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And the Andes!

My love affair with Chile continued today when I went on a field excursion to the Chilean Andes (Figure 1). I joined a group of delegates attending a conference on Hydrology on an outing to the San Pablo de Truega experimental watershed. The tour took us past some experimental stream gauges, designed to test the impact of forest thinning on stream flow. The site has two streams with monitoring gauges: a control stream in a relatively undisturbed natural forest stand and a treatment stream in a thinned forest stand. So far their results indicate that stream flow is vastly increased in the thinned site, primarily because fewer trees intercept rainwater and return less water to the atmosphere via transpiration, so more water ends up as run-off. Consequently results from this watershed are assisting foresters to manage the land, and also assist scientists in predicting future changes in water supply, an important ecosystem service.

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The highlight of the trip for me was definitely our hike to El Presidente – the largest Nothofagus tree in the forest (Figure 2). On the hike I saw magnificent Saxagothea, Nothofagus and Laureliopsis trees, and a Darwin Frog (Rhinoderma darwinii)! This unusual little creature relies on camouflage to avoid being detected by predators, resembling a fallen leaf (Figure 2). Another interesting aspect about the frog is that the male Darwin’s frog protects the eggs for about three to four weeks. After the female lays the eggs in the leaf litter the male guards them until the developing tadpoles begin to move, and then he ingests the eggs and retains them in his vocal sac! The baby frogs hatch about three days later after which the male frog continues to carry them in his vocal sac until they hop out and disperse. Remarkable.

After the hike we had a traditional Chilean barbecue. It was excellent, and I was absolutely stuffed with delicious steak, potato salad and blood sausage. Needless to say that most of the tour group slept on the bus on the way home.

I was pleased that the Andes lived up to (and exceeded) my expectations, both in terms of the diversity of plants, but also the beauty of the forests. These ecosystems really are magnificent, and I very much hope to return to them one day.

Journey to another distant world: Chile

Visiting South American temperate rainforests had always been on my wishlist, and recently I had the opportunity to go see some of these beautiful ecosystems in Chile. The opportunity arose when Rocio Urrutia, a researcher at the Universidad Austral de Chile in Valdivia, invited me to collaborate with her on a research project investigating the potential impacts of future climate change on temperate Chilean rainforest species (Figure 1). The focal species of the project is Alerce (Fitzroya cuppresoides), a conifer species often referred to as the “redwood of the south”. This magnificent tree is threatened by drought events, habitat destruction, and illegal logging, and Rocio and her colleagues are doing some fantastic work with the aim of promoting conservation of the trees and the forests that they occur in.

Upon my arrival in Validivia, I was immediately struck by the trees; Many of them seemed oddly familiar. On the way to the city from the airport my taxi drove past Chilean firetrees in full bloom (Embothrium coccineum, members of the Proteaceae), and magnificent southern beech trees (several Nothofagus species). I am particularly fond of species of the Proteaceae, mostly as a result of having grown up in South Africa where Protea, Leucospermum and Leucadendron are common features of the Fynbos flora (and also as a consequence of having studied the Fynbos flora for my dissertation).

One of the reasons for my trip to Chile was to participate in a discussion around the conservation of Alerce (Fitzroya cuppresoides). The mini conference was excellent (Figure 2). Among other things, I learned that even though the mean annual rainfall of Alerce Costera is over 4000 mm, Alerce trees can experience water stress during dry years as a consequence of the shallow, sandy soils. I was also highly impressed to learn that Fitzroya is the second longest living tree in the world (and I met the individual who dated the tree – the wonderful Antonio Lara!). I found this remarkable because these trees are quite different in appearance from the longest living trees in the world, the Bristlecone Pines. Alerce is tall, and flourishes in its native habit (moist temperate rainforest); in stark contrast the Bristlecone Pines appear to persevere rather than grow in arid mountains of North America. It really is unfortunate that these Alerce forests are threatened by climate change and deforestation. Overall the conference was incredible. It was fantastic to learn about the ongoing research at the University.

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After the formalities of the conference were completed, my wonderful hosts, Rocio and Aldo took me and a few other colleagues (Jarmilla Pittermann and Jonathan Barichivich) on a field excursion to see the Alerce Costero forest (Figure 3). The forest is a two-hour drive from Valdivia and the site of much long-term monitoring and experimental research conducted by Rocio, Jonathan and their colleagues.

