Riparian Forest Stands Research Articles

The effects of floods, droughts and elephants on riparian tree mortality in a semi-arid savanna

Riparian forests have declined around the world over the past century. This is mostly attributed to alteration of river flow regimes and abstraction of alluvial groundwater, although in Africa damage from elephants is often considered the primary cause. Large stands of riparian forest along the Limpopo River in Mapungubwe National Park (South Africa) were transformed to woodland between 1990 and 2005, and water stress resulting from reduced river flows and abstraction, an extreme flood and canopy infestation by climbing plants were identified as contributing causes. Recent recolonization of the area by elephant has created an additional potential driver of mortality. To determine if tree losses have continued and gain further insights into the causes - particularly the relative importance of water stress versus debarking by elephant - tagged trees were surveyed annually from 2011 to 2022. Rates of mortality were higher than in the previous decade for four of the five dominant tree species. Bank erosion from flooding remained a cause but accounted for far less mortality than in the past. For individuals not lost to floods, survival analysis indicated that low rainfall was the primary driver of mortality. Canopy infestation by climbers did not decrease survival, and while elephant damage was common for all species and most likely killed some individuals, it had far less effect than our measures of water availability. Isotopic analysis of xylem, soil, river and groundwater revealed few differences in source water use between species, and marginal contributions from the alluvial aquifer. All species relied on deep soil water, illustrating a key linkage between rainfall and survival under the current hydrological regime. Persistence of the remaining large trees at this site is highly unlikely, considering the altered flow regime of the river and likelihood that future climate change will exacerbate water stress. Given the degree of ecosystem change over the past four decades, future conservation should shift focus to the recruitment and establishment of other large tree species, particularly those tolerant of water stress and elephant browsing.

AN ECOLOGICAL ASSESSMENT OF THE STATE OF SMALL RIVERS IN THE MIDDLE TAIGA SUBZONE OF KARELIA

A multidisciplinary survey of three small rivers emptying to Lake Onego was carried out; information was collected regarding the aquatic biota, the species and age structure of riparian forests, their floristic diversity, and soils. The integral indicator chosen to assess the ecological condition of the watercourses was the characteristics of the rivers’ fish fauna, in particular fish of the Salmonidae family. Surveys of the rivers and riparian forest communities yielded records of 181 vascular plant species (11 of them macrophytes), 11 moss species, 2 lichen species; the fish fauna was made up of 9 species. Overall, the riparian forests featured a relatively wide range of typological diversity. The tree stands varied from the poor Ledum types (site class V) to the most productive Oxalis types (site classes III–I). Analysis of the tree species and age structure of forests in the riparian buffers revealed a prevalence of stable coniferous tree stands in good condition. Statistically reliable correlations were detected between the fish fauna and the tree species composition and inventory characteristics of the riparian forest stands, soil morphological characteristics, and the species diversity of the living ground cover and macrophytes. The species diversity of the riparian and the aquatic biotas were found to correlate positively with each other. Fish numbers were seen to negatively correlate with some characteristics of riparian forest soils (forest floor thickness, podzolic horizon), while the correlation with the humus horizon thickness was positive. Significant positive correlations were identified between aquatic organisms (fish, zoobenthos) and a majority of the stream’s hydrological parameters. The resultant up-to-date information about water-forest system components is important for understanding the role of small streams, which, alongside the scant officially recognized “spawning” rivers, are an ecological niche in the life cycle of salmonid fishes in Northwest Russia.

Valutazione speditiva della potenzialità fitodepurativa di boschi ripariali

Abstract: This technical note describes a quick methodology to classify the phytodepurative potential of riparian forest stands. Some municipalities located within landscapes characterized by both intensive agricultural and industrial activities in Central Italy are considered as test areas. Starting from the on-screen interpretation of high-resolution digital aerial orthophotos, supported by accurate ground surveys and GIS operations, it has been possible to map the riparian forest stands and classify each of them based on factors representing their phytodepurative potential. The proposed mapping process, feasible and easily replicable, provides a support tool for analysis and planning related to phytoremediation and/or to identify conservation and environmental management priorities and, depending on the goals of the phytoremediation objectives, to define where to locate eventual specific technical interventions.

