The potential for forest canopy litterfall interception by a dense fern understorey, and the consequences for litter decomposition

Most studies on litter decomposition have assumed that all falling plant litter reaches the ground where it then decomposes. In many forests a proportion of this litter may in fact be intercepted by understorey vegetation, but the ecological significance of this remains poorly understood. We performed two experiments in a temperate rainforest in southern New Zealand, in which there was a dense understorey of the crown fern Blechnum discolor. The fronds of this fern originate from a crown, and have a funnel‐like arrangement that can trap falling litter and prevent it from reaching the ground. The first experiment measured the effects of ferns on the spatial distribution of litter accumulation over one year. The ferns intercepted a substantial proportion of the total litterfall, and the fern crowns (from which the fronds originate) retained 10% of the total incoming litterfall (despite occupying only 2% of the ground area). The retained litter had a substantially higher ratio of twig to foliar litter than did the incoming litterfall. Further, much of the litter not retained on the crowns of the ferns accumulated at the base of the fern trunks. The second experiment considered litter decomposition in fern crowns versus the ground under the ferns. The litter that had accumulated in the crowns was characterized by higher microbial basal respiration and active microbial biomass than was the litter that had accumulated on the ground. The use of litterbags revealed that litter decomposition rates were significantly higher on the fern crowns than on the ground at 30 cm and 60 cm from the fern trunks. These results show that litter interception ameliorates the decomposer environment and increases the rate of litter decomposition. In total, this study provides evidence for understorey ferns greatly influencing both the spatial distribution of litterfall and the decomposition of plant litter. Although the ecological role of understorey vegetation in forested ecosystems has received little attention to date, our results point to understorey species as an important driver of forest ecosystem processes.     

地形对桂西南喀斯特山地森林地表植物多样性及分布格局的影响

利用协方差分析、曲线回归拟合及典范对应分析(CCA),研究了地形因子对桂西南喀斯特森林地表植物多样性及不同生长型地表植物分布格局的影响.结果表明： 共调查到152种地表植物,其中,蕨类植物37种、草本44种、藤本9种、灌木62种;协方差分析显示,海拔与地表植物个体数和丰富度显著相关,坡向对地表植物丰富度具有显著影响;地表植物的个体数和丰富度与海拔梯度存在显著的非线性相关性;CCA分析显示,坡向对蕨类植物的分布格局影响显著,坡度对草本、藤本和灌木的分布格局影响显著.蕨类植物对坡向引起的水热条件改变响应更为敏感,坡度对土壤水分、养分的作用大于高程,是影响本区域草本、藤本和灌木3种地表植物分布的主要地形因子.     

Competitive Interactions among First‐Year and Second‐Year Plants of the Invasive,Biennial Garlic Mustard (Alliaria petiolata) and Native Ground Layer Vegetation

We studied the effects of hand weeding of second‐year plants of the biennial garlic mustard (Alliaria petiolata) on first‐year plants (seedlings) and native ground layer vegetation. Garlic mustard is a Eurasian species that has invaded deciduous forest ground layers in eastern North America. Treatments consisted of a control and an early or late weeding of second‐year garlic mustard. The early treatment (early March) was applied before garlic mustard seeds had germinated and when most native species were dormant. The late treatment (mid‐May) occurred after plants had bolted, flowering was occurring, and most native species and new garlic mustard seedlings were actively growing. Pre‐treatment data were obtained in 2004 and treated and control plots were sampled in 2005, 2006, and 2007. No significant treatment effects were observed in 2004 or 2005. In 2006, mean cover of first‐year plants was higher in the early weeding treatment than in the late weeding treatment and control. In 2007, mean cover of first‐year garlic mustard was higher in the control than in either of the two weeding treatments. There were no significant treatment effects in any year on native vegetation cover, bare ground, or the five most abundant native species. Our data indicate that (1) late weeding of garlic mustard provided more effective control than early weeding because late weeding allows second‐year plants to compete with garlic mustard seedlings for a longer period of time and (2) competition between first‐ and second‐year plants is responsible for alternating dominance of first‐year and second‐year garlic mustard plants.     

