Forest-alpine Tundra Ecotone Research Articles

The expansion of evergreen and deciduous shrubs changed the chemical characteristics and biological community of alpine meadows soil

Global warming drives shrubs expansion. However, it is unclear how shrubs expansion affect the nutrients cycling, decomposer diversity and activity of alpine meadows. We selected two dominant shrub species in an alpine forest-Tundra ecotone on the eastern Tibetan Plateau: Rhododendron lapponicum (evergreen shrubs), and Sorbus rufopilosa (deciduous shrubs), the shrub-free tundra site as the control site. The fauna community diversity, microbial biomass, extracellular enzyme activity and enzyme stoichiometry of organic soil and mineral soil layer were determined to explore the effects of shrubs expansion. The soil total nitrogen, microbial biomass carbon and nitrogen, and some extracellular enzyme activity of the two shrubs were higher than those in CK. In addition, deciduous shrub expansion had a stronger effect on meadows ecosystem process than evergreen shrub expansion. However, both of them may alleviate the limitation of nitrogen and phosphorus in alpine meadows ecosystem, and the expansion of evergreen shrubs may also contribute to the accumulation of particulate organic matter. It is of great significance to probe the biogeochemical cycle of alpine meadows ecosystems under climate change.

Thermal responses of mountain birch and Siberian larch of an alpine forest-tundra ecotone to climate change

We applied thermogravimetric analysis to ten successive growth rings of Siberian larch and the same number of mountain birch individuals sampled in the alpine forest-tundra ecotone of Kuznetsk Ala Tau mountain ridge to compare physical and chemical responses of the species wood to climate change. Our analysis of the correlation of the wood thermal parameters with air temperature and precipitation revealed that early and latewood cellulose and lignin in the birch were more sensitive to climatic changes as compared to the larch. June–August weather conditions appeared to largely control the chemical composition of the birch early and latewood. Air temperature had a marked influence during synthesis of both early and latewood cell walls, whereas precipitation influenced only latewood. Thermogravimetric analysis of growth rings formed in alpine forest-tundra proved to be an effective tool to study the influence of climatic and weather variability on lignin-carbohydrate complex of deciduous and conifer tree species.

Higher soil fauna abundance accelerates litter carbon release across an alpine forest-tundra ecotone

Upward shifts of alpine treelines and shrub expansion are occurring under climate change, and Abies faxoniana (AF) and Rhododendron lapponicum (RL) may become distributed at higher altitudes. How do abiotic factors and litter quality modulate the effects of soil fauna on carbon release in this context? A field decomposition experiment involving the foliar litter of AF and RL was conducted along an elevation gradient encompassing coniferous forest, alpine shrubland and alpine meadow by using litterbags with different mesh sizes (3 and 0.04 mm). The objective was to determine the influences of soil fauna, litter quality and abiotic factors on species-specific carbon release and their contributions during litter decomposition. Our findings demonstrated that higher soil fauna abundance and diversity facilitated litter carbon release. The contribution rates of soil fauna to carbon release (Cfau) decreased with elevation increasing and decomposition time. Cfau are influenced by soil faunal diversity, dominant fauna groups (Collembola, Oribatida, Mesostigmata), and abiotic factors (temperature). Soil fauna significantly and directly regulated carbon release, abiotic factors indirectly regulated carbon release via altering soil fauna community composition and litter quality. This study improve our understanding in the mechanisms of decomposer contributions to carbon cycling in the context of global climate change.

Grazing and warming effects on shrub growth and plant species composition in subalpine dry tundra: An experimental approach

