NEWS are used to reflect the different parameters of environmental change .
“ They are ‘ proxies ’ in that they are not direct reflections of past change but are linked to them ,” says Gillson . “ For example , we can reconstruct changes in fossil pollen abundance and use this to infer changes in vegetation ; in this case , the pollen is a proxy for vegetation abundance .”
Paleoproxies can come from lake or wetland sediment , soil , and tree rings and include charcoal to indicate fire history , diatoms to indicate climate and dung fungal spores to indicate herbivory .
“ In our lab , we collect sediment cores from wetlands and extract fossil pollen and other proxies from multiple points along the core to reconsruct change over time . We [ use ] AMS radiocarbon dating so that we can describe changes in vegetation relative to key environmental and social-ecological changes .”
Why is this important ?
While satellite imagery is commonly used to track rates of deforestation over time , Gillson says that sometimes the data do not go back far enough to define vegetation composition before intensive human impact , which means the risks of restoring a site with the wrong vegetation and doing more damage than good to an ecosystem are much higher in often well-intended , climate change mitigation initiatives like global tree-planting drives .
“ While this approach [ global tree-planting drives ] can have benefits if carefully planned and managed , there is also a risk that afforestation on ancient open , grassy and mosaic landscapes can be bad for biodiversity and ecosystem services .”
The paleoecology work Gillson and her team do can help to ensure this does not happen by comparing current with past forest extent . Although exact locations cannot be reconstructed from fossil pollen , they can compare changes in the relative abundance of forest and fynbos over time .
“ What will be particularly important at Grootbos will be to see how extensive forests were before European settlement , when we know that timber harvesting might have led to depletion of forests ,” she notes . “ We can also look at forest composition and help identify trees that might have been lost from current forests due to preferential harvesting of high-value timber .”
Gauld-Angelucci adds : “ The hope is that this research will add an additional layer of explanation onto the area and we can be that much more certain that what we are doing is the appropriate intervention .”
The dangers of restoring a site with incorrect vegetation
Using the example of Grootbos , Gillson explains that while restoration of former forest patches would be ecologically valuable , expansion into former fynbos areas could threaten unique plants and is likely to be unsustainable because of the fire and water sensitivities .
“ The drive to plant trees can damage the biodiversity of other ecosystems , for example , fynbos shrublands , grasslands , and mosaic landscapes that would naturally have been a mix of forest and nonforest patches . This is especially the case when non-native tree species are used . As well as taking up space , they can affect ecological processes like soil formation , hydrology and fire .” By identifying the past forest extent and composition , as well as which open landscapes were ancient or man-made , can help guide conservation and restoration that includes a wider range of ecosystem types and is better for biodiversity and ecosystem services .
Figure 4 . Tree-planting plans to offset carbon in the ancient grasslands ( above ) and everything it supports . ( Image : Unsplash / Tanya Paquet )
Grassroots Vol 21 No 4 December 2021 24