Alley cropping of willows and grassland for bioenergy provision: productivity, tree-crop interactions and energy balance

The demand for biomass for bioenergy has increased rapidly in industrialized countries in the recent years. Biogenic energy carriers are known to reduce CO2 emissions. However, the resource-inefficient production of biomass often caused negative impacts on the environment, e.g. biodiversity losses, nitrate leaching, and erosion. The detrimental effects evolved mainly from annual crops. Therefore, the aim of modern bioenergy cropping systems is to combine yield stability and environmental benefits by the establishment of mixed-cropping systems. A particular emphasis is on perennial crops which are perceived as environmentally superior to annual crops. Agroforestry systems represent such mixed perennial cropping systems and consist of a mix of trees and arable crops or grassland within the same area of land. Agroforestry practices vary across the globe and alley cropping is a type of agroforestry system which is well adapted to the temperate zone, with a high degree of mechanization. Trees are planted in rows and crops are planted in the alleyways, which facilitates their management by machinery. This study was conducted to examine a young alley cropping system of willows and two grassland mixtures for bioenergy provision under temperate climate conditions. The first part of the thesis identified possible competition effects between willows and the two grassland mixtures. Since light seemed to be the factor most affecting the yield performance of the understory in temperate agroforestry systems, a biennial in situ artificial shade experiment was established over a separate clover-grass stand to quantify the effects of shade. Data to possible below- and aboveground interactions among willows and the two grassland mixtures and their effects on productivity, sward composition, and quality were monitored along a tree-grassland interface within the alleys. In the second part, productivity of the alley cropping system was examined on a triennial time frame and compared to separate grassland and willow stands as controls. Three different conversion technologies (combustion of hay, integrated generation of solid fuel and biogas from biomass, whole crop digestion) were applied to grassland biomass as feedstock and analyzed for its energetic potential. The energetic potential of willow wood chips was calculated by applying combustion as conversion technique. Net energy balances of separate grassland stands, agroforestry and pure willow stands evaluated their energy efficiency. Results of the biennial artificial shade experiment showed that severe shade (80 % light reduction) halved grassland productivity on average compared to a non-shaded control. White clover as heliophilous plant responded sensitively to limited radiation and its dry matter contribution in the sward decreased with increasing shade, whereas non-leguminous forbs (mainly segetal species) benefited. Changes in nutritive quality could not be confirmed by this experiment. Through the study on interactions within the alleys of the young agroforestry system it was possible to outline changes of incident light, soil temperature and sward composition of clover-grass along the tree-grassland interface. Nearly no effects of trees on precipitation, soil moisture and understory productivity occurred along the interface during the biennial experiment. Considering the results of the productivity and the net energy yield alley cropping system had lower than pure grassland stands, irrespective of the grassland seed mixture or fertilization, but was higher than that for pure willow stands. The comparison of three different energetic conversion techniques for the grassland biomass showed highest net energy yields for hay combustion, whereas the integrated generation of solid fuel and biogas from biomass (IFBB) and whole crop digestion performed similarly. However, due to the low fuel quality of hay, its direct combustion cannot be recommended as a viable conversion technique, whereas IFBB fuels were of a similar quality to wood chip from willow.

The wind in the willows: flows in forest canopies in complex terrain

Forest canopies are important components of the terrestrial carbon budget, which has motivated a worldwide effort, FLUXNET, to measure CO2 exchange between forests and the atmosphere. These measurements are difficult to interpret and to scale up to estimate exchange across a landscape. Here we review the effects of complex terrain on the mean flow, turbulence, and scalar exchange in canopy flows, as exemplified by adjustment to forest edges and hills, including the effects of stable stratification. We focus on the fundamental fluid mechanics, in which developments in theory, measurements, and modeling, particularly through large-eddy simulation, are identifying important processes and providing scaling arguments. These developments set the stage for the development of predictive models that can be used in combination with measurements to estimate exchange at the landscape scale.

Pan en los sauces : La aparición del dios Pan en The Wind in the Willows de Kenneth Grahame y sus ilustraciones

De las numerosas ilustraciones que se hicieron en más de un siglo para la novela El viento en los sauces (1908), de Kenneth Grahame, haremos un breve recorrido histórico por las primeras cinco que re-crean la escena en el capítulo "El flautista en el umbral del alba", en la que del dios griego Pan, con sus patas de cabra, torso humano y flauta, se aparece a los protagonistas. Observaremos el valor que se le otorga a la deidad, qué elementos del relato se representan y cómo. Compararemos estos dos tipos de lenguaje para este caso, y las ilustraciones entre sí

Pan en los sauces : La aparición del dios Pan en The Wind in the Willows de Kenneth Grahame y sus ilustraciones

De las numerosas ilustraciones que se hicieron en más de un siglo para la novela El viento en los sauces (1908), de Kenneth Grahame, haremos un breve recorrido histórico por las primeras cinco que re-crean la escena en el capítulo "El flautista en el umbral del alba", en la que del dios griego Pan, con sus patas de cabra, torso humano y flauta, se aparece a los protagonistas. Observaremos el valor que se le otorga a la deidad, qué elementos del relato se representan y cómo. Compararemos estos dos tipos de lenguaje para este caso, y las ilustraciones entre sí

Pan en los sauces : La aparición del dios Pan en The Wind in the Willows de Kenneth Grahame y sus ilustraciones