AbstractQuestionsVegetation in the forest–tundra ecotone faces changes in both climate and land‐use. While climate warming is an important driver of vegetation growth and composition, herbivory may have opposing effects. In the present study, we experimentally test how removal of sheep herbivory affects the vegetation in an alpine forest–tundra ecotone, and how responses are manifested at higher temperatures.LocationDovre Mountains, Central Norway.MethodsShrub growth (height and cover) and ground layer composition were analysed each third year over an 18‐year period in a nested, three‐factorial experiment (ambient temperature and herbivory; ambient temperature and no herbivory; increased temperature and no herbivory). Fencing and open‐top‐chambers were used as expedients. Treatment effects and interactions over time were analysed using linear mixed effects models and ordination.ResultsShrub height and cover increased over time due to reduced herbivory, but without additional warming effect. Lichen cover declined in all treatments over time, but more rapidly and earlier under warming treatment (significant after three years). Contrary to expectations, there was no statistically significant increase in woody species due to warming, although evergreen woody species displayed a trend shift after six years, comprising a sharp decline towards year twelve. Litter accumulated in all treatments, but at higher rates under warming (significant after nine years).ConclusionsOur results disclose removal of sheep herbivory as a prominent driver of shrub growth, with warming as a subordinate driver in the studied alpine vegetation. The warming‐driven increased litter abundance may, however, be caused by the decrease of wind inside chambers and the subsequent absence of wind‐driven removal of litter. This chamber effect and the displayed timing differences in vegetation responses call for the critical use of short‐term experimental data in predictions of long‐term consequences of environmental change.

Microclimate exerts greater control over litter decomposition and enzyme activity than litter quality in an alpine forest-tundra ecotone

Plant litter decomposition is an important biogeochemical process in terrestrial ecosystems. Although climate and substrate quality controls over litter decomposition are reasonably well understood, their impacts on lignocellulose degradation and lignocellulolytic enzymes remain elusive. Here, the decomposition of three leaf litters derived from Salix paraplesia (SP), Deyeuxia scabrescens (DS), and Ajuga ovalifolia (AO), was studied across an alpine forest-tundra ecotone during one snow-covered season with the objective of distinguishing between the effects of microclimate and litter quality on litter decomposition rates and lignocellulolytic enzymes. The results showed that both microclimate and litter quality affected lignocellulose degradation rates and lignocellulolytic enzyme activities; however, microclimate factors had the greater effects. Interestingly, freeze-thaw cycles and moisture were the predominant factors explaining the variations in decomposition rate and enzyme activities. Higher cellulose degradation rates were associated with higher cellulose concentrations. Cellulolytic enzymes had a greater effect on litter decomposition than did ligninolytic enzymes at the early decomposition stage. Litter decomposition and enzyme activities should be given more attention under global climate change, as the direction and magnitude of changes in microclimate factors and litter quality could strongly influence the nutrient cycling and energy fluxes of alpine ecosystems.

Impacts of soil fauna on lignin and cellulose degradation in litter decomposition across an alpine forest-tundra ecotone

The degradation of lignin and cellulose is the primary ecological process in terrestrial ecosystems; these chemical changes have been associated with the subsequent colonization and activity of decomposer flora and fauna. To evaluate the contribution of soil fauna on lignin and cellulose degradation during litter decomposition, we conducted a field experiment along an elevation gradient: coniferous forest, alpine timberline and alpine meadow, and monitored Abies faxoniana and Rhododendron lapponicum foliar litter decomposition with litterbags of different mesh sizes. We observed soil fauna significantly accelerated litter decay. Soil fauna effect on cellulose degradation rate was significantly accelerated in the snowing period (213-320d), which were 19.3%, 12.36%, 27.96% in A. faxoniana litter and 9.2%, 32.65%, 22.11% in R. lapponicum litter in the coniferous forest, alpine timberline and alpine meadow, respectively. By contrast, lignin degradation rates by soil fauna were higher in the later stages (321-554d). In addition, the average monthly contribution of soil fauna effect on cellulose degradation rate mainly occurred during the first year. However, the contribution of lignin degradation by soil fauna was higher in coniferous forest and alpine meadow, where they were 13.84% and 18.06% in A. faxoniana, and 14.5% and 10.1% in R. lapponicum litter. Elevation gradient and seasonal dynamics will influence on activity of soil fauna, which may modify the impacts of soil fauna on lignin and cellulose degradation during litter decomposition. Elucidating the role of soil fauna in litter decomposition is important for understanding the formation of soil organic matter in alpine ecosystems.

