•Deadwood helps in creating favorable regeneration microsites, mitigating soil surface temperature and reducing drought stress for the juvenile stage.•Deadwood contributes efficiently to protecting ...seedlings from browsing.•Deadwood protection effect can be isotropic or anisotropic depending on the season.
Mountain forest dynamics and ecosystems services are critically influenced by disturbances, in particular storm events. After extensive disturbance, the large amount of deadwood lying on ground and the necessity for restoring the forest cover with natural regeneration are two critical issues to be dealt with. Salvage logging is the most common post-disturbance management strategy, but it does not consider the strategic role of coarse woody debris (CWD) in favoring regeneration establishment and survival. The aim of this study is to analyze how CWDcontributes to creating favorable microsites for regeneration, increasing seedling establishment probability, after a large windthrow in the eastern Italian Alps. We focused on two different facilitative mechanisms provided by CWD, microsite amelioration and seedling protection, by planting a set of seedlings in the surroundings of deadwood elements. The former mechanism was analyzed by measuring temperature and SWC (Soil Water Content) locally, while for the latter we recorded evidence of browsing at the end of the season. For each trial, we established control sites in empty areas nearby with no CWD presence in order to infer its contribution. The results show that north-facing microsites on south-exposed slopes offer significantly lower temperature and fewer water stress for saplings, in comparison to south-facing microsites. More in general, saplings on deadwood-mitigated microsites are less exposed to desiccation, which mitigates the transplanting shock and facilitates the establishment. Moreover, the presence of lying deadwood increases roughness and, as a consequence, the cost for browsers to reach the seedlings. Using a coefficient expressing this increment, we underline the significant protective effect of CWD against deer browsing. The results of our study highlight the importance of deadwood in providing favorable regeneration microsites, enhancing the probability of sapling establishment and survival, protecting them from deer browsing.
Chamaecyparis obtusa var. formosana is an ecologically and economically important species in Taiwan, with a high affinity for fog immersion. Our study aims to identify possible stress factors that ...induce seedling mortality and investigate how different ecological factors influence seedlings’ early-stage safe site requirements. We focused on the effect of large-scale climatic variables, small-scale microhabitat conditions, and biotic interactions on seedling survival and establishment by applying seasonal seedling survival monitoring and establishment surveys on both regional and local scales. We identified two alternative ways of seedling death, by environment-induced mortality and as a result of herbivory. Opposite effects of the same environmental factors on different causes of mortality showed that seedlings might need to balance the risks posed by both mortality causes to optimize their growing conditions. On a regional scale, we observed a limited effect of regional climatic variables (namely fog frequency) on seedlings’ establishment and survival but noted a similar seasonal survival pattern among regions. We hypothesize that short-duration droughts during the transition from Plum rain to typhoon season are one of the key mechanisms of environment-induced mortality. On a local scale, we found that decayed coarse wood debris (CWD) facilitates seedling establishment by providing a “safe site”, likely due to increased colonization of small-stature bryophytes and decreased litterfall accumulation. The effect of bryophytes on seedling establishment varies depending on their thickness, with thicker ones having stronger negative effects. Aside from the bryophytes, the accumulation of litter hindered seedling establishment. We argue that to safeguard the regeneration of Chamaecyparis obtusa var. formosana population in natural forests, preserving CWD in the forest floor as a safe site for the seedlings after tree-replacing disturbance is essential, particularly under ongoing climate change where more frequent and prolonged drought events are predicted.
•CWD provides “safe site” for the establishment of the seedlings at local scale.•All regions encompassed similar seasonal patterns of seedling mortality.•Bryophyte facilitation and litterfall avoidance drive CWD as safe sites.•Preserving CWD is vital for the seedlings under predicted prolonged droughts.
•The greatest loss of mass was recorded in fresh habitats.•The high moisture content slowed the wood decay process in the boggy habitats.•FWD can be a useful source of nutrients that can be released ...in to the soil.•Wood species and habitat moisture had the greatest influence on the wood properties.
