Riparian zones possess an unusually diverse array of species and environmental processes. The ecological diversity is related to variable flood regimes, geographically unique channel processes, altitudinal climate shifts, and upland influences on the fluvial corridor. The resulting dynamic environment supports a variety of life-history strategies, biogeochemical cycles and rates, and organisms adapted to disturbance regimes over broad spatial and temporal scales. Innovations in riparian zone management have been effective in ameliorating many ecological issues related to land use and environmental quality. Riparian zones play essential roles in water and landscape planning, in restoration of aquatic systems, and in catalyzing institutional and societal cooperation for these efforts.

The Ecology of Interfaces: Riparian Zones

Natural flood plains are among the most biologically productive and diverse ecosystems on earth. Globally, riverine flood plains cover > 2 × 106 km2, however, they are among the most threatened ecosystems. Floodplain degradation is closely linked to the rapid decline in freshwater biodiversity; the main reasons for the latter being habitat alteration, flow and flood control, species invasion and pollution. In Europe and North America, up to 90% of flood plains are already ‘cultivated’ and therefore functionally extinct. In the developing world, the remaining natural flood plains are disappearing at an accelerating rate, primarily as a result of changing hydrology. Up to the 2025 time horizon, the future increase of human population will lead to further degradation of riparian areas, intensification of the hydrological cycle, increase in the discharge of pollutants, and further proliferation of species invasions. In the near future, the most threatened flood plains will be those in south-east Asia, Sahelian Africa and North America. There is an urgent need to preserve existing, intact flood plain rivers as strategic global resources and to begin to restore hydrologic dynamics, sediment transport and riparian vegetation to those rivers that retain some level of ecological integrity. Otherwise, dramatic extinctions of aquatic and riparian species and of ecosystem services are faced within the next few decades.

/pdf/riverine-flood-plains-present-state-and-future-trends-1jrn98ubsi.pdf

Riverine flood plains: present state and future trends

Null models in ecology

Riparian corridors possess an unusually diverse array of species and environmental processes. This "ecological" diversity is related to variable flood regimes, geomorphic channel processes, altitudinal climate shifts, and upland influences on the fluvial corridor. This dynamic environment results in a variety of life history strategies, and a diversity of biogeochemical cycles and rates, as organisms adapt to disturbance regimes over broad spatio-temporal scales. These facts suggest that effective riparian management could ameliorate many ecological issues related to land use and environmental quality. We contend that riparian corridors should play an essential role in water and landscape planning, in the restoration of aquatic systems, and in catalyzing institutional and societal cooperation for these efforts.

The Role of Riparian Corridors in Maintaining Regional Biodiversity

Changes in plant community diversity and floristic composition on environmental and geographical gradients

We suggest here that large-scale natural forest disturbance and primary succession in the lowland rainforests of the Peruvian Amazon is caused by lateral erosion and channel changes of meandering rivers. Our results indicate that in the upper Amazon region, primary succession on newly deposited riverine soils is a major mode of forest regeneration. Landsat imagery analyses show that 26.6% of the modern lowland forest has characteristics of recent erosional and depositional activity; 12.0% of the Peruvian lowland forest is in successional stages along rivers. This successional development is used to classify the western Amazon rainforests according to their geomorphological erosion–deposition pattern. We also propose that by causing high site turnover, disturbance and variation in forest structure, the river dynamics may be a major factor creating and maintaining the high between-habitat (β-type) species diversity characterizing the upper Amazon1.

