Forest Floor Water Research Articles

Mixed plantation regulates forest floor water retention and temperature sensitivity in restored ecosystems on the Loess Plateau, China

Ongoing warming and frequent extreme rainfall are endangering hydrological functioning in reforested ecologically vulnerable areas. The forest floor plays an important role in water conservation; however, knowledge of water retention of forest floor and its temperature sensitivity under climate change remains limited particularly in restored ecosystems. Here, we investigated and sampled litter and topsoil from three monoculture plantations, two mixed plantations, and one natural grassland on the hilly and gullied Loess Plateau. We used an artificial climate incubator to simulate different climate conditions and measure the effects on litter and topsoil water retention. Generalized additive models were used to explore the relationships between temperature sensitivity of water-retention capacity and influencing factors. The results showed that mixed plantations shortened the water retention time of litter and topsoil. In addition, mixed plantations significantly improved the maximum water-holding capacity of litter, but reduced the maximum water-holding capacity of topsoil. Litter water-retention capacity temperature sensitivity (LTS) was significantly greater than that of soil (STS). Moreover, communities with strong LTS generally had weak STS. Nonetheless, mixed plantations tend to have a more stable forest floor water-retention capacity. Soil porosity, bulk density, litter mass, and canopy openness were the key factors affecting the maximum water-holding capacity and water-retention capacity of forest floors. Overall, our results indicated that mixed plantations adjusted the water retention time of the forest floor and had a more stable water-retention capacity, which was of great significance for plantation management in arid and semi-arid regions.

Impact of Phytophthora agathidicida infection on canopy and forest floor plant nutrient concentrations and fluxes in a kauri-dominated forest.

Kauri dieback, caused by Phytophthora agathidicida, is a biotic disturbance that poses a recent threat to the survival of kauri (Agathis australis) forests in New Zealand. Previous studies have shown that throughfall and stemflow play an important role in the kauri forests’ internal nutrient cycle. However, the effects of P. agathidicida infection on canopy and forest floor nutrient fluxes in kauri forests remain unknown. Here, we measured throughfall, stemflow and forest floor water yield, nutrient (potassium, calcium, magnesium, manganese, silicon, sulfur, sodium, iron) concentrations and fluxes of ten kauri trees differing in soil P. agathidicida DNA concentration, and health status. We did not observe an effect of soil P. agathidicida DNA concentration on throughfall, stemflow, and forest floor water yield. Throughfall and forest floor nutrient concentrations and fluxes decreased (up to 50%) with increasing soil P. agathidicida DNA concentration. We found significant effects on potassium and manganese fluxes in throughfall; calcium and silicon fluxes in forest floor leachate. A decline in canopy and forest floor nutrient fluxes may result in soil nutrient imbalances, which in turn may negatively impact forest productivity and may increase the susceptibility of trees to future pathogen infection in these ecologically unique kauri forests. Given our findings and the increasing spread of Phytophthora species worldwide, research on the underlying physiological mechanisms linking dieback and plant–soil nutrient fluxes is critical.

Mixed Plantation Regulates Forest Floor Water Retention and Temperature Sensitivity in Restored Ecosystems

Mixed Plantation Regulates Forest Floor Water Retention and Temperature Sensitivity in Restored Ecosystems

Predicting Urea Hydrolysis in a Loblolly Pine Forest Floor

In a pine forest, urea hydrolysis rates can vary widely. The rate of urea hydrolysis is controlled by the amount of urease enzyme, temperature, pH, urea concentration, but at the soil surface, soil water potential is an especially critical factor because it may vary widely in short periods of time due to precipitation, dews, and rapid evaporation. The objective of this study was to describe the quantitative relationship between soil water and urea hydrolysis rates in a loblolly pine (Pinus taeda L.) forest floor. Hydrolysis rates were measured in a pine forest with time after urea was applied in seven studies performed at different times that varied widely in soil water content and temperature. Separately in a laboratory study, the urea hydrolysis rates were measured in pine needles and in the humified layer at different water potentials. Results showed that although well‐defined relationships were found between urea hydrolysis rates and forest floor water potentials, the urea hydrolysis rates measured in the field could not be predicted based on these relationships and the water potential of the forest floor pine needles at the time of urea application. However, the percent of urea hydrolyzed at 3 and 29 d could be predicted accurately from the initial water potential of new needles and an interaction between initial water potential and relative humidity days.

