A new article about facilitation cascades has been published by Christine Angelini and Brian Silliman from the University of Florida. It is such an interesting contribution to our understanding of epiphyte ecology that I'm going to dedicate four blogs to it. This week: application in New Zealand.
The application of this model to the Tillandsia of Georgia worked really well, now I want to see if it will work for temperate New Zealand forests.
The application of this model to the Tillandsia of Georgia worked really well, now I want to see if it will work for temperate New Zealand forests.
The primary foundation species is the host tree because epiphyte species mostly rely on host trees for access to light. Let's say we have a tawa (Beilschmiedia tawa) host tree. The bare branches will support minimal flora and fauna communities but as it grows away from the shady forest floor it will become the first step in a facilitation cascade.
A foundation species, tawa (Beilschmiedia tawa). Photo: Akos Kokai.
Our secondary foundation species is often moss. Moss provides substrate and moisture that facilitates the arrival of invertebrates and other epiphytes such as orchids and ferns. It therefore increases both the diversity and abundance of plants and animals that can establish (type C cascade).
Moss providing substrate for ferns and small shurbs. Photo: C. Kirby.
But that isn't the end of the story! If a nest epiphyte species such as kahakaha (Collospermum hastatum) arrives on the moss, it will again significantly increase the diversity and abundance of flora and fauna communities (still type C). These large plants can host many plants and invertebrates as well as the occasional bird and reptile. If nest epiphytes do not establish the community will generally be smaller and less diverse. There are even species that depend on nest epiphytes, for example: tawhiri karo (Pittosporum cornifolium). Therefore we might consider nest epiphytes to be tertiary foundation species, adding another step to Angelini and Silliman's process:
I suppose it all depends on your interpretation! If you consider the moss to be the foundation species it works more like the Georgia example but then the moss requires the host tree... what are your thoughts?
To finish, here is a photo illustrating the significant habitat that nest epiphytes can create for many other species.
To finish, here is a photo illustrating the significant habitat that nest epiphytes can create for many other species.
Nest epiphytes in the Waitakere Ranges. Photo: C. Kirby.
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