Leaf Litter Retention Research Articles

Habitat heterogeneity increases leaf litter retention and fragmentation in a Cerrado savanna stream

Leaf litter fragmentation is one of the main determinants of the availability of food resources for aquatic biota, and this process is strongly influenced by the retention capacity of streams. Retention capacity depends on habitat heterogeneity, as well as on other factors such as leaf litter characteristics and microhabitat diversity. However, the effects of these factors have not yet been clearly understood. In this study, our hypotheses were as follows: (i) habitat heterogeneity increases leaf litter retention, particularly of larger leaves, and (ii) water flow enhances leaf litter fragmentation by promoting physical abrasion of leaf litter, particularly of softer leaves. We tested these hypotheses using (i) the proportion of leaves in transport and the variation of retentive structures such as rock, pebbles, trunks, and roots for habitat heterogeneity in three reaches and (ii) litterbags of two mesh sizes (fine and coarse) incubated in riffle and pool habitats in three reaches of a headwater stream of the Cerrado biome. Our results demonstrated that habitat heterogeneity and leaf litter size increased leaf litter retention rates, and that water flow is an important factor for leaf litter fragmentation in tropical streams. Large leaves interacted with local conditions of streambed heterogeneity (trunks and roots) to reduce transport distances, and hydrology (water flow) accelerated the fragmentation of soft leaves. Our findings suggest that management strategies promoting the accumulation of woody leaf litter ​in the streambed (trunks and roots) can be valuable to increase the retention capacity of streams, on the other hand the water flow increases the processing of allochthonous organic matter.

Floodplain Preconditioning of Leaf Litter Modulates the Subsidy of Terrestrial C and Nutrients in Fluvial Ecosystems

Leaf litter can be retained in floodplains for several months before it enters rivers as lateral inputs. During this period, the environmental conditions on the floodplain can alter leaf litter chemistry and, consequently, affect its subsequent processing in the river. We analysed the effect of contrasting floodplain conditions on the chemical composition of leaf litter and its leachates, and how this affected their biodegradability and processing in rivers. To do so, we placed reed leaf litter (Phragmites australis) in open- and closed-canopy habitats of three floodplain sites with contrasting climates (semiarid Mediterranean, humid Mediterranean and continental) for 105 days. We then used litterbags in a river to examine the decomposition of preconditioned leaf litter in comparison with a control (non-preconditioned litter), and laboratory assays to examine the biodegradation of their leachates. Contrasting conditions on the floodplain prompted differences in the nutrient content of leaf litter among floodplain sites. Preconditioning caused a generalized decline in the C content and an increase in the lignin content of leaf litter. Even so, preconditioning did not affect litter decomposition rates in the river, although it did reduce decomposition efficiency and biodegradability of leachates. Shredder colonization of litter was variable and generally higher on preconditioned litter, but not significantly so. Different floodplain conditions had no influence on the aquatic processing of preconditioned litter. Our results demonstrate that the retention of leaf litter in terrestrial environments can affect C budgets of fluvial ecosystems and the recipient food web by reducing the input and the biodegradability of C and nutrients.

Changes in the chemical compositions of leaf litter in the canopy of a Japanese cedar plantation

ABSTRACTCanopy leaf litter is typically unevenly distributed due to interception by branches and epiphytes and/or due to attachment to branches and tree trunks. Japanese cedar (Cryptomeria japonica) trees hold a large amount of canopy litter that stays attached to foliage and branches for several years before litterfall. Litter retention in the canopy is predicted to affect the chemical composition of litterfall and throughfall. We analyzed the chemical compositions of water-soluble materials washed from the leaves and those of the leaf residues with different leaf litter ages to clarify the effect of leaf-litter retention in the canopy of Japanese cedar trees. Chemical components of the leaf litter after the washing procedure show temporal changes in total carbon, total nitrogen, and carbon/nitrogen ratio just after senescence and prior to litterfall. Higher inorganic ion concentrations in soluble materials from old dead leaves (ODL) dead for more than 2 years suggest the importance of ODL in leaching and catching chemical components in the canopy. Our results show that Japanese cedar canopies retain the various qualities of leaf litter, which are produced by senescence, leaching, and catching dry deposition, and that a large amount of dissolved components leach from dead leaves that are still attached to the canopy.