Among cradles and museums: seasonally dry forest promotes lineage exchanges between rain forest and savanna

ABSTRACTBackground: Cerrado comprises heterogeneous vegetation types. The flora of the vegetation types has distinct biogeographic origins and thus can be hypothesised to have distinct evolutionary imprints.Aims: We hypothesised that the flora of riparian forest was phylogenetically overdispersed, whereas those of more open habitats were phylogenetically clustered.Methods: We built a species-level phylogeny for 1,663 species of trees, shrubs and palms and analysed the pattern of lineage distribution, alpha and beta phylogenetic diversity among Cerrado vegetation types (riparian forest, rocky savana, savana and seasonally dry forest - SDTF).Results: We found a gradient of high phylogenetic diversity and overdispersion from riparian forests towards phylogenetic clustering in vegetation in more open and drier habitats. Habitat shifts were common along the evolutionary history of all families analysed and most families showed a high frequency of shifts from SDTF to riparian forest and savanna.Conclusions: SDTF seems to be a transitional habitat in evolutionary terms, promoting lineage exchanges between stands of riparian forest and savanna. While riparian forest can be seen as a ‘museum’, that harbours ancient lineages, savanna and rocky savanna are a ‘cradle’ of derived lineages. Habitat shifts are an important underlying drive of high present-day Cerrado flora diversity.

Altered water uptake patterns of Populus deltoides in mixed riparian forest stands

Plant water uptake plays an important role in regulating ecosystem water balance and its productivity. However, previous studies regarding plant water uptake were primarily conducted in wet areas under seasonal drought conditions, with a limited understanding of the proportion and drivers of plant water uptake under humid conditions. Actually, climate change and variations in global precipitation patterns could simultaneously trigger seasonal drought and flooding. Therefore, it is critical to explore patterns and mechanisms for plant water uptake under humid conditions in wet regions. Here, we employed dual stable isotopes of hydrogen and oxygen coupled with a Bayesian mixing model (MixSIAR) to explore the water uptake patterns of Populus deltoides in two types of riparian forests (pure vs. mixed stand of P. deltoides), under different magnitudes of rainfall (7.9, 15.4 and 34.1 mm), in the Middle-Lower Reaches of the Yangtze River in China. We further used both partial correlation and variation partitioning analyses to determine the relative importance of soil variables and plant properties affecting the proportion of P. deltoides water uptake from different soil layers. Our results revealed that compared to pure stands, P. deltoides in mixed stands had a lower water uptake proportion from deep soil layers (60–80, 80–100 cm) and had higher water uptake from shallow soil layers (0–20, 20–40 cm) under 15.4 mm and 34.1 mm rainfall events. Our results also revealed that plant properties such as leaf biomass, fine root biomass, and diameter at breast height were the primary factors influencing water uptake by P. deltoides. This suggests that P. deltoides in mixed stands could increase the proportion of water uptake from shallow soil layers through altering plant attributes. These findings indicate that mixed stands could restrain frequent extreme rainfall events and subsequent flooding, suggesting more resilience towards future climatic variability.

Understanding hydrogeomorphological dynamics and the distribution of large wood jams to promote sustainable river management strategies

Key Messages Bank erosion and old‐growth upstream riparian forest stands have been identified as key factors for large wood (LW) recruitment in the river system. The concentration of LW jams is greater in the first 12 km of the study reach and gradually decreases downstream because of the widening and deepening of the channel. To manage LW jams, the interdependence of recruitment and accumulation areas, as well as the relationships between hydrogeomorphology and LW dynamics, should be considered.

Management of Riparian Buffers: Upslope Thinning with Downslope Impacts

We examined the potential of using upslope density management to influence growth and drought tolerance of trees in untreated downslope riparian forests. Increment cores from Douglas-fir trees in three mature stands in western Oregon, USA, were collected and measured. Trees responded to an apparent edge effect up t o1 5 m downslope of thinned areas but not downslope of gaps. Growth responses in riparian trees were not affected by slope or potential solar radiation (as a function of location and topography). In addition, in a retrospective analysis of tree growth and allocation patterns (represented by the ratio of earlywood to latewood) and climate after treatment over a 12-year period, trees in our study area did not appear to be water limited and did not show a strong correlation with regional drought metrics. We hypothesize that vegetation layers in these riparian forest stands responded differentially to additional resources becoming available as a result of thinning, with overstory trees in riparian areas responding downslope of thinned uplands and subdominant canopy layers responding downslope of gaps. Our study demonstrates that managers can affect riparian forests with upland treatments to a limited spatial extent, which may be the only option in areas where direct riparian management is restricted due to concerns for other ecosystem services.