Successful biological control of mist flower (Ageratina riparia) in New Zealand: Agent establishment, impact and benefits to the native flora

The white smut fungus (Entyloma ageratinae) and the gall fly (Procecidochares alani) were released in New Zealand in 1998 and 2001 respectively to suppress mist flower (Ageratina riparia). The fungus established and spread rapidly, crossing 80 km of sea to Great Barrier Island within 2 years. The mean number of P. alani galls increased exponentially to 1.96/stem at release sites, but dispersal was slow. The impact of the biocontrol agents was monitored once annually from 1998/99 to 2003/04, at up to 51 sites in the North Island. The mean percentage of live leaves infected with fungus rapidly reached nearly 60%. Maximum plant height declined significantly. In heavy infestations, mean percentage cover of mist flower declined from 81 to 1.5%. Galls were only recorded towards the end of the impact study, and at low mean numbers. As mist flower declined, the species richness and mean percentage cover of native plants increased. In contrast, the species richness and mean percentage cover of exotic plants (excluding mist flower) did not change significantly. Many plant species colonizing the plots were important native mid- or late-successional shrubs or trees. With few exceptions, the exotic plant species common in the plots were not weeds that appeared to threaten native forest habitats. There was only a weak “replacement weed effect” from the potentially serious invader African club moss (Selaginella kraussiana). These data, together with reports of reduced threats to rare endemic plants from mist flower, suggest this rapid, well-monitored weed biocontrol program was very successful.     

贵州东部常绿落叶阔叶混交林碳素积累及其分配特征

以雷公山自然保护区常绿落叶阔叶混交林为研究对象,对其碳素含量、碳密度及分配特征进行了研究。结果表明:生态系统碳素含量表现为乔木层(418.58 g/kg)灌木层(387.26 g/kg)草本层(382.80 g/kg)枯落物层(378.11 g/kg)土壤层(31.48 g/kg),差异极显著(P﹤0.01),乔木不同器官表现为干根叶枝,差异不显著(P0.05),灌、草层均表现为地上地下,土壤碳素含量随土层深度的增加而减少;生态系统碳密度为234.68 t/hm2,表现为土壤层(170.00 t/hm2)乔木层(57.02 t/hm2)枯枝落叶层(5.48 t/hm2)灌木层(1.81 t/hm2)草本层(0.37 t/hm2),分别占生态系统碳密度的72.44%、24.30%、2.34%、0.77%和0.16%;植被层碳密度为58.79 t/hm2,占了生态系统碳密度的25.09%;乔木层各器官以树干的碳密度最高,占了乔木层碳密度52.43%;灌木层、草本层地上部分碳密度分别是地下部分的2.85倍1.64倍;土壤表层(0—20 cm)碳密度为70.40 t/hm2,显著高于其它各层(P﹤0.001),占了土壤(0—80 cm)碳密度的41.41%,有很强的表聚性,因此,防止地表的水土流失,可有效保持土壤对碳的吸存。     

Contrasting Predictors of Fern versus Angiosperm Decomposition in a Common Garden

We evaluated differences in the rates and correlates of decomposition among 32 fern and angiosperm litter types collected in Hawai'i. Leptosporangiate ferns were separated into groups based on phylogeny: 'polypod' ferns, a monophyletic clade of ferns that diversified in the Cretaceous, and all other ('non-polypod') ferns that diversified earlier. We measured initial litter chemistry (nutrients and carbon chemistry), and mass loss and nitrogen (N), phosphorus (P), and calcium (Ca) of litter tissue during a 1-yr incubation in a common garden. Nutrient concentrations and carbon (C) chemistry differed significantly among litter types, and litter turnover ( k -values) ranged from 0.29 to 8.31. Decomposition rates were more closely correlated with nutrient concentration than is typically observed. Lignin:N was the best predictor of decomposition across all litter types combined; however, among plant groups different predictors of decomposition were important. Nitrogen and P concentrations best predicted fern decomposition, whereas C chemistry, particularly lignin concentration, was more important for angiosperm (monocot and dicot) decomposition. Among native plants, non-polypod ferns decomposed significantly more slowly than both polypod ferns and angiosperms. Contrary to our hypothesis, fern litter did not decompose more slowly than angiosperm litter overall. Nutrient dynamics in litter were affected by initial litter concentration more than phylogeny; low-nutrient litter immobilized more nutrients than high-nutrient litter. Systematic differences in rates of decomposition, and the importance of nutrients in predicting fern decomposition, imply that changes in species composition within ferns and between ferns and angiosperms could influence the functioning of ecosystems where ferns are important forest components.     

