Habitat characteristics and macroinvertebrate assemblages in boreal forest streams: relations to catchment silvicultural activities

We compared the stream habitat characteristics and macroinvertebrate assemblages of boreal headwater streams in both the Finnish and the Russian parts of a single river basin, the Koitajoki River. Over the last 50 years, the Finnish side of the catchment has been managed using modern forestry techniques, whereas Russian side has remained nearly unexploited and is near to its natural state. Differences in silvicultural activities were observed to contribute to differences in habitat structure. The channel habitats were in fairly natural state in the Russian reference streams, whereas the impacted Finnish sites were cleared and straightened. In comparison with the impacted channels, the abundance of coarse woody debris (CWD) was 10–100-fold higher in the reference streams. Implications on the forestry-induced deterioration of water quality were also observed. On the contrary, only small differences in macroinvertebrate assemblages were detected. Despite the lower amount of retentive structures (CWD), significantly higher relative abundance of shredders was observed in the forestry-impacted streams. Otherwise the zoobenthic communities were quite similar in the two subcatchments. We suggest that several mechanisms may explain this similarity: (1) community structure is controlled by naturally acidic conditions, (2) the adverse impacts of forestry on habitat structure and water quality of streams may be compensated by increased input of deciduous litter and organic compounds from drained, structurally young riparian forests and (3) macroinvertebrate species have flexible feeding habits and may thus readily adapt to changing conditions.     

Small-scale movements of lotic macroinvertebrates with variations in flow

1. The small-scale movements and distribution patterns of invertebrates were observed in an attempt to identify the various mechanisms by which organisms may use flow refugia during flow disturbances. The microdistribution of lotic macroinvertebrates was examined in two replicate, non-circulating laboratory flumes with variations in flow among microhabitat patches (≈ 0.015–0.035 m²). The discharge in one experimental flume was manipulated to mimic spates and alter near-bed flow patterns; the other flume acted as a control. After an initial settling period, the position and behaviour of animals within the flumes was recorded before, during and after a simulated spate. Three species with contrasting flow microhabitat preferences and movement behaviour were examined. 2. At low discharge, the microdistribution of all three study species in flumes was broadly consistent with field observations. In the field, the optimum current speed was lowest for adults of the dytiscid beetle, Oreodytes sanmarkii, and highest for mayfly nymphs, Ephemerella ignita, with nymphs of the stonefly, Leuctra inermis, most abundant at intermediate velocities. In the flumes, O. sanmarkii occurred only in very low velocity areas, L. inermis occurred widely throughout the flumes with highest density in low velocity areas and E. ignita also occurred throughout the flumes, but maximum density was in moderately high velocity areas. 3. Increased discharge did not reduce the total number of individuals in experimental versus control flumes for any of the three species studied, although total numbers did decrease over the observation period in both treatments. Simulated spates resulted in a change in the microdistribution of O. sanmarkii and E. ignita, but not L. inermis, such that numbers were reduced in very high velocity microhabitats and animals accumulated in lower flow areas, analogous to flow refugia. These distributional shifts were attributed to movements of individuals among microhabitats. 4. Both active and passive modes of movement contributed to the accumulation of E. ignita and O. sanmarkii in low flow microhabitats (i.e. flow refugia). Some nymphs of E. ignita actively crawled from high to low flow microhabitats. Both species drifted between microhabitats. Drift entry could be active or passive, whereas regaining the substratum was active: O. sanmarkii swam down and E. ignita altered its body posture to promote sinking.     