De las numerosas ilustraciones que se hicieron en más de un siglo para la novela El viento en los sauces (1908), de Kenneth Grahame, haremos un breve recorrido histórico por las primeras cinco que re-crean la escena en el capítulo "El flautista en el umbral del alba", en la que del dios griego Pan, con sus patas de cabra, torso humano y flauta, se aparece a los protagonistas. Observaremos el valor que se le otorga a la deidad, qué elementos del relato se representan y cómo. Compararemos estos dos tipos de lenguaje para este caso, y las ilustraciones entre sí

Manipulation of the phenolic chemistry of willows by gall-inducing sawflies

The ability to induce galls on plants has evolved independently in many insect orders, but the adaptive significance and evolutionary consequences of gall induction are still largely unknown. We studied these questions by analyzing the concentrations of various plant defense compounds in willow leaves and sawfly galls. We found that the galls are probably nutritionally beneficial for the sawfly larvae, because the concentrations of most defensive phenolics are substantially lower in gall interiors than in leaves. More importantly, changes in chemistry occur in a similar coordinated pattern in all studied willow species, which suggests that the insects control the phenolic biosynthesis in their hosts. The resulting convergence of the chemical properties of the galls both within and between host species indicates that the role of plant chemistry in the evolution of host shifts may be fundamentally less significant in gallers than in other phytophagous insects.

Phytoremediation of Metal Contamination using Salix (willows)

Abandoned hardrock mines and the resulting Acid Mine Drainage (AMD) are a source of vast, environmental degradation that are toxic threats to plants, animals, and humans. Cadmium (Cd) and lead (Pb) are metal contaminants often found in AMD. In my mine outwash water samples, cadmium and lead concentrations were 19 and 160 times greater than concentrations in control waterways, and 300 and 40 times greater than EPA Aquatic Life Use water quality standards, respectively. I tested the phytoremediation characteristics of three montane willows native to the Rocky Mountains: Salix drummondiana, S. monticola, and S. planifolia. I tested the willows’ accumulation and tolerance characteristics of cadmium and lead contamination. I found that S. drummondiana accumulated more cadmium in stems than both S. monticola and S. planifolia, and that all three willow species accumulated similar concentrations of lead. I found similar trends for leaf accumulation. I also found that S. monticola had a greater growth and tolerance to the lower lead concentrations than high lead concentrations in addition to containing higher field stem concentrations of lead than S. planifolia. Salix planifolia contained nearly 2.5 times greater concentrations of cadmium in field stems than S. drummondiana. Based on my results, S. drummondiana could aid in aboveground accumulation of cadmium polluted watersheds, and S. monticola could aid in aboveground accumulation and tolerance of lead pollution.

The harp on the willows ; Remembering Zion ; Farewell to Egypt ; The church in the house ; The dew of Hermon and Destination of the Jews /

Mode of access: Internet.

The harp on the willows : Remembering Zion, Farewell to Egypt, The church in the house, The dew of Hermon, and Destination of the Jews.

Mode of access: Internet.

The genus Salix (willows) in the Black Hills of South Dakota /

Literature cited: p. 73-74.

Shoot growth dynamics and photosynthetic response to increased nitrogen availability in the alpine willow salix-glauca

Plants subjected to increases in the supply of resource(s) limiting growth may allocate more of those resources to existing leaves, increasing photosynthetic capacity, and/or to production of more leaves, increasing whole-plant photosynthesis. The responses of three populations of the alpine willow, Salix glauca, growing along an alpine topographic sequence representing a gradient in soil moisture and organic matter, and thus potential N supply, to N amendments, were measured over two growing seasons, to elucidate patterns of leaf versus shoot photosynthetic responses. Leaf-(foliar N, photosynthesis rates, photosynthetic N-use efficiency) and shoot-(leaf area per shoot, number of leaves per shoot, stem weight, N resorption efficiency) level measurements were made to examine the spatial and temporal variation in these potential responses to increased N availability. The predominant response of the willows to N fertilization was at the shoot-level, by production of greater leaf area per shoot. Greater leaf area occurred due to production of larger leaves in both years of the experiment and to production of more leaves during the second year of fertilization treatment. Significant leaf-level photosynthetic response occurred only during the first year of treatment, and only in the dry meadow population. Variation in photosynthesis rates was related more to variation in stomatal conductance than to foliar N concentration. Stomatal conductance in turn was significantly related to N fertilization. Differences among the populations in photosynthesis, foliar N, leaf production, and responses to N fertilization indicate N availability may be lowest in the dry meadow population, and highest in the ridge population. This result is contrary to the hypothesis that a gradient of plant available N corresponds with a snowpack/topographic gradient.

The ecological impact of different mechanisms of chronic sub-lethal toxicity on feeding and respiratory physiology

Sub-lethal toxicity tests, such as the scope-for-growth test, reveal simple relationships between measures of contaminant concentration and effect on respiratory and feeding physiology. Simple models are presented to investigate the potential impact of different mechanisms of chronic sub-lethal toxicity on these physiological processes. Since environmental quality is variable, even in unimpacted environments, toxicants may have differentially greater impacts in poor compared to higher quality environments. The models illustrate the implications of different degrees and mechanisms of toxicity in response to variability in the quality of the feeding environment, and variability in standard metabolic rate. The models suggest that the relationships between measured degrees of toxic stress, and the maintenance ration required to maintain zero scope-for-growth, may be highly nonlinear. In addition it may be possible to define critical levels of sub-lethal toxic effect above which no environment is of sufficient quality to permit prolonged survival.