The impact of Broussonetia papyrifera (L.) vent. on community characteristics in the forest and forest–savannah transition ecosystems of Ghana

Following its introduction in the late 1960s, Broussonetia papyrifera L. Vent. Moraceae (paper mulberry) has emerged as a major exotic invasive species in Ghana's forest ecosystems. This study was carried out to assess the effects of B. papyrifera invasion on community composition in forest and forest–savannah transition ecosystems. Comparative and removal experiments were conducted in paired B. papyrifera invaded versus uninvaded plots. In the comparative assessment, species composition was found to be similar in both invaded and uninvaded plots. However, relative per cent cover of resident species and guilds including Chromolaena odorata, indigenous broadleaves and indigenous grasses were significantly lower in invaded plots. Seven months after B. papyrifera was experimentally removed from invaded stands, cover by indigenous broadleaves increased by 35%, as against only 5% in control plots at the forest site. However, at the transition site, the increase in per cent cover of indigenous broadleaves (18%) was not significantly different from control (2.5%) plots. We conclude that B. papyrifera has the capacity to reduce the abundance of indigenous broadleaf species, although its removal is more likely to favour regeneration in a forest than a forest–savannah transition ecosystem.     

The impact of two introduced biocontrol agents, Phytomyza vitalbae and Phoma clematidina, on Clematis vitalba in New Zealand

Insecticide and fungicide exclusion experiments were performed to determine the impact of two biological control agents, an agromyzid leaf-mining fly Phytomyza vitalbae Kaltenbach and a coelomycete fungal pathogen Phoma clematidina (Thüm.) Boerema, on the growth and percentage cover of Clematis vitalba L. (Ranunculaceae) plants. Both insecticide and fungicide treatments significantly reduced control agent damage to C. vitalba leaves over one growing season at Blenheim, New Zealand. However, damage attributable to both agents was rather low and population peaks of both agents occurred in late fall, after the main period of stem growth. There was no significant impact of treatment on growth and only a minor (8–10%), but significant, reduction in percentage cover of C. vitalba was recorded. Disease symptoms were generally only expressed late in the growing season, when leaves were senescent, and were correlated with Py. vitalbae damage. Therefore, we tentatively conclude that alone, Ph. clematidina is insufficiently pathogenic to induce disease symptoms during the main growing season of C. vitalba. Selection criteria for any future potential biocontrol pathogen, therefore, need to evaluate inherent epidemiological factors before introduction, to ensure the candidate agent is an aggressive primary pathogen that can exert maximum disease attack on the target plant. Furthermore, the potential of Py. vitalbae to exist as an asymptomatic endophyte indicates that extra care may be required when assessing survey results for non-target attack, and when testing candidate pathogen biological control agents for host specificity.     

Properties of a new strain of tobacco streak virus from Clematis vitalba (Ranunculaceae)

A distinct strain of tobacco streak virus (TS V/Cle), isolated in Yugoslavia from wild Clematis vitalba showing chlorotic spots or yellow netting of the leaves and from many symptomless shrubs, is described. TSV/Cle was seed transmitted in C. vitalba (70%), and in the experimental hosts Chenopodium quinoa (80%), Nicotiana benthamiana and N. megalosiphon. It was also detected in the pollen of infected C. quinoa. Purified virus preparations mostly contained quasi-spherical particles measuring 24–26 × 28, 26–28 × 28–30 and 28–31 × 32–36 mn, and sedimented in sucrose density gradient and analytical centrifugation as three components with sedimentation coefficients of 76S, 87S and 98S. The virus contained a single polypeptide species of mol. wt of c. 25 000. Unfractionated TSV/Cle preparations contained four RNA species with mol. wts, estimated by gel electrophoresis in agarose, of 1.1 × 10⁶, 0.9 × 10⁶, 0.7 × 10⁶ and 0.3 × 10⁶. In comparative experiments, TSV/Cle differed from four reference strains of TSV (TSV/B, TSV/HF, TSV/RN, and TSV/Ro) in host range and in symptoms induced in some common hosts. In agar gel double diffusion tests it was more closely related to TSV/B and TSV/M (SDI = 5) than to TSV/HF (SDI = 7), TSV/RN (SDI = 7) or TSV/Ro (SDI = 5–8). Immunoelectrophoresis experiments clearly distinguished TSV/Cle from the reference strains. TSV/Cle strain was detected in C. vitalba plants from distant and climatically different regions in Yugoslavia.     