Effects of food supplies and water temperature on growth rates of two species of freshwater tropical shrimps

Summary Growth rates of individual freshwater shrimp of the species Atya lanipes and Xiphocaris elongata were measured in a second‐order stream in the Luquillo Experimental Forest in Puerto Rico over 10 years (1997–2007). Shrimp living at lower altitudes in warmer water and wider stream channels with more algal and detrital foods were predicted to grow and reproduce more rapidly. Shrimp were marked and recaptured periodically in pools located at three altitudes to determine whether temperature affected growth rates among individual A. lanipes and X. elongata. Mean annual water temperatures ranged from 20 to 24 °C with the uppermost pool being cooler than the lower pools. Mean annual growth rates for Atya and Xiphocaris were 0.27 and 0.1 mm carapace length, respectively, for all three populations. Differences in growth were partially influenced by how each species obtains its food. Atya is a filter feeder and scraper and has continuous access to suspended organic particles and biofilms. The slower growth rate for Xiphocaris elongata is most likely a result of the wider range in quality and accessibility of food resources. Differences in pool morphology and depths probably affected differences in food availability. Increased leaf litter retention in the deeper upper and lower pools probably increased shrimp growth rates, while washout of leaf litter from the relatively shallow, elongate mid‐altitude pool decreased Atya lanipes growth rates. These long‐lived, slow‐growing shrimp species transform a wide range of organic materials into their biomass. Because of the slow growth rates of these detritivores shrimp, tropical storms, hurricanes, droughts or other disturbances could have persistent, long‐term impacts on detrital processing and on the populations of their predators.

The trophic role of a forest salamander: impacts on invertebrates, leaf litter retention, and the humification process

Woodland (Plethodontid) salamanders are the most abundant vertebrates in North American forests, functioning as predators on invertebrates and prey for higher trophic levels. We investigated the role of Ensatina (Ensatina eschscholtzii) in regulating invertebrate numbers and leaf litter retention in a northern California forest. Our objective was to examine how salamander predation on invertebrates affects leaf litter retention and the amount available for soil‐building and carbon capture at the litter‐soil interface. We used field enclosures to quantify the effects of Ensatina on invertebrates and litter retention over two wet seasons, using moisture as a covariate. In the first year Ensatina reduced Coleoptera (beetles) and Diptera (flies) larvae >2 mm, adult Coleoptera, Collembola (springtails), and Formicidae (ants), and increased Oribatid mites, larvae <2 mm (Diptera and Coleoptera), Diplopoda (millipedes), and Aranaea (spiders) <2 mm by reducing their competitors and predators. A single Ensatina in a 1.5m2 enclosure increased litter retention by 13.3% ± 3.6% (mean ± SE) compared to controls, facilitating the capture of 200 kg/ha of carbon. At a similar density range‐wide this would equate to 72.3 metric tons/yr of carbon in one season potentially sequestered in forest soil rather than entering the atmosphere. In the second year invertebrate densities doubled in response to early rains such that while salamanders reduced the numbers of the same taxa, effect sizes were lower compared to year one, producing biological effects that failed to achieve statistical significance. However, three taxa did significantly increase in year two (Annelida [worms], Psocoptera [barklice], and Chelonethida [pseudoscorpions]). Litter retention in year two was greater on treatment plots by 5.6% ± 4.6%; however, high variability across plots precluded statistical significance. Ensatina suppressed some invertebrate taxa, released others, increased leaf litter retention, and facilitated greater carbon capture in both years; however, the strength of the effects were modulated by the bottom‐up effects of the timing and amount of precipitation in year two.