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.     

Rapid nutrient cycling in leaf litter from invasive plants in Hawai’i

Physiological traits that contribute to the establishment and spread of invasive plant species could also have impacts on ecosystem processes. The traits prevalent in many invasive plants, such as high specific leaf areas, rapid growth rates, and elevated leaf nutrient concentrations, improve litter quality and should increase rates of decomposition and nutrient cycling. To test for these ecosystem impacts, we measured initial leaf litter properties, decomposition rates, and nutrient dynamics in 11 understory plants from the Hawaiian islands in control and nitrogen + phosphorus fertilized plots. These included five common native species, four of which were ferns, and six aggressive invasive species, including five angiosperms and one fern. We found a 50-fold variation in leaf litter decay rates, with natives decaying at rates of 0.2–2.3 year^–1 and invaders at 1.4–9.3 year^–1. This difference was driven by very low decomposition rates in native fern litter. Fertilization significantly increased the decay rates of leaf litter from two native and two invasive species. Most invasive litter types lost nitrogen and phosphorus more rapidly and in larger quantities than comparable native litter types. All litter types except three native ferns lost nitrogen after 100 days of decomposition, and all litter types except the most recalcitrant native ferns lost >50% of initial phosphorus by the end of the experiment (204–735 days). If invasive understory plants displace native species, nutrient cycling rates could increase dramatically due to rapid decomposition and nutrient release from invasive litter. Such changes are likely to cause a positive feedback to invasion in Hawaii because many invasive plants thrive on nutrient-rich soils.     

城市绿化植物-凋落物-土壤系统碳氮磷化学计量特征研究

以福建福州市常见的15种乔木、灌木和草本绿化植物为对象,连续2年取样测定了这些植物、凋落物、立地土壤、土壤微生物量C、N、P含量,探讨城市绿化植物-凋落物-土壤系统生态化学计量特征,为中国城市绿化植物的生态功能恢复与植被重建提供科学依据。结果表明:(1)绿化植物不同器官C、N、P含量均表现为草本灌木乔木、C含量N含量P含量、叶茎根,呈现出叶的富集作用;绿化植物各器官化学计量比(C/N、C/P、N/P)也表现出基本一致的乔木灌木草本的变化趋势;各绿化植物对N的再吸收率极显著高于对P的再吸收率(P0.01),绿化植物N和P再吸收率表现为乔木灌木草本,不同绿化植物对N的再吸收率差异均显著(P0.05),对P的再吸收率差异均不显著(P0.05)。(2)绿化植物凋落物C、N、P含量基本表现为草本灌木乔木,其中不同绿化植物凋落物P含量差异不显著。(3)绿化植物立地土壤C、N、P含量表现为草本灌木乔木,但其N/P差异不显著;土壤微生物量C、N、P含量基本表现为草本灌木乔木,其相应的C/N、C/P、N/P差异均不显著。(4)植物-土壤-凋落物-土壤微生物量(C、N、P)均随着生长季温度的升高而降低,随着年降水量的增加而升高,P素的回归系数绝对值明显低于C素和N素;植物-凋落物-土壤的C与N含量、N与P含量、C/P与N/P、以及土壤和植物的C/N与N/P之间均呈显著正相关关系,而凋落物的C/N与N/P之间呈显著负相关关系;典范对应CCA排序中,植物高度、冠幅、茎粗、比叶面积和叶面积指数对植物-凋落物-土壤-土壤微生物量C、N、P含量和C/N、C/P和N/P具有较大影响作用,其中高度、冠幅和茎粗与比叶面积和叶面积指数呈负相关关系,与凋落物-土壤-土壤微生物量C、N、P含量呈负相关关系,与植物C、N、P含量呈正相关关系;而凋落物-土壤-土壤微生物量C、N、P含量与其C/N、C/P和N/P均具有一定的正相关关系。     

