Livestock Trampling Reduces the Conservation Value of Beetle Communities on High Quality Exposed Riverine Sediments

Exposed riverine sediments (ERS) are habitat for a large number of rare and threatened specialist species of invertebrates and are of considerable conservation importance. Livestock trampling is believed to be one of the most widespread causes of damage to ERS habitats in the UK, and as such, its effects were the focus of this investigation. Beetle density was measured at two points within 25 distinct patches of habitat along ∼ ∼47 km of the Afon Tywi special site of scientific interest in South Wales, which is known to support an extremely good quality ERS beetle fauna in a UK context. Partial canonical correspondence analyses were used to explore the relationship between beetle assemblage and a range of environmental variables. The percentage of fine (<8 mm) sediments, median sediment size, distance downstream, cattle stocking levels, and counts of sheep faeces were found to best relate to beetle abundance and assemblage structure. Species richness was positively associated with stocking levels, probably because of the addition of species associated with resultant elevated levels of silt and organic matter. The ERS quality score, which is a measure of conservation value based on the rarity of specialist ERS beetles, was negatively associated with measures of trampling damage. It was therefore concluded that livestock trampling reduces the conservation value of beetle communities on high quality ERS and management should restrict trampling in sites of high conservation importance.     

Vegetation mapping with the aid of low-altitude aerial photography

Abstract. A technique for fine-scale vegetation mapping with the aid of low-altitude aerial photography was developed. The procedure is as follows: 1. The site is divided into a lattice pattern - in case the site is too large to fit into a single photograph with satisfactory resolution. The coordinates of every lattice point are surveyed to be used as control points for geometric correction. A photograph of each block of the lattice is taken using a remote-controlled camera system lifted by a captive helium balloon. 2. The vegetation is classified on the basis of a phytosociological survey. 3. The shapes and locations of vegetation patches appearing in the photographs are entered into a computer, using a digitizer. A geometric correction is carried out through coordinate transformation referring to the coordinates of the control points and subsequently a draft vegetation map is produced. Finally, discrepancies are corrected and the map is coloured to produce the final version of the vegetation map. This technique was applied to vegetation mapping at a bar, 500 m wide and 2 km long, in the river Yoshino in Shikoku, Japan. A fine-scale vegetation map was obtained and used to analyse the influence of plants on geomorphic processes and community-specific hydrogeomorphic conditions on the bar.     

Spatial variation in density of stream benthic fishes in northern Hokkaido, Japan: does riparian vegetation affect fish density via food availability?

The densities of two benthic fishes, the Siberian stone loach (Noemacheilus barbatulus) and the wrinklehead sculpin (Cottus nozawae), and the biomass of their food resources (i.e., periphyton and benthic invertebrates) were compared between forest and grassland streams in northern Hokkaido, Japan, to examine whether riparian deforestation had positive effects on the benthic fishes via enhancement of food availability. The comparisons indicated that riparian vegetation had little influence on periphyton, invertebrates, or fishes. Regression analysis indicated that spatial variations in loach and sculpin densities were explained more by substrate heterogeneity, competitor abundance, or both, rather than by food abundance. However, when the two species were combined as benthic insectivores, a strong correlation was found between total benthic fish density and invertebrate biomass. Our results suggest that, although total benthic fish abundance was food limited, riparian vegetation had no positive effects via food availability on the benthic fishes in our streams.     

Purification processes, ecological functions, planning and design of riparian buffer zones in agricultural watersheds

Two international meetings on ecological engineering, with a focus on riparian buffer zones, served as the source for selected papers in this special issue: (1) an International Workshop on Efficiency of Purification Processes in Riparian Buffer Zones: Their Design and Planning in Agricultural Watersheds, jointly organised by Hokkaido University, Japan, the National Agricultural Research Center for Hokkaido Region, Japan, Civil Engineering Research Institute of Hokkaido, Japan, and the Institute of Geography, University of Tartu, Estonia, and held from 5 to 9 November 2001 in Kushiro City, Hokkaido, Japan; and (2) an International Conference on Ecological Engineering for Landscape Services and Products, jointly organised by the International Ecological Engineering Society (IEES) and Lincoln University, Christchurch, New Zealand, and held from 25 to 29 November 2001 in Christchurch, New Zealand. At these two meetings, altogether 94 oral presentations (17 from invited speakers) and 15 posters by representatives from 21 countries were presented. The editorial paper highlights trends in investigation of the purification processes in riparian buffer zones as well as planning, design and management aspects of riparian buffers regarding the wide spectrum of their ecological functions; it characterises the two international meetings which served as sources for the selected papers and briefly explains the main aspects of these papers.     