The potential for biological control of invasive alien aquatic weeds in Europe: a review

A retrospective analysis shows that invasive, alien, free-floating and emergent aquatic weeds in Europe are good targets for classical biological control, and that genus-specific chrysomelid and curculionid beetles offer the most potential. Ludwigia spp., Azolla filiculoides, Lemna minuta, Crassula helmsii and Hydrocotyle ranunculoides should be prioritised as targets. Fungal pathogens have been under-utilised as classical agents but, whilst they may have some potential against free-floating weeds, they appear to be poor candidates against submerged species, although the suitability of arthropod agents against these difficult targets still merits investigation. The use of indigenous pathogens as inundative agents (mycoherbicides) shows some promise.     

Geringe Samenbank von beweidbaren Arten für die Etablierung von Waldweiden im Schweizer Mittelland

Kipfer T. and Bosshard A. 2007. Low seed bank of herb species suitable for grazing hampers the establishment of wood pastures in the Swiss lowlands. Bot. Helv. 117: 159 – 167. Controlled forest grazing is expected to yield benefits for biodiversity conservation, landscape quality, and in some cases also for land use economy. In the Swiss lowlands, first attempts are being made to reintroduce forest grazing in productive beech forests, but methodic experience is still limited. One main issue concerns the development of the vegetation after forest stands have been thinned to improve light conditions: Will grassland vegetation establish spontaneously? The present study analyses the composition of the soil seed bank of four beech forest stands. The seed bank density ranged from 1’244 to 28’651 seeds m⁻². Seed banks mainly consisted of forest and ruderal species; most abundant were Juncus effusus, Carex sylvatica, Rubus spp. and Clematis vitalba. Seeds of grassland plants were restricted to a few species, and their abundance in the seed bank decreased rapidly with increasing distance from the forest edge. These results reveal that there is little potential for grasslands to develop spontaneously from the seed bank. The introduction of grassland species of local origin using the green hay method is therefore recommended to prevent soil degradation during the first years of grazing, to fulfil minimal biodiversity requirements and to lower the risk of an establishment of neophytes and other problematic plant species. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. Manuskript angenommen am 2. September 2007     

杉木林改造成乡土阔叶林对林下植物物种组成和多样性的影响

把杉木林改造成乡土阔叶林,不仅能提供高价值木材,而且能够提升生态系统服务功能,是我国目前改造退化针叶林最常见的经营模式之一,但这些改变对其林下植物物种组成和多样性的影响及机制我们尚知之甚少。以南亚热带杉木林采伐迹地上重新种植的杉木林、红锥林和米老排林为研究对象,调查研究其灌木层和草本层植物物种组成和多样性,结果表明：（1）和杉木林相比,改造后的红锥林和米老排林灌木层的植物物种丰富度和多样性均呈极显著降低（P<0.01）,但其草本层植物只有物种丰富度极显著降低（P<0.01）,多样性均无显著变化（P>0.05）;（2）主成分分析（PCA）表明改造后的林分灌木层和草本层的植物物种组成发生明显的变化,冗余分析（RDA）确定导致林分灌木层植物物种组成发生变化的主要原因是杉木林改造成红锥林和米老排林后的冠层透光率、土壤碳氮比、土壤含水量和凋落物碳氮比的显著变化,而冠层透光率和土壤碳氮比的显著变化是导致其林下草本层植物物种组成发生明显变异的主要因子;（3）方差分解结果显示微地形、乔木特性和土壤理化性质的独立效应对灌木层和草本层植物物种组成的影响高于它们的交互效应。该研究为科学经营管理人工林和提高人工林生态系统多功能性提供科学依据。     

