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by fires, hurricanes, floods, droughts, and diseases all affected animal and plant popula-
tions; the effects of these disruptions would cascade throughout the complex web of trophic
interactions, leading to ecological changes that were only a surprise to those who had
expected stability. Predicting population sizes, rates of growth, carrying capacity, and max-
imum sustainable yield was therefore fraught with difficulty. Furthermore, human struc-
tures like fishing fleets, work forces, and market demand are usually relatively uncoupled
from the intrinsic rates of population recovery, and it is no surprise that some populations
became disastrously overharvested.
As a result, national parks and game reserves that had been founded with the explicit
intention of maintaining balance were changing in surprising ways, and management inter-
ventions often had unexpected and undesirable outcomes (Holling and Meffe 1996). Where
fire suppression had been the goal, wildfires raged because of accumulating fuel loads. 'Wil-
derness' areas that had been cleared of people began to change as traditional management
systems that had persisted for millennia were lost. Long-lived trees, harvested at apparently
sustainable rates, were failing to recruit. Removal of predators, with the aim of preserving
game animals, led to overpopulation of some species and much heavier impact on vegetation
than had previously been the case (du Toit et al. 2003, Holt and Barfield 2009).
The baseline conditions on which national parks and protected areas were founded proved
to be no more than transitory snapshots in an ever-changing environment. For example,
many reserves in Africa were founded at a time when ecosystems were still recovering from
the effects of massive die-offs of herbivores caused by rinderpest and a century of overhunt-
ing by big-game hunters and ivory traders. As a result, many African savannas had unusually
high densities of trees when protected areas were founded. When herbivore populations
rebounded in the twentieth century, it was difficult for managers to know how to interpret the
changes that they saw: was declining tree cover simply a return to precolonial levels or an
unprecedented degradation towards grassland, or even desert? (Dublin et al. 1990, Holdo
et al. 2009).
As the dynamic nature of ecosystems emerged, some biologists expressed scepticism that
the balance of nature even existed (Elton 1930, Wu and Loucks 1995). New models to explain
variability and flux were needed and ecologists became intrigued by how the different envi-
ronmental and biological elements interacted and changed over time. Charles Gleason
argued that, contrary to Clementsian succession, mentioned above, communities were in
fact much more fluid assemblages that changed over time and were only loosely associated
(Gleason 1926).
Ecologists needed new frameworks to understand the patterns that they saw in landscapes.
A landmark paper by Alexander Watt (1947), in his Presidential address to the British Ecologi-
cal Society, compared ecosystem structure and function across diverse habitats and high-
lighted similarities in their spatial and temporal dynamics. Watt noticed that all of the
landscapes had a patch dynamic structure in which vegetation varied cyclically between
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