Ulrik Ilstedt | Swedish University of Agricultural Sciences (original) (raw)

Papers by Ulrik Ilstedt

This study evaluates the effects of ground-skidding operations on the physical and chemical prope... more This study evaluates the effects of ground-skidding operations on the physical and chemical properties of soil at different levels of slope gradient and traffic frequency. Three levels of traffic (four, eight and 16 passes of a rubber-tired skidder Timberjack 450 C), and two levels of slope gradients (gentle b20%, and steep ≥20%) were applied in three replicates consequently, 18 plots with 10 m long by 4 m wide were utilized in the study. In each sampling plot, three lines were set up perpendicular to the skidding direction. At three different points on each line (left track, between track and right track) one sample was taken from forest floor and the 0–10 cm soil layer. Soil bulk density, forest floor biomass, organic carbon (OC), nitrogen (N), phosphorus (P), potassium (K) and soil acidity (pH) were affected by traffic frequency and slope gradient. The soil class of our study area in soil classification according to WRB was Combisols. Soil texture was analyzed using the Bouyoucos hydrometer method and was determined to be clay loam along the trails. Soil bulk density was 60% higher in samples taken from skid trails compared with samples taken from an undisturbed area. The average forest floor biomass ranged from 2185 kg ha −1 to 243 kg ha −1 on the skid trails, while the respective value was 3335 kg ha −1 for the undisturbed area. Skidding caused a decrease in the amount of soil OC (by 38%) and the concentrations of N (57%), P (25%), K (31%) and hydrogen ions (33%) compared with undisturbed areas. Increased soil disturbance occurred more markedly with fewer passes on the steeper trail. The dramatic increase in soil disturbance on the skid trail with a slope N20% is presumably associated with the difficulties of skidding on steep terrain. To minimize soil disturbance , skidding should be confined to areas with more gentle slopes and alternative harvesting methods should be used where slope gradients exceed 20%. We hypothesized that skidding can jeopardize the sustainability of forest ecosystems by creating unfavorable changes in soil characteristics and nutrient status.

Water scarcity constrains the livelihoods of millions of people in tropical drylands. Tree planti... more Water scarcity constrains the livelihoods of millions of people in tropical drylands. Tree planting in these environments is generally discouraged due to the large water consumption by trees, but this view may neglect their potential positive impacts on water availability. The effect of trees on soil hydraulic properties linked to groundwater recharge is poorly understood. In this study, we performed 18 rainfall simulations and tracer experiments in an agroforestry parkland in Burkina Faso to investigate the effect of trees and associated termite mounds on soil infiltrability and preferential flow. The sampling points were distributed in transects each consisting of three positions: (i) under a single tree, (ii) in the middle of an open area, and (iii) under a tree associated with a termite mound. The degree of preferential flow was quantified through parameters based on the dye infiltration patterns, which were analyzed using image analysis of photographs. Our results show that the degree of preferential flow was highest under trees associated with termite mounds, intermediate under single trees, and minimal in the open areas. Tree density also had an influence on the degree of preferential flow, with small open areas having more preferential flow than large ones. Soil infiltrability was higher under single trees than in the open areas or under trees associated with a termite mound. The findings from this study demonstrate that trees have a positive impact on soil hydraulic properties influencing groundwater recharge, and thus such effects must be considered when evaluating the impact of trees on water resources in drylands.

