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Dive into the research topics where Rory P. D. Walsh is active.

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Featured researches published by Rory P. D. Walsh.


Earth-Science Reviews | 2000

Soil water repellency: its causes, characteristics and hydro-geomorphological significance

Stefan H. Doerr; Richard A. Shakesby; Rory P. D. Walsh

Abstract Water repellency (hydrophobicity) of soils is a property with major repercussions for plant growth, surface and subsurface hydrology, and for soil erosion. Important advances have been made since the late 1980s in identifying the range of environments affected by water repellency, its characteristics and its hydro-geomorphological impacts. This review summarises earlier work, but focusses particularly on these recent advances and identifies remaining research gaps. The associations of water repellency with (a) soils other than coarse-textured ones, (b) an expanding list of plant species, and (c) a widening range of climates other than seasonally dry types have been recurrent themes emphasised in recent literature. Nevertheless, knowledge about the extent of water repellency amongst world soils is still comparatively sparse. Its origin by the accumulation of long-chained organic compounds on or between soil particles is now widely accepted, but understanding of their exact chemical composition and means of attachment to particle surfaces remains incomplete. The transient nature of water repellency has been found to be mainly associated with fluctuations in soil moisture, but the precise processes and required conditions for the changes from hydrophobic to hydrophilic and vice versa are so far only poorly understood. Significant advances relating to the hydro-geomorphological impacts of hydrophobic layers have been made since the late 1980s in identifying and separating the various effects of such layers on surface and subsurface water flow. It has become evident that these effects in turn are influenced by variables such as the frequency and effectiveness of flow pathways through hydrophobic layers as well as their position and transitory behaviour. Recent literature has continued to highlight the role of water repellency in promoting soil erosion and it is now recognised that it can promote rainsplash detachment and soil loss not only by water, but also by wind. Major research gaps, however, remain in (a) isolating the erosional impact of water repellency from other factors, and (b) identifying the exact role of, and the interactions between the different variables controlling development and effectiveness of flow pathways through hydrophobic soil. Improved understanding of the effects of soil water repellency will enable its overall role in surface and subsurface hydrological and erosional processes to become more clearly defined.


Journal of Hydrology | 2000

The erosional impact of soil hydrophobicity: current problems and future research directions.

Richard A. Shakesby; Stefan H. Doerr; Rory P. D. Walsh

Abstract Soil hydrophobicity affects the susceptibility of soils to erosion in a variety of ways (e.g. increased aggregate stability, reduced infiltration capacity, enhanced overland flow), but there are problems concerning the overall assessment of its erosional impact. Three current problems are discussed: (1) poor isolation of hydrophobicity from other effects; and poor understanding of its overall impact; (2) areally, at slope and catchment scales; and (3) temporally, over periods of months or years rather than on a storm basis. These problems are highlighted with reference to the literature and to research in Portugal on highly hydrophobic forest soils. A conceptual model relating erosion risk to three key aspects of soil hydrophobicity (temporal contiguity, spatial contiguity and the thickness of any overlying hydrophilic soil) is presented in order to provide a framework for future research into hydrophobicity–soil erosion links.


Soil Science | 1998

Spatial variability of soil hydrophobicity in fire-prone eucalyptus and pine forests, Portugal

Stefan H. Doerr; Richard A. Shakesby; Rory P. D. Walsh

Because of its implications for slope hydrology and soil erosion in the region and the lack of previous work on (i) spatial variability of hydrophobicity and (ii) hydrophobicity in a wet Mediterranean environment, this paper assesses the in situ severity and spatial variability of hydrophobicity of surface soils in dry summer conditions in burnt and unburnt Pinus pinaster and Eucalyptus globulus forests in north-central Portugal. Results of experiments to explore the origin of hydrophobicity are also reported. The molarity of ethanol droplet (MED) technique was employed. The average severity of hydrophobicity (MED > 24%) in both long-unburnt and recently burnt forests is among the highest recorded. In contrast to other studies, spatial variability of hydrophobicity is generally low for all land types. This is thought to be caused by a comparatively high release rate and thorough distribution of hydrophobic substances aided by the relatively wet climate combined with the fairly uniform character of the commercial forest stands investigated. Although forest fires are usually thought either to increase (for low ground temperatures) or to destroy (for high ground temperatures) surface soil hydrophobicity, burning in the study area had little impact on surface hydrophobicity. This is attributed to (i) preburn hydrophobicity already so severe that the organic compounds released from the litter during burning contribute no detectable additional hydrophobic effects and (ii) fire temperatures insufficient to destroy surface hydrophobicity. The results suggest that the relative spatial uniformity of hydrophobicity in the study area is induced by the planting of E. globulus or P. pinaster. The litter layers of both species, and the root zone in the case of E. globulus, are identified as sources of hydrophobic substances. Extreme hydrophobicity in E. globulus stands is found to develop within 2 years of planting on previously hydrophilic plowed terrain.


