Robert A. Francis

A critical review on the utility of DNA barcoding in biodiversity conservation

This article considers the utility of DNA barcodes for conservation. DNA barcoding is a molecular tool that uses standardised genetic primers, traditionally the 600- to 800-segments of the mitochondrial gene cytochrome c oxidase I, to classify species. It has become increasingly popular as an efficient way of studying and categorising species to prioritise conservation efforts. A challenge remains, however, in using this information to provide a universally acceptable species concept. Genetic barcoding may focus conservation strategies on populations that have differences in mitochondrial DNA rather than on species. DNA barcodes might also provide potentially useful information about taxa that are relatively well studied—rather than those that require more research. The argument is made that DNA barcoding can provide useful taxonomic data, but should be used with caution to prevent it from being used out of context. DNA barcoding is an increasingly fashionable and novel concept that has generated optimism in enhancing biodiversity assessments—however, this approach should be used in conjunction with other methods for effective conservation efforts.

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.

Wall ecology: A frontier for urban biodiversity and ecological engineering:

Walls are extensive, ubiquitous urban ecosystems that can act as habitat for a range of different species and support non-standard cosmopolitan assemblages. Most investigations into wall ecology have focused on botanical surveys rather than testing hypotheses, but it is apparent that walls can be surprisingly diverse. They also have the potential to be ecologically engineered to encourage a greater diversity and range of species. This review considers the development of wall ecology, highlighting the key characteristics of walls that have been found to influence their ability to support species, with a focus on higher plants. It then examines the kinds of plant assemblages that are found on walls and the broader role of walls within urban biodiversity, before discussing the potential for ecological engineering of walls. Some progress has recently been made in the latter area with the installation of living walls and the physical engineering of wall materials, but much more needs to be done to effectively increase their physical complexity and habitat quality. Walls therefore represent a substantial potential (as well as existing) habitat within urban areas.

INITIAL ESTABLISHMENT OF VEGETATIVE FRAGMENTS WITHIN THE ACTIVE ZONE OF A BRAIDED GRAVEL-BED RIVER (RIVER TAGLIAMENTO, NE ITALY)

The sprouting of vegetative propagules disseminated hydrochorously throughout the active zones of braided rivers is a potentially important method of riparian tree establishment for some species. The hydrogeomorphological characteristics of the immediate local environment (patch), upon which the propagules are deposited, can have a significant influence on survivorship and shoot growth. We conducted a field experiment along the River Tagliamento, Italy during 2003, which involved the planting of Salix elaeagnos and Populus nigra cuttings (vegetative fragments) within exposed sediment patches differing in their relative elevations and sedimentary characteristics. Both species are found in riparian systems throughout Europe and are employed in riparian restoration/conservation schemes. The experiment was designed to examine the influence of environmental factors on the survivorship and shoot growth of these species immediately following propagule deposition. The study plots were comprised of a mix of silt, sand, and gravel. Small amounts of clay and organic matter (maximum 1 % and 1.3%, respectively, by weight) were present. Relation between survivorship and growth of the two species and environmental characteristics were explored using a combination of Principal Components and regression analyses. Probability of survival for both species was found to be greater in patches containing relatively greater amounts of clay and organic matter and low proportions of sand in relation to gravel. However, Salix elaeagnos had greater survival probability at lower elevations with relatively higher moisture levels, while the reverse was true for P. nigra. Both species were similar in their growth response to environmental variables, growth primarily being supported by relatively higher levels of clay, organic matter, and moisture, and lower elevations. Populus nigra survivorship was greater than that of S. elaeagnos, although shoot growth from S. elaeagnos exceeded that of P. nigra. The study highlights the influence of abiotic factors within a river’s active zone on vegetative sprouting and indicates the interspecific variations that can be observed in riparian tree species with similar life-history traits. The findings have implications for river management, restoration, and conservation efforts.

Urban river wall habitat and vegetation: observations from the River Thames through central London

Along heavily engineered urban rivers, river walls and embankments represent the most common habitat available to riparian vegetation. This paper presents the first study into river wall vegetation and the influence of wall surface materials on plant diversity. We were concerned with investigating the plant diversity of such wall habitats, assessing relationships between different wall surface materials and plant diversity, and determining whether river wall and embankment habitats along the River Thames through central London could support native riparian species alongside more typical urban wall flora. Fifteen sites along the River Thames through central London were surveyed to describe wall flora and establish relationships between plant diversity and wall materials. Walls were not species rich, but contained a mix of terrestrial and riparian species. Stone walls with surface fractures and heterogeneous wall surfaces were conducive to plant diversity at the local scale, while wall surface heterogeneity was also important at the landscape scale. Some stratification of vegetation was observed based on wall position relative to flow disturbance. The potential exists for walls to act as sites for habitat improvement and reconciliation ecology within urban rivers.