Die Verteilung der leitenden Strukturen in der Achse vonClematis vitalba (Ranunculaceae)

The vascular pattern and its origin are described in connection with the differentiation of ground tissue in the shoot. Leaf arrangement ofClematis vitalba L. is decussate, and the vascular pattern appears rather simple at first: From internode to internode six strands—three from each leaf—alternate. About six internodes from the shoot apex, the pattern is completed by accessory strands which do not leave the axis and differentiate near the primary bark and exactly between the old strands. The formation of the acessory strands is not caused by the enlargement of the axis alone, because the balance between ground and vascular tissue is already regulated by the enlargement of the primary strands.

Zweiter Beitrag der Serie Die Sproßentwicklung vonClematis vitalba (Ranunculaceae) vgl. den ersten Beitrag:Schnettker (1976).     

Land-snail faunas in indigenous rainforest and commercial forestry plantations in Kakamega Forest, western Kenya

We examine the diversity and structure of land-snail faunas in indigenous rainforest communities and three types of forestry plantation in Kakamega Forest, western Kenya. Using plot-based, standardized sampling consisting of fixed-time direct searching and fixed-volume litter sieving we estimated molluscan diversity and abundance in monoculture plantation plots of the exotic, non-African tree species Bischofia javanica and Pinus spp., and the central African tree Maesopsis eminii which is an indigenous component of the Kakamega rainforest. Overall, 41, 39, 41 and 34 mollusc species were recorded in indigenous forest, Maesopsis, Bischofia and Pinus plantations respectively. The mean number of species and mean number of specimens per plot were 15–49% and 6–54% lower respectively in the plantations relative to indigenous forest. Abundance and species number were suppressed the most in the Pinus stands, and the least in the plantations of indigenous Maesopsis. Species per plot, Shannon index and abundance were lowest in the Pinus plantation and highest in the indigenous forest. Snails were more abundant in Maesopsis than in Bischofia, but mean species per plot and total species number did not differ significantly between these plantation types. Shannon evenness indices showed that the indigenous forest faunas were more uniform in terms of species abundance, whereas the three plantation types were dominated by a small number of species. Several species were confined to the indigenous rain forest. Although most species were present in both indigenous forest and plantations, many species were significantly more abundant in the rainforest communities. The potential use of groups of these species as indicators of forest conditions is discussed. Overall, the Maesopsis and Bischofia plantations support a substantial proportion of the indigenous rainforest's mollusc fauna. This maybe partly because of the relatively close proximity of indigenous stands to plantations, which can facilitate recolonisation. However, the finding illustrates that plantations hold the potential, at least in some circumstances, to provide alternative habitats for forest molluscs where indigenous rainforest has been cleared.     

Sampling indigenous ground‐living beetles in a stand of non‐native tree privet (Ligustrum lucidum) in New Zealand raises new management questions

Small urban forest reserves in New Zealand have been shown to have value in conserving indigenous beetle diversity. However there is little information available on the ability of non‐native vegetation areas such as tree privet to support indigenous beetle assemblages. To investigate this for one site, ground‐living beetles were collected using pitfall traps over a year at a small urban forest of the invasive tree Ligustrum lucidum (tree privet) in Auckland, New Zealand. A total of 815 beetles were found, from 20 families and 42 relative taxonomic units. Using monthly data, there was no correlation between soil moisture and diversity index (P = 0.805) or species richness (P = 0.375). These results raise the question of whether urban patches of non‐native tree privet may have potential as reservoirs of beetle diversity, if only until they are replaced with native vegetation.     