When we arrived I was awestruck to be standing amongst Nothofagus, Fitzroya, Pilgerodendron and Saxagothea. Incredible. My mind wandered to the last time I was standing in a mixed Nothofagus-conifer temperate forest. That time, I was travelling in New Zealand, but the similarities between the two forests are striking. Of course, the similarity between the southern hemisphere flora is no coincidence. The splitting of the ancient continent of Gondwana resulted in many shared families between the countries, including the Proteaceae, Myrtaceae, and Podocarpaceae. Antarctica was also a part of this supercontinent, as demonstrated by the abundance of fossils of tree species that occur on the cold continent. Remarkably, some of the fossil species still exist in the Alerce Costero temperate rainforest; I was amazed to see Nothofagus antarctica trees for the first time, surviving in a small drainage basin frequently exposed to very cold conditions (Figure 4). Its occurrence on Hoste Island (one of the southernmost islands in Chile) earns Nothofagus antarctica the wonderful distinction of being the southernmost tree on earth! Tangible, living evidence of these ancient geographic links between the southern hemisphere land masses.

After our walk through the forest and the research sites we retired to a small cafe located on the outskirts of the Alerce Costero National Park. Jonathan’s mother runs a tiny cafe where she provides warm refreshment in the form of coffee and baked goods (Figure 5). It was delightful. We crowded into the cozy, warm room and had an incredible lunch.

Finally, we decided to see the big Grandpa of the forest: the largest Alerce of the region (Figure 6). This tree is one of the few remaining large trees of the forest, with most of the large trees having been cut down in previous centuries for timber. It is incredible! It has a known diameter of at least 4m and is at least 2000 years old according to tree rings obtained by Antonio Lara (It is probably much older, since the inner core has rotted away with time).  Jonathan mentioned that the sex of the tree is actually unknown (Fitzroya is dioecious, meaning that, like humans, individuals can have seperate sexes). However, they aim to find this information out later this year….and Jonathan suspects that the tree is actually the Grandma of the forest.

So far my experience of Chile has been wonderful, and I still have a week to go here. It is great to be among southern hemisphere trees again and to learn about more remarkable southern hemisphere forests!

Low vulnerability to xylem embolism in leaves and stems of North American oaks

Have you ever wondered how plants become damaged and die during drought? As a post-doctoral researcher investigating plant physiological responses to water deficit, I spend most of my time thinking about this question. A very smart young lady once told me that it’s obvious…they run out of water. In one sense, she is absolutely correct: when the leaf mesophyll cells run out of water (desiccate), they become unable to maintain normal physiological function, which ultimately leads to death. But this explanation is not entirely satisfactory: It does not tell us about the precise processes that lead to desiccation, whether there is a particular threshold of desiccation that plants fail to recover from, and how different species might vary in their capacity to withstand desiccation. I have been investigating these questions in Californian oaks, and recently published my findings in the scientific journal Plant Physiology.

To find a satisfactory answer to the question, we need to revise some fundamentals about how plants function. Not having a heart, or a mechanism to pump water to the tops of their canopies, trees rely on gradients in water concentrations. Water naturally and passively moves from places of high concentration to areas of low concentration. As water is drawn out of the pores on leaves (stomata), it is replaced by water from the rest of the plant. Plants replace this water lost to the dry atmosphere by taking up moisture from the soil. Within the plant water is transported in xylem: from the roots, all the way to the leaf mesophyll cells. Think of this process as similar to an elastic band being stretched from the tops of the canopies. As the environment dries, plants find it harder and harder to extract moisture from the soil. The elastic band stretches…

Xylem embolism

We currently think that as the tension in the water column increases, air is eventually drawn into the xylem vessels and the elastic band snaps. This process creates an air pocket that blocks the transport of water, know as embolism. Xylem embolism represents a significant, drought-induced damaging process in land plants. As plants embolise they lose the capacity to hydrate the downstream cells in the leaves. So this partly answers our question: the point at which plants experience embolism is the point at which they begin to suffer (mostly irreversible) damage.