Leaf litter retention in tropical streams in Hong Kong

Leaf litter can be an important food resource in small forest streams, but its availability to detritivorous macroinvertebrates depends on stream retentiveness. Previous work in Hong Kong streams revealed a scarcity of large detritivores, and it is possible that this reflects the availability or instability of litter resources. Using leaf analogues made from waterproof paper, we undertook short-term experiments to measure the retentiveness of eight Hong Kong streams under baseflow conditions during the dry season; four streams had coarse bed sediments (boulder dominated) and four had relatively fine sediments (cobble-gravel dominated). Initially we compared the transport properties of soaked and unsoaked leaf analogues with the leaves of four native trees in one of the streams. Soaked and unsoaked analogues were used to mimic waterlogged and newly-fallen leaves. Mean travel distances (S p ) of leaves and analogues in the study streams ranged from 1-22 m. These are comparable to values recorded from similar-sized streams in temperate latitudes. Unsoaked analogues traveled further (mean S p = 10.2 m versus 3.1 m) than soaked analogues in all study streams, but retention behaviour of analogues generally matched that of real leaves. Mean travel distances of both analogue types were unrelated to streambed sediment size or sediment heterogeneity, but travel distance of soaked analogues was positively related to stream discharge. Litter retention remained high over a six-day period in one of the streams, suggesting that litter would be readily available to detritivores during periods with stable discharge, and that the scarcity of shredders must be caused by other factors.

Litter retention in Tasmanian headwater streams after clear-fell logging

Clear-fell logging around small headwater streams in Tasmanian wet eucalypt forests was predicted to affect both the retention of leaf litter and the composition and size of leaf packs. Retention structures were surveyed in six natural streams and six streams in forest regenerated 3–5 years after clear-fell and burn logging. Logged streams had more wood, but retained less leaves than natural streams, and consequently had fewer and smaller leaf packs. Leaf packs from natural streams contained 200% more leaves, bark and twigs than packs from logged streams. The effect of buoyancy on leaf retention was assessed with release and recapture of marked Eucalyptus obliqua and Nothofagus cunninghamii leaves. Eucalypt leaves were more likely to be trapped by retention structures on the bed of the stream, while smaller, more buoyant N. cunninghamii leaves were mainly trapped by leaf packs. Leaf packs in natural streams were formed on a matrix of small twigs and long strips of bark, shed from the upper branches of mature stringybark eucalypts, while leaf retention was reduced in logged streams because there are no mature trees to provide effective retention structures. Changes to the channel form increase both discharge and sedimentation. These factors have strong implications for downstream nutrient processing and riverine food webs.

Response of secondary production by macroinvertebrates to large wood addition in three Michigan streams

Summary1. We measured responses in macroinvertebrate secondary production after large wood additions to three forested headwater streams in the Upper Peninsula of Michigan. These streams had fine‐grained sediments and low retention capacity due to low amounts of in‐channel wood from a legacy of past logging. We predicted that wood addition would increase macroinvertebrate secondary production by increasing exposed coarse substrate and retention of organic matter.2. Large wood (25 logs) was added haphazardly to a 100‐m reach in each stream, and a 100‐m upstream reach served as control; each reach was sampled monthly, 1 year before and 2 years after wood addition (i.e. BACI design). Macroinvertebrate secondary production was measured 1 year after wood addition in two habitat types: inorganic sediments of the main channel and debris accumulations of leaf litter and small wood.3. Overall macroinvertebrate production did not change significantly because each stream responded differently to wood addition. Production increased by 22% in the main‐channel of one stream, and showed insignificant changes in the other two streams compared to values before wood addition. Changes in main‐channel macroinvertebrate production were related to small changes in substrate composition, which probably affected habitat and periphyton abundance. Macroinvertebrate production was much greater in debris accumulations than in the main‐channel, indicating the potential for increased retention of leaf litter to increase overall macroinvertebrate production, especially in autumn.4. Surrounding land use, substrate composition, temperature and method of log placement are variables that interact to influence the response of stream biota to wood additions. In most studies, wood additions occur in altered catchments, are rarely monitored, and secondary production is not a common metric. Our results suggest that the time required for measurable changes in geomorphology, organic matter retention, or invertebrate production is likely to take years to achieve, so monitoring should span more than 5 years, and ecosystem metrics, such as macroinvertebrate secondary production, should be incorporated into restoration monitoring programs.

