Composition Of Riparian Forests Research Articles

Riparian forest composition affects stream litter decomposition despite similar microbial and invertebrate communities

Cross-boundary flows of energy and nutrients link biodiversity and functioning in adjacent ecosystems. The composition of forest tree species can affect the structure and functioning of stream ecosystems due to physical and chemical attributes, as well as changes in terrestrial resource subsidies. We examined how variation in riparian canopy composition (coniferous, deciduous, mixed) affects adjacent trophic levels (invertebrate and microbial consumers) and decomposition of organic matter in small, coastal rainforest streams in southwestern British Columbia. Breakdown rates of higher-quality red alder (Alnus rubra) litter were faster in streams with a greater percentage of deciduous than coniferous riparian canopy, whereas breakdown rates of lower-quality western hemlock (Tsuga heterophylla) litter were independent of riparian forest composition. When invertebrates were excluded using fine mesh, breakdown rates of both litter species were an order of magnitude less and were not significantly affected by riparian forest composition. Stream invertebrate and microbial communities were similar among riparian forest composition, with most variation attributed to leaf litter species. Invertebrate taxa richness and shredder biomass were higher in A. rubra litter; however, taxa evenness was greatest for T. heterophylla litter and both litter species in coniferous streams. Microbial community diversity (determined from terminal restriction fragment length polymorphisms) was unaffected by riparian forest or litter species. Fungal allele richness was higher than bacterial allele richness, and microbial communities associated with lower-quality T. heterophylla litter had higher diversity (allele uniqueness and richness) than those associated with higher-quality A. rubra litter. Percent variation in breakdown rates was mostly attributed to riparian forest composition in the presence of invertebrates and microbes; however, stream consumer biodiversity at adjacent trophic levels did not explain these patterns. Riparian and stream ecosystems and their biotic communities are linked through exchange and decomposition of detrital resources, and we provide evidence that riparian forest composition affects stream ecosystem catabolism despite similarities in microbial and invertebrate communities.

Composition and Structure of Riparian Forest Dominated by Tsuga canadensis: Contrasts Between Old-Growth and Second-Growth Stands in Northwestern Pennsylvania

Riparian forests of northwestern Pennsylvania's Allegheny High Plateau are often dominated by eastern hemlock, Tsuga canadensis, a tree species under threat from the introduced hemlock woolly adelgid (Adelges tsugae). It is vital to document the structure and composition of these forests before adelgid invasion to understand how they may respond to this disturbance and to provide information useful for future restoration and management efforts. To meet these goals, we compared the composition and structure of old-growth and second-growth stands in a T. canadensis-dominated riparian forest along Henry Run, Cook Forest State Park, Pennsylvania. Tsuga canadensis strongly dominated the large tree stratum of the old-growth stand, followed by Betula lenta and Fagus grandifolia. Tsuga canadensis and Pinus strobus were codominant in the second-growth stand with B. lenta, Fraxinus americana, and Acer rubrum as secondary species. Seedlings and saplings of dominant tree species in both old-growth and second-growth stands were under represented relative to small and large trees, indicating regeneration difficulties. The alien shrub Berberis thunbergii was the only sapling species to occur in the second-growth stand, perhaps a land-use legacy, but was absent from the seedling stratum. We predict that the potential loss of T. canadensis from the canopy at Henry Run may cause a shift in composition to B. lenta and/or P. strobus as these species capture gaps created by dead and dying T. canadensis. However, browsing pressure by white-tailed deer (Odocoileus virginianus) and competition with B. thunbergii may affect regeneration success of specific tree species and ultimately, future forest canopy composition.

Studies on riverine flora of Pamba river basin, Kerala

AbstractRiparian forests are ecotonal assemblage of aquatic and terrestrial habitats. The composition of riparian forests of Pamba River is an amalgamation of riverine, evergreen, deciduous and wetland flora. The floristic investigation of the riparian forests of Pamba river basin revealed taxonomically 433 species which include 410 angiosperms, 3 gymnosperms and 20 pteridophytes. The dominant families based on the number of species are Poaceae, Euphorbiaceae, Rubiaceae, Cyperaceae and Fabaceae. The flora consists of a diverse blend of 99 evergreen, 36 deciduous, 50 wetland, 15 shola-grassland, 46 cultivated and 44 riverine components. The river basin holds 17.5 % endemism and 17 RET species. The riparian tree species identified in the present investigation are Barringtonia racemosa, Calophyllum inophyllum, Crateva magna, Dillenia indica, Elaeocarpus tuberculatus, Garcinia gummi-gutta, Humboldtia vahliana, Largestromea speciosa, Neolamarkia kadamba, Ochrenauclea missionis, Syzigium salicifolium, Talipatri tiliaceaum and Trewia nudiflora. It is assumed that these potential tree species might have a crucial role to maintain the ecological integrity of the riparian zones and floodplain for the restoration of Pamba river.

