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: a model to explain the application.

To understand and predict species assemblages and interactions in different facilitation cascades we can use the Foundation Species-Biodiversity model: 

According to this model, facilitation cascades can be described using three categories based on the difference that secondary foundation species make to the community:

Type A: 
Secondary foundation species support more individuals of species that are already in the community (increased abundance) by providing functional traits that are similar to those of the foundation species.

Type B: 
Secondary foundation species provide habitat for different individuals (increased diversity) by providing different functional traits than the foundation species.

Type C: 
Secondary foundation species support more individuals of the existing species AND individuals of new species (increased abundance AND diversity) through the provision of a range of traits. 

Notes: some secondary species may not significantly increase either abundance or diversity, and facilitation cascades can switch if environmental conditions change.

Examples of each facilitation cascade. Simplified from Angelini & Silliman:

Type A: 

Foundation species: shoal grass
Secondary foundation species: manatee grass

Manatee grass facilitates an increase in the abundance of resident invertebrates and fish by providing more habitat of a similar nature. In other words, more of the same services.

Type B:

Foundation species: turtle grass
Secondary foundation species: pen shells

Pen shells facilitate increased diversity by providing places for fish to lay eggs. In other words, new and different services.

Type C:

Foundation species: mangroves
Secondary foundation species: oysters

Oysters facilitate both an increase in diversity and abundance. They provide more habitat for species that already inhabit mangrove roots but also provide habitat for species that are oyster-dependant.

Next week: application of all of this theory to New Zealand epiphytes!

An exciting 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: an epiphyte study.

Angelini & Silliman (In Press) conducted a range of experiments in Southern USA to investigate the relationships between Southern live oak trees (Quercus virginiana) and Spanish moss (Tillandsia usneiodes) a common epiphyte that is infact in the bromeliad, not moss, family. I'll briefly run through some of the interesting things that they discovered.

Oak-Tillandisa-insect facilitation cascade:

• Oak trees are a foundation species that provide habitat for Tillandsia 
• Tillandsia is a secondary foundation species that provides habitat for a diverse and abundant community of invertebrates
  

Key evidence:
Tillandsia relies on oak trees to provide conditions that it can establish and survive in. In this part of the world the conditions on the ground are hot and dry and very unfavourable for Tillandsia.

Within an oak tree, clumps of Tillandsia (called festoons) increase the structure, or physical space, available for insect habitat as well as stabilising temperature and humidity. This increases not only the abundance of invertebrates already present in the tree, but also in the number of species, the different types of feeding guilds (e.g. decomposers, herbivores), and the life stages (e.g. juveniles, adults). These invertebrates cannot survive on the tree without the epiphytic Tillandsia.

One example of the Tillandsia providing for invertebrates also happens to be my favourite part of this study: 
The researchers found that Tillandsia acts as a nursery by protecting juvenile crickets from spider predation. This experiment involved releasing baby crickets onto A) a branch with no epiphytes and B) a branch with Tillandsia, then letting the spiders loose! After 12 hours they counted live crickets and inspected dead crickets to find that the branch with Tillandsia had a 95 % cricket survival rate while the bare branch had only 60 % and all dead crickets had spider wounds... can't argue with that!

Next week: a model to understand the roles that different species play in facilitation cascades.

Aotearoa, New Zealand is home to a diverse group of climbing plants called vines. Vines are plants that germinate and have roots in forest soil but, unlike trees and shrubs, cannot stand upright without support from other plants. 

I use the term "variable vines" because our 25+ species exhibit many different lifestyle and morphological characteristics. We have vines that climb their hosts using: leaves, tendrils, hooks, stems or roots. We have vines that become woody while others are herbaceous. We have vines that reach top of the highest trees and become a dominant feature in the canopy while others only climb a few metres up the trunk of their host tree. We even have one vine species that taps into the stem of its host and takes resources to aid its own growth (Cassytha paniculata)!