The impact of bird's nest ferns on stemflow nutrient concentration in a primary rain forest, Sabah, Malaysia

Bird's nest ferns (Asplenium nidus complex) (Yatabe & Murakami 2003) are common epiphytes of the Old World tropics and house a high abundance of arthropods (Ellwood & Foster 2004). Through interception and retention of leaf litter (Paoletti et al. 1991, Piggott 1996, Richardson 1999), epiphytes interrupt litterfall dynamics (Clark et al. 1998, Nadkarni & Matelson 1991) and delay the return of nutrients to the forest floor (Nadkarni 1984). Precipitation percolating through the canopy as throughfall is enriched as nutrients are leached from plant surfaces (Levia & Frost 2006). Water flowing down the trunk of trees as stemflow is further enriched from prolonged contact and accumulated nutrient deposits on the trunk (Levia & Frost 2003, Liu et al. 2002). Epiphytes can alter stemflow nutrient concentrations by slowing water percolation and by nutrient uptake and release (Awasthi et al. 1995, Strigel et al. 1994).

Flow‐substrate interactions create and mediate leaf litter resource patches in streams

Summary1. The roles that streambed geometry, channel morphology, and water velocity play in the retention and subsequent breakdown of leaf litter in small streams were examined by conducting a series of field and laboratory experiments.2. In the first experiment, conditioned red alder (Alnus rubra Bongard) leaves were released individually in three riffles and three pools in a second‐order stream. The transport distance of each leaf was measured. Several channel and streambed variables were measured at each leaf settlement location and compared with a similar number of measurements taken at regular intervals along streambed transects (‘reference locations’). Channel features (such as water depth) and substrate variables (including stone height, stone height‐to‐width ratio, and relative protrusion) were the most important factors in leaf retention.3. In the second experiment, the role of settlement location and reach type in determining the rate of leaf litter breakdown was examined by placing individual conditioned red alder leaves in exposed and sheltered locations (on the upper and lower edges of the upstream face of streambed stones, respectively) in riffle and pool habitats. After 10 days, percent mass remaining of each leaf was measured. Generally, leaves broke down faster in pools than in riffles. However, the role of exposure in breakdown rate differed between reach types (exposed pool > sheltered pool > sheltered riffle > exposed riffle).4. In the third experiment, the importance of substrate geometry on leaf litter retention was examined by individually releasing artificial leaves upstream of a series of substrate models of varying shape. Substrates with high‐angle upstream faces (were vertical or close to vertical), and that had high aspect ratios (were tall relative to their width), retained leaves more effectively.5. These results show that streambed morphology is an important factor in leaf litter retention and breakdown. Interactions between substrate and flow characteristics lead to the creation of detrital resource patchiness, and may partition leaf litter inputs between riffles and pools in streams at baseflow conditions.

Ecosystem recovery in restored headwater streams: the role of enhanced leaf retention

Summary There is controversy over how the success of ecological restoration should be measured. Traditionally, emphasis has been placed on species diversity and other community attributes, whereas the restoration of ecosystem processes has received less attention. Here, we combine replicated field experiments and a field survey to provide an ecosystem‐level measure of stream restoration success. Numerous headwater streams in Finland, and in many other parts of the world, have been channelized for timber transport, resulting in channels with simplified structure and flow. Recently, programmes have been launched to restore these streams to their pre‐channelization condition. While the efficacy of restoration in improving fish habitat has been tested, little is known about effects on other stream biota or on the retention of leaf litter, despite its importance in trophic dynamics of forested headwater streams. Using a before‐after‐control‐intervention (BACI) designed experiment with multiple reference and experimental streams, we examined restoration‐induced changes in retention efficiency by conducting leaf‐release experiments before (1993) and after (1996) restoration. Substrate heterogeneity increased, but moss cover decreased dramatically following restoration. Retention efficiency in restored streams was higher than in channelized, but lower than in natural, streams. Algae‐feeding scrapers were the only macroinvertebrate group whose density increased significantly after restoration. Aquatic mosses were a key retentive feature in both channelized and natural streams, but their importance to retention was strikingly reduced by restoration. During restoration work, mosses are detached from large areas of the stream bed, exposing bare stone surfaces for colonization by periphytic algae. A more effective restoration technique would involve the use of moss transplants, or the addition of large woody debris, to increase retentiveness and thus enhance the availability of organic material to benthic consumers. This case study on rivers illustrates how restoration projects benefit from an ecosystem perspective and from measures of ecosystem processes in assessing restoration success.