How do riparian woody seedlings survive seasonal drought?

In semi-arid regions, a major population limitation for riparian trees is seedling desiccation during the dry season that follows annual spring floods. We investigated the stress response of first-year pioneer riparian seedlings to experimental water table declines (0, 1 and 3 cm day(-1)), focusing on the three dominant cottonwood and willows (family Salicaceae) in California's San Joaquin Basin. We analyzed growth and belowground allocation response to water stress, and used logistic regression to determine if these traits had an influence on individual survival. The models indicate that high root growth (>3 mm day(-1)) and low shoot:root ratios (<1.5 g g(-1)) strongly predicted survival, but there was no evidence that plants increased belowground allocation in response to drawdown. Leaf δ(13)C values shifted most for the best-surviving species (net change of +3.5 per mil from -30.0 ± 0.3 control values for Goodding's willow, Salix gooddingii), implying an important role of increased water-use efficiency for surviving water stress. Both S. gooddingii and sandbar willow (S. exigua) reduced leaf size from controls, whereas Fremont cottonwood (Populus fremontii) sustained a 29% reduction in specific leaf area (from 13.4 to 9.6 m(2) kg(-1)). The functional responses exhibited by Goodding's willow, the more drought-tolerant species, may play a role in its greater relative abundance in dry regions such as the San Joaquin Basin. This study highlights the potential for a shift in riparian forest composition. Under a future drier climate regime or under reduced regulated river flows, our results suggest that willow establishment will be favored over cottonwood.

Changes in riparian forest composition along a sedimentation rate gradient

Riparian forests are highly valued for maintaining water quality through the retention of sediments and nutrients. They also provide some of the most diverse and species-rich habitats in the world. What is largely unknown, however, is how sediment deposition affects plant community composition in these forests. The objective of this study was to examine changes in plant community composition across a gradient of increasing rates of sedimentation in riparian forests in the southeastern Coastal Plain, USA. Seventeen plots were established within riparian forests receiving between 0 and 5.5 cm year−1 of sediment deposits. Species density and biomass estimates were collected annually from 2002 to 2006 for overstory and mid-story plant species within each plot. Percent cover and nested frequency of understory plant species were determined annually during 2004–2006. Measures of community composition in the understory, mid-story, and overstory layers of forests were compared to changes in environmental factors associated with increased sedimentation. In the understory, annual, exotic, and upland species had higher importance values in plots receiving high sediment deposition. The densities of shade-intolerant and N-fixing species in the mid-story also increased with increasing sedimentation rates. Increased overstory mortality was associated with high sedimentation rates, though increases in understory light levels in these gaps were not the main driver of understory species changes. Edaphic factors, such as soil texture, moisture, and temperature, were significantly correlated to species composition in all three forest layers, suggesting that changes in soil physical structure due to sedimentation may drive community-level changes in these forests.

Impacts of Wildfire on the Composition and Structure of Riparian Forests in Southern California

In southern California, wildfire is a ubiquitous agent shaping plant communities. Although fire impacts have been widely studied in chaparral-covered uplands, few data are available regarding fire and riparian vegetation. This study provides an example of the impact of a severe fire on riparian habitat. Plant species found in southern California gallery forests are typically adapted to maintaining populations following flood disturbances; we seek to determine whether structural and compositional changes following fire here demonstrate a similar quasi-equilibrium response. We sampled 65 quadrats on 11 transects along two streams in the Los Padres National Forest to characterize tree species size–class distributions before and after the 2002 Wolf Fire. We tested whether species exhibited differential patterns of survivorship and regeneration following the fire, and also tested for spatial variability in mortality within the floodplain. Alnus rhombifolia dominated the pre-fire forest, but experienced severe mortality in the fire and showed very limited resprouting after 3 years. Other prominent taxa (Populus, Salix, Quercus spp.) also lost considerable standing basal area, but had substantially greater rates of resprouting, resulting in a dramatically altered post-fire vegetation composition and structure. Fire impacts did not vary with landform position, leading to a distinctive homogenizing disturbance that contrasts with the spatially zoned and relatively stabilizing compositional influence that flood events have in this same riparian setting.