Forest floor properties across sharp compositional boundaries separating trembling aspen and jack pine stands in the southern boreal forest

Jack pine and trembling aspen are two early-seral boreal tree species with contrasting nutrient cycling strategies. Both species may form adjacent mono-specific stands separated by sharp compositional boundaries. We hypothesized that such boundaries result in wider functional ecotones. Spatial transitions in humus forms, forest floor chemistry and microbial communities were assessed across 32 m long transects set perpendicular to sharp compositional boundaries separating four jack pine and aspen stands. Split moving window analysis (SMWA) and moving window regression analysis (MWRA) were used to locate functional boundaries and ecotones. We found a gradual transition from moder (aspen) to mor (jack pine) humus spanning 16 m across the compositional boundary. An abrupt increase in forest floor water content at 3 m within jack pine stands was possibly due to aspen roots foraging for water beyond the boundary. The functional boundary and associated ecotone for forest floor pH, C:N ratio, Mg and ammonification were skewed toward jack pine stands, likely the result of aspen leaf dispersal. Low nitrification rates throughout jack pine stands and up to 11 m into aspen stands suggested that jack pine roots might extend far within aspen stands and produce metabolites that suppress nitrification. SMWA performed on the multivariate dataset of microbial fatty acids (FAs) revealed three distinct forest floor microbial communities that were skewed toward jack pine stands. Pine-type communities were associated to fungal FAs, pine-type and transition-type communities to non-fungal eukaryotic FAs, and aspen-type communities to bacterial FAs. Taken collectively, our data delimit a 24 m wide functional ecotone straddling sharp compositional boundaries separating trembling aspen and jack pine stands. We conclude that the functional diversity of boreal landscapes, where adjacent mono-specific stands are prevalent, is related to the patchiness of the landscape.

A hillslope forest floor (duff) water budget and the transition to local control

AbstractThe partially decomposed organic layer (duff: F and H layers) of the forest floor is an important boundary between the soil and atmospheric processes. Here we use both empirical data and a three‐dimensional coupled heat and water budget model to explain the duff hydrological hillslope shift between very brief wet periods when lateral flow in the duff and infiltration into the mineral soil occur and dry periods when evaporative flow dominates and both lateral and mineral soil flow are not important. The duff moisture transitions from wet to dry periods were the result of low lateral flow which moves liquid and water vapour only centimetres to metres, very rapidly and mostly in the H layer immediately after precipitation. During wet periods, the net lateral fluxes were negative on divergent areas and positive on convergent areas of the hillslope, leading to a net moisture loss in divergent areas and a net gain in convergent areas. The response to lateral flow in the H layer was more rapid than in the F layer. The transition from the lateral downwards flow to mineral soil to evaporative control was within approximately 48 h of precipitation. Canopy species and aspect were important with lodgepole pine, southwest aspect and 4‐cm deep duff controlled by evaporative processes while Engelmann spruce, northeast aspect and 30‐cm duff were more controlled by hillslope redistribution processes. Copyright © 2010 John Wiley & Sons, Ltd.

Characteristics of the forest floor water retention in the Carpathian experimental catchment basin of the Trzebuńka brook

Characteristics of the forest floor water retention in the Carpathian experimental catchment basin of the Trzebuńka brook

Isotopic assessment of NO3− and SO42− mobility during winter in two adjacent watersheds in the Adirondack Mountains, New York

