Undulating Landscapes Research Articles

The “Lund Moraine” – the geomorphic limit of the last Young Baltic ice advance in the Öresund region

ABSTRACT Here we present geomorphological evidence of a previously unrecognised ∼50 km long, ice-marginal moraine complex in southwestern Skåne, southernmost Sweden, which we name the “Lund Moraine”. This lobate moraine marks a sharp boundary between heavily streamlined and gently undulating landscapes, and closely outlines the extent of the “Lund till/diamicton”. We interpret that the moraine was formed by a northward readvance, corresponding to a last Young Baltic readvance of the Scandinavian Ice Sheet into Öresund. Consequently, we infer that the “Lund till/diamicton” was formed subglacially, in contrast to earlier interpretations of it being a waterlain diamicton. Based on previously published dates, stratigraphically below “Lund till/diamicton”, we infer that this readvance occurred sometime after c. 16 cal. ka BP. This readvance could offer an explanation to the apparent discrepancy of observations of the postglacial marine limit from outside and inside the Lund Moraine. Our observations will hopefully settle the ∼50 years long controversy concerning the extent or even existence of such a readvance into Öresund. We expect that our findings will guide further work towards disentangling the complex deglacial history of Skåne and the wider Öresund region.

Detection of Soil Erosion Hotspots in the Croplands of a Typical Black Soil Region in Northeast China: Insights from Sentinel-2 Multispectral Remote Sensing

Global efforts to restore the world’s degraded croplands require knowledge on the degree and extent of accelerated soil organic carbon (SOC) loss induced by soil erosion. However, the methods for assessing where and to what extent erosion takes place are still inadequate for precise detection of erosion hotspots at high spatial resolution. Drawing on recent advances in multitemporal Sentinel-2 remote sensing to create a bare soil composite that reflects erosion-induced variations in soil spectral signatures, this study attempted to develop a spectra-based soil erosion mapping approach to pinpoint eroded hotspots in a typical catchment located in the black soil region of northeast China as characterized by undulating landscapes. We built a ground-truth dataset consisting of three classes of soils representing Severe, Moderate and Low erosion intensity because of their inter-class contrasts in estimated erosion rates from 137Cs tracing. The spectral separability of different erosion classes was first tested by a combined principal component and linear discriminant analysis (PCA-LDA) against laboratory hyperspectral data and then validated against Sentinel-2-derived broadband spectra. The results show that PCA-LDA produced excellent classification accuracy (Kappa coefficient > 0.9) for both data sources and even more so for Sentinel-2 spectra, highlighting the effectiveness of the multitemporal approach to extract bare soil pixels. Further investigations into the spectral curves enabled identification of distinctive spectral features representative of shifting soil albedo and biochemical composition due to erosion-induced SOC mobilization. A classification scheme comprising the spectral features was applied to the Sentinel-2 bare soil composite for pixel-wise soil erosion mapping, in which 15.9% of the cropland area was detected as erosion hotspots, while the Moderate class occupied 65.4%. Comparing the erosion map to a NDVI map demonstrated the negative impact of soil erosion on crop growth from a spatial perspective, highlighting the potential of the proposed approach to aid targeted cropland management for food security and climate.

Formation of Colluvisols in different soil regions and slope positions (Czechia): Stratification and upbuilding of colluvial profiles

Colluvisols represent a significant part of the erosional catena in undulating landscapes, often changed by long-term agricultural management. The present study provides a detailed description of the stratigraphy, properties and development of colluvial profiles in two geologically, climatically and historically different areas of Czechia, situated in the loess region of South Moravia and Central Bohemian Upland, built on plutonic rocks. For the first time in Czechia, colluvial profiles were dated and interpreted in terms of the history of human impact on the landscape and Holocene climatic fluctuations. Four profiles were excavated in the toe-slope and side valley areas. A multidisciplinary approach combining absolute dating by optically stimulated luminescence, assessing 137Cs activity and micromorphological, mineralogical and geochemical analysis was applied to identify the period and mode of deposition of each layer. In both areas, a predominantly rapid, event-based sedimentation with thick recently deposited layers was identified in the toe-slopes, while the side-valleys are characterized by gradual, slower and older sedimentation. Peaks of erosion activity at both plots were distinguished in the High and Late Middle Ages and the recent period since 1950. In both periods, significant changes in anthropogenic pressure on the landscape, whether due to increased population density or agricultural intensification, were identified as the main trigger. Nevertheless, significant associations were also found with climatic events in the periods in question. In both areas, colluvial layers corresponding to the pre-Neolithic period were also found, probably exclusively associated with the influence of contemporary climate.