However, substantial debate surrounds the capacity of species with long xylem vessels to resist embolism. Some studies have shown that species are highly vulnerable to embolism, and regularly experience this during dry periods, while others suggest that plants are actually less vulnerable to embolism. Our paper investigated whether recent methodological developments could help resolve this controversy within oaks, a  charismatic, ecologically important, temperate angiosperm genus. We were hoping to shed further light on the importance of xylem vulnerability to embolism as an indicator of drought tolerance in long-vesselled trees. To do so we used a non-invasive optical technique to visualise embolism in leaves and stems of eight oak species from the Mediterranean-type climate region of California, USA. Basically we took a lot of photos of trees as they dried down and monitored when they embolised.

We show that the point at which air enters into leaves ranges from −1.70 MPa to −3.74 MPa, and from −1.17 MPa to −4.91 MPa in stems (pure water is 0 MPa and plants normally operate above -1.5 MPa). Consequently, our results show that long-vesselled North American oak species are more resistant to embolism than previously thought, and support the hypothesis that avoiding stem embolism is a critical component of drought tolerance in woody trees. So now we can say exactly when particular oak species start to fail during drought.

This information is useful, as it allows us to predict how oaks might respond to future drought events. It tells exactly when they will start to lose function, and become damaged. In fact, our study shows that accurately quantifying xylem vulnerability to embolism is essential for understanding species distributions along aridity gradients and predicting plant mortality during drought. All we need to do is monitor their water status to know whether they will recover or not. Ultimately, this is why physiological studies, such as ours, are important: They allow us to be precise in understanding how plants respond to climate change.

How plants respond to drought provides insights into climate change survival

Globally, droughts have had a negative impact on many plant species. This has led to much higher rates of mortality than usual. Understanding how different species are likely to respond to drought is crucial to accurately predicting the impact of future climate change on plant communities.

Plants in South Africa’s Western Cape area have tremendous variation in their sensitivity to drought. Photo: A. Betzelberger.
Plants in South Africa’s Western Cape area have tremendous variation in their sensitivity to drought. Photo: A. Betzelberger.

It can be extremely challenging to find meaningful ways to describe plants’ many different types of responses to drought, particularly in biodiverse areas. Scientists have been working to develop a new system in which plant functional traits can be used to assess the range of drought tolerance in diverse plant communities.

Why some plants shrivel and die and others don’t
Although it may be tempting to think that drought is bad for all plant species, there is tremendous variation in their sensitivity to drought. For several decades, plant scientists have been attempting to figure out what determines this variation. But there are no simple universal measurements of drought tolerance. Instead, scientists usually rely on long-term experimental manipulations.

The difficulty of assessing drought tolerance makes it challenging to work with large numbers of species. It is critically important that we do so, particularly within the world’s biodiversity hotspots – they are incredibly important systems for the planet. They include the tropical rainforests – the lungs of the planet – and many economically significant ecosystems such as South Africa’s fynbos.

Trade-off between water loss and carbon uptake
A recent paper offers a solution to the challenge. It proposes using simple plant characteristics or traits to identify the different strategies that species adopt to cope with drought. The beauty of using plant traits is that they are relatively easy to measure, and can be gathered for a large number of species. The system uses combinations of easily measured plant traits to get an index for drought tolerance in much the same way as body mass index works in humans. You can measure relatively simple traits like weight and height and combine these to determine how a person might react to stress or exercise.

To predict how different plant species respond to drought the researchers focused their trait selection on the classic water-loss versus carbon-uptake trade-off that plants face. When land plants open their stomata to allow carbon dioxide to enter the leaf for photosynthesis, they inevitably lose water. This creates a carbon-uptake-water loss trade-off, particularly under water limiting conditions. During periods of drought plants face a dilemma – to continue to photosynthesise and risk desiccation or close the stomata to conserve water but risk starvation.

Studies were conducted to determine how plants like the Protea adapted to drought. Photo: A. West.
Studies were conducted to determine how plants like the Protea adapted to drought. Photo: A. West.

