Willow Stands Research Articles

Entwicklung der Laufkäferfauna (Coleoptera: Carabidae) einer Kurzumtriebsplantage über einen Zeitraum von 9 Jahren

In order to evaluate the importance of short-rotation coppice (SRC) as habitat for ground beetles, a SRC with stands of different tree species (poplar, willow, rowan) in the municipality of Schapen (NW-Germany) was investigated during several years and different rotation-phases using pitfall traps. Regardless of the plantation-age, the cultivated tree species and the rotation-phase, the ground beetle fauna of the surveyed SRC was dominated by widespread and common generalists. Species of conservation concern (exclusively xerothermophilic species) were found only sporadically and had their main occurrence in the two years following the establishment of the plantation. During this phase, Harpalus griseus, a rare and threatened species in Lower Saxony, was detected in large numbers. After 8 and 9 years respectively, species numbers as well as the number of specimens on the entire SRC and within its different stands were considerably lower than in the early establishment phase. The partial harvest of the poplar and willow stands caused a significant change in ground beetle communities and a strong increase in the activity of openland species. However, openland generalists were the main beneficiaries, while pioneer species like Harpalus griseus occurred only sporadically. Woodland species were found only rarely even in the 9th year after establishment. We conclude that the conservational value of SRC as habitat for ground beetles is generally limited, decreases with increasing plantation-age and that a mosaic of different tree stands, rotation-phases and headlands is not sufficient to promote pioneer species of conservation concern. In order to provide permanently suitable conditions for these species, additional measures extending beyond the regular management of the plantations are required. These should aim at the creation of sun-exposed ruderal habitats with a patchy herb layer and high proportions of bare ground within accompanying structures of SRC like headlands or rides.

Environmental Effects among Differently Located and Fertile Sites on Forest Basal-Area Increment in Temperate Zone

Environmental properties differently influence the growth of forest tree species. The antagonistic effects of variable environmental properties classify the forest response according to various tree compositions among different sites. The division of the forest response was assessed in 52 stands arranged into 26 types of 13 site management populations (MPs) in 5 areas in the Czech Republic territory. The assessment was performed using time-series multiple regressions of basal-area increment from pure immature stands of Norway spruce (Picea abies), Scots pine (Pinus sylvestris), oaks (Quercus sp.), ash (Fraxinus excelsior) and willows (Salix sp.) dependent on the interpolated average temperatures, annual precipitation, atmospheric concentrations of SO2, NOx and O3 and soil properties over the period 1971–2008 at p < 0.05. Site MPs differentiated the forest response to a greater extent than tree species. The response of the forests was significantly distributed by means of the montane, upland and waterlogged sites. The multiple determination index (r2) ≥ 0.6 indicated an adaptable tree increment but an interval of r2 between 0.80–0.92 implied forest sensitivity to variability in environmental properties on non-waterlogged sites. The index r2 < 0.6 suggested a fluctuating forest increment that reflects environmental variability inconsistently. The fluctuating increment most affected the spruce and pine stands grown from upland to submontane locations. Montane spruce stands, as well as rock pines, appeared to be one of the most sensitive ones to environmental change. Floodplain forests seemed as adaptable to variable environmental properties.

Habitat use and behavioral patterns of Cassin's Kingbird (Tyrannus vociferans) in an urban park of Mexico City

Changes in vegetation structure and species composition affect habitat use and behavior in most bird species by altering the distribution and abundance of their resources. We explore how the mating and foraging behavior of Cassin's Kingbirds (Tyrannus vociferans) varies by habitat type within a 2,450 ha urban park in Mexico City. The study site includes primarily water bodies, riparian vegetation, willow and Montezuma cypress stands, maize fields, and grasslands. We recorded kingbird behavior twice a week along 21 transects throughout 2012 and 2015. Courtship and reproductive behaviors were displayed in autumn (Sep) and early winter (Dec). Intraspecific agonistic behaviors were associated with courtship and mating events, particularly in 2015. Cassin's Kingbird generally favored open vegetation. The main foraging strategy in open habitats was flycatching but foliage gleaning became frequent when mistletoe plants produced fruits in infested willow stands. The use of mistletoe fruits, presumably a secondary diet item, coincided with the breeding season. In addition to these observations, our study is the first report of Cassin's Kingbird winter mating at low latitudes.

