Grass-mediated Capture of Resource Flows and the Maintenance of Banded Mulga in a Semi-arid Woodland

Val Jo Anderson; Ken C. Hodgkinson

doi:10.1071/bt96019

Grass-mediated Capture of Resource Flows and the Maintenance of Banded Mulga in a Semi-arid Woodland

Australian Journal of Botany ◽

10.1071/bt96019 ◽

1997 ◽

Vol 45 (2) ◽

pp. 331 ◽

Cited By ~ 36

Author(s):

Val Jo Anderson ◽

Ken C. Hodgkinson

Keyword(s):

Soil Water ◽

Isotope Composition ◽

Life Forms ◽

Grazing Pressure ◽

Perennial Grasses ◽

Xylem Water Potential ◽

Scarce Resources ◽

Landscape Processes ◽

Acacia Aneura ◽

Semi Arid

It has been proposed for semi-arid and arid regions that the scarce resources of water and nutrients normally limiting plant growth are distributed patchily in the landscape in order to maintain both stability and productivity (Tongway 1990). ‘Fertile patches’ are maintained by the concentration of resources during flows and when resource control is weakened their persistence is threatened. This proposition was tested by comparing water relations of perennial life-forms in the nutrient and water rich ‘island-bands’ of mulga (Acacia aneura F.Muell. ex Benth.) shrubs, with and without perennial grasses. Dawn xylem water potential (dawn ψx) and stable hydrogen isotope composition data showed that A. aneura and companion grasses competed for soil water, whereas the poplar box (Eucalyptus populnea F.Muell.) trees accessed additional sub-soil water. During a drying cycle, dawn ψx of A. aneura on the upslope portion of ‘island-bands’ was –2 MPa where grass was abundant, and –4.8 MPa where grasses were killed by heavy grazing. On the downslope portions, dawn ψx of A. aneura was similar at –4.2 MPa. Recruitment of A. aneura was occurring in the upslope portion, but was less where there were no grasses. There were more dead A. aneura shrubs on the downslope portion and in grass-free ‘island-bands’. The results suggest that removal of perennial grasses by grazing shortens the period of water supply to A. aneura shrubs in ‘island-bands’ and they prematurely die during low rainfall periods. Furthermore, continued grazing pressure from domestic and non-domestic herbivores will prevent restoration of landscape processes necessary for the survival of these shrubs and associated flora.

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The Influence of Recent Grazing Pressure and Landscape Position on Grass Recruitment in a Semi-Arid Woodland of Eastern Australia.

The Rangeland Journal ◽

10.1071/rj9960003 ◽

1996 ◽

Vol 18 (1) ◽

pp. 3 ◽

Cited By ~ 13

Author(s):

VJ Anderson ◽

KC Hodgkinson ◽

AC Grice

Keyword(s):

Seedling Emergence ◽

Perennial Grass ◽

Soil Surface ◽

Grazing Pressure ◽

Perennial Grasses ◽

Run Off ◽

Eastern Australia ◽

Annual Grasses ◽

History Of ◽

Semi Arid

This study examined the effects of previous grazing pressure, position in the landscape and apparent seed trapping capability of soil surface micro-sites on recruitment of the perennial grass Monachather paradoxa (mulga oats) in a semi-arid woodland. Seedling emergence was counted on small plots which had been kept moist for one month. The plots were on bare ground, or at grass tussocks, or at log mounds, sited in the run-off, interception and run-on zones of paddocks that had been grazed for six years at 0.3 and 0.8 sheep equivalent/ha. Few naturally occurring perennial grass seedlings emerged on any of the sites. The level of previous grazing pressure influenced the recruitment of grasses from natural sources as well as from seed of M. paradoxa broadcast on the soil surface; significantly more grass seedlings recruited in paddocks stocked at 0.3 than at 0.8 sheep/ha. Emergence of the sown grass did not differ significantly between the three zones in the landscape, but trends in the data suggest the interception zone may have been the most favourable. Recruitment from in situ grass seed was highest in the mulga grove (run-on) zone. Most seedlings of the sown grass emerged around the bases of existing perennial grass tussocks, but recruitment of volunteer perennial and annual grasses was more evenly distributed between the mulga log-mounds and perennial grass tussocks. It is concluded that very low levels of readily germinable seed of perennial grasses remained in the soil at the end of the drought and that areas with a history of high grazing pressure have less probability of grass recruitment when suitable rain occurs.

