Leaf and root extracts of the invasive shrub, Lonicera maackii, inhibit seed germination of three herbs with no autotoxic effects

In addition to effects mediated by resource competition, some invasive plants may impact surrounding vegetation by secreting compounds that are directly inhibitory to growth. Lonicera maackii, an invasive Asian shrub of forests and open areas in eastern and midwestern North America, has devastating effects on understory vegetation, some of which persist even after this shrub is removed. In this study, we explored the potential of aqueous extracts of the leaves and roots of this plant to inhibit seed germination of Impatiens capensis, Alliaria petiolata, Arabidopsis thaliana, and L. maackii in Petri dish bioassays. Both L. maackii root and leaf extracts significantly decreased germination in the three herb species. This inhibitory effect generally increased with increasing extract concentration and was more pronounced with application of leaf extract than root extract. However, when the same extracts were applied to seeds of L. maackii itself, germination was delayed in some cases, but was not significantly reduced by the end of the experiment. Germination of L. maackii seeds even reached significantly higher levels in some extract treatments than in no-extract controls. This implies that L. maackii can successfully inhibit the germination of other plants with few autotoxic effects and may even promote the germination of its own seeds.     

Plant–pollinator interactions between an invasive and native plant vary between sites with different flowering phenology

Floral displays of invasive plants have positive and negative impacts on native plant pollination. Invasive plants may also decrease irradiance, which can lead to reduced pollination of native plants. The effects of shade and flowers of invasive plant species on native plant pollination will depend on overlap in flowering phenologies. We examined the effect of the invasive shrub Lonicera maackii on female reproductive success of the native herb Hydrophyllum macrophyllum at two sites: one with asynchronous flowering phenologies (slight overlap) and one with synchronous (complete overlap). At each site, we measured light availability, pollinator visitation, pollen deposition, and seed set of potted H. macrophyllum in the presence and absence of L. maackii. At both sites, understory light levels were lower in plots containing L. maackii. At the asynchronous site, H. macrophyllum received fewer pollinator visits in the presence of L. maackii, suggesting shade from L. maackii reduced visitation to H. macrophyllum. Despite reduced visitation, H. macrophyllum seed set did not differ between treatments. At the synchronous site, H. macrophyllum received more pollinator visits and produced more seeds per flower in the presence of co-flowering L. maackii compared to plots in which L. maackii was absent, and conspecific pollen deposition was positively associated with seed set. Our results support the hypothesis that co-flowering L. maackii shrubs facilitated pollination of H. macrophyllum, thereby mitigating the negative impacts of shade, leading to increased seed production. Phenological overlap appears to influence pollinator-mediated interactions between invasive and native plants and may alter the direction of impact of L. maackii on native plant pollination.     

Shading by invasive shrub reduces seed production and pollinator services in a native herb

Plant invasions disrupt native plant reproduction directly via competition for light and other resources and indirectly via competition for pollination. Furthermore, shading by an invasive plant may reduce pollinator visitation and therefore reproduction in native plants. Our study quantifies and identifies mechanisms of these direct and indirect effects of an invasive shrub on pollination and reproductive success of a native herb. We measured pollinator visitation rate, pollen deposition, and female reproductive success in potted arrays of native Geranium maculatum in deciduous forest plots invaded by the non-native shrub Lonicera maackii and in two removal treatments: removal of aboveground L. maackii biomass and removal of flowers. We compared fruit and seed production between open-pollinated and pollen-supplemented plants to test for pollen and light limitation of reproduction. Plots with L. maackii had significantly lower light, pollinator visitation rate, and conspecific pollen deposition to G. maculatum than biomass removal plots. Lonicera maackii flower removal did not increase pollinator visitation or pollen deposition compared to unmanipulated invaded plots, refuting the hypothesis of competition for pollinators. Thus, pollinator-mediated impacts of invasive plants are not limited to periods of co-flowering or pollinator sharing between potential competitors. Geranium maculatum plants produced significantly fewer seeds in plots containing L. maackii than in plant removal plots. Seed set was similar between pollen-supplemented and open-pollinated plants, but pollen-supplemented plants exhibited higher seed set in plant removal plots compared to invaded plots. Therefore, we conclude that the mechanism of impact of L. maackii on G. maculatum reproduction was increased understory shade.     

