I often find myself focussing a bit much on particular species of epiphytes, vines and mistletoes but I think there is a lot to be learnt from looking at the complete host tree. So this week we'll do just that, with some host trees from around the North Island of New Zealand: Photos by C. Kirby unless otherwise stated. All rights reserved.
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When it comes to hosting epiphytes, not all tree species are equal. As I've mentioned earlier, large trees are well recognised as having greater epiphytic communities than small trees because they provide a greater surface area for establishment, intercept more light and water, and have generally been around longer to accumulate epiphytic communities. However, there are other important factors that are conducive to the successful establishment of epiphytes:
So here it is, New Zealand's "top 10" host trees with their key epiphyte-friendly features 10. Northern rata - large trees provide high light and large limbs 9. Totara - stringy bark and broad branches 8. Rewarewa - porous and deep forks 7. Mahoe - many habitats in the knarly branches of large trees 6. Kohekohe - widely space limbs 5. Rimu - large trees provide high light and large limbs 4. Tawa - high light environment and large limbs 3. Titoki - knarly wide limbs and deep forks trap resources 2. Pukatea - damp habitat and big forks 1. Tree ferns - possibly the perfect substrate for epiphytes Disclaimers:
These trees were pretty casually assessed and with a fair amount of bias. I based my judgements on the suitability for epiphyte establishment which is why tree ferns won even though their small size means that they do not host large communities. I also used data on host trees in the North Island from mine and Kirsty Myron's and theses, as well as personal observations. I realise that species like kahikatea can have HUGE epiphyte loads when they are really large, but the young trees are poor hosts whereas species like pukatea and titoki seem to be good hosts from the start. I am very open to suggested changes... what do you think? what have I missed from the South Island? “It is not going to be easy” I said to my partner Steve Pearce, who had kindly volunteered to be my field assistant for the next two months. “It’s a rainforest and it’s winter. It will be cold, wet, you’ll get covered in leeches and you’ll probably lose feeling in your legs from hanging in your harness all day.” Not much of a sales pitch I will admit, however, to my thrill-seeking partner, it only added to the adventure. And an adventure it was. Getting to spend 2 months in pristine forests, swinging around the canopies of majestic rainforest trees and devoting all day studying incredibly fascinating epiphytes has been one of the best experiences of my life. Back in May this year, we surveyed 50 trees over an altitudinal gradient from 300m to 1100m above sea level in the glorious Border Ranges National Park, Australia. The World Heritage listed National Park is an extensive area of subtropical rainforest that covers 3,600 square km in northern New South Wales, adjacent to the Queensland border. The aim of my PhD is to look at how epiphytes are distributed along environmental gradients of light and moisture, both within the host tree and across an altitudinal slope. We found 34 species of vascular epiphytes (18 species of orchid and 16 species of fern), including the incredibly special Beech Orchid (Dendrobium falcorostrum), which occurs exclusively on Antarctic Beech trees (Nothofagus mooreii) which inhabit the cool temperate mountain tops of the Border Ranges NP. We also found over 42 morpho-species of moss, although at this stage identification has been somewhat difficult so many are still unnamed as yet. Athough I am still in the tedious stage of analysing the data, some interesting patterns have already started to emerge. Vascular epiphyte diversity was highest at around 500m in elevation, while moss diversity peaked a bit higher at around 700m. About half of the vascular species and three quarters of the moss species showed distinct preferences in their altitudinal range. For example, some of the large ferns such as the Staghorn (Platycerium superbum) and Elkhorn fern (P. bifurcatum) only occurred at lower altitudes (possibly due to temperature excluding them from the cooler mountain top), while the filmy ferns (Hymenophyllum sp.) and the Dagger Orchid (Dendrobium pugioniforme) are more common at higher altitudes where there is higher levels of moisture.