Assessing the Effects of Periodic Flooding on the Population Structure and Recruitment Rates of Riparian Tree Forests

Riparian forest stands are subjected to a variety of hydrological stresses as a result of annual fluctuations in water levels during the growing season. Spring floods create additional water-related stress as a result of a major inflow of water that floods riverside land. This exploratory study assesses the impacts of successive floods on tree dynamics and regeneration in an active sedimentation area, while determining the age of the stands using the recruitment rates, tree structure and tree rings based on dendrochronological analysis. Environmental data were also recorded for each vegetation quadrat. In total, 2633 tree stems were tallied throughout the quadrats (200 m2), and tree specimens were analyzed based on the various flood zones. A total of 720 specimens were counted (100 m2 strip) to measure natural regeneration. Higher recruitment rates are noted for the no-flood zones and lower rates in active floodplains. During the period of the establishment of tree species, the survival rates are comparable between the flood zones and the no-flood zones. Tree diameter distribution reveals a strong predominance of young trees in flooded areas. Different factors appear to come into play in the dynamics of riparian forest stands, including the disruptions associated with successive flooding.

Effect of hydrologic regime and forest age on Collembola in riparian forests

The principal objective of the study was to assess factors of primary importance for collembolan community variability measured in riparian forest stands of different age after traditional clear cutting within natural and altered hydrologic regimes. The study was conducted in the Ukrainian part of the Latorica river floodplain where the largest stands of the highly protected medio-European Querco—Ulmetum minoris fluvial forests can be found. Six oak forest stands were investigated on the river floodplain: three in a natural section (inside levee) of the floodplain, which have their original features preserved with periodical inundation, and three in a section separated by a flood control embankment (outside levee) and subjected to serious damage by drainage. In each section the three stands sampled were represented by different ages regenerated with clear-cutting (>3 years, >8 years and >112 years).Differences in hydrologic regimes were central to identification of a predictable and explainable percentage of variation in species composition of Collembola communities in fluvial forests. The hydrologic regime factor was correlated with the basic structural attributes of collembolan communities, such as abundance, species richness and some ecological traits. Season accounted for a higher degree of variation in collembolan communities than did the age of forest stands. We conclude that differences in hydrologic regime are of much higher importance in structuring collembolan communities in riparian forests than are the ages of stands.

Flexural behaviour of selected riparian plants under static load

Soil bioengineering techniques use plants as construction material for civil and hydraulic engineering purposes such as reinforcement of slopes and erosion control of embankments. The interactions of plants and stress from natural processes have to be quantified to assess such soil bioengineering systems from an engineering point of view.The objective of this study is to investigate the flexural behaviour of stems and branches of four riparian species of the Southern Brazilian region, suitable for soil bioengineering purposes (Phyllanthus sellowianus Müll. Arg., Sebastiania schottiana (Müll. Arg.) Müll. Arg., Salix humboldtiana Willd. and Salix×rubens Schrank). 50 green stems of each species were collected in the surroundings of Santa Maria city (29°35′S, 53°32′W), state of Rio Grande do Sul, Brazil, and subjected to static bending tests. Specimens were tested with their bark, immediately after harvesting. The setup of the bending tests was based on the DIN standard (DIN 52186) for 3-point bending tests. Measurements were carried out to obtain characteristic stress×strain diagrams for each stems. The following data analyse resulted in characteristic parameters to describe the overall deformation behaviour (elastic – MOE and plastic – MOR). An additional parameter according to Denardi (2007) was introduced: the “angle of inflection”. This parameter describes the elastic and plastic deformation behaviour of a plant under load from an engineering point of view.Results showed that P. sellowianus and S. schottiana are very appropriate for the protection of river banks according to the criteria of stem flexural behaviour, rupture strength, angle of inflection, growth rate and plant size. P. sellowianus is the most flexible species, followed by S. schottiana, S. humboldtiana and Salix×rubens. Therefore riparian forest stands of S. humboldtiana and Salix×rubens need more frequent maintenance in order to keep flexibility.