Habitat use and behavioral patterns of Cassin's Kingbird (Tyrannus vociferans) in an urban park of Mexico City

Changes in vegetation structure and species composition affect habitat use and behavior in most bird species by altering the distribution and abundance of their resources. We explore how the mating and foraging behavior of Cassin's Kingbirds (Tyrannus vociferans) varies by habitat type within a 2,450 ha urban park in Mexico City. The study site includes primarily water bodies, riparian vegetation, willow and Montezuma cypress stands, maize fields, and grasslands. We recorded kingbird behavior twice a week along 21 transects throughout 2012 and 2015. Courtship and reproductive behaviors were displayed in autumn (Sep) and early winter (Dec). Intraspecific agonistic behaviors were associated with courtship and mating events, particularly in 2015. Cassin's Kingbird generally favored open vegetation. The main foraging strategy in open habitats was flycatching but foliage gleaning became frequent when mistletoe plants produced fruits in infested willow stands. The use of mistletoe fruits, presumably a secondary diet item, coincided with the breeding season. In addition to these observations, our study is the first report of Cassin's Kingbird winter mating at low latitudes.

Net Energy Balance and Fuel Quality of an Alley Cropping System Combining Grassland and Willow: Results of the 2nd Rotation

With the central aim to reduce greenhouse gas emissions, agroforestry systems have become popular because they can provide biomass for bioenergy conversion and thus help replace fossil energy. This article compares the net energy balances of three biomass conversion techniques for an agroforestry system consisting of willows and two types of grassland biomass as well as separate stands of grassland and willow. The period of investigation was the second willow rotation (4–6 years after establishment). The biomass conversion techniques included combustion of hay (CH), integrated generation of solid fuel and biogas from biomass (IFBB), and anaerobic whole crop digestion (WCD). Compared to the first rotation (years 1–3), the net energy yield of the willow stands significantly increased. Nevertheless, the separate stand of willow had higher net energy yield than the agroforestry system. The IFBB technique led to an improvement in solid fuel quality through demineralization. CH and IFBB provided higher net energy yields than WCD.

Does soil bioengineering benefits aquatic biodiversity? An empirical study of the relative influence of local and regional drivers on benthic macroinvertebrate assemblages

Riverine ecosystems form a dendritic network in which landscape and catchment-scale properties influence freshwater community structure. Placed in a restoration framework, this suggests that regional drivers can overrule the benefit of measures aiming at improving local habitat quality. Disentangling the relative influence of local and regional drivers on freshwater communities is thus crucial for ecosystem management and restoration. Along riverbanks, soil bioengineering is often used to both control erosion and improve ecological conditions. Soil bioengineering techniques aim at copying naturally functioning riverbank models and can thus be viewed as riparian ecosystem restoration. Nevertheless, these techniques are mostly designed at the local scale and are implemented in a broad range of rivers. This implies large variations in regional drivers, which may greatly influence the response of freshwater communities to restoration efforts. We studied 37 riverbanks, from civil engineering to soil bioengineering, plus natural willow stands, in the foothills of the Alps and Jura Mountains, and assessed the relative influence of local (terrestrial and aquatic habitat conditions) and regional (water quality, hydrological context and land cover composition) drivers on benthic macroinvertebrate assemblages. Using multivariate GLM and structural equation modelling, we investigated variations in the taxonomic and functional composition and in the diversity of native, exotic, shredder and scraper taxa to both set of drivers. Our results showed that soil bioengineering improved local habitat conditions, with an increase in the vegetation density and in the aquatic habitat quality. These changes directly influenced functional composition but indirectly diversity patterns. Instead, we found that native and shredder species richness increased between civil engineered and soil bioengineered structures, suggesting a positive effect of vegetated riverbanks on other local abiotic factors (i.e. shade, water temperature, organic matter supply). Our results also showed that macroinvertebrates were more influenced by regional than by local drivers. Thus, the hydrological context best explained the composition of taxa feeding habits and variation in taxa diversity, with larger abundance and richness of scrapers and shredders in small headwater streams. Land cover ranked second in explaining variation in functional composition. Also, the diversity of natives, scrapers and shredders increased as the proportion of predominantly urban landscapes decreased. Finally, the abundance of scraper and native species increased with water quality, while the richness of exotic species decreased. Overall, these results highlight the hierarchical structure of local and regional drivers on freshwater communities. Along river networks, catchment-scale properties and landscape attributes are major drivers of macroinvertebrate assemblages. Soil bioengineering improves habitat quality and as such appears to be a good compromise solution to control erosion and support freshwater communities, even though this nature-based solution cannot solve anthropogenic pressures at larger scales. To improve the efficiency of restoration efforts, integrated approaches accounting for both local and regional drivers remains a priority.

