Higher Soil Water Content Research Articles

Temperature- and moisture-dependent soil water repellency induced by the basidiomycete Agaricus bisporus

Abstract Soil water repellency (SWR) has been reported to regularly occur in many soils under various climatic conditions. Despite the commonness of this soil property the mechanisms leading to the occurrence of SWR are largely unknown. The aim of this experiment was to test the hypothesis that the basidiomycete Agaricus bisporus promotes SWR, and that this fungal-induced SWR is dependent on soil moisture and temperature. We report that A. bisporus strongly induces SWR. We further show that the water content during the cultivation of A. bisporus on soil as well as drying temperature of the soil after the incubation experiment significantly affected SWR. Water drop penetration time (WDPT) of the soil ranged from 0.5 s in the samples cultivated at high soil water content (20%, w/w) and subsequently freeze dried, to more than 162 min in the soils that were kept at the low water content (13.8%, w/w) and were subsequently dried at 80 °C. These findings show that fungal activity potentially can promote dramatic SWR. The strong increase in SWR due to heating of the soil to 80 °C supports the view that SWR can be caused by a rearrangement of organic substances. For this reason, we discuss surface-active proteins produced by basidiomycetes as potential drivers of the SWR observed in our experiment.

Effects of tillage and fallow period management on soil physical behaviour and maize development

Abstract Effects of two tillage treatments and two fallow period managements under continuous maize cropping on soil temperature, soil water dynamics and maize development were evaluated over a 4-year period (2005–2008). Tillage treatments were conventional tillage with mouldboard ploughing and conservation tillage with disk harrowing. The fallow period managements were bare soil or soil sown with a cover crop after maize harvest. For each year, topsoil temperature (0–20 cm-depth) was lower under conservation tillage systems at sowing, from 0.8 to 2.8 °C. This difference persisted several weeks after sowing, and disappeared afterwards. Under conservation tillage, higher soil water content was generally measured at sowing and during the growing season strong fluctuations were observed at 40 cm-depth. Under conventional tillage, soil water content varied mainly in the tilled layer (20 cm-depth). Tillage and fallow period management affected water flow rate at 40 cm-depth. During the maize growing season, the lowest drainage volumes were measured in 2006 and 2008 under conservation tillage in cover cropped plots. No effect of fallow period management on maize development and yield was observed but significantly higher yields were measured under conservation tillage in 2005 and 2007. From this 4-year experiment under continuous maize cropping, using cover crop and reducing tillage intensity enhanced water use efficiency while maintaining or increasing maize yields.

Experimental studies on the effects of the “Conversion of Cropland to Grassland Program” on the water budget and evapotranspiration in a semi-arid steppe in Inner Mongolia, China

Since the late 1990s China has promoted the “Conversion of Cropland to Forest and Grassland Program” (CCFGP) as the largest environmental restoration program in the world. Because more water was required for established vegetation, it was assumed that evapotranspiration (ET) and water use in an older restored grassland would be greater than that in a younger restored grassland and that water shortages would then become more severe for further vegetation establishment in a semi-arid steppe due to the extraction of the established vegetation. To verify this hypothesis, a field experiment was carried out in 2008–2009 at seven sites of different ages after restoration. The hypothesis was tested using the Bowen ratio system together with other comparative methods. Results showed that less rainfall would infiltrate the deeper soil layer as the period of time after restoration increased and that the natural steppe site had the shallowest infiltration depth (10 cm or less). However, the youngest restored grassland site had the deepest infiltration depth and the highest soil water content. These results also showed that transpiration and ET rates were higher in the natural steppe site and older restored sites than those in the younger restored sites. Furthermore, it was found that the ratio between soil evaporation and ET was generally lower for all seven sites, which indicated that transpiration was a dominant component in ET. These results indicated that more water was used for vegetation establishment in the older restored grassland than that in the younger restored grassland. Our hypothesis was proved to be true. Meanwhile, it was also found that the dominant species changed from annual herbs (species had lower drought tolerance ability) in the younger restored grassland to perennial grasses in the older restored grassland (species had higher drought tolerance ability). Therefore, it was concluded that the natural steppe was able to utilize more water for vegetation establishment and it used water more efficiently than the restored steppe, while the older restored steppe used water more efficiently than the younger restored steppe. Because changes of vegetation type from annual to perennial not only increased evapotranspiration, but also changed the water budget, more attention should be paid to water shortage when undertaking the CCFGP in semi-arid steppes.

