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Enduring a decade of drought: Patterns and drivers of vegetation change in a semi-arid grassland

Publication date: January 2017
Source:Journal of Arid Environments, Volume 136

Author(s): Gitanjali S. Bodner, Marcos D. Robles

This study evaluated patterns and drivers of vegetation change in a semi-arid grassland in southern Arizona across eleven years of extended drought and high temperatures, 2004–2014. Changes included declines in C4 perennial grass basal cover with patchy grass mortality, leaf litter increases, shrub declines, and increases in non-native grass Eragrostis lehmanniana. Linear mixed-effects models identified precipitation during January–June “extended spring” as the best predictor of grass basal cover, especially when plots were grouped by soil and topographic features. Models showed that a decrease in extended spring precipitation from 150 to 50 mm was associated with loss of one-quarter to one-half of plots' total grass cover. Association of grass declines with this novel season of drought is especially relevant because global circulation models predict steep declines in spring rainfall. Increasing E. lehmanniana dominance was also associated with native grass declines. There was little support over this time for predicted effects of livestock grazing or shrub encroachment. This study demonstrated how monitoring data from working landscapes can improve ecological understanding of drought. Findings also suggest managers could improve chances for sustaining resilience by responding to rainfall in multiple seasons, monitoring for mortality events, and establishing contingency plans for various types of drought. The article is open access ( http://www.sciencedirect.com/science/article/pii/S0140196316301628)

Variation in soil carbon stocks with depth along a toposequence in a sub-humid climate in North Africa (Skikda, Algeria)

Original Research Article

  • Pages 25-33
  • Zohra Bounouara, Tiphaine Chevallier, Jérôme Balesdent, Joele Toucet, Mahtali Sbih, Martial Bernoux, Noureddine Belaissaoui, Ouarda Bouneb, Rabah Bensaid
  • Journal of Arid Environments | Vol 141, Pgs 1-86, (June 2017) | ScienceDirect.com

Deep soil carbon (>30 cm) is the primary pool of soil organic carbon (SOC). However, deep SOC is often not included in carbon inventories or management strategies, especially in North-Africa. The objective of the study was to determine the distribution and the main factors governing SOC storage along a representative toposequence in North-Eastern Algeria. The soil organic matter (SOM) was characterized by SOC content, carbon stocks, particle size distribution and mineralization potential.

The amount and the dynamics of the deep SOC depended on the topographical position. In the mountain soils, most of the SOC stock (100 t C ha−1) was in the topsoil (0–30 cm) and associated with the >50 μm fractions (plant materials) whereas in the piedmont and alluvial plain soils, most of the SOC stock (168 t C ha−1) was accumulated in subsoil (30–100 cm) and associated with the <20 μm fractions (mineral fractions). The SOC in the subsoil contributed to SOC potential of mineralization and should not be underestimated, especially in the alluvial cultivated plains. This carbon should be considered as an important component in agro-ecological agriculture but it is also a potential source of CO2.(http://www.sciencedirect.com/science/journal/01401963/141)

Perched wetlands: An explanation to wetland formation in semi-arid areas

Pages 34-39; Brigitte L. Melly, Denise M. Schael, Phumelele T. Gama

Journal of Arid Environments | Vol 141, Pgs 1-86, (June 2017) | ScienceDirect.com

 

This research demonstrates the importance of “perches”, a hard, impermeable sub-surface layer, for ephemeral wetland development in a semi-arid area. Over 1700 wetlands were identified in the Nelson Mandela Bay Municipality (NMBM), Eastern Cape, South Africa. The average wetland density in the Municipality is approximately nine wetlands per 10 km2. This density is high considering the climate of the NMBM, where annual evapotranspiration rates are approximately three times higher (1800 mm) than the average annual rainfall (613 mm). The NMBM is diverse in terms of its climate, vegetation types, geomorphology and underlying geology. This environmental diversity has resulted in a range of wetland types. Previous research in the Municipality has indicated that the majority of these systems are precipitation driven, with minimal groundwater input. Therefore, other environmental processes facilitate the formation of wetlands. For this study, data from 46 wetland sites were used that were situated across the different environments in the NMBM (geology, climate etc.). Thirty-four wetlands were perched, and were from all three of the different wetland types studied: depressions, seeps and wetland flats. A dense clay layer was found at 14 sites, across different geological and sediment types. Calcrete lenses were recorded at seven sites that were associated with aeolian deposits. A shallow bedrock layer was also observed at nine sites on quartzitic sandstones of the Peninsula Formation. In conclusion, this study has highlighted that perches are key for wetland development in some semi-arid areas.(http://www.sciencedirect.com/science/journal/01401963/141)

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