The reestablishment of pastures on abandoned cattle lands lowered prices for pasture products, and also triggered conversion of existing pasture into cropland. The resulting land-use change increased total annual food production in a moderate scenario from the current level of 17.8–23.1 petacalories (10^15 calories), which amounted to a production increase of 30%. At the same time, there was a 19% reduction in the amount of payments to farmers required to preserve tropical forests – one of the world’s greatest terrestrial carbon stores.

Abstract:

Future increase of atmospheric nitrogen deposition in tropical regions is expected to have negative impacts on forests ecosystems and related biogeochemical processes. In tropical mountain forests topography causes complex streamflow and rainfall patterns, governing the atmospheric transport of pollutants and the intensity and spatial variability of deposition. The main goal of the current study is to link spatio-temporal patterns of upwind nitrogen emissions and nitrate deposition in the San Francisco Valley (eastern Andes of southern Ecuador) at different altitudinal levels. The work is based on Scanning Imaging Absorption SpectroMeter for Atmospheric CHartographY (SCIAMACHY) retrieved-NO2 concentrations, NOx biomass burning emissions from the Global Fire Emissions Database (GFEDv3), and regional vehicle emissions inventory (SA-INV) for urban emissions in South America. The emission data is used as input for lagrangian atmospheric backward trajectory modeling (FLEXTRA) to model the transport to the study area. The results show that NO3 À concentrations in occult precipitation samples are significantly correlated to long-range atmospheric secondary nitrogen transport at the highest meteorological stations (MSs) only, whereas for NO3 À concentrations in rain samples this correlation is more pronounced at the lower MSs. We conclude that ion concentrations in occult precipitation at the uppermost MSs are mainly linked to distant emission sources via the synoptic circulation impinging the more exposed higher sites. Lower correlations close to the valley bottom are due to a lower occult precipitation frequency and point to a contamination of the samples by local pollution sources not captured by the used emission data sources.

Abstract:

In the anthropogenic fire-disturbed ecosystem of the San Francisco Valley in the Andes of southeastern Ecuador, dense stands of an aggressive invasive weed, the southern bracken fern (Pteridium arachnoideum and Pteridium caudatum), dominate the landscape. To secure sustainable land management in the region, a comprehensive understanding of bracken spatial-distribution patterns and life cycle dynamics is crucial. We investigated the possibility of detecting bracken-infested areas and frond status (live, fungi-infected, and dead) by means of a high-resolution QuickBird scene from October 2010 and spectral signatures based on field spectroscopy. After image pre-processing, a two-step classification procedure first delineates the bracken-infested area by means of a maximum-likelihood hard classification. The probability-guided unmixing classifier with field-derived end-members is applied in the second step to obtain the fractional cover of the different frond statuses per pixel. The results showed that the areas infested by bracken could be distinguished from the other land-cover classes with high accuracy (overall accuracy of 0.9973). Also, the three frond statuses could be accurately classified at the sub-pixel level. The ‘dead’ class was the dominant frond status at the time of image acquisition (October 2010). We conclude that the extreme dry spell in October 2010 was particularly responsible for this dominance.

Abstract:

