AskNature

“A forest ‘remembers’ its predisturbance composition and structure by the presence of at least three interacting parts (Nystrom and Folke 2001; Lundberg and Moberg 2003; Folke et al. 2004): biological legacies, mobile links, and support areas. Biological legacies are species, patterns, or structures that persist within a disturbed area and act as sources of ecosystem recovery, such as large living and dead trees or tree clusters that provide seeds, buried rhizomes or roots, and nutrients to the regenerating stand (Franklin and MacMahon 2000). In some cases these legacies may be biased towards structures or patches that are more likely to survive the disturbance, such as wet or low-lying sites during forest fires. Mobile links are ‘keystone’ organisms that move between habitats and ecosystems after a disturbance to provide essential ecosystem processes that are lacking, such as pollination, seed dispersal, or nutrient translocation, by connecting areas that may be widely separated spatially or temporally (Lundberg and Moberg 2003). Support areas refer to landscape patches or habitats that maintain viable populations of mobile links (Lundberg and Moberg 2003). Together these interacting parts play a pivotal role in renewal and reorganization of a disturbed system.” (Drever et al. 2006:2289-2290)

“We term this network of species, their dynamic interactions between each other and the environment, and the combination of structures that make reorganization after disturbance possible; the ‘ecological memory’ of the system (21, 22)…The ecological memory is a key component of ecological resilience, i.e. the capacity of the system to absorb disturbances, reorganize, and maintain adaptive capacity (25)…The ecosystem renewal cycle in forests gives rise to a coarse mosaic of patches in different stages of a forest cycle (67), initiated by disturbance and comprising a series of structural phases; commonly recognized are the i) gap (in our terms reorganization), ii) building (exploitation), iii) mature (conservation), and eventually iv) degenerative (release) phases (68, 69). The build-up of ecological memory in the form of biological legacies and species in the mosaic landscape usually takes several forest generations during which the soil is formed and nutrient pools and decomposer organisms are accumulated. Although it is common to characterize forest types by particular disturbance regimes, most forests are affected by various disturbances acting at different temporal and spatial scales (Fig. 3; 70-73). Organisms in natural forests have adapted, over evolutionary time, to the characteristic disturbance regimes of these forests. Boreal taiga forests and Mediterranean forests (74) are often disturbed by large-scale fires, while temperate deciduous forests, e.g. beech in Central Europe, mainly are affected by small-scale windthrows.” (Bengtsson et al. 2003:389, 392, 393)