Rates Of Landscape Change Research Articles

Development of cosmogenic nuclide capabilities in South Africa and applications in Southern African geomorphology

ABSTRACT Cosmogenic nuclide (CN) applications offer methods to quantify rates of landscape change and of dating geomorphological deposits and surfaces. Over the past two decades, CNs have been used to determine denudation rates, constrain uplift rates and determine burial ages of sediments in different geomorphological settings across the Southern African landscape. Here, we first give an overview of the landscape evolution of Southern Africa and how CN-based studies have contributed to this subject. Then we give a compilation of CN denudation data from Southern Africa, which show that average erosion rates have decreased by an order of magnitude since the late Cenozoic. Finally, we present the state of CN infrastructure and capabilities in South Africa as well as envisaged future developments. An Accelerator Mass Spectrometer (AMS) has become operational for carbon-14, beryllium-10 and aluminium-26 measurements at the National Research Foundation (NRF) iThemba Laboratory for Accelerator Based Sciences (LABS) in Gauteng since 2017. The measurements’ accuracy and precision compare well with other AMS laboratories internationally. Local sample preparation laboratories are currently available with limited capabilities and are mostly still under development.

Agents of landscape change in southern New Zealand, 1896–1920

The records of two large stock and station agents, Loan & Mercantile Agency in Dunedin and Wright Stephenson in Invercargill, allowed us to track the timing, nature, magnitude and rate of landscape change in southern New Zealand between 1896 and 1920. This period extends from the final years of subdivision of large estates, and includes closer settlement, the shift from pastoral farming to intensive agriculture, growth of dairying, and increasing mechanisation of agriculture. These changes are reflected in clients’ annual expenditures on capital items such as fencing and building materials, tools and implements, materials for drains.

A cosmogenic view of erosion, relief generation, and the age of faulting in southern Africa

Southernmost Africa, with extensive upland geomorphic surfaces, deep canyons, and numerous faults, has long interested geoscientists. A paucity of dates and low rates of background seismicity make it challenging to quantify the pace of landscape change and determine the likelihood and timing of fault movement that could raise and lower parts of the landscape and create associated geohazards. To infer regional rates of denudation, we measured 10Be in river sediment samples and found that south-central South Africa is eroding ~5 m m.y.−1, a slow erosion rate consistent with those measured in other non-tectonically active areas, including much of southern Africa. To estimate the rate at which extensive, fossil, upland, silcrete-mantled pediment surfaces erode, we measured 10Be and 26Al in exposed quartzite samples. Undeformed upland surfaces are little changed since the Pliocene; some have minimum exposure ages exceeding 2.5 m.y. (median, 1.3 m.y.) and maximum erosion rates of We directly dated a recent displacement event on the only recognized Quaternary-active fault in South Africa, a fault that displaces both silcrete and the underlying quartzite. The concentrations of 10Be in exposed fault scarp samples are consistent with a 1.5 m displacement occurring ca. 25 ka. Samples from this offset upland surface have lower minimum limiting exposure ages and higher maximum erosion rates than those from undeformed pediment surfaces, consistent with Pleistocene earthquakes and deformation reducing overall landscape stability proximal to the fault zone. Rates of landscape change on the extensive, stable, silcretized, upland pediment surfaces are an order of magnitude lower than basin-average erosion rates. As isostatic response to regional denudation uplifts the entire landscape at several meters per million years, valleys deepen, isolating stable upland surfaces and creating the spectacular relief for which the region is known.

Considering spatial and temporal scale in landscape‐genetic studies of gene flow

Landscape features exist at multiple spatial and temporal scales, and these naturally affect spatial genetic structure and our ability to make inferences about gene flow. This article discusses how decisions about sampling of genotypes (including choices about analytical methods and genetic markers) should be driven by the scale of spatial genetic structure, the time frame that landscape features have existed in their current state, and all aspects of a species' life history. Researchers should use caution when making inferences about gene flow, especially when the spatial extent of the study area is limited. The scale of sampling of the landscape introduces different features that may affect gene flow. Sampling grain should be smaller than the average home-range size or dispersal distance of the study organism and, for raster data, existing research suggests that simplifying the thematic resolution into discrete classes may result in low power to detect effects on gene flow. Therefore, the methods used to characterize the landscape between sampling sites may be a primary determinant for the spatial scale at which analytical results are applicable, and the use of only one sampling scale for a particular statistical method may lead researchers to overlook important factors affecting gene flow. The particular analytical technique used to correlate landscape data and genetic data may also influence results; common landscape-genetic methods may not be suitable for all study systems, particularly when the rate of landscape change is faster than can be resolved by common molecular markers.