Lateral channel migration effects on riparian forest structure and composition, Congaree River, South Carolina, USA

Lateral channel migration initiates complex and dynamic biogeomorphic responses that are fundamental to the creation and maintenance of riparian habitats along low-gradient, coastal plain rivers. This study examines the effects of lateral migration rates on the structure and composition of riparian forests along the Congaree River, Congaree National Park, in the Atlantic Coastal Plain, South Carolina. Lateral channel migration rates were measured in a GIS using aerial photos from 1938–2006. Forest variables were measured from a stratified-random sample of 25 paired edge-interior plots, and analyzed using Mann-Whitney tests, Spearman’s correlations, multi-response permutation procedures (MRPP), and non-metric multi-dimensional scaling (NMS) ordinations. Lateral channel migration produced a significant directional control on riparian forests. Pointbar forests exhibited classic forward succession dependent on spatial and temporal controls related to elevation, flood frequency, and lateral migration rates. Cutbank forests responded positively to exposure along the edge and increased in structural complexity with increasing proximity to the river; density, basal area, and richness varied inversely with lateral migration rates. Cutbank edges with low lateral migration allowed longer time for trees to colonize and they contained greater density, basal area, and richness. Cutbanks with high lateral migration contained lower tree density, basal area, and richness.

The influence of timber harvest on the structure and composition of riparian forests in the Coastal Redwood region

The composition and structure of riparian forests in the coast redwood region were analyzed in relation to the length of time since timber harvest, and the width of riparian buffer zone. Ten sites were sampled in the central range of the coast redwood forest type within a variety of post-harvest age groups and riparian buffer zone widths. Data was collected using randomly selected sample plots adjacent to perennial coastal steams. Correlation Fisher's r to z tests and two-tailed t-test were used to examine the relationship between the sample variables and the experimental parameters “years since harvest”, and “width of buffer.” Results indicate that canopy cover was negatively correlated to “years since harvest” with the highest level of canopy cover found on the youngest sites and the lowest level found on the old-growth sites. The hardwood to conifer dominance ratio and the basal area of Alnus rubra (red alder) were correlated negatively to both “years since harvest” and “buffer width” indicating that timber harvest favored hardwood species. Late seral associates such as Oxalis oregana (redwood sorrel), Anthyrium filix- femina (lady fern), and Vaccinium parviflorum (billberry) were found preferentially in older forests and sites with wider buffer zones, while non-native species such as Hedera helix (English ivy), Pampas cortedaria (pampas grass), and Myosotis latifolia (forget-me-not) were found preferentially in younger forests and areas with smaller buffer zones.

Assessing the extent and diversity of riparian ecosystems in Sonora, Mexico

Conservation of forested riparian ecosystems is of international concern. Relatively little is known of the structure, composition, diversity, and extent of riparian ecosystems in Mexico. We used high- and low-resolution satellite imagery from 2000 to 2006, and ground-based sampling in 2006, to assess the spatial pattern, extent, and woody plant composition of riparian forests across a range of spatial scales for the state of Sonora, Mexico. For all 3rd and higher order streams, river bottomlands with riparian forests occupied a total area of 2,301 km2. Where forested bottomlands remained, on average, 34% of the area had been converted to agriculture while 39% remained forested. We estimated that the total area of riparian forest along the principal streams was 897 km2. Including fencerow trees, the total forested riparian area was 944 km2, or 0.5% of the total land area of Sonora. Ground-based sampling of woody riparian vegetation consisted of 92, 50 m radius circular plots. About 79 woody plant species were noted. The most important tree species, based on cover and frequency, were willow species Salix spp. (primarily S. goodingii and S. bonplandiana), mesquite species Prosopis spp. (primarily P. velutina), and Fremont cottonwood Populus fremontii. Woody riparian taxa at the reach scale showed a trend of increasing diversity from north to south within Sonora. Species richness was greatest in the willow-bald cypress Taxodium distichum var. mexicanum—Mexican cottonwood P. mexicana subsp. dimorphia ecosystem. The non-native tamarisk Tamarix spp. was rare, occurring at just three study reaches. Relatively natural stream flow patterns and fluvial disturbance regimes likely limit its establishment and spread.

