Over a century of epiphytic build up
When branches fall here, they often bring down a mass of epiphytes with them. It seems likely that, in some cases, it is the weight of those that causes the branch to fall. A combination of mature trees and a benign and humid climate means that epiphytes are a significant feature of our canopy. ‘Widow-makers’, Mark says, utilising the term for things that have the potential to fall from above and kill. It is a gender defined term, which I guess comes because it has a longstanding application in forestry which remains a traditionally male occupation.
There is an entire self-sown and self maintaining environment in this one tree
One of the characteristics of New Zealand native forest is the high incidence of epiphytes which are simply organisms (in this case, plants) that grow on the surface of another plant, getting moisture and such nutrients as they need from the air and rain and then from the debris that builds up around them. Because these epiphytes are perched up trees, they are vulnerable to drying out so are more commonly found in areas protected by other trees rather than on solitary specimens standing in exposed isolation. We also get regular rain here and have high humidity levels no matter the season. Add to that the fact that our native forest and bush is almost entirely evergreen. There are very few deciduous natives – a total of only 11 different species that are fully deciduous in winter. Most New Zealand gardens use a wide range of evergreen plants and shrubs, usually outnumbering the deciduous selections. So we have situations that are hospitable to epiphytes.
Add in to that mix, maturity. Because we have many well-established trees here, some dating back close to 150 years, there has been time for epiphytes to get a grip on their hosts.
Drooping spleenwort and leather leaf on the trunk of a tall queen palm
Where do these plants come from? Mostly a combination of wind and birds. Some of our trees have entire mixed colonies growing in them. The dominant epiphyte here is the collospermum, C. hastatum, but we have other species of both collospermum and astelia perching up high too. Also assorted ferns, particularly the native climbing ferns, Pyrrosia eleagnifolia or ‘leather-leaf’ fern and Asplenium flaccidum or ‘Drooping Spleenwort’ which is prettier than it sounds. We even get native orchids appearing in these epiphytic colonies but NZ native orchids are perhaps best described as being very subtle in appearance.
The host tree is leaning badly, the twining vines and thicker trunks are all southern rata
The rata is to the South Island what the pohutakawa is to the North Island, though we do have the northern rata as well. These are all the same family (so all metrosideros) but different species. Think of them being like cousins, perhaps. So the South Island rata is M. umbellata. That rata is an epiphyte, relying on an established tree to climb. Unlike most of the perennial types of epiphyte, it can eventually kill its host. In forest conditions, the rata is so well established by then that it can stand on its own, forming a hollow-trunked tree (the hollow centre being where the host tree has decayed away). We think it far more likely that our rata will not be sufficiently anchored to the ground to stay standing. The nearly deceased host tree – a eucalypt – has developed a definite lean and we think the whole shebang may fall sooner rather than later.
Like an octopus, Prunus yedoensis ‘Ivensii” with epiphytic collospermum
I did get the ladder and do some tree climbing to take out most of the collospermum from the Prunus yedoensis ‘Ivensii’ because I like this flowering cherry and I could see the collospermum were getting the upper hand rather than maintaining an equilibrium.
Generally, we just leave the epiphytes alone. Sometimes the weight will get too much and massive clumps will fall, often bringing down branches on the way. They are usually so heavy we have to dismantle them to remove them. In times gone by, Mark used to follow the Orchid Society practice of gathering up the decaying gigi (fallen collospermum) to use as potting mix for the growing of orchids. That was before the days of granulated bark potting mixes. Left to their own devices, epiphytes are just a part of nature – a naturally occurring matrix in fact. It adds an upper layer of interest to the garden while also creating its own ecological environment quite independent from human intervention.
Whenever we have to do a clean-up that involves fallen epiphytes, we just relocate the largest pieces we can manage to the back areas of woodland where they can continue to provide habitat and add diversity.
Mark is surveying a sizeable branch brought down by the heavy burden of epiphytes
In the meantime, there is another branch waiting to fall…