Radio-tracking wildlife with drones: a viewshed analysis quantifying survey coverage across diverse landscapes

Radio-tracking tagged wildlife remains a critical research technique for understanding the movements, behaviours and survival of many species. However, traditional hand-held tracking techniques on the ground are labour intensive and time consuming. Therefore, researchers are increasingly seeking new technologies to address these challenges, including drone radio-tracking receivers. Following the implementation of drone radio-tracking techniques for five different threatened species projects within different habitat and landscape types, we identified the need to quantify the relative spatial extent of surveys using both drone and hand-held techniques for each project. This was undertaken using viewshed analyses. These analyses demonstrated that survey coverage with drone-based radio-tracking was substantially greater than that of hand-held radio-tracking for all species and landscapes examined. Within mountainous landscapes, drone radio-tracking covered up to four times the area of hand-held tracking, whereas in flat to undulating landscapes, drone surveys covered up to 11.3 times the area that could be surveyed using hand-held techniques from the same locations on the ground. The viewshed analyses were also found to be a valuable visualisation tool for identifying areas for targeted surveys to reduce the risk of ‘losing’ tagged animals, which has traditionally been one of the biggest radio-tracking challenges.

Subsurface Moisture Regulates Himalayan Groundwater Storage and Discharge

AbstractThrough the release of groundwater, most mountain rivers run year‐round despite their small catchments and sporadic precipitation. This makes mountain ranges important sources of reliable freshwater for downstream populations in many parts of the world. However, due to a lack of ground instrumentation, little is known about groundwater dynamics in mountainous landscapes. Recent research has shown that the amount of moisture trapped in the soil and weathered rocks in the vadose zone can significantly buffer groundwater recharge and runoff but the wider recognition of this effect on major mountain systems has not been yet established. In this study, we test whether the moisture reservoir has an impact on hydrological fluxes in a steep Himalayan catchment during three monsoon seasons. We measured an array of parameters including relative seismic velocity changes from ambient noise correlations. This noninvasive technique allows us to monitor groundwater dynamics in conjunction with classical hydrological measurements. We found that the moisture saturation in the vadose zone controls the onset of groundwater recharge and runoff and therefore determines the annual water availability supplied by monsoon precipitation. We model this dynamic using a surface layer that has a finite storage capacity that controls the connectivity of surface flux to groundwater. The extension of this concept, which is thought to apply widely in flat and undulating landscapes, to steep mountain topography with thin and discontinuous soils underlain by regolith and bedrock has important implications for mountain hydrology.

Forage legumes from the Mediterranean Fynbos biome of South Africa with potential for domestication: slope aspect affects tissue fibre and mineral composition

Fabaceae plants contribute greatly to a high quality of pasture in rangelands, because of high levels of protein in their tissues. Despite this established importance, only a few southern African legumes have been evaluated for nutritional value and domestication. The Overberg renosterveld vegetation of the Fynbos biome occupies undulating landscapes that have multiple slope aspects, creating variable microclimatic conditions affecting nutrient dynamics, species richness and plant chemical compositions. We assessed the effect of slope aspect on fiber and mineral composition of forage species present to provide information on the importance of slope for species characterization and nutritional value for domestication. Tissue samples from six replicates of the same species occurring on opposing aspects were collected for nutritional assessment. Results on the data showed that fibre and mineral composition differed in species occurring on different slopes, albeit with few exceptions. The concentrations of P, K and Mg in some species were significantly higher on the cooler and wetter south facing slopes relative to north facing slopes. Nutrient elements in soil samples collected from each site varied with slope aspects and elements. It is recommended that topography should be considered when studying forage nutritional assessments as part of future domestication programs.

