Journal article

Contrasting mechanisms of resilience at mesic and semi-arid boundaries of fynbos, a mega-diverse heathland of South Africa


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Publication Details

Author list: Gillson L, Macpherson AJ, Hoffman MT

Publisher: Elsevier

Publication year: 2020

Journal: Ecological Complexity

Volume number: 42

Start page: 1

End page: 12

Total number of pages: 12

ISSN: 1476-945X


Abstract

Biome boundaries are expected to be sensitive to changes in climate and disturbance, because it is here thatecological communities are at environmental, ecological or disturbance limits. Using palaeoecology to studyecosystem dynamics at biome boundaries provides opportunities for understanding ecosystem resilience orsensitivity at ecologically meaningful timescales, and under varying climatic and disturbance conditions.The fynbos biome is a megadiverse Mediterranean type shrubland, found only in South Africa, that isthreatened by climate change, land-use change and invasion by alien species. We used palaeoecological recordsfrom the semi-arid and mesic boundaries of the fynbos biome to test hypotheses regarding ecosystem resilienceover timescales of centuries to millennia. We hypothesised that fynbos would expand at its mesic boundary at theexpense of afrotemperate forest under drier and / or morefire prone conditions. In contrast, we hypothesisedthat at the semi-arid boundary, fynbos would expand at the expense of succulent karoo under wetter and coolerand / or morefire-prone conditions. Contrary to our expectations, the fossil pollen record at both biomeboundaries showed remarkable stability at centennial - millennial timescales. To explain our results, we gen-erated new hypotheses exploring possible mechanisms that might confer resilience.At the mesic (temperate) boundary, we suggest that decreased seasonality of rainfall during drier phasesfavouredfire and fynbos persistence, while in wetter periods, increased seasonality of rainfall resulted in en-hanced summer drought stress, inhibiting forest expansion. At this boundary, internal reorganisation from grassyto proteoid fynbos states conferredresilience through resistance.At the succulent karoo boundary, we suggest thatincreased aridity was offset by less seasonality of rainfall, which enhanced biomass and allowedfire to persist,favouring persistence of fynbos. At this boundary, fynbossensu strictoretreated during arid phases but recoveredduring climate amelioration, consistentwith resilience through recovery. In both cases, this mega-diverse, dis-turbance-adaptedflora provided a range of traits that enabled fynbos to persist despite environmental pertur-bation. Ourfindings agree with general observations that for ecosystems in regions of ample resource availability(i.e. at the mesic boundary), biotic interactions and disturbance tend to become more important in ecosystemdynamics, whereas in regions of scarce resources (in this case water scarcity at the semi-arid boundary) abioticstress is more important. Ourfindings contribute to debates over the mechanisms that confer resistance andresilience to environmental change. Understanding and conserving the processes and mechanisms underpinningits resilience will be critical to effective conservation plannin


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Last updated on 2020-16-10 at 14:52