Catena | 1996

Soil hydrophobicity variations with depth and particle size fraction in burned and unburned Eucalyptus globulus and Pinus pinaster forest terrain in the Águeda Basin, Portugal

Stefan H. Doerr; Richard A. Shakesby; Rory P. D. Walsh

A laboratory programme of water drop penetration tests is used to investigate the nature of hydrophobicity of soils in burnt and unburnt Eucalyptus globulus and Pinus pinaster forest areas of northern Portugal. Variations in hydrophobicity of air-dried soil with soil depth, soil particle size fraction, land use and burn history are assessed. Results differ from those found by many other studies in several respects: (1) fire was not found to enhance hydrophobicity, as unburnt and old-burn soils are as hydrophobic as newly-burnt ones; (2) hydrophobicity was found to be characteristic of soils from the surface down to the weathered (Cw) horizon rather than confined to a near-surface layer, (3) it is also associated with the finer rather than the coarser size fractions of the soils. Soils under E. globulus are distinctly more hydrophobic than those under P. pinaster. Implications for the generation of overland flow are briefly explored.


Catena | 1999

Nutrient losses in eroded sediment after fire in eucalyptus and pine forests in the wet Mediterranean environment of northern Portugal

Andrew D. Thomas; Rory P. D. Walsh; Richard A. Shakesby

Nutrients sorbed onto eroded sediment from small bounded plots installed in newly burned and unburned Eucalyptus globulus and Pinus pinaster forests in the Agueda Basin, north-central Portugal were measured over an 18-month period. The data are used to determine: (i) the effects of fire on nutrient loss, (ii) the importance of fire-induced losses on soil fertility, and (iii) temporal variations in nutrient losses. Fire increased losses of total nitrogen, exchangeable potassium and available phosphorus by 3–4 orders of magnitude. This is attributed to increased erosion and high nutrient concentrations at the soil surface in the burned forests, where burning of organic matter and vegetation increased nutrient availability. Enhanced rates of loss were sustained for at least 3 years, resulting in much greater post-fire nutrient losses than reported in drier regions of the Mediterranean. Losses of available P had the greatest potential for reductions in soil fertility.


Journal of Hydrology | 2000

Hydrological implications of soil water-repellency in Eucalyptus globulus forests, north-central Portugal

A. J. D. Ferreira; Celeste Coelho; Rory P. D. Walsh; Richard A. Shakesby; A. Ceballos; Stefan H. Doerr

Soil water-repellency (hydrophobicity) is a widespread property of Eucalyptus globulus and Pinus pinaster forest soils in central and north littoral Portugal and is particularly severe during the summer dry conditions. This paper attempts to assess the impact of water repellency on overland flow and runoff generation at plot and catchment scales for two types of terrain with differing land management and degree of soil hydrophobicity: (i) highly hydrophobic land with regenerating eucalyptus forest following fire; and (ii) largely hydrophilic land on which deep-ploughing prior to planting eucalyptus seedlings had eliminated hydrophobicity. Overland flow responses were monitored over a 40-month period for two 8 m × 2 m plots and streamflow was recorded continuously at gauging stations for two small catchments of predominantly regrowth eucalyptus and ploughed/ planted eucalyptus, respectively. Soil hydrophobicity was assessed using the Water Drop Penetration Time (WDPT) test. Seasonal variations in the factors influencing plot overland flow response were assessed for each land management type using multivariate analysis. For the regrowth eucalyptus plot, overland flow generation was found to be negatively correlated with antecedent soil moisture in summer (suggesting that hydrophobicity-linked Hortonian overland flow is then dominant), but positively related to throughflow in winter (suggesting that saturation overland flow generation in a hydrophilic-phase soil was at that time the dominant mechanism). In the ploughed/planted areas, negative correlations with soil moisture were found neither in summer nor winter. Rainfall amount (and in winter also antecedent precipitation) were found to be the variables most strongly and positively related to overland flow volume. The plot results are compared with streamflow responses for the small catchments.