Short-Rotation Coppice Managed According to Ecological Guidelines—What Are the Benefits for Phytodiversity?

In recent years, the impact of short-rotation coppice (SRC) on biodiversity has been a regular subject of research and ecological guidelines have been developed to make biomass cultivation on SRC more compatible with biodiversity concerns. However, since these guidelines are only implemented voluntarily by farmers, there are barely any SRC that are managed according to ecological guidelines. Consequently, knowledge about their importance for farmland biodiversity and about the impact of different measures for increasing biodiversity remains scarce. Therefore, three experimental SRC, which are managed according to ecological guidelines and thus include stands of different tree species (varieties of poplar (Populus) and willow (Salix), rowan (Sorbus aucuparia), silver birch (Betula pendula)) and different growth-stages within the same site, were investigated with regard to their importance as habitat for vascular plants. Species numbers and species composition were compared with the following habitat types: afforestations (AFO), young (HE-Y) and old hedges (HE-O), field margins (FM) and arable land (AL). Furthermore, different stand types (i.e., stands with different tree species and growth-stages, headlands, clearings) within these SRC were surveyed and compared. Species numbers of SRC were similar to HE-Y, AFO and FM and significantly higher than in AL and HE-O. The composition of plant communities in SRC differed considerably from the other farmland habitats, especially from AL, HE-O and FM. Within the SRC, most stand types had similar species numbers. Only the non-harvested poplar stands were particularly species-poor. Harvesting led to increased species numbers. This increase was significant for the poplar stands but only moderate for the willow stands. With regard to their species composition, the different stand types differed considerably in many cases. We conclude that SRC, which are managed according to ecological guidelines, can be an additional measure to promote phytodiversity in agricultural landscapes as they contain relatively high species numbers (of mainly common and adaptable species) and support distinct plant communities that differ from other farmland habitats. Therefore, measures such as the cultivation of different tree species or sectional harvesting could be offered as agri-environmental schemes to further increase the ecological sustainability of biomass production on SRC.

A semi‐commercial case study of willow biomass production in the northeastern United States

AbstractShrub willow (Salix spp. and hybrids) is a biomass crop well adapted to the northeastern United States. We assessed the biomass productivity of six willow cultivars in a 14.5‐ha field in Pennsylvania through two rotation cycles of 3 yr each, comparing the realized and biophysical yield potential. We also evaluated the relationship of yield with plant density and the harvest efficiency. The realized yield of the best cultivars was about 8 Mg ha–1 yr–1, well below the calculated harvestable potential of 14 Mg ha–1 yr–1. Uniform stands of willow without planting gaps may maximize yield with 8 × 103 plants ha–1, but upright cultivars may benefit from higher densities. Harvest is relatively slow at 1 ha h–1 or 20 Mg h–1 in the longest rows with optimal ground conditions, which makes the harvest cost per hour high. Biotic stresses built up gradually during the 7 yr of the experiment affecting two cultivars severely. The cultivar S. miyabeana × S. viminalis ‘Preble’ was defoliated by a growing population of willow leaf beetle (Plagiodera versicolora), whereas the cultivar S. purpurea ‘Fish Creek’ was affected by two fungal diseases and suffered a major stand loss in the winter of 2019/2020. Both examples justify breeding for insects and diseases resistance. The moderate harvestable yield and high harvest cost imply that in the northeastern United States, the viability of willow for bioenergy with carbon capture and storage as a tool to reduce CO2 emissions may depend on the provision and monetization of additional ecosystem services.

Functional traits of individual varieties as determinants of growth and nitrogen use patterns in mixed stands of willow (Salix spp.)

