Litter Removal Plots Research Articles

Soil moisture and plant growth responses to litter and defoliation impacts in Parkland grasslands

Soil moisture can limit plant production in cool-temperate grasslands, particularly under recent increases in drought severity and predictions of future climate change. This necessitates research that examines moisture mitigation strategies under the dominant land use of grazing. We examined the effectiveness of plant litter in regulating soil moisture dynamics and associated plant production in a native grassland and tame pasture in the Aspen Parkland of Alberta, Canada during 2007/2008, specifically testing (1) how litter and defoliation (as a surrogate for grazing) alter the micro-environment at the soil surface, (2) whether litter, in combination with defoliation, alters forage production, and (3) whether production changes can be linked to observed micro-environmental changes created by litter modification. The full factorial randomized complete block design consisted of three litter treatments (litter removal, in situ control, and double litter) and three defoliation treatments (undefoliated control, light defoliation to 6.5 cm stubble height, and heavy defoliation to 2.5 cm). Soil moisture levels were assessed over four periods after summer precipitation to examine soil moisture depletion. Plant phenological development and canopy cover were also assessed throughout 2007, and biomass was measured in August 2007 and 2008. Abundant litter (up to 14,000 kg ha −1) improved soil moisture levels in both native and tame grasslands by either maintaining higher absolute moisture levels or reducing total moisture loss after rainfall. Both litter removal and double litter reduced total growing season production compared to in situ levels at the Native Site, despite highest vegetation cover in litter removal plots. High litter levels also improved growth of individual grass tillers at this site, but negatively impacted sexual production. Conversely litter removal improved overall production at the Tame Site, although litter did enhance grass tiller recovery following mid-season defoliation at both sites, in part due to positive influences on soil moisture. Treatment effects on plant production were less pronounced in 2008 than in 2007. Overall, high litter levels improve soil moisture retention and can improve or stabilize plant production particularly in native prairie sites, and can provide an important drought management strategy in the Aspen Parkland.

Soil mono- and disaccharides and amino acids as influenced by plant litter and root processes in a subtropical moist forest of southwest China

Soil mono- and disaccharides (SS) and total free amino acids (AA) can influence soil microbial activities, whether they are derived from decomposition of organic materials or from plant root exudates. To quantify the relative importance of aboveground plant litter input and belowground inputs of root exudates and root debris on SS and AA, we conducted litter removal, root trenching and tree girdling experiments in a subtropical moist forest of southwest China. We found that concentrations of SS and AA had pronounced seasonal fluctuations. Litter removal markedly reduced SS concentrations, but it had no effect on AA concentrations. Concentrations of SS were significantly correlated with litterfall that had occurred 2 months earlier in the control plots, but that correlation was not observed in the litter removal plots. Multiple-linear regressions of soil respiration and soil temperature on AA concentrations were significant in both control and litter removal plots, but not in the root trenching or tree girdling plots. These results suggest that SS levels are likely to be regulated by aboveground plant litter input, and concentrations of AA are affected by microbial activity that fluctuates with soil temperature and belowground carbon input.

Responses of a California annual grassland to litter manipulation

AbstractQuestion:What are the physical and chemical effects of plant litter on annual grassland community composition, above‐ground net primary production (ANPP), and density?Location:California annual grassland.Methods:We manipulated litter and light levels independently and in concert. Litter removal and litter addition treatments tested both the physical and chemical impacts of litter's presence. We additionally simulated the effect of litter physical shading by using shade cloth, and added powdered litter to test for the chemical impacts of decomposing litter.Results:Increased whole litter and shading decreased grass germination and establishment, but not that of forbs or legumes. Species shifts occurred within all groups across treatments, including a transition from small‐seeded to large‐seeded grass and legume species with increased shading. ANPP was highest in control plots (473 ± 59 g/m2), and species richness was highest in litter removal plots. While the physical effects of litter via shading were significant, the chemical effects of adding powdered litter were negligible.Conclusions:This work suggests that over one growing season, the physical impacts of litter are more important than chemical impacts in shaping community structure and ANPP in annual grasslands. Changes in light availability with altered litter inputs drive shifts in species and functional group composition. Litter feedbacks to ANPP and species composition of local patches may help maintain diversity and stabilize ANPP in this grassland.

