For a plant life on the edge, like on a cliff face, should be peaceful. But Nigel Chaffey discovers one species has a real talent for annoying others.
As an enterprising plant having successfully shunned the sight and company of humankind, you might at least expect to be left alone. For example, choosing to establish yourself on vertical rock faces and cliffs you’d have thought you’d be safe from human interference. After all, what self-respecting vertiginous vegetation would have imagined in their wildest flights of fancy that desperately clinging to such high, precipitous, dangerous geological features would be considered a suitable past-time for a supposedly intelligent animal?
Well, one of the gods in her infinite wisdom – and seemingly in need of a bit of a laugh – chose to allow Homo ‘sapiens’ var. piton-piton to evolve. This forlorn creature is regularly seen scrambling over rock faces – places where no sensible, so-called civilised human being should ever go (let alone be seen there). And this rock-hugging activity is not without its consequences to plants dwelling in such areas, as considered by Michael Tessler and Theresa Clark.
Specifically, this elevationally unfazed duo investigated the impact of ‘bouldering’ upon vegetation in the Shawangunks (New York, USA) – ‘a world-renowned climbing destination’. Whilst bouldering – the ‘sport’ of unroped climbing of boulders generally < 3.5 m tall – is on the rise (!), its impact upon the natural environment remains to be fully assessed. In their assessment, Tessler and Clark found, perhaps not unsurprisingly, that bouldering led to lower species richness and vegetation cover on climbed boulders, with the greatest reduction occurring on the faces of mid-height boulders (where most climbing occurs). Consequently, they recommend that ‘visitation rates and the proportion of boulders climbed in conservation areas be monitored and kept at low levels.’* As a confirmed plantophile, Mr P Cuttings goes further and recommends that ALL visitors should be kept at low levels at those sites, and preferably no higher than ground level at all times. Communing with, and getting up close-and-personal to, nature is all very well. But try to leave it intact, please.
Still, there may be at least one benefit of this rock-climbing activity; the generation of dust. As the mineralogical surface is pounded by limbs, hammers, hard-hats, harnesses, etc., the rock is slowly worn away and converted to dust. And it is such dust – pulverised geology – that is being recognised as a major contributor of nutrients to ecosystems other than those where the dust is originally generated.** For example, Sarah Aciego et al. show the importance of dust that is presumed to derive from the deserts of Asia in contributing nutrients to the Sierra Nevada ecosystems of California (USA), thousands of miles distant.
However, if your existing environment is crumbling around you (maybe due to the unregulated activities of rock-climbing humanoids) and you need to relocate, what’s probably the next best thing to natural rocks (from a lithophyte’s point of view)? Buildings! But that habitat is not without its own challenges, vertical or otherwise. Indeed, so demanding can such an anthropogenic substrate be that species growing there oftentimes don’t look like they’re supposed to. Identifying such individuals with the tried-and-tested field criteria of morphological characteristics can therefore be tricky. Which is why Wolfgang Hofbauer (of the Fraunhofer Institute for Building Physics) has had recourse to DNA barcoding to assess the true biodiversity of mosses in the built environment.
DNA barcoding ‘uses a very short genetic sequence from a standard part of the genome the way a supermarket scanner distinguishes products using the black stripes of the Universal Product Code (UPC)’. Thanks to this method plant individuals that may superficially look the same can be assessed objectively and independently for their true – rather than apparent – genetic/taxonomic similarity. Hofbauer et al. have used this approach to identify the building-occupying individuals of the moss genus Schistidium. Vertical surfaces, evolution’s great leveller? Discuss…
* This study adds to previous work by Susan Moyle Studlar et al. that examined the force needed to dislodge various bryophytes and lichens from sites frequented by rock-climbers in West Virginia (USA). A cliff-based vegetation study of an area where rock-climbing is likely to increase in future – and which therefore provides important base-line data to assess its impact – is provided by Laura Boggess et al. for Big South Fork National River and Recreation Area (Tennessee, USA). And for a review of the whole rock-climbing and cliff-face vegetation side of things, try Andrea Holzschuh’s critical review, ‘Does rock climbing threaten cliff biodiversity?’.
** Additionally, the occasional climber that falls from the rock-face to his/her doom but remains undiscovered must surely add nutrients to the foot of the cliff, thereby providing some nourishment to the basal flora (and fauna…).
Tessler, M., & Clark, T. A. (2016). The impact of bouldering on rock-associated vegetation. Biological Conservation, 204, 426–433. https://doi.org/10.1016/j.biocon.2016.10.004
Aciego, S. M., Riebe, C. S., Hart, S. C., Blakowski, M. A., Carey, C. J., Aarons, S. M., … Aronson, E. L. (2017). Dust outpaces bedrock in nutrient supply to montane forest ecosystems. Nature Communications, 8, 14800. https://doi.org/10.1038/ncomms14800
Hofbauer, W. K., Forrest, L. L., Hollingsworth, P. M., & Hart, M. L. (2016). Preliminary insights from DNA barcoding into the diversity of mosses colonising modern building surfaces. Bryophyte Diversity and Evolution, 38(1), 1. https://doi.org/10.11646/bde.38.1.1
Studlar, S. M., Fuselier, L., & Clark, P. (2015). Tenacity of Bryophytes and Lichens on Sandstone Cliffs in West Virginia and Relevance to Recreational Climbing Impacts. Evansia, 32(3), 121–135. https://doi.org/10.1639/079.032.0303
Boggess, L. M., Walker, G. L., & Madritch, M. D. (2017). Cliff Flora of the Big South Fork National River and Recreation Area. Natural Areas Journal, 37(2), 200–211. https://doi.org/10.3375/043.037.0209
Holzschuh, A. (2016). Does rock climbing threaten cliff biodiversity? – A critical review. Biological Conservation, 204, 153–162. https://doi.org/10.1016/j.biocon.2016.10.010