Earthworms, a means to accelerate removal of hydrocarbons (PAHs) from soil? A mini-review

Abstract Contamination of soil with hydrocarbons occurs frequently. Restoring contaminated soils is costly and time consuming. Earthworms accelerate the removal of hydrocarbons as they burrow through soil by rendering contaminants available for microbial degradation, by feeding on the organic matter that harbour contaminants, and by improving soil structure and aeration. Polycyclic aromatic hydrocarbons (PAHs) are recalcitrant hydrocarbons that can contaminate the environment and can thus serve as models to study the factors that control the removal of petroleum from soil. The effect of earthworms on the removal of PAHs was reviewed. It was found that earthworms have the capacity to accelerate the removal of PAHs and their degradation products from soil. However, large numbers of earthworms are required, which might be expensive. Moreover, it may be difficult to provide sufficient organic material as feed while simultaneously maintaining high soil water content to allow burrowing.

Leaf litter manipulations alter soil physicochemical properties and tree growth in a Neotropical savanna

This study was aimed to assess the role that leaf litter play in nutrient cycling, nutrient soil availability and ecosystem processes in an oligotrophic tropical savanna. A four year experiment was performed in a Neotropical savanna from the Brazilian plateau (cerrado), in which litter levels were modified, and the resulting changes in biophysical and chemical soil properties were studied. Changes in organic matter decomposition, soil respiration and stem growth of the six most common tree species were also monitored. Compared to litter removal plots, double litter plots had lower maximum soil temperature and higher soil water content, and litter decomposition rates in one of three species studied, consistent with higher soil respiration rates observed in this treatment. With the exception of Ca, there were no significant differences in nutrients between the removal, natural and double litter plots, even though most nutrients tended to increase in the double litter plots by the end of the experimental period, while in the control plots nutrient levels remained relatively constant. Of the six tree species used for growth analysis, only one, Sclerolobium paniculatum, a fast growing species with shallow roots, had a significant increase in stem growth due to litter addition. Preliminary results over four years indicate that litter removal and addition resulted in some significant changes and tendencies that indicate that litter is effectively altering ecosystem processes. The information obtained also suggest that nutrient cycling in plots with natural litter levels (control plots) was in a closed loop; most nutrients released by litter decomposition and mineralization were absorbed and reutilized immediately by the plants, thus minimizing nutrient leakage outside the system.

Floristic composition and soil characteristics of tropical freshwater forested wetlands of Veracruz on the coastal plain of the Gulf of Mexico

We studied the influence of geomorphological setting and soil properties on the vegetation structure, composition and diversity of five forested coastal wetlands in Veracruz on the Gulf of Mexico. These swamps are located on floodplains and in dune depressions. We recorded 109 woody and herbaceous species. The most frequent species were the trees Pachira aquatica, Annona glabra, Diospyros digyna and Ficus insipida subsp. insipida, the lianas Dalbergia brownei and Hippocratea celastroides and the hemi-epiphyte Syngonium podophyllum. The Shannon- H diversity index varied from 2.659 to 3.373, density from 1750 to 2289 stems ha −1 and basal area from 32.7 to 76.42 m 2 ha −1. The classification analysis defined two groups: one corresponded to forested wetlands along the floodplain (Apompal, Cienaga, Chica) and the other included Mancha and Salado, in dune depressions. PCA ordination of soil parameters during the rainy season explained 67.0% and during the dry season 69.1% of the total variance. In the rainy season Mancha and Salado samples remain close together because they have lower Mg, Na, K, % Total C and % Total N values. Apompal and Chica samples remain close to each other because of their high levels of % Total C, % Total N, Mg, Na and high soil water content. Cienaga samples are separated from the others because of high values of P, Ca and Eh as well as high water levels. In general, soil parameter ordination during the dry season showed that redox potential, P, water level and water content decreased in the forested wetlands and Na values increased in Chica. The soil textures identified were clay, sandy clay loam, sandy loam and clay loam; clay texture dominated alluvial processes in the floodplain (e.g., Cienaga). The forested wetlands in the floodplains had similar vegetation and the same happened in the dune depressions but soil characteristics were more variable in both cases. Plant diversity in floodplains tends to be relatively high, and the presence of adjacent tropical forests probably increases its richness, except in cases in which there are stressing factors, such as salinity. The forested wetlands studied showed dominant floristic elements, which extend north into Florida such as A. glabra and Ficus aurea. Other dominant elements such as P. aquatica are also found in Central and South America. The forested wetlands studied are subjected to continuous deforestation to transform the land into farming or ranching activities, this being a common practice throughout the distribution range of these forests.