Short rotation plantations of willows (Salix spp.) have high biomass production potential in many parts of the world, and may frequently support ecosystem services related to nutrient cycling. A plantation management enhancing favorable environmental impacts that are conducive to maintaining ecosystem services is a main challenge in establishing sustainable biomass production systems. There is evidence supporting the hypothesis that biomass production and nutrient cycling can be increased by supporting ecosystem niche differentiation (complementarity) through enhancing the number of plant species or varieties grown in the stand. However, the specific trait values of the individual components (e.g., varieties) in a mixed community could also be more important than the community diversity per se. We assessed, at community level, the plant trait profiles related to growth and nitrogen (N) use for four different Salix varieties that were taxonomically distinct at species or genotype level (‘Björn’, ‘Jorr’, ‘Loden’, ‘Tora’) and field-grown in unfertilized plots of pure and mixed communities during one cutting cycle in Central Sweden. The aims were to use elements of functional growth analysis for exploring the mechanistic relationships between various traits related to growth and N use at stand level in our pure and mixed willow communities; and to address two hypotheses related to (i) the effect of diversity level on above-ground traits linked to growth, N uptake efficiency, N productivity and N conservation; and (ii) the influence of individual variety identities on the growth and N use traits observed in a mixture. Diversity level had no significant effect on the traits assessed here, and we thus found no evidence in support of our hypothesis that traits linked to growth, N uptake and use are significantly affected by the diversity level per se. In most but not all cases, the admixing effects on trait values were explained by the effects of the individual variety characteristics assessed in monocultures in combination with their relative share in the respective mixtures. The absence or presence of individual varieties strongly affected community-averaged (stand level) trait values. Therefore, the design of desirable variety mixtures is suggested that combine, for example, the high nutrient conversion efficiency that certain varieties achieve in mixed stands with the specific nutrient acquisition characteristics of other varieties.

Edible wild plants growing in adjacent spontaneous vegetation of energy plantations in southwest Slovakia

This paper evaluates the potential and perspectives of wild plant species and macrofungi from short rotation coppice. The research was conducted during the years 2014 - 2018 in stands of short rotation coppice willow and miscanthus grass in southwest of Slovakia. Evaluated wild plant species and macrofungi were divided into four groups (green vegetables, fruits and seeds, flowers and nectar, subterranean parts). The results showed that ground flora of short rotation coppice consisted of 74 edible species from 34 botanical families. Asteraceae, Rosaceae, Poaceae, Polygonaceae and Cichoriaceae families were represented the most. From the evaluated categories the most species belonged to the category with consumable aerial parts like leaves and shoots (59 species). The similar representation of species was found in the category of wild fruits and seeds consumed in the raw or preserved state and in category of edible subterranean parts (27 species and 22 species respectively). Principal component analysis showed that the edible parts with the strongest effect on the functional group differentiation were the fruits, seeds and subterranean parts.

Efficiency control of landfill leachate irrigation on energy crops

Leachate constitutes the major long-term em1ss1on from landfills. A possible treatmentmethod is collection and subsequent irrigation on short rotation coppice during the growingseason, for example onto willow stands (salix). Theoretically, irrigation allows both a volumereduction and a reduction of potentially hazardous leachate contents, such as nitrogen, organiccarbon and heavy metals. In this work, both hydraulic and reductive efficacy of leachateirrigation at the municipal solid waste landfill Ronneholm, in Southern Sweden, have beeninvestigated by means of a water and a mass balance. For the latter, the emission values ofcopper, chromium, nickel, zinc and total nitrogen were used, This study covers the periodfrom November 2002 until December 2003. The water balance and the mass balance weremodelled with a straight-forward box-model. The results suggest the importance of favourableirrigation schemes and the importance of sedimentation for leachate heavy metal reduction.Water balance calculations pinpointed potential for improving the efficiency of the leachatevolume reduction. In addition, the susceptibility of emission values for short term water levelchanges was checked by daily sampling during a week, at a across section of the landfill.Initial results suggest that measured heavy metal concentrations fluctuate with water levels inthe landfill body. This might be utilised to optimise irrigation schemes. A simple water andmass balance model has proved to be an effective method to both control leachate treatmentand to serve as a starting point to develop leachate reduction schemes.