Water scarcity contributes to the poverty of around one-third of the world's people. Despite many... more Water scarcity contributes to the poverty of around one-third of the world's people. Despite many benefits, tree planting in dry regions is often discouraged by concerns that trees reduce water availability. Yet relevant studies from the tropics are scarce, and the impacts of intermediate tree cover remain unexplored. We developed and tested an optimum tree cover theory in which groundwater recharge is maximized at an intermediate tree density. Below this optimal tree density the benefits from any additional trees on water percolation exceed their extra water use, leading to increased groundwater recharge, while above the optimum the opposite occurs. Our results, based on groundwater budgets calibrated with measurements of drainage and transpiration in a cultivated woodland in West Africa, demonstrate that groundwater recharge was maximised at intermediate tree densities. In contrast to the prevailing view, we therefore find that moderate tree cover can increase groundwater recharge, and that tree planting and various tree management options can improve groundwater resources. We evaluate the necessary conditions for these results to hold and suggest that they are likely to be common in the seasonally dry tropics, offering potential for widespread tree establishment and increased benefits for hundreds of millions of people. Two-thirds of the world's population may live in water-limited regions by 2025 1. In Africa about 340 million people already lack access to adequate and hygienic sources of water, such as groundwater 2. Limited water constrains food production, nutrition, and health as well as impacting opportunities for education, work, and improved livelihoods. Reliable access to clean water is essential for achieving the UN Sustainable Development Goals. Forests have often been described as 'sponges' storing rain water and slowly releasing it to maintain groundwater and streams during dry periods 3–5. Formerly, this sponge theory and related ideas motivated policies aimed at conserving and restoring forests 5–7. In recent decades, however, these ideas have lost credibility as studies show that forest clearance generally leads to increased and afforestation to reduced water yields 3,8,9. Therefore a contrasting trade-off theory–in which more trees means less water–has become the dominant paradigm. This trade-off theory predicts that as tree densities increase, water losses from transpiration and interception dominate their hydrological effects 6,8,10. In the tropics the trade-off theory rests on limited evidence. The few available studies compare extremes: open land versus closed forest, or grasslands versus dense plantations 11. Despite the recognition that trees can improve

This manuscript describes optimization method to find the parameters of the hydrologic tank model... more This manuscript describes optimization method to find the parameters of the hydrologic tank model using Excel VBA and Solver. A continuous sigmoid function was introduced to replace a commonly used discrete function in calculating water flow from each reservoir. Options of objective error functions were also made available to be selected to minimize errors.

The manuscript contains throughout solutions to the Darcy and Richards’ equation by means of Expl... more The manuscript contains throughout solutions to the Darcy and Richards’ equation by means of Explicit and Implicit schemes of Finite Difference method subjected to various boundary conditions, uniform or varied initial conditions including source/sink terms. The computer program is written in Microsoft Excel Spreadsheet combined with Visual Basic. It is the main pupose that the user can follow every step of calculations, advantages and disadvantages of using different schemes, and also effects of applying different types of boundary conditions. Descriptions of how to build computer program in Microsoft Excel also are given in Appendices.

One of the awaited major climatic change feedbacks on the biosphere-atmosphere CO2 exchange is th... more One of the awaited major climatic change feedbacks on the biosphere-atmosphere CO2 exchange is the change in degradation rate of organic material in response to increased temperature. Despite the recent intense research efforts on the temperature sensitivity of organic matter degradation, large uncertainties on the controlling factors still remain. Theoretical analysis reveals an increased temperature sensitivity with the degree of recalcitrance to decomposition of organic matter compounds. One crucial research issue is therefore to find suitable descriptors of the organic chemical composition that allow modeling of the temperature sensitivity in organic matter degradation. In addition we also hypothesize that the metabolic status of the microorganisms, i.e. the relative contribution of catabolic and anabolic activity to the CO2 production also importantly affects the temperature sensitivity of organic matter decomposition. In this study we show how the variation in temperature sens...

Soil Biology and Biochemistry, 2008

We studied nutrient limitation and availability for soil microbial respiration after additions of... more We studied nutrient limitation and availability for soil microbial respiration after additions of glucose (C), in combination with nitrogen (N) and phosphorus (P) in soil samples taken from parklands of Vitellaria paradoxa and Faidherbia albida. We hypothesized that in these P-fixing soils: (i) after C addition, respiration will be limited by P, but P-limitation will be lower under tree canopies;

Soil Biology and Biochemistry, 2003

... of wildfires in natural forests, secondary forests, and controlled fire for agricultural purp... more ... of wildfires in natural forests, secondary forests, and controlled fire for agricultural purposes can ... In a recent study in Malaysia, streams draining areas in secondary vegetation were ... This was mainly explained by the increased openness, greater drought susceptibility and larger ...