Constraints on treeline advance in a warming climate: a test of the reproduction limitation hypothesis

Several mechanistic hypotheses have been developed to explain the existence of alpine treelines worldwide. The reproduction limitation hypothesis (RLH) postulates that reproductive processes such as seed production and dispersal are restricted in treeline environments, thereby limiting the establishment of new individuals in advance of extant treelines. Despite its popularity, no study has tested this hypothesis in a comprehensive fashion. In this experiment, we attempted to answer whether there are enough viable seeds being dispersed beyond treeline for sexually mediated treeline advance, and what the implications of climate change might be on these processes. We established 30 plots across two aspects (north vs. south) and three elevational habitats (forest, treeline and tundra) in a white spruce (Picea glauca) boreal forest-alpine tundra ecotone in southwest Yukon, Canada. In each plot, tree characteristics, seed production and predispersal damage were measured. Additionally, eight dispersal trays were positioned in each plot to measure seed rain, and germination trials with and without predation exclosures were constructed in a subset of plots to quantify dispersal and germination success. Results were highly variable both temporally and spatially. In 2014, a mast year, 69% of adult trees produced cones compared to 0.4% in the following year. Higher density of trees in forest plots compared to treeline and tundra resulted in greater seed production at lower elevations. Across all plots, 88% of seeds were damaged before dispersal or were not viable. Treeline plots had significantly greater predispersal damage. Seed rain was greater in south-facing plots than north-facing plots. Less than 2% of seeds produced on the landscape were dispersed into Tundra plots, located 50 m above treeline. There was a net movement of seeds from the north-facing slope to the south at our study site, likely due to prevailing winds during the dispersal period. Germination counts were more than double on north-facing slopes and one-third higher inside exclosures. Cumulatively, the results provide some evidence for the RLH. Collectively, the high amount of predispersal damage and non-viable seeds, variability associated with dispersal and significant seed predation can functionally influence treeline dynamics. These findings suggest that global treeline distribution models, which rely largely on temperature, may not be entirely accurate for predicting treeline advance—at least at finer temporal scales. Many stochastic factors need to align temporally for successful advance, which is likely to result in a lag of many decades between the period of temperature amelioration and an increased number of trees beyond extant treelines.

The effect of topography on arctic-alpine aboveground biomass and NDVI patterns

Topography is a key factor affecting numerous environmental phenomena, including Arctic and alpine aboveground biomass (AGB) distribution. Digital Elevation Model (DEM) is a source of topographic information which can be linked to local growing conditions. Here, we investigated the effect of DEM derived variables, namely elevation, topographic position, radiation and wetness on AGB and Normalized Difference Vegetation Index (NDVI) in a Fennoscandian forest–alpine tundra ecotone. Boosted regression trees were used to derive non-parametric response curves and relative influences of the explanatory variables. Elevation and potential incoming solar radiation were the most important explanatory variables for both AGB and NDVI. In the NDVI models, the response curves were smooth compared with AGB models. This might be caused by large contribution of field and shrub layer to NDVI, especially at the treeline. Furthermore, radiation and elevation had a significant interaction, showing that the highest NDVI and biomass values are found from low-elevation, high-radiation sites, typically on the south-southwest facing valley slopes. Topographic wetness had minor influence on AGB and NDVI. Topographic position had generally weak effects on AGB and NDVI, although protected topographic position seemed to be more favorable below the treeline. The explanatory power of the topographic variables, particularly elevation and radiation demonstrates that DEM-derived land surface parameters can be used for exploring biomass distribution resulting from landform control on local growing conditions.