Factors that shape the elevational patterns of plant diversity in the Yatsugatake Mountains,Japan

Elevation is involved in determining plant diversity in montane ecosystems. This study examined whether the distribution of plants in the Yatsugatake Mountains, central Japan, substantiated hypotheses associated with an elevational diversity gradient. Species richness of trees, shrubs, herbs, ferns, and bryophytes was investigated in study plots established at 200‐m elevational intervals from 1,800 to 2,800 m. The changes in plant diversity (alpha and beta diversities, plant functional types, and elevational ranges) with elevation were analyzed in relation to climatic factors and elevational diversity gradient hypotheses, that is, mass effect, mid‐domain effect, and Rapoport''s elevational rule. In addition, the elevational patterns of dominance of plant functional types were also analyzed. A comparison of alpha and beta diversities revealed that different plant groups responded variably to elevation; the alpha diversity of trees and ferns decreased, that of herbs increased, whereas the alpha diversity of shrubs and bryophytes showed a U‐shaped relationship and a hump‐shaped pattern. The beta diversity of shrubs, herbs, and bryophytes increased above the subalpine–alpine ecotone. In accordance with these changes, the dominance of evergreen shrubs and graminoids increased above this ecotone, whereas that of evergreen trees and liverworts decreased. None of the plant groups showed a wide elevational range at higher elevations. These elevational patterns of plant groups were explained by climatic factors, and not by elevational diversity gradient hypotheses. Of note, the changes in the dominance of plant groups with elevation can be attributed to plant–plant interactions via competition for light and the changes in physical habitat. These interactions could alter the elevational diversity gradient shaped by climatic factors.     

The distribution of the millipede Ommatoiulus moreleti (Diplopoda, Julida: Julidae) in relation to other Ommatoiulus species on the south-western Iberian Peninsula

Ommatoiuius moreleti (Lucas) occurs naturally in Portugal and Spain, and has been introduced to some Atlantic Islands, South Africa and southern Australia, where it is widespread and numerous.
In southern Portugal and south-west Spain, O. moreleti shares its range with O. oliveirae (Verhoeff), O. cingulatus (Attems) and several undescribed Ommatoiulus spp. In a study area where O. moreleti was confined to deep litter beneath Quercus trees, O. oliveirae predominated in litter of the bushes Cistus spp., while O. cingulatus was most numerous in an area dominated by grasses and herbs, but with little litter. The three species tended to eat different food items, but this probably reflected local availability rather than preference.
Ommatoiulus moreleti has a distinct western boundary which broadly corresponds with changes in the quantity of litter on the ground. The distribution of O. moreleti was related to the availability of deep litter, often provided by Pinus and Quercus trees, but also by dense shrubs and heath, and undisturbed grassland.
In addition to providing food, litter provides a refuge for O. moreleti. Grassland species such as O. cingulutus live where there is little litter, and probably have to dig deep in the soil to avoid summer desiccation and predation of immature stages. It is suggested that soil hardness and litter depth may be important determinants in the distribution of O. moreleti , and relative digging ability may explain the partitioning of the habitat between the three species studied.     

重庆喀斯特地区现代花粉组合与植被的关系

重庆喀斯特地区4种不同地貌单元的81份表土和苔藓样品的孢粉分析结果表明:(1)研究区植物孢粉组合共由109科属组成。除金佛山外,其他植被退化严重地区样点均以草本和蕨类植物占据优势(剔除石漠化治理大量引种的马尾松、柳杉和侧柏等乔木花粉),其次是乔木植物花粉(主要为马尾松),灌木植物花粉含量很低,显示该区植被退化严重;(2)孢粉组合的PCA分析能够很好地将研究区的现代孢粉组合区分开来,较好地反映了重庆喀斯特地区不同地貌单元的植被特征,特别是石漠化区植被退化严重的孢粉组合特征。生态保护较好、自然植被发育的金佛山地区具有106科属的乔木、灌木与草本孢粉类型,以及高含量的乔木花粉,而喀斯特石漠化地区的鸡公山(46科属)、青木关镇(56科属)和南平镇(50科属)则表现为乔灌木孢粉类型较少;(3)银杉作为金佛山特有的孑遗植物,其花粉含量明显低于松属花粉,说明其花粉不利于远距离传播;(4)随着土地利用强度的增加,现代孢粉组合中乔灌木花粉含量和种类越少,草本和蕨类植物孢粉含量越多,且以耕地杂草为主。因此,土地利用方式的变化是喀斯特石漠化区次生植被及其现代孢粉组合变化的主要影响因素。研究可为重庆喀斯特地区土地利用策略的制定,重庆及其周边地区第四纪古植被、古气候和古环境重建研究,以及中国孢粉数据库建设提供基本数据和科学依据。     