Effect of freezing-thawing on nitrogen mineralization in vegetation soils of four landscape zones of Changbai Mountain

We studied the effect of freezing-thawing on nitrogen (N) mineralization of four vegetation soils from typical vegetation zones of Changbai Mountain with a laboratory incubation experiment. The soils were treated with two levels of soil water content, representing the low and high soil water contents found during late autumn and early spring in Changbai Mountain, respectively, and underwent cycling of freezing at −5 or −25°C and thawing at 5°C up to 15 times. The main purpose of this study was to examine the effects of freezing temperature, frequency of freezing-thawing cycles, and soil water content on N mineralization of four soils to reveal the different effects of spring and autumn freezing-thawing on soil N mineralization in Changbai Mountain. The results showed that inorganic N in the soils increased 1.67–26.77 times after 15 cycles of freezing-thawing, but N mineralization rate decreased with increased cycling of freezing-thawing. The lower freeze temperature and higher soil water content generally enhanced soil N mineralization. The results implied that freezing-thawing of vegetation soils to increase soil N mineralization to favor the growth of plants, and also increase the possibility of runoff loss of soil nutrients, is more effective in the spring than in the autumn.

Paired comparison of water, energy and carbon exchanges over two young maritime pine stands (Pinus pinaster Ait.): effects of thinning and weeding in the early stage of tree growth

The effects of management practices on energy, water and carbon exchanges were investigated in a young pine plantation in south-west France. In 2009-10, carbon dioxide (CO(2)), H(2)O and heat fluxes were monitored using the eddy covariance and sap flow techniques in a control plot (C) with a developed gorse layer, and an adjacent plot that was mechanically weeded and thinned (W). Despite large differences in the total leaf area index and canopy structure, the annual net radiation absorbed was only 4% lower in plot W. We showed that higher albedo in this plot was offset by lower emitted long-wave radiation. Annual evapotranspiration (ET) from plot W was 15% lower, due to lower rainfall interception and transpiration by the tree canopy, partly counterbalanced by the larger evaporation from both soil and regrowing weedy vegetation. The drainage belowground from plot W was larger by 113 mm annually. The seasonal variability of ET was driven by the dynamics of the soil and weed layers, which was more severely affected by drought in plot C. Conversely, the temporal changes in pine transpiration and stem diameter growth were synchronous between sites despite higher soil water content in the weeded plot. At the annual scale, both plots were carbon sinks, but thinning and weeding reduced the carbon uptake by 73%: annual carbon uptake was 243 and 65 g C m(-2) on plots C and W, respectively. Summer drought dramatically impacted the net ecosystem exchange: plot C became a carbon source as the gross primary production (GPP) severely decreased. However, plot W remained a carbon sink during drought, as a result of decreases in both GPP and ecosystem respiration (R(E)). In winter, both plots were carbon sources, plots C and W emitting 67.5 and 32.4 g C m(-2), respectively. Overall, this study highlighted the significant contribution of the gorse layer to mass and energy exchange in young pine plantations.