Journal of Tropical Ecology | 1996

DROUGHT FREQUENCY CHANGES IN SABAH AND ADJACENT PARTS OF NORTHERN BORNEO SINCE THE LATE NINETEENTH CENTURY AND POSSIBLE IMPLICATIONS FOR TROPICAL RAIN FOREST DYNAMICS

Rory P. D. Walsh

Archival rainfall data are used to investigate changes in drought frequency and severity in Sabah and other parts of northern Borneo since the late nineteenth century. Two measures of drought severity are used: drought duration (given by the number of consecutive months with less than 100 mm rain); and drought intensity (indexed by the cumulative rainfall deficit below 100 mm per month of a drought sequence). Within northern Borneo dry periods are very short (< 3 months) and infrequent in Sarawak, south-western Sabah, Brunei and central and western Kalimantan; droughts occur seasonally, but are comparatively short in north-western Sabah; droughts are less frequent, but more severe in eastern Sabah and parts of eastern Kaliman- tan. In coastal Sabah and Brunei, there has been a statistically significant increase in the frequency and severity of droughts since the late 1960s. At Sandakan, two drought-prone epochs in 1877- 1915 and 1968-92 (each experiencing five droughts of at least 4 months duration) are identified, separated by a 52-year period that was nearly drought-free. At Sandakan also, the ecologically damaging 1982-3 drought was neither as long or severe as those of 1903 and 1915. Links with El Nifio-Southern Oscillation events are found to be not as strong as previous studies have suggested. Possible implications of the spatial and temporal patterns in drought magnitude-frequency for differences in tropical rain forest character within the region are discussed.


Soil Research | 2005

Temporal dynamics of water repellency and soil moisture in eucalypt plantations, Portugal

G. Leighton-Boyce; Stefan H. Doerr; Richard A. Shakesby; Rory P. D. Walsh; A. J. D. Ferreira; A. K. Boulet; Celeste Coelho

This paper investigates water repellency and soil moisture under 4 different Eucalyptus globulus plantations in Portugal. On 8 occasions over a 16-month period, measurements were made at 3 depths (surface, 0.10 and 0.20 m) at 60 points on four 10 by 18 m grids. The main results are: (i) at all sites and depths, spatial frequency of repellency (defined as percentage of repellent grid points) followed a moisture-related seasonal cycle, its amplitude being greatest for the longest established site, where surface repellency was contiguous in dry late-summer conditions, but was entirely absent after wet winter conditions; (ii) at a few points at 2 sites, repellency persisted during winter; (iii) repellency severity was dichotomously distributed regardless of season (i.e. soils were generally either wettable or highly repellent); and (iv) at the longest established site, when soil moisture was 27% soils were wettable. This may either support the existence of a ‘transition zone’, or be an artefact of the different scales of repellency and soil moisture assessments. Reasons for the observed changes in repellency and their relationship with soil moisture and antecedent rainfall are explored and soil hydrological implications discussed.


Applied Geography | 1996

Limiting the soil degradational impacts of wildfire in pine and eucalyptus forests in Portugal: A comparison of alternative post-fire management practices

Richard A. Shakesby; David J Boakes; Celeste Coelho; Aj Bento Gonçalves; Rory P. D. Walsh

Abstract In newly burnt and unburnt pine and eucalyptus forest in Portugal, overland flow and soil losses were monitored to assess the impacts of the following post-fire treatments: application of different quantities of logging litter; rip-ploughing compared with minimum tillage prior to planting eucalyptus seedlings; and clearance of pine needles and vegetation. Eucalyptus logging litter reduced soil losses by up to 95 per cent. The impact of pine logging litter was equivocal, but removal of pine needles increased soil losses elevenfold. Implications for soil longevity, soil quality and land management strategy are discussed.


Philosophical Transactions of the Royal Society B | 2011

Changes in forest land use and management in Sabah, Malaysian Borneo, 1990-2010, with a focus on the Danum Valley region.

Glen Reynolds; Junaidi Payne; Waidi Sinun; Gregory Mosigil; Rory P. D. Walsh

In an earlier special issue of this journal, Marsh & Greer summarized forest land use in Sabah at that time and gave an introduction to the Danum Valley Conservation Area. Since that assessment, during the period 1990–2010, the forests of Sabah and particularly those of the ca 10 000 km2 concession managed on behalf of the State by Yayasan Sabah (the Sabah Foundation) have been subject to continual, industrial harvesting, including the premature re-logging of extensive tracts of previously only once-logged forest and large-scale conversion of natural forests to agricultural plantations. Over the same period, however, significant areas of previously unprotected pristine forest have been formally gazetted as conservation areas, while much of the forest to the north, the south and the east of the Danum Valley Conservation Area (the Ulu Segama and Malua Forest Reserves) has been given added protection and new forest restoration initiatives have been launched. This paper analyses these forest-management and land-use changes in Sabah during the period 1990–2010, with a focus on the Yayasan Sabah Forest Management Area. Important new conservation and forest restoration and rehabilitation initiatives within its borders are given particular emphasis.

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A. J. D. Ferreira

Polytechnic Institute of Coimbra

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Carla S. S. Ferreira

Polytechnic Institute of Coimbra

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Kawi Bidin

Universiti Malaysia Sabah

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Ian Douglas

University of Manchester

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