Avian Seed Dispersal of an Invasive Shrub

The incorporation of an animal-dispersed exotic plant species into the diet of native frugivores can be an important step to that species becoming invasive. We investigated bird dispersal of Lonicera maackii, an Asian shrub invasive in eastern North America. We (i) determined which species of birds disperse viable L. maackii seeds, (ii) tested the effect of gut passage on L. maackii seeds, and (iii) projected the seed shadow based on habitat use by a major disperser. We found that four native and one exotic bird species dispersed viable L. maackii seeds. Gut passage through American robins did not inhibit germination, but gut passage through cedar waxwings did. American robins moved mostly along woodlot edges and fencerows, leading us to project that most viable seeds would be defecated in such habitats, which are very suitable for L. maackii. We conclude that L. maackii has been successfully incorporated into the diets of native and exotic birds and that American robins preferentially disperse seeds to suitable habitat.     

Clidemia hirta Invasion at the Pasoh Forest Reserve: An Unexpected Plant Invasion in an Undisturbed Tropical Forest1

Clidemia hirta is a highly invasive shrub in tropical forests throughout the world, but has had little success invading mainland sites and undisturbed forests. In the early 1990s, this plant was found to have invaded an unexpected site, an undisturbed continental tropical forest at Pasoh, Peninsular Malaysia. In 1997, a study was conducted of the C. hirta population at the Pasoh Forest Reserve. A demographic survey of the 50–ha long–term research plot at Pasoh located 1002 C. hirta individuals, 69 of which were reproductive at the time of the study. All but 8 individuals were located in high light gaps or gap edges. Relative growth rates were significantly higher in gaps and gap edges than in the understory, and no reproductive individuals were found in the understory. Mean plant size and dry biomass density increased steadily over the course of the study, while the observed mortality rate was 0 percent over two months. The biomass density of Clidemia at Pasoh was <500 g/ha at the conclusion of this study, but because the population is confined almost exclusively to high light environments, its density in these sites is much higher. The location of C. hirta plants in gaps was significantly correlated with past disturbance by wild pigs, suggesting that soil disturbance and light availability are essential for their establishment. The implication of this study is that by competing with native species in gaps, C. hirta invasion has the potential to alter forest regeneration at Pasoh. Changing land use practices near the reserve have increased the number of wild pigs, and thus the level of disturbance, which may explain the recent success of C. hirta at Pasoh.     

The invasive shrub,<Emphasis Type="Italic"> Lonicera maackii</Emphasis> , reduces growth and fecundity of perennial forest herbs

Effects of invasive plant species on native plant species are frequently assumed or inferred from comparisons, but rarely quantified experimentally. Such quantification is important to assessing risks and impacts of invasives. We quantified the effects of Lonicera maackii, an exotic shrub invasive in many eastern North American forests, on survival, growth, and reproduction of three perennial herbs: Allium burdickii, Thalictrum thalictroides , and Viola pubescens. We predicted that the spring ephemeral, A. burdickii , would be most impacted, due to early leaf expansion of L. maackii. Field experiments were carried out in two deciduous forest stands, one (Greggs Woodlot, GW) disturbed and the other (Western Woods, WW) relatively undisturbed. In each stand, individual herbs were transplanted into a blocked design of 60 plots where L. maackii was present, absent, or removed, and monitored for 5 growing seasons. Lonicera maackii did not affect survival of transplants, but reduced growth and final size of individuals of all three species. For two of the species, A. burdickii and V. pubescens, L. maackii reduced the proportion of live plants flowering in both stands, and reduced the seed or fruit number per flowering individual in GW. For T. thalictroides the proportion flowering was not affected, but seed number per flowering plant was reduced by L. maackii in both stands. For all three species, cumulative seed production over the course of the study was reduced by L. maackii. Overall, effects on the spring ephemeral, A. burdickii, were similar to effects on the other herbs. Because mortality of these established individuals was not affected, short-term studies might conclude forest herbs are unaffected by invasive shrubs. However, the growth and reproduction impacts documented here suggest that populations are impacted in the long-term.     