Biogeochemical cycling of N and S was examined at two watersheds in the Adirondack Mountains, New York, to better understand the retention and loss of these elements during winter and spring snowmelt. We analyzed stable isotope compositions of NO3− (δ15N‐NO3−, δ18O‐NO3−) and SO42− (δ34S‐SO42−, δ18O‐SO42−), along with concentrations and fluxes of NO3− and SO42−, in precipitation, throughfall, snowpack, snowmelt, soil water, groundwater, and stream water. Isotopic results showed no evidence of NO3− and SO42− transformations in the forest canopy and snowpack; however, markedly decreased δ18O values of NO3− and SO42− in forest floor water suggest that microbial processing occurred in organic soil horizons. Similarly low δ18O values of NO3− and SO42− were observed in forest floor and mineral soil leachates, groundwater, and streams. Over the winter observation period, most of the NO3− and SO42− in stream water was from a watershed‐derived source, whereas atmospheric contributions were relatively minor. Despite differences in soil water NO3− concentrations between watersheds, the isotopic composition of NO3− (δ15N‐NO3−, δ18O‐NO3−) was similar, and indicated that in both watersheds most of the NO3− was produced by nitrification in the forest soils. Although there was likely some contribution of SO42− from microbial oxidation of carbon‐bonded sulfur, most of the stream water SO42− appeared to be derived from weathering of S‐containing bedrock or parent material. The decreased δ18O values of NO3− and SO42− in upper soil horizons indicate that atmospheric deposition of N and S was not directly linked with stream water losses, even during winter and spring snowmelt.

Linking Foliar Chemistry to Forest Floor Solid and Solution Phase Organic C and N in Picea abies [L.] Karst Stands in Northern Bohemia

Dissolved organic carbon and nitrogen (DOC and DON) produced in the forest floor are important for ecosystem functions such as microbial metabolism, pedogenesis and pollutant transport. Past work has shown that both DOC and DON production are related to litterfall and standing stocks of C and N in the forest floor. This study, conducted in spring, 2003, investigated variation in forest floor water extractable DOC (WEDOC) and DON (WEDON) and forest floor C and N as a function of lignin, cellulose and N contained in live canopy foliage across eight Picea abies [L.] Karst stands in northern Bohemia. Based on Near Infrared Spectroscopy (NIR) analysis of foliar materials, lignin:N and cellulose:N content of the youngest needles (those produced in 2002) were positively and significantly related to WEDOC (R 2 = 0.82–0.97; P<0.01) and to forest floor C:N ratio (R = 0.72–0.78; P<0.01). Foliar N was strongly and negatively related to WEDOC and C:N ratio (R = −0.91 and 0.72; P<0.05) among our study sites. WEDON was positively correlated to foliar lignin:N (R = 0.48; P<0.05; n=40). Forest floor C pools were not positively correlated with foliar lignin and cellulose and forest floor N pools were not positively correlated with foliar N. Instead, a significant negative correlation was found between forest floor N pools and foliar cellulose (R=−0.41; P<0.05), and between forest floor C pools and foliar N (R = −0.44; P<0.05). From a remote sensing standpoint, our results are important because canopy reflectance properties are primarily influenced by the most recent foliage, and it was the chemistry of the most recently produced needles that showed a stronger relationship with forest floor WEDOC and C:N ratio suggesting forest floor production of WEDOC can be calculated regionally with remote sensing.

Spatial variability of throughfall water and chemistry and forest floor water content in a Douglas fir forest stand

Abstract. This study focuses on spatial variability of throughfall water and chemistry and forest floor water content within a Douglas fir (Pseudotsuga menziesii, Franco L.) forest plot. Spatial patterns of water and chemistry (NH4+, NO3‾, SO42-, Cl‾, Mg2+, Ca2+, Na+ and K+) were compared and tested for stability over time. The spatial coefficient of variation (CV) was between 18 and 26% for amounts of throughfall water and ions, and 17% for forest floor water content. Concentrations and amounts of all ions were correlated significantly. Ion concentrations were negatively correlated with throughfall water amounts, but, except for NH4+, there was no such relation between throughfall water and ion amounts. Spatial patterns of throughfall water fluxes and forest floor water contents were consistent over time; patterns of ion fluxes were somewhat less stable. Because of the spatial variability of forest floor thickness and drainage, it was not possible to relate patterns in throughfall water directly to patterns in water content. The spatial variability of throughfall nitrogen and forest floor water contents can cause significant variability in NO3‾ production within the plot studied. Keywords: nutrient throughfall, forest floor water, spatial variability, time-stability, nitrogen