Changes in foliar litter decomposition of woody plants with elevation across an alpine forest–tundra ecotone in eastern Tibet Plateau

To determine litter decomposition rates at different elevations in the alpine forest–tundra ecotone under climate change scenarios in which woody plants shift their ranges upward, litterbags containing foliar litter were incubated on the surface of forest, tree line, and alpine meadow soils (3900, 4000, and 4200 m above sea level, respectively) in the eastern Tibet Plateau of China in October 2012. The selected woody plant species were Abies faxoniana, Betula albosinensis, Sorbus rufopilosa, Rhododendron taliense, Lonicera lanceolata, and L. myrtillus. Mass loss, carbon (C), nitrogen (N), and phosphorus (P) release, and cellulose and lignin degradation in litter were examined from retrieved litterbags over a 6 month period at the end of one snow-covered season. The results showed that the mass loss of A. faxoniana, L. lanceolata, and S. rufopilosa litter, but not that of the other species, was accelerated at higher elevations. Abies faxoniana, B. albosinensis, and S. rufopilosa C release, A. faxoniana and S. rufopilosa N release, L. myrtillus, L. lanceolata, and S. rufopilosa P release, B. albosinensis, S. rufopilosa, and R. taliense cellulose degradation, and L. myrtillus lignin degradation significantly increased with increasing elevation. These results imply that changes in foliar litter decomposition with elevation, although species-specific, could indicate a possible shift in woody plant composition in the alpine forest–tundra ecotone under climate change scenarios. Thus, further studies regarding how elevation shifts could alter litter decomposition and ecosystem sustainability are warranted.

Reaction of coniferous trees in the Kuznetsk Alatau alpine forest-tundra ecotone to climate change

In recent decades there has been an increase in the radial growth of Larix sibirica Ledeb., Pinus sibirica Du Tour, and Abies sibirica in the Kuznetsk Alatau alpine forest-tundra ecotone. Larch growth correlates positively with summer temperatures; cedar and fir growth is determined by temperature, precipitation, and sunshine duration. It is shown that the current growth of maturing larch trees is about 55% higher than that of a similar age group observed 200 years ago. The rate of larch advancement along the height gradient is estimated at 1 m/10 years. A periodical limitation of the radial growth in fir by winter and summer temperatures is found; the strongest correlation is revealed with summer temperatures (r = 0.9). The growth rate of all conifers correlates highly with the concentration of CO2 in the atmosphere (r = 0.42–0.84). Increased winter temperatures induce the transformation of the elfin forms in larch and cedar (the early 1970s) and later fir (the early 1980s) into vertical forms.

Seasonal dynamics in soil microbial biomass carbon and nitrogen and microbial quantity in a forest-alpine tundra ecotone, Eastern Qinghai-Tibetan Plateau, China

Aims The forest-alpine tundra ecotone is one of the most conspicuous climate-driven ecological boundaries. However, dynamics of soil microbial biomass and quantity during different stages of the growing season in the ecotone remain unclear. Our objective was to understand the temporal and spatial variations of microbial biomass and quantity to explore the main drivers in the ecotone. Methods We collected soil samples in a forest-alpine tundra ecotone (dark-conifer forest, timberline, treeline, dense shrub, sparse shrub and alpine meadow) during early, mid and late growing season (EGS, MGS and LGS). The number and species composition of soil microorganisms were determined by means of the plate count method. Soil microbial biomass carbon (MBC) and nitrogen (MBN) were measured by the chloroform fumigation leaching method. Important findings Vegetation and seasonality significantly influence MBC, MBN and microbial community structure. Microbial biomass distribution among vegetation types was different in the three stages of the growing season. MBC above treeline was higher than below during EGS and MGS. The MBC of dark-conifer forest, timberline and treeline during LGS was significantly increased, and MBC differences among different vegetation types decreased. There were significant differences in measured soil microbial quantity between aboveand below-treeline vegetation types; bacteria of dense shrub were highest among vegetation types. The amount of cultivated microorganisms was LGS>EGS>MGS. The ratio of MBC to MBN was the highest and the quantity of fungi increased largely late in the growing season. Statistical analysis showed that there were significant correlations between MBN and bacteria, fungi and actinomyces quantity, while only MBC and fungi quantity were 刘洋等: 青藏高原东缘高山森林-苔原交错带土壤微生物生物量碳、氮和可培养微生物数量的季节动态 383 doi: 10.3724/SP.J.1258.2012.00382 significantly correlated (p < 0.05). Litter input and snow cover late in the growing season were external factors of microbial seasonal variation. Soil microbes and alpine plants competing for nitrogen may be internal factors. Plant nitrogen absorption early in the growing season and microorganisms’ nitrogen fixation late in the growing season enhanced the alpine ecosystem’s nitrogen fixation and utilization. Climate warming may extend the growing season of alpine plants, increasing the alpine soil microbial biomass, and accelerate the decomposition of soil organic matter, which may change soil carbon sequestration rates in the alpine ecosystem.

