Disproportionate Contribution of Riparian Inputs to Organic Carbon Pools in Freshwater Systems

A lack of appropriate proxies has traditionally hampered our ability to distinguish riverine organic carbon (OC) sources at the landscape scale. However, the dissection of C₄ grasslands by C₃-enriched riparian vegetation, and the distinct carbon stable isotope signature (δ¹³C) of these two photosynthetic pathways, provides a unique setting to assess the relative contribution of riparian and more distant sources to riverine C pools. Here, we compared δ¹³C signatures of bulk sub-basin vegetation (δ¹³C_VEG) with those of riverine OC pools for a wide range of sites within two contrasting river basins in Madagascar. Although C₃-derived carbon dominated in the eastern Rianala catchment, consistent with the dominant vegetation, we found that in the C₄-dominated Betsiboka basin, riverine OC is disproportionately sourced from the C₃-enriched riparian fringe, irrespective of climatic season, even though δ¹³C_VEG estimates suggest as much as 96% of vegetation cover in some Betsiboka sub-basins may be accounted for by C₄ biomass. For example, δ¹³C values for river bed OC were on average 6.9 ± 2.7‰ depleted in ¹³C compared to paired estimates of δ¹³C_VEG. The disconnection of the wider C₄-dominated basin is considered the primary driver of the under-representation of C₄-derived C within riverine OC pools in the Betsiboka basin, although combustion of grassland biomass by fire is likely a subsidiary constraint on the quantity of terrestrial organic matter available for export to these streams and rivers. Our findings carry implications for the use of sedimentary δ¹³C signatures as proxies for past forest-grassland distribution and climate, as the C₄ component may be considerably underestimated due to its disconnection from riverine OC pools.     

Mechanisms of Riparian Cottonwood Decline Along Regulated Rivers

Decline of riparian forests has been attributed to hydrologic modifications to river flows. However, little is known about the physiological and structural adjustments of riparian forests subject to modified flow regimes, and the potential for forest restoration using historic flow regimes is poorly understood. In this paired river study, we compared hydrology, water relations, and forest structure in cottonwood-dominated floodplains of the regulated Green River to those of the unregulated Yampa River. We measured floodplain groundwater levels, soil water availability, cottonwood xylem pressure (Ψ_xp), and leaf-level stomatal conductance (g_s) to assess current impacts of river regulation on the water status of adult cottonwoods. We also simulated a flood on the former floodplain of the regulated river to evaluate its impact on cottonwood water relations. Canopy and root structure were quantified with estimates of cottonwood leaf area and percent live canopy and root density and biomass, respectively. Regulation of the Green River has lowered the annual peak flow yet raised minimum flows in most years, resulting in a 60% smaller stage change, and lowered soil water availability by as much as 70% compared to predam conditions. Despite differences in water availability, daily and seasonal trends in Ψ_xp and g_s were similar for cottonwoods on the regulated and unregulated rivers. In addition, soil water added with the experimental flood had little effect on cottonwood water relations, contrary to our expectations of alleviated water stress. Green River cottonwoods had 10%–30% lower stand leaf area, 40% lower root density, and 25% lower root biomass compared with those for Yampa River cottonwoods. Our results suggest that water relations at the leaf and stem level are currently similar for Yampa and Green River trees due to structural adjustments of cottonwood forests along the Green River, triggered by river regulation.     

Avian Density and Nest Survival on the San Pedro River: Importance of Vegetation Type and Hydrologic Regime