Deadwood is an essential element of forest ecosystems that is a source of nutrients and serves a very important role in the maintenance of biodiversity. Our study aimed to determine the decomposition rate of various species of deadwood while considering habitat conditions, especially moisture content. The study was carried out in the Czarna Rózga Reserve in central Poland. Research plots were designated in a habitat moisture gradient (fresh, wet, and boggy). Eleven wood species were included in the study in two forms (40-mm-long/40-mm-diameter cylinders and 50x50x22 mm cubes). Wood samples were placed directly on the soil surface. After 40 months, these were removed for laboratory analysis. A significant impact of habitat moisture on the decomposition processes of wood samples was observed. The greatest loss of mass (50%, on average) was recorded under fresh habitat conditions. A higher moisture content slowed down the wood decomposition process. In the boggy habitat, the weight loss was 34%, on average. Our research confirmed that fine woody debris may constitute a useful source of nutrients in forest ecosystems that can be released over a short period of time.
The accumulation of large wood debris around bridge piers obstructs the flow, producing increased upstream water levels, large horizontal structural loadings, and flow field modifications that can ...considerably exacerbate scour. These effects have frequently been held responsible for the failure of a large number of bridges around the world, as well as for increased risk of flooding of adjacent areas. Yet little is currently known about the time evolution and processes responsible for the formation and growth of these debris piles. This paper is aimed at deciphering the whole life of debris accumulations through an exhaustive set of 570 experiments in which debris elements were individually introduced into a flume and accumulated at a pier model downstream. Our findings show that in all experiments, the growth of accumulations is halted at a critical stage, after which the jam is removed from the pier by the flow. This condition typically coincides with the time when the dimensions of the accumulations are maxima. The values of the accumulation maximum size display a clear dependence on flow characteristics and debris length distribution. On the other hand, other variables have shown much weaker effects on the geometry of the accumulations. For a given debris length, accumulations are wide, shallow, and long at low flow velocities but become narrower, deeper, and shorter with increasing velocities. A comparison of results of accumulations formed with debris of uniform and nonuniform size distributions has revealed that the former can be up to 2.5 times wider than the latter.
Key Points
Experimental results show that the growth of debris jams at piers is halted at a critical stage
New relations are proposed between the size of debris jams and flow and debris variables
Accumulations formed with uniform are considerably larger than with nonuniform debris
Abstract During our field surveys, two types of woody debris deposition were found. One is deposition of individual wood pieces and the other is formation of woody debris jams at obstructions such as ...a bridge. To investigate behavior of wood debris jam at a bridge, a series of flume experiments was performed in a smooth acrylic rectangular flume. A model of an arch bridge was used as an obstacle in river. The arch bridge was based on Yoriguci bridge. Wooden cylinder was used as model of wood debris. An interpretation of experimental results shows that the wood debris jam can be determined by number of released wood pieces and shaded area of obstructions. These experimental results also reveal that wood debris jam formed by the model bridge contribute to backwater rise. From investigation on flow around model bridge, it is clearly shown the presence of backwater rise caused by the number of wood pieces trapped by a model of an arch bridge. The results also show that the loss coefficient depends on trapped wood pieces. A simple procedure was proposed in this study which seem to provide for predicting backwater rise due to wood debris jam at obstructions.
In the Amazon basin, approximately 60% of rainforest thrives on geologically old and highly weathered soils, thus decomposition represents an important mechanism for recycling nutrients from organic ...matter. Although dead logs and branches constitute up to 14% of the carbon stored in terrestrial ecosystems, woody debris decomposition and mainly the effect of direct nutrient cycling by plant root interaction is poorly studied and often overlooked in ecosystem carbon and nutrient budgets. Here we monitored the decomposition of five different local woody species covering a range of wood density by conducting a long‐term wood decomposition experiment over two years with factorial root presence and phosphorous (P) addition treatments in a central Amazonian rainforest. We hypothesized that woody debris decomposition is accelerated by colonizing fine roots mining for nutrients, possibly strongly affecting wood debris with lower density and higher nutrient concentration (P). We found that root colonization and P addition separately increased wood decay rates, and although fine root colonization increased when P was added, this did not result in a change in wood decay. Nutrient loss from wood was accelerated by P addition, whereas a root presence effect on nutrient mobilization was only detectable at the end of the experiment. Our results highlight the role of fine roots in priming wood decay, although direct nutrient acquisition by plants seems to only occur in more advanced stages of decomposition. On the other hand, the positive effect of P addition may indicate that microbial nutrient mobilization in woody material is driven mainly by wood stoichiometry rather than priming by root activity.