Influence of woody debris on nutrient retention in catastrophically disturbed streams

The role of woody debris in nutrient cycling was investigated in two catastrophically disturbed streams in the Pacific Northwest that had been subjected to large inputs of wood. One study site in each catchment had all woody debris removed (take section), while the debris in the other study site was left intact (leave section). Nitrate, phosphate and chloride (a conservative tracer) were released in each section and nutrient retention was monitored at downstream stations. Phosphate was removed from solution more than nitrate, probably due to the high N : P ratio in the stream water. However, there were no major differences in nutrient retention between the take and leave sections. In contrast, experiments in recirculating chambers showed that woody debris and cobbles exhibited higher nitrate and phosphate uptake per unit surface area than sand/gravel or fine particulate organic matter. The high uptake rates of woody debris and cobbles may be related to their suitability for colonization by heterotrophic microorganisms and algae. Wood may not influence nutrient retention significantly at the reach level because of its low surface area relative to other substrates. However, wood may be very important at small spatial scales because of its high uptake activity.     

Long-term movement of 15N tracers into fine woody debris under chronically elevated N inputs

Two key questions in the study of large-scale C (carbon) and N (nitrogen) cycling in temperate forests are how N cycling in soil detritus controls ecosystem-level retention of elevated N deposition, and whether elevated N deposition is likely to cause increases in C pools. The large C:N ratios in woody detritus make it a potentially important contributor to N retention, if N immobilization increases, and a potentially important contributor to C sequestration, if pool sizes increase. We studied N concentrations, C:N ratios, and pool sizes of N and biomass in fine woody debris (FWD < 5 cm diam.) 12 years into a long-term N-amendment study in two contrasting forests, a naturally-regenerated forest dominated by Quercus spp., and a 63-yr old plantation of Pinus resinosa. We also quantitatively recovered ¹⁵N tracers (originally applied as ¹⁵NH₄ and ¹⁵NO₃) in FWD, eight years following their application in the same study, in both ambient and N-amended plots. We used these data to test predictions of tracer redistributions made by a biogeochemical process model that included ¹⁵N. Results from the N pool-size analysis and the ¹⁵N tracer-recovery analysis indicated that under elevated N inputs of 5 g N m^–2 yr^–1 (as NH₄NO₃) over the decadal time period, only 0.15%–0.76% of the elevated N inputs were recovered in FWD of N-amended plots relative to ambient. Any increase in N immobilization in wood appeared to be minimal, in agreement with model predictions. Under N amendments, pool sizes of C in FWD were not significantly different from ambient, whereas pool sizes of N were marginally higher. Patterns of ¹⁵NH₄ vs. ¹⁵NO₃ recovery, treatment differences, and forest-type differences suggested that plant uptake, rather than detrital immobilization, was the dominant mechanism of ¹⁵N tracer movement into FWD. This result indicates that plant-soil cycling operating over a decadal time scale or longer controls C:N ratios and N pool sizes in woody debris.     

Woody debris contribution to the carbon budget of selectively logged and maturing mid-latitude forests

Woody debris (WD) is an important component of forest C budgets, both as a C reservoir and source of CO₂ to the atmosphere. We used an infrared gas analyzer and closed dynamic chamber to measure CO₂ efflux from downed coarse WD (CWD; diameter≥7.5 cm) and fine WD (FWD; 7.5 cm>diameter≥2 cm) to assess respiration in a selectively logged forest and a maturing forest (control site) in the northeastern USA. We developed two linear regression models to predict WD respiration: one based on WD temperature, moisture, and size (R ²=0.57), and the other on decay class and air temperature (R ²=0.32). WD respiration (0.28±0.09 Mg C ha⁻¹ year⁻¹) contributed only ≈2% of total ecosystem respiration (12.3±0.7 Mg C ha⁻¹ year⁻¹, 1999–2003), but net C flux from CWD accounted for up to 30% of net ecosystem exchange in the maturing forest. C flux from CWD on the logged site increased modestly, from 0.61±0.29 Mg C ha⁻¹ year⁻¹ prior to logging to 0.77±0.23 Mg C ha⁻¹ year⁻¹ after logging, reflecting increased CWD stocks. FWD biomass and associated respiration flux were ≈7 times and ≈5 times greater, respectively, in the logged site than the control site. The net C flux associated with CWD, including inputs and respiratory outputs, was 0.35±0.19 Mg C ha⁻¹ year⁻¹ (net C sink) in the control site and −0.30±0.30 Mg C ha⁻¹ year⁻¹ (net C source) in the logged site. We infer that accumulation of WD may represent a small net C sink in maturing northern hardwood forests. Disturbance, such as selective logging, can enlarge the WD pool, increasing the net C flux from the WD pool to the atmosphere and potentially causing it to become a net C source.Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.     