Abstract: Lowland riparian vegetation in the southwestern United States is critically important for maintaining a high richness and density of breeding birds. Further investigation is needed within riparian corridors, however, to evaluate the relative importance of vegetation type and hydrologic regime for avian density and nest survival as targets for regional conservation or restoration efforts. We estimated the densities of 40 bird species and for species grouped on the basis of nest height and dependence on surface water in gallery cottonwood–willow (Populus spp.–Salix spp.) forests, saltcedar (Tamarix spp.) shrub lands, and terrace vegetation types along a gradient in the hydrologic regime of the San Pedro River, Arizona, USA. We also assessed nest survival for shrub-nesting insectivores and herbivores. Canopy-nesting birds as a group and 14 individual bird species reached their greatest densities in cottonwood forests regardless of the hydrologic regime. Water-dependent birds as a group reached their highest density in both intermittent- and perennial-flow cottonwood stands, but certain species occurred almost exclusively in perennial-flow sites. Two shrub-nesting species and the brown-headed cowbird (Molothrus ater) were most abundant in saltcedar shrub lands, and the brown-headed cowbird was most abundant in saltcedar stands with intermittent flows. Mesquite (Prosopis spp.) and big sacaton (Sporobolus wrightii) grassland each maintained the highest densities of certain species within ≥1 hydrologic regime. Shrub-nesting insectivores had the greatest nest survival in cottonwood, including Arizona Bell's vireo (Vireo bellii arizonae), and also had lower proportions of nests parasitized and preyed upon, although 95% confidence intervals among vegetation types overlapped. Nest survival for both shrub-nesting insectivores and herbivores was lowest in intermittent-flow saltcedar, although, again, confidence intervals overlapped. Nest survival was lower in parasitized than nonparasitized nests in mesquite and across vegetation types for Arizona Bell's vireo and in cottonwood for Abert's towhee (Pipilo aberti). Riparian management that maintains heterogeneous riparian vegetation types, including floodplain vegetation comprising cottonwood–willow gallery riparian forests with some stretches of perennial flow, are important for maintaining the high diversity and abundance of breeding birds on the San Pedro River and probably across the region. Cottonwood stands also appear to maintain highest nest survival for some shrub-nesting birds.     

Wide-Area Estimates of Stand Structure and Water Use of Tamarix spp. on the Lower Colorado River: Implications for Restoration and Water Management Projects

Tamarix spp. removal has been proposed to salvage water and allow native vegetation to recolonize western U.S. riparian corridors. We conducted wide‐area studies on the Lower Colorado River to answer some of the scientific questions about Tamarix water use and the consequences of removal, combining ground surveys with remote sensing methods. Tamarix stands had moderate rates of evapotranspiration (ET), based on remote sensing estimates, averaging 1.1 m/yr, similar to rates determined for other locations on the river and other rivers. Leaf area index values were also moderate, and stands were relatively open, with areas of bare soil interspersed within stands. At three Tamarix sites in the Cibola National Wildlife Refuge, groundwater salinity at the site nearest to the river (200 m) was relatively low (circa 2,250 mg/L) and was within 3 m of the surface. However, 750 and 1,500 m from the river, the groundwater salinity was 5,000–10,000 mg/L due to removal of water by the Tamarix stands. Despite the high groundwater salinity, the sites away from the river did not have saline surface soils. Only 1% of the mean annual river flow is lost to Tamarix ET on the Lower Colorado River in the United States, and the opportunities for water salvage through Tamarix removal are constrained by its modest ET rates. A possible alternative to Tamarix removal is to intersperse native plants among the stands to improve the habitat value of the riparian zone.     

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.     

Transpirational Water Loss in Invaded and Restored Semiarid Riparian Forests

The invasive tree, Tamarix sp., was introduced to the United States in the 1800s to stabilize stream banks. The riparian ecosystem adjacent to the middle Rio Grande River in central New Mexico consists of mature cottonwood (Populus fremontii) gallery forests with a dense Tamarix understory. We hypothesized that Populus would compensate for reduced competition by increasing its water consumption in restored riparian plots following selective Tamarix removal, resulting in similar transpiration (T) among stands. The northern study site included a Populus stand invaded by Tamarix (INV_N) and a restored Populus‐only stand (RES_N), as did a southern site (INV_S and RES_S) approximately 80 miles south. At each site, 20 × 20–m plots were established where up to 16 stems were monitored throughout the 2004 growing season using thermal dissipation sapflow sensors. Populus sapflux rates were greater in restored stands, suggesting those trees compensated for understory removal by using more water. Sapflow was scaled to estimate stand‐level T based on a quantitative assessment of sapwood basal area (A_sw) by species. Although exotic species represented 85 and 91% of the total stems in the invaded stands, it amounted to only 3% (INV_S) and 4% (INV_N) of the total A_sw, contributing proportionately less to T compared to Populus. Our results indicate that removing Tamarix from the Populus understory in this riparian forest had a minimal impact on stand water balance. Riparian restoration of the type discussed herein should focus primarily on enhancing riparian health rather than generating water.     