The relative importance of landscape and community features in the invasion of an exotic shrub in a fragmented landscape

Although invasive plants are recognized as a major ecological problem, little is known of the relative importance of plant community characteristics versus landscape context in determining invasibility of communities. We determined the relative importance of community and landscape features of 30 woodlots in influencing the invasion of Lonicera maackii. We sampled woodlots using the point‐quarter method and calculated canopy openness and basal areas and densities of shrub, sapling and tree species, as well as woody species richness. We used aerial photos and ArcView GIS to calculate landscape parameters from the same woodlots using a buffer distance of 1500 m. We used logistic and linear regression analyses to determine the community and landscape factors that best explain L. maackii presence and density. We also tested whether woodlot invasion by L. maackii begins at woodlot edges. Presence of L. maackii was significantly explained only by distance from the nearest town (logistic regression, p=0.017); woodlots nearer town were more likely to be invaded. Among invaded woodlots, density of L. maackii was positively related to the amount of edge in the landscape (partial R²=0.592) and negatively related to total tree basal area (partial R²=0.134), number of native woody species (partial R²=0.054), and sapling shade tolerance index (partial R²=0.054). Lonicera maackii in woodlot interiors were not younger than those on the perimeters, leading us to reject the edge‐first colonization model of invasion. Our findings reveal that landscape structure is of primary importance and community features of secondary importance in the invasion of L. maackii. This shrub is invading from multiple foci (towns) rather than an advancing front. Connectivity in the landscape (i.e. the number of corridors) did not promote invasion. However, edge habitat was important for invasion, probably due to increased propagule pressure. The community features associated with L. maackii invasion may be indicators of past disturbance.     

Influence of light and soil moisture on Sierran mixed-conifer understory communities

Sierra Nevada forests have high understory species richness yet we do not know which site factors influence herb and shrub distribution or abundance. We examined the understory of an old-growth mixed-conifer Sierran forest and its distribution in relation to microsite conditions. The forest has high species richness (98 species sampled), most of which are herbs with sparse cover and relatively equal abundance. Shrub cover is highly concentrated in discrete patches. Using overstory tree cover and microsite environmental conditions, four habitats were identified; tree cluster, partial canopy, gap, and rock/shallow soil. Herb and shrub species were strongly linked with habitats. Soil moisture, litter depth and diffuse light were the most significant environmental gradients influencing understory plant distribution. Herb cover was most strongly influenced by soil moisture. Shrub cover is associated with more diffuse light, less direct light, and sites with lower soil moisture. Herb richness is most affected by conditions which influence soil moisture. Richness is positively correlated with litter depth, and negatively correlated with direct light and shrub cover. Disturbance or management practices which change forest floor conditions, shallow soil moisture and direct light are likely to have the strongest effect on Sierran understory abundance and richness.     

Direct topsoil transfer to already planted reforestation sites increases native plant understory and not ruderals

Forests restored passively or by tree planting can take many decades to be recolonized by native forest understory plant species, if at all. Our study tested (1) the ability of forest topsoil transfer to accelerate the recovery of native forest plant communities in post-agricultural reforestation sites after tree-planting and without previous topsoil removal and (2) the effect of adding combinations of woody debris (WD), shrub plantings, and shade shelters (SS) on top of the transferred topsoil. Five 12.5 × 10 m treatment blocks were established in each of three recipient sites, which included two post-agricultural reforestation sites, and one abandoned gravel pit site. Each treatment blocks received forest topsoil and a combination of additional treatments. Treatment and control plots were sampled for all vascular species in spring and summer. Native forest plant species richness in topsoil recipient plots was similar (p > 0.05) to that of mature donor forest sites, and significantly higher (p < 0.05) than that of passive control plots in the recipient sites. The plant community composition of all topsoil recipient plots had also become more like the donor forests and less like recipient site controls. Only the unplanted gravel pit-site increased in non-native ruderal plant species after topsoil transfer. The addition of WD, shrub plantings, or SS had no significant effect after two growing seasons. We recommend that topsoil should when possible be added where trees have already been planted, allowing for shorter time to canopy closure and thereby higher survival of shade-adapted understory species.     

