Throughfall and soil properties in shaded and unshaded coffee plantations and a secondary forest: a case study from Southern Colombia

In Colombia coffee production is facing risks due to an increase in the variability and amount of rainfall, which may alter hydrological cycles and negatively influence yield quality and quantity. Shade trees in coffee plantations, however, are known to produce ecological benefits, such as intercepting rainfall and lowering its velocity, resulting in a reduced net-rainfall and higher water infiltration. In this case study, we measured throughfall and soil hydrological properties in four land use systems in Cauca, Colombia, that differed in stand structural parameters: shaded coffee, unshaded coffee, secondary forest and pasture. We found that throughfall was rather influenced by stand structural characteristics than by rainfall intensity. Lower throughfall was recorded in the shaded coffee compared to the other systems when rain gauges were placed at a distance of 1.0 m to the shade tree. The variability of throughfall was high in the shaded coffee, which was due to different canopy characteristics and irregular arrangements of shade tree species. Shaded coffee and secondary forest resembled each other in soil structural parameters, with an increase in saturated hydraulic conductivity and microporosity, whereas bulk density and macroporosity decreased, compared to the unshaded coffee and pasture. In this context tree-covered systems indicate a stronger resilience towards changing rainfall patterns, especially in mountainous areas where coffee is cultivated

Characterization of cocoa production, income diversification and shade tree management along a climate gradient in Ghana

Reduced climatic suitability due to climate change in cocoa growing regions of Ghana is expected in the coming decades. This threatens farmers' livelihood and the cocoa sector. Climate change adaptation requires an improved understanding of existing cocoa production systems and farmers' coping strategies. This study characterized current cocoa production, income diversification and shade tree management along a climate gradient within the cocoa belt of Ghana. The objectives were to 1) compare existing production and income diversification between dry, mid and wet climatic regions, and 2) identify shade trees in cocoa agroforestry systems and their distribution along the climatic gradient. Our results showed that current mean cocoa yield level of 288kg ha-1yr-1 in the dry region was significantly lower than in the mid and wet regions with mean yields of 712 and 849 kg ha-1 yr-1, respectively. In the dry region, farmers diversified their income sources with non-cocoa crops and off-farm activities while farmers at the mid and wet regions mainly depended on cocoa (over 80% of annual income). Two shade systems classified as medium and low shade cocoa agroforestry systems were identified across the studied regions. The medium shade system was more abundant in the dry region and associated to adaptation to marginal climatic conditions. The low shade system showed significantly higher yield in the wet region but no difference was observed between the mid and dry regions. This study highlights the need for optimum shade level recommendation to be climatic region specific

Feinwurzeldynamik und Ressourcenaufnahme in einem Südecuadorianischen Bergregenwald in Abhängigkeit von der Meereshöhe