Soil fertility along toposequences of the East India Plateau and implications for productivity, fertiliser use, and sustainability

Abstract. In common with other undulating landscapes in Asia, wetland rice (Oryza sativa) on the East India Plateau (EIP) was once confined to hydrologic discharge areas or lowlands, but progressive terracing has now allowed rainfed transplanted rice to encroach upon upland recharge areas, with potential effects on both hydrology and soil fertility. Hydrologic variation down the toposequence and its implications for rice production have been well documented but not the variation in soil fertility. Measurements of soil chemical fertility in seven of 24 EIP districts were used to evaluate variation between and within small watersheds stratified down the toposequence into six land classes that reflect hydrology and land use (three with rice and three without; 36 fields per watershed). We aimed to provide a basis for future research to improve the management of soil fertility. Soils overall were acid, with 14 % of fields requiring liming (pH < 5.0) and 44 % requiring management of further acidification (pH 5.0–5.4). Organic carbon (OC, mean 0.9 %) and cation exchange capacity (CEC; mean 10.7 cmolc kg−1) were low. Available phosphorus (P) was mostly very low (mean Bray P 4.3 mg kg−1) and extractable potassium (K) low to marginal (mean 88 mg kg−1). Non-rice soils generally had lower pH, OC, and CEC than rice soils but higher P and K. Amongst rice fields, those higher in the toposequence had lower pH, OC, and CEC but more P and K. These results are discussed in the context of nutrient flows in the landscape, leading to the conclusion that terracing uplands has reduced the delivery of sediment-bound P to lowlands where, even with organic P recycling, low inputs of inorganic fertiliser have led soil P to decline and become the primary constraint to the yield of wet season crops. Soil K is on the same trajectory. P and K fertiliser use must increase substantially to sustain the system, which is a challenge for risk-averse subsistence farmers. Field-specific recommendations are needed despite systematic toposequence differences because of variability between fields within land classes.

Landscape dependent changes in soil properties due to long-term cultivation and subsequent conversion to native grass agriculture

On farmland in undulating landscapes, soil organic carbon (SOC) stocks depend on landscape position. In the North American Prairie Pothole region, we compared a native prairie reference site with a nearby farm undergoing transition to perennial agriculture (“restoration”) after a century of producing annual crops. We quantified legacy effects of farming at four upland landscape positions (to 0.9-m soil depth) and three wetland positions (to 1.0-m soil depth). We also quantified short-term (4years) changes in SOC stocks (to 0.15-m soil depth) during restoration, and how these changes were impacted by historic erosion.Surface (to 0.05-m soil depth) measurements indicated degradation of the cropland soil relative to the prairie at all landscape positions due to less soil organic matter (SOM) and altered soil properties (e.g., water aggregate stability and microbial activity). All upland and wetland positions of the farm lost SOC stocks (Mgha−1) relative to the prairie in the top 1.5 Ggha−1 of soil (~14-cm depth). However, when considering a larger mass of soil, 4.5Ggha−1 (~39-cm depth), loss of SOC stocks was significant (p<0.001) only at the summit (46Mgha−1) and shoulder (63Mgha−1) landscape positions. Differences in SOC stocks between farm and prairie were smaller and not significant at the backslope, footslope, and in wetlands.Contrary to expectations, sites of soil deposition did not accumulate soil carbon after restoration. Accretion of soil C during restoration differed according to the severity of historic erosion (p<0.001), with severely eroded soils gaining soil C at the fastest rate. Historic loss of clay at the shoulder and backslope and subsoil compaction in the wetlands may prevent these landscape positions from full restoration of soil C stocks, net primary productivity, and historic vegetation.