Riparian areas in the Canadian boreal forest and linkages with water quality in streams

Riparian areas in the Canadian boreal forest represent the transition zone between terrestrial and aquatic ecosystems. We review factors that influence riparian vegetation communities and the associated interactions with boreal streams. Regional and local drivers (e.g., climate, edaphic factors, and natural disturbances) that affect upland boreal vegetation also operate in riparian areas. However, the proximity of riparian areas to the stream channel not only modifies some of these drivers, but it means that the stream itself becomes a driver of riparian vegetation dynamics. For example, hydrological disturbances like flooding and ice scour affect soil texture and alter successional pathways, sometimes completely denuding streambanks of vegetation. Even in riparian areas unaffected by such catastrophic disturbances, saturated soil conditions can influence riparian forest composition and nutrient cycling. Saturated soils support lower mineralization rates, therefore organic layers store relatively more carbon and nitrogen than adjoining upland soils, and primary productivity is generally lower. Saturated soils also have implications for the ability of the riparian area to “buffer” streams from inputs of water and nutrients. For example, reducing conditions in riparian soils could be the sites for nitrate removal from groundwater by denitrification. Spatial variation in weather, soils, vegetation cover, slope, accumulation of organic matter, geographic location, and relief undoubtedly add to the complexity of understanding the role of riparian systems in Canada’s vast boreal forest. However, the opportunity to identify patterns relating to riparian areas will assist in our understanding and management of these multifaceted systems.

Influence of floods on natural riparian forests along the Ergis River, west China

The riparian forests along the Ergis River, west China, composed mainly of Salicaceae species, play an important role in eco-environment protection and sustainable development of local agriculture, stockbreeding, and social economy of the northern desert region of Xinjiang Uygur Autonomous Region. The study of the influence of floods on the natural riparian forests is imperative for the understanding of the successional process and the acceleration of conservation and restoration of forests. By investigating the relationship between floods and dispersal of seeds, sprouting, natural regeneration, the structure of the forests, and their current distribution, we conclude that: 1) the ripening and dispersal periods of Salicaceae species seeds overlap largely with flood occurrence periods, and the sprouting and natural regeneration of seeds depend greatly on flood events; 2) floods supply soil water and increase groundwater level of riparian land through flood irrigation and horizontal infiltration to maintain the normal growth of the riparian forests; 3) floods have a decisive influence on the structure, composition, and distribution pattern of riparian forests, and any disturbance in the water flow has a profound effect on these characteristics. Given these facts, some management measures for conservation and restoration of the riparian forests are proposed, including the establishment of riparian forest buffer belt, bank stabilization measures, and maintenance of flood protection.

Effects of fluvial geomorphology on riparian tree species in Rekifune River, northern Japan

Classification of riverbed geomorphic surfaces based on flooding frequency was conducted and the relationship between their distribution and river morphology was analyzed, to provide an understanding of the structure and species composition of riparian forests dominated by Chosenia arbutifolia. The channel floors of two contrasting river morphologies (bar-braided and incised meandering channels), were divided into five geomorphic surfaces (gravel bar, lower and upper floodplains, secondary channel, and terrace) based on the water level of a 2-yr and a 20-yr recurrence interval. The environmental variables of the same geomorphic surfaces showed similar trends regardless of braided and meandering channel morphology, but differed significantly among the five geomorphic surfaces, which influenced the dominance of tree species. The geomorphic surface map based on recurrence interval of flood and physiognomical vegetation map based on aerial photos appeared almost identical. Geomorphic surface distribution, determined by river channel dynamics and the sediment transport processes occurring at a larger scale and a longer time frame, played an important role in shaping the structure and composition of the riparian forests. C. arbutifolia dominated gravel bar, and the upper and lower floodplains, because these geomorphic surfaces were characterized by gravelly soils which have lower soil moisture availability than soils of other geomorphic surfaces. Thus, an extensive distribution of C. arbutifolia in the braided channel section can be attributed to the frequent lateral migrations of river channels, which resulted in a high ratio of gravel bars, and lower and upper floodplains. In order to preserve indigenous plant communities in riparian zone, dynamic nature and processes of braided rivers should be maintained.

