A 50 year study shows grass cover has increased in shrublands of semi-arid South Africa

Masubelele, Mmoto L.; Hoffman, M. Timm; Bond, William J.; Gambiza, James

doi:10.1016/j.jaridenv.2014.01.011

Cited by 49 publications

(26 citation statements)

References 47 publications

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“…Observations based on remote sensing show a tendency towards increased vegetation cover and productivity 8,99 , and these are supported by in situ observations using matched photographs that reveal stable or increasing vegetation cover 106 , particularly of the grass component 107 . Historically, grassland shifts have been responsive to climatic changes 108 .…”

Section: Perspectives | Insightmentioning

confidence: 69%

Future of African terrestrial biodiversity and ecosystems under anthropogenic climate change

2015

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A frican ecosystems and biodiversity are biologically and ecologically unique, attract substantial tourism revenue, and provide significant ecosystem services at local, regional and global levels. It is projected that anthropogenic climate change is likely to have adverse impacts on African ecosystems and their biodiversity 1 , but projections of impacts based on a range of methodologies diverge widely. This is partly due to contrasting scenarios of future precipitation, but much more importantly due to critical differences between approaches to modelling biodiversity impacts and their assumptions. These differences relate to the extent to which different modelling approaches incorporate the effects of atmospheric CO 2 and disturbance (fire, mammal herbivory) on ecosystem structure and productivity 2,3 , and relative strengths in accounting for temperature-versus water-related controls on biodiversity. Projections of large declines in biodiversity under combined scenarios of climate and socioeconomic development 4,5 may not take these uncertainties into account. The most recent report by the IPCC on African vegetation change 1 reflects this well in stating with high confidence that "substantial uncertainties are inherent in these projections [future changes in terrestrial ecosystems] because vegetation across much of the continent is not deterministically driven by climate alone".These issues require urgent resolution, because there are significant and immediate implications for biodiversity risk assessments, and adaptation and mitigation responses relevant for policymakers and land managers. The evidence necessary to resolve these divergences is indicative but far from adequate, primarily because of a dire lack of empirical evidence and information on both climate and atmospheric CO 2 impacts on the structure and function of waterlimited and disturbance-dependent ecosystems in tropical and subtropical climates 6,7 .More than any other continent, Africa's ecosystems are water limited 8 and disturbance driven (by wildfire and mega-herbivores) 9 , with a high representation of C 4 grass-dominated ecosystems 10,11 . Palaeoecological changes in climate and atmospheric CO 2 since the Miocene have strongly shaped the vegetation, disturbance regimes and biodiversity of these ecosystems 12 . Because the continent straddles the tropics and subtropics in both hemispheres, an enormous area over which climatic conditions are conducive to vegetation flammability emerged during the late Miocene 13 . The Projections of ecosystem and biodiversity change for Africa under climate change diverge widely. More than other continents, Africa has disturbance-driven ecosystems that diversified under low Neogene CO 2 levels, in which flammable fire-dependent C 4 grasses suppress trees, and mega-herbivore action alters vegetation significantly. An important consequence is metastability of vegetation state, with rapid vegetation switches occurring, some driven by anthropogenic CO 2 -stimulated release of trees from disturbance control. Thes...

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Section: Perspectives | Insightmentioning

confidence: 69%

Future of African terrestrial biodiversity and ecosystems under anthropogenic climate change

2015

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“…Where grasses are present, there is limited ground-based evidence of woody dieback and conversion of shrub cover to grassland, whereas reports of increased woody cover are more numerous (Table 2). Masubelele et al (2014) report increased grass cover using long-term data from eight sites in southern Africa, but in the most recent sampling period ) most relevant to our discussion, half of these sites show increases in the ratio of shrub cover to grass cover. Secondly, carbon dioxide fertilization, a possible large-scale driver of structural change, is expected to favor increases in woody plants rather than herbaceous cover (as discussed in the previous section).…”

