The forest canopy is often referred to as the last unexplored frontier for biological science because there is still a lot to learn in this tree-top world.
However, I've come to realise that in this country full of naturalised exotic species it may also be the last uninvaded frontier. Thinking about all of the native plant life-forms (trees, shrubs, herbs, ferns, vines, epiphytes, mistletoes etc.), the epiphytes and mistletoes of the forest canopy are possibly the only group that aren't widely invaded by exotic species.
However, I've come to realise that in this country full of naturalised exotic species it may also be the last uninvaded frontier. Thinking about all of the native plant life-forms (trees, shrubs, herbs, ferns, vines, epiphytes, mistletoes etc.), the epiphytes and mistletoes of the forest canopy are possibly the only group that aren't widely invaded by exotic species.
A beautiful vista of native canopy species. Photo: Olivia Henwood.
Why are exotic species largely absent from our forest canopies? Here are a few ideas:
Harsh habitat: the climatic extremes of the forest canopy likely restrict the opportunities for common exotic species to establish.
Habitat integrity: the majority of epiphyte habitat is in old-growth forests. These places have the large trees, high humidity and relatively stable climates that epiphytes and mistletoes thrive in. The lack of disturbance in these forests likely limits the invasion threat.
Not in favour: most exotic species in New Zealand are garden escapees that were brought from a garden setting in their homeland. I suspect that the lack of epiphytic species in these overseas gardens means that not many epiphytes have ever been brought here (thankfully).
Just wait: without intentional introductions, the invaders rely on accidental arrival. These largely haven't occurred yet but changes in global climate patterns might make this more likely.
Harsh habitat: the climatic extremes of the forest canopy likely restrict the opportunities for common exotic species to establish.
Habitat integrity: the majority of epiphyte habitat is in old-growth forests. These places have the large trees, high humidity and relatively stable climates that epiphytes and mistletoes thrive in. The lack of disturbance in these forests likely limits the invasion threat.
Not in favour: most exotic species in New Zealand are garden escapees that were brought from a garden setting in their homeland. I suspect that the lack of epiphytic species in these overseas gardens means that not many epiphytes have ever been brought here (thankfully).
Just wait: without intentional introductions, the invaders rely on accidental arrival. These largely haven't occurred yet but changes in global climate patterns might make this more likely.
But wait....
An exotic epiphytic fig in Auckland City. Photo: C. Kirby.
There are a few species that have begun naturalising in urban environments. The photo above shows an exotic epiphytic fig in an exotic palm tree in Auckland. This is a common sight around the city and a cause of concern for native urban bush fragments.
Weeding privet from a titoki in Hamilton City. Photo: Fiona Clarkson.
There are also species that are very good at taking the odd canopy opportunity! The photo above is of me with a privet seedling that I've removed from the trunk fork of a titoki in Hamilton City.
An exotic orchid irresponsibly planted in a native forest patch. Photo: C. Kirby.
And finally, there are also some occasions where exotic orchids are intentionally introduced in forests. The idea is probably to "beautify" our native ecosystems but I personally don't see any logic here, especially considering the invasion risk.
To finish, let's be clear on something: It is very undesirable to have ANY exotic species in our native forests. They displace native species, interrupt natural processes and restrict ecosystem functioning. They do not provide the services that our native fauna rely on and they threaten the integrity and resilience of these highly interwoven systems. Please take any opportunity you have to reduce these threats from exotic species.
To finish, let's be clear on something: It is very undesirable to have ANY exotic species in our native forests. They displace native species, interrupt natural processes and restrict ecosystem functioning. They do not provide the services that our native fauna rely on and they threaten the integrity and resilience of these highly interwoven systems. Please take any opportunity you have to reduce these threats from exotic species.
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