A critical review of field techniques employed in the survey of large woody debris in river corridors: a central European perspective

Abstract

In forested watersheds, large woody debris (LWD) is an integral component of river channels and floodplains. Fallen trees have a significant impact on physical and ecological processes in fluvial ecosystems. An enormous body of literature concerning LWD in river corridors is currently available. However, synthesis and statistical treatment of the published data are hampered by the heterogeneity of methodological approaches. Likewise, the precision and accuracy of data arising out of published surveys have yet to be assessed. For this review, a literature scrutiny of 100 randomly selected research papers was made to examine the most frequently surveyed LWD variables and field procedures. Some 29 variables arose for individual LWD pieces, and 15 variables for wood accumulations. The literature survey revealed a large variability in field procedures for LWD surveys. In many studies (32), description of field procedure proved less than adequate, rendering the results impossible to reproduce in comparable fashion by other researchers. This contribution identifies the main methodological problems and sources of error associated with the mapping and measurement of the most frequently surveyed variables of LWD, both as individual pieces and in accumulations. The discussion stems from our own field experience with LWD survey in river systems of various geomorphic styles and types of riparian vegetation in the Czech Republic in the 2004-10 period. We modelled variability in terms of LWD number, volume, and biomass for three geomorphologically contrasting river systems. The results appeared to be sensitive, in the main, to sampling strategy and prevailing field conditions; less variability was produced by errors of measurement. Finally, we propose a comprehensive standard field procedure for LWD surveyors, including a total of 20 variables describing spatial position, structural characteristics and the functions and dynamics of LWD. However, resources are only rarely available for highly time-demanding surveys. We therefore include a set of core LWD metrics for routine baseline surveys of individual LWD pieces (diameter, length, rootwad size, preservation of branches and rootwad, geomorphological/ecological function, stability/mobility) and wood accumulations (number of LWD pieces, geometrical dimensions, channel blockage, wood/air ratio), which may provide useful background information for river management, hydromorphological assessment, habitat evaluation, and inter-regional comparisons.

A dimensionless statistical analysis of logjam form and process

“…The development of a method of quantitatively comparing and contrasting logjams in varied environments is needed in order to help standardize reporting of studies and to understand quantitatively how the influence of logjams varies in different environments (Wohl et al, 2010;Máčka et al, 2011;Wohl et al, 2011;MacVicar and Piégay, 2012). Without such a system, it is often only possible to develop theories of logjam effects based on localized data sets, and it remains difficult to test such theories critically.…”

Large wood budget and transport dynamics on a large river using radio telemetry

“…Recent studies largely consist of either wood budgets Marcus et al, 2011;Wohl, 2011), longitudinal surveys (Lassettre et al, 2008;Wohl and Goode, 2008;Moulin et al, 2011), site specific studies (Moulin and Piégay, 2004;Gurnell et al, 2005) or reviews of previous studies (Bisson et al, 1987;Gurnell et al, 2002;Mácka et al, 2011). Much of the recent LW research is related to increasing channel complexity to produce diverse fish and macro-invertebrate habitat, bank armoring, sediment storage, and carbon sequestration.…”

Wood export prediction at the watershed scale

“…Field measurements were collected from wood export accumulations at the end of summer seasons in WY2010, WY2012, and WY2013 on dry land after reservoir levels receded. A minimum of 100 wood piece dimensions were recorded each year using the large wood criteria of ≥ 1 m length and ≥ 10 cm diameter (Macka et al, 2011). These three field efforts yielded mean and standard deviation wood piece length of 2.8 ± 2.1 m, median 2.0 m, and diameter of 25 ± 18 cm, median 19 cm.…”