Abundance and Production of Riparian Trees in the Lowland Floodplain of the Queets River, Washington

Riparian zones associated with alluvial rivers are spatially dynamic, forming distinct vegetative mosaics that exhibit sharp contrasts in structure and processes related to the underlying biophysical template. The productivity of riparian plants, especially trees, influences streamside community characteristics as well as the forms and fluxes of organic matter to adjacent streams – thereby strongly impacting patterns of channel morphology, water flow, sedimentation, and habitat in rivers. As part of a comprehensive investigation of riparian dynamics in coastal rain forest rivers of the Pacific Northwest (USA), we examined riparian tree abundance (density, basal area, and biomass) and rates of production (basal area growth [BAI] and bole wood biomass increase [P]) of seven common species – red alder (Alnus rubra), Sitka spruce (Picea sitchensis), bigleaf maple (Acer macrophyllum), western hemlock (Tsuga heterophylla), black cottonwood (Populus trichocarpa), vine maple (Acer circinatum) and willow (Salix spp.) – in the lowland floodplain of the Queets River (Olympic National Park), Washington. Measurements were made annually for three years (1999 – 2001) in 16 permanent plots on three biophysical templates that formed a toposequence – active floodplain, young terrace and mature terrace. Stem density was highest in the active floodplain (∼27,000 stems/ ha), decreasing in the young terrace (∼2,700 stems /ha) and the mature terrace (∼500 stems/ha). Basal area and total stem biomass were lowest in the active floodplain (∼16 m2/ha and ∼18 Mg dry weight/ha, respectively) and higher on the young terrace (∼32 m2/ha and ∼134 Mg dry weight/ha) and on the mature terrace (∼69 m2/ha and ∼540 Mg dry weight /ha). Total plot-scale BAI was not significantly different among the physical templates with mean values ranging from approximately 1.4 (low terrace) to approximately 2.8 m2/ha/y (active floodplain). In contrast, P was significantly higher on the mature terrace (10.3 Mg/ha) than the active floodplain (3.2 Mg/ha) but there was no significant difference between young terrace (6.5 Mg/ha) and mature terrace. For the entire Queets River floodplain (57 km² over 77 km of river length), the mature terrace contributed 81% of the total annual production (28,764 Mg) whereas the active floodplain and young terrace accounted only for 5 and 14%, respectively. Overall, we show that riparian trees grow quickly in this coastal Pacific Northwest system and that the older riparian forests on mature terraces are the main contributors to stem production at the plot and floodplain scales for at least 350 years after stand initiation. This suggests that, in combination with the rapid lateral migrations of many alluvial rivers, the older riparian forests on those terraces are important and sustained sources of organic matter (especially large woody debris, LWD) that, over decades to centuries, shape the character of coastal rivers in the Pacific Northwest.     

Denitrification and nitrous oxide emissions from riparian forests soils exposed to prolonged nitrogen runoff

Compared to upland forests, riparian forest soils have greater potential to remove nitrate (NO₃) from agricultural runoff through denitrification. It is unclear, however, whether prolonged exposure of riparian soils to nitrogen (N) loading will affect the rate of denitrification and its end products. This research assesses the rate of denitrification and nitrous oxide (N₂O) emissions from riparian forest soils exposed to prolonged nutrient runoff from plant nurseries and compares these to similar forest soils not exposed to nutrient runoff. Nursery runoff also contains high levels of phosphate (PO₄). Since there are conflicting reports on the impact of PO₄ on the activity of denitrifying microbes, the impact of PO₄ on such activity was also investigated. Bulk and intact soil cores were collected from N-exposed and non-exposed forests to determine denitrification and N₂O emission rates, whereas denitrification potential was determined using soil slurries. Compared to the non-amended treatment, denitrification rate increased 2.7- and 3.4-fold when soil cores collected from both N-exposed and non-exposed sites were amended with 30 and 60 μg NO₃-N g⁻¹ soil, respectively. Net N₂O emissions were 1.5 and 1.7 times higher from the N-exposed sites compared to the non-exposed sites at 30 and 60 μg NO₃-N g⁻¹ soil amendment rates, respectively. Similarly, denitrification potential increased 17 times in response to addition of 15 μg NO₃-N g⁻¹ in soil slurries. The addition of PO₄ (5 μg PO₄-P g⁻¹) to soil slurries and intact cores did not affect denitrification rates. These observations suggest that prolonged N loading did not affect the denitrification potential of the riparian forest soils; however, it did result in higher N₂O emissions compared to emission rates from non-exposed forest soils.     

