All posts by Rob Skelton

About Rob Skelton

I am a post doctoral researcher at the University of California Berkeley (USA), examining fundamental questions in plant physiology and ecology. I completed my PhD at the University of Cape Town (South Africa) in 2014. My dissertation was an investigation into the role of plant hydraulics in determining the response of Fynbos to drought. I have also conducted postdoctoral research at the University of Tasmania (Australia), where I examined the physiological factors that influence gas exchange in plant communities. In my spare time I enjoy appreciating nature, particularly interesting plants, and thinking about evolution. I think people benefit tremendously from having forests and natural plant communities to explore, and think we should do more to promote their conservation.

Journey to a distant world: New Zealand

The poem Journey to the end of the night suggests that “To travel is very useful, it makes the imagination work”. Certainly, travelling around New Zealand with Derek (a friend from Cape Town) has given my imagination a serious workout and exposed me to a unique world. It was a fairly intense journey: we drove almost the entire lengths of both the North and South Islands in just under two weeks. We started in Auckland in the North and ended up in Christchurch in the South.

Pic. 1: Boiling mud-pools in Rotorua, North Island.
Pic. 1: Boiling mud-pools in Rotorua, North Island.

My overarching impression is that New Zealand is one of the most dramatic places to visit on earth: the natural scenery is spectacular and remarkably different to much of what I’ve seen before. It is a land of diversity, captured most noticeably by the array of geological formations of the two islands. Parts of both the South and North Islands have ancient landscapes, the oldest rocks dating from the Cambrian (~500 m ybp). The islands forming New Zealand originally formed part of the vast continent of Gondwana, which also explains the botanical affinity with Australia, Antartica and South America (but more on that later). Yet, the North Island also has plenty of volcanic and geothermal activity, which produce relatively recent, fertile soils and plains. On our way to Wellington from Whakatani we stopped off in Rotorua, where the volcanic activity is most noticeable through the sulphurous smell and the boiling mud-pools (Pic. 1).

Pic. 2: Kauri (Agathis australis) trees in Hunua Falls Reserve close to Auckland, North Island.
Pic. 2: Kauri (Agathis australis) trees in Hunua Falls Reserve close to Auckland, North Island.
Pic. 3: Southern Beech trees (Nothofagus) tend to dominate the forests of the South Island.
Pic. 3: Southern Beech trees (Nothofagus) tend to dominate the forests of the South Island.

The complexity of the geological history is reflected in an impressively diverse collection of plant communities. Some of the more ancient landscapes provide a refugia of sorts to ancient Gondwanan lineages of plants and animals. Many of these landscapes struck me as being a throwback to the time of the dinosaurs: I could imagine massive Brontosaurus browsing on the tall tree ferns (Cyathia and Dicksonia) and Kauris (Agathis australis) (Pic. 2). More recently exposed landscapes are dominated by angiosperms (flowering plants of more recent origin than gymnosperms and ferns), including the Southern Beech (Nothofagus) forests. A particularly striking example is Milford Sound in the south west, which is a staggeringly impressive sound with incredibly steep cliffs (Pic. 4). Here, most of the mountains rising straight from sea level are greater than 1500m and appear to be ancient landscapes. Puzzlingly, much of the flora associated with these mountains is of recent origin: Beech trees (Nothofagus) tend to dominate the forest (Pic. 3&4). The explanation is that the vast, tall mountain ranges of the west coast were only uplifted less than 10 million years ago by the action of the north island plate crashing into the southern island plate. Before that the land was submerged.

Pic. 4: Milford Sound in the South Island.
Pic. 4: Milford Sound in the South Island.
Pic. 5: A Kea (Nestor notabilis) on the South Island.
Pic. 5: A Kea (Nestor notabilis) on the South Island.

In contrast to the staggering diversity of plant life, we saw remarkably few animals. Although the fauna of NZ is nothing to write home about in terms of diversity of species, there are some interesting flightless birds and some magnificent parrots. We managed to spot a Kea (closely related to Australian lorikeets) on the South Island: it’s the largest parrot in the world and the only parrot found in alpine environments (Pic. 5). We also spent one afternoon in Whakatani in the North Island tracking Kiwis (Apteryx mantelli, a close relative of ostriches). Perhaps somewhat fittingly, although we managed to track a few down we didn’t actually see any of them (as they are nocturnal and incredibly shy).

Pic. 6: Water has the power to move mountains, as illustrated by The Chasm close to Milford Sound.
Pic. 6: Water has the power to move mountains, as illustrated by The Chasm close to Milford Sound.

Another striking feature of New Zealand is the impact of water on the landscape. I saw vast cave networks (the Waitomo caves), glaciers and deep water-carved chasms (Pic 6&7). Unfortunately, even the refugia of the South Island landscape are not impervious to the reach of human impact: climate change is threatening to vastly transform the landscape. The glaciers are retreating and new land is being opened up for recolonisation of vegetation (Pic. 7 gives a sense of this rapid change).

Pic. 7: Franz Josef Glacier on the West Coast of the South Island is retreating rapidly due to climate change.
Pic. 7: Franz Josef Glacier on the West Coast of the South Island is retreating rapidly due to climate change.

We spent very little time in cities, for two reasons: Although we intentionally avoided cities as much as possible, there also just aren’t that many people in New Zealand and distances between cities are quite large. City highlights for me included Queenstown (where we spent a relaxing day doing the luge and playing frisbee golf in the botanic gardens), Wellington (where we watched a rugby game…no trip to New Zealand would be complete without seeing the national sport) and Christchurch (where we spent an afternoon taking in the devastation of the 2011 earthquakes and walking around the museum).

