A range of different ferns

Dark and brooding. Image by Adrian Paterson.

The fern is emblematic of New Zealand, appearing on most of our national sports teams and as a default for our nonofficial flag. The fern seems like a good choice to represent the people and places on our shaky islands. Ferns are unassuming, green and not flashy, getting their ecosystems jobs done quietly and efficiently. Not concerned with the limelight, but quietly confident and happy to remain in the background.

Walking through most of our native places we are never far from ferns. They fill our undergrowth, obscure our vision through the bush, even block out the sky in their tree forms. Ferns make New Zealand green, and dark, and brooding. It’s easy to imagine lost secrets in our fern-filled forests; lost moa, lost moose, lost worlds.

The silver fern adorns the jerseys of the All Blacks, our national rugby team. The All Blacks have dominated international rugby for the last 15 years, winning the last two world cups. It always amuses me that such a potent force is represented by the humble fern. It feels appropriate though, as the team is quietly confident, efficient and sometimes a little dark and brooding.

The fern is a national logo for most New Zealand teams. Image by Adrian Paterson.

Perhaps not too surprisingly, ferns have not been that well-studied in New Zealand. They lack the lack the colour of rata, the majesty of kauri, the sheer doggedness of tussock and the obviousness of southern beeches. Even some seemingly basic questions about fern distributions have not been answered. Are there patterns in the distributions of ferns in New Zealand? Are there factors, like life history traits and habitats that affect range size? Do ferns that are evolutionary cousins share similar range sizes compared to more distant relatives?

Cathy Mountier, in her BSc honours project at Lincoln University, decided to get an answer to these questions. She assembled a team of experts that you need to attack this question. From Lincoln University there was Tim Curran (plant trait evolution) and Adrian Paterson (evolutionary analyses), from Auckland University of Technology there was Hannah Buckley (plant distribution and statistical analyses) and Brad Case (spatial analyses), and from Te Papa Tongarewa there was Leon Perrie (fern systematics) and Patrick Brownsey (fern taxonomy).

A lost world? Image by Adrian Paterson.

Cathy collected data from over 250 individual fern species. For each species this included their known distribution throughout New Zealand as well as traits including spore colour, plant size, growth form, habitat preference, altitude, endemicity and so on. She used mixed-effect models to test 21 predictions. These included predictions about traits, such as that epiphytic species (ferns that grow on other plants, usually trees) would have larger distributions than other ferns as they can take advantage of the tall trees to assist in wind dispersing their seeds. She found that they do.

Other predictions were about habitat, such as that fern species in open habitats would have larger distributions than other ferns as there are fewer physical obstacles to wind dispersion of their seeds. They don’t. Or that introduced fern species would have smaller ranges than native ferns as they have only been in New Zealand for a few hundred years. They do. Or that fern species that live over a greater altitudinal zones will have greater ranges as they are more tolerant to different environments compared to ferns that favour a particular zone. They do. And so on.

Spore capsules on underside of fern frond. Image by Adrian Paterson

Cathy collected the first comprehensive data set for ferns from New Zealand and this is now published in the New Zealand Journal of Ecology. This is a great achievement for a BSc honours project as well as very significant piece of work for New Zealand (and global) fern ecology. Many of the results are reasonably obvious, which is the nature of working with such a big data set. Most species had small range sizes and a few had large ranges. The size of introduced ferns species ranges matched the length of time that they had been in New Zealand (and the opportunity to spread). Spore colour and frond shape did not affect the distributions of species.

Sometimes in science, though, it is good to confirm what we think we know. Sometimes we can be very mistaken in what we think we know. For example, fern species with close relatives found over much of the world would be expected to have larger ranges in New Zealand compared to ferns with relatives with restricted ranges. Why? Because you would expect that the ability that enabled these species to spread all over the world would possess traits that would let you live all over New Zealand. But Cathy found no relationship between global and New Zealand distribution.

Mostly, though, Cathy found what she predicted. Just like the fact that ferns are so important to New Zealand. Or that the All Blacks are so dominant.

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