River dynamics and the diversity of Amazon lowland forest

SUMMARY (1) The major proportion of western Amazon forests grow on fluvial deposits and thus originated in floodplain environments. The fluviodynamic character of the sites initially colonized by plants was studied along different river types, and this information was combined with botanical observations from the same areas. Special emphasis was given to colonizing plant distribution and survival in relation to the abiotic environment. (2) Four frequently occurring landform types, each rich in microforms, were recognized in relation to the colonization process: fluvial bars, swales, abandoned channels and riverbanks. They are affected by seasonal fluctuations in the rivers and tend to be narrow, curved or linear patches. Local site and colonizing vegetation characteristics vary considerably between different river types (meandering or braided, rich or poor in suspended sediment). (3) The newly deposited fluvial sediments are poor in organic carbon and nitrogen. Colonization begins either with immigrant propagules dispersed by wind or water, or with the invasion of species by vegetative means. Usually numbers of individuals are few, and the initial vegetation pattern is a reflection of the small-scale mosaic of microsites. The pioneer flora (125 species recorded) includes many widespread perennial herbs, and seeds of most forest species do not germinate in the dry sediments. Herbaceous colonist species are almost non-existent in suspension-poor rivers of low erosion rate. (4) The persistence of the initial plant assemblage is controlled by the evolution of fluvial landforms. Only a few species among the set of colonists are significant in later forest succession. These include Tessaria integrifolia and Gynerium sagittatum, which resist moderate flood damage and resprout after burial. Mature seed populations of these 10- 15-m-tall species are abundant at the outermost margin of the successional forest just beyond the fluvial bars. The low representation of tree species in the colonizing phase suggests that the extreme environmental conditions at the river margins differ from other natural environments along the Amazon. (5) Aquatic succession on lakes affected by suspension-rich waters starts with genuine floating species. The general habits of these vegetation assemblages and their species composition are highly similar in the 'white-water' floodplains of the study area. An annual vegetation flush characteristically follows the flood period. On the other hand, macrophyte vegetation is almost non-existent on the floodplain lakes of suspension-poor rivers.

New site formation and colonizing vegetation in primary succession on the

The major proportion of western Amazon forests grow on fluvial deposits and thus originated in floodplain environments. The fluviodynamic character of the sites initially colonized by plants was studied along different river types, and this information was combined with botanical observations from the same areas. Special emphasis was given to colonizing plant distribution and survival in relation to the abiotic environment. Four frequently occurring landform types, each rich in microforms, were recognized in relation to the colonization process : fluvial bars, swales, abandoned channels and riverbanks (...)

https://www.jstor.org/stable/info/2261087

New site formation and colonizing vegetation in primary succession on the western Amazon floodplains.

Vegetation was classified and mapped along the small meandering River Kamajohka in peatlands in northernmost Finland. The results show a mosaic of thirteen communities, mainly woody grasslands and mire types. They may be schematically arranged into a developmental order that represents the flood-controlled successions on well-drained and poorly-drained areas. Channel migration largely determines the bound- aries between vegetation groups, and river migration is a natural perturba- tive factor that causes continuous site turnover. All of the current floodplain vegetation has originated from riparian primary successions, and all riparian vegetation may be destroyed by further river erosion. Some vascular plants benefit from special habitats created by river channel migration, though flood influences (duration and magnitude) are probably the most important factors affecting species distribution. Six recent chan- nel abandonments illustrate the heterogenous nature of sedimentary pat- terns and vegetation successions; they are important components of the vegetation mosaic along the river.

River dynamics and vegetation mosaicism: a case study of the River Kamajohka, northernmost Finland

Lateral migration of Amazonian lowland rivers causes a vegetation succession on recently deposited fluvial sediments. The forest ground is formed gradually in se- quence, giving rise to age-zonation of the successional stages. Using Landsat MSS maps and field observations, we studied variations in fluvial landform evolution and river character. The widely used characterizations of the rivers ac- cording to their suspension-load character and channel pattern were evaluated in relation to the vegetation succes- sion. Sequential successional forests appear extensively along meandering white-water rivers, which are rich in sus- pended sediments and are characterized by mobile channels. Conversely, vegetation zonation is less pronounced at the margins of slowly eroding suspension-poor rivers. Line transects were established to document meander develop- ment along eight different rivers. The chemical composition of the recently deposited alluvium differs markedly both among rivers and along the transects. Concentrations of organic carbon and nitrogen increase toward the meander neck along with the acid reaction of the soil. The rate of riv- erine forest regeneration in Peruvian lowland Amazonia was extrapolated on the basis of erosion data from four different rivers, and suggests that approximately 130 km2 of forest is annually eroded and replaced by successional vegetation, the equivalent of 0.2% of the present floodplain area of this region.

Maarit Puhakka

Papers

River dynamics and the diversity of Amazon lowland forest

New site formation and colonizing vegetation in primary succession on the

New site formation and colonizing vegetation in primary succession on the western Amazon floodplains.

River dynamics and vegetation mosaicism: a case study of the River Kamajohka, northernmost Finland

River types, site evolution and successional vegetation patterns in Peruvian Amazonia