All in all I had a great time. I’m not surprised that dramatic, fantasy films like the Lord of Rings were filmed in New Zealand. I would certainly love to return and do some more exploring: the natural beauty is something to behold more than once. But for now I think I’ll give my imagination a rest.

Remarkable hydraulic tales from diverse fynbos functional types

“When you can measure what you are speaking about, and express it in numbers you know something about it.” Lord Kelvin

Imagine walking within any natural region of the world and being able to understand how it works: What ecological processes are unfolding? How did the surrounding species come to be there? How do so many different species coexist? What does the future hold in store for this community? How incredible would it be if we could uncover the world’s secrets.  What wonders might be revealed!

Imagine walking within any natural region of the world and being able to understand how it works
Fig. 1: Imagine walking within any natural region of the world and being able to understand how it works

Many people think that all humans share an innate biophilia: a love and appreciation of natural life. But can we extend that passion to an understanding? This question has driven biologists for centuries and has shaped my own personal experience. As a scientific realist I believe that the scientific method can make real progress in describing real features of the world. A large part of me agrees with the sentiment expressed by Lord Kelvin; that you can only really know something when you can measure it. Yet, the natural world is complex and it requires much patience and focus to unravel its secrets.

I have begun my ambitious quest with an interest in plant ecophysiology, the study of how individual plants function and how this influences much larger processes at the community- or even global-level. I like to think of these various levels as being interconnected: if you can understand what drives organisms and processes at one level, you can understand what emerges at the next. This is often referred to as a bottom-up, mechanistic approach to ecology.

Measuring plant functionality and determining major environmental drivers is no easy task. There are no simple, universal measures of plant health or ecosystem functionality. Instead, ecophysiologists frequently rely on a range of proxy measures, such as carbon assimilation, plant water loss or nutrient uptake (Figures 2 and 3). These measures are often labour intensive and time consuming to collect and require a generally optimistic disposition. The task is made even more challenging in regions where the environmental conditions vary rapidly or when communities contain incredibly high numbers of very different species.

A primary goal of ecophysiologists is to capture plant response to varying environmental conditions: here I monitor leaf level gas exchange using an infra-red gas analyser
Fig. 2: A primary goal of ecophysiologists is to capture plant response to varying environmental conditions: here I monitor leaf level gas exchange using an infra-red gas analyser
A primary goal of ecophysiologists is to capture plant response to varying environmental conditions: here I record plant water status using a scholander pressure chamber.
Fig. 3: A primary goal of ecophysiologists is to capture plant response to varying environmental conditions: here I record plant water status using a scholander pressure chamber.

The particular plant community that I first began to explore happens to be within one of those more challenging regions: South Africa’s Cape Floristic Region. A series of fortunate events culminated in me studying toward my Ph.D. at the University of Cape Town under the supervision of Dr. Adam West. To get closer to an understanding of Fynbos1 (Fig. 4), I needed to capture the response of several different types of plants to environmental conditions at a remarkably high resolution. This, in brevity, was the broad aim of my Ph.D., which I initiated in February 2011 and have recently completed.

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Of course, I was not the first to attempt an investigation into the drivers of plant response for diverse functional types in the fynbos. Perhaps a more specific aim of the project was to build on those previous studies by providing a picture of plant response at a greater resolution. Fortunately, recent advances in miniature sapflow2 technology allowed me to embark upon capturing near-continuous sapflow data for coexisting fynbos species. This essentially allowed me to record a proxy of transpiration at a very high resolution over fairly long periods. This provided an advance on the previous periodic campaign-based gas exchange measurements, where individuals had gone out every couple of weeks or months and recorded instantaneous measures of plant response.

To tackle the problem of high species diversity, I decided to make use of the functional type concept, where species that share similar (functional) traits are grouped into a single category. The idea being that similar looking species are likely to be analogous in ecophysiological functioning. I chose three species representative of the three major fynbos functional types: restioid, ericoid and proteoid (Fig. 5). The particular species I decided to focus on in the study were Cannomois congesta (Restionaceae), Protea repens (Proteaceae) and Erica monsoniana (Ericaceae), which all co-occur at Jonaskop in the Riviersonderend mountains. Monitoring the sapflow of these species, coupled with monitoring of environmental variability using a micrometeorological station, allowed me to gain an understanding of what the important environmental factors are and how response to them differs among fynbos species.

Fig. 5: The three fynbos functional types: Tall proteoid shrub (left), grass-like restioid and fine-leaved ericoid (right).
Fig. 5: The three fynbos functional types: Tall proteoid shrub (left), grass-like restioid and fine-leaved ericoid (right).

From the outset of the project I suspected that with all this variability and diversity there may be different “strategies” of water use. I was hoping for different “hydraulic tales” for different species and I was not disappointed. I have been able to show that each of these species displays distinct reliance on summer and winter rainfall events. For example, the shallow-rooted Erica species is more reliant on infrequent, yet periodic summer rainfall events compared to Protea and Cannomois. The deep-rooted Protea species does not respond to those events, but appears to “recharge” only during the heavy winter rainfall season. Remarkably, the shallow-rooted Cannomois species appears to rely on episodic moisture sources, such as cloud or fog events. The next step for me is to use these different responses to determine how vulnerable our communities are to potential long-term changes in environmental conditions. For instance, if we lose the summer rainfall events, does this mean that Erica species are vulnerable? At least for now, however, I can say that I am one step closer to knowing something about fynbos.

1 Fynbos (derived from the Dutch term fijn-bos or fine bush) is the vernacular term given to the plants of the Cape Floristic Region.

2 Sapflow technology uses the movement of heat through a stem to monitor water movement and provides an idea of when a plant is turning on and off.