High‐resolution riparian vegetation mapping to prioritize conservation and restoration in an impaired desert river

In highly impaired watersheds, it is critical to identify both areas with desirable habitat as conservation zones and impaired areas with the highest likelihood of improvement as restoration zones. We present how detailed riparian vegetation mapping can be used to prioritize conservation and restoration sites within a riparian and instream habitat restoration program targeting 3 native fish species on the San Rafael River, a desert river in southeastern Utah, United States. We classified vegetation using a combination of object‐based image analysis (OBIA) on high‐resolution (0.5 m), multispectral, satellite imagery with oblique aerial photography and field‐based data collection. The OBIA approach is objective, repeatable, and applicable to large areas. The overall accuracy of the classification was 80% (Cohen's κ = 0.77). We used this high‐resolution vegetation classification alongside existing data on habitat condition and aquatic species' distributions to identify reaches' conservation value and restoration potential to guide management actions. Specifically, cottonwood (Populus fremontii) and tamarisk (Tamarix ramosissima) density layers helped to establish broad restoration and conservation reach classes. The high‐resolution vegetation mapping precisely identified individual cottonwood trees and tamarisk thickets, which were used to determine specific locations for restoration activities such as beaver dam analogue structures in cottonwood restoration areas, or strategic tamarisk removal in high‐density tamarisk sites. The site prioritization method presented here is effective for planning large‐scale river restoration and is transferable to other desert river systems elsewhere in the world.     

Factors affecting the regeneration and distribution of riparian woodlands along a northern prairie river: the Red Deer River,Alberta, Canada

Abstract. Flooding patterns and variations in the composition and successional trends of riparian vegetation in the upper and lower Red Deer River in southern Alberta, Canada, were studied in order to establish which flood regimes were most important in the regeneration and maintenance of riparian vegetation communities, with a particular focus on riparian poplars. The dominant riparian tree in the upper river is Populus balsamifera with some Picea glauca and in the lower river Populus deltoides (the plains cottonwood). Dendrochronological studies of the poplars along the river show that major periods of regeneration correspond with major flood events during the record period. Extensive cottonwood regeneration occurred in the period 1900–20, corresponding with a series of floods, some as high as the 1 in 100-year event. In addition, just prior to and during this period there was a significant reduction in use of the floodplain by bison, clearance of forests and a higher incidence of fires in upper reaches of the river and a series of high rainfall years. A series of floods greater than the 1 in 10-year flood occurred in the 1950s and stimulated the most extensive regeneration of poplars experienced since the 1920s. Parts of the lower Red Deer floodplain are now at elevations well above the 1 in 100-year flood event. It is suggested that fringe replenishment of riparian poplars is currently the dominant form of regeneration and that the large stands of mature poplars found on the floodplain, initiated during the end of the last century and first decades of this century, are unlikely to be replaced unless large floods (>1 in 50-year events) occur again. Construction of the Dickson Dam above the city of Red Deer in 1983 has led to attenuation of floods and a reduced likelihood that extensive flooding and poplar regeneration will occur again. A number of recommendations are made regarding flow management to both retain the fringe regeneration of poplars currently occurring and to stimulate more widespread regeneration of poplars on the floodplain.     

Root architecture of riparian trees: river cut-banks provide natural hydraulic excavation, revealing that cottonwoods are facultative phreatophytes

Plant root architecture reveals the sources of water and nutrients but tree root systems are large and difficult to analyze. With riparian (floodplain) trees, river cut-banks provide natural hydraulic excavation of root systems and this presents a unique study opportunity. Subsequently, we developed the ‘Cut-bank Root Method’, a simple, quantitative approach for analyzing the distribution of coarse roots, based on analyses of photographs of river cut-banks. These reveal the vertical extent of roots and median root depths (R_d). We applied this method along six rivers draining the Canadian Rocky Mountains and observed tenfold difference in R_d. The floodplain forests were dominated by cottonwoods and from mountain to prairie zones we observed progressively deeper roots of Populus trichocarpa (black cottonwood, R_d ~ 0.3 m), P. balsamifera (balsam poplar), P. angustifolia (narrowleaf cottonwood), and P. deltoides (prairie cottonwood, R_d ~ 0.9 m), which had R_d similar to P. fremontii (Fremont cottonwood) in Nevada, USA. Roots were shallower for co-occurring facultative riparian trees, with R_d ~ 0.1 m for P. tremuloides (trembling aspen) and Picea glauca (white spruce). Across the Canadian sites, R_d for cottonwoods were strongly associated with a growth season moisture index (May through September precipitation—potential evapotranspiration; R² = 0.97, P < 0.001). Thus, in wetter climates, riparian cottonwoods were shallow-rooted and would be more dependent upon rain than stream flow. Conversely, in the drier semi-arid regions the cottonwoods were phreatophytic, with deeper root systems in the capillary fringe above the alluvial ground-water table. These phreatophytic cottonwoods would be highly dependent upon stream flow and vulnerable to declining river flows due to river regulation or climate change.     

