Pteridium aquilinum capens
This may be opening a can of fronds, and I already have an inkling from other "threads" of Tony's opinion on the matter, but I would like to try and get a handle on the perceived/actual invasiveness or otherwise of what we commonly refer to as bracken.
My enquiry is not so much focused on whether it is indigenous to South Africa per se, but more on whether it is seen as a threat to biodiversity in particular areas.
I am doing (very minor) research on a (very small) catchment just outside Grahamstown on the Mountain Drive commonage. It falls within the the Albany Centre of plant endemism and the Suurberg Quartzite Fynbos.
Bracken, associated with a number of alien and invader tree species and bramble, etc., “infests” a significant extent of this valley-bottom wetland, which is surrounded by grassland.
My assumption was that the bracken is an “alien” – but it is not listed as such in the CARA tables. I note however, that it is the only South African fern not actively protected, and I also detect that it may be only somewhat grudgingly described as "indigenous". I have heard various opinions – that it is naturalised; that it is regarded as a pest species only in certain areas; that it is indeed an invader and as such should be eradicated, that it is one of the most widespread "weeds" in the world (?!). Certainly in areas of Scotland it is seen as a threat to grazing and to bird populations as it relentlessly replaces other vegetation. Its multiple toxicity to stock, as well as its abundance is of concern there - but this is not Scotland!
However, observably, it establishes dense stands in any area on the grassy north-facing slopes of the Grahamstown Commonage where there is moisture. One can pick out hillslope seeps and wetland boundaries by the bracken - surely this is not "ideal" in terms of the range of species that should be present and that are being out-competed?
I would be grateful if you could direct me to any literature that would shed light on this issue. I have done some delving on Google Scholar and come up with little that is specific to South Africa.
Bracken
I am not aware of any research on the topic.
And why should there not be SOME "successful" species in Fynbos: why should ALL the species be rare? Would you be so concerned if it was a "pretty" species?
Certainly the population dynamics and habitat specificity of Bracken (and perhaps even the geographical genetic relationships) would bare some studies. And it would be great to know why in some areas it comes to dominate, whereas in 99% of its populations it is just a minor to insignificant component of the vegetation.
But note that it is considered a "cape" subspecies and that it is confined to the subcontinent. So its being an invader from elsewhere is extremely unlikely, although the possibility of hybridization and thus of superior Frankenflora strains is a possibility, except:
why on earth would anyone bring it here to the Cape? - it is everywhere anyway, so why bring another strain from elsewhere. It is not asif the Scottish strain is better eating or has a prettier spore ...
My impression is that it is a good coloniser of disturbed areas, especially those under pines. How pristine is your area - or was it under plantation or invaders in the past?
Bracken: http://ispot.org.za/species_dictionary/Pteridium%20aquilinum%20subsp...
Bracken
That's the nub of it. The Mountain Drive Commonage and its several little catchments have been subjected to serial abuse, and the approach currently is rehabilitative. A dam was constructed across its two major streams, and it was planted to pine, gum, cassuarina, golden willow and a number of other exotics during the mid 1800s "to beautify the hills". These trees were logged out, starting 30 years later and ultimately in the 1990s by WFW. Erosion, (prompted by logging, fires, construction and subsequent neglect of access roads, freehand bulldozing of quadbike tracks, and cyclical drought) has been severe, and various attempts at rehab-ing stream channels/wetlands-turned-dongas over the last 10 or 15 years, using the downed logs, tyres from the quad-bike tracks, THAT tussocky grass, etc, have been undertaken. ALL the observations I have posted since I joined this site have been from the catchment of one little stream that flows into Grey Dam.
There is much to be found on the hills and in the valleys that seems to be indigenous to this region, but there appears to be more that may not be. Appropriate management and rehab of the streams and their wetlands is desirable, but with wetlands a little knowledge (and mine is infinitesimal) can be a disastrous thing - not that it is in any way my responsibility to manage any rehab work, but at the moment it is the subject of both my curiosity and a small coursework project (which has turned into an all-consuming quest for answers to difficult questions).
So a first step is to try and determine the present state, and foundational questions revolve around an estimation of "alien veg". Which brings me back to the status of bracken. As I've described, "pristine" was a description abandoned long ago, but "recovering" could be good. Is bracken pioneering this recovery or advantageously suppressing it?
There is no judgement to be made based on prettiness or otherwise of this or that species, but from what we know of other surrounding areas, desirability can be assessed.: What should we encourage and discourage to assist the Commonage to achieve its biodiversity potential?
Simply put: When I draw little blocks on my catchment plan denoting alien vs indigenous veg - is bracken in or out? So far the answer has depended on the inclinations of the person to whom I'm speaking at the time, rather than on research-based fact.
Laura
Only options:
Given that it is a colonizer of disturbed areas and is indigenous, you should mark it as indigenous.
But you have not told us your restoration time frame. If it is 200 years then ignore the Bracken: it is just doing its job. Let it get on with it, and if it does have methods of excluding other species, then time will sort it out.
If you want to restore it over the next 5 years, then I am afraid I cannot help unless you tell me exactly what you want to "restore" it to and can provide a "target community" as a guideline of what you are trying to attain. And even then, the best advice might be to up your time frame by a few more decades at least.
Timeframes.
Interesting concept, timeframes. Will have to go off and think about that, but my instinctual response is that schedules can be set for restorative actions, but less easily for responses. So, for example, we know that we should keep eradicating gum, pine, and wattle propagules, and it would seem like a good plan to control the erosion as proactively as possible. And yes, "setting the stage" (e.g. by removing pine, gum and wattle) and allowing "nature" to do its work in its own way would be optimal.
So your feeling is that bracken would be part of that process, and that wading in and "opening up" those areas would be superfluous and possibly even counter-productive in terms of encouraging a return to what we would deem to be a "more natural state", regardless of the time frame?
?
Laura
depends
No if your target was short-term and your resources infinite, you could "speed up" the process and reduce the cover of Bracken and increase the cover of other species.
But for normal funds and resources - best to take a longer-term timeframe, encourage natural processes and only interfere when you have to.