In the present thesis, implications of pasture establishment, fertilization and abandonment on soil C and nutrient dynamics were investigated for the mountain rainforest region of southern Ecuador. Over the past decades the natural forest of the study area has been threatened by conversion to cattle pastures. However, the soil fertility of these extensively grazed pastures (active pastures) declines continuously during pasture use. The invasion of bracken fern (Pteridium arachnoideum) leads to pasture abandonment when bracken becomes dominant. In order to reveal the mechanisms behind the deterioration of soil fertility, biotic and abiotic soil properties and their interaction were analyzed along a land?use gradient (natural forest – active pasture – abandoned pasture). The ecosystem disturbance of the mountain rainforest through pasture use changed the microbial function and structure, and affected soil CO2?C fluxes. Annually, 2 Mg soil CO2?C ha?1 were additionally emitted from the pasture land. This acceleration in soil respiration rates was related to accelerated rates of microbial C mineralization and fine?root respiration. The high?quality, N?rich above? and belowground residues of the pasture grass (S. sphacelata, C4?plant), especially the huge fine?root biomass, provided a high C and N availability for soil microbes. Compared to the forest, increased soil pH and accelerated base saturation were further factors beneficial for soil microbial growth and metabolism of the upper mineral soil at active pastures. Three times higher amounts of microbial biomass C and a significant shift in the microbial community structure towards a higher relative abundance of Gram(?)? bacteria and fungi were observed. Long?term pasture use and the invasion of bracken (C3?plant) diminished beneficial effects for microbes, causing a significant decrease in the C, net, and gross N mineralization rates as well as a two?third reduction in the microbial biomass. A preferential substrate utilization of grass?derived C4 by the soil microbes resulted in a rapid decline of the C4?pool. As a consequence, the less available C3?pool from bracken and former forest increased its dominance in the SOC?pool, further decreasing pasture productivity and finally causing pasture abandonment. The lower quality and quantity of above? and belowground residues of the bracken (high lignin content, C/N) resulted in resource?limited conditions that influenced the microbial function to greater extent than their structure. The microbial structure seemed to be sensitive mainly to soil pH along the land?use gradient. Thus, a disconnection between microbial structure and function was identified. Fertilization experiments were conducted both in the lab and in the field to evaluate the impact of urea and/or rock phosphate amendment on SOM dynamics and on pasture productivity of active pastures. After combined fertilization the pasture yield was most efficiently increased by 2 Mg ha?1 a?1, indicating a NP?limitation of grass growth. Furthermore, the fodder quality was improved by a higher content of P and Ca in the grass biomass. The microorganisms of the active pasture soil responded with an adaptation of their structure to the increased substrate availability in the short term, but did not change their initial functions in the long term. After urea/ rock phosphate addition a significant increase in the relative fungal abundance was detected, but neither a microbial limitation of energy nor of N or P was observed. However, urea addition accelerated gaseous losses of soil CO2?C in the short term. In the study area, pronounced alterations in ecosystem functioning due to land?use changes were detected, especially in soil C and N cycling rates. For a sustainable land?use in this region it is crucial to prevent pasture degradation and to rehabilitate degraded pastures in order to protect the prevailing mountain rainforest ecosystem. It is of crucial importance for active pasture soils to maintain or even increase resource availability, being one indicator of soil fertility. In this context, the soil organic matter has to be retained in the long?term to maintain high microbial activity and biomass, and thus pasture productivity. A moderate fertilization with urea and rock phosphate can be a first step to provide continuous nutrient supply for grass growth and to strengthen livestock health through increased fodder quality. However, the risk of further additional emissions of soil CO2?C due to increased loads of urea fertilizer application has to be kept in mind. Overall, for the establishment of a sustainable land?use management the control of bracken invasion and an adjusted nutrient management are needed. Further investigations on the reduction of soil nutrient losses and increased nutrient use efficiencies of plants, such as combined planting with legumes or the usage of cultivars with special nutrient acquisition strategies, should be in the focus of future work.

Abstract:

Previous research from the tropics indicates that AMF may be well adapted to organic soils and even represent the dominant mycorrhizal form, though the extraradical part of the symbiosis was omitted as in most other tropical studies. Our study aims at characterizing the extraradical part of arbuscular mycorrhizal fungi (AMF) in a highly organic tropical montane forest soil in Southern Ecuador. Based on recent studies on the interaction of AM fungal hyphae and litter we hypothesized that within the organic layer AM hyphae grow in close contact with decomposing material. To test this idea, AM fungal hyphal distribution in the organic layer was determined by directly staining roots and decomposing leaves and extracting hyphae from the remaining particulate organic material. AM and non-AM fungal hyphae were analyzed, as well as root colonization patterns. Our results showed that AMF indeed represented the dominant mycorrhizal form with an average root colonization of 43%. The extraradical AM hyphal length ranged from 2 to 34 m g?1 soil with a mean of 10.4 m g?1 soil (equals 3.1 m cm?3 soil), and therefore exceeded root length about 13-fold. As hypothesized, 29% of AM extraradical hyphae were closely attached to decomposing leaves. These hyphae were mainly located at the leaf surface, though in some parts leaf veins and inner leaf tissues were colonized. More than half of AM hyphal biomass was detected on the root surface, a pattern potentially driven by the predominant Paris-type AMF. Non-AM fungal hyphae colonized decomposing material to a significantly greater extent, though hyphal length attached to roots was equal. This study supports the adaptation of AMF to highly organic soils in the tropics and the existence of a widespread extraradical mycelium, which is not readily detectable by standard methods. The close association with decomposing leaves most likely improves direct nutrient uptake from decomposed material and points to a potential indirect contribution of AMF to the decomposition process.