Perspectives on biogeomorphology, ecosystem engineering and self-organisation in island-braided fluvial ecosystems

Abstract

Using the River Tagliamento, Italy, as an example, we examine the role of self-organisation in the formation and dynamics of vegetated islands in fluvial ecosystems. We consider how various biogeomorphic processes, such as feedbacks between tree growth and sedimentation, influence island self-assembly, as well as the potential influences of island landforms on resource distribution and shifts in ecosystem state. Despite the abundance of island landforms of different sizes and ages in island-braided reaches along the River Tagliamento, island formation is only found within a specific hydrological and sedimentary envelope, and depends upon a delicate balance of biotic-abiotic feedbacks. As a result, island landforms tend to be lost when river functioning is altered by human interventions. We argue that the specific biogeomorphic processes and self-organisation associated with river island dynamics offer an example of biogeomorphic inheritance, in which reciprocal feedbacks between species and geomorphic processes favour engineer species and promote the future development of the landforms. Thus, islands represent extended phenotypes -or external expressions of genetic traits -of key riparian ecosystem engineers. This capacity to modify the physical environment has important implications for landform evolution and riparian biodiversity. In conclusion, we propose several topics that merit investigation to improve our understanding of the biogeomorphology and self-organisation of river island systems.

The emergence of an ‘evolutionary geomorphology’?

“…Cottonwood currently combines 'r' (ruderal opportunistic) traits at the juvenile stage with K (competitive) traits at the adult stage when it reaches its sexual maturity on stabilized surfaces. The initial abiotic conditions selected the r traits in the long term, whereas the K traits may correspond to an evolutionary feedback associated with engineer effects [28]. Thus, even if the described engineer effects may seem to be negative in the short term, they appear to be rather positive in the long term.…”

Quantification of landform heterogeneity and its relationship with ecological patterns in broad-scale post-mine rehabilitation

“…The results indicated that in the context of this study site, the heterogeneity in relief (LHI1, LHI2 and LHI3) showed the most frequent relationships with the ecological variables followed by heterogeneity in slope (LHI4, LHI7, LHI8), aspect The heterogeneity of geomorphic and ecological processes provides resilience of these systems to small disturbances through system adjustments (Simon, 1998, Francis et al, 2009). Multi-scale and multi-dimensional relationships between topographic differentiation, soil properties and vegetation are known to exist (Solon et al, 2007).…”

“…Biogeomorphic interactions are believed to be at the roots of ecosystem state transitions (Francis et al, 2009) and hence it may have great potential in assessment of rehabilitation of mined lands. The relief features and ecological processes interact with each other in such a way that the entire system appears to work through a self-regulating.…”

“…The relief features and ecological processes interact with each other in such a way that the entire system appears to work through a self-regulating. According to Francis et al (2009), the concept of 'self-organisation' is potentially relevant to biological systems from molecular to ecological level. This could be because the feedbacks between different bioticabiotic and process components of ecosystems often induce a hierarchy of self-reinforcing states (Phillips, 2009).…”

“…Higher biotic and abiotic heterogeneity reduces vulnerability of ecosystems against allogenic disturbances (Francis et al, 2009). At the same time, the biodiversity that has evolved in response to the bio-physical conditions at any given locality develops morphological changes, life-cycle changes and associations with other ecosystem components.…”