Revegetation Methods for High-Elevation Roadsides at Bryce Canyon National Park, Utah

Establishment of native plant populations on disturbed roadsides was investigated at Bryce Canyon National Park (BCNP) in relation to several revegetation and seedbed preparation techniques. In 1994, the BCNP Rim Road (2,683–2,770 m elevation) was reconstructed resulting in a 23.8‐ha roadside disturbance. Revegetation comparisons included the influence of fertilizer on plant establishment and development, the success of indigenous versus commercial seed, seedling response to microsites, methods of erosion control, and shrub transplant growth and survival. Plant density, cover, and biomass were measured 1, 2, and 4 years after revegetation implementation (1995–1998). Seeded native grass cover and density were the highest on plots fertilized with nitrogen and phosphorus, but by the fourth growing season, differences between fertilized and unfertilized plots were minimal. Fertilizers may facilitate more rapid establishment of seeded grasses following disturbance, increasing soil cover and soil stability on steep and unstable slopes. However the benefit of increased soil nutrients favored few of the desired species resulting in lower species richness over time compared to unfertilized sites. Elymus trachycaulus (slender wheatgrass) plants raised from indigenous seed had higher density and cover than those from a commercial seed source 2 and 4 years after sowing. Indigenous materials may exhibit slow establishment immediately following seeding, but they will likely persist during extreme climatic conditions such as cold temperatures and relatively short growing seasons. Seeded grasses established better near stones and logs than on adjacent open microsites, suggesting that a roughened seedbed created before seeding can significantly enhance plant establishment. After two growing seasons, total grass cover between various erosion‐control treatments was similar indicating that a variety of erosion reduction techniques can be utilized to reduce erosion. Finally shrub transplants showed minimal differential response to fertilizers, water‐absorbing gels, and soil type. Simply planting and watering transplants was sufficient for the greatest plant survival and growth.     

Seed bank survival of an invasive species,but not of two native species,declines with invasion

Soil-borne seed pathogens may play an important role in either hindering or facilitating the spread of invasive exotic plants. We examined whether the invasive shrub Lonicera maackii (Caprifoliaceae) affected fungi-mediated mortality of conspecific and native shrub seeds in a deciduous forest in eastern Missouri. Using a combination of L. maackii removal and fungicide treatments, we found no effect of L. maackii invasion on seed viability of the native Symphoricarpos orbiculatus (Caprifoliaceae) or Cornus drummondii (Cornaceae). In contrast, fungi were significant agents of L. maackii seed mortality in invaded habitats. Losses of L. maackii to soil fungi were also significant in invaded habitats where L. maackii had been removed, although the magnitude of the effect of fungi was lower, suggesting that changes in soil chemistry or microhabitat caused by L. maackii were responsible for affecting fungal seed pathogens. Our work suggests that apparent competition via soil pathogens is not an important factor contributing to impacts of L. maackii on native shrubs. Rather, we found that fungal seed pathogens have density-dependent effects on L. maackii seed survival. Therefore, while fungal pathogens may provide little biotic resistance to early invasion by L. maackii, our study illustrates that more work is needed to understand how changes in fungal pathogens during the course of an invasion contribute to the potential for restoration of invaded systems. More generally, our study suggests that increased rates of fungal pathogen attack may be realized by invasive plants, such as L. maackii, that change the chemical or physical environment of the habitats they invade.     

广西凭祥不同年龄红椎林林下植物物种多样性及其环境解释

林下植被作为森林生态系统的重要组成部分,其在调控森林群落结构和功能上发挥着至关重要的作用。从揭示人工林林下植物物种组成的关键控制因素的目标出发,以不同年龄红椎林灌木层和草本层的植物群落作为研究对象,采用野外调查和室内分析相结合的方法,重点探究林下植物物种组成与环境因子之间的关系及其关键控制因子。研究结果表明:不同年龄红椎林的林下植物物种组成存在明显差异;RDA结果表明,胸高断面积是影响灌木层物种组成的最主要因子,胸高断面积、坡度和海拔能显著影响影响草本层的物种组成;方差分解结果表明,所调查的生物和非生物因子分别解释灌木层和草本层物种组成变异的63%和47%,微环境和植物之间的相互作用是影响林下植物群落物种变异的最主要因素,而土壤与微环境、土壤与植物两者之间,以及微环境、植物和土壤三者之间的相互作用对林下植物群落的物种组成的影响较小,甚至无影响,微环境的独立效应对林下植物物种组成的影响高于植物或土壤因素。     

