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Fire, flood, pestilence and war


Playing with complexity is part of the professional life of a statistician, and nowhere is this more evident than in ecology, as Felix Grant explains


bigger playground than ecology. It starts off at the same size as the planet, layers dimensionally upwards and downwards from human scale, has multiple expressions in uncountably many scientific study domains, extends backwards and forwards in time. And throughout all of that, it is intrinsically statistical. Te surge of public attention to the


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environment in the 1960s and 1970s aſter publication of Rachel Carson’s Silent Spring[1] was a key factor in making me a statistician, and many others of my generation make the same admission. Hippy illusion gave way to irresistible glimpses into endless unexplored vistas of complexly related data – and then came scientific computing to make the adventure feasible. Ecology is, in conceptual essence, a statistical


study of chreodic systems in perpetual flux, with dynamic equilibrium frequently rearranged by catastrophic shear planes.


Fire Of those catastrophic interruptions, fire is the most dramatic both at the human scale and in terms of local destruction. As I write this, forest fires are in the news from Canada, Colombia, Madeira, Western Europe, and many parts


14 SCIENTIFIC COMPUTING WORLD


tatisticians, despite popular perceptions to the contrary, are as fond of play as the next person – and for a statistician there is no


of the United States. Each fire will reset the biological clock to zero and open up a race to re-colonise the space by everything that walks, flies, germinates or driſts on the wind. A major controversy, in which statistical


evidence and methods are deployed by both sides, is whether preventing large fires promotes or reduces ecological processes and biodiversity. Statistical evidence in favour of intervention derives primarily from tree-ring reconstruction studies, which suggest that historical forest consisted of populations of widely-spaced, long-lived trees untouched by low-level brush fires which cleared ephemeral undergrowth. Analysis[2]


of western US


historical records and current GIS data, however, suggests that the composition of forests varied widely, with some areas fitting the existing model whereas others grew much more densely and with full, persistent lower- tier growth. Tis argument no doubt has a long way to run, but the new analysis does raise questions about the ecological benefits of woodland management. In Colombia, observers retreating just


ahead of the fire-front have been monitoring the movement and behaviour of the fauna. Te researchers are interested in patterns of response, seeking to discover species norms


Historical tree densities in the western United States, based on survey reconstructions, from Williams and Baker[2]


and the chreodic limits to probabilistic variation from them. Multimodal capture methods stream data back for central analysis in Statistica, supplemented by on the spot work in SigmaPlot. Interim findings feedback to fine-tune practice and priorities on the ground. Fire is dependent on a number of factors,


notably climate and environment, and its presence or absence can definitively shape ecologies over very long periods. Te Norway spruce, for example, established itself as the dominant swamp forest tree species across much of Norway and Sweden aſter recurrent burn-back cleared existing land, thereaſter its presence created conditions in which subsequent major fire was suppressed. In some areas, however, this pattern did not occur: absence of any major fire leſt islands of deciduous species. Principal component analysis of pollen spectra in a long-term study of vegetation and fire history suggests[3] that this may have been the result of broader changes to local climate brought about by such an extensive predominant vegetation change.


Flood Flooding is an ecological disrupter of a different but no less decisive kind, oſten with longer-lasting effects, leading to greater analytic complexity in its unravelling. Where fire sterilises a habitat and leaves it to start anew, flood-water mixes mutually incompatible types of habitat, shiſts survival gradients, and moves organisms and material around. If the water recedes relatively quickly, a


Schematic diagram of human/wildlife coexistence at different scales (left) and temporal overlap of tiger (broken lines) with human (solid lines) activity patterns (right), from Carter et al[4]


frequent result is that some plant species have endured while others have perished. Tere will almost always have been chemical and physical changes in the soil. Silt and decaying organic matter may enrich the soil or poison it. If the waters do not recede, then a new aquatic ecology will establish itself in conditions


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