Relationships between simulated water stress and mortality and growth rates in underplanted Toona ciliata Roem. in subtropical Argentinean plantations

Toona ciliata Roem. (Australian red cedar) requires a nurse-tree overstory to prevent damage from drought and irradiation in some regions of north-eastern Argentina. T. ciliata was planted in the understory of Pinus taeda L. (625 stems/ha), Pinus elliottii Engelm. × Pinus caribaea Morelet (625 stems/ha), and Grevillea robusta A. Cunn. (833 stems/ha) nurse trees, which were thinned to 0, 25, 50, 75 and 100% of the initial densities. We measured initial T. ciliata mortality and growth as well as Leaf Area Index (LAI) based on light transmission. T. ciliata soil water availability and its effect on early growth and mortality were examined by modelling drought stress using the two-dimensional forest hydrology model ForWaDy. Simulated patterns in T. ciliata water stress for the different overstory treatments were consistent with observed patterns of mortality. Early mortality was lowest with a G. robusta overstory, with corresponding lowest drought stress values and high modelled soil water contents in the top soil layer in intermediate and high overstory densities. Mortality was highest with a P. elliottii × P. caribaea overstory in treatments with the highest modelled drought stress values in the most open treatments. The model supported our field observations by indicating that water stress was an important limitation to T. ciliata survival and growth on our study sites. The linkage between T. ciliata establishment success, early growth and soil water availability as indicated by ForWaDy, leads us to conclude that the model is a suitable stand management tool for guiding establishment of T. ciliata plantations.

Irrigation Quantity Effects on Anthracnose Disease of Annual Bluegrass

ABSTRACTIrrigation can influence both turf vigor and playability of putting greens. Anthracnose (Colletotrichum cereale Manns sensu lato Crouch, Clarke, and Hillman) has become an increasingly destructive disease of annual bluegrass (ABG) [Poa annua L. f. reptans (Hausskn.) T. Koyama] putting greens, particularly when turf is under stress. This 3‐yr field study evaluated the effects of irrigation quantity (100, 80, 60, and 40% of reference evapotranspiration [ETo]) on anthracnose severity of ABG mowed daily to 3.2 mm. Severe drought stress (40% ETo) increased anthracnose severity in 2006, 2007, and 2008. Anthracnose was less severe under 60% ETo irrigation, and irrigating at 80% ETo reduced severity compared to 60% ETo Irrigating at 100% ETo initially reduced anthracnose severity compared to 40% ETo; however, 100% ETo resulted in similar disease severity later in the 2006 and 2008 seasons. While this response was not observed late in the 2007 season, plots maintained at 100% ETo had turf quality similar to plots irrigated at 40% ETo later in each year due in part to increased algal development. Irrigation to replace 80% ETo typically resulted in the least amount of disease and the best turf quality throughout the trial. Thus, irrigation to minimize drought stress while also avoiding continuous high soil water content is beneficial in reducing anthracnose and maintaining acceptable turf performance.

Is forage productivity of meadows influenced by the afforestation of upstream hillsides? A study in NW Patagonia

Meadows are important reserves of water, with a key role in the maintenance of the biodiversity and productivity of ecosystems. In Patagonia, Argentina, afforestation with fast-growing exotic conifers has slowly but continuously increased over recent decades; though unfortunately, knowledge of the effects of afforestation on water resources remains scarce, with no information at all related to its impact on water dynamics and productivity of meadows located downslope to it. The effects of Pinus ponderosa afforestation on water dynamics (soil moisture contents and groundwater level) and productivity (aboveground forage productivity) of Northwest Patagonia meadows under xeric and humid conditions were analyzed. In the humid meadow, gravimetric soil water content, groundwater level and forage productivity were similar downslope of forested and non-forested slopes, with a trend towards higher forage productivity on the forested slope. In the xeric meadow, gravimetric soil water content was always higher downslope of the non-forested slope, with no difference in groundwater level between treatments. Forage productivity was statistically similar between situations (downslope of forested and non-forested slopes), with a trend towards higher productivity in the zone with higher soil water content. The main difference in the latter was related to differences in soil texture between zones. These results suggest that coniferous plantations located upstream of this type of meadow do not produce a direct effect on its aboveground forage productivity. These systems have high complexity linked to precipitation, geomorphology and previous history of land use, which determine primarily soil water dynamics and consequently, forage productivity.