“Livewood”: Geomorphic and Ecological Functions of Living Trees in River Channels

Although the geomorphic and ecological importance of large wood in streams and rivers is well recognized, most studies consider only dead wood in channels. However, we have observed that living parts of trees are often found within active channels and that this “livewood” shares functions with both instream dead wood and live riparian trees, while also providing some functions unique to living woody material within a channel. We describe the mechanisms that produce livewood and illustrate its characteristics and influences on riparian and stream ecosystems with examples from Europe, North America, and New Zealand. We hypothesize that, compared with dead wood in channels, livewood (a) persists longer because of greater stability and greater resistance to decay, and (b) imparts greater structural complexity (with associated hydraulic roughness and retentiveness). The phenomenon of livewood implies that a broader range of tree species and sizes than previously considered may contribute functionally important wood to channels. We encourage the study of livewood in a range of forest-stream ecosystems to test our hypotheses and further our understanding of how forests interact with rivers and streams.

An investigation into the receptivity of undergraduate students to assessment empowerment

Providing empowerment to students with regard to assessment procedures is a potential mechanism for increasing students’ satisfaction with their education programme and environment. The receptivity of students is likely to vary according to several factors, including their confidence in the ability of assessors to adequately judge the quality of their work, their understanding of assessment procedures and the degree of autonomy they feel is appropriate. Their perception of these factors can also be expected to vary according to how advanced they are in their degree programme. This paper presents the results of a pilot study into the receptivity of first‐ and third‐year undergraduate geography students to various mechanisms and concepts associated with assessment empowerment. Some receptivity to empowerment relating to choice of assessment was observed in first‐year students but the greatest receptivity was found in third‐years, at both individual and community empowerment levels. Third‐year students displayed an increased desire for assessment choice, criteria choice and community empowerment, and decreasing confidence in the lecturer as assessor. Based on these initial results, a methodology for incorporating assessment empowerment into undergraduate teaching is outlined.

Positioning urban rivers within urban ecology

Rivers are important components of many urban systems, and research into urban rivers is increasing internationally, both in scope and intensity. As an introduction to a special section on urban rivers, this short article briefly highlights some key trends in urban river research based on a survey of published articles from Web of Knowledge, before summarising the contributions made by the special section papers. In particular, there has been a general increase in work on urban rivers since the 1990s, with a more dramatic increase from 2001. Most published research has concentrated on water quality and its wider environmental implications; ecologically, many studies have focused on autecology, community ecology or river restoration/rehabilitation, with the main emphasis on macroinvertebrates or fish. Geographically, most studies have taken place in North America (mainly the US) and Asia (mainly China). In the large majority of cases research has been on relatively small rivers within urbanised catchments rather than large, heavily urbanised systems within major towns or cities. Given the wide range of topics and studies relating to urban river research, a detailed meta-analysis of the urban river ecology literature would be a useful endeavour. The six papers included in the special section of this issue provide a sample of some of key and emerging themes within recent urban river research, and originate from a session on the understanding and management of urban rivers held at the Royal Geographical Society (with IBG) Annual Meeting in 2010, at Imperial College London.

26 Gravel bars: a key habitat of gravel-bed rivers for vegetation

This papers examines the importance of gravel bars in terms of a substrate for recruitment, colonisation and development of ground flora and woody vegetation via two European case studies. Experimental work on the River Tagliamento in Italy is used to explore the role of substrate particle size and elevation on recruitment and growth of seedlings and cuttings (Populus nigra L. and Salix elaeagnos Scop.). Meanwhile on the River Tummel in Scotland, the pattern of vegetation communities are related to bar morphology and sedimentology via field survey. Both studies reveal the critical importance of bar morphology and substrate particle size, via their control on inundation frequency, substrate stability and moisture availability, in terms of vegetation development on gravel bars from the initial colonisation stage to vegetation communities present after more than decade.

An experimental comparison of silica gel and quartz sand grains as sediment media for growing vegetation at the laboratory scale

Abstract.In this technical note we compare silica gel grains and quartz sand as sediment media for vegetation root growth in laboratory experiments for ecohydrology and ecohydraulics. Silica gel grains become quite transparent when saturated with water. This would be useful in order to non-invasively observe the rate of growth of plant roots and plan parallel laboratory experiments made in more typical sand sediments. In this work, we compare the results of preliminary tests conducted using quartz sand with the same grain size distribution of silica gel grains. We show that the complex microstructure of silica gel grains seems to influence the evaporation and, in turn, plant growth dynamics. The potential and limitations of the use of silica grains are accordingly discussed in light of more detailed experiments.