Tracking two plant traits
The scientists recognised that two plant traits would be critical to determine which side of the trade-off different species tended to err towards. The first trait relates to how a plants’ internal plumbing responds to dehydration: the ability of the xylem to withstand desiccation. Water is transported from the soil through the stem to the leaves under tension, which gets greater under drought stress. When the plants become too dehydrated the water column breaks and air enters the stem, which blocks the vessel. This is similar in some sense to an embolism in human arteries and is potentially as fatal for a plant as it prevents them from moving sugars to where they are needed.

The second trait relates to the breathing apparatus, or stomatal response of a plant. Stomata operate like variable resistors on the leaf surface, opening and closing in response to desiccation. The sensitivity of the stomata varies between species. In some species they may be highly responsive to changes in water status and less so in others.

Scientists have known for a while that both xylem vulnerability and stomatal response varies between species. But the association between these traits and the ability of a species to survive droughts remained unclear. The key missing element was how the xylem and stomatal responses are co-ordinated within a species. Very few studies have addressed co-ordination between stomatal regulation and xylem vulnerability and then used this to predict how likely a species is to die during drought.

Lessons offered up by Fynbos
To test the system, the authors studied fynbos communities in South Africa’s Western Cape. These highly species-rich plant communities are recognised as one of the world’s biodiversity hotspots and contain three major plant functional types: the familiar proteas, restios and ericas.

Restios are highly diverse in fynbos, which makes these communities more resilient to change. Photo: R. Skelton
Restios are highly diverse in fynbos, which makes these communities more resilient to change. Photo: R. Skelton

Different species adopted a continuum of strategies. It ranged from a risky, low safety-margin response to a more conservative approach to water loss. A key finding was that species which were more conservative and closed their stomata earlier in response to desiccation were less likely to incur xylem embolism. On the other hand, species that closed their stomata later were more likely to incur xylem embolism.

It was also possible to make predictions about how different species might die during drought. Worryingly, the study suggests that many restios and ericas appear to be particularly sensitive to drought. This may lead to shifts in the future composition of fynbos communities.

On a more positive note, the study also showed that all three familiar fynbos plant types had representative species from the full range of responses. This suggests we are less likely to see any one plant type disappear. It highlights the importance of biodiversity for landscape resilience. Having species of each functional type respond differently to drought may allow a community to be more resilient in the face of change

This article was originally published on The Conversation. Read the original article here:

https://theconversation.com/how-plants-respond-to-drought-provides-insights-into-climate-change-survival-44017

Also, the PNAS paper can be downloaded here:

http://www.pnas.org/content/112/18/5744.abstract

Thoroughly modern conifers?

Who could compete with the angiosperms?

“The redwoods, once seen, leave a mark or create a vision that stays with you always. No one has ever successfully painted or photographed a redwood tree. The feeling they produce is not transferable. From them comes silence and awe. It’s not only their unbelievable stature, nor the color which seems to shift and vary under your eyes, no, they are not like any trees we know, they are ambassadors from another time.” John Steinbeck from Travels with Charley in search of America

Some of the most impressive trees on earth are conifers: a redwood (Sequoia sempervirens) is the tallest tree in the world and a bristlecone pine (Pinus longaeva) is the oldest. Yet, redwoods (plants of the subfamily Sequoioideae) and several other conifers are often considered to be relics, primitive survivors from a distant era (Figure 1). Many would agree with Steinbeck’s sentiment that conifers are ambassadors from another time.

Indeed, the three extant genera known colloquially as the “redwoods” – Sequoia, Sequioadendron and Metasequoia – are all that remain of a once-much larger, ancient sub-family: the Sequoioideae. The fossil record shows that the Sequoioideae were widespread in the Cretaceous (about 140 to 70 million years ago), being particularly dominant in northern latitudes. However, the reign of the redwoods began to draw to a close in the late Eocene and continued throughout the Oligocene, when both the range and diversity of Sequoioideae declined. Today only three species cling on in refugial areas in China and California, and all of them are highly threatened by climate change and habitat destruction.

The demise of the redwoods is captured well by the fortunes of the genus Metasequoia. The genus has a very extensive fossil record and was one of the most common taxa in the Cretaceous and Paleocene in the Northern Hemisphere. At least three distinctive fossil species have been described from this era (although there may have been as many as twenty according to some authors). And as if to further emphasize the point that Metasequoia is a remnant genus, the only extant species – Metasequoia glyptostroboides – was first described from fossil material in 1941 and, following the later discovery of living plants in China in 1948, is commonly regarded as a living fossil.

