Plant Cuttings

Humans are good for forests

You are all forgiven for doing a ‘double-take’ upon reading that headline. Usually it’s all bad news when humans and forests are concerned, so a statement to the contrary is noteworthy. The item concerns ancient humans, but is more convoluted and nuanced – Cuttingsesque…? – than that five word heading implies. Andrew Trant et al. reveal an intriguing connection between enhanced growth of Western Red Cedar (Thuja plicata) at coastal sites in British Columbia (Canada) and the dietary practices of First Nations’ peoples 6,000 years ago.

Oysters
Oysters, shellfish that are neither fish nor here all within their shells. David Monniaux / Wikipedia

The tale develops thus. A long history of exploitation of such marine-sourced foods as shellfish (which are not fish*, but marine molluscs such as oysters, mussels and clams) by seacoast-dwelling humans results in accumulations of heaps of their discarded shells. Being calcium carbonate (CaCO3)-based, these shells are rich in calcium (an essential plant nutrient), which is released into the soil of these so-called ‘midden’ sites. Additionally, and along with charcoal (derived from the partial burning of plant material such as branches and tree-trunks), the CaCO3 increases soil pH which helps to make phosphorus** (another essential plant nutrient), and other nutrients, more readily available. Furthermore, the charcoal and mollusc shells also help improve soil drainage.

The overall effect of humans consuming large amounts of marine molluscs – to serve a human nutritional need – is much-improved soil – which serves a plant nutritional need – and supports enhanced growth of trees such as T. plicata, i.e. improved forest productivity.

Although Western Red Cedar has great cultural significance to the indigenous peoples of British Columbia, it is a moot point whether the accumulation of seashell heaps was a deliberate act calculated to enhance the growth of this magnificent tree. It’s more likely to be an unintended – if welcome – consequence of humans being tidy. However, and as the authors conclude, “Coastal British Columbia is the first known example of long-term intertidal resource use enhancing forest productivity”. So, whether intentional or not, humans can be good for forests.

That rather heart-warming tale notwithstanding, it still seems to be the case that modern-day humans are trying their level best to trash the planet. For, and as James Watson*** et al. conclude, humans are responsible for “alarming losses comprising one-tenth … of global wilderness areas over the last two decades, particularly in the Amazon (30%) and central Africa (14%)”. So, what have humans lost in the intervening six millennia? Humanity…? Has that ancient shellfish desire become simply selfish…? Discuss!

*To add to the confusion (which really is entirely avoidable if people didn’t get into bad habits like adding the suffix ‘–fish’ to things to make them more palatable by pandering to humans’ food ‘sensitivities’!), fish – e.g. cod, mullet, sharks, grouper – now have to be designated as ‘finfish’, to distinguish them from ‘shellfish’…

** But, please, can we have phosphorus correctly spelt in the article? It’s shown as phosphorous [emphases are Mr Cuttings’] in the abstract, and throughout the text; although laudably consistent, this is still wrong!

*** And for those who may be wondering, that’s James Watson of the School of Geography, Planning, and Environmental Management, University of Queensland (Australia) / Wildlife Conservation Society, Bronx, NY (USA), not the ‘other’ one, of double helix fame.

[Ed. – for an up-to-date assessment of the state of the world’s forests more globally, check out the 2016 Report from the United Nations (UN) Food and Agricultural Organization (FAO). An interesting footnote to the shellfish-sustained cedars’ story is provided by work by Catherine A. Pfister et al.. They report a decrease in mussel shell thickness – and consequent reduction in calcium per discarded mussel shell – over the past few thousand years, which may be in part due to increased ocean acidification from human-elevated atmospheric CO2 levels. Therefore, the ability of modern-day shellfish midden sites to sustain the growth of Western Red Cedar as in those of days gone by is likely to be diminished, which is indirect support for Mr Cuttings’ suggestion of reduced humanity amongst more recent human populations.]

References

Andrew J. Trant, Wiebe Nijland, Kira M. Hoffman, Darcy L. Mathews, Duncan McLaren, Trisalyn A. Nelson, Brian M. Starzomski, 2016, 'Intertidal resource use over millennia enhances forest productivity', Nature Communications, vol. 7, p. 12491 http://dx.doi.org/10.1038/ncomms12491

P. J. WHITE, 2003, 'Calcium in Plants', Annals of Botany, vol. 92, no. 4, pp. 487-511 http://dx.doi.org/10.1093/aob/mcg164

James E.M. Watson, Danielle F. Shanahan, Moreno Di Marco, James Allan, William F. Laurance, Eric W. Sanderson, Brendan Mackey, Oscar Venter, 2016, 'Catastrophic Declines in Wilderness Areas Undermine Global Environment Targets', Current Biology, vol. 26, no. 21, pp. 2929-2934 http://dx.doi.org/10.1016/j.cub.2016.08.049

Catherine A. Pfister, Kaustuv Roy, J. Timothy Wootton, Sophie J. McCoy, Robert T. Paine, Thomas H. Suchanek, Eric Sanford, 2016, 'Historical baselines and the future of shell calcification for a foundation species in a changing ocean', Proceedings of the Royal Society B: Biological Sciences, vol. 283, no. 1832, p. 20160392 http://dx.doi.org/10.1098/rspb.2016.0392

About the author

Nigel Chaffey

Nigel is a botanist and full-time academic at Bath Spa University (Bath, near Bristol, UK). As News Editor for the Annals of Botany he contributes the monthly Plant Cuttings column to that august international botanical organ. His main goal is to inform (hopefully, in an educational, and entertaining way...) about plants and plant-people interactions.