Dynamic equilibrium among erosion, river incision, and coastal uplift in the northern and central Apennines, Italy

Erosion, river incision, and uplift rates in the northern and central Apennines, Italy, since 0.9 Ma, are determined from new cosmogenic nuclide data. Beryllium-10 concentrations in modern and middle Pleistocene sediments indicate erosion rates from 0.20 to 0.58 mm/yr. These rates are similar to estimates of sediment yield (0.12–0.44 mm/yr), river incision (0.35 mm/yr), and uplift (0.01–1.0 mm/yr) rates inferred from other methods that integrate landscape process rates since the early Pleistocene. These rates of landscape change are significantly lower than long-term exhumation rates of ∼1.2 mm/yr since ca. 4.5 Ma, inferred from thermochronometry. Collectively, these data suggest that hillslope erosion and river incision rates in the northern and central Apennines have balanced local uplift rates for ∼1 My, but that exhumation rates have slowed significantly since emergence of the mountain chain in the Pliocene. This condition of dynamic equilibrium was potentially achieved within ca. 3 Ma, similar to some model predictions of hillslope and fluvial system adjustment.

Rates of landscape change at the northern fringe of the Swiss Alps: Historical and recent tendencies

There seems to be a general consensus nowadays among the public in many countries that landscape transformation has accelerated drastically. This study examines the question if cultural landscape change has really accelerated during the 20th century on the border of the Swiss Alps. Different cultural landscape change processes, such as the expansion of the built-up area or the road network, and their transformation rates are distinguished and the impact of the local context and the topographical conditions are investigated. A detailed spatial investigation was conducted covering the last 120 years using GIS and topographic maps. The detected transformation rates were analysed with respect to processes, the study areas and their topography. By the end of the 20th century, the acceleration tendencies seem to have given way to a deceleration. We found considerable variation in transformation rates according to the local context and topographical conditions. For planning and policy this means not only considering transformation rates as such but also looking more closely at spatial and contextual specifics in order to be able to account for the susceptibility of spaces or elements for high transformation rates.

Driving forces and rates of landscape change as a promising combination for landscape change research—An application on the northern fringe of the Swiss Alps

Landscape change is driven by various actors and forces which trigger a specific rate of change. Today, many landscapes change in a direction and with a rate considered unsustainable. Historical insights on actors, driving forces and resulting changes can provide a valuable basis to efficiently control or direct changes. In this paper actors and driving forces of landscape change of the last 120 years are studied in five areas on the northern fringe of the Swiss Alps. Rates of landscape change were reconstructed based on maps. Expert interviews with farmers, politicians, planners and historians as well as historical documents helped in identifying actors and driving forces of the detected landscape change. The contributions of actors and driving forces to landscape change were analyzed by type of driving force (political, economic, cultural, technological and natural/structural). The analysis revealed some key forces, like technological innovations and attitudes and beliefs, operating on several institutional levels and influencing landscape change on a broad basis. Comparing the municipalities disclosed no significant differences regarding the relative contributions of different actors. However, a comparison of the time period before and after World War II revealed distinctive differences in relevant actors and driving forces. Thus, decision-making, policy, and planning must be aware of changing actors and driving forces over time.

Assessing Land Cover Change in Hydro-Climatic Data Network Watersheds Using NALC Imagery

Land cover conversion is known to alter the hydrologic regimes of watersheds. While connections between land cover and runoff are generally known, not all land cover alterations result in detectable changes in streamflow, and the quantity of land cover change required to yield a detectable change in streamflow is unknown over a range of watersheds. The connection between land cover change and streamflow was explored for a Hydro-Climatic Data Network (HCDN) watershed. HCDN is a database of USGS gauged streams commonly used to assess the influence of climatic change on streamflow. Watersheds included in the HCDN have been screened to represent "unimpaired" streamflow. Implicit in this definition is the assumption that land cover is relatively unaltered over the streamflow time series. Imagery from the North American Landscape Characterization (NALC) project was analyzed to detect land cover change from 1972 to 1992 in an Oregon watershed selected from the HCDN. A post-classification change detection yielded a 44% rate of landscape change over 20 years. Changes in land cover classes by dominant soil types were paired with the L-THIA model of Purdue University to quantify the effect of land cover change on runoff. Despite land cover changes, simulations confirmed that runoff remained unchanged. This report summarizes recommended steps for applying NALC imagery to detection of landscape change in other watersheds.

Rain forest invasion of eucalypt‐dominated woodland savanna, Iron Range, north‐eastern Australia: II. Rates of landscape change

