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SAEON initiates lowland fynbos and renosterveld observation site ... with help from the Rufford Foundation

By Jasper Slingsby, Scientist, SAEON Fynbos Node
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The field site during a site visit with reserve managers and CapeNature staff. Vegetation surveys are typically conducted in spring because many species are shrivelled up and without flowers in other seasons, making them impossible to identify.

The tattered remains of a unique and highly diverse flora

Lowland ecosystems in the Western Cape are severely degraded, with more than 90% of lowland fynbos and renosterveld transformed for agriculture and other land use. Less than 2% of the vegetation’s original extent is conserved on a few small private, provincial or municipal reserves. The remaining fragments persist on farms as small corners or hills that cannot be ploughed or are otherwise not suitable for agriculture.

These systems harbour an excessive number of rare and endangered endemic plant and animal species and are of major conservation concern globally. Unfortunately, invasive alien plants and the loss of natural fire and herbivory regimes further intensify the plight of these fragments and their unique biodiversity, creating serious questions for their conservation and management.

One of the more insidious pressures is that of invasive alien grass species. These grasses negatively impact on indigenous plant species by increasing competition for light, water and nutrients, and affect animals by changing the habitat structure, limiting their movement, and reducing the availability of desirable indigenous plant species.

Perhaps most damaging is that the alien grasses increase the flammable biomass, causing more frequent and/or more intense fires. These changes in fire regime can cause high mortality in animal populations and can reduce the vegetation’s ability to regenerate post-fire.

The tortoise and the rares

In January 2012 disastrous fires burnt critically endangered vegetation that made up >80% of the remaining habitat of the geometric tortoise, a lowland fynbos and renosterveld endemic listed as one of the world’s 100 most endangered species. This prompted herpetologists that study the tortoise, CapeNature’s Scientific Services and the managers of the reserves to approach the SAEON Fynbos Node to commission a study to monitor post-fire recovery of the tortoise’s habitat.

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The geometric tortoise is a lowland fynbos and renosterveld endemic listed as one of the world’s 100 most endangered species (Picture courtesy of CapeNature)

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The Multi-Minidisc-Meter (MMM) was specifically designed by Frans Radloff (Cape Peninsula University of Technology) as an adaptation of the disc pasture meter method for fine-leaved shrublands. Each pin holds a minidisc that is dropped and the height at which it makes contact with a plant recorded. The method is time-consuming, but can be used to calibrate other faster methods.

Funding was sourced from a Small Grant from the Rufford Foundation, and a plot-based vegetation monitoring study was devised to test for impacts of alien grasses and high stocking rates of indigenous large mammals on plant diversity and vegetation structure. Since many of the alien grasses were introduced to improve forage for domesticated ungulates, one of the hypotheses is that stocking indigenous large mammal herbivores that once occurred in the vegetation naturally should reduce the grass biomass and consequent impacts without further degrading the vegetation.

The study was also designed to be able to feed into downstream projects, with plots laid out in a manner that allows them to provide ground-truth data for remote-sensing studies, and plant collection protocols set so that specimens can potentially be used for the development of DNA barcodes and the determination of tortoise diet.

Getting underway

Kicking off a project of any nature requires careful planning and preparation. In addition to the project’s sampling design, which was planned with inputs from collaborating researchers and reserve managers, the actual selection of sites and determination of field protocols are critical to the success of any project. Fortunately the vegetation plots can only be surveyed in spring (late August to early November), leaving time to get prepared.

SAEON Fynbos Node staff have been working on developing efficient, non-destructive methods of measuring vegetation structure and biomass, and have conducted field visits with reserve staff to identify appropriate plot locations and develop preliminary species lists prior to the planned spring 2014 survey.

When performing a study of this nature it is critical that the sites would be near identical in the absence of the treatments (i.e. presence/absence of alien grasses and high/low herbivory), otherwise one may find significant differences in species diversity etc. among sites even in the absence of the treatment (e.g. a very wet vs a very dry site). To account for this, Fynbos Node staff have been doing rapid preliminary surveys to identify sites of similar soil type, drainage and dominant species within each treatment area.

Quantifying the amount and spatial arrangement of plant biomass is important for assessing the suitability of vegetation as habitat for particular animal species and for understanding a number of other ecosystem functions. For example, dense vegetation coverage close to the soil surface may reduce the mobility of crawling vertebrates, but may also maintain higher soil moisture by reducing evaporation directly from the soil.

Unfortunately these are not easy parameters to quantify, especially if one cannot destructively sample the plants. Fortunately there are a number of non-destructive sampling techniques that can be converted into measures of biomass and vegetation structure using scaling relationships. SAEON researchers are playing with multiple methods including a Multi-Minidisc-Meter (MMM), vegetation height profiles and an AccuPAR ceptometer.

Looking ahead

This preliminary study is aimed at determining the impacts of alien grasses and indigenous herbivores on the diversity, biomass and structure of lowland fynbos and renosterveld in the first few years after fire, but establishing the sites opens avenues for further research. Firstly, using these plots as calibration sites for satellite imagery allows potential applications such as mapping of intact lowland fynbos and renosterveld fragments and the extent of alien grass invasion.

Secondly, the collection of plant specimens and DNA samples allows subsequent development of DNA barcodes that can be used to aid in the identification and conservation of many of the threatened plant species that occur in the sites. DNA barcodes can also be used to determine animal diets by using the barcodes as a reference for matching DNA sequences obtained from animal scat. This has many applications for their conservation and management.

Lastly, there is much evidence to suggest that Fynbos ecosystems are most vulnerable in the first few years after fire. Disturbance in the form of invasive alien species, overgrazing or extreme drought, heat or waterlogging in this period can greatly alter the subsequent composition of the vegetation. This can alter the post-fire recovery trajectory or even shift the system to an alternate state with different functional properties in terms of hydrology, nutrient cycling, habitat structure and fire.

Unfortunately our current ability to predict or detect the early signs of altered recovery trajectories and their implications is limited because there have been very few studies of post-fire succession to provide a baseline expectation. Repeat surveys of these plots in later years, and monitoring of their functional properties, will help build this baseline.

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