Facilitation and herbivory during restoration of California coastal sage scrub

Using nurse plants to facilitate native plant recruitment in degraded habitats is a common restoration practice across various arid and semiarid environments. Living trees or shrubs are typically considered nurse plants, whereas dead shrubs left in the landscape from prolonged drought are understudied prospective facilitators for native plant recruitment. The interaction between nurse plants and biotic pressures, such as herbivory, on native recruitment is also not well understood in semiarid plant communities. We investigated the effects of facilitation and herbivory on native seedling germination, growth, and survival in the restoration of degraded coastal sage scrub (CSS) habitat. Native shrub seedlings (Artemisia californica and Salvia mellifera) were planted, and native annual species (Amsinckia intermedia, Deinandra fasciculata, Phacelia distans, and Pseudognaphalium californicum) were sown in three Shrub Type treatments (live shrub, dead shrub, and exposed areas), with a nested Cage treatment (no cage and cage) in each Shrub Type treatment. Annual species grew equally well in all Shrub Type treatments; shrub seedlings grew largest in exposed areas. While there was little evidence of facilitation for all species tested, there were strong positive effects of caging on growth and establishment of all species. Caging palatable native species or planting species with anti‐herbivory traits around target plants may be more strategic approaches compared to using nurse plants in restoring degraded CSS after extended drought.     

杉木人工林林下植物多样性及其环境对不同间伐强度的短期响应

以江西省官山林场的杉木人工林为研究对象,探究不同间伐强度（0%、20%、40%）物种多样性、地上生物量、林分光环境和土壤理化性质及其之间的相关性。结果表明：（1）林下物种数量随间伐强度的增加而增加,林下灌木层优势种不断变化,而草本层一直不变。（2）林下植物各多样性指数均随间伐强度的增大而增大,除Margalef指数外,其余各指数均在间伐40%与未间伐间呈显著差异。（3）灌木层地上生物量占总生物量的主体,且随间伐强度的增大而增大,不同间伐强度间差异显著,而草本层却呈相反趋势。（4）叶面积指数随间伐强度的增加而下降,冠层开度、林下直射光、散射光、总光照随之上升,但仅在间伐40%后显著。（5）土壤全氮含量间伐后显著上升,但土壤磷、钾、有机质含量均显著下降（6）灌木层多样性指数与灌木层地上生物量、土壤全氮呈显著正相关,与草本层地上生物量、速效磷、全钾含量呈显著负相关。草本层多样性指数与冠层开度、林下直射光、林下散射光、林下总光照呈显著正相关,与草本层地上生物量、叶面积指数呈显著负相关。总之,林下植物地上生物量、土壤化学性质是影响灌木层多样性指数变化的主要控制因子,林分光环境是影响草本层的主要控制因子。就本研究3种间伐强度而言,该地杉木人工林的最适宜间伐强度为40%。     

林窗尺度对马尾松人工林林下灌草层优势种生态位的早期影响北大核心CSCD

马尾松作为中国广泛栽植的乡土树种,其人工林群落结构简单和生物多样性低下是普遍存在的生态学问题。探究不同林窗尺度对马尾松人工林林下植被群落的影响,可为马尾松人工林近自然经营提供理论依据。该研究在45 a生马尾松人工林中分别设置A(50 m^(2))、B(100 m^(2))、C(200 m^(2))和D(667 m^(2))4种不同尺度的林窗,以不做任何处理的马尾松人工林作为对照(CK),探究采伐开窗后林窗内自然更新1 a后的灌草层植物组成、优势种生态位宽度和生态位重叠度分布特征。结果显示:(1)除100 m^(2)林窗下灌木层物种数与对照无显著差异外,其余林窗灌草层物种数均显著高于对照(P<0.05),且200 m^(2)林窗下灌草层物种数均最多,分别为35种和20种;4种林窗下灌草层物种丰富度指数较对照均显著增加(P<0.05),最大值均出现在200 m^(2)林窗下,其值分别为对照的1.5倍和2.6倍。(2)林窗增加了灌草层喜光植物种类,且在200 m^(2)林窗下种类最多,灌木层喜光植物有13种,草本层喜光植物有5种。(3)4种林窗下灌草层优势种中,喜光植物生态位宽度均较大,200 m^(2)林窗下灌草层生态位宽度平均值最小,其对资源利用程度低,重要值与生态位宽度之间无显著相关性(P>0.05)。(4)4种林窗下灌草层优势种间生态位重叠度指数均较小。667 m^(2)林窗下,灌草层优势种平均生态位重叠度指数最小,分别为0.029和0.024,200 m^(2)林窗下灌草层优势种高生态位重叠度占总数比例最大,分别为20%和23.8%。研究表明,采伐开窗促进了马尾松人工林林下植被发育,丰富了林下植物多样性,有利于马尾松林稳定持续发展,对精准提升马尾松人工林质量具有重要意义。     

