Modeling spatial variability in the life-cycle costs of low-volume forest roads

Cost estimation is probably the most decisive factor in the process of computer-aided, preliminary planning for low-volume road networks. However, the cost of construction is normally assumed to be route-independent for a specific project area, resulting in sub-optimal layouts. This is especially true for mountainous terrain and in areas with unstable subsoil. Here, we present a model for more accurately estimating spatial variability in road life-cycle costs, based on terrain surface properties as well as geological properties of the subsoil. This parametric model incorporates four structural components: embankment, retaining structures, pavement, and drainage and stream-crossing structures. It is linked to a geo-database that allows users to derive location-specific parameter values as input. In applying this model, we have demonstrated that variability in costs ranges widely for mountainous areas, with the most expensive construction being approximately five times greater there than on more favorable sites. This variability strongly affects the optimal layout of a road network. First, when location-specific slope gradients are considered, costs are reduced by about 17% from those calculated via currently available engineering practices; when both slope gradient and geotechnical formations are included, those costs are decreased by about 20%. Second, the length of the road network is increased by about 4% and 10% respectively, compared with current practices.     

Genetic differences between autochthonous and breeding populations of common cypress (Cupressus sempervirens L.) in Greece

Individuals were selected for resistance against the imperfect fungus Seiridium cardinale Wag in six common cypress populations (Cupressus sempervirens L.) in Greece. A total of 109 resistant clones and 140 trees from their base populations were surveyed at several allozyme loci. The comparison yielded information on changes in genetic variation due to artificial selection. The genetic structure of the breeding populations was similar to their base populations. Nevertheless, the number of rare alleles among the resistant clones had decreased, showing a similar trend at most loci and for most comparisons. Possible implications for breeding strategies are discussed.     

Stand density and growth of Norway spruce (<Emphasis Type="Italic">Picea abies</Emphasis> (L.) Karst.) and European beech (<Emphasis Type="Italic">Fagus sylvatica</Emphasis> L.): evidence from long-term experimental plots

On the basis of nine Norway spruce (Picea abies (L.) Karst.) and ten European beech (Fagus sylvatica L.) thinning experiments in Germany, for which both residual and removed stock had been registered first during 1870, I scrutinize how moderate and heavy thinning from below (B-, C-grade) affects the production of merchantable volume compared with light thinning (A-grade). In relation to A-grade, cumulative merchantable volume (CV) of B- and C-grade amounts in average to 103–107% in juvenile and to 97–102% in mature Norway spruce stands. The corresponding findings for European beech are 101–106% and 94–102%. CV of individual stands varies between 89% and 130% for Norway spruce and 73% and 155% for European beech (CV of A-grade = 100%). These findings are substantiated by the relation between stand density (SDI) and periodic annual increment (PAI). On the B- and C-grade plots of spruce and beech, respectively, SDI was reduced down to 41–91% and 31–83% of the A-grade. When SDI is reduced in young stands, PAI follows a unimodal curve. Norway spruce’s PAI culminates in 109% if SDI is reduced to 59%; European beech’s PAI culminates in 123% when density is reduced to 50%. Whereas Norway spruce’s growth reacts most positively on thinning under poor site conditions and with increment reduction on favourable sites, European beech behaves oppositely. With stand development the culmination point of the unimodal relation moves towards maximum density, so that in older stands PAI follows the increasing pattern, which is the left portion of a unimodal curve. A model is presented which apparently unifies contradictory patterns of stand density–growth reactions by integrating relative stand density, average tree size and site fertility effects, and makes the findings operable for forest management.     