Avian Responses to Restoration: Nest-Site Selection and Reproductive Success in Song Sparrows

AbstractRiparian habitats typically support high diversity and density of both plants and animals. With the dramatic loss of riparian habitats, restoring them has become a priority among conservation practitioners. Diversity and density of avian species tend to increase following riparian restoration, but little is known about how restored habitats function to meet particular species' needs. Habitat structure is an important factor affecting species diversity and density and can influence nest-site selection and reproductive success. To evaluate habitat restoration, we examined interactions between habitat structure, nest-site selection, and nesting success in Song Sparrows (Melospiza melodia) nesting in restored, mature, and young naturally regenerating stands of riparian forest. We found that stand types differed markedly in structure, and that habitat structure influenced both nest-site selection and rates of nest loss to predation. Comparison of habitat structure among the three stand types indicated that restored stands offered fewer acceptable nest sites and poorer protection from nest predation. Concordant with those differences in habitat structure, Song Sparrows showed trends toward less density in restored stands than in mature forest, and had poorer nesting success as a result of predation.

AVIAN RESPONSES TO RESTORATION: NEST-SITE SELECTION AND REPRODUCTIVE SUCCESS IN SONG SPARROWS

Riparian habitats typically support high diversity and density of both plants and animals. With the dramatic loss of riparian habitats, restoring them has become a pri- ority among conservation practitioners. Diversity and density of avian species tend to in- crease following riparian restoration, but little is known about how restored habitats func- tion to meet particular species' needs. Habitat structure is an important factor affecting species diversity and density and can influence nest-site selection and reproductive success. To evaluate habitat restoration, we examined interactions between habitat structure, nest- site selection, and nesting success in Song Sparrows (Melospiza melodia) nesting in restored, mature, and young naturally regenerating stands of riparian forest. We found that stand types differed markedly in structure, and that habitat structure influenced both nest-site se- lection and rates of nest loss to predation. Comparison of habitat structure among the three stand types indicated that restored stands offered fewer acceptable nest sites and poorer protection from nest predation. Concordant with those differences in habitat structure, Song Sparrows showed trends toward less density in restored stands than in mature forest, and had poorer nesting success as a result of predation. Received 26 August 1999, accepted 27 No- vember 2000.

Avian species richness in different-aged stands of riparian forest along the middle Rio Grande, New Mexico : G. H. Farley, L. M. Ellis, J. N. Stuart & N. J. Scott Jr, Conservation Biology, 8(4), 1994, pp 1098–1108

Avian species richness in different-aged stands of riparian forest along the middle Rio Grande, New Mexico : G. H. Farley, L. M. Ellis, J. N. Stuart & N. J. Scott Jr, Conservation Biology, 8(4), 1994, pp 1098–1108

Riparian edge effects on boreal balsam fir bird communities

Riparian forests are often identified as prime habitat for wildlife because of the presence of particular plant communities and edges creating a highly developed and diversified vegetation structure. However, in the northeastern boreal forests of Canada, where narrow land–water ecotones with abrupt edges are quite common, the relative habitat value of riparian forests remains to be demonstrated. We compared bird communities of eight pairs of riparian and nonriparian plots, similar in vegetation structure and composition, to verify the relative value for breeding birds of typical coniferous riparian forest stands of the southern boreal region of eastern Quebec. Bird abundance (P = 0.02), richness (P = 0.03), and diversity (P = 0.02) were significantly higher in the riparian stands, where the spatial sequence of three distinct habitats (a balsam fir (Abiesbalsamea (L.) Mill.)–northern white cedar (Thujaoccidentalis L.) forest, a narrow alder (Alnusrugosa (Du Roi) Spreng.) - grass wetland, and water) created high horizontal vegetation diversity. In riparian stands median bird richness and density were, respectively, 23.5 species and 437.5 territories/km2 compared with 19.0 species and 348.2 territories/km2 for interior stands. Nine species were observed exclusively in riparian plots. In addition to the species usually found in the studied nonriparian forests, the riparian plots were used by species typically related to the water edge such as the Northern Waterthrush (Seiurusnoveboracensis Gmelin) and Rusty Blackbird (Euphaguscarolinus Miiller) as well as species associated with the shrub and grass wetland such as the American Robin (Turdusmigratorius L.), the Veery (Catharusfuscescens Stephens), and the Common Yellowthroat (Geothlypistrichas L.). The shrub-foraging guild showed higher abundance in riparian stands. The tree-foraging and tree-bole foraging guilds, however, were comparable in both groups of stands. In this study, the natural conditions prevailing along he riparian sites appeared mostly positive for the breeding-bird community; it created what is perceived as being an "edge effect." The edge effect can be defined, in this case, as being the additional density and number of species induced by the added horizontal vegetation diversity created by the close association of three extremely different ecosystems: a forest stand, an aquatic ecosystem, and a narrow but distinct shrub-grass wetland. This also confirms the necessity of distinguishing natural edges that are permanent features of the landscape from induced edges created by human activity.