Increased Litterfall in Tropical Forests Boosts the Transfer of Soil CO2 to the Atmosphere

Aboveground litter production in forests is likely to increase as a consequence of elevated atmospheric carbon dioxide (CO2) concentrations, rising temperatures, and shifting rainfall patterns. As litterfall represents a major flux of carbon from vegetation to soil, changes in litter inputs are likely to have wide-reaching consequences for soil carbon dynamics. Such disturbances to the carbon balance may be particularly important in the tropics because tropical forests store almost 30% of the global soil carbon, making them a critical component of the global carbon cycle; nevertheless, the effects of increasing aboveground litter production on belowground carbon dynamics are poorly understood. We used long-term, large-scale monthly litter removal and addition treatments in a lowland tropical forest to assess the consequences of increased litterfall on belowground CO2 production. Over the second to the fifth year of treatments, litter addition increased soil respiration more than litter removal decreased it; soil respiration was on average 20% lower in the litter removal and 43% higher in the litter addition treatment compared to the controls but litter addition did not change microbial biomass. We predicted a 9% increase in soil respiration in the litter addition plots, based on the 20% decrease in the litter removal plots and an 11% reduction due to lower fine root biomass in the litter addition plots. The 43% measured increase in soil respiration was therefore 34% higher than predicted and it is possible that this ‘extra’ CO2 was a result of priming effects, i.e. stimulation of the decomposition of older soil organic matter by the addition of fresh organic matter. Our results show that increases in aboveground litter production as a result of global change have the potential to cause considerable losses of soil carbon to the atmosphere in tropical forests.

Moisture and substrate availability constrain soil trace gas fluxes in an eastern Amazonian regrowth forest

Changes in land‐use and climate are likely to alter moisture and substrate availability in tropical forest soils, but quantitative assessment of the role of resource constraints as regulators of soil trace gas fluxes is rather limited. The primary objective of this study was to quantify the effects of moisture and substrate availability on soil trace gas fluxes in an Amazonian regrowth forest. We measured the efflux of carbon dioxide (CO2), nitric oxide (NO), nitrous oxide (N2O), and methane (CH4) from soil in response to two experimental manipulations. In the first, we increased soil moisture availability during the dry season by irrigation; in the second, we decreased substrate availability by continuous removal of aboveground litter. In the absence of irrigation, soil CO2 efflux decreased during the dry season while irrigation maintained soil CO2 efflux levels similar to the wet season. Large variations in soil CO2 efflux consistent with a significant moisture constraint on respiration were observed in response to soil wet‐up and dry‐down events. Annual soil C efflux for irrigated plots was 27 and 13% higher than for control plots in 2001 and 2002, respectively. Litter removal significantly reduced soil CO2 efflux; annual soil C efflux in 2002 was 28% lower for litter removal plots compared to control plots. The annual soil C efflux:litterfall C ratio for the control treatment (4.0–5.2) was consistent with previously reported values for regrowth forests that indicate a relatively large belowground C allocation. In general, fluxes of N2O and CH4 were higher during the wet season and both fluxes increased during dry‐season irrigation. There was no seasonal effect on NO fluxes. Litter removal had no significant impact on N oxide or CH4 emissions. Net soil nitrification did not respond to dry‐season irrigation, but was somewhat reduced by litter removal. Overall, these results demonstrate significant soil moisture and substrate constraints on soil trace gas emissions, particularly for CO2, and suggest that climate and land‐use changes that alter moisture and substrate availability are therefore likely to have an impact on atmosphere chemistry.

Effect of litter removal on species richness and acidification of a mixed oak-pine woodland

Eutrophication of woodland ecosystems and disappearance of acidophilous species have often been observed in central and western Europe over recent decades. Considerable increase in air-borne nitrogen and sulphur has been invoked as responsible for these processes in most studies. Historic data indicate that for hundreds of years man removed litter and fodder from many woodlands in these areas. As a result, woodland soils became poorer and more acid than they were originally. Cessation of the removal of materials may resulted in soil enrichment and eutrophication of many woods. This hypothesis was tested in a 16-year litter removal experiment in an acidophilous mixed oak–pine wood in southern Poland. It was found that litter removal resulted in substantial impoverishment of soil. After 16 years soil of the litter removal plots contained significantly less P, Mg and Ca, and had a lower cation exchange capacity (CEC) in the epihumus subhorizon, and less Ca and a lower CEC in the humus and lessivage horizons than soil in the control plots. Vascular plant species and bryophytes colonized the litter removal plots much more frequently. Within 16 years species richness increased in the field layer of these plots, but abundance of dominant species and character of vegetation remained unchanged, while vegetation of the control plots changed from acidophilous to neutrophilous. Disappearance in the control plots of vascular plants species and mosses common in mixed woodlands was caused by thick litter layer which impeded seed germination and seedling development, and by competition of dominant species. The results obtained suggest that acidophilous vegetation in the field layer of the study wood was associated with material removal by man over a long time, and its eutrophication largely resulted from the cessation of traditional methods of management.

