A Model of Woody-Herbaceous Biomass Relationships in Eucalypt and Mesquite Communities

Scanlan, Joseph C.

doi:10.2307/4002530

Cited by 31 publications

(15 citation statements)

References 5 publications

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“…Trees influence patterns in pasture productivity via the net effects of stimulatory and competitive processes. Stimulatory processes include enhanced water infiltration, nutrient accumulation, and microclimate regulation, whereas competitive processes relate to competition between trees and pasture grasses for light and nutrients (50). As a result of this balance, pasture productivity and profitability peak at intermediate levels of tree cover (13,14).…”

Section: Discussionmentioning

confidence: 99%

Reversing a tree regeneration crisis in an endangered ecoregion

Fischer¹,

Stott²,

Zerger

et al. 2009

Proc. Natl. Acad. Sci. U.S.A.

156

154

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Global food demand is growing rapidly. Livestock grazing can provide a valuable source of protein, but conventional grazing is often unsustainable. We studied an 800,000-ha section of a threatened ecoregion in southeastern Australia. Conventional management in the region involves continuous livestock grazing with few rest periods and regular fertilizer application. By using remotely sensed data on tree cover and extensive field data on livestock grazing regimes, soil chemistry, tree diameters, and tree regeneration, we show that the region is facing a tree regeneration crisis. Under conventional management, across the region, millions of hectares of land currently supporting tens of millions of trees will be treeless within decades from now. This would have severe negative ramifications for biodiversity and key ecosystem services, including water infiltration and shade provision for livestock. However, we identified an unexpected win-win solution for tree regeneration and commercial grazing. A relatively new practice in the region is fast-rotational grazing, characterized by prolonged rest periods in between short, intensive grazing events. The probability of regeneration under fast-rotational grazing was up to 4-fold higher than under conventional grazing, and it did not differ significantly from the probability of regeneration in ungrazed areas. In addition, trees were more likely to regenerate where soil nutrient levels were low. These findings suggest that the tree regeneration crisis can be reversed by applying low-input, fastrotational grazing. New policy settings supporting these practices could signal a turning point for the region, from ecological decline to ecological recovery.countryside biogeography ͉ grassy box woodlands ͉ holistic management ͉ rotational grazing ͉ scattered trees

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Section: Discussionmentioning

confidence: 99%

Reversing a tree regeneration crisis in an endangered ecoregion

Fischer¹,

Stott²,

Zerger

et al. 2009

Proc. Natl. Acad. Sci. U.S.A.

156

154

View full text Add to dashboard Cite

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“…Although not unexpected (Scanlan 1992), it further highlights the structural shift from grasslands to dense thorn forests. The economic implications are significant as it is occurring on one of the most productive parts of the Pilbara landscape, where carrying capacities reach 9 ha/ cattle unit (cu) for C. ciliaris and 20 ha/cu for E. xerophila grass as compared with 60 ha/cu for spinifex grasslands in the same habitat and 280 ha/cu for spinifex on low hills and rises (Payne et al 2003).…”

Section: Demographymentioning

confidence: 93%

Population Ecology of Hybrid Mesquite (Prosopis Species) in Western Australia: How Does it Differ from Native Range Invasions and What are the Implications for Impacts and Management?

Klinken

Graham²,

Flack

2006

Biol Invasions

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Beneficial exotic trees and shrubs have been widely spread throughout semiarid and arid regions of the world. These trees and shrubs can however cause severe negative impacts. Mesquite (Prosopis species), native to the New World, is one example which continues to be promoted despite causing serious impacts both in its native and introduced ranges. We describe the population structure of the largest population of fire-tolerant hybrid mesquite (P. velutina Â P. glandulosa var. glandulosa Â P. pallida) in Australia, which was intentionally established in the 1930s. We compare it with invasive populations within its native range, and consider the implications for managing exotic mesquite invasions. We found relatively high juvenile densities at all levels of canopy cover (<30% to 90-100%), and low mortality rates for both juveniles and adults (<2%/y), which suggests that populations are still in an early phase of invasion. Exotic populations differed from native range populations in being more dense (average 4,859 adults/ha), having a sizable sapling (seedling and juvenile) bank that can remain quiescent under canopy cover (average 10,914 seedlings and juveniles/ha), failing to act as nurse plants for native shrubs (<8 native shrubs/ha), and almost totally excluding the herbaceous (grass) layer (average 0.3% cover). Our results suggest that ecosystem impacts in the introduced range are likely to be even worse, and management even more difficult, than has already been reported for invasions within its native range. The lack of feasible means for managing highly invasive, broad-scale mesquite populations need to be addressed, and needs to be considered explicitly when promoting mesquite as a beneficial plant.

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“…This may result from an initial stimulatory effect of shrubs on grass production beneath shrub canopies (Scanlan 1992; Tiszler and R. Virginia unpublished work). In contrast, the proportion of C 4 -C in LFC decreased in dune Bkb (~44%) and Btkb (~18%) horizons.…”

Section: Horizon Samplementioning

confidence: 96%

Carbon isotopes reveal soil organic matter dynamics following arid land shrub expansion

1997

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Over the past century, overgrazing and drought in New Mexico's Jornada Basin has promoted the replacement of native black grama (Bouteloua eriopoda Torr.) grass communities by shrubs, primarily mesquite (Prosopis glandulosa Torr.). We investigated the effects of shrub expansion on the distribution, origin, turnover, and quality of light (LFC) and heavy (HFC) soil organic matter (SOM) fractions using δC natural abundance to partition SOM into C (grass) and C (shrub) sources. Soil organic matter beneath grasses and mesquite was isotopically distinct from associated plant litter, providing evidence of both recent shrub expansion and Holocene plant community changes. Our δC analyses indicated that SOM derived from mesquite was greatest beneath shrub canopies, but extended at least 3 m beyond canopy margins, similar to the distribution of fine roots. Specific C activities of LFC indicated that root litter is an important source of SOM at depth. Comparison of turnover rates for surface LFC pools in grass (7 or 40 years) and mesquite (11 or 28 years) soils and for HFC pools by soil depth (∼150-280 years), suggest that mesquite may enhance soil C storage relative to grasses. We conclude that the replacement of semiarid grasslands by woody shrubs will effect changes in root biomass, litter production, and SOM cycling that influence nutrient availability and long-term soil C sequestration at the ecosystem level.

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A Model of Woody-Herbaceous Biomass Relationships in Eucalypt and Mesquite Communities

Cited by 31 publications

References 5 publications

Reversing a tree regeneration crisis in an endangered ecoregion

Reversing a tree regeneration crisis in an endangered ecoregion

Population Ecology of Hybrid Mesquite (Prosopis Species) in Western Australia: How Does it Differ from Native Range Invasions and What are the Implications for Impacts and Management?

Carbon isotopes reveal soil organic matter dynamics following arid land shrub expansion

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