Soil bioengineering techniques enhance riparian habitat quality and multi-taxonomic diversity in the foothills of the Alps and Jura Mountains

Riparian zones have disproportional ecological importance relative to their size. For decades, the functionality of riparian zones has been altered, with detrimental consequences on biodiversity. Recently, riparian zone restoration has become a major issue. When channel mobility cannot be restored and when erosion control is of primary concern, soil bioengineering techniques are often viewed as a compromise solution. We studied 37 riverbanks, from civil engineering to soil bioengineering, plus natural willow stands, in the foothills of the Alps and Jura Mountains. Using a principal component analysis, we first studied whether terrestrial and aquatic habitat variables varied among riverbank stabilization structures and bank stabilization age and built a synthetic index of riparian habitat quality reflecting the multivariate similarity of riverbank sites. Then, using a modelling approach, we tested whether multi-taxonomic diversity responded to changes in habitat quality and to broad-scale environmental variables (i.e., climate, hydrology and land cover). Soil bioengineering techniques, especially willow fascines and to lower extend vegetated crib wall, enhanced riparian habitat quality by allowing for a greater richness and density of pioneer tree species but also for a larger cover of high quality aquatic micro-habitats. This increase in riparian habitat quality induced an increase in both terrestrial and aquatic species diversity, highlighting the added-value of soil bioengineering techniques to restore riparian biodiversity. This may confirm that stabilization structures made of willow fascines are better suited than stabilization structures made of artificial substrata to support riparian species. Also, beyond the positive effect of soil bioengineering techniques for riparian biodiversity, we found that climatic, hydrological and land cover variables strongly influenced diversity patterns. Thus, multi-taxonomic diversity decreased along larger rivers and in landscapes dominated by urban areas. This may indicate that the full added value of soil bioengineering techniques for biodiversity will only become apparent if more attention is paid to mitigating the negative impact of human activities in the vicinity of riparian zones and if larger scale environmental parameters are taken into account as early as possible in restoration project. Therefore, we strongly recommend that riverbank restoration projects, based on the active introduction of native pioneer tree species, should be planned at the catchment scale.

Genetic diversity and stand structure of neighboring white willow (Salix alba L.) populations along fragmented riparian corridors: a case study

Abstract Remnant riparian woodlands have an important landscape function, due to their ability to act as ecological corridors. In this study we used molecular markers to assess the genetic variation occurring within and between spontaneous white willow (Salix alba L.) riparian woodlands. Our main goal was to evaluate the extent to which the fragmentation of a woodland corridor along a heavily impacted river in northeastern Italy and stand structural conditions may have affected the population genetics. Although having different structures, the three examined white willow stands showed high estimates of genetic similarity, as well as low genetic differentiation between them, indicating that they shared a similar gene pool and that the stands could result from a common set of individual genotypes, and should be regarded as metapopulations. The magnitude of genetic diversity within each of the stands and genetic differentiation between them, despite their high sexual reproductive capacity associated with a highly marked gene flow, suggest that these stands are dynamic and capable of adaptive responses to possible changes in their fluvial environment. However, the factors influencing genetic diversity should be interpreted from a long-term perspective. Fluvial geomorphic patterns in regulated rivers may be modified to a degree that could lead to changes in dispersal processes, sexu­al reproduction vs. asexual propagation, and hence genetic diversity.

First-rotation growth and stand structure dynamics of tree species in organic and conventional short-rotation agroforestry systems

Short-rotation agroforestry systems can potentially maintain agricultural production and promote conservation of soil and biodiversity, especially if grown organically. Hereby, species-specific stand growth determines woody biomass yield and influences management decisions like planting density and harvest requirements. Studies of longer-term growth dynamics in Southern Germany are scarce and none analyzed differences between conventional and organic systems. In this study, four tree species (black alder, black locust, poplar clone Max 3, and willow clone Inger) were planted in an alley-cropping configuration in Southern Germany, grown under organic and conventional systems, and monitored from 2009 to 2012. Growth was assessed with stem base diameter, height, aboveground woody biomass, sprouting, and survival. The tree species did not show a uniform ranking in biometric variables and biomass over time. Four-year mean annual biomass increment (MAI) ranged from 7 to 10 t ha−1 a−1, with poplar and locust having the highest growth rates. Willow had the lowest MAI, as it had a low diameter growth paired with a low wood density, but it developed the highest number of shoots because of increased sprouting in the last year. Size inequality and skewness of the dominant stems increased for all species throughout the years suggesting asymmetric competition. Size inequality as well as mortality was greatest for black locust. Furthermore this was the only species, which developed a right skewed SBD distribution and the highest diameter size range. Size inequality was smallest for poplar and willow, with no or only minimal mortality. Alder was inbetween. For black locust and alder no difference in growth traits between organic and conventional systems appeared after four years. Organic poplar and willow stands performed better than conventional ones after the second year, leaving unclear whether this can be attributed to management or site effect.