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Small-scale resource heterogeneity in semi-arid landscapes

Pacific Conservation Biology ◽

10.1071/pc940201 ◽

1994 ◽

Vol 1 (3) ◽

pp. 201 ◽

Cited By ~ 99

Author(s):

David J. Tongway ◽

John A. Ludwig

Keyword(s):

Grazing Pressure ◽

Arid Ecosystems ◽

Small Scale ◽

Patchy Distribution ◽

Landscape Degradation ◽

Term Change ◽

Regulation Mechanisms ◽

Acacia Aneura ◽

Semi Arid

Patchy distribution of plant populations is a hallmark of arid and semi-arid ecosystems. This has been attributed to the patchy distribution of scarce or limiting resources across the landscape and within the soil itself. Behind these descriptive properties are a range of processes which are the causal mechanisms of resource allocation, conservation and utilization within the landscape. Terrain-controlled mechanisms have been previously described in respect of groved mulga (Acacia aneura) communities. This paper describes a set of resource regulation mechanisms which are largely controlled by plants and plant communities and which are effective at fine scales. The actual mechanisms are inferred from field observations, and validated by looking for the net effects of defined processes acting over time. Plant-mediated resource control is inherently more sensitive to grazing pressure than terrain-controlled processes, because herbivores are able to quickly and drastically alter the density and basal cover of plants, and so change the effectiveness of the control processes. This may lead to a long-term change in system function. This paper examines the generality of these propositions in a series of contrasting landscape types, and proposes a framework by which landscape degradation can be assessed by examining the modes of basic resource regulation.

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Determinants of seasonal changes in availability of food patches for elephants (Loxodonta africana) in a semi-arid African savanna

PeerJ ◽

10.7717/peerj.3453 ◽

2017 ◽

Vol 5 ◽

pp. e3453 ◽

Cited By ~ 5

Author(s):

Bruce W. Clegg ◽

Timothy G. O’Connor

Keyword(s):

Soil Water ◽

Loxodonta Africana ◽

Life Forms ◽

Food Density ◽

Regression Equations ◽

African Savanna ◽

Plant Life Forms ◽

Plant Groups ◽

Influence Of Food ◽

Semi Arid

Loss of biodiversity caused by impact of elephants (Loxodonta africana) on African woodlands may require a management response, but any action should be based on an understanding of why elephants choose to utilise trees destructively. Comprehension of elephant feeding behaviour requires consideration of the relative value of the plant groups they may potentially consume. Profitability of available food is partly determined by the time to locate a food patch and, therefore, as a foundation for understanding the influence of food availability on diet selection, key controls on the density of grass, forb, and browse patches were investigated across space and time in a semi-arid African savanna. Density of food patches changed seasonally because plant life-forms required different volumes of soil water to produce green forage; and woody plants and forbs responded to long-term changes in soil moisture, while grasses responded to short-term moisture pulses. Soil texture, structure of woody vegetation and fire added further complexity by altering the soil water thresholds required for production of green forage. Interpolating between regularly-timed, ground-based measurements of food density by using modelled soil water as the predictor in regression equations may be a feasible method of quantifying food available to elephants in complex savanna environments.

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Effects of soil water regime and grazing on vegetation diversity and production in a hyperseasonal savanna in the Apure Llanos, Venezuela

Journal of Tropical Ecology ◽

10.1017/s0266467403001299 ◽

2004 ◽

Vol 20 (2) ◽

pp. 209-220 ◽

Cited By ~ 22

Author(s):

Guillermo Sarmiento ◽

Marcela Pinillos ◽

Marta Pereira da Silva ◽

Dimas Acevedo

Keyword(s):

Water Content ◽

Soil Water ◽

Biomass Accumulation ◽

Grazing Pressure ◽

Perennial Grasses ◽

Plant Production ◽

Vegetation Diversity ◽

Floristic Inventory ◽

Ground Biomass ◽

Relative Water

Soil water content and above-ground biomass accumulation, above 10 cm high, were measured monthly in a flooded savanna ecosystem under grazing pressure and under cattle exclusion, during two growth cycles. Near-to-the-ground and below-ground biomass were measured three times during this period. Besides, composition, species richness and diversity were obtained through a floristic inventory. Despite a relatively high floristic richness and diversity, Panicum laxum is the dominant species throughout the study area, while three other perennial grasses, Paspalum chaffanjonii, Leersia hexandra and Axonopus purpusii, also reach high values of cover and biomass. Each of them reacts specifically to flooding, drought and grazing conditions. This ecosystem shows a strongly seasonal behaviour, with primary production, mortality and decomposition sharply timed by soil relative water content. Both drought and water excess seem to limit plant production, even more during wet years when the savanna might remain flooded for up to 4 mo. Some structural and functional differences between the grazed and the protected systems are demonstrated, but under the actual, relatively low stocking rate, the grazed savanna produces as much forage as the ungrazed one.