Landscape Heterogeneity of Differently Aged Soil Organic Matter Constituents at the Forest–Alpine Tundra Ecotone, Niwot Ridge, Colorado, U.S.A

One of the major remaining obstacles to understanding how ecosystems process carbon (C) and nitrogen (N) within soil organic matter (SOM) is landscape heterogeneity. While many studies have investigated landscape heterogeneity in total SOM C and N, less information exists on landscape patterns for differently aged constituents within SOM. These differently aged constituents can show distinct landscape-level patterns and levels of heterogeneity that contribute to our understanding of the production and decomposition processes that create SOM. Using field measurements from an alpine-subalpine ecosystem and geostatistical analyses, I show here that C and N in the older more recalcitrant SOM of mineral soil have more defined spatial patterns and are less heterogeneous than C and N in the newer more labile SOM of mineral soil at the forest-alpine tundra ecotone (SOM C: CV = 45% in older, 59% in newer; partial sill [sill minus nugget, i.e., percent of variation explained by spatial autocorrelation] = 38% in older, 11% in newer; SOM N: CV = 50% in older, 48% in newer; partial sill = 6% in older, 44% in newer). I also demonstrate that C∶N ratios show better spatial patterns and reduced landscape heterogeneity when compared with their constituent C and N concentrations (CV of total SOM C = 41%, total SOM N = 31%, total SOM C∶N = 20%; partial sill of total SOM C = 15%, total SOM N = 18%, total SOM C∶N = 64%). The reduced heterogeneity and strong relationships between C and N in older SOM suggest that landscape variation in the chemical composition of the SOM in mineral soils converges over time, possibly as a result of greater chemical variation in plant inputs relative to the products of decomposition reactions.

Spatio-temporal ranging behaviour and its relevance to foraging strategies in wide-ranging wolverines

Conservation of carnivores in an increasingly changing environment is greatly helped by understanding the decision-making processes underlying habitat patch choice. Foraging theory may give us insight into spatio-temporal search patterns and consequent foraging decisions that carnivores make in heterogeneous and fluctuating environments. Constraints placed on central-place foragers in particular are likely to influence both foraging decisions and related spatio-temporal movement patterns. We used discrete choice models to investigate the spatio-temporal ranging behaviour of GPS collared female wolverines (Gulo gulo) with dependent cubs in south-central Norway. Activity patterns, home range use and selection for elevation were analyzed in relation to spatial and temporal covariates (daily and seasonal) and related to different foraging behaviours. In spring, wolverines showed restricted movement patterns around rendezvous sites at high elevations by day, whereas during the night animals were active at lower elevations. Over the summer, this daily pattern in intensity of use diminished and their overall selectiveness for elevation decreased as cubs grow more mobile and independent. At the onset of autumn, wolverines showed intensive use of the profitable forest-alpine tundra ecotone. We argue that reproducing wolverines deployed a foraging strategy attuned to altering their movement patterns throughout the summer to address a continuous, but diminishing, trade-off between providing both food and shelter for their offspring. Incorporating spatially and temporally explicit activity patterns and home range use in discrete choice resource selection models thus enhances the understanding of the motives behind wolverine resource utilization in space and time. Such knowledge may provide guidance to managers designing regional-scale zoning, in order to facilitate carnivore recovery and to minimize conflicts with human activities.