Dynamic nitrogen deposition thresholds during forest stand development in a Douglas fir forest analysed with two nitrogen models SMART2 and MERLIN

Abstract. This study focuses on spatial variability of throughfall water and chemistry and forest floor water content within a Douglas fir (Pseudotsuga menziesii, Franco L.) forest plot. Spatial patterns of water and chemistry (NH4+, NO3‾, SO42-, Cl‾, Mg2+, Ca2+, Na+ and K+) were compared and tested for stability over time. The spatial coefficient of variation (CV) was between 18 and 26% for amounts of throughfall water and ions, and 17% for forest floor water content. Concentrations and amounts of all ions were correlated significantly. Ion concentrations were negatively correlated with throughfall water amounts, but, except for NH4+, there was no such relation between throughfall water and ion amounts. Spatial patterns of throughfall water fluxes and forest floor water contents were consistent over time; patterns of ion fluxes were somewhat less stable. Because of the spatial variability of forest floor thickness and drainage, it was not possible to relate patterns in throughfall water directly to patterns in water content. The spatial variability of throughfall nitrogen and forest floor water contents can cause significant variability in NO3‾ production within the plot studied. Keywords: nutrient throughfall, forest floor water, spatial variability, time-stability, nitrogen

Forest floor water dynamics and root water uptake in four forest ecosystems in northwest Amazonia

A common feature in the undisturbed forest ecosystems in the Middle Caquetá (Colombian Amazonia) is the presence of a thick litter layer with abundant fine roots over mineral soils which are highly weathered and very low in available nutrients. In these situations, the litter layer or the forest floor (FF) may play an important role in the forest water balance, controlling water fluxes and nutrient cycling. We investigated the forest floor water dynamics in four representative forest ecosystems in the Middle Caquetá, Colombian Amazonia (tertiary sedimentary plain, high terrace, low terrace and the rarely inundated flood plain). Meteorological conditions were measured on hourly basis, FF water storage capacity, TDR water content in the FF and litterflow or FF drainage were measured daily over a two year period. A dynamic model was developed to simulate FF water storage, root water uptake and drainage to the mineral soil. The four-parameter model was calibrated applying a step-wise procedure. Analysis of collected data showed that FF water content was generally lower in the sedimentary plain than in the other ecosystems, whereas FF water storage was the highest due to a high FF mass. The average storage capacity per unit FF thickness was 1.23 mm cm −1. The sensitivity analysis and calibration of model parameters highlighted the relevance of storage capacity as the most sensitive parameter for the FF water dynamics. For the validation period, there is a good agreement between predicted and measured FF water storage and especially between predicted total drainage from the forest floor and measured litterflow. Model predictions indicate that water uptake from the FF’s during the validation period (190 days) differed between ecosystems, ranging from 15 to about 28% of the reference transpiration. This seems to be related to the fraction of fine roots in the FF in each ecosystem and to the water availability. On the other hand, total drainage to the mineral soil was very similar among ecosystems, except for the sedimentary plain, where total drainage was the lowest with about 87% of incoming throughfall.

Plot-scale spatial patterns of soil water content, pH, substrate-induced respiration and N mineralization in a temperate coniferous forest

Samples of two perpendicular transects from an even-aged Norway spruce ( Picea abies) forest were used for geostatistical analysis of forest floor water content (WC), pH, substrate-induced respiration (SIR, a measure of microbial biomass), and N mineralization (Nmin). Nmin data did not fulfil the stationarity assumptions of geostatistics and had to be detrended prior to analysis. All variables exhibited spatial structure. The degree of spatial dependence was generally high (60%–95%). pH and SIR were isotropically distributed; WC and Nmin were anisotropic. Three different scales of spatial variability were detected at the site. (1) A fine-scale pattern with ranges <1 m that was attributed to retarded decomposition, poor chemical and structural diversity of P. abies litter, and lacking bioturbatic activity of earthworms. (2) A mesoscale pattern was indicated by sinoidal periodicity of most variograms, with inflection points every 1.0–1.5 m. This periodicity probably reflected the influence of regularly spaced tree individuals. (3) Nmin and WC exhibited unexplained long-range trends that exceeded transect length.