Removal of invasive shrubs alters light but not leaf litter inputs in a deciduous forest understory

The establishment and spread of non‐native, invasive shrubs in forests poses an important obstacle to natural resource conservation and management. This study assesses the impacts of the physical removal of a complex of woody invasive shrub species on deciduous forest understory resources. We compared leaf litter quantity and quality and understory light transmittance in five pairs of invaded and removal plots in an oak‐dominated suburban mature forest. Removal plots were cleared of all non‐native invasive shrubs. The invasive shrubs were abundant (143,456 stems/ha) and diverse, dominated by species in the genera Ligustrum, Viburnum, Lonicera, and Euonymus. Annual leaf litter biomass and carbon inputs of invaded plots were not different from removal plots due to low leaf litter biomass of invasive shrubs. Invasive shrub litter had higher nitrogen (N) concentrations than native species; however, low biomass of invasive litter led to low N inputs by litter of invasive species compared to native. Light transmittance at the forest floor and at 2 m was lower in invaded plots than in removal plots. We conclude that the removal of the abundant invasive shrubs from a native deciduous forest understory did not alter litter quantity or N inputs, one measure of litter quality, and increased forest understory light availability. More light in the forest understory could facilitate the restoration of forest understory dynamics.     

Ammonium can stimulate nitrate and nitrite reductase in the absence of nitrate in Clematis vitalba

Nitrogen assimilation was studied in the deciduous, perennial climber Clematis vitalba. When solely supplied with NO₃^– in a hydroponic system, growth and N-assimilation characteristics were similar to those reported for a range of other species. When solely supplied with NH₄⁺, however, nitrate reductase (NR) activity dramatically increased in shoot tissue, and particularly leaf tissue, to up to three times the maximum level achieved in NO₃^– supplied plants. NO₃^– was not detected in plant material that had been solely supplied with NH₄⁺, there was no NO₃^– contamination of the hydroponic system, and the NH₄⁺-induced activity did not occur in tobacco or barley grown under similar conditions. Western Blot analysis revealed that the induction of NR activity, either by NO₃^– or NH₄⁺, was matched by NR and nitrite reductase protein synthesis, but this was not the case for the ammonium assimilation enzyme glutamine synthetase. Exposure of leaf disks to N revealed that NO₃^– assimilation was induced in leaves directly by NO₃^– and NH₄⁺ but not glutamine. Our results suggest that the NH₄⁺-induced potential for NO₃^– assimilation occurs when externally sourced NH₄⁺ is assimilated in the absence of any NO₃^– assimilation. These data show that the potential for nitrate assimilation in C. vitalba is induced by a nitrogenous compound in the absence of its substrate and suggest that NO₃^– assimilation in C. vitalba may have a significant role beyond the supply of reduced N for growth.     

Carabid beetles (Coleoptera: Carabidae) in coniferous plantations in Hokkaido,Japan: effects of tree species and environmental factors

The distribution, species composition and abundance of carabid beetles in monospecific plantations of three different coniferous tree species (Japanese spruce, Sakhalin fir and larch) were investigated by baited pitfall traps in Hokkaido, Japan. In total, 16 150 carabid beetles consisting of 31 species in 13 genera were collected in 2011 and 2012. The most predominant species was Pterostichus thunbergii Morawitz, followed by Synuchus melantho (Bates) and Carabus opaculus (Putzeys). Average numbers of beetles per trap were significantly reduced in larch. Large‐sized Carabus species (C. arboreus arboreus Lewis and C. opaculus) were collected in large numbers in Japanese spruce. There was no significant difference in diversity and equitability among the three kinds of plantation. The ordination of redundancy analysis showed that medium‐sized forest generalists, Pterosticus subovatus (Motschulsky) and P. thunbergii, were highly associated with Japanese spruce and Sakhalin fir, and the forest specialist Synuchus nitidus (Motschulsky) was with Sakhalin fir. In contrast, in larch there was no such associated forest species, and some species of Carabus, Pterostichus and Synuchus were considerably reduced in number, suggesting that larch has unfavorable effects on some forest species. The most important environmental variables influencing carabid assemblages were soil moisture and foliage layer cover. Practices in forest management to minimize the effects of plantations on carabid assemblages are discussed.     