Soil Biology and Biochemistry, 2000

Soil Biology and Biochemistry, 2011

Soil Biology and Biochemistry, 2005

ABSTRACT

Forest Ecology and Management, 2007

Forest Ecology and Management, 2004

This study evaluates the effects of ground-skidding operations on the physical and chemical prope... more This study evaluates the effects of ground-skidding operations on the physical and chemical properties of soil at different levels of slope gradient and traffic frequency. Three levels of traffic (four, eight and 16 passes of a rubber-tired skidder Timberjack 450 C), and two levels of slope gradients (gentle b20%, and steep ≥20%) were applied in three replicates consequently, 18 plots with 10 m long by 4 m wide were utilized in the study. In each sampling plot, three lines were set up perpendicular to the skidding direction. At three different points on each line (left track, between track and right track) one sample was taken from forest floor and the 0–10 cm soil layer. Soil bulk density, forest floor biomass, organic carbon (OC), nitrogen (N), phosphorus (P), potassium (K) and soil acidity (pH) were affected by traffic frequency and slope gradient. The soil class of our study area in soil classification according to WRB was Combisols. Soil texture was analyzed using the Bouyoucos hydrometer method and was determined to be clay loam along the trails. Soil bulk density was 60% higher in samples taken from skid trails compared with samples taken from an undisturbed area. The average forest floor biomass ranged from 2185 kg ha −1 to 243 kg ha −1 on the skid trails, while the respective value was 3335 kg ha −1 for the undisturbed area. Skidding caused a decrease in the amount of soil OC (by 38%) and the concentrations of N (57%), P (25%), K (31%) and hydrogen ions (33%) compared with undisturbed areas. Increased soil disturbance occurred more markedly with fewer passes on the steeper trail. The dramatic increase in soil disturbance on the skid trail with a slope N20% is presumably associated with the difficulties of skidding on steep terrain. To minimize soil disturbance , skidding should be confined to areas with more gentle slopes and alternative harvesting methods should be used where slope gradients exceed 20%. We hypothesized that skidding can jeopardize the sustainability of forest ecosystems by creating unfavorable changes in soil characteristics and nutrient status.

Water scarcity constrains the livelihoods of millions of people in tropical drylands. Tree planti... more Water scarcity constrains the livelihoods of millions of people in tropical drylands. Tree planting in these environments is generally discouraged due to the large water consumption by trees, but this view may neglect their potential positive impacts on water availability. The effect of trees on soil hydraulic properties linked to groundwater recharge is poorly understood. In this study, we performed 18 rainfall simulations and tracer experiments in an agroforestry parkland in Burkina Faso to investigate the effect of trees and associated termite mounds on soil infiltrability and preferential flow. The sampling points were distributed in transects each consisting of three positions: (i) under a single tree, (ii) in the middle of an open area, and (iii) under a tree associated with a termite mound. The degree of preferential flow was quantified through parameters based on the dye infiltration patterns, which were analyzed using image analysis of photographs. Our results show that the degree of preferential flow was highest under trees associated with termite mounds, intermediate under single trees, and minimal in the open areas. Tree density also had an influence on the degree of preferential flow, with small open areas having more preferential flow than large ones. Soil infiltrability was higher under single trees than in the open areas or under trees associated with a termite mound. The findings from this study demonstrate that trees have a positive impact on soil hydraulic properties influencing groundwater recharge, and thus such effects must be considered when evaluating the impact of trees on water resources in drylands.