Effects of High Soil Water Content and Temperature on Soil Respiration

The aim of this study was to quantify the effects of high soil water content and soil temperature on soil respiration. With an automatic system, soil respiration, soil water content, and soil temperature at 5-cm depth were measured at 10-min intervals for 22 days. The measurements were carried out at three locations with high soil water content and soil temperature. Results showed that soil respiration and soil water content were negatively correlated (P < 0.01); rainfall did not stimulate any obvious pulse of soil respiration. There was an obvious hysteresis effect between soil respiration and soil temperature. Without considering the hysteresis effect, the temperature dependence parameter (q(10)) of soil respiration on soil temperature was underestimated. With the consideration of the hysteresis effect between soil temperature and soil respiration, the estimated q(10) values were in the range of 1.2 to 2.1, and the estimated basal respiration values were in the range of 0.5 to 2.5 mu mol m(-2) sec(-1) for the three measurement points. Based on more than 2,200 data points, reasonable relationships in the diurnal scale were established between soil respiration and soil water content, as well as soil temperature. The relationships should be useful to estimate soil respiration based on soil temperature and moisture data.

Soil water content, maize yield and its stability as affected by tillage and crop residue management in rainfed semi-arid highlands

Rainfed crop management systems need to be optimized to provide more resilient options to cope with projected climatic scenarios forecasting a decrease in mean precipitation and more frequent extreme drought periods in Mexico. Soil water content (0–60 cm) was measured during three crop cycles in maize plots with different agronomic management practices in a long-term rainfed experiment (established in 1991) in the highlands of Mexico. Maize yields of 1997–2009 were reported. Crop management practices varied in (1) tillage (conventional [CT] vs. zero tillage [ZT]) and (2) residue management (full or partial retention and removal). ZT with residue retention had higher soil water content than management practices involving CT and ZT with residue removal which provided a buffer for drought periods during the growing seasons. In 2009, a cycle with a prolonged drought during vegetative growth, this resulted in yield differences of up to 4.7 Mg ha−1 between ZT with (partial) residue retention and the other practices. Averaged over 1997–2009, these practices had a yield advantage of approximately 1.5 Mg ha−1 over practices involving CT and ZT with residue removal. ZT with (partial) residue retention used rainfall more efficiently and resulted in a more resilient agronomic system than practices involving either CT or ZT with residue removal.

Runoff estimation in southern Brazil based on Smith's modified model and the Curve Number method

► We model surface runoff for different soil classes and management system. ► Runoff can be estimated based on rainfall intensity , land slope and soil porosity . ► The Smith's modified model estimates runoff for no-tillage management system. ► Curve Number overestimates the cumulative runoff for no-tillage management system. The objective of this work was to measure and model the runoff for different soils classes at different rainfall intensities (30, 60 and 120 mm h −1 ) in Southern Brazil. A portable rainfall simulator with multiple nozzles was used to simulate these rainfall intensities. For each soil, the initial time and runoff rate, rainfall characteristics (total, duration and intensities), surface slope, crop residue amount and cover percentage, soil densities (bulk and particle), soil porosity (bulk, macro and micro), textural fractions (clay, silt and sand), and the initial and saturated soil water content were measured. The runoff measured was compared to Smith's modified and Curve Number (USDA-SCS) models. The cumulative runoff losses were 67, 45 and 27% of the total rainfall, for a Rhodic Paleudalf, Typic Quartzipsamment and Rhodic Hapludox, respectively. An inverse relationship was observed between initial runoff and the runoff rate, independently of the soil surface and rainfall conditions. Increasing rainfall intensity decreased the time to runoff and increased runoff rate. The Smith's modified model overestimated the cumulative runoff by about 4%. The Smith's modified model presented a better estimate for both higher and lower rainfall intensities (120 and 30 mm h −1 ). The SCS Curve Number model overestimated the cumulative runoff by about 34%. This large overestimate is probably due to that the model did not take into account the soil tillage system used in the field by farmers, particularly for irrigated conditions. The combination of high porosity, low bulk density and presence of crop residue on soil surface decreased runoff losses, independently of the soil texture class. Smith's modified model better estimated the surface runoff for soil with a high soil water content, and it was considered satisfactory for Southern Brazil runoff estimations. The SCS Curve Number model overestimated the cumulative runoff and its use needs adjustments particularly for no-tillage management system.