Exotic wildland weeds serve as reservoirs for a newly introduced cole crop pest,Bagrada hilaris (Hemiptera: Pentatomidae)

The role of wildland weeds that serve as alternate hosts for insect pests has not been directly examined for the potential to sustain pest populations or facilitate pest outbreaks. The development of weed biological control programmes is also complicated by weed species that are closely related to economically important or native plants, especially rare or special status species. In recent surveys in southern California, USA, we found a newly introduced insect pest of cole crops, Bagrada hilaris Burmeister (Bagrada bug), feeding on Brassicaceae weeds in riparian areas adjacent to agricultural fields where cole crops are routinely grown. Insect populations grew to levels well over action thresholds and caused severe damage to populations of the invasive weed, Lepidium latifolium (perennial pepperweed). The numerical response of B. hilaris on L. latifolium and other Brassicaceae weeds in natural areas may pose a significant challenge to effectively managing pest populations in crops. However, the accidental introduction of this insect provides the opportunity to examine plant–insect interactions with important implications for development of biologically based control methods for weeds.     

甘南铁线莲, 甘肃毛茛科一新种

该文描述了自甘肃南部发现的毛茛科铁线莲属的一新种,甘南铁线莲。     

Land use history, hurricane disturbance, and the fate of introduced species in a subtropical wet forest in Puerto Rico

Tropical forests are suffering from increasing intensities and frequency of disturbances. As a result, non-native species accidentally introduced or intentionally planted for farming, plantations, and ornamental purposes may spread and potentially invade undisturbed native forest. It is not known if these introduced species will become invasive, as a result of recurrent natural disturbances such as hurricanes. Using data from three censuses (spanning 15 years) of a 16-ha subtropical wet forest plot, we investigated the impact of two hurricanes on populations of plant species that were planted in farms and plantations that were then abandoned and from the natural spread of species introduced into Puerto Rico in the past. The populations of four species (Citrus paradis, Mangifera indica, Musa sp., and Simarouba glauca) changed little over time. Six species (Artocarpus altilis, Calophyllum calaba, Genipa americana, Hibiscus pernambucensis, Syzygium jambos, and Swietenia macrophylla) declined between the first two censuses after Hurricane Hugo, then increased again in Census 3 after Hurricane Georges. Spathodea campanulata gradually increased from census to census, while Coffea arabica declined. These introduced species represent only a small part of the forest basal area and few show signs of increasing over time. The number of stems per plant, new recruits, and the growth rates of these introduced species were within the ranges of those for native plant species. The mortality rates over both census intervals were significantly lower for introduced species (<5% year⁻¹) than for native ones (15% year⁻¹). Many new recruits established after Hurricane Hugo (prior to this study) had opened the forest canopy and these high mortality rates reflect their death as the canopy recovered. Only Swietenia macrophylla and Syzygium jambos showed an increase in stem numbers in the closed canopy area of forest that had suffered limited human disturbance in the past. A future increase in frequency of disturbance may enable greater stem numbers of introduced species to establish, while lower-mortality rates compared to native species, may allow them to persist during inter-hurricane intervals. An increase in the population of introduced species, especially for those that grow into large trees, may have an impact on this tropical forest in the future.     