Scale‐dependent occupancy patterns in reptiles across topographically different landscapes

Understanding what factors influence species occupancy in human‐modified landscapes is a central theme in ecology. We examined scale‐dependent habitat relationships and site occupancy in reptiles across three topographically different study areas in south‐eastern Australia. We collected presence–absence data on reptiles from 443 sites associated with three long‐term biodiversity monitoring programs, on four to seven occasions, between 2001 and 2013. We characterised sites by the following four variable domains: 1) field design, 2) topography, 3) local‐scale vegetation attributes and 4) landscape‐scale vegetation cover. We constructed occupancy models for 14 species and used an information‐theoretic approach to compare multiple alternative hypotheses to explain occupancy within and between study areas. We modelled detection probability and used the model with the lowest AIC in subsequent analyses. We then modelled occupancy probability against all subsets of the variable groups (field design, topography, local‐ and landscape‐scale vegetation), as well as a model that held occupancy constant (null model). We found that local‐scale vegetation attributes were important for explaining site occupancy in 12/19 possible models, although, in several cases model fit was improved by the addition of topographic variables or native vegetation cover in the surrounding landscape. Occupancy models for widespread species were broadly congruent across study areas. We demonstrate that topographic variables are important for explaining reptile occupancy in hilly landscapes, and local‐ and landscape‐scale variables are important for explaining reptile occupancy in flat or gently undulating landscapes. Management actions that improve habitat complexity at a site‐level, and encompass entire topographic gradients, will have greater benefit to woodland reptiles than simply increasing vegetation cover in the surrounding landscape.

Modernity, Islam and an African Culture

The human quest for the meaning of life is an unending one marked by undulating landscapes. In order to confront the flux of experience generated by this quest for meaning, the human embraces science, morality, politics and religion. Religion is said to provide the basis for transcendental values which give humans succour after the physical and material struggles have ended. At the same time, religion also uses the observable social world as the starting point for the embrace of transcendental values. In this essay, an attempt is made to examine the interconnectedness of modernity (which has its basis in the social world), Islam (which provides the human with transcendental values) and an African culture (which serves as a nexus of modernity and Islam). The essay is basically an exercise in analysis whereby the readers are made to draw some compelling inferences.Keywords: Modernity, Islam, African culture, Values, Human happiness

Reproducing CO2 exchange rates of a crop rotation at contrasting terrain positions using two different modelling approaches

In undulating landscapes erosion is largely responsible for the spatial distribution of C stocks in agricultural soils. Whether these stocks contribute to global atmospheric CO2 concentrations as source or sink of CO2 is under constant debate. Periodic CO2 measurements were carried out at a hummocky ground moraine site grown with maize, fodder rye and sorghum using dynamic non-steady-state transparent and opaque chambers. Flux calculation for CO2 was conducted using the empirical gap-filling model of Hoffmann et al. (2015b), which uses temperature and radiation to simulate ecosystem respiration (Reco) and gross primary production (GPP) and to calculate net ecosystem CO2 exchange (NEE). This model was compared with a process-based agro-ecosystem simulation model, MONICA, which was tested for its ability to simulate Reco, GPP and NEE, using the empirical model as benchmark. Both models simulated GPP and Reco in the same order of magnitude, with MONICA simulating a considerably higher amount of CO2 produced by photosynthesis for maize and less deviating CO2 produced by photosynthesis for the other crops and CO2 consumed by respiration for all crops as compared to the empirical model. Both models largely agree in CO2 flux patterns, but show considerable differences directly after harvest and during bare soil periods. Strengths and weaknesses of both approaches were discussed and synergies of applying both approaches in conjunction were identified in a way that (i) MONICA may act as an independent method to identify significant deviations from the optimum crop growth pattern and thus point at times during which assumptions of the empirical model for simulating NEE may be violated and that (ii) the empirical model may act as a calibration benchmark for MONICA flux simulations.

Geospatial assessment of soil erosion vulnerability at watershed level in some sections of the Upper Subarnarekha river basin, Jharkhand, India