When it comes to reproduction some vines have a few large showy flowers (e.g. Clematis species), some have many small and brightly coloured flowers (e.g. Metrosideros species) while others are very subtle (e.g. Muehlenbeckia species). Fruiting sees a range of colourful fruit (e.g. Passiflora tetrandra, Rubus species) plain wind-dispersed seeds (e.g. Metrosideros species) or tiny spores (e.g. Blechnum filiforme). The following provides a snap shot of some of this variety.

Nonvascular epiphytes are the mosses, lichens and liverworts that we find growing on other plants. They do not have the plumbing systems that higher plants have to pump water and resources around their stems and leaves. This means no xylem or phloem and a generally small stature.

Nonvascular plants are a very important group epiphytes. They are commonly the first epiphytes to colonise a young, bare host tree and provide substrate that other plants require for attachment. They contribute to forest biodiversity and processes and can be found from the bottom to the very top of host trees.

The trouble with nonvascular epiphytes is that they are hard to identify. This means that they often get overlooked in epiphyte surveys and studies. Dr Kathrin Affeld discussed in her talk at the 2013 NZ Epiphyte Workshop the importance and challenges of including these plants in epiphyte studies. I admit that I know very little about New Zealand’s nonvascular epiphytes and have not found any feasible way to include them in the NZ Epiphyte Survey Programme. I am very interested in any thoughts on this – how can we start paying more attention to nonvascular epiphytes?

In a new viewpoint article, Professor Gerhard Zotz has clarified the use of ‘hemiepiphyte’ and proposed the rejection of the term ‘secondary hemiepiphyte’.

The current classification of canopy plants typically has three main groups: (1) holoepiphytes; (2) hemiepiphytes; and (3) climbing plants. Holoepiphytes are those that germinate and complete their life cycle on other plants. Climbing plants are vines (also called lianas) that require the structural support of other plants to reach the canopy; these can be further defined as herbaceous or woody categories. Hemiepiphytes are plants that have a root connection with the forest floor at some stage in their life cycle and can be further differentiated into primary and secondary categories:

• Primary hemiepiphytes are plants that establish this connection to the ground after germinating in the canopy 
  

• Secondary hemiepiphytes begin life on the ground, climb to the canopy and then lose their link with the ground. 
  

This is how the current classifications relate to each other (please note that this is my interpretation):

Classification of hemiepiphytes has been confusing for many years – especially secondary hemiepiphytes (SH). Here is a conceptual picture of the difference between primary and secondary hemiepiphytes that I’ve drawn and below that, a list of problems with these classifications.

The problems:

As explained by Zotz (2013), there are multiple problems with the term ‘secondary hemiepiphyte’:

1.      Inconsistent use of SH has resulted in ambiguous application of the term and confusion over which species fit in this group.

2.      It is difficult to determine if any one species is a SH because although the main ground connection may be lost, adventitious roots can re-connect with the soil and these roots can be hard to find and trace.

3.      The term implies a close relationship with primary hemiepiphytes when there are in fact significant functional differences between the two groups, including: the location of germination; the growth form; the source of water and nutrients; and the structural support mechanisms.

A solution:

Zotz (2013) proposes that the use of the term SH is discontinued and that all climbing plants which germinate on the ground and possibly lose parts of their ground connection are instead referred to as ‘nomadic vines’. This change would achieve the following clarification:

1.      It should stop the ambiguous classification of canopy species and facilitate compatibility of data sets in higher-level studies. Also, the use of ‘primary’ with hemiepiphyte will be redundant and ‘hemiepiphyte’ will only refer to species that germinate on another plant and establish a connection with the forest floor.

2.      There will no longer be an implied functional relationship between the primary and secondary hemiepiphytes but instead the similarity of SH with vines/lianas will be highlighted

3.      Species that only sometimes lose their connection with forest soil will fit within ‘nomadic vines’. This new term can also accommodated the occasional germination of these species in the canopy.

This is how the proposed classifications relate to each other when based on the location of germination (please note that this is my interpretation):

What are your thoughts? How does this new classification apply in New Zealand? Do you think any of our species can be classified as nomadic vines?