Mirroring the story of the northern hemisphere giants is that of the once-great southern hemisphere conifer family, the Araucariaceae (Figure 2). In the Cretaceous the araucarians were widespread in the southern hemisphere (and even extended into the northern hemisphere). Today, most species are found in moist rainforest refugia in New Caledonia and Papua New Guinea. The number of genera has fallen from approximately six during the Cretaceous to three that are extant. One of the extant genera (Wollemia) contains only a single species (Figure 3). Similar to the story of Metasequoia, Wollemia nobilis was first described from fossils and was only discovered in a refugial valley in Australia in 1994. Another living fossil!

The two most likely reasons for the decline of these noble plant families were climate change and the rise of the angiosperms. Global cooling in the Eocene and Oligocene appear to have had a major impact on conifer diversity and abundance. Aridification and the evolution of fire-adapted flora in many parts of the world may also have contributed to their decline. The flowering plants (angiosperms) also evolved 120 million years ago and have since expanded to fill many of the niches previously occupied by gymnosperms. Angiosperms have been suggested to be more competitive, faster growing and better adapted to fire than conifers. Indeed the angiosperms are truly an incredible group, accounting for over 80% of the roughly 297 000 species of known land plants (Figure 4). In comparison gymnosperms account for less than 0.5%. Angiosperms are the dominant plant forms in the tropics and subtropics: most of the species in the rainforests tend to be angiosperms. Modern broadleaved tree species are the lungs of our planet. If humans had to choose five families to coexist with into the future, we would almost certainly choose the grasses (Poaceae), daisies (Asteraceae), orchids (Orchidaceae), madders (Rubiaceae) and legumes (Fabaceae). Together these five families contain approximately a third of all plant species and contain the most ecologically and economically important species. So for all the splendour and nobility of the gymnosperms, the angiosperms are indispensable.

So it seems as though the Sequoioideae and the Araucariaceae have had their heyday, along with the dinosaurs that once browsed on their foliage. Yet, just as with the dinosaurs, perhaps it is time to reconsider whether this idea pertains to all conifers. The Pinaceae and the Cupressaceae appear to have radiated fairly recently and occupy vast tracts of land, particularly in the boreal zones of the northern hemisphere. Pines (actual pines…and not “pines” from the southern hemisphere) are tremendously important economically. Junipers are both diverse and widespread. Yet, despite their areal dominance, the pines and junipers still tend to be restricted to more marginal growing areas: northern latitudes and deserts or semi-deserts. Species of these families found in the tropics tend to occupy mountain slopes or moist refugia. Few can compete with modern broadleaved species in the tropics.

Only one conifer group that I know of seems to have taken on the angiosperms at their own game in the tropics and done surprisingly well. Surprisingly, the Podocarpaceae have diversified in recent times in the tropics. The reason behind this is linked to their leaf shape. More basal podocarps, such as Lagarostrobos franklinii or Microcachrys tetragona, cling on (just as the redwoods do) in refugial habitats. These more basal species tend to have scale-like leaves and slow growth rates. Yet, a group of species within the Podocarpaceae have developed broader, flattened leaves or phyllodes and more efficient conducting networks in their leaves (Figure 5). These innovations allow them to have relatively high growth rates, which in turn allows them to compete with angiosperms. Evolution never fails to innovate.

Apart from being a natural tale about the underdog triumphing against the odds, this story also provides some deeper insight into how evolution proceeds. It shows how inadequate it is to label species as either “modern” or “ancient”. Instead, it is more accurate to think that all extant lineages are good enough. Conifers, like the dinosaurs, were once the dominant plants on land. As always, whether a lineage persists through time is partly based on luck and partly on innovation. Although many conifer lineages succumbed to the voracity of time others have subsequently persisted and, like many podocarps, have even radiated. Like the birds, these extant lineages are thoroughly modern: they survive and compete successfully with other modern taxa. It is erroneous to think of birds and podocarps as remnant species. Instead, the next time you find yourself ogling over a yellowwood consider how thoroughly modern it is.