Undulating landscapes of Chhotanagpur plateau of the Indian state of Jharkhand suffer from soil erosion vulnerability of varying degrees. An investigation was undertaken in some sections of the Upper Subarnarekha River Basin falling within this state. An empirical equation known as Universal Soil Loss Equation (USLE) was utilized for estimating the soil loss. Analysis of remote sensing satellite data, digital elevation model (DEM) and geographical information system (GIS)–based geospatial approach together with USLE led to the soil erosion assessment. Erosion vulnerability assessment was performed by analyzing raster grids of topography acquired from Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) Global DEM data. LANDSAT TM and ETM+ satellite data of March 2001 and March 2011 were used for inferring the land use–land cover characteristics of the watershed for these years, respectively. USLE equation was computed within the GIS framework to derive annual soil erosion rates and also the areas with varying degrees of erosion vulnerability. Erosion vulnerability units thus identified covered five severity classes of erosion ranging from very low (0–5 ton ha−1 yr−1) to very severe (> 40 ton ha−1 yr−1). Results indicated an overall increase of erosion in the year 2011 as compared to the erosion computed for the year 2001. Maximum soil erosion rate during the year 2001 was found up to 40 ton ha−1 yr−1, whereas this went up to 49.80 ton ha−1 yr−1 for the year 2011. Factors for the increase in overall erosion could be variation in rainfall, decrease in vegetation or protective land covers and most important but not limited to the increase in built-up or impervious areas as well.

Soil characteristics in relation to groundwater for selected Dark Brown Chernozems in southern Alberta

Limited information exists on soil characteristics in relation to groundwater for undulating morainal landscapes of the Dark Brown soil zone in western Canada. A 4-yr (1985-1988) field study was conducted in southern Alberta to investigate these relationships for selected Dark Brown Chernozems. Soil morphology, physical and chemical properties of the soil horizons, water fluxes in the saturated zone, and tritium content of shallow groundwater were determined at nine sites. Three Orthic Dark Brown Chernozemic soils occurred in groundwater recharge areas with water tables ≥1.81 m, indicating that leaching of carbonates from the B horizons was consistent with downward groundwater flow. The other three Orthic soils occurred in groundwater discharge areas, and they may have developed because of deeper (≥2.60 m) water tables. High water-soluble Na in these latter three Orthic soils suggested a sodic influence from a shallower water table sometime in the recent past. The two Calcareous Dark Brown Chernozems, and saline Calcareous Dark Brown Chernozem occurred in groundwater recharge areas. One calcareous soil at a lower slope position had a shallow (0.84-2.02 m) water table, suggesting carbonates were brought upward into the Cca horizon from the groundwater. The other calcareous soil at the upper slope position had a deeper (&gt;6.62 m) water table, suggesting carbonates were leached downward and precipitated in the Cca horizon. The saline Calcareous Dark Brown Chernozem was located in an area of groundwater recharge with a deeper (4-9 m) water table, suggesting that salinization likely occurred sometime in the past. Groundwater flow conditions during this study could not explain the genesis of some soils in this study area, suggesting that past groundwater, climatic, and environmental conditions need to be considered to explain the genesis of some relict soils.

Patterns of water and tillage erosion on topographically complex landscapes in the North American Great Plains

Two field sites located in the northern region of the North American Great Plains were examined to investigate the contributions of water and tillage erosion towards total soil erosion in topographically complex landscapes (hummocky and undulating landscapes). Results indicated that both water and tillage erosion contributed substantially to total erosion in the undulating landscape while tillage erosion dominated in the hummocky landscape. The patterns of water, tillage and total soil erosion can be predicted using landscape segmentation in such landscapes. Soil properties and crop yield are also related to soil erosion. Landscape segmentation can be used as a simple tool to more easily represent the spatial variability of soil erosion and affected biophysical processes such as crop production, nutrient cycling, greenhouse gas emission and pesticide fate, and to target soil conservation practices toward the most intensive erosion processes on given landform elements.

Evaluation of perennial pasture legumes and herbs to identify species with high herbage production and persistence in mixed farming zones in southern Australia