Avian Species Richness in Different‐Aged Stands of Riparian Forest Along the Middle Rio Grande, New Mexico

Riparian forests are important for maintaining vertebrate species richness in the southwestern United States, but they have become restricted in distribution due to both historical and current management practices. In order to counteract continued loss of this habitat, several mitigation programs were developed in the middle Rio Grande Valley of New Mexico. Three areas ranging from 50 to 140 ha were revegetated with native trees using pole planting and cattle exclosures, and changes in vegetation structure were quantified after 2, 3, and 5 years of growth. As expected, the older site contained the most heterogeneous mix of plant species and the greatest structural diversity. We compared year‐round avian use of the revegetated sites with a mature cottonwood forest site of approximately 30 years of age. As the revegetated sites matured and salient habitat features changed, the population dynamics of individual avian species and patterns of guild structure varied. The older revegetated sites showed a greater similarity to the mature cottonwood site, suggesting that reclamation efforts established quality riparian habitats for birds in as little as 5 years. The revegetated sites appeared especially important for Neotropical‐migrant birds. We suggest that a mosaic of riparian woodlands containing mixtures of native tree and shrub species of different size classes is necessary to maintain avian species richness in the middle Rio Grande drainage, and probably throughout the southwestern United States.

Long-term cyclic dynamics of simulated riparian forest stands

The temporal dynamics of riparian forest stands in the American Midwest are examined for different conditions of climate, river flow, and soil type. Spectral analysis is performed on tree densities, and changes in the basal area of species are also analyzed. Different spectral densities are found. The dynamic behavior of forest stands can be attributed primarily to the life history traits of the dominant species; in different environmental conditions, different dominant species result in different cyclic responses of stand-level variables. In the simulation, warmer and/or drier conditions would result in a more diverse forest with less distinct cyclic behavior than in cooler and/or wetter conditions dominated by one or two species. Within the more diverse community of warmer conditions, differences in the competitive abilities of species at different stages of asynchronous life histories may explain the dynamic behavior of stand-level variables.

Soil N mineralization and nitrification in relation to nitrogen solution chemistry in a small forested watershed

Spatial variations in soil processes regulating mineral N losses to streams were studied in a small watershed near Toronto, Ontario. Annual net N mineralization in the 0–8 cm soil was measured in adjacent upland and riparian forest stands using in situ soil incubations from April 1985 to 1987. Mean annual rates of soil N mineralization and nitrification were higher in a maple soil (93.8 and 87.0 kg.ha−1) than in a pine soil (23.3 and 8.2 kg.ha−1 ). Very low mean rates of mineralization (3.3 kg.ha−1) and nitrification (3.4 kg.ha−1) were found in a riparian hemlock stand. Average NO3-N concentrations in soil solutions were 0.3–1.0 mg.L−1 in the maple stand and >0.06mg.L−1 in the pine stand. Concentrations of NO3−N in shallow ground water and stream water were 3–4× greater in a maple subwatershed than in a pine subwatershed. Rapid N uptake by vegetation was an important mechanism reducing solution losses of NO3−N in the maple stand. Low rates of nitrification were mainly responsible for negligible NO3−N solution losses in the pine stand.