Changes in satellite‐derived vegetation growth trend in temperate and boreal Eurasia from 1982 to 2006

Monitoring changes in vegetation growth has been the subject of considerable research during the past several decades, because of the important role of vegetation in regulating the terrestrial carbon cycle and the climate system. In this study, we combined datasets of satellite‐derived Normalized Difference Vegetation Index (NDVI) and climatic factors to analyze spatio‐temporal patterns of changes in vegetation growth and their linkage with changes in temperature and precipitation in temperate and boreal regions of Eurasia (> 23.5°N) from 1982 to 2006. At the continental scale, although a statistically significant positive trend of average growing season NDVI is observed (0.5 × 10^?3 year^?1, P = 0.03) during the entire study period, there are two distinct periods with opposite trends in growing season NDVI. Growing season NDVI has first significantly increased from 1982 to 1997 (1.8 × 10^?3 year^?1, P < 0.001), and then decreased from 1997 to 2006 (?1.3 × 10^?3 year^?1, P = 0.055). This reversal in the growing season NDVI trends over Eurasia are largely contributed by spring and summer NDVI changes. Both spring and summer NDVI significantly increased from 1982 to 1997 (2.1 × 10^?3 year^?1, P = 0.01; 1.6 × 10^?3 year^?1P < 0.001, respectively), but then decreased from 1997 to 2006, particularly summer NDVI which may be related to the remarkable decrease in summer precipitation (?2.7 mm yr^?1, P = 0.009). Further spatial analyses supports the idea that the vegetation greening trend in spring and summer that occurred during the earlier study period 1982–1997 was either stalled or reversed during the following study period 1997–2006. But the turning point of vegetation NDVI is found to vary across different regions.     

Resizing a River: A Downscaled,Seasonal Flow Regime Promotes Riparian Restoration

While riverine organisms are adapted to the natural flow regime, it is impractical to fully restore natural flows along most regulated rivers. We propose an alternative with the delivery of downscaled flow regimes that provide the seasonal patterns that are essential for aquatic and riparian ecosystems. The Bridge River in British Columbia provided a novel case study as a downscaled flow regime commenced in 2000 along a reach that had generally experienced no flow for the prior half‐century. The experimental flow delivered a mean discharge of about 3 m³/s, versus the pre‐dam mean of 100 m³/s, with a seasonal pattern that mimicked the natural snowmelt‐dominated pattern. To assess the environmental response, we investigated black cottonwoods, Populus trichocarpa, the dominant riparian trees, in the pre‐flow versus post‐flow intervals, using tree ring interpretation for growth analyses and age determination. Sparse mature trees established prior to the 1948 damming did not show significant growth changes in the pre‐ versus post‐flow intervals. In contrast, younger trees that established closer to the river in the decade prior to 2000 displayed significant growth increases by 2002, and juveniles established after 2000 demonstrated faster initial growth than juveniles established before 2000. Further, bands of cottonwood saplings resulted from seedling recruitment along the new river fringe, particularly in 2002, 2003, and 2004, years with gradual flow recession. These responses demonstrate that a downscaled, seasonal flow regime provided environmental benefit, thereby restoring some river function and resulting in a resized river flanked by narrow and reproducing cottonwood bands.     

Biomass and production of a naturally regenerated oak forest in southern Korea

Biomass and production of two stands with Quercus variabilis Bl. as the dominant species (stands 1 and 3) and one with Q. mongolica Fisch. as the dominant species (stand 2) were investigated in southern Korea. Stands 1 and 3 naturally occurred on sites with southerly aspects while stand 2 naturally occurred on northerly aspects; stand ages were similar for the three stands (36–38 years old). Total above- and belowground biomass including understory vegetation (Mg ha^–1) was 108.4 for stand 1, 115.6 for stand 2, and 132.0 for stand 3, respectively. Understory vegetation constituted 17.4% of the total biomass in stand 1 but only 3.7–4.5% in stand 2 and stand 3. Roots constituted 20.1–24.6% of the biomass of the overstory vegetation. Although stand 3 showed the highest total biomass, net production was highest in stand 2 at 12.6 (Mg ha^–1 year^–1); net production levels for stands 1 and 3 were 11.7 and 11.1 (Mg ha^–1 year^–1), respectively. It appeared that the differences in site conditions related to aspect influenced the distribution of naturally regenerated oak species within a relatively small area and resulted in differences in biomass and production among the stands.     