Management practices for control of ragwort species

The ragwort species common or tansy ragwort (Jacobaea vulgaris, formerly Senecio jacobaea), marsh ragwort (S. aquaticus), Oxford ragwort (S. squalidus) and hoary ragwort (S. erucifolius) are native in Europe, but invaded North America, Australia and New Zealand as weeds. The abundance of ragwort species is increasing in west-and central Europe. Ragwort species contain different groups of secondary plant compounds defending them against generalist herbivores, contributing to their success as weeds. They are mainly known for containing pyrrolizidine alkaloids, which are toxic to grazing cattle and other livestock causing considerable losses to agricultural revenue. Consequently, control of ragwort is obligatory by law in the UK, Ireland and Australia. Commonly used management practices to control ragwort include mechanical removal, grazing, pasture management, biological control and chemical control. In this review the biology of ragwort species is shortly described and the different management practices are discussed.     

Exotic Grasses Potentially Slow Invasion of an N-fixing Tree into a Hawaiian Woodland

This paper examines the effect of an abundant non-native species, Schizachyrium condensatum, on establishment of a later arriving, but very potent invader, Myrica faya, in a seasonally dry forest on the island of Hawaii. Using a replicated removal experiment, we determined that S. condensatum, a perennial C4 grass, reduced recruitment of M. faya, an N-fixing tree species. Recruitment of Myrica was 90% higher in S. condensatum removal plots compared to controls. We believe that because S. condensatum substantially reduces light at the soil surface it reduces germination and early seedling growth of the M. faya. This revised version was published online in July 2006 with corrections to the Cover Date.     

Habitat use and seed removal by invasive rats (Rattus rattus) in disturbed and undisturbed rain forest,Puerto Rico

Despite frequent occurrences of invasive rats (Rattus spp.) on islands, their known effects on forests are limited. Where invasive rats have been studied, they generally have significant negative impacts on native plants, birds, and other animals. This study aimed to determine invasive rat distribution and effects on native plant populations via short‐term seed removal trials in tropical rain forest habitats in the Luquillo Experimental Forest, Puerto Rico. To address the first objective, we used tracking tunnels (inked and baited cards inside tunnels enabling animal visitors’ footprints to be identified) placed on the ground and in the lower canopy within disturbed (treefall gaps, hurricane plots, stream edges) and undisturbed (continuous forest) habitats. We found that rats are present in all habitats tested. Secondly, we compared seed removal of four native tree species (Guarea guidonia, Buchenavia capitata, Tetragastris balsamifera, and Prestoea acuminata) between vertebrate‐excluded and free‐access treatments in the same disturbed and undisturbed habitats. Trail cameras were used to identify animals responsible for seed contact and removal. Black rats (Rattus rattus) were responsible for 65.1% of the interactions with seeds, of which 28.6% were confirmed seed removals. Two plant species had significantly more seeds removed in disturbed (gaps) than undisturbed forest. Prestoea acuminata had the lowest seed removal (9% in 10 days), whereas all other species had >30% removal. Black rats are likely influencing fates of seeds on the forest floor, and possibly forest community composition, through dispersal or predation. Further understanding of rat–plant interactions may be useful for formulating conservation strategies.     

Relationships between the density of two potential restoration tree species and plant species abundance and richness in a degraded Afromontane forest of Kenya

In recent years, there have been considerable efforts to restore degraded tropical montane forests through active restoration using indigenous tree species. However, little is known about how these species used for restoration influence other species. In this study, two potential restoration species, Albizia gummifera and Neoboutonia macrocalyx, are investigated with regard to the relationship between their density and the abundance and richness of other plant species. The study was conducted in a degraded forest consisting of disturbed transition zones and secondary forest. Our results show positive relationships between the density of A. gummifera and the abundance of tree seedling and sapling richness in the transition zones and in the secondary forest. Shrub richness was negatively related to the density of A. gummifera. Abundance and richness of tree saplings and shrubs were positively related to N. macrocalyx density both in the transition zones and in the secondary forest. Herb species richness declined with N. macrocalyx density in the transition zones but increased with N. macrocalyx density in the secondary forest. The positive relationships between the density of the two tree species and species richness of other woody species suggest that both A. gummifera and N. macrocalyx can be suitable for active restoration of degraded mountain forests within their natural range.