We are looking forward to next year, when we head out to undertake another season of field work in the Wet Tropics of North East Queensland. It will be interesting to compare the subtropical realm of the Border Ranges NP to the tropics of Far North Queensland. Who knows what fascinating epiphytes we will find up north? For more information you can contact me: Jennifer Sanger jennifer.sanger (at) utas.edu.au PhD Student School of Geography and Environmental Studies University of Tasmania Click here for the full epiphyte photo album. Most epiphytic species have no access to the soil of the forest floor and simply live off the water and nutrients stored in small pockets of canopy soil. Canopy soil is the organic matter that has gathered in branch forks or nest epiphytes. Canopy soil usually exists in relatively small volumes and therefore does not store a lot of water. Even after rain events, this resource quickly dries out. What does this mean for epiphytes? Presumably, it means that they need to be able to cope with frequent drought and to use water during the short time that it is present. This topic was part of my MSc research: I investigated the response of the epiphytic shrub puka (Griselinia lucida) to drought, along side its (mainly) ground-dwelling cousin kapuka, (Griselinia littoralis). I found that puka and kapuka can tolerate a low level of drought stress but their key response to extended drought was to effectively shut-down. The graph below shows the stomatal conductance (y axis, high conductance = high photosynthesis, low conductance = low photosynthesis) as water potential (x axis) dropped. The filled circles are results from puka and the open symbols are kapuka. What this indicates is a shut-down of function as the soil dried out, this reduces the risk of complete desiccation and death because water is not being lost through photosynthesis. The shut-down is a useful way to avoid damage but the key is to be able to re-activate normal function when water becomes available (after rain or fog). Griselinia lucida (puka) showed a very quick response after 70 days in drought. The following photos show the same plant on day one (A) after rewatering, day two (B) and day three (C). To summarise, epiphytes grow in canopy habitats because they can cope with drought conditions and quickly respond to water when it becomes available.
If a virgin, old-growth forest is disturbed or destroyed (like so many in NZ and around the world) and then grows back over time (forming a "secondary forest"), how long does it take for the local epiphyte population to return? This question is important because old-growth tropical and (some) temperate forests have diverse and abundant epiphyte populations which are integral for the sustainable function of the forest. The answer is... we don't know. However, some (lucky!) researchers in the tropics are working on this. A paper recently published by Woods & DeWalt (available on this page) studied the epiphyte populations of four secondary forests in Panama that had been left to recover after disturbance for 35, 55, 85 and 115 years. They found that after 115 years some characteristics of old-growth epiphyte populations had returned:
So it appears that, given enough time, epiphyte richness and composition will recover. However, not everything recovered:
The authors speculate that this slow recovery of epiphyte density "may be due to a low probability of colonisation of young host trees caused by epiphyte dispersal limitation". They also say: "Given another 100 years, epiphyte densities in secondary forests in central Panama might approach old-growth levels, but we conclude that, in the short-term, secondary moist forests are unlikely to compensate biologically for the loss of biological diversity and ecosystem functioning that high epiphyte densities provide. In tropical moist forests, oldgrowth forests are invaluable for the conservation of epiphytes, and secondary forests need more than 115 yr to recover all aspects of old-growth forest community structure." I believe that New Zealand's canopy environment would also take a very long time to accumulate the epiphyte diversity, composition and density of old-growth forests. Does anyone out there know how long New Zealand's epiphytes take to grow? It would be particularly interesting to know how old the big nest epiphytes of some forests are!
My colleague Rebecca recently took a holiday to Eastern Australia where she visited the Lamington National Park in Queensland and saw a plethora of epiphytes! The common species of this area were nicely summarised by Winter et al. (1983) who studied the method of photosynthesis in common Australian epiphyte and vine species. Some of their results are presented in the following figure: ![]() Summary of epiphyte distribution on a 40 m emergent Ficus watkinisiana tree in a subtropical rainforest in Dorrigo National Park, New South Wales. The symbols refer to photosynthetic mode for each species: ‘+’ = pronounced CAM photosynthesis (Crassulacean acid metabolism is a carbon fixation pathway that evolved in some plants as an adaptation to arid conditions), ‘±’ = weak CAM, and ‘-’ = C3 photosynthesis (considered to be present in species less adapted to arid conditions). Signs in brackets mean that the suggested mode has been inferred from leaf succulence (Winter et al. 1983). We share species numbered 2 and 12 and the genera represented by 2, 4, 7, 8, 10, 11, 12, and 21 in our epiphyte/vine flora. Here are some photos of these plants and their relations, please submit a comment if you would like to name the nameless! Thanks to Jennifer Sanger for help with these.
While scanning a list of NZ's epiphytes, vines and mistletoes to find inspiration for this week's blog, I noticed that three species - one epiphyte, one vine, and one mistletoe have similar specific epithets (the second part of their scientific name): Passiflora tetrandra - kohia, NZ passionfruit (vine) Peperomia tetraphylla - peperomia (epiphyte) Peraxilla tetrapetala - pikirangi, red mistletoe (mistletoe) "tetra" means "four" when used in the formation of compound words. The people who named these species were giving us clues by describing their features. So what does each mean? Passiflora tetrandra = four stamens The yellowish-green flowers of our native passionfruit have four stamens. This species is the only tendril climber in New Zealand and is known for its small, bright orange, spherical fruit. Peperomia tetraphylla = four-leaved The leaves of this succulent epiphyte are arranged in fours. This species has minute flowers on spikes that occur on the end of stems. It only grows in the northern North Island. Peraxilla tetrapetala = four-winged This must refer to the four flower petals that burst apart when their fused tip is broken by a nectar-hungry bird. This species mainly grows on beech trees in the North and South Islands and is classified as "declining".