When is a Pine not a Pine? And what’s in a name anyway?

Early European explorers of the Southern Hemisphere appear to have had a great desire to view their newly discovered worlds* as extensions of their motherland. The British, in particular, saw a little bit of Britain in most of the places they visited. Yet, for the resemblance that many of these places had for their original namesake locations in the northern Hemisphere, I can only conclude that these early seafarers must have been suffering from homesick-induced acute astigmatism. British explorers saw fit to compare land that was as remote and arid as they could endure with the lush countryside of South Wales, Salem, Albany and Bath! Some of these Southern Hemisphere namesakes resemble the original British landscapes about as closely as a sunny, clover covered playing field resembles a dune during a dust devil. Both regions have soil and weather, but that’s about where the similarities end.

Pic 1: The small cones of Microcachrys only superficially resemble strawberries.
Pic 1: The small cones of Microcachrys only superficially resemble strawberries (Photo credit: Rob Wiltshire).

British explorers were also terribly uninventive with their names: New South Wales, New Caledonia, New England[1]. This platitudinous naming style extended to plants, and so we have the king billy pine, pencil pine, celery top pine, and the strawberry pine[2]! Apparently the qualifying trait for being called a “pine” was the possession of a stem and green leaves. Now, perhaps I should be more lenient on the British explorers for their banal approach to nomenclature; Shouldn’t we attribute a lack of originality to scurvy or some weird tropical disease and move on? After all, surely one of the uses of a name is to identify something? I am willing to concede this when it comes to place names: afterall, most people know where New South Wales is or are unlikely to mistake the South African city of East London for a spot on the east bank of the Thames. Unfortunately, I cannot be so generous when it comes to the naming of biological organisms.

Pic 2: Athrotaxis selaginoides (pencil pine) at home in a tarn in Tasmania.
Pic 2: Athrotaxis selaginoides (pencil pine) at home in a tarn in Tasmania.

Many common names of biological organisms do not even get over the first hurdle of uniquely identifying an organism. The Cabbage Tree, for example, is a wonderful, large tree in South Africa (Cussonia), but a type of palm in New Zealand (Cordyline australis). So, common names of plants are often dull and fail to distinguish between two different organisms; we’re not off to a good start. And it gets worse…My much larger, concern with common plant names is that they omit any indication of evolutionary relatedness. To understand what this means and why it is important, we need to understand how scientific names are given to organisms.

Pic 2: This New Zealand cabbage tree (Cordyline) looks nothing like South Africa's cabbage tree (Cussonia).
Pic 3: This New Zealand cabbage tree (Cordyline australis) looks nothing like South Africa’s cabbage tree (Cussonia).

Carl Linneaus, the father of modern taxonomy, in 1753 published one of the most influential texts of modern taxonomy called Species Plantarum. In it, Linnaeus described the system of binomial nomenclature, where each species is given two latin names: one for the genus to which it belongs and the other for the species. The system works by grouping individuals sharing similar characteristics into either genera or species: individuals within a species share more characteristics than those within a genus. For example, members of our own species, Homo sapiens (i.e. humans), all share more traits with other Homo sapiens than we do with members of a different species of the same genus, such as Homo erectus (extinct early man). As we move up the tree of relatedness, we observe that we share even fewer characteristics with species of a different genus, such as Pan troglodytes (i.e. Chimpanzees). Knowing the genus and species of an organism helps us to provide a broader evolutionary context for each different organism, which common names often do not capture.

The case for preferring scientific names over common names can be made using the pines that I mentioned earlier: the king billy pine, pencil pine, celery top pine and the strawberry pine. None of these species are pines. True pines are members of the Pinaceae (they belong to the genus Pinus[3]) and were, prior to human intervention, (almost) entirely restricted to the Northern hemisphere[4]. The Pinaceae were named after the Greek Pites, which is a term for resin (This is also apparently the derivation of Pituitary gland). However, none of the Australian “pines” belong within the Pinaceae; instead they belong to sister families (Podocarpaceae, Cupresaceae and Araucariaceae) and only some produce resin. The southern group of “pines” have a very different evolutionary story to tell from the Pinaceae: a story (mostly) of Gondwana, as opposed to Laurasia[5] . The mutual reference to the term pines is based on superficial similarities in the appearances of the leaves and confuses the true evolutionary relatedness of these organisms.