Tropische Bergregenwälder erstrecken sich über große Höhenstufen und sind damit unterschiedlichen klimatischen Bedingungen ausgesetzt. Eine charakteristische Veränderung dieser Ökosysteme ist die Abnahme der oberirdischen und die Zunahme der unterirdischen Biomasse mit ansteigender Meereshöhe. Waldbestände in großen Höhenlagen sind zudem durch mächtige organische Auflagen und relativ nasse Bodenverhältnisse gekennzeichnet. Für den Kohlenstoff- und Nährstoffkreislauf spielt der Umsatz von Feinwurzeln eine wichtige Rolle in diesen Ökosystemen. Das Wissen über Feinwurzelumsätze in tropischen Bergregenwäldern ist bisher jedoch sehr begrenzt. Ebenso ist nicht viel über die Wasser- und Nährstoffaufnahmekapazität von Wurzeln auf unterschiedlichen Höhenstufen bekannt.Die vorliegende Arbeit wurde in fünf südecuadorianischen Bergregenwaldbeständen entlang eines Höhengradienten von 1050 bis 3060 m üNN durchgeführt. Ziel der Studie war es, (1) den Einfluss von Temperatur und Bodeneigenschaften auf den Feinwurzelumsatz entlang des Gradienten mit Hilfe von Minirhizotronen zu untersuchen, (2) die Bedeutung von Nährstofflimitierung und Staunässe für die Aktivität von Feinwurzeln durch ein Düngungs- bzw. Austrocknungsexperiment zu testen sowie die N-Aufnahmefähigkeit von Feinwurzeln durch ein 15N-Tracer-Experiment zu erfassen und (3) mit Miniatur-Saftflusssystemen die Abhängigkeit des Wurzelsaftflusses von Umweltvariablen zu untersuchen sowie anatomische Charakteristika von Wurzelquerschnitten zu analysieren.Der Umsatz von Feinwurzeln (d < 2 mm) war in dem untersten und dem obersten Waldbestand signifikant höher (0.9 cm cm-1 Jahr-1) als in den drei Bestände auf mittleren Höhenstufen (ca. 0.6 cm cm-1 Jahr-1). Der Umsatz von Feinstwurzeln (d < 0.5 mm) war generell höher als der Feinwurzelumsatz (d < 2 mm) und überschritt 1.0 cm cm-1 Jahr-1 an den beiden Endpunkten des Transektes. Der Feinwurzelumsatz nahm demnach vom prae-montanen zum montanen Bestand ab, wie man es vom Einfluss niedrigerer Temperatur auf physiologische Prozesse erwarten würde, nahm jedoch mit noch größerer Meereshöhe wieder zu. Dieser nicht-lineare Trend lässt sich durch ein Überlappen des Temperatureffektes mit anderen Umweltgradienten in der oberen Hälfte des Höhentransektes erklären. Neben der Temperatur sind vermutlich ungünstige Bodenbedingungen der Grund für die verkürzte Lebensdauer der Feinwurzeln in hochmontanen Bergregenwäldern. Ein hoher Feinwurzelumsatz ist offenbar eine Anpassungsstrategie von Bäumen an limitierende Umweltbedingungen in großen Höhenlagen.Das Düngungsexperiment ergab nach einer P-Düngung das stärkste Wurzelwachstum auf 1050 m, und nach einer N-Düngung auf 3060 m, was darauf schließen lässt, dass prae-montane Wälder P limitiert sind, während hochmontane Wälder eher N limitiert sind. Nährstoffkonzentrationen in Feinwurzeln, insbesondere N, nahmen signifikant mit zunehmender Höhe ab, was auf eine verminderte Nährstoffverfügbarkeit mit zunehmender Meereshöhe deutet. Das Austrocknungsexperiment lieferte keine Hinweise auf eine reduzierte Feinwurzelmortalität unter trockeneren Bodenbedingungen. Nässe scheint somit keine Erklärung für den hohen Feinwurzelumsatz in großen Höhenlagen zu sein. Das 15N-Tracer-Experiment ergab eine konstant hohe Aufnahmerate von Nitrat und Ammonium auf allen drei Flächen (1050, 1890 und 3060 m), was annehmen lässt, dass Feinwurzeln in hochmontanen Bergregenwäldern eine verminderte Nährstoffverfügbarkeit durch eine hohe Nährstoffaufnahmekapazität kompensieren.Saftfluss in Wurzeln folgte deutlich täglichen und saisonalen Schwankungen des Wasserdampf-Sättigungsdefizits der Luft (VPD) in den drei Waldbeständen auf 1050, 1890 und 3060 m, nahm aber etwa um den Faktor drei zwischen dem untersten und dem obersten Bestand ab. Eine verminderte Saftflussrate wurde beobachtet, wenn VPD über mehrere Tage überdurchschnittlich hoch war. VPD wurde als einflussreichster Umweltfaktor für die Wurzelwasseraufnahme identifiziert, sein Einfluss nahm aber mit zunehmender Meereshöhe ab. Dagegen stieg der Einfluss von Temperatur mit zunehmender Höhe stark an und war in dem höchstgelegenen Bestand der Faktor mit dem größten Einfluss auf den Wurzelsaftfluss. Anatomische Analysen von Wurzelquerschnitten ergaben abnehmende Gefäßdurchmesser mit zunehmender Meereshöhe. Die theoretische hydraulische Leitfähigkeit nahm dadurch um mehr als das 10-fache entlang des Höhentransektes ab. Die Temperaturabnahme mit zunehmender Meereshöhe wirkt folglich über verschiedene Mechanismen auf die Wurzelwasseraufnahme: (i) den physikalischen Wasserfluss im Boden-Pflanze-Atmosphäre-Kontinuum durch die höhere Viskosität des Wassers und eine Abnahme von VPD, (ii) durch ein vermindertes Wachstum von Zellen der leitenden Gefäße, (iii) durch eine verminderte Nährstoffverfügbarkeit und (iv) durch eine möglicherweise verminderte Aquaporin-Aktivität in den Wurzeln.Tropical mountain rainforests extend over large elevational gradients with diverse climatic conditions. They are characterised by a decrease of above ground biomass, and a pronounced increase of fine root biomass with increasing elevation. Forest stands at higher elevations are further characterised by thick organic layers and very moist soil conditions. The turnover of fine roots plays an important role in the cycling of carbon and nutrients in theses ecosystems. However, the knowledge about the patterns of fine root dynamics in tropical mountain rainforests is still scarce. Likewise, not much is known about water and nutrient uptake capacities of roots at different elevations.The present study was conducted in five forests stands along an elevational transect between 1050 and 3060 m asl in a mountain rainforest of South Ecuador. It aimed (1) to analyse the effect of temperature and soil conditions on fine root turnover along the elevational transect by means of minirhizotrons; (2) to assess the role of nutrient limitation and water-logging for fine root activity by means of a fertilization and throughfall exclusion experiment, respectively; as well as to examine nitrogen uptake capacity of fine roots by 15N tracer application; and (3) to investigate the dependence of root sap flow on environmental variables by means of miniature heat balance sap flow gauges, and to analyse related anatomical characteristics of root cross sections.Fine root turnover (d < 2 mm) was significantly higher in the lowermost and the uppermost stand (0.9 cm cm-1 yr-1) than in the three mid-elevation stands (0.6 cm cm-1 yr-1). The turnover of finest roots (d < 0.5 mm) was higher compared to the root cohort with d < 2 mm, and exceeded 1.0 cm cm-1 yr-1 at the lower and upper elevations of the transect. Hence fine root turnover decreased from pre-montane to mid-montane forests as would be expected from an effect of low temperature on root turnover, but it decreased further upslope despite colder temperatures. It is assumed that this non linear altitudinal trend of fine root turnover originates from an overlapping of a temperature effect with other environmental gradients in the upper part of the transect. Adverse soil conditions may reduce root longevity at high elevations, and are thus additional factors besides temperature that control root dynamics in tropical mountain forests. The fast replacement of fine roots is possibly used as an adaptive mechanism by trees to cope with limiting environmental conditions.The fertilizer study revealed highest root growth stimulation after P addition at 1050 m, and after N addition at 3060 m, thus pre-montane forests may be presumably limited by the availability of P, whereas upper montane forests are rather limited by the availability of N. The concentrations of major nutrients in fine root tissue dropped significantly along the elevational transect, with strongest reductions observed for N. This may support the assumption of a decreased nutrient availability with increasing altitude. Throughfall exclusion at 3060 m did not reduce fine root mortality in this forest stand, hence high soil moisture contents do not seem to be a main stressor leading to high fine root turnover rates in upper montane forests. The 15NO315NH4 uptake study yielded a constantly high nitrate and ammonium uptake capacity of fine roots at altitudes at 1050, 1890 and 3060 m, suggesting that fine roots in upper montane forests compensate for low nutrient supplies with high nutrient uptake capacities.Root sap flow followed marked diurnal and seasonal courses in the forest stands at 1050, 1890 and 3060 m. Sap flow decreased roughly by a factor of three between the lowermost and the uppermost forest stand. A reduced sap flow was observed when VPD was above average for several days. VPD was identified as the most influential environmental factor controlling root water uptake, but its significance decreased with increasing altitude. In contrast, the influence of temperature increased along the elevational transect, and was identified as the most influential factor determining root sap flow at 3060 m. Anatomical analyses of root cross-sections provided evidence for decreasing vessel diameters with increasing altitude. Theoretical hydraulic conductivity was found to decrease more than ten fold from 50.2 m² MPa-1 s-1 at 1050 m to 4.0 m² MPa-1 s-1 at 3060 m. It is concluded that the temperature decrease with increasing altitude acts on water uptake through several pathways, (i) on the physics of water flow in the soil-plant-atmosphere continuum (increasing viscosity of water, decreasing VPD), (ii) by reducing vessel cell growth, (iii) by restricting nutrient availability (which may lead to smaller vessels), and (iv) possibly by lowering aquaporine activity in the roots