So what about the meaning of the genus names? Well according to the NZ Plant Conservation Network: Peperomia is from the Greek peperi (pepper) and homoios (resembling), referring to its resemblance to a true pepper (to which it is closely related) Passiflora simply means "passion flower" But I haven't yet found information for the meaning of Peraxilla - does anyone out there have information?? On the 31st of August, a large team of Waikato explorers set off on an adventure to Rangitoto Island Scenic Reserve, in the Hauraki Gulf of the Auckland region. The weather was absolutely stunning and we were rewarded for our early start with a wonderful 8 hours wandering around the lava flows of this 600 year old volcano. The scoria of this island is very well drained and extremely exposed to sun and wind... doesn't this sound familiar? The volcanic environment is very similar to the canopy habitat of epiphytes, they both have very little water storing capacity and a vulnerability to high light and winds. As a result... Rangitoto Island is inhabited by many epiphytic species, by the end of the day we were calling it Epiphyte Island! Here is a list of species growing on the scoria of Rangitoto that commonly occur as epiphytes:
These Rangitoto plants are growing saxicolously (on rock) which is not uncommon for epiphytic species. We all highly recommend spending some time on this beautiful island - it is a completely different world - full of interesting species!
Microsorum is a genus of ferns that has members in Africa, India, China, Madagascar, south-east Asia, Australia, some south Pacific Islands and, of course, New Zealand. "Microsorum" refers to the small sori (clusters of spores) on the underside of the leaves which are a splendid orange-brown colour. Our Microsorum trio all grow epiphytically but can also occur on the ground/rocks. The trio consist of the endemic mountain hounds tongue fern (Microsorum novae-zealandiae) and two species that we share with Australia: kōwaowao (M. pustulatum subsp. pustulatum) and mokimoki (M. scandens). All three species have thick creeping rhizomes from which leaves on thin stipes emerge. The fronds are often variable, ranging from single, linear fronds to ten or more thin lobes (pinnae). Mountain hounds tongue fern only occurs in the North Island. It has beautiful golden scales along its rhizome and the largest fronds of the three species. Kōwaowao has the broadest frond lobes within which very distinct veins are visible. The rhizome of this species can be blue-green with brown spots. Mokimoki is known as 'fragrant fern' because the fronds have '...an agreeable delicate scent' (Colenso 1892b). The juvenile, undivided fronds can often look like frills on the trunks of tree ferns.
Kōwaowao and mountain hounds tongue fern can germinate on host trees and grow without a connection to the forest floor. In contrast, mokimoki climbs tree trunks and always maintains a connection to soil. The epiphytic flora of New Zealand has interesting similarities with the epiphytes of tropical rainforests. For example, we have diverse epiphytic species that belong to many different plant groups: ferns, orchids, shrubs etc. However, these groups of plants also have stark differences and today's example is the cacti! Forget what comes to mind when you imagine a cactus because the cacti of tropical Americas do not grow in sand nor do they have large spikes. Species such as those belonging to Rhipsalis grow as epiphytes and have long leaves without any spikes. They also have tiny flowers and fruit that emerge from the leaves. Species of Rhipsalis are thought to have specialist relationships with one group of tropical birds. A recent study by Guaraldo and colleagues compared the requirements for Rhipsalis seed germination to that of mistletoes; a plant group that is considered to rely on specialist dispersers. Both of these plant groups have sticky seeds that are most successful if they are stuck in the fork of a large branch with suitable bark. Species of Rhipsalis are even known as "mistletoe cactus" because the fruit are so similar. Interestingly, the seeds of Rhipsalis and mistletoe species are both primarily distributed by Euphonia birds. These birds do a good job of establishing sticky seeds because they smear the seeds onto a host branch rather than dropping them, providing a much better chance for establishment. New Zealand's epiphytic flora does not have any cacti species, nor any known specialist bird relationships. We do know that some mistletoe species rely on tui and bellbirds for pollination and that the woody vine kiekie might have had a relationship with bats in the past (before they were lost from many areas) but these plants aren't epiphytes - maybe epiphytes like the Pittosporum shrubs species have (or had) important relationships with fauna, it is after all still unclear how their seeds are dispersed. Is anyone out there looking for a research topic?!
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Catherine KirbyI work with NZ's native vascular epiphytes at the University of Waikato. I completed an MSc on epiphyte ecology and the shrub epiphyte Griselinia lucida and have recently published the Field Guide to NZ's Epiphytes, Vines & Mistletoes. Categories
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