Relation between soil organic matter and yield levels of nonlegume crops in organic and conventional farming systems

The aim of this study was to evaluate the interaction between yield levels of nonleguminous crops and soil organic matter (SOM) under the specific conditions of organic and conventional farming, respectively, and to identify implications for SOM management in arable farming considering the farming system (organic vs. conventional). For that purpose, correlations between yield levels of nonlegume crops and actual SOM level (C_org, N_t, C_hwe, N_hwe) as well as SOM‐level development were examined including primary data from selected treatments of seven long‐term field experiments in Germany and Switzerland. Yield levels of nonlegume crops were positively correlated with SOM levels, but the correlation was significant only under conditions of organic farming, and not with conventional farming treatments. While absolute SOM levels had a positive impact on yield levels of nonlegumes, the yield levels of nonlegumes and SOM‐level development over time correlated negatively. Due to an increased demand of N from SOM mineralization, higher yield levels of nonlegumes obviously indicate an increased demand for OM supply to maintain SOM levels. Since this observation is highly significant for farming without mineral‐N fertilization but not for farming with such fertilization, we conclude that the demand of SOM‐level maintenance or enhancement and thus adequate SOM management is highly relevant for crop production in organic farming both from an agronomical and ecological point of view. Under conventional management, the agronomic relevance of SOM with regard to nutrient supply is much lower than under organic management. However, it has to be considered that we excluded other possible benefits of SOM in our survey that may be highly relevant for conventional farming as well.     

Precipitation and dew in a soybean canopy: Spatial variations in leaf wetness and implications for Phakopsora pachyrhizi infection

With the occurrence of soybean rust (Phakopsora pachyrhizi) now a seasonal problem in the United States, increased research is needed to ascertain the potential transmission of this disease among soybean (Glycine max L.) in major growing regions throughout the nation. The fungal disease spores are deposited on leaves in the lower region of the canopy through rain events or wind transport from nearby plants during the growing season and must then have moist conditions on the lower trifoliolates for several hours in order to infect the plant. These moist conditions can be achieved through any form of wetness. This wetness was measured in a soybean canopy at West Lafayette, IN, during the summer of 2007 using resistance-grid wetness sensors located at three heights representative of the top, mid-level, and lowest trifoliate of the canopy. Temperature, relative humidity, wind speed, and precipitation measurements were used to determine the cause of wetness. Over the course of the experiment, wetness events were classified as dew, rain, or neither. The dew events were then compared to rain events with an emphasis on differences in vertical and horizontal duration of wetness. Dew events were found to be the dominant wetness source in the upper canopy. Rain events were the most dominant cause of wetness in the lower canopy. Upper canopy wetness events had the longest duration. Horizontal variation in wetness and wetness duration was large.     

Water allocation and management in an emerging spate irrigation system in Makanya catchment, Tanzania

Although spate irrigation systems are risk-prone, they can be an important component for livelihood security in semi-arid areas. Spate uses water (flood water), which upstream users often do not require, as rainfall during these periods is more than sufficient. The use of this flood water for spate irrigation is therefore a good opportunity to convert water with a low opportunity cost to high value water. As more rivers are closing, due to socio-economic and climate changes, spate irrigation may become increasingly relevant in semi-arid areas. Spate irrigation systems pose institutional and technical challenges: collective action is challenged by complex upstream-downstream interactions between users within the system, and the high labour demands for regular reconstruction of temporary diversion weirs and intake structures. This paper describes a spate irrigation system in Makanya village, Tanzania that emerged in response to increased upstream water use. We use three of the four dimensions (hydrological, hydraulic and sociological) of spate irrigation proposed by Van Steenbergen (1997) to assess the Makanya spate irrigation system. The Makanya spate irrigation system has an organisational structure that is similar to the canal irrigation (furrow) committees located upstream, and effectively deals with the institutional demands of managing water in spate irrigation systems. Water allocation is reminiscent to the water sharing arrangements existing in the full irrigation system, which previously was in place at the site and in the high- and midlands of the Makanya catchment and therefore set this system apart from the traditional spate irrigation practice elsewhere. Technically, a major challenge is the reconstruction of the head works after each flood. Another aspect is the changes in the river bed. Flash floods carry sediments that deposit on the fields, raising the elevation of the irrigated land every year and making it increasingly difficult for the river water to enter the plots. Improving system efficiency through modernisation of the diversion and distribution structures in this case is not feasible due to the huge amounts of sediments delivered to the system each year. Instead investments in conjunctive use of groundwater could be the solution because it involves a relatively small intervention, minimises the physical disturbance of the system, and therefore is likely to respect the existing locally developed water management arrangements.