Seedling competition between native cottonwood and exotic saltcedar: implications for restoration

Altered hydrology of southwestern United States rivers has led to a decline in native cottonwood (Populus deltoides). Areas historically dominated by cottonwood have been replaced by invasive saltcedar (Tamarix chinensis). Restoration of historic hydrology through periodic flooding of riparian areas has been a means of restoring native species. However, due to similarity in germination requirements of cottonwoods and saltcedars, flooding may create an unwanted increase in the number of saltcedar seedlings. Therefore, we evaluated competitive aspects of these co-occurring species in an extant riparian habitat in the arid southwestern US. We measured effects of competition between cottonwood and saltcedar seedlings and among cottonwood seedlings during the first growing season following seedling establishment in 360, 0.5 × 0.5-m plots at the Bosque del Apache National Wildlife Refuge, New Mexico. We used five interspecific density treatments and five intraspecific density treatments. Cottonwood seedling biomass and height were twice that of saltcedar seedlings across all density treatments. As density of cottonwood increased, intraspecific competition increased in severity and biomass of cottonwood seedlings decreased. At 4 plants/0.25 m², cottonwood seedlings had the greatest biomass; whereas, survival was highest at 10 plants/0.25 m². Our results support greenhouse studies and suggest that if favorable germination conditions are established for cottonwood in floodplains, saltcedar seedlings that cogerminate could be outcompeted by native cottonwood seedlings.     

Recovering Riparian Plant Communities with Wolves in Northern Yellowstone,U.S.A.

Gray wolves (Canis lupus) were extirpated from Yellowstone National Park in the 1920s. The ensuing seven decades marked a period when wild ungulates, principally Elk (Cervus elaphus), extensively used woody browse species in the upper Gallatin and northern winter ranges, thus limiting the capability of establishing plants to grow more than 100 cm in height. Following the reintroduction of wolves in the mid‐1990s, we evaluated patterns of woody browse species recovery within riparian areas of these winter ranges. Measurements indicated that cottonwood (Populus spp.) recruitment (growth of seedlings/sprouts into tall saplings and trees) was occurring for the first time in several decades. A spatially patchy increase in the heights of young willow (Salix sp.) and cottonwood in the upper Gallatin and northern winter ranges, respectively, was also found within riparian transects comprising nearly 20 km in total length. Within some transects, heights of woody species have begun to exceed 200 cm (the approximate upper browse level of Elk). Results are consistent with the reestablishment of a tri‐level trophic cascade involving wolves, ungulates, and riparian vegetation. We additionally present conceptual models of vegetation recovery, illustrating differences in plant height responses to behaviorally and density‐mediated trophic cascades. Northern Yellowstone’s “experiment in time,” whereby wolves were removed and then reintroduced, provides new insights regarding how top predators can influence the structure and biodiversity of terrestrial ecosystems. Restoration ecologists and policymakers should consider the potential benefits of large predators as an option for helping restore degraded ecosystems.     

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 δ¹³C 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 m² 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.     

Direct seeding for riparian tree re-vegetation: Small-scale field study of seeding methods and irrigation techniques

Restoration of wetland and associated ecosystems is a major goal of land management agencies throughout the world. On the lower Colorado River, creation of riparian forests is planned to mitigate riparian habitat degradation by historic land-use conversions and river management. Current restoration practices use propagated plant stock. If direct seeding can be implemented, genetic and structural diversity could be enhanced at restoration sites even while reducing costs compared to vegetative propagation methods. A small-scale field study was implemented in Cibola, Arizona, to determine the effectiveness of direct seeding of Fremont cottonwood (Populus fremontii), Goodding's willow (Salix gooddingii), and coyote willow (S. exigua). For the first growing season, establishment of Fremont cottonwood averaged 7% of pure live seed rates for all treatments combined, whereas establishment of willows was less than 1%. Volunteer species were abundant, with grasses dominating cover and biomass after one growing season. Saltcedar (Tamarix ramosissima) established in abundance, but showed lower growth rates than Fremont cottonwood during the first growing season. Monitoring for three growing seasons indicated higher growth rates and survival of Fremont cottonwood compared to all volunteer species. Study results indicated that direct seeding of Fremont cottonwood is likely to be an efficient method for tree re-vegetation. Additional studies are required for willow species to determine if establishment from seed can be increased through enhanced weed control and elimination of Fremont cottonwood from the seed mix.     