Long‐term changes in the ground thermal regime of an artificially drained thaw‐lake basin in the Russian European north

AbstractLong‐term (1982–1995) observations of the ground thermal regime of a drained thaw‐lake basin in the Pechora Lowlands of the Russian European north revealed a high spatial and temporal variability in the ground temperature response to artificial drainage. The thermal response was controlled by the atmospheric climate and by evolution of the landsurface following drainage. Observed changes in permafrost conditions were related to three climatic subperiods identified from air and ground temperature trends. The first (1982–1984) was characterized by gradual ground cooling associated with partial formation of permafrost patches under the initial stage of formation of marshy meadows. The second (1985–1987) involved strong ground cooling, resulting in the formation of a subsurface permafrost layer beneath most of the basin. The third (1988–1995) was marked by a gradual increase in annual mean ground temperature, promoting partial permafrost degradation under marshy meadows and willow stands. Initially, newly aggraded permafrost remained under peat mounds and tundra meadows. The spatial pattern of permafrost change can be attributed to heterogeneous landsurface evolution and variable snow thickness. Four distinct ground temperature regimes are distinguished: (i) thawed ground, (ii) deep permafrost, (iii) unstable permafrost and (iv) stable permafrost.

Продуктивность и санитарное состояние древостоев ивы ломкой в поймах средних и малых рек Центрального Черноземья

The article is devoted to the study of conformities to law of accumulation of barrel wood stock and change of the age sanitary state of brittle willow (Salix fragilis L.) stands, growing on the banks of the middle and small rivers. Research was conducted on the example of the test areas, set in August, 2010, in flood bottom of Shchigor River, Shchigor district, Kursk region. It is educed, that the largest stands of brittle willow are in wet habitat with flow ground waters in flood bottom.

Reintroduced Eurasian beavers (Castor fiber): colonization and range expansion across human-dominated landscapes

The protected Eurasian beaver Castor fiber is recolonizing its former range hereby entering human-dominated landscapes. This ecosystem engineer can cause considerable damage to human infrastructures and agriculture, by feeding, digging and damming. To prevent human–wildlife conflict and ensure continued support from the local residents, a better understanding of habitat selection is required. By using species distribution models (SDMs) to quantify habitat requirements in our study area in Flanders, Belgium, based on 1792 occurrence data from 71 territories, and a fine-scale land use and vegetation map, we explored the potential for future beaver settlements. The results indicate that even in a highly human-dominated landscape, there is sufficient habitat available to support beaver populations. We highlight the importance of distance to water, willow stands, wetland vegetation and poplar trees. We show that there is currently sufficient habitat to support 924 territories (619–1515, 90% confidence interval) in Flanders (but this does not imply these locations are conflict-free). Our findings indicate that 12 year after the reintroduction, there continues to be a large expansion potential, both in range and in densities within the currently recolonized area. Our results can be used as a management tool in order to evaluate possible risks linked with the return of beavers in a human dominated landscape. At these critical locations, increased monitoring or structural measures can prevent conflicts. By preventing or quickly resolving human wildlife conflicts, long-term coexistence between humans and beavers can be achieved.