Response of Pinus sibirica and Larix sibirica to climate change in southern Siberian alpine forest–tundra ecotone

A warming climate provides competitive advantages to Siberian pine (Pinus sibirica Du Tour) in areas with sufficient precipitation. The warmer temperatures observed in central Siberia over the past three decades appear to have had a noticeable effect on growth of Siberian pine and larch (Larix sibirica Ledeb.) in the south Siberian Mountain forest–tundra ecotone. Larch is more tolerant of harsh climates and exhibits an arboreal growth form, whereas Siberian pine is in krummholz form. Larch also has an advantage at the upper tree limit and in areas with low precipitation. Since the mid-1980s there have been measurable increases in growth increments, stand densification, regeneration propagation into the alpine tundra and transformation of krummholz into arboreal forms. Warming winter temperatures have been sufficient for increased survival of regeneration. Regeneration responded to temperature increase of 1°C by migration to areas 10–40 m higher in elevation. Regeneration has propagated into the alpine tundra at the rate of ~1.0–2.0 m year−1. Siberian pine and larch regeneration surpassed their upper historical limit by 10–80 m in elevation. While increased tree growth and migration into alpine tundra areas affect the regional carbon balance, it will also decrease albedo, which may increase warming at the regional level.

Tree spatial patterns and environmental relationships in the forest–alpine tundra ecotone at Niwot Ridge, Colorado, USA

AbstractForest–alpine tundra ecotones (FTEs) are dynamic transition zones between forest and alpine tundra ecosystems that play an important role in regulating ecological processes, which are in turn directly influenced by the spatial patterns of trees and environmental constraints such as topography and climate. Our objectives were to characterize the spatial patterns of tree species and size classes, determine whether spatial patterns of trees differed among three FTE types, and examine FTE‐ and tree‐environmental relationships in our study area on Niwot Ridge, CO, USA. Overall, spatial aggregation was more extensive for seedlings than saplings or trees. Distributions were largely random in limber pine but were highly aggregated in Engelmann spruce and especially subalpine fir, reflecting these species’ relative shade tolerance and expected sequence of establishment following disturbance. Fragmented and patchy tree distributions were observed in the FTE with the most heterogeneous topography, characterized by high relief and associated physical disturbances. The least patchy distributions were associated with the FTE containing a relative absence of disturbance. Intermediate levels of tree aggregation were associated with low topographic relief and presence of meadows and wetlands. Our results emphasize the importance of spatial structure as an initial controlling factor of vegetation pattern in FTEs occurring in the same landscape.

Geomorphological limits to self-organization of alpine forest-tundra ecotone vegetation

Feedback in the establishment of vegetation has been shown to produce spatial patterns that differ from the geomorphological basis for resources. The dynamics of these spatial patterns have been characterized as self-organization because local processes produce them at landscape scales. Geomorphic patterns could, however, enhance or disrupt the processes that lead to patterns and the interpretation of self-organization. A simulation model that showed such indication of self-organization at alpine forest-tundra ecotones is modified to incorporate a geomorphic feature commonly seen in this environment – solifluction steps – as an exogenous condition in the model. Analyses linking spatial patterns and rates of advance of vegetation indicate that such geomorphic patterns do not alter the dynamics of vegetation until the size of the patterns is about double that of the dimension within which endogenous dynamics operate. The sizes of some geomorphic patterns incorporated in the model are probably larger than any realistic solifluction feature at such ecotones in western North America.

Decomposition rates of buried substrates increase with altitude in the forest-alpine tundra ecotone

Decomposition rates were measured across the forest-alpine tundra ecotone on two mountains in the Colorado Front Range. Cotton strips decomposed in the surface soils of forest, krummholz, and tundra plots for one year. We expected decomposition rates to decline with altitude or be most rapid in the krummholz. Surprisingly, decomposition rates increased from forest to tundra on Mt. Evans and remained constant across the ecotone on Niwot Ridge, highlighting differences in biogeochemical processes between two nearby mountains with otherwise similar alpine and subalphine ecosystems. Our results support the concept that decomposition rates exhibit a curvilinear relationship with soil temperature and moisture. However, soil moisture was found to be the primary factor controlling cellulose decomposition rates in soils in the forest-alpine tundra ecotone. Cellulose decomposition rates increased with soil depth indicating greater microbial activity in the mineral soil than in the organic horizon due to greater soil moisture. In addition to microbial activity, decomposition rates in the tundra may be enhanced by physical degradation from freeze-thaw events and vigorous root growth.