Pic 3: Phyllocladus asplenifolius has stems which look like leaves.
Pic 4: Phyllocladus asplenifolius has stems which look like leaves.

Quite apart from providing accurate evolutionary context for different species, the scientific names are also often more descriptive and informative. The genus of Phyllocladus, for example, is derived from the fact that the “leaves” are not leaves at all, but are modified stems called phyllodes. The common name for Phyllocladus, the celery top pine, was given to describe the superficial resemblance to celery. To name it after a celery is not only tenuous, but also misses the information captured by the scientific name. The same can be said for the strawberry pine, whose female cones only superficially resemble a strawberry[6]. Microcachrys (meaning “little cone”) more than adequately captures the reproductive structures of this species.

Protea, a wonderfully diverse genus in South Africa's Fynbos.
Pic 5: Protea is a wonderfully diverse genus in South Africa’s Fynbos.

My final gripe with common names is that scientific names often tell evocative stories. Proteus was a Greek god who had the ability to elusively change shape. The Proteaceae, a diverse family of plants occurring mostly in South Africa’s Fynbos and Australia’s South West floral regions, is named after this God. Species of the Proteaceae exhibit an incredibly diverse array of leaf morphologies: some, like Leucadendron argenteum (from the latin argenteus meaning silver) have incredibly hairy, reflective leaves giving them a silver appearance, while others are bright yellow. Some leaves are smooth, while others, including several Banksia species, have serrated margins[7].

Pic 5: Leucadendron argenteum has remarkably silver leaves.
Pic 6: Leucadendron argenteum has remarkably silver leaves.

So what’s in a name? If it’s a scientific name it may actually contain quite a bit, including fascinating tales, history and a bit of evolutionary context. Latin may be a “dead language”, but it breathes life into botanical nomenclature.

Notes

*”Newly discovered” for them, at least.

[1] In contrast, early Dutch settlers seem to have been far more descriptive in naming places: In South Africa, for example, one finds many wonderfully descriptive or evocative place names in Afrikaans, such as  “Bloemfontein” (flower fountain), “Vergenoegd” (Far enough! I can just imagine the conversation among two, tired early adventurers: “Jannie, where have we come to now?!” “Far enough, Petra!”) and “Riviersonderend” (River without an end).

[2] The practise of naming every conifer after a pine seems to still exist: as recently as 1994 living specimens of a species known previously from 120 m year old fossils (Wollemia of Araucariaceae) was called the Wollomi pine.

[3] Many Pinus species are widely used in forestry and will be familiar to most people

[4] One species, Pinus merkusii, crosses the equator in Sumatra and is found as far as 2°S.

[5] My next blog post (Thoroughly modern conifers) explores these stories in more detail.

[6] Although “Creeping pine” has also been used to describe Microcachrys, this is shared with several other species.

[7] Joseph Banks was the official botanist on board the HMS Endeavour from 1768 to 1771 on its voyage around the southern hemisphere and which was captained by Captain James Cook. His is a remarkable story captivatingly told in “The Age of Wonder” by Richard Holmes and I strongly suggest reading it.

The Roots of Splendour

I am not usually disposed to religious experiences, so the few fleeting moments of spirituality that I recently experienced came as quite a surprise. Although it is hard to convey exactly what I felt, it will suffice to state that my experiences involved sensations of awe and deep reverence. The circumstances that triggered the emotions in all instances – the roots of my splendour – was my close proximity to magnificent trees.

Pic 1: Growing in the harshest of environments, this gnarly old Bristlecone Pine gets his picture taken by Ed February.
Pic 1: Growing in the harshest of environments, this gnarly old Bristlecone Pine gets his picture taken by Ed February.

The first experience occurred when I was walking along the Methuselah Trail in the White Mountains in California. The White Mountains are home to some incredibly old, incredibly gnarly trees: the Bristlecone pines[1]. And the Methuselah trail is where the oldest of the Bristlecone pines grow (although to suggest that these individuals “grow” might be an exaggeration: perhaps it is better to say the Bristlecone pines persevere).

