Problems of Pattern and Scale

Community ecology is often based on the concept of a continuum in time and space. Spatial scale has been neglected for a long time, and spatial homogeneity was often taken for granted, with spatial heterogeneity being seen as a necessary evil. However, there are different spatial levels of distribution of single plants and plant communities according to species composition and structural characteristics (e.g. forest trees or communities in small island patches or in extensive areas of several thousand hectares on large plains). Furthermore, today most landscapes are structured and determined by human activities, which influence the patterns of land and forest use depending on their size. If we deal with problems of pattern and processes of vegetation, plant coexistence and competition, then scaling issues are regarded as indispensable and fundamental to all ecological investigations because many single processes occur on different spatial scales, for example, photosynthesis (cellular scale), growth (individual scale) and species distribution (landscape scale) (Levin 1992).

Although fixing the scale along a hierarchy can be subjective, understanding the difference between fine (small) and coarse (large) processes becomes important. Furthermore, it is important to know the difference between the ecological and geographical understanding of scale. For landscape ecologists, cartographers and geographers, a small scale is a large area seen on a map with few details (e.g. landscape mosaic, array of patches, 1:100,000). In contrast, for a biological ecologist, small scale means a small part of a map showing many details (e.g. a habitat patch, 1:1000). Even patches can apply to different scales; special patterns demand special scales. For example, in applied ecology, for decision makers in agricultural planning or nature conservation, three spatial scales are most frequently used: within habitat, habitat mosaic (landscape) and macro-scale (regional, landscape mosaic).

The basis for choosing a certain scale is the degree of heterogeneity of a given environment and the specific research question being asked. There is no single “correct” natural scale. Patterns will also change across scales, where differences within a square-metre patch are likely to differ from those at the landscape scale. Further, describing an ecosystem will typically require multiple scales, ranging from the flower head of a thistle to the presence of a tree species across the Mediterranean landscape. In a fine- scale approach, species “a” and “b” may occur in different plots. In such a fine-scale approach, the diverse zonation of plant communities of a complex riverside vegetation becomes visible (Fig. 17.25). These details would be lost in a broad-scale approach using a landscape transect of a large river valley owing to necessary generalisation (Fig. 17.12).

In this context it is important to define the finest details (units), which should be visible in the chosen scale (grain), and the area chosen for investigation (extent). All three depend largely on the size of the organism or the community. In a fragmented landscape, the distance between fragments of the same quality is taken into account for the choice of an adapted scale. Grain and extent change with every change of scale. For large-scale investigations remote sensing has quite often been used; it is even useful for plant communities but would not be used at the individual scale.

Even if all these aspects are considered, we must realise that the choice of a certain scale for a certain spatial analysis is based on the individ ual perception of the research problem. The chosen scale seems “right” or “appropriate”, but ultimately it is still arbitrary. To obtain better answers to the comprehensive questions surrounding how environmental heterogeneity changes with scale, Wiens (1989) proposed a multiscale approach, where better insight into the interrelations between scale-dependent patterns and their causes occurs within different ecosystems. New macro-scale approaches have also been suggested, prompted by problems of global change and also based on methodological reflections coming from landscape ecology. These concern especially the study of the arrangement of larger ecological systems in space. Certain spatial patterns can only be interpreted on a larger scale, and only on such a scale can a better understanding of these patterns and ecological processes in this new field of macroecology be obtained (Gaston and Blackburn 2000). We illustrate these aspects with some examples in what follows.

Two centuries ago, Alexander von Humboldt (1807) recognised that species richness declined significantly as one follows the latitudinal gradient from the tropics to the extratropical regions. Based on the distribution of mammals, Rapoport (1975) found also a greater species diversity in the tropics, and Stevens (1992) underlined these findings and added an altitudinal gradient to this so-called Rapaport’s rule, to which also many exceptions have been noted. Latitude can be regarded as a surrogate for different environmental gradients, for example, changes in temperature, insolation, seasonality—on large scales, such as hemispheres, continents and countries (Sect. 20.3). Moles et al. (2009) studied global patterns in plant height, a decisive character of a species’ ability to compete for light, and found a close relationship between latitude and height due to a major difference in plant strategy between low- and high-latitude systems. Nobis et al. (2012) used a large-scale global approach to analyse the variation of morphological traits (especially needle characteristics). They detected a strong latitudinal correlation with phylogenetic signals due to a phylogenetic structural environmental variation among the 103 Pinus species they studied.

In Switzerland, the relationships between species richness, neophytes and their environment were analysed using a 1-km²-grid-system approach. The results suggest that climate and land use are the primary forces behind environmental change. Neophytes were found to increase in abundance with global warming, with the highest rates occurring within urban regions. Again in Switzerland, along an elevation gradient (263-3175 m a.s.l.) within 400 km² plots the interspecific variation of 708 plant species of adult age showed clearly that temperature was the most important environmental factor in increases in age with higher elevations. Further, it was found that under warmer conditions at lower elevations the lifespan of many species was shorter. This indicates that global warming could contribute to faster species turnover, favouring shortlived species (Nobis and Schweingruber 2013).

The altitudinal gradient is a very powerful basis for testing ecological and evolutionary responses of plants and plant communities to natural environmental influences (Korner 2003). Changing temperature, together with radiation and other climatic trends, leads not only to a zonation of communities with different floristic composition but also different structurally defined communities. The phenotypic variations of pine needles (including their xeromorphic characteristics) have been assessed along a transect (ranging from lowland desert to a mountainous cloud forest) within five Canary islands as a means of describing large- scale altitudinal differentiation, and it was found that environmental changes mainly described the differences, taking into account phylogenetic influences (Lopez et al. 2008).

There are still methodological problems in the complex field of scale-based plant and plant community monitoring and in applying the results for issues such as agricultural and forest management and conservation planning. However, large- scale projects such as the Swiss Biodiversity Biomonitoring Programme are being designed to produce information about the dynamics of biodiversity at different, but especially large, scales.

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