By Jan Hanspach
I reckon that there are as many definitions of landscape ecology as there are landscape ecologists. One of the shortest and clearest definitions I found was that “a landscape is an area that is heterogeneous in at least one variable of interest” (Turner et al., 2001). Instantly, three new questions arise from that: How large is an “area”? What the heck is “heterogeneity”? And what could be a “variable of interest” in landscape ecology?
The answer to the first question is simple with the wisdom of a few decades of hindsight on landscape ecology: a landscape can be anything between a few square meters and several hundred square kilometers.
The second answer is simple too: an area is heterogeneous if it’s not homogenous. And that’s the point where things stop being simple. Heterogeneity is a concept with a myriad of meanings, and heterogeneity in one regard can even be homogeneity in another. Let’s try the more scholarly description given by Jianguo Wu in an editorial (2006): “In general, heterogeneity refers to a multiscaled structure composed of intertwining patchiness and gradients in space and time”. Heterogeneity thus refers to patches and gradients that happen to be in a landscape, and very importantly, he refers to a structure, i.e. spatial characteristics of landscape components. And indeed, landscape ecology is one of the few fields in ecology where space is consistently raised as a basic principle (island biogeography is another). (There are even more to calculate landscape heterogeneity than there are landscape ecologists. That’s why I don’t cover that issue here…) And although all this is already enough to contemplate for a few days it’s not yet the whole story: Wu makes it even more complicated. He says heterogeneity is “multiscaled”. As if the concept of heterogeneity wasn’t complex enough! Scale thus is the third principle of landscape ecology (after space and heterogeneity).
Ok, let’s give the scaly thing a try and answer the third question with it too. Do you still remember the third question? No? It was: what’s a variable of interest to a landscape ecologist? A landscape ecologist can be studying any interactions that determines the distribution and abundance of organisms (Krebs 2001). Let’s just image the following scene: It’s almost the end of a sunny day on a pasture in Transylvania (like in the picture). If you were a vegetation scientist (say, like Carl Troll who coined the term landscape ecology in 1939) you would ecstatically rave about the richness of plant species in the picture. Just now a butterfly passes by searching for a neat place to place its eggs. The butterfly doesn’t care about plants species richness too much since the larvae of this particular species happens to feed on only one species and it sees the pasture as a landscape made of patches of delicious plants within the useless rest. And indeed, after a having fluttered a few meters, our butterfly finds its larval food plant and happily finishes its day by laying her eggs. In that instant, a pack of hungry wolves breaks out of the forest, searching for a tasty flock of sheep. They haven’t had prey for quite a few days and are so keen for meat that they neither care about the egg-laying butterfly nor the overwhelming plant species richness. Unluckily for the wolves, there are no sheep on the pasture today. What seemed very heterogeneous to the vegetation scientist and a bit less heterogeneous to the butterfly thus appears stomach-achingly homogenous to the wolves. Take-home message: Heterogeneity depends on how someone sees the landscape. Different needs and interests are realized on a certain spatial extent (a few meters for the butterfly versus several kilometers for the wolves) and a certain grain size (tiny plant to the butterfly and fat sheep to the wolves) – which together we refer to as scale. Moreover, heterogeneity depends on who sees the landscape. The human perspective may not necessarily equal a species’ perspective and the perspective of one species may not equal that of another.
If you made it through the text so far (and you are not a landscape ecologist), you may have asked what this spiel is all about and why we should care about landscape ecology. And that’s the point where we come to what this blog is meant to be about: sustainability. The answer comes from Richard Forman in the preface of his book “Land Mosaics” (1995):
“Indeed, landscapes and regions are exactly the right scale for sustainability. Local ecosystems are commonly transformed in days or years, whereas land mosaic transformations usually occur incrementally over generations. Humans avoid long-term planning and decisions, whereas sustained human-land interactions require them. Large area is a surrogate for long term.”
Landscape ecology is right where sustainability science needs to be: at the interface of regional planning, geography, the social sciences, economics, and ecology. Its breadth of definitions, though blurry at first sight, carries the potential to bring people from many different fields together and solve problems in an integrative way. It’s no surprise these advantages come at a cost. Landscape ecology is continuously challenged by finding appropriate scales and means to describe heterogeneity and spatial patterns in a way that is relevant for ecological and social processes. Integration and inter-disciplinarity hold many advantages but also may suffer from challenges, such as finding clear methodological frameworks, communicating across disciplinary boundaries, and attracting sufficient funding (see Sherren et al., 2010). Despite all that, landscape ecology is an exciting field with a huge potential to foster sustainable land use.
Forman, R. (1995) Land Mosaics: The Ecology of Landscapes and Regions. Cambridge University Press, Cambridge.
Sherren, K., Fischer, J., Clayton, H., Schirmer, J. & Dovers, S. (2010) Integration by case, place and process: transdisciplinary research for sustainable grazing in the Lachlan River catchment, Australia. Landscape Ecology, 25, 1219-1230.
Turner, M. G., Gardner, R. H. & O’Neill, R. V. (2001) Landscape ecology in theory and practice. Springer-Verlag, New York.
Wu, J. G. (2006) Landscape ecology, cross-disciplinarity, and sustainability science. Landscape Ecology, 21, 1-4.