Section: Other Possible Explanations Of Observed Greeningmentioning

confidence: 83%

Examining the linkage between shrub encroachment and recent greening in water‐limited southern Africa

2015

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Abstract. There have been reports of widespread increases in satellite-derived vegetation indices in drylands across the globe. At the same time, there are numerous field-based observations of increases in the density of small woody plant species, a process known as shrub encroachment. We compare groundbased observations of shrub encroachment with information from 14 years of Tropical Rainfall Measuring Mission (TRMM) precipitation data, Moderate Resolution Imaging Spectroradiometer (MODIS) Normalized Difference Vegetation Index (NDVI) and MODIS land cover data for southern Africa, focusing on areas that receive less than 1000 mm of precipitation per year. Cumulative precipitation and maximum NDVI were computed for each year and linear regression analysis was used to correct for interannual variability in precipitation. Accounting for precipitation effects, we found an underlying, overall greening in southern Africa, with NDVI increasing þ3.34% on average over the 2000-2013 study period. Over 15% of the region is undergoing statistically significant change, strongly biased towards greening. The strongest greening was in a coherent band stretching from northern Namibia to Lesotho. Ground-based reports of shrub encroachment tend to overlap with strong greening; we suggest that these processes are linked. Reports that intersect our period of record showed overwhelmingly positive trends, indicating that our method is suitable for detecting shrub encroachment. Shrublands and savannas accounted for 78% of the study region. Savannas did not change appreciably (À0.21% total change) from 2000-2013 while shrublands were greening faster than any other land cover type over the same period (þ8.93%). Fast rates of greening in this biome may be indicative of shrub expansion. Large-scale shrub encroachment will have important consequences for dryland degradation and global carbon dynamics.

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“…Changes we observed in South Africa where non‐seasonal states (SLN) transitioned to seasonally moisture‐limited states (SLD) are consistent with the expansion of grasses into semi‐desert shrublands, as has been reported in the region by Masubelele et al . (). The widespread changes we observed in Australia are potentially consistent with studies that have shown change in both temperate (Lunt et al ., ) and tropical regions in Australia (Bowman et al ., ; Murphy et al ., ), but these studies focus on structural change (often woody cover change) and such changes do not cleanly align with our analyses which emphasize changes in vegetation activity.…”

Section: Discussionmentioning

confidence: 99%

Defining functional biomes and monitoring their change globally

Higgins

Buitenwerf

Moncrieff

2016

Global Change Biology

106

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Biomes are important constructs for organizing understanding of how the worlds' major terrestrial ecosystems differ from one another and for monitoring change in these ecosystems. Yet existing biome classification schemes have been criticized for being overly subjective and for explicitly or implicitly invoking climate. We propose a new biome map and classification scheme that uses information on (i) an index of vegetation productivity, (ii) whether the minimum of vegetation activity is in the driest or coldest part of the year, and (iii) vegetation height. Although biomes produced on the basis of this classification show a strong spatial coherence, they show little congruence with existing biome classification schemes. Our biome map provides an alternative classification scheme for comparing the biogeochemical rates of terrestrial ecosystems. We use this new biome classification scheme to analyse the patterns of biome change observed over recent decades. Overall, 13% to 14% of analysed pixels shifted in biome state over the 30-year study period. A wide range of biome transitions were observed. For example, biomes with tall vegetation and minimum vegetation activity in the cold season shifted to higher productivity biome states. Biomes with short vegetation and low seasonality shifted to seasonally moisture-limited biome states. Our findings and method provide a new source of data for rigorously monitoring global vegetation change, analysing drivers of vegetation change and for benchmarking models of terrestrial ecosystem function.

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A 50 year study shows grass cover has increased in shrublands of semi-arid South Africa

Cited by 49 publications

References 47 publications

Future of African terrestrial biodiversity and ecosystems under anthropogenic climate change

Future of African terrestrial biodiversity and ecosystems under anthropogenic climate change

Examining the linkage between shrub encroachment and recent greening in water‐limited southern Africa

Defining functional biomes and monitoring their change globally

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