Microbial biomass and nitrogen cycling responses to fertilization and litter removal in young northern hardwood forests

The influence of site fertility on soil microbial biomass and activity is not well understood but is likely to be complex because of interactions with plant responses to nutrient availability. We examined the effects of long-term (8 yr) fertilization and litter removal on forest floor microbial biomass and N and C transformations to test the hypothesis that higher soil resource availability stimulates microbial activity. Microbial biomass and respiration decreased by 20–30 % in response to fertilization. Microbial C averaged 3.8 mg C/g soil in fertilized, 5.8 mg C/g in control, and 5.5 mg C/g in litter removal plots. Microbial respiration was 200 µg CO2-C g−1 d−1 in fertilized plots, compared to 270 µg CO2-C g−1 d−1 in controls. Gross N mineralization and N immobilization did not differ among treatments, despite higher litter nutrient concentrations in fertilized plots and the removal of substantial quantities of C and N in litter removal plots. Net N mineralization was significantly reduced by fertilization. Gross nitrification and NO3− immobilization both were increased by fertilization. Nitrate thus became a more important part of microbial N cycling in fertilized plots even though NH4+ availability was not stimulated by fertilization.

Ectomycorrhizal root growth in scots pine stands in response to manipulation of litter and humus layers

The effect on ectomycorrhizal root growth in a nitrogen-enriched planted stand of Scots pine (Pinus sylvestris L.) on podzolic sandy soil to manipulation of litter and humus layers (removal, doubling and control treatments) was examined, and compared to ectomycorrhizal root growth in an untreated naturally established Scots pine stand on nutrient-poor non-podzolic sandy soil. Half a year after manipulation of litter and humus layers in the planted stand, ingrowth-cores to a depth of 60 cm were installed in both stands. Scots pine roots were sampled four times during two growing seasons. Ectomycorrhizal roots were found at all sampled soil depths to 60 cm in all plots. Root growth and ectomycorrhizal development were greater in the naturally established stand than in all plots in the planted stand. Numbers of ectomycorrhizal root tips in the litter and humus removal plots were generally higher than in the control plots in the planted stand until May 1992. Doubling litter and humus did not significantly affect root length or the numbers of ectomycorrhizal root tips. The N dissolved , NH4 + and NO3 – concentrations and the organic matter content in the upper 5 cm of the mineral soil in the planted stand on podzolic sandy soil were generally higher and the pH significantly lower than in the naturally established stand on non-podzolic sandy soil. Root growth and ectomycorrhizal development in the secondary stand may have been negatively affected by the chemical composition of the podzolic sandy soil.

Effects of litter removal on the germination of Anemone nemorosa L.

In a recent article, Eriksson (1995) showed high germination rates in Anemone nemorosa . To check whether ERIKSSON'S results are also valid in Central Europe, a litter removal experiment was carried out in Northeastern Switzerland. In both experimental series, litter removal plots and control plots, high germination of A. nemorosa occured. Nevertheless, litter removal greatly enhanced germination of A. nemorosa . A significant correlation between seedling number and ramet density within the plots pointed to a dominance of very local dispersal. These facts lead to the hypothesis that reproduction by seeds in A. nemorosa as well as vegetative reproduction by clonal growth are of great importance for the maintenance of populations of this species. Surprisingly, no successful germination of A. nemorosa was detected in seed bank investigations.

Tree litter and the lower limits of subalpine herbs and grasses in the Brindabella Range, ACT

Abstract Herbs and grasses form a dense understorey in subalpine woodlands dominated by Eucalyptus pauciflora but are absent from stands of Eucalyptus dives immediately down slope. We hypothesized that a relatively high rate of litter accumulation beneath E. dives was responsible for the downward limit of subalpine plants. We tested this hypothesis by removing litter and by adding E. dives litter to plots in both forest types during two growing seasons. Litter accumulation rates were 50% higher under E. dives than E. pauciflora, but understorey bio‐mass in control plots was eight times higher under E. pauciflora than E. dives. After the first growing season, seedling densities in both forest types were significantly higher in plots from which litter had been removed but, after the second growing season, understorey biomass was not higher in litter removal plots. The results indicate that litter has the potential to limit germination in both forest types, but that environmental filters other than litter subsequently limit recruitment and are ultimately responsible for the lower distributional limits of subalpine herbaceous species.

Water stress in longleaf pine induced by litter removal

Forest litter layer acts as a nutrient pool to support future growth of trees and as a blanket which intercepts and absorbs rainfall and insulates soil from evaporative water loss. Litter disturbance can modify either of these functions. Soil moisture content and xylem pressure potential were determined in a longleaf pine plantation for 7 weeks following litter removal. Two weeks following treatment, xylem pressure potential of trees in control, red straw removal and total litter removal plots diverged. Trees in the total litter removal plot had the lowest xylem pressure potential (i.e. most stressed), control trees had the highest xylem pressure potential, and trees in the red straw removal plot were intermediate. Differences in xylem pressure potential among treatments were consistent throughout the season, regardless of precipitation or drought. Soil moisture content also showed different patterns based on the particular litter removal treatment. Differeces in soil water content and xylem pressure potential could explain observed growth reductions of trees in plantations where litter had been removed. Therefore consideration of the potential modification of both the hydrologic and nutrient cycles should be made prior to litter removal.