Ninety-one perennial legumes and herbs (entries) from 47 species in 21 genera were evaluated at sites in New South Wales, South Australia and Western Australia over 3 years from 2002 to 2005 to identify plants with superior herbage production, persistence and the potential to reduce ground water recharge. Evaluation was undertaken in three nurseries (general, waterlogged soil and acid soil). Medicago sativa L. subsp. sativa (lucerne) cv. Sceptre was the best performing species across all sites. In the general and acid soil nurseries, Cichorium intybus L. (chicory) cv. Grasslands Puna was the only species comparable with Sceptre lucerne in terms of persistence and herbage production. Trifolium fragiferum L. cv. Palestine and Lotus corniculatus L. SA833 were the best performing species on heavy clay soils prone to waterlogging. Three Dorycnium hirsutum (L.) Ser. accessions persisted well on acid soils, but were slow to establish. Short-lived perennial forage legumes, such as Onobrychis viciifolia Scop. cv. Othello, and three Hedysarum coronarium L. entries, including cv. Grasslands Aokou, had high herbage production in the first 2 years and may be suitable for short-term pastures in phased pasture-crop farming systems. T. uniflorum L. and M. sativa subsp. caerulea SA38052 were highly persistent and could play a role as companion species in mixtures or ground cover species for undulating landscapes. Cullen australasicum (Schltdl.) G.W. Grimes SA4966 and Lotononis bainesii Baker cv. Miles had poor establishment, but were persistent. Chicory, T. fragiferum and L. corniculatus were identified as species, other than lucerne, with the most immediate potential for further selection to increase the diversity of perennial legumes and herbs adapted to southern Australian environments.

Tillage and water erosion on different landscapes in the northern North American Great Plains evaluated using 137Cs technique and soil erosion models

Total soil erosion is the integrated result of all forms of soil erosion — wind, water and tillage. It has been recognized that in topographically complex landscapes, individual soil erosion processes and their interactions all contribute towards total soil erosion. In this study, two field sites, representing different landscapes in the northern region of the North American Great Plains, were examined. Water and tillage erosions were estimated using the established water and tillage erosion models and total soil erosion was estimated using the 137Cs technique. We determined that the patterns of water and tillage erosion across the landscapes are mainly dependent on topographic features and they are fundamentally different within topographically complex landscapes. On the slope of undulating landscapes, tillage and water erosion both contribute considerably to total soil erosion. On the knoll of hummocky landscapes, tillage erosion dominates the pattern of total soil erosion. Tested against the Cs measurements, the patterns of total soil erosion cannot be well estimated by water or tillage erosion model alone unless one of the two erosion processes predominate over the other erosion processes. Combining water and tillage erosion models generally provides better estimations of total soil erosion than the component models on their own. Most soil properties and crop yield were found to be closely correlated with total soil erosion. For a given erosion process, the soil erosion patterns estimated using different models with reasonable parameter settings were similar to each other. However, it is necessary to choose an optimal model and to obtain accurate parameters for the purpose of accurate assessments of the erosion rates.

Hydrological Evaluation of Septic Disposal Field Design in Sloping Terrains

The most common form of onsite domestic wastewater treatment in the United States is the septic system. Although the design of these systems has been well established, no systematic evaluation of septic system performance exists for sloping hardpan soils. In this paper, we develop a simple hydrologic model for assessing the probability of failure for a set of hydrologic conditions, septic loading rates, and soil and landscape parameters that are readily available for sloping soils. To demonstrate the model capabilities, input data for a septic field of a two-person residence in the New York City drinking water basin in the Catskills was utilized. Our analysis showed that the saturated hydraulic conductivity, depth to the impermeable layer, and slope of the drain field are critical parameters to assess in the design and siting of these systems. We concluded that septic systems perform poorly in undulating landscapes where the hydraulic conductivity is low and the impermeable layer is close to the surface. Under prolonged rainfall conditions on these soils, the septic field and downslope field saturate, causing hydraulic failure of the septic system and saturation in the downslope field; as a result, effluent may be routed directly to streams via overland runoff.

The sensitivity of lizards to elevation: A case study from south‐eastern Australia

ABSTRACTLizard distribution patterns were examined in relation to elevation in two undulating landscapes. We asked three specific questions: (1) Were different lizard species associated with particular elevations? (2) Did biological attributes of lizards (e.g. body size, colour, reproduction strategy, etc.) vary with elevation? (3) Did species richness of lizards vary with elevation? Field data were collected in two undulating production landscapes in south‐eastern Australia, approximately 100 km to the west of the Australian Capital Territory. Lizards were surveyed using 648 pitfall traps and 3840 m of drift fence. Both study landscapes were divided into 50 m elevation classes. For each elevation class, survey effort, the capture rate of individual species, and species richness were recorded. Correspondence analysis was used to sort lizards according to their altitudinal distribution profiles. Analysis of variance was used to examine if biological attributes of lizards were related to their altitudinal distribution profiles. Generalized linear modelling was used to relate elevation to the capture rate of individual species, and to species richness. Lizard species differed in their altitudinal preferences. Skinks, taxa with a Bassian distribution or distribution restricted to the Great Dividing Range, dark‐bodied species and viviparous species were more likely to inhabit high elevations. Elevation was significantly related to the capture rate of seven species, and ecologically similar species replaced one another as elevation increased. Species richness peaked significantly at intermediate elevations in both landscapes. We conclude that lizards were highly sensitive to elevation. Elevation changes of as little as 50 m may be related to a change in species richness or species composition. Future research should assess if reptiles in other undulating landscapes with a temperate climate are similarly sensitive to elevation. If so, conservation activities in these landscapes need to consider the full spectrum of topographic positions and elevations.