Rural-urban food, nutrient and virtual water flows in selected West African cities

Impacts of increasing population pressure on food demand and land and water resources have sparked interest in nutrient and water balances and flows at a range of scales. In IWMI Research Report 115, it was tried for the first time to quantify rural-urban food flows for selected cities in Ghana and Burkina Faso to analyse their dependency on food supplied from rural vs. peri-urban vs. urban farming. Both, the urban nutrient and water footprints are closely interlinked. Currently, 80-95 percent of the domestic water used and the nutrients consumed go to waste without treatment or resource recovery. The economic dimensions are significant. Options to reduce the environmental burden by closing the rural-urban water and nutrient cycles are discussed

Resource use and GHG emissions of eight tropical fruit species cultivated in Colombia

Introduction. The cultivation of high-value fruit species is a profitable agricultural activity in many tropical countries; however, intensive fruit cultivation may depend on high amounts of external inputs. The objective of our study was to quantify and compare the resource use during the cultivation of eight tropical fruit species (Rubus glaucus, Solanum quitoense, Passiflora edulis, Cyphomandra betacea, Physalis peruviana, Ananas comosus, Persea americana and Mangifera indica) commonly cultivated in Colombia. It further aimed to identify greenhouse gas (GHG) emissions in the selected production systems and to highlight the potential to contribute to climate change mitigation efforts. Materials and methods. The analysis was based on data from agricultural databases and applied a life-cycle assessment with energy use and GHG emissions as impact categories. Furthermore, economic indicators were taken into account with the aim of integrating the environmental and economic goals of production systems. Results and discussion. Among the eight fruit species studied, mango (Mangifera indica) was found to have the lowest and tree tomato (Cyphomandra betacea) the highest emission profile. The variability in resource use among growers of the same species was high, indicating the need to improve management abilities at the farm level. Mineral fertilizer production was the highest contributor to GHG emissions. GHG- and energy-efficient management alternatives would have a high potential to reduce the carbon footprint of fruit cultivation