A ‘floodplain large-wood cycle’ is hypothesized as a mechanism for generating landforms and influencing river dynamics in ways that structure and maintain riparian and aquatic ecosystems of forested ...alluvial river valleys of the Pacific coastal temperate rainforest of North America. In the cycle, pieces of wood large enough to resist fluvial transport and remain in river channels initiate and stabilize wood jams, which in turn create alluvial patches and protect them from erosion. These stable patches provide sites for trees to mature over hundreds of years in river valleys where the average cycle of floodplain turnover is much briefer, thus providing a future source of large wood and reinforcing the cycle. Different tree species can function in the floodplain large-wood cycle in different ecological regions, in different river valleys within regions, and within individual river valleys in which forest composition changes through time. The cycle promotes a physically complex, biodiverse, and self-reinforcing state. Conversely, loss of large trees from the system drives landforms and ecosystems toward an alternate stable state of diminished biogeomorphic complexity. Reestablishing large trees is thus necessary to restore such rivers. Although interactions and mechanisms may differ between biomes and in larger or smaller rivers, available evidence suggests that large riparian trees may have similarly fundamental roles in the physical and biotic structuring of river valleys elsewhere in the temperate zone.
► A “floodplain large-wood cycle” structures many Pacific coastal river valleys. ► The cycle promotes a physically complex, biodiverse, and self-reinforcing state. ► Large trees can similarly structure river valleys in other regions. ► Attention to large-diameter tree species can be critical to restoring rivers.
From a lifecycle perspective, assessing bridge vulnerability is a key element of implementing effective risk mitigation and management strategies. This study offers an integrated and computationally ...efficient approach to evaluate bridges' vulnerability to failure due to hydrodynamic and wood debris forces and the concurrent action of local scour. The vulnerability analysis follows a stochastic approach and is developed through a case‐study analysis of a bridge that has a high proneness to flood‐related hazards. The modelling of the wood debris accumulation is accomplished based both on a Standard approach and on findings drawn from up‐to‐date research data. It is found that the shape of wood debris accumulation envisioned in the first approach has a particularly adverse effect on the bridge's vulnerability, exposing its limitations. A detailed and comprehensive methodology for assessing the risk related to flood hazards on bridges is also presented. It is perceived that not only will this new tool be valuable in estimating the flood loss assessment on bridges, but it will also be beneficial for facilitating decision‐making processes and in finding effective countermeasures for risk mitigation of flood‐related hazards.
Francolí River (Catalonia, Iberian Peninsula).
The aim is the reconstruction of the October 2019 flash flood, that was documented through extensive field work: rainfall (300 mm in just a few hours), ...flood marks, times of flood passage and witnesses' snapshots and reports, channel changes, log drift (20,000 trees) and woody debris at bridges, as well as large damage and six fatalities. The methods are: hydrological model built for the rainfall-runoff in the basin and the flood routing in the river, use of hydraulic principles such as flow at waterfalls, flow against obstacles (trees), etc. and finally 1D/2D free surface numerical models.
The uppermost 100 km2 produced discharges of 700 m3/s (up to 50 m3/s/km2, locally). Three bridges failed, but their cascading failure (when one failure triggers the next one downstream) was not proved. The main channel widened more than 10 times, dragging away soil and vegetation like a bulldozer. The resulting large wood debris that clogged two bridges worsened the inundation. An anomalous flow downstream, probably a surge of around 1090 m3/s, due to the failure of a woody jam at a narrow bridge, took two lives. Water Authority is now warning flood planners that vegetated, torrential basins may cause catastrophic floods in the valley towns, if their narrow bridges are sensitive to woody debris.
•Extensive field work proved specific discharges up to 50 m3/s/km2 in a flash flood.•Besides three bridge failures, the woody debris clogged two more bridges.•A surge due to the failure of a bridge woody jam took two lives.
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