Canopy manipulations of exotic Bitter Willow (Salix elaeagnos) forest for indigenous seedling recruitment: A pilot study

SummaryThe invasive exotic tree species Bitter Willow (Salix elaeagnos; Salicaceae) has colonised areas of rank exotic grassland and has been found to contain indigenous seed, dispersed by frugivorous birds into the monospecific stands. This small pilot study examined whether indigenous seedlings that have germinated in the understorey of exotic Bitter Willow stands could be stimulated to establish through the creation of small‐scale canopy gaps. In Bitter Willow forest, four single Bitter Willow trees were poisoned to create canopy gaps. Light transmission and seedling regeneration of tree and shrub species were assessed beneath both the four manipulated and three comparable intact Bitter Willow canopies. Over 3 years, seedling height and density increased more beneath opened compared to intact Bitter Willow canopies. These results suggest that Bitter Willow can fill the roles of both a facilitative nurse and a perch tree. Larger‐scale canopy manipulation experiments of both Bitter Willow and other Salix species are needed to determine the full potential of canopy manipulations for forest restoration.

An analytical toolkit for polyploid willow discrimination.

Polyploid breeding is an important means for creating elite willow cultivars, and therefore provokes an active demand for discriminating the ploidy levels of natural willow stands. In this study, we established an analytical toolkit for polyploid willow identification by combining molecular markers and flow cytometry (FCM). A total of 10 single-copy fully informative SSRs were chosen for marker-aided selection based on a segregation test with a full-sib willow pedigree and a mutability test with a collection of natural willow stands. Aided by these molecular markers, we performed polyploid selection in two tree species and two shrub species of the genus Salix. The ploidy levels of the investigated samples were further examined using a flow cytometer. It was previously shown that results from marker-aided selection were consistent with those from FCM measurements. Based on ploidy level assessment in different willow species, it was found that tree willows were dominantly tetraploid, whereas shrub willows were most frequently diploid. With this analytical toolkit, polyploids can be rapidly screened from a large number of natural stands; thereafter, the exact ploidy levels of the polyploid candidates can be efficiently confirmed by FCM. This analytical toolkit will greatly enhance polyploid breeding programs for willows.

The impact of an invasive ambrosia beetle on the riparian habitats of the Tijuana River Valley, California.

The Tijuana River Valley is the first natural habitat in California to be substantially invaded by the Kuroshio Shot Hole Borer (KSHB, Euwallacea sp.), an ambrosia beetle native to Southeast Asia. This paper documents the distribution of the KSHB in the riparian vegetation in the valley and assesses the damage done to the vegetation as of early 2016, approximately six months after the beetle was first observed in the valley. I divided the riparian habitats into 29 survey units so that the vegetation within each unit was relatively homogenous in terms of plant species composition, age and density. From a random point within each unit, I examined approximately 60 individuals of the dominant plant species for evidence of KSHB infestation and evidence of major damage such as limb breakage. In the 22 forested units,I examined the dominant arroyo and black willows (Salix lasiolepis Benth. and S. gooddingii C.R. Ball), and in the seven scrub units, I examined mule fat (Baccharis salicifolia (Ruiz & Pav.) Pers.). Evidence of KSHB infestation was found in 25 of the 29 units. In the forest units, infestation rates ranged from 0 to 100% and were high (>60%) in 16 of the units. In the scrub units, infestation rates ranged from 0 to 33%. Infestation rates were significantly correlated with the wetness of a unit; wetter units had higher infestation rates. Evidence of major physical damage was found in 24 units, and dense stands of willows were reduced to broken trunks in several areas. Overall, I estimated that more than 280,000 (70%) of the willows in the valley were infested, and more than 140,000 had suffered major limb damage. In addition, I recorded evidence of KSHB infestation in the other common plant species in the valley; of the 23 species examined, 14 showed evidence of beetle attack. The four species with the highest rates of infestation were native trees in the Salicaceae family. The three species considered to be the worst invasive plants in the valley, Ricinus communis L., Tamarix ramosissima Ledeb. and Arundo donax L., had low rates of infestation. Several findings from this study have significance for resource managers: (1) the KSHB attack caused extensive mortality of trees soon after being first discovered so, if managers are to control the spread of the beetle, they will need to develop an effective early detection and rapid response program; (2) infestation rates were highest in units that were wet, so resource managers trying to detect the beetle in other areas should thoroughly search trees near water, particularly nutrient-enriched water; (3) the infestation appears to be a novel form of disturbance, and the affected forests may need special management actions in order to recover; and (4) the infestation has altered the structure of the forest canopy, and this is likely to promote the growth of invasive plant species that were relatively inconspicuous in the forests prior to the beetle attack but will now need more attention.