Species composition and environments of riparian forests consisting of Lagerstroemia subcostata var. fauriei, an endangered species on Yakushima Island

Species composition and environments of riparian forests consisting of Lagerstroemia subcostata var. fauriei, an endangered species on Yakushima Island

DISTRIBUTION AND HABITAT OF COLUMBIA TORRENT SALAMANDERS AT MULTIPLE SPATIAL SCALES IN MANAGED FORESTS OF NORTHWESTERN OREGON

Abstract We examined relationships between Columbia torrent salamanders (Rhyacotriton kezeri) and biotic and abiotic habitat attributes at landscape and reach (within-stream) scales in managed forests of northwestern Oregon, USA. In 2000, we found 851 torrent salamanders in 58% of 119 headwater (first-order) streams from randomly selected 2.58-km2 sections of the study area. Landscape-level variation in torrent salamander distribution and relative abundance was related to abiotic landform features that included parent geology, elevation, and aspect, but variation was not related to age or composition of adjacent riparian forests. In 2001, we conducted a more detailed study of salamander occurrence and abundance within 179 10-m stream reaches stratified by geology and gradient. The stream reaches were randomly selected from 40 streams known to contain salamanders. We recorded 1,224 salamanders from 92 (51%) of the stream reaches. Akaike's Information Criterion (AIC) model selection indicated that the globa...

Application of a forest gap model for prediction of browsing effects on riparian forest succession

Selective browsing by white-tailed deer ( Odocoileus virginianus) severely impacts seedling dynamics within riparian forests on the Patuxent Research Refuge, MD. To evaluate the long-term implications of browsing for forest dynamics, field studies of seedling recruitment, seedling growth, and photosynthetic performance are used to adapt a forest gap model (ZELIG) for simulating browsing interactions with tree species life history characteristics. Primary alterations to the model include addition of small seedling demography, soil saturation effects, shade adaption of tree photosynthesis, and browsing algorithms. Simulated stands were subjected to browsing as a function of total seedling density. If a stand is browsed, then seedling species are browsed selectively based on deer feeding preferences. Model output without browsing impacts closely matches current riparian forest composition. Simulated browsing depresses total forest basal area during mid-succession by reducing regeneration and growth of early successional yellow poplar ( Liriodendron tulipifera), allowing late successional American beech ( Fagus grandifolia) to gain earlier dominance. Greater browsing intensities increase the impact on basal area and displace overall forest composition further from control conditions. Control and browsing simulations converge toward an American beech dominated forest in late succession. Thus browsing interacts with tree species life history strategies to alter the rate of succession, but not the long-term trajectory of succession. Further advances in simulating the impacts of deer browsing will benefit from incorporating landscape-scale deer population dynamics and spatially explicit distributions of forest trees.

The relative importance of fire and watercourse proximity in determining stand composition in mixed conifer riparian forests

Factors related to the composition of riparian forest stands on three streams in the northern Sierra Nevada mixed conifer forest type were related to proximity to the water course and years since fire. Using a linear regression analysis 46 variables were correlated to the natural log of distance from the thalweg “ln(distance)” including a highly significant positive correlation to dominance and percent canopy cover of conifers, and a significant negative correlation to the same variables when applied to hardwoods. Twenty six variables were correlated to years since fire “years” including similar correlations to the dominance and cover of hardwood and conifer species. However, the significance of the correlation and the degree of sample variability described by fire age was relatively low in comparison to that found for distance from the thalweg. In addition the relative frequency of fire scars increased in a linear fashion with distance from the watercourse. The results of this study indicate that the importance of fire as a determining influence on forest composition declines in proximity to the riparian zone.

A 5000-year record of disturbance and vegetation change in riparian forests of the Queets River, Washington, U.S.A.

