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Tracking traits from East to West: Do plant traits hold the key to understanding climate change in the Cape?
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Understanding how Fynbos vegetation assemblages have changed over the past few decades is key to predicting how they will respond to future climatic changes.
Fortunately Fynbos has a rich history of vegetation survey work, providing researchers with the opportunity to develop long-term records of change in plant communities retrospectively.
For the past four years, Fynbos Node scientist Jasper Slingsby has been collaborating with researchers from the University of Connecticut (UConn) and the University of Cape Town (UCT) to do just this, revisiting old vegetation survey plots in order to investigate temporal changes in Fynbos vegetation assemblages.
Extensive surveys of Cape Point, undertaken by Hugh Taylor in 1966 and Sean Privett in 1996, and of the Baviaanskloof, surveyed by Douglas Euston-Brown in 1991, have provided the perfect opportunity to study contrasting sites with very different climatic regimes. Cape Point experiences highly seasonal winter rainfall, and Baviaanskloof experiences rainfall throughout the year.
Cape Point was resurveyed by Ross Turner and Stuart Hall in 2010 and Baviaanskloof by Douglas Euston-Brown in 2011, providing the longest known records of change in Fynbos vegetation communities.
Sampling along a climatic gradient
In the winter of 2012 we visited new survey sites, aiming to collect plant trait data across the climate gradient in the hopes that understanding how traits vary along a spatial gradient will inform our expectations for shifts in the trait composition of communities as climate changes through time. To achieve this aim, we sampled sites with existing vegetation community survey data in the Langeberg, Kogelberg and Cederberg regions (Figure 1).
The Cederberg experiences highly seasonal rainfall, but has the lowest mean annual rainfall of all the sites. It also has the highest maximum temperatures in January. Kogelberg is also highly seasonal, but has higher mean annual rainfall, while the Langeberg has year-round rainfall, but lower mean annual rainfall than Baviaanskloof.
An extended field trip in June and July saw Fynbos researchers spending two weeks in each location, sampling as many of the abundant species in the area as possible. Trait data were collected to investigate how different species may respond to change, based on the traits they possess, and also how species traits may vary over a climatic gradient.
We collected samples from three individuals of each species and measured leaf area, length and width, leaf and stem dry matter content, leaf reflectance and leaf thickness. We are planning to perform isotopic analysis on all our leaf samples.
We also collected tissue samples and herbarium specimens of each of our species to submit to the Barcode of Life project for DNA sequencing.
Scientific minds
Our team was headed up by Dr Jasper Slingsby, Prof. John Silander (UConn), and Dr Cory Merow (UConn post-doc). In various combinations at different times it consisted of Hayley Kilroy (UConn PhD student), Timothy Moore (UConn PhD student), Emma Gray (Fynbos Node intern), Beth Timpe (UConn PhD student), Steve Mollmann (UConn PhD student), Jenny Leonard (UCT MSc student), as well as visiting friends Nancy Silander and Carwen Leeb-Du Toit.
This impressive collection of scientific minds would have been useless without the expertise of our botanical consultant Douglas Euston-Brown, who spent every waking moment ensuring the correct identification of hundreds of species, both in the field and back at the herbarium.
Field work with some exciting discoveries
We started our trip in the Kogelberg, where a mammoth field and lab work session meant we managed to sample 281 different Fynbos species in only two weeks. Much to our excitement one of these species turned out to be an undescribed species from the genus Tetraria.
While in the Kogelberg we were extremely lucky with the weather (always a gamble in the Cape winter) and only had a few mornings when we were unable to sample due to howling wind and rain. We were less fortunate with the weather while at Wildcliff Conservancy, which was to be our base in the Langeberg, and many days were spent entering data due to stormy conditions outside.
However, by now we were a well-oiled machine and despite all of the hold-ups we were still able to sample 280 species in our two weeks. Wildcliff proved to be a fantastic field base, with lots of space, interesting field books and a large store of useful equipment.
We were lucky enough to visit two areas during our time in the Cederberg. The first week was spent in the Southern Cederberg on Driehoek Farm, nestled in the Welbedacht Valley below Tafelberg. This afforded a stunning backdrop to our fieldwork and Cape Nature granted us access to drive right up to the base of Tafelberg, the highest point we had thus far sampled.
Many of the species we were sampling had been sampled in the other regions, and it was exciting to observe how much intraspecific variation there is in the Fynbos, not only in leaf traits, but also in growth habit. Some familiar species were unrecognisable in the dry Cederberg climate.
We spent our second week in the northern Cederberg at Traveller’s Rest, just north of the Pakhuis Pass. Here we were practically living in the Karoo, and the striking contrast to the comparatively lush vegetation of the Langeberg was noted by all.
Once again Cape Nature was extremely accommodating to our cause and we were granted access to the Heuningvlei Road, a stunning management track through some of the most spectacular rock formations in the Cederberg. This desolate pass is little visited by people, and is filled with endemics and rare species. We found another undescribed species of Tetraria, as well as an extremely rare species of Cyperaceae, Carpha schlechteri, which has been collected only twice since 1950.
During our two weeks in the Cederberg we sampled another 250 species, bringing the total number of species sampled to 811, over 600 of which were unique.
Comprehensive record of traits and habitat
The field trip provided us with a comprehensive record of plant species traits and habitat, allowing us to investigate the functional importance of traits with respect to global change for sites along a climatic gradient. The much needed data will help us to develop mechanistic models for the prediction of species response to global change. It has also allowed us to make a significant contribution to the Barcode of Life project, allowing for the sequencing of 400 as yet unsequenced species. We now also have a valuable photographic database of all of our species.
In order to continue to add to our now extensive database of vegetation traits in the Cape Floristic Region, we hope to perform additional repeat vegetation surveys at other sites in the next few years, particularly in the Cederberg Nature Reserve Complex and the Jonkershoek Valley, which will ensure that we have an extensive database of geographic locations and plant traits in climatically distinct sites throughout the Cape Floristic Region.
The funding source for this project is the "NSF Dimensions of Biodiversity: Parallel Evolutionary radiations in Protea and Pelargonium in the Greater Cape Floristic Region, Award number 1046328". To learn more about this project, click here.
Figure 1. Mean annual rainfall and rainfall seasonality in the sampled plots. Darker colours indicate more rainfall (top) or more seasonally restricted rainfall (bottom).
