Wood dynamics in upland streams under different disturbance regimes

Abstract

This paper presents reach scale large wood (LW) budgets of 12 upland streams in the Okanagan Basin of British Columbia. The study included 100 m long reaches at three wildfire sites and three undisturbed sites in the Interior Douglas‐fir (IDF) biogeoclimatic zone, and three recent Mountain Pine Beetle (MPB) infestation sites and three undisturbed sites in the Montane Spruce (MS) zone. Detailed information on wood recruitment, output and storage were obtained from repeated annual surveys. Recruitment from the riparian zone was found to dominate wood inputs, with fluvial import of secondary importance. In undisturbed streams, wood exhumation was found to be of tertiary importance, but was not observed in disturbed streams. Relative wood length was found to be a strong predictor of wood stability, with wood length to channel width and wood diameter to channel depth ratios of 1:1 forming an approximate maximum threshold of wood mobility. Volumetric decomposition was, on average, a third of the value of fluvial export, and the average residence time of wood in the channels was 20 years. In undisturbed reaches, wood storage indicated a slow depletion of wood from the channels. In the disturbed reaches, wildfire was found to significantly increase annual wood recruitment by more than an order of magnitude over undisturbed or control streams. MPB had not significantly increased LW recruitment, but is expected to increase over the coming decades. Storage rates at the disturbed streams indicated a net accumulation of wood over the study period. Copyright © 2012 John Wiley & Sons, Ltd.

Drivers of Low Instream Large Wood Retention and Imprints of Wood Mobility in Mountain Nonperennial Streams of a Mediterranean Semiarid Environment

“…Therefore, the pioneering observations from Greece and Portugal suggest low instream wood abundance in small streams across the European Mediterranean region, which is generally characterized by a long history of human influence on land cover, including on riparian corridors (Cooper et al, ). For comparison with streams of similar dimensions draining arid and semiarid environments but with a colder climate and dominant coniferous forests, higher average LW volumes of 43.1 m 3 /ha were documented in northern Wyoming (Nowakowski & Wohl, ), and much higher LW frequencies (14–88 LW/100 m) and volumes (26–290 m 3 /ha) were reported from British Columbia (King et al, ). However, our measured LW volume was low, similar to the median values (15.8 and 21.7 m 3 /ha) obtained from two study regions of New Mexico recently affected by high‐magnitude floods and debris flows (Wohl et al, ).…”

Simulating riparian disturbance: Reach scale impacts on aquatic habitat in gravel bed streams

“…The magnitude of the postfire toppling increase is supported by research in streams in British Columbia, which has shown that fires increase the recruitment rate by an order of magnitude or more [ King et al ., ], and is conservative relative to toppling rates measured by Bendix and Cowell []. The period of pulsed wood increase is followed by a 50 year period in which no toppling or riparian recruitment occurs as the regenerating forest matures.…”

Recent advances quantifying the large wood dynamics in river basins: New methods and remaining challenges

“…Quantitative information on the volume of wood required to maintain adequate habitat is generally lacking in the literature, as well as the role of episodic disturbances in supplying wood to rivers [ Miller et al ., ; Benda et al ., ; King et al ., ], despite the fact that the typical distribution of wood storage in relatively undisturbed rivers and streams might be used as the upper limit of what is ecologically useful. The range of values shown in Figures and is quite large, and it is a challenge for ecological research to define the lower limit of the volume of wood required to maintain ecological functioning in various environments.…”