Pic. 2: This individual is so old and grows so slowly that the prevailing wind results in "horizontal stratification": an indication of the vast passage of time in it's lifetime.
Pic. 2: This individual is so old and grows so slowly that the prevailing wind results in “horizontal stratification”: an indication of the vast passage of time in it’s lifetime.

The oldest Bristlecone pine, Methuselah, has been dated as 4800 years old. It was alive before the pyramids were built and the mammoth was extinct. It was a seedling at a time when humans were domesticating the horse and using papyrus for paper. Jesus was not yet a twinkle in God’s eye. Just imagine what incredible scenes Methuselah, sitting atop its rocky perch, must have witnessed in its lifetime: exploration by the first people of America, the building of railways, the first planes flying overhead and people taking selfies with their iPhones. If knowledge comes with age, what incredible wisdom they must have.

Pic. 3: Gratuitous selfies with ancient trees. From left to right: Adam West, Rob Skelton, Ed February. Photo credit: Dr. Adam West, August 2014.
Pic. 3: Gratuitous selfies with ancient trees. From left to right: Adam West, Rob Skelton, Ed February. Photo credit: Dr. Adam West, August 2014.

The second sensation of reverence occurred whilst I walked the Massey Track in the Hunua Falls National Park in New Zealand. Situated close to Auckland, one of New Zealand’s biggest cities, this magnificent nature reserve is home to Kauri trees (Agathis australis). Although the Kauri trees are not the oldest (in terms of individuals: the genus is relatively old), they have incredible stature.

Pic. 4: Hunua Falls Reserve near Auckland, New Zealand.
Pic. 4: Hunua Falls Reserve near Auckland, New Zealand.

I have also visited giant Redwoods (Sequioadendron giganteum) in Yosemite National Park in California and they are equally as impressive (if not more so; although it is hard to pick between the two without becoming sizeist). The sun-worshiping crown of the trees in Hunua Falls was more than 40m above where I sat[2]. Their height, stature and perpetual focus on the heavens combined to make me feel almost completely irrelevant. I was merely an interested bystander. In one sense this is what links the Kauris to the Bristlecone Pines, to which my lifespan is a mere blink of an eye in its life[3]: I am a pedestrian along their long illuminated paths.

Pic. 5: Kauri (Agathis australis) trees in Hunua Falls Reserve close to Auckland, North Island.
Pic. 5: Kauri (Agathis australis) trees in Hunua Falls Reserve close to Auckland, North Island.

I can only flounder at explanations for the sense of approximate spirituality I felt. People have been worshiping natural deities for centuries. Trees are frequently symbols of life, fertility and natural purity. Trees are providers of shade, bearers of fruit and playgrounds. Evergreen trees symbolise undying life, while deciduous trees often symbolize renewal, rejuvenation or even immortality. To me, all of these are true and certainly add to my sense of respect. But I also think that my most recent personal experiences with some of these trees came with the sense of irrelevance. The trees that I observed would happily go on living without me. And the rest of humanity too.

Yet, unfortunately we are making ourselves ever more relevant to these magnificent trees. Climate change is threatening many different species and ecosystems: California is in the grips of a severe drought, threatening both the Redwoods and possibly the Bristlecone Pines. The Kauris are falling to drought as well, even in the moist forests of New Zealand. Part of the problem there is the presence of Phytophthora, a type of fungus that attacks the roots, prohibiting access to moisture and nutrients and rendering the individuals susceptible to drought.

The good news is that I suspect trees will outlive humanity. In the meantime (and in the words of Desiderata), we would do well to tread quietly and remember what peace there may be in silence.

Notes

[1] Bristlecone pines, Pinus longaeva, are genuine pines, of the family Pinaceae. They produce resin.

[2] The tallest tree in the world is a Coastal Redwood, Sequioa sempervirens, measured at 115.6m.

[3] A wonderful story from Terry Pratchett’s Reaper Man involves the Counting Pines, trees which are so old that they do not register events on a human time scale. For example, logging is not something that they register and so they keep wondering why their neighbours keep disappearing. Thanks to Linda-Liisa Veromann for bringing this brilliant story to my attention.

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 witnessing a game of their 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.