Carbon, nitrogen, and hydrogen isotope ratios in creekside trees in western Kansas

Three species of creekside trees were monitored weekly during the 2007 and 2008 growing seasons. The 2007 growing season was wet early, but became drier as the season progressed. In contrast, the 2008 growing season was dry early, but became wetter as the season progressed. Creekside trees were measured to determine effects of changing water regimes on leaf-level processes. Lonicera tatarica plants were compared to Morus alba and Celtis occidentalis trees. Leaves were monitored for changes in stomatal conductance, transpiration, δ¹³C, δ¹⁵N, δD, leaf temperature, and heat losses via latent, sensible, and radiative pathways. δD of creek water was more similar to ground water than to rain water, but the creek was partially influenced by summer rains. δD of bulk leaf material was significantly higher in individuals of C. occidentalis compared to the other species, consistent with source water coming from shallower soil layers. Despite decreasing water levels, none of these tree species showed signs of water stress. There were no significant differences between species in stomatal conductance or transpiration. Leaf δ¹³C was significantly lower in individuals of L. tatarica compared to the other species. Differences in δ¹³C were attributed to a lower carboxylation capacity, consistent with lower leaf nitrogen content in L. tatarica plants. Leaf δ¹⁵N was significantly lower in individuals of L. tatarica compared to the other species, consistent with uptake of a different N source. Two of the three sites appeared to be affected by inorganic N from fertilizer run-off. Evidence is presented that these species acquired water and nitrogen from different sources, resulting from differences in root uptake patterns.     

Determinants of regional and local patterns in the floras of braided riverbeds in New Zealand

Aim To determine the composition and biogeographical origins of the native and naturalized flora of braided shingle riverbeds in New Zealand and whether the proportion of naturalized species is greater than in similar habitats elsewhere in the world. To test whether regional species pools, landscape matrix configuration, and local riverbed environment are all equally important in determining community structure in these systems. Location The braided reaches of four catchments on each of the eastern and western sides of North Island and South Island, New Zealand. Methods Plotless records of all native and naturalized seed plant and fern species on disturbed mobile surfaces were made over the length of four rivers. Altitude, climate variables, riverbed attributes, and surrounding land‐cover from maps were recorded for each site. For all species, the taxonomy, life form, origin and history, and presence within the province through which the rivers flowed, was obtained from published floras. Direct and indirect ordination and variance partitioning were employed to examine how native and naturalized species composition varies among and within rivers, and the degree to which this variation reflects climate, characteristic of riverbeds, and the surrounding land‐cover. Regression was used to determine how much introduction date and native geographical range influence the frequency of naturalized species. Results The total riverbed flora of 289 species comprises 40% native species and 60% naturalized species, both dominated by Asteraceae and Poaceae. The relative contributions of other plant families differ, and the two groups comprise different life‐form spectra. Native species occur across fewer rivers (mean 1.6 rivers) than naturalized species (mean 2.1 rivers). Species common in at least one river system tend to be widespread, occurring in at least three rivers. The rivers differ in their floras, with distinctions between North Island and South Island, and eastern and western rivers. The South Island rivers have more native species and a higher proportion of their regional native species pools than North Island rivers, whereas they have a lower proportion of their naturalized species pools. Introduction date and native geographical range are correlated with frequency of individual naturalized species. Geographical position and climate, riverbed variables of substrate size and seepage presence, and the type of adjacent land‐cover, differ between rivers and are significantly related to species composition. Land‐cover variables alone account for 46% of the explained variation in species composition, environmental variables alone 32% and components of the environment and land‐cover that co‐vary, 22%. Main conclusions New Zealand shingle riverbeds are among the riparian communities in the world most invaded by naturalized species but comparisons are difficult because studies of similar riverbeds are rare. New Zealand riverbeds are dominated by short‐lived terrestrial species from Eurasia. Native species are most frequent in South Island rivers draining extensive high mountains, and their abundances are determined to a greater extent by riverbed processes than are those of the naturalized species, which are more abundant when the surrounding landscape is modified. The distribution of the naturalized flora is not yet at equilibrium with the environment. Each river has a distinctive flora determined by ambient environmental factors, aspects of the riverbed environment itself, adjacent land‐cover reflecting the presence of native vegetation, the intensity of human modification or use, and invasion history.