She developed the tree top Barbie as a pop icon ambassador to promote women in science, and to appeal to budding young canopy scientists. She has introduced science into prisons, and encouraged artists and musicians to portray the forest canopy in their work. She even managed to get a rap artist to write a song about preserving the tree canopy!

As scientists, we talk to each other, but we all already agree that biodiversity and conservation is crucial to the continued functioning of forest ecosystems. We need to talk to the wider community, and tell them why we should all save the forests we love.

Take 18 minutes out of your Friday to watch the video below, and let your mind wander about all the possibilities!

http://www.youtube.com/watch?v=rN7VcY1f-1Q

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:

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:

• bark type: fissures and cracks can trap water and resources while flaking and peeling bark is unhelpful for secure attachment.
• architecture: large, widely spaced limbs provide good habitat while small, clumped branches block light and break under the weight of large loads.
  
• climate: if you grow in dry and harsh environments, you unfortunately don't have much chance of making the top ten! Trees that live in humid places (like valley floors) are inherently going to provide better habitat for canopy species.

So here it is, 
New Zealand's "top 10" host trees
with their key epiphyte-friendly features 

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.