AbstractAim To explore rates of rain forest expansion and associated ecological correlates in Eucalyptus‐dominated woodland savanna vegetation in north‐eastern Australia, over the period 1943–91.Location Iron Range National Park and environs, north‐east Queensland, Australia. This remote region supports probably the largest extent of lowland (< 300 m) rain forest extant in Australia. Rainfall (c. 1700 mm p.a.) occurs mostly between November and June, with some rain typically occurring even in the driest months July–October.Methods Interpretation of change in lowland rain forest vegetation cover was undertaken for a 140 km2 area comprising complex vegetation, geology and physiography using available air photos (1943, 1970 and 1991). A GIS database was assembled comprising rain forest extent for the three time periods, geology, elevation, slope, aspect, proximity to streams and roads. Using standard GIS procedures, a sample of 6996 10 × 10 m cells (0.5% of study area) was selected randomly and attributed for vegetation structure (rain forest and non‐rain forest), and landscape features. Associations of rain forest expansion with landscape features were examined with logistic regression using the subset of cells that had changed from other vegetation types to rain forest, and remained rain forest over the assessment period, and comparing them with cells that showed no change from their original, non‐rain forest condition.Results Rain forest in the air photo study area increased from 45 km2 in 1943 to 78.1 km2 by 1970, and to 82.6 km2 by 1991. Rainfall (and atmospheric CO2 concentration) was markedly lower in the first assessment period (1943–70). Modelled rates of rain forest invasion differed predominantly with respect to substrate type, occurring faster on substrates possessing better moisture retention properties, and across all elevation classes. Greatest expansion, at least in the first assessment period, occurred on the most inherently infertile substrates. Expansion was little constrained by slope, aspect and proximity to streams and roads. On schist substrates, probability of invasion remained high (> 60%) over distances up to 1500 m from mature rain forest margins; on less favourable substrates (diorite, granites), probability of expansion was negligible at sites more than 400 m from mature margins.Main conclusions (i) Rain forest expansion was associated primarily with release from burning pressure from c. the 1920s, following major disruption of customary Aboriginal lifestyles including hunting and burning practices. (ii) Decadal‐scale expansion of rain forest at Iron Range supports extensive observations from the palaeoecological literature concerning rapid rain forest invasion under conducive environmental conditions. (iii) The generality of these substrate‐mediated observations requires further testing, especially given that landscape‐scale rain forest invasion of sclerophyll‐dominated communities is reported from other regions of north‐eastern Australia.

Landscape Heterogeneity Effects on Scaling and Monitoring Large Areas Using Remote Sensing Data

Given the increasing rate of landscape change, researchers have realized that managing natural resources sustainably requires knowledge about ecosystems over more than one temporal and spatial scale. Monitoring ecosystem integrity implies sampling over long periods of time and space to identify any significant changes. Subsequently, remote sensing has become integral to many large-scale monitoring efforts. Nonetheless, there remain aspects related to scaling which limit the ability to detect landscape change with a maximal amount of inference. While successive analyses can be used to estimate errors, it is not clear how spatial reorganization resulting from scaling has diluted the signal of the processes embodied within the observed patterns. To achieve a maximal amount of inference, it is first necessary to match three scales: spatial heterogeneity, the scales of the ecological processes creating landscape heterogeneity, and the spatial and temporal resolutions of the image used in the analysis. We discuss the relationship between scale of spatial pattern, image analysis, and scale of process and how their interactions affect large-scale monitoring quality. In particular, we assert that the interactions between pattern and process need to be considered explicitly when designing large-scale monitoring to accurately describe ecological change. This study and others further support the suggestion that monitoring be coupled with spatio-temporal models to elucidate the mapping from pattern to process across scales. It is stressed that future research efforts be directed to understanding the characterization of space-time relationships implicit in pattern and that we move beyond the space-time duality approach to analysis.

Cosmogenic isotope data support previous evidence of extremely low rates of denudation in the Dry Valleys region, southern Victoria Land, Antarctica

Abstract Quantitative estimates of denudation rates in different tectonic and climatic environments are of fundamental importance to an understanding of long-term landscape development. Little quantitative information is currently available on minimum denudation rates, although this is important in placing constraints on the maximum survival potential of individual landforms or erosion surfaces in terrestrial environments. The persistence for up to >15 Ma of a hyper-arid, polar climate in the ice-free Dry Valleys area of southern Victoria Land, Antarctica, makes this a highly probable environment for minimum terrestrial denudation rates. 40 Ar/ 39 Ar dating constraints on the mimimum formation ages of individual landforms indicates generally little modification of even minor features over the past few million years. Relatively, the highest rates of denudation occur at low elevations near the Ross Sea coast. By contrast, rates of landscape change are exceedingly slow at elevations above c. 1500 m in the western Dry Valleys where landforms with a relief of a only a few metres have survived with minimal modification since the mid-Miocene. Measurements of in situ -produced cosmogenic isotopes indicate that even on rectilinear slopes maximum denudation rates may be only c. 1 m Ma −1 , with rates falling to <0.2m Ma −1 at some locations on low relief surfaces at high elevation.

Part-Time Farming and its Implications for the Rural Landscape: A Preliminary Analysis

Part-time farm businesses are assuming an increased importance within the structure of British agriculture. It is often suggested that their reduced dependence on the financial and technological treadmills driving farm development leads them to have less impact than full-time producers on the farmed landscape. Some evidence in support of this view, drawn from a survey of landscape change between 1970 and 1985 on more than 200 farms in southern England, is presented. At the same time, the findings caution against generalisation and emphasise the need to disaggregate the results. In particular, it is essential to ascertain the different roles part-time farming is playing in the development of capitalist agriculture and the strategies of farm households. There is as much variation in the rates of landscape change between types of part-time business as between full-time and part-time farming.