Estimates of Little Ice Age Climate Inferred through Historical Rephotography, Northern Uinta Mountains, U.S.A

I replicated and analyzed six photographs taken in A.D. 1870 near the subalpine forest-alpine tundra ecotone in the northern Uinta Mountains to quantify changes in the distribution of vegetation. Three dramatic differences were noted. First, the historical photographs document a treeline 60 to 180 m (mean of ∼100 m) lower than at present, with greater depression on west-facing slopes. Given the modern lapse rate for mean July temperature (6.9°C km−1), this difference corresponds to a temperature depression in A.D. 1870 of 0.4 to 1.2°C (mean of 0.7°C). Second, timberline forests in A.D. 1870 were significantly (P < 0.01) less dense, with tree densities approximately half those measured in the modern photographs. Third, the area of floodplain meadows decreased ∼75% from A.D. 1870 to the present. Because the original photographs were taken within a few decades of the end of the Little Ice Age, ca. A.D. 1850, I assumed that differences in vegetation distribution documented in the repeat photographs represent the biotic response to climate warming over the past ∼130 yr. This analysis provides an independent estimate of the magnitude of growing season temperature depression during the Little Ice Age.

Humus Forms in the Forest-Alpine Tundra Ecotone at Stillberg (Dischmatal, Switzerland): Spatial Heterogeneity and Classification

In the forest-alpine ecotone at Stillberg (Dischmatal/Switzerland) the morphology of humus forms and the spatial variability of organic layer properties were investigated. At northeast-exposed gully sites mulls with high acidity in the Ahorizon occur. They were classified after the Canadian classification of humus forms as Rhizomulls. Mors occur on ridges and on their east- and north-exposed aspects. They can be differentiated by the ratio between the thickness of the Fhorizon and the combined thickness of the F- and H-horizon. The relative thickness of the F-horizon increases significantly in the order: east aspects < ridges < north aspect. The humus forms of the east aspects and the ridges were classified as Humimors and those of the north aspects as Hemimors. The Canadian classification was suitable to describe the properties of the horizons and to classify the humus forms. The results of a grid sampling at the study sites and the computation of nonergodic correlograms show that the spatial variability of organic-layer thickness, bulk density, and moisture is high (CV around 50%), with a pronounced small-scale heterogeneity (range usually below 2 m and more than 50% variability occurs within 0.3 m). Only 33% of the variance of organic-layer thickness were explained by site and vegetation structure, but in spite of the low percentage both proved to be a significant factor. In the forest-alpine tundra ecotone about 30 to 35 soil samples per site are needed for a reliable estimation of the mean of the organic-layer thickness.

Humus Forms in the Forest-Alpine Tundra Ecotone at Stillberg (Dischmatal, Switzerland): Spatial Heterogeneity and Classification

In the forest-alpine ecotone at Stillberg (Dischmatal/Switzerland) the morphology of humus forms and the spatial variability of organic layer properties were investigated. At northeast-exposed gully sites mulls with high acidity in the A-horizon occur. They were classified after the Canadian classification of humus forms as Rhizomulls. Mors occur on ridges and on their east- and north-exposed aspects. They can be differentiated by the ratio between the thickness of the F-horizon and the combined thickness of the F- and H-horizon. The relative thickness of the F-horizon increases significantly in the order: east aspects < ridges < north aspect. The humus forms of the east aspects and the ridges were classified as Humimors and those of the north aspects as Hemimors. The Canadian classification was suitable to describe the properties of the horizons and to classify the humus forms. The results of a grid sampling at the study sites and the computation of nonergodic correlograms show that the spatial variability of organic-layer thickness, bulk density, and moisture is high (CV around 50%), with a pronounced small-scale heterogeneity (range usually below 2 m and more than 50% variability occurs within 0.3 m). Only 33% of the variance of organic-layer thickness were explained by site and vegetation structure, but in spite of the low percentage both proved to be a significant factor. In the forest-alpine tundra ecotone about 30 to 35 soil samples per site are needed for a reliable estimation of the mean of the organic-layer thickness.