Effects of soil water and nitrogen supply on the photosynthetic characteristics of &lt;I&gt;Jatropha curcas&lt;/I&gt; seedlings

Aims Jatropha curcas is a drought-resistant perennial that can be used for bio-energy to replace petro-diesel. However, J. curcas is still a wild plant and basic agronomical properties are not thoroughly understood. When it is grown in commercial plantations with regular irrigation, we do not know how J. curcas will respond to changes in the environment. Our objective was to evaluate the effects of different soil water and nitrogen supplies on the photosynthesis characteristics of J. curcas seedlings. Methods We exposed seedlings of J. curcas to three watering regimes (80%, 50% and 30% of field water holding capacity (FC)) and two nitrogen (N) regimes (with or without N-fertilization) and determined how N-fertilization affects the photosynthetic light and CO2 response curve, maximal quantum yield of PSII, and N and pigments contents under different soil water conditions. Important findings With N-fertilization, we detected significant increases in apparent quantum yield (AQY), light compensation point (LCP), maximum net photosynthetic rate (Pmax), carboxylation efficiency (CE), photorespiration rate (Rp), dark respiration rate (Rd) and nitrogen content with the increase of soil water content. Highest values of photosynthesis parameters occurred with 80% FC with N-fertilization. Without N-fertilization, all photosynthesis parameters had the opposite trends with the increase of soil water content. Furthermore, with 30% FC the nitrogen content of seedlings with N-fertilization was significantly higher than without N-fertilization. AQY, PSII maximum photochemical efficiency (Fv/Fm) and chlorophyll and carotenoids contents was nearly the same with and without N-fertilization, but other parameters were significantly lower without N-fertilization. Thus, under N-poor soil condition J. curcas grew better under the relatively low soil water conditions and photosynthesis of J. curcas was impacted by high soil water content. While with N-fertilization, J. curcas performed better under high soil water content.

A change of soil properties and forest vegetation present in burned areas in Geyjoksan, Daejeon metropolitan city

This study was conducted to investigate changes on burned areas after a forest fire in Geyjoksan which occurred in April 2000. Both soil physicochemical properties and vegetation present were analyzed in burned and unburned sites of pinus densiflora according to two slope aspects(south and north-facing slopes). The results of the analysis are as follows. The appearance species of vegetation were 21, 15 and 18 for burned site, burned site-1 and burned site-2 of pinus densiflora community respectively, indicating that the occurrence of forest fire and slope aspects affect vegetation appearance. The pH values at 0~10cm soil depth of unburned and burned sites of pinus densiflora community were 5.04 and 5.12 respectively with no significant difference between them. Mean organic matter, total nitrogen and available P also had no significant difference. This results indicate that the forest recover its former pH, total nitrogen, mean organic matter and available P over time after a forest fire. North-facing slope had relatively higher soil water content thus implying that its pH values of soil lower than south-facing slope. On the other hand, south-facing slope had high organic matter and available P content of soil as compared to north-facing slope. With south facing slope having high water contents, humus was accumulated due to slow organic matter decomposition. The pH values also decreased due to organic acids from humus. However, we observed that organic matter and P concentration in soil increased.

Study on Carbon Flux of Littoral in XiangXi river During Water Discharge

Riparian ecosystems are an important transition zone between river ecosystem and the terrestrial ecosystems and play an important role in the global carbon cycle of terrestrial ecosystems. The study was carried out in littoral in XiangXi river, which was the larger tributary and nearest to the Three Gorges Dam. Gas exchange rates were measured to explore the main factors controlling the carbon flux of littoral in XiangXi river using chamber method during water discharge in 2011. The results showed that in the early of water discharge, net ecosystem exchange (NEE) of 165- 175 m a.s.l. was 2.17 ± 0.53 μmol m-2 s-1, which was markedly lower than that of over 175 m a.s.l. (-1.04 ± 0.62 μmol m- 2 s-1, P < 0.05). Total ecosystem respiration (TER) of 165-175 m a.s.l. was 3.21 ± 0.52 μmol m-2 s-1, which was little lower than that of over 175 m a.s.l. (3.79 ± 0.94 μmol m-2 s-1), but there was no statistically significant difference (P > 0.05). The study indicated that being experienced flooding, the lower areas in littoral of the main stream of Xiangxi river might be a weak carbon source due to lower vegetation cover, higher soil water content and different soil microbial in the early of water discharge.