Water scarcity contributes to the poverty of around one-third of the world's people. Despite many... more Water scarcity contributes to the poverty of around one-third of the world's people. Despite many benefits, tree planting in dry regions is often discouraged by concerns that trees reduce water availability. Yet relevant studies from the tropics are scarce, and the impacts of intermediate tree cover remain unexplored. We developed and tested an optimum tree cover theory in which groundwater recharge is maximized at an intermediate tree density. Below this optimal tree density the benefits from any additional trees on water percolation exceed their extra water use, leading to increased groundwater recharge, while above the optimum the opposite occurs. Our results, based on groundwater budgets calibrated with measurements of drainage and transpiration in a cultivated woodland in West Africa, demonstrate that groundwater recharge was maximised at intermediate tree densities. In contrast to the prevailing view, we therefore find that moderate tree cover can increase groundwater recharge, and that tree planting and various tree management options can improve groundwater resources. We evaluate the necessary conditions for these results to hold and suggest that they are likely to be common in the seasonally dry tropics, offering potential for widespread tree establishment and increased benefits for hundreds of millions of people. Two-thirds of the world's population may live in water-limited regions by 2025 1. In Africa about 340 million people already lack access to adequate and hygienic sources of water, such as groundwater 2. Limited water constrains food production, nutrition, and health as well as impacting opportunities for education, work, and improved livelihoods. Reliable access to clean water is essential for achieving the UN Sustainable Development Goals. Forests have often been described as 'sponges' storing rain water and slowly releasing it to maintain groundwater and streams during dry periods 3–5. Formerly, this sponge theory and related ideas motivated policies aimed at conserving and restoring forests 5–7. In recent decades, however, these ideas have lost credibility as studies show that forest clearance generally leads to increased and afforestation to reduced water yields 3,8,9. Therefore a contrasting trade-off theory–in which more trees means less water–has become the dominant paradigm. This trade-off theory predicts that as tree densities increase, water losses from transpiration and interception dominate their hydrological effects 6,8,10. In the tropics the trade-off theory rests on limited evidence. The few available studies compare extremes: open land versus closed forest, or grasslands versus dense plantations 11. Despite the recognition that trees can improve

This manuscript describes optimization method to find the parameters of the hydrologic tank model... more This manuscript describes optimization method to find the parameters of the hydrologic tank model using Excel VBA and Solver. A continuous sigmoid function was introduced to replace a commonly used discrete function in calculating water flow from each reservoir. Options of objective error functions were also made available to be selected to minimize errors.

The manuscript contains throughout solutions to the Darcy and Richards’ equation by means of Expl... more The manuscript contains throughout solutions to the Darcy and Richards’ equation by means of Explicit and Implicit schemes of Finite Difference method subjected to various boundary conditions, uniform or varied initial conditions including source/sink terms. The computer program is written in Microsoft Excel Spreadsheet combined with Visual Basic. It is the main pupose that the user can follow every step of calculations, advantages and disadvantages of using different schemes, and also effects of applying different types of boundary conditions. Descriptions of how to build computer program in Microsoft Excel also are given in Appendices.

One of the awaited major climatic change feedbacks on the biosphere-atmosphere CO2 exchange is th... more One of the awaited major climatic change feedbacks on the biosphere-atmosphere CO2 exchange is the change in degradation rate of organic material in response to increased temperature. Despite the recent intense research efforts on the temperature sensitivity of organic matter degradation, large uncertainties on the controlling factors still remain. Theoretical analysis reveals an increased temperature sensitivity with the degree of recalcitrance to decomposition of organic matter compounds. One crucial research issue is therefore to find suitable descriptors of the organic chemical composition that allow modeling of the temperature sensitivity in organic matter degradation. In addition we also hypothesize that the metabolic status of the microorganisms, i.e. the relative contribution of catabolic and anabolic activity to the CO2 production also importantly affects the temperature sensitivity of organic matter decomposition. In this study we show how the variation in temperature sens...

Soil Biology and Biochemistry, 2008

We studied nutrient limitation and availability for soil microbial respiration after additions of... more We studied nutrient limitation and availability for soil microbial respiration after additions of glucose (C), in combination with nitrogen (N) and phosphorus (P) in soil samples taken from parklands of Vitellaria paradoxa and Faidherbia albida. We hypothesized that in these P-fixing soils: (i) after C addition, respiration will be limited by P, but P-limitation will be lower under tree canopies;

Soil Biology and Biochemistry, 2003

... of wildfires in natural forests, secondary forests, and controlled fire for agricultural purp... more ... of wildfires in natural forests, secondary forests, and controlled fire for agricultural purposes can ... In a recent study in Malaysia, streams draining areas in secondary vegetation were ... This was mainly explained by the increased openness, greater drought susceptibility and larger ...

Soil Biology and Biochemistry, 2000

Soil Biology and Biochemistry, 2011

Soil Biology and Biochemistry, 2005

ABSTRACT

Forest Ecology and Management, 2007

Forest Ecology and Management, 2004