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Spatial and Temporal Pattern in the Grazing of Grasses by Sheep Within a Semi-Arid Wooded Landscape.

The Rangeland Journal ◽

10.1071/rj9950154 ◽

1995 ◽

Vol 17 (2) ◽

pp. 154 ◽

Cited By ~ 4

Author(s):

KC Hodgkinson ◽

JW Terpstra ◽

WJ Muller

Keyword(s):

Woody Plant ◽

Perennial Grass ◽

Grazing Pressure ◽

Perennial Grasses ◽

Spatial And Temporal Variation ◽

Grass Species ◽

Plant Mortality ◽

Research Facility ◽

Semi Arid ◽

Domestic Stock

Grazing the woodlands of semi-arid and arid Australia by domestic stock has extensively collapsed perennial *grass populations and thereby fostered woody plant increase. This study examined the pattern of grazing of individual grass plants by sheep in the landscape of a semi-arid woodland, and a model was developed describing the spatial and temporal influences on the grazing pressure placed on plants. Plants of two widespread perennial grass species differing in palatability, Eragrostis eriopoda and Thyridolepis mitchelliana, were examined weekly in two contrasting periods at the CSIRO Lake Mere Research Facility. The plants were located throughout the landscape in lightly- and heavily- stocked paddocks. Patterns of grazing in space and time were determined by examining the grazing of marked tillers. No preference was shown for previously ungrazed plants and only occasionally were previously grazed plants preferred. Thyridolepis mitchelliana plants were slightly preferred over E. eriopoda plants. Landscape zones receiving water and nutrients from elsewhere were preferred for grazing but the effect was weak. The foliage biomass of herbaceous plants in the immediate vicinity of a grass plant did not influence the number of tillers grazed nor the probability of the plant being grazed. Overall the defoliation of individual plants by sheep was weakly determined by landscape location, stocking level, plant species and prevailing forage on offer. The influence of spatial and temporal variation was small; random grazing of grass plants was the rule. This finding suggests that the grazing pressure on palatable perennial grasses in the paddocks of semi-arid woodlands will be similar across wooded landscapes and that spatial variability in plant mortality could be due to. the combined effect of plant water stress, which varies spatially and temporally, and grazing pressure which varies temporally but not spatially.

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Herbage Production Following Rainfall Redistribution in a Semi-Arid Mulga (Acacia Aneura) Woodland in Western New South Wales.

The Rangeland Journal ◽

10.1071/rj9980206 ◽

1998 ◽

Vol 20 (2) ◽

pp. 206 ◽

Cited By ~ 18

Author(s):

JC Noble ◽

RSB Greene ◽

WJ Muller

Keyword(s):

Soil Water ◽

New South ◽

Water Storage ◽

Rainfall Event ◽

Soil Water Storage ◽

Stocking Rate ◽

South Wales ◽

Run Off ◽

Acacia Aneura ◽

Semi Arid

The effects of stocking rate (nominally ranging from 0.3 up to 0.8 dry sheep equivalents per ha) on rainfall redistribution, soil-water storage and herbage production were studied in three contiguous geomorphic zones (run-off, interception and run-on zones) in a semi-arid mulga (Acacia aneura) woodland in western New South Wales. The amount of rainfall redistribution increased directly with rainfall but there was no significant effect of stocking rate on the amount of soil-water stored in various zones. while soil-water storage differed little between zones following a minor rainfall event (11.9 mm), it was significantly higher (P < 0.001) in the run-on zone following a major rainfall event (42.7 mm). The interception zone was by far the most productive herbage zone contributing a significantly (P < 0.01) disproportionate amount of forage (c. 90% of total paddock production at low stocking rates) despite this zone only occupying a relatively small proportion (c. 12%) of landscape catenae. Herbage in the interception zone principally comprised palatable C3 perennial grasses such as Thyridolepis mitchelliana (mulga grass) and Monachather paradoxa (bandicoot grass). Experimental manipulation confirmed the fundamental importance of rainfall redistribution as a landscape process mediating herbage production in these semi-arid plant communities. Dry matter production by Eragrostis eriopoda (woollybutt) was significantly enhanced (P < 0.05) in the run-off zone when incident rainfall was retained in situ by metal barriers. Conversely, production by Thyridolepis mitchelliana in the lower interception zone was significantly depressed (P < 0.01) where similar barriers prevented access by overland flow. The results are discussed in the context of developing conservative management strategies designed to maintain effective landscape processes in these extensive ecosystems.