Death model for tussock perennial grasses: a rainfall threshold for survival and evidence for landscape control of death in drought

We investigated relationships between rainfall (and landscape, zonation and nearby grazing disturbance) and the death rates of four perennial grass species in a highly functional semi-arid wooded grassland in eastern Australia. Two grasses were palatable C3 species (Monachather paradoxa Steud. and Thyridolepis mitchelliana (Nees) S. T. Blake) and two were unpalatable C4 species (Aristida jerichoensis (Domin) Henr. var. subspinulifera Henr. and Eragrostis eriopoda Benth.). During the 10-year study the grasses were protected from large herbivore grazing within paddocks continuously grazed by sheep. Death occurred only during droughts and rates of death were species-dependent. When plotted against several water availability indices, rainfall and rainfall/evaporation during the preceding 3 months provided best predictions of death. Longer preceding periods gave inferior predictions. A 3-month rainfall total of 75 mm and a 3-month rainfall/evaporation ratio of 0.15 were survival critical thresholds below which deaths began. The 3-month rainfall totals, rainfall/evaporation and estimated water status of plants were equally reasonable predictors of deaths, but were inconsistent in their effectiveness. Rainfall was adopted for the grass death model; death begins when 3-month rainfall total declines below a threshold of 75 mm and the death rate rises with lower rainfall. Position of plants in the gently undulating landscapes influenced water status and, hence, death rates. Water status of grasses on the two water-shedding zones and the ‘flat’ zone were similar at each assessment, but higher on ‘ridge run-on’ and ‘toe-of-slope’ zones. Foliage height and diameter also influenced death rate but were species dependent. Basal diameter did not influence death rate. Survivorship of several perennial grass species at widely spaced sites in south-eastern Australia provided equivocal support for generality of the grass death model.

Erosion-preventive crop rotations and water erosion rates on undulating slopes in Lithuania

A combination of perennial grass species and selected crop rotations can help prevent soil erosion in upland regions and minimize the risk of soil erosion and associated water pollution (to both terrestrial and aquatic ecosystems). Research data were obtained on sandy loam Eutric Albeluvisols at the Kaltinenai Research Station of the Lithuanian Institute of Agriculture on the undulating hilly topography of the Zemaiciai Uplands of Western Lithuania. The aim was to identify crops and crop rotations that would minimize soil erosion. Measured water erosion rates over 18 yr of field experiments were: 3.2–8.6 m3 ha-1 yr-1 under winter rye, 9.0–27.1 m3 ha-1 yr-1 under spring barley and 24.2–87.1 m3 ha-1 yr-1 under potatoes. Perennial grasses completely prevented water erosion, while the erosion-preventive grass-grain crop rotations (&gt;50% grass) decreased soil losses on arable slopes of 2–5°, 5–10° and 10–14° by 75–80%. The grain-grass crop rotation (&lt;50% grass) decreased rates by 23–24% compared to the field crop rotation. The main attributes of the proposed soil conservation systems were the careful selection of optimum erosion-preventive ecosystems (sod-forming perennial grasses or erosion-preventive crop rotations) with high erosion-resisting capabilities. These selected systems varied in response to slope gradient and thus assist erosion control and ecological stability of the undulating topography of Lithuania. These results may have wider applicability on the undulating landscapes of the temperate agricultural zone. Key words: Undulating upland topography, water erosion rates, erosion-preventive crop rotations, temperate climate