Forest floor water content dynamics in a Douglas fir stand

Abstract This paper considers the hydrology of the forest floor within a homogeneous Douglas fir forest. Time domain reflectometry measurements show that forest floor water contents have considerable spatial variabilities but similar temporal dynamics. Simple linear relations can be used to translate forest floor water content dynamics from one site in a forest to another. Forest floor evaporation rates were calculated using a previously developed forest floor evaporation model and a year of soil water and micrometeorological data. For a relatively wet site within the stand the calculated evaporation rate was 137 mm year−1, for a more representative site 112 mm year−1 and for a dry site 76 mm year−1. These amounts range between 7 and 13% of the total yearly forest evapotranspiration. Together with throughfall rates and transpiration rates, these forest floor evaporation rates served as boundary conditions to a soil water model with which we simulated forest floor and mineral soil water content dynamics. The simulations showed that throughfall and drainage dynamics determine the forest floor water content dynamics in wet conditions. In dry periods, forest floor evaporation and, to a lesser extent, root water uptake determine forest floor water content dynamics. The same simulations showed that 25% of the forest floor evaporation is replenished by capillary rise from the mineral soil.

Forest floor evaporation in a dense Douglas fir stand

Forest floor evaporation was measured with an accurate weighing lysimeter during 44 days in early spring and summer. The Penman–Monteith approach was used to model the evaporation rates as well as the temperature difference between forest floor surface and air at 1m height. Values of resistance parameters were slightly different when the Penman–Monteith model was optimized for measured evaporation rates or for measured temperature differences. These discrepancies were partly due to field variability in forest floor water contents but also because our approach considered the forest floor to be isothermal. With the appropriate parameter sets, the model was able to predict measured hourly forest floor evaporation rates and surface temperature dynamics satisfactorily.We show that in the forest discussed in this paper the Penman–Monteith ventilation term dominates over the available energy term. As a result the evaporation flux is matched by an almost equal, sensible heat flux but in opposite direction. Forest floor water content dynamics have a strong control over the evaporation flux. Spatial variability in forest floor water contents cause the 44-day average forest floor evaporation to range from 0.19mmd−1 in a dry part of the forest to 0.3mmd−1 in a wet part with 0.23mmd−1 as a site representative value. © 1997 Elsevier Science B.V.

Biodegradability of Dissolved Organic Matter in Forest Throughfall, Soil Solution, and Stream Water

AbstractHigh concentrations of dissolved organic matter (DOM) were leached into rainwater passing through the canopy and forest floor of an oak (Quercus spp.)‐hickory (Carya spp.) forest in the southern Appalachian Mountains. More than 95% of this dissolved organic C (DOC) and N (DON) was removed as water percolated through the soil profile and left the ecosystem in stream water. Our objective was to examine the importance of decomposition in the removal of DOC and DON. Samples of DOM from throughfall, forest floor water, soil water from A and B soil horizons, and stream water were all adjusted to a common initial DOC concentration, inoculated with soil and stream microbes, and incubated in solution for 134 d. In general, only 14 to 33% of the DOC in forest floor, soil solution, and stream samples decomposed during the incubation. The relative order of average decomposition of DOC from the various strata was, from fastest to slowest; throughfall, Oi horizon (forest floor), Oa horizon (forest floor), B horizon, stream, AB horizon, isolated fulvic acid, and upper A horizon. In short, biodegradability of DOM in the ecosystem profile declined vertically from throughfall to the A horizon and then increased with depth. The DON generally did not decay faster than the DOC — results consistent with the idea that hydrolysis of organic N is linked to mineralization of DOC rather than occurring selectively in response to the biochemical need for N. Throughfall DOM could be decomposed during its passage through the upper soil, but decomposition seems too slow to be responsible for the bulk of removal of DON and DOC that occurs in the mineral soil. Adsorption, rather than biodegradation, is more likely responsible for maintaining low DOC substrate concentrations in the mineral soil and preventing its loss into stream water.