Retention of leaf litter in streams from riparian plantings in southern Ontario, Canada

This study examines the short-term leaf litter retention from three tree species used in rehabilitative streamside plantings at Washington Creek, southern Ontario, Canada. The number of leaves retained under different riparian conditions (wide tree buffer, meandering; narrow tree buffer, meandering; narrow tree buffer, channelized) differed significantly (P streambank > debris dams > roots > wood. Results from this study may aid in the design of riparian plantings within the scope of agroforestry systems.

Influence of Riparian Vegetation on Invertebrate Assemblages in a Recently Formed Stream in Glacier Bay National Park, Alaska

Influence of the development of riparian vegetation on benthic invertebrate assemblages was analyzed in a recently formed stream in southeast Alaska. Several features of riparian interaction were documented: 1) invertebrate use of willow catkins entering streams in summer, 2) invertebrate use of submerged alder roots as a substrate for attachment and as a source of building material for caddisfly cases, and 3) retention of leaf litter by salmon carcasses. The development of riparian vegetation markedly influenced colonization of the stream by certain invertebrate taxa and thereby played an important role in the successional sequence of macroinvertebrates and overall assemblage development in this new stream.

Budgets and retention of leaf litter in Horonai Stream, southwestern Hokkaido, Japan.

Budgets and retention of leaf litter in Horonai Stream, southwestern Hokkaido, Japan.

Recovery of macroinvertebrate communities from stream habitat restoration

1. Many streams channelized for timber floating in Finland are now being restored to their original condition. The most frequently used restoration structures are boulder dams, flow deflectors, excavations and channel enlargements. By increasing substrate heterogeneity and leaf litter retention, restoration may enhance the formation of detritivore-dominated macroinvertebrate assemblages. In this study, macroinvertebrate communities in streams with differing recovery periods (from 0 to 16 years) from restoration, were compared with those in channelized and near-pristine streams. 2. Water depth and current velocity were lower, and relative bed roughness higher in restored than in dredged channels. Moss cover was negligibly low in recently restored streams, but mosses had recovered well within three years from restoration. The standing stock of leaf litter was lower than in natural streams, but in most cases higher than in channelized streams. 3. Abundances of all invertebrates were highest in natural streams and lowest in streams restored 1 month before sampling. All other restored streams had abundances comparable to, or slightly lower than, those in channelized streams. There was a tendency toward higher abundances of shredders with a long recovery period, but streams restored 8 or 16 years ago still contained relatively sparse shredder populations. 4. Canonical Correspondence Analysis of the October data could be attributed to among-site variation in habitat hydraulics, moss cover and leaf litter. Dredged channels with high velocities and low bed profiles, and natural streams with high retention efficiency were the end points of this gradient. There was little indication of macroinvertebrate assemblages approaching pristine conditions with a longer recovery period. 5. Enhanced litter retention increases the capacity of restored streams to support high abundances of detritivorous invertebrates. Indirectly, restoration may also benefit animals that are not dependent on detrital food. Clearly, macroinvertebrates and other non-vertebrate components of the stream biota should be given a higher priority in the design and execution of stream restoration programmes. © 1998 John Wiley & Sons, Ltd.

Enhancing litter retention in streams

SUMMARY1. Dobson & Hildrew (1992) enhanced leaf litter retention in four streams by placing small plastic leaf traps in manipulated stretches. Litter standing crop and the local abundance of shredders was increased, relative to control stretches, in all sites save one which was naturally highly retentive. These results could indicate food limitation in these detritivores, but might have occurred in response to an altered hydraulic regime or increased habitat availability.2. Shear stress was characterized in the four streams manipulated by Dobson & Hildrew (1992). This was carried out on three occasions in both the manipulated and control stretches of each stream. While there was evidence that the manipulation of retention did influence near‐bed flows, these changes were not consistent enough to explain the response of shredding invertebrates to experimental manipulation.3. In a further experiment, we exposed real and artificial leaves to colonization by invertebrates. Shredders, collectors and predators all colonized real leaves in preference to plastic substitutes.4. These results support the hypothesis that detritivorous macroinvertebrates exploit aggregations of leaf litter primarily as sources of food, rather than as habitat or habitat modifier.

Leaf litter retention and its implications for shredder distribution in two headwater streams

Leaf litter retention and its implications for shredder distribution in two headwater streams