We used fossil pollen, charcoal, and sediment stratigraphy in three small hollows to investigate disturbance events and changes in the composition of riparian forests on a small section of the Queets River floodplain, Olympic Peninsula, Washington. The records ranged in age from approximately 500 years at two sites 300 and 550 m from the river, to 5000 years at a site 800 m from the river. Approximately 400–600 years BP, the two sites nearest the river were either inundated by a very large flood or covered by the active channel, which would have occupied a substantially different position than its present course. Following inundation or channel movement, the pollen record suggests that Alnus rubra Bong., the primary mesic forest colonizer in the Pacific Northwest, increased and was then replaced by Picea sitchensis (Bong.) Carrière and Tsuga heterophylla (Raf.) Sarg. At the site farthest from the river, two fires occurred within the last ca. 4500 years. One of the fires was followed by a period of shrub dominance and succession to Tsuga heterophylla. The other fire did not cause a change in the pollen record. A recent unprecedented rise in Tsuga heterophylla pollen, which began ca. 1000 years BP, might be in response to cooling during the Little Ice Age. Overall, the small hollow records highlight the complex effect of floods, fire, and possibly climate change on riparian forests of the Queets River.

INFLUENCES OF ENVIRONMENT AND DISTURBANCE ON FOREST PATTERNS IN COASTAL OREGON WATERSHEDS

Modern ecology often emphasizes the distinction between traditional theories of stable, environmentally structured communities and a new paradigm of disturbance-driven, nonequilibrium dynamics. However, multiple hypotheses for observed vegetation patterns have seldom been explicitly tested. We used multivariate statistics and variation partitioning methods to assess the relative influences of environmental factors and disturbance history on riparian and hillslope forests. Our study area was the Cummins Creek Wilderness, located in the Oregon Coast Range. Most of the wilderness burned at least once between the mid-19th and early 20th centuries, creating a mosaic of younger forests with a few old-growth patches. Species composition on hillslopes varied primarily along a climatic gradient from moist maritime environments to drier inland climates but was relatively insensitive to forest age structure. The abundance of Tsuga heterophylla, a fire-sensitive, late-successional tree species, decreased with distance from old-growth patches, suggesting possible seed-source limitations following the historical fires. In contrast to species composition, hillslope forest structure was primarily related to fire history but was largely independent of environmental gradients. Old-growth structure characteristics such as large dominant trees, large snags, high down-wood volumes, and high tree size diversity increased with stand age and with the presence of remnant trees that survived the fires. Riparian forests had high shrub cover, abundant hardwoods, and high down-wood volumes, while the conifer-dominated hillslopes had high overstory density and basal area. Maritime climates and their associated plant species extended further inland in riparian areas than on hillslopes. Advance regeneration densities were higher in riparian forests within 5 km of the coast than in any other portion of the study area. Riparian forest structure and composition were related to both environmental and disturbance variables, with stream gradient and size integrating much of the fine-scale variability in disturbance regimes. No single theoretical framework was sufficient to explain the vegetation patterns observed in these forested watersheds. Our findings suggest a conceptual model of forest landscapes in which the relative influences of environment and disturbance on vegetation patterns are contingent on the facet of vegetation considered (composition vs. structure) and the portion of the landscape examined (hillslope vs. riparian).

Structure and Composition of Riparian Boreal Forest: New Methods for Analyzing Edge Influence

Structure and Composition of Riparian Boreal Forest: New Methods for Analyzing Edge Influence

Structure and composition of unmanaged riparian forests in the coastal mountains of Oregon, U.S.A.

We characterized the structure and composition of unmanaged riparian forests in three river basins in Oregon's coastal mountains. Our objective was to evaluate stand attributes at three spatial scales: streamside (site), drainage network (stream order), and basin (subregion). Data on basal area, species composition, snag density, canopy cover, and tree regeneration were collected along transects at 124 sites. Conifer basal area increased with distance from stream, a trend similar among subregions, and was highest at sites along first-order streams. Hardwood basal area was relatively constant with distance from stream and was proportionally higher at sites along second- and third-order streams than at sites along first-order streams. Conifer and hardwood tree regeneration occurred infrequently and varied by topographic position, stream order, and subregion. Conifer regeneration was associated with basal area of shade-tolerant conifers and appeared to be limited by shrub competition. The unmanaged forests we studied were characterized by a patchy mosaic of structure and composition. Hardwoods and shrubs were major components of the near-stream environment in these forests, whereas dominance of conifers was limited to hillslopes. It appears that fine-scale patterns associated with proximity to the stream are influenced by coarser scale factors such as valley-floor width and climate.