Factors influencing presence–absence of oak (Quercus spp.) seedlings after conservation-oriented partial cutting of high forests in Sweden

We studied occurrence of oak seedlings (Quercus robur L. and Q. petraea Liebl.) in 11 semi-natural oak-rich temperate forests in south Sweden after partial cutting (mean harvest; 26% of basal area). Earlier studies show that canopy openness is positively correlated with oak seedling performance. We used 20 pairs of subplots in each forest, with and without oak seedlings and matched with respect to canopy openness, to analyse other factors associated with seedling establishment and growth. The height of the ground layer (herbs and woody plants) had negative influence, i.e. higher height was associated with reduced probability of seedling occurrence. Higher soil water content had positive influence on seedling occurrence. Protection of seedlings by e.g. Rubus spp., twigs or dead wood was associated with lower seedling occurrence, but seedlings that did establish there tended to be taller. Type of ground vegetation and species composition did not differ between subplots with and without oak seedling. Thus, after conservation-oriented partial cutting of closed canopy high forests, increasing height of the ground vegetation disfavours oak seedlings (independent of canopy openness). High soil moisture favours oak seedlings, as does protected microsites for seedlings that can maintain high growth rate among their competitors.

Imaging spectroscopy in soil-water based site suitability assessment for artificial regeneration to Scots pine

In a humid northern boreal climate, the success rate of artificial regeneration to Scots pine ( Pinus sylvestris L.) can be improved by including a soil water content (SWC) based assessment of site suitability in the reforestation planning process. This paper introduces an application of airborne visible-near-infrared imaging spectroscopic data to identify suitable subregions of forest compartments for the low SWC-tolerant Scots pine. The spatial patterns of understorey plant species communities, recorded by the AISA (Airborne Imaging Spectrometer for Applications) sensor, were demonstrated to be dependant on the underlying SWC. According to the nonmetric multidimensional scaling and correlation results twelve understorey species were found to be most abundant on sites with high soil SWCs. The abundance of bare soil, rocks and abundance of more than ten species indicated low soil SWCs. The spatial patterns of understorey are attributed to time-stability of the underlying SWC patterns. A supervised artificial neural network (radial basis functional link network, probabilistic neural network) approach was taken to classify AISA imaging spectrometer data with dielectric (as a measure volumetric SWC) ground referencing into regimes suitable and unsuitable for Scots pine. The accuracy assessment with receiver operating characteristics curves demonstrated a maximum of 74.1% area under the curve values which indicated moderate success of the NN modelling. The results signified the importance of the training set’s quality, adequate quantity (>2.43 points/ha) and NN algorithm selection over the NN algorithm training parameter optimization to perfection. This methodology for the analysis of site suitability of Scots pine can be recommended, especially when artificial regeneration of former mixed wood Norway spruce ( Picea abies L. Karst) - downy birch ( Betula pubenscens Ehrh.) stands is being considered, so that artificially regenerated areas to Scots pine can be optimized for forestry purposes.

Einfluss der Wurzeln auf das Wasserspeichervermögen hydromorpher Waldböden | Significance of roots for soil water storage capacity of hydromorphic forest soils

In this study we investigated the significance of roots for the water storage capacity of hydromorphic forest soils in the northern Pre-Alps of Switzerland. Irrigation experiments were conducted on 1 m2 plots with high initial soil water content. A total of 67 horizons were investigated for water content variations using time domain reflectometry (TDR). The data was processed using a physically based model, which assumes gravity-driven and viscosity-controlled water flow along pore walls in the form of thin water films. The model calculates the contact length (L) between mobile water and the stationary parts of the soil water system in the horizontal plane. L characterises porosity which is effectively involved in water flow. A multiple linear regression analysis of all investigated horizons, including root density, bulk density and texture as predictors for L, demonstrated that the root density had the best explanatory value for L (R2 = 0.63). Thus, it can be assumed that increases in root density increase water storage capacity. Considering the extent of hydromorphicity in horizons, the relationship between root density and contact length was only significant in topsoils and hydromorphic subsoils. An increase of root density by 50% in hydromorphic subsoils would increase short-time water storage capacity from 0.03 to 0.05 m3/m3, while higher root densities in topsoils did not increase water storage capacities. To improve the water retention potential of flood protection forests on hydromorphic soils, we suggest promoting deep-rooting species which are able to sustain anaerobic periods in soils.