Northern tamarisk beetle (Diorhabda carinulata) and tamarisk (Tamarix spp.) interactions in the Colorado River basin

Northern tamarisk beetles (Diorhabda carinulata) were released in the Upper Colorado River Basin in the United States in 2004–2007 to defoliate introduced tamarisk shrubs (Tamarix spp.) in the region's riparian zones. The primary purpose was to control the invasive shrub and reduce evapotranspiration (ET) by tamarisk in an attempt to increase stream flows. We evaluated beetle–tamarisk interactions with MODIS and Landsat imagery on 13 river systems, with vegetation indices used as indicators of the extent of defoliation and ET. Beetles are widespread and exhibit a pattern of colonize–defoliate–emigrate, so that riparian zones contain a mosaic of completely defoliated, partially defoliated, and refoliated tamarisk stands. Based on satellite data and ET algorithms, mean ET before beetle release (2000–2006) was 416 mm/year compared to postrelease (2007–2015) ET of 355 mm/year (p < 0.05) for a net reduction of 61 mm/year. This is lower than initial literature projections that ET would be reduced by 300–460 mm/year. Reasons for the lower‐than‐expected ET reductions are because baseline ET rates are lower than initially projected, and percentage ET reduction is low because tamarisk stands tend to regrow new leaves after defoliation and other plants help maintain canopy cover. Overall reductions in tamarisk green foliage during the study are 21%. However, ET in the Upper Basin has shown a steady decline since 2007 and equilibrium has not yet been reached. Defoliation is now proceeding from the Upper Basin into the Lower Basin at a rate of 40 km/year, much faster than initially projected.     

Current population estimate and distribution of the African buffalo in Chebera Churchura National Park,Ethiopia

An investigation into the population status and distribution of the African buffalo (Syncerus caffer Sparrman, 1779) in Chebera Churchura National Park, Ethiopia, was carried out during the wet and dry seasons of 2012–2015. This study tested the hypothesis that buffalo would demonstrate seasonal habitat preferences and changes in population density. Sample counts were carried out in an area of 1215 km². The estimated buffalo population was 5193 individuals, with the population density of 4.3/km². The population showed an increase from 2617 to 5194 individuals during 2006–2015. Males comprised 42.6%, while females 46.7% of the population. Age structure was dominated by adults, which constituted 52.5% of the total population. Subadults comprised 24.3% and young 12.4% of the population. Larger herds of up to 30 individuals were observed during the wet season, and smaller herds of a minimum of four individuals were seen during the dry season. The mean herd sizes during the wet and dry seasons were 29.59 and 16.95, respectively. They were observed more in the riverine vegetation types during the dry season. Of the total, 57.6% utilized riverine habitat during the dry season, whereas 39.8% used this habitat during the wet season. Relative abundance of food sources, green vegetation cover and availability of water were the major factors governing their distribution in the present study area.     

Trophic basis of production in tropical headwater streams,Puerto Rico: an assessment of the importance of allochthonous resources in fueling food webs

The relative importance of allochthonous and autochthonous resources in fueling tropical headwater streams remains an open topic. We combined estimates of secondary production and assessment of its trophic basis to determine which resources were responsible for animal production. We studied benthic insect assemblages in two streams in the Luquillo Experimental Forest, Puerto Rico. Habitat-weighted production estimates were similar in both streams (528.5 and 591.5 mg m⁻² year⁻¹), but production was over twice as high in pool versus riffle habitats. The mayfly Neohagenulus (Leptophlebiidae) was a major contributor to total production (259.1 and 352.2 mg m⁻² year⁻¹). All taxa relied heavily on amorphous detritus and plant tissue. Aquatic insect production was similar to that reported for shrimp assemblages in the same study area, but low relative to temperate region estimates. The trophic basis of production appears to be allochthonous organic matter, which agrees with the small size and closed canopy cover over the study streams. This is the first study quantifying the production and trophic basis of the non-shrimp macroinvertebrate assemblage in tropical island streams. We also provide support for the importance of riparian vegetation as the main energy sources for stream tropical stream food webs.