湖南栎类天然次生林林分空间结构对灌木物种多样性的影响

林分空间结构会显著影响其林下植被多样性,为明确其影响灌木物种多样性的关键因子,以栎类天然次生林为研究对象,利用Pearson简单相关分析、多元线性逐步回归法与典型相关分析探索乔木层空间结构与林下灌木物种多样性的相关关系,为保护林下植被多样性提供生态经营建议。以混交度、聚集指数和开敞度表达林分空间结构,以Margalef指数、Pielou指数和AuclairGoff指数作为灌木物种多样性评价指标,利用3种统计分析方法分析两者之间的相关关系,研究结果表明:(1)Pearson相关分析结果显示混交度对灌木层Pielou指数和AuclairGoff指数影响显著(P0.05),其余指数均不显著;(2)多元线性逐步回归分析结果显示林下灌木物种多样性受到多个林分空间指标的综合影响,其中Pielou指数受到混交度、聚集指数和开敞度的显著影响,AuclairGoff指数受到混交度与开敞度的显著影响;(3)典型相关分析结果显示,第一对典型相关变量通过显著性检验,典型相关系数为0.5427,林分空间结构与灌木层多样性指标两组变量在整体上相关性较强,其中混交度是影响力最大的变量。因此,欲提高栎类天然次生林下灌木物种多样性,应选择以调整树种结构为主,综合考虑林木空间分布格局的调整方案。     

Exotic Lonicera species both escape and resist specialist and generalist herbivores in the introduced range in North America

The enemy release hypothesis predicts that invasive plant species may benefit from a lack of top-down control by co-evolved herbivores, particularly specialists, in their new range. However, to benefit from enemy escape, invasive plants must also escape or resist specialist or generalist herbivores that attack related species in the introduced range. We compared insect herbivore damage on the exotic shrub, Lonicera maackii, the native congener Lonicera reticulata, and the native confamilial Viburnum prunifolium in North America. We also compared the laboratory preference and performance of a North American honeysuckle specialist sawfly (Zaraea inflata) and the performance of a widespread generalist caterpillar (Spodoptera frugiperda) on cut foliage from native and exotic Lonicera species. L. maackii received significantly lower amounts of foliar herbivory than L. reticulata across three seasons, while damage levels observed on V. prunifolium for two seasons was generally intermediate between L. reticulata and L. maackii. The specialist sawfly damaged L. reticulata heavily, but was not detected on L. maackii in the field. There were few statistical differences in the performance of sawfly larvae on L. reticulata and L. maackii, but the sawfly achieved higher pupal masses on L. reticulata than on L. maackii, and they strongly preferred L. reticulata over L. maackii when given a choice. The sawfly was unable to complete development on native L. sempervirens and non-native L. japonica. In contrast, the generalist caterpillar performed similarly on all Lonicera species. While L. maackii experienced little herbivory in the field compared to native relatives in the same habitat, laboratory assays indicate L. maackii appears to be a suitable host that escapes selection by the specialist, but L. japonica and L. sempervirens are highly resistant to it. These findings indicate that both enemy escape and resistance (to a specialist, but not a generalist herbivore) may contribute to the success of exotic Lonicera species.     

