When asking for the relevance of grain and extent for conservation planning the question of the general relevance of grain and extent in biology comes up. As Wiens (1989) explained in his essay review Spatial scaling in ecology, processes at broader scales can affect phenomena at small extents or grains and vice versa. Applying this to conservation planning entails a remarkable number of necessary questions to ask and investigations for conservation actions.
Currently often investigated grains and extents? ? Why? Social/ governmental structures (mismatches)
In past and now investigated grains and extents/ scales
In the past, biodiversity was often considered as static and predictable, that means investigations often were made at only one scale (Poiani et al.
2000). Nowadays, there are still two main scales: the local and global one (Vazquez et al. 2008) but the considerations get more holistic and thus dynamic; different biological levels (species, communities, ecosystems ) influence the conservation planning. The challenge hereby is to develop practical guidelines for appropriate actions (Poiani et al. 2000).
Still a big issue is human made systems which constrain the proper definition of spatial scale. Often the scope of an extent is solely confined by governmental boundaries (e.g. country boarders). Through this restriction, institutions might be hindered to choose the appropriate scale which can distort finding crucial ecological patterns. This impacts especially long-term conservation planning (Guerrero et al. 2013). One could call this mismatch between the system of governmental institutions and ecological processes they are supposed to manage sociological scale, which contains besides the space and time scale also representation and organization (Cumming et al.
[Can grain & extent also be applied to sociological scale?!]
One example that names the conservation planning challenges is the Kimbe Bay, located in the Coral Triangle near Papua New Guinea. Trying to protect this marine area, the researcher face three main issues: 1) the central government only has constrained influence on sea resource management, 2) data on regional planning level are very few and coarse, and 3) social factors such as unclear right of possession in some areas (Mills et al. 2010). One can see that institutional issues as well as extent and grain play a big role in conservation planning.
Mismatches in scale
Choosing the grain, the question asked in the study must be kept in mind. There are many cases in which the investigated grain is bigger or smaller than the area that must be conserved. If the investigated grain is too small there probably must be done more studies about the given extent to find the most appropriate place for the grain. Is the opposite the case, i.e. the investigated grain bigger than the extent of conserved area, the measures might not fit all over the whole extent (Vazquez et al. 2008).
Connectivity/ Conservation network design; patch prioritization
In the past, there were some approaches where nature conservation was tried in an isolated area, for example with closing the North American boarders about 100 years ago. During time, this island approach turned out to be not appropriate because through increasing human population and thus, more anthropogenic interventions in nature, the area was fragmented more and more. Connectivity and larger core areas with buffering zones between them and human used areas have not been considered in conservation planning measures (Soul? und Terborgh 1999). Considering North America as extent in this case, the influence of grains or rather their interaction was totally neglected.
One main reason for conservation planning is trying to keep the ecosystem services, nature provides us. The Grain for Green Program wants to increase ecosystem services in a mountainous area in southwest China and therefore studies this area regarding spatial patterns occurring among different scales. Indeed, they found a strong coherence between spatial characteristic scales and the different distribution patterns of land use. In this case, they used the lacunarity index to find relationships between patterns, distribution of data gaps and heterogeneity of the investigated area to estimate how ecosystem services may be influenced (Fan und Xiao 2020).
Not many studies try to quantify the impact of extent and grain in conservation planning. Huber et al. (2010) tried to do so with their study in the Central Valley ecoregion of California. They investigated the area at a local and regional scale, so they changed the grain within a consistent extent. The result indicates that studying only one scale may neglect ecological patterns and processes at another scale; in this particular case many larger-scale connections were not found in the local investigations of the same extent. Areas which are ecologically important at both scales could be used for prioritization as they could be important at several scales. Pascual-Hortal and Saura (2007) even suggest that consideration of extent and grain resulting in prioritization of the patches is more important than general overall scale investigations.
Extent & Grain levels vs. interactions (cross-scale)
A crucial issue for conservation planning is scalability. Yamakita and Nakaoka (2011) did a study on seagrass bed dynamics in Tokyo Bay, where they investigated different indices of grain and extent and their behavior regarding scalability. Their study was based on a theory by Wu (2003) who suggested that grain follows certain patterns at changing scale, whereas extent has a refracted scaling manner which means vegetation can behave differently in different extent sizes even though the driving forces were the same. The results of the seagrass study converged with Wus theory. For conservation planning, especially this linearity of changing grain can be a good part of predicting behavior on different scales within a given extent.
Another investigated issue across scales can be the neighboring effect, which describes how organisms effect other organisms nearby. In Yamakitas and Nakaokas (2008) neighboring effect study on seagrass they compared different grain sizes in increasing and decreasing process (unvegetated to vegetated state and vice versa). They could confirm their hypothesis of the positive neighboring effects at smaller grains which can be explained by the root growth of seagrasses. Applying this result to conservation planning, one must keep in mind that small grains tend to have greater neighboring effects.
It is not enough to just take several scales and levels into account; they rather must interact dynamically with each other. Currently, too little attention is given to these cross-level and cross-scale interactions (Cash et al. 2006). Also, the interaction of time and spatial scale should not be neglected. The results of French et als (2016) study about coastal and estuarine geomorphic behavior suggest that time and spatial scale are not as dependent on each other as common literature assumes. For this reason, they plead for an appropriate complexity which includes all the necessary parameters but does not make the system more complex as it must be. As conserving nature gets more urgent nowadays, society must solve several challenges regarding conservation planning in limited time.
Although a simple system is useful for handling conservation planning, the nowadays often used simplified community-based studies will not be enough to display the complexity ecosystems have, for example thinking of system openness. We further must not only understand that scale is important in conservation, rather we must understand the interaction and dependencies of different scales and levels (Berkes 2006). One could ask in the context of practicability if the complex management of conservation may be a bigger challenge than the scaling issue itself.
For implementing an appropriate conservation planning, the importance of cross-scale and cross-level actions has to be acknowledged; existing mismatches in levels, scales and the interface of governmental institutions and the conservation issues they manage have to be eliminated. Heterogeneity and plurality are topics that must be recognized and dealt with. If we miss the chance to nest the scales and levels small grains in terms of area and time can result in large-scale and long-term problems (Cash et al. 2006).