Wood‐Associated Macroinvertebrate Fauna in Central European Streams

An overview of macroinvertebrates associated with wood debris is given, with the main focus on Central European fauna. In general, three categories of macroinvertebrate wood relations are distinguished: taxa frequently associated with wood but not xylophagous, facultative xylophagous taxa and obligate xylophagous taxa. The adaptations in the life history, ethology and physiology of species representing these three groups are reviewed. From literature and our own investigations, 15 taxa inhabiting Central European freshwater ecosystems are known to be obligate xylophagous, 22 taxa are facultatively xylophagous. From field observations another 41 taxa presumably feed on wood although no gut content analyses and laboratory experiments have yet been carried out. From 25 taxa other forms of close association to CWD are known (feeding on epixylic biofilm, use as a refuge, or as an attachment point). Possible pathways of xylophagy evolution are discussed and unresolved aspects of aquatic invertebrate wood relations are listed.     

On the Relationships between Ground-dwelling Spider (Araneae) Assemblages and Dead Wood in a Northern Sugar Maple Forest

Downed woody material (fallen logs) offers ground-dwelling spiders (Araneae) ideal sites for nesting and foraging, but little is known about what characteristics of dead wood influence spider assemblages. In a maple forest of Forillon National Park, in eastern Québec (Canada), spider assemblages on, adjacent to, and away from fallen logs were compared. We also tested how log type (coniferous vs. deciduous) and decomposition stage influenced spider assemblages. Sampling was done for an intensive four-week period using both litter samples and pitfall traps. A total of 5613 spiders representing 83 species from 16 families was collected. Spiders were affected by the presence of logs, as both species diversity and total number of individuals collected were significantly higher on the log surface compared to the forest floor. Ordination analysis revealed a distinct compositional difference between the spider fauna found on the wood surface compared to the forest floor. Wood type and decomposition stage had few significant effects on spider assemblages, except that less decayed logs supported higher spider diversity than logs in advanced stages of decay. Dead wood is clearly important for generalist predators such as spiders, further supporting the conservation importance of fallen logs in northern forest ecosystems.     

森林粗死木质残体的概念及其分类

森林粗死木残体 (Coarse woody debris,CWD)在不同的文献中有不同的定义 ,没有通用而确切的概念用来描述 CWD,对研究结果的比较造成了很大障碍。 2 0世纪 90年代以来 ,随着景观生态学的发展 ,以及对 CWD生态功能的深入研究 ,国外的森林管理和研究机构 (例如 USDA Forest Service和 L TER)为了把 CWD放在区域以及景观尺度上进行比较 ,对 CWD的概念等进行了统一 ,将其直径标准由原来的≥ 2 .5 cm调整到≥ 10 cm,但是我国在此方面还没有与国际接轨 ,仍采用旧标准 (≥ 2 .5 cm ) ,这样的研究结果难于和国外进行比较 ,不利于我国 CWD的长期深入研究。另外 ,有关 CWD的分类一直以来也没有形成一个完整的分类系统 ,我国也缺少 CWD分类方法的介绍。鉴于以上情况 ,综合国内外近年来在 CWD方面的研究动态 ,综述了 CWD的概念和分类情况 ,并初步提出较综合的 CWD概念及其分类系统 ,以供相关研究者讨论和参考 ,为我国的 CWD研究起到推动作用     

Short-term decompositional state does not influence use of wood by macroinvertebrates in subtropical, coastal plain streams