Context dependency of the allelopathic effects of Lonicera maackii on seed germination

Allelopathic effects of invasive plants on native flora may be mitigated by the abiotic and biotic environment into which the allelochemicals are released. Lonicera maackii (Amur honeysuckle), an invasive plant of the eastern deciduous forest, suppresses seed germination in laboratory assays. We investigated how L. maackii leachate interacts with abiotic conditions and with the soil microbial community. First, we tested the effects of leaf extract from L. maackii on germination of the native woodland herb, Blephilia hirsuta, under different light and soil conditions. We found that germination of Blephilia hirsuta was reduced by L. maackii extract, but abiotic conditions did not interact with this effect. We also tested the effects of leaf extract on germination of five native woodland species and L. maackii placed in sterile or live soil. There was an overall suppressive effect of L. maackii extract on itself and the other five native species tested. However, L. maackii extract interacted with live soil in ways that differed with the species being tested and, in some cases, changed over time. Our results indicate that allelopathic potential of L. maackii shows context dependency with respect to soil microorganisms and native species identity but not to light conditions or soil type. Our results imply that restoration of invaded areas may require active reintroduction of species sensitive to allelopathy in live soil. Further, laboratory assays of allelopathy should consider the interaction of allelochemicals with biotic and abiotic conditions to more accurately predict the impacts of allelopathy on plant communities.     

Competitive effects of the invasive shrub,Lonicera maackii (Rupr.) Herder (Caprifoliaceae), on the growth and survival of native tree seedlings

Invasive plants are often associated with reduced cover of native plants, but rarely has competition between invasives and natives been assessed experimentally. The shrub Lonicera maackii, native to northeastern Asia, has invaded forests and old fields in numerous parts of eastern North America, and is associated with reduced tree seedling density in Ohio forests. A field experiment was conducted to test the effects of established L. maackii on the survival and growth of transplanted native tree species. The experiment examined above-ground competition (by removing L. maackii shoots) and below-ground competition (by trenching around transplanted seedlings). The effects of above-ground competition with L. maackii were generally more important than below-ground competition, though both were detected. Shoot treatment was the key determinant for the survival of all species except P. serotina, whereas trenching only enhanced survival for A. saccharum caged and P. serotina, and only in the shoot removal treatment. For the surviving seedlings, L. maackii shoot removal increased growth of A. saccharum seedlings protected with cages, but actually reduced the growth of unprotected Q. rubra and A. saccharum seedlings, indicating that L. maackii shoots confer some protection from deer browsing. Significant interactions between root and shoot treatment on Q. rubra growth parameters, specifically greatest growth in the shoot present & trenched treatment, is attributed to protection from deer browsing combined with release from below-ground competition. Despite this protective function of L. maackii shoots, the overall effect of this invasive shrub is increased mortality of native tree seedlings, suggesting it impacts the natural regeneration of secondary forests.     

我国南方4种常见人工林林下植物多样性特征及影响因素

为了解长期植被恢复的成熟人工林林下植物组成与多样性特征及其影响因素,基于广东鹤山生态系统国家野外科学观测研究站的南亚热带人工林生态系统,对环境相似(坡度、坡向、海拔)、30 a生4种类型人工林(桉树混交林、马占相思纯林、乡土混交林、针叶混交林)进行调查研究,分析林下植物组成和物种多样性(Shannon-Wiener指数、Simpson指数、Pielou指数)特征。结果表明,人工林林下植物类型丰富,均可形成乔-灌-草垂直结构;4种林型林下植物组成既有相似性,也有差异性,桉树混交林与针叶混交林、马占相思纯林与乡土混交林的灌木层组成相似;桉树混交林与马占相思纯林、乡土混交林与针叶混交林的草本层组成相似,而桉树混交林与针叶混交林的草本层组成极不相似。林分类型影响林下植物多样性,马占相思纯林林下灌草多样性显著低于其他3种混交林(P<0.05),灌木物种数、个体数最少;针叶混交林林下物种丰富度最高。林分郁闭度与林下植物多样性呈正相关(P<0.001),林下植物分布与土壤养分含量相关,桉树混交林、马占相思纯林林下植物多样性与不同形态氮含量相关,有效磷、全磷影响乡土混交林林下物种的分布,针叶混交林受土壤酸碱度、全钾的影响较为明显。在4种人工林林下植物群落中,乡土混交林多样性,均匀度最高,优势度最低,具有更佳的保育和维持林下生物多样性功能。因此,乡土树种混交林更适用于生态公益林构建或对一些针叶林及外来树种纯林进行林分改造。