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Influence of soil water on stress–strain behaviour of a compacting soil in semi-arid Kenya

Soil and Tillage Research ◽

10.1016/j.still.2005.07.008 ◽

2006 ◽

Vol 89 (2) ◽

pp. 144-154 ◽

Cited By ~ 11

Author(s):

A.N. Gitau ◽

L.O. Gumbe ◽

E.K. Biamah

Keyword(s):

Soil Water ◽

Stress Strain ◽

Strain Behaviour ◽

Semi Arid

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The Root-Soil Water Relationship Is Spatially Anisotropic in Shrub-Encroached Grassland in North China: Evidence from GPR Investigation

Remote Sensing ◽

10.3390/rs13061137 ◽

2021 ◽

Vol 13 (6) ◽

pp. 1137

Author(s):

Xihong Cui ◽

Zheng Zhang ◽

Li Guo ◽

Xinbo Liu ◽

Zhenxian Quan ◽

...

Keyword(s):

Soil Water ◽

Root Distribution ◽

Preferential Flow ◽

Distribution Density ◽

Vertical Direction ◽

Additive Models ◽

Depth Interval ◽

Soil Core ◽

Semi Arid ◽

Free Area

To analyze the root-soil water relationship at the stand level, we integrated ground-penetrating radar (GPR), which characterized the distribution of lateral coarse roots (>2 mm in diameter) of shrubs (Caragana microphylla Lam.), with soil core sampling, which mapped soil water content (SWC) distribution. GPR surveys and soil sampling were carried out in two plots (Plot 1 in 2017 and Plot 2 in 2018) with the same size (30 × 30 m2) in the sandy soil of the semi-arid shrubland in northern China. First, the survey area was divided into five depth intervals, i.e., 0–20, 20–40, 40–60, 60–80, and 80–100 cm. Each depth interval was then divided into three zones in the horizontal direction, including root-rich canopy-covered area, root-rich canopy-free area, and root-poor area, to indicate different surface distances to the canopy. The generalized additive models (GAMs) were used to analyze the correlation between root distribution density and SWC after the spatial autocorrelation of each variable was eliminated. Results showed that the root-soil water relationship varies between the vertical and horizontal directions. Vertically, more roots are distributed in soil with high SWC and fewer roots in soil with low SWC. Namely, root distribution density is positively correlated with SWC in the vertical direction. Horizontally, the root-soil water relationship is, however, more complex. In the canopy-free area of Plot 1, the root-soil water relationship was significant (p < 0.05) and negatively correlated in the middle two depth intervals (20–40 cm and 40–60 cm). In the same two depth intervals in the canopy-free area of Plot 2, the root-soil water relationship was also significant (p < 0.01) but non-monotonic correlated, that is, with the root distribution density increasing, the mean SWC decreased first and then increased. Moreover, we discussed possible mechanisms, e.g., root water uptake, 3D root distribution, preferential flow along roots, and different growing stages, which might lead to the spatially anisotropic relationship between root distribution and SWC at the stand level. This study demonstrates the advantages of GPR in ecohydrology studies at the field scale that is challenging for traditional methods. Results reported here complement existing knowledge about the root-soil water relationship in semi-arid environments and shed new insights on modeling the complex ecohydrological processes in the root zone.

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Modeling Insights into Precipitation Deuterium Excess as an Indicator of Raindrop Evaporation in Lanzhou, China

Water ◽

10.3390/w13020193 ◽

2021 ◽

Vol 13 (2) ◽

pp. 193

Author(s):

Fenli Chen ◽

Mingjun Zhang ◽

Athanassios A. Argiriou ◽

Shengjie Wang ◽

Qian Ma ◽

...

Keyword(s):

Arid Region ◽

Quantitative Methods ◽

Isotope Composition ◽

Sampling Site ◽

Western China ◽

Cloud Base ◽

Deuterium Excess ◽

Semi Arid Region ◽

Semi Arid

The deuterium excess in precipitation is an effective indicator to assess the existence of sub-cloud evaporation of raindrops. Based on the synchronous measurements of stable isotopes of hydrogen and oxygen (δ2H and δ18O) in precipitation for several sites in Lanzhou, western China, spanning for approximately four years, the variations of deuterium excess between the ground and the cloud base are evaluated by using a one-box Stewart model. The deuterium excess difference below the cloud base during summer (−17.82‰ in Anning, −11.76‰ in Yuzhong, −21.18‰ in Gaolan and −12.41‰ in Yongdeng) is greater than that in other seasons, and difference in winter is weak due to the low temperature. The variations of deuterium excess in precipitation due to below-cloud evaporation are examined for each sampling site and year. The results are useful to understand the modification of raindrop isotope composition below the cloud base at a city scale, and the quantitative methods provide a case study for a semi-arid region at the monsoon margin.

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