Woody debris is an important habitat component, particularly in streams that lack other hard substrates. Research suggests a general relationship between increasing invertebrate density, diversity, and taxa richness with increasing wood decay in lotic systems, with some authors observing invertebrate taxonomic succession as decay proceeds. We designed a field experiment using colonization of known-aged woody debris in two streams to examine patterns in invertebrate colonization, density, diversity, richness, and succession. After aging woody debris 0–6 weeks in laboratory tanks and then placing the debris in the two subtropical, coastal plain streams for five additional weeks, we did not detect any statistical relationship between invertebrate density, diversity, evenness, richness, or life-history pattern with increasing woody debris decay, nor did we detect any relationships between the colonization or abundance of individual taxa and the decompositional state of the wood. In this paper, we propose two non-exclusive explanations for these trends based on opportunistic colonization and evolutionary filtering. Despite the apparent unimportance of decompositional state, woody debris still supported many taxa and remains an important habitat component. Our research further supports the importance of flooding and maintenance of intact riparian and floodplain forests to the woody debris dynamics and macroinvertebrates in coastal plain lotic systems.     

Effects of Large Woody Debris Addition on Stream Habitat and Brook Trout Populations in Appalachian Streams

Large woody debris (LWD) was added to eight streams in the central Appalachians of West Virginia to determine if stream habitat could be enhanced and brook trout (Salvelinus fontinalis) populations increased. Brook trout populations were assessed one year prior to habitat manipulation and 3 years post-habitat manipulation. LWD was added by felling approximately 15 trees per 300 m stream reach. Four of the streams had LWD added to one 300 m reach with 300 m unmanipulated reaches upstream and downstream of the manipulated reach to observe within-stream effects of LWD additions on brook trout density. The remaining four streams had LWD added to three 300 m reaches and these streams were compared to those with only a single 300 m manipulated reach to observe the effects of the extent of habitat manipulation on brook trout density. New pools were formed by the addition of LWD, but overall pool area did not increase significantly in reaches where LWD was added. The relatively high gradient and coarse substrate of these streams may have precluded the added LWD from having a significant influence on stream channel morphology and habitat complexity. No pools were formed in the highest gradient stream, while the stream with the most pools formed had the lowest gradient. Brook trout populations fluctuated following habitat manipulations, and there was no overall effect of the LWD additions on within-stream variability in brook trout density. When there were significant differences among-streams with different extents of LWD additions, those streams receiving LWD additions over a large extent had the greatest brook trout densities. The full potential of added LWD to change stream habitat and influence on brook trout populations may take more time to develop than the 3 years post-manipulation period of this study.     

Concept and Classification of Coarse Woody Debris in Forest Ecosystems

Coarse woody debris (CWD) is generally considered as dead woody materials in various stages of decomposition,including sound and rotting logs,snags,and large branches.CWD is an important functional and structural component of forested ecosystems and plays an important role in nutrient cycling,long-term carbon storage,tree regeneration,and maintenance of heterogeneous environmental and biological diversity.However,the definition and classification of CWD have been the subject of a long debate in forest ecology.CWD has not been precisely defined.Recently,with the rapid development of landscape ecology in CWD,the USDA Forest Service and the Long Term Ecological Research (LTER)have provided a standardized definition and classification for CWD,which makes data comparison in landscape scale possible.Important characteristics of their definition include:(1) a minimum diameter (or an equivalent crosssection) of CWD≥10 cm at the widest point (the woody debris with a diameter from 1 to 10 cm should be defined as fine woody debris,and the rest is litterfall);and (2) sound and rotting logs,snags,stumps,and large branches (located above the soil),and coarse root debris (larger than 1 cm in diameter).This classification has greatly facilitated CWD studies.Therefore,it has been widely applied in some countries (particularly in North America).However,this classification has long been a source of confusion for forest ecologists in China.Furthermore,different definitions and criteria are still adopted in individual studies,which makes the interpretation and generalization of their work difficult.This article reviewed recent progress in classifying CWD,with an emphasis on introducing the classification system of the USDA Forest Service and the LTER.It is expected that this review will help facilitate the development of standardized definition and classification suitable to forest ecosystems in China.