Effects of re‐introducing fire to a central Florida sandhill community

Abstract. A southern ridge sandhill site in central Florida, USA, was burned in 1989, 1991, and 1995 after 63 years of fire‐suppression to simulate a pre‐settlement fire regime. Fire changed species abundance and vegetation structure but caused only minimal changes in species turnover and diversity. There was a general trend for an increase in the cover of herbs following fire but this was a statistically significant effect for only one species, Liatris tenuifolia var. tenuifolia. Aristida beyrichiana increased, litter cover and litter depth were significantly reduced, and ground lichens were eliminated in response to burning. Scrub oaks and palmettos in the ground cover and small shrub layers (height ≤ 1 m) either increased or did not respond to burning, reflecting strong post‐fire resprouting. Diversity in the ground cover and small shrub layers were not affected by fire. Scrub oaks and palmettos in the large shrub and overstorey layers (height > 1 m) were reduced in density, basal area, and longest canopy measurements in response to fire. Species diversity also decreased within these layers following fire. Some Pinus elliottii var. densa survived fire, but their density was reduced. All Pinus clausa were eliminated by fire. Periodic burning can suppress the dominance of shrubs (Quercus spp.) while increasing the cover of grasses and herbs in southern ridge sandhill vegetation.     

Vegetation factors influencing the establishment and growth of the endangered Japanese orchid,Cypripedium macranthos var. rebunense

Cypripedium macranthos var. rebunense is a well-known endangered terrestrial orchid that is endemic to the cool-temperate Rebun Island off the coast of northwestern Hokkaido, Japan. The present study aimed to identify suitable methods for conservation of this orchid through management of the natural vegetation. We analyzed the vegetation types and plants growing sympatrically with this orchid using two-way indicator species analysis (TWINSPAN) and detrended correspondence analysis (DCA) ordination. Reproductive orchids can survive in various broad-leaved and short to medium-height herbaceous meadows with high plant species richness at a small scale in coastal regions. In order to maintain C. macranthos var. rebunense populations, succession to dense and tall large-leaved herbs, Sasa scrub, shrubs, and trees, should be suppressed. Favorable vegetation for the establishment of seedlings of this orchid includes narrow-leaved, medium-sized grasses, sedges, herbs, mosses, and prostrate mat-forming shrubs. The ground cover offered by these plants and their litter may favor stability of moisture, temperature, and suitable light conditions at the ground surface. In situ seed sowing at such ‘safe sites’ is a potential low-impact technique to enhance seedling recruitment of this orchid.     

Effects of weed abundance and frequency of hand weeding on the establishment of transplanted Imperata cylindrica

Imperata cylindrica is an important component of grasslands in several Asian countries. Its vigorous rhizome elongation enables the plant to quickly cover bare ground, making it a candidate for revegetation projects. In these projects, initial and subsequent management practices often differ. Initial management strategies are important for encouraging rapid cover by the target species. We tested the effects of initial hand weeding on I. cylindrica cover and weed growth over 2 years. Two types of soil (A and B) were scattered on a recently constructed river embankment at a depth of 10 cm. Both soils A and B are nutrient-poor and high (> 7.0) pH. Plots were hand-weeded once or twice a year (W₁ and W₂ treatments, respectively), or mowed but not weeded (M treatment) with four replications. Plug plants of I. cylindrica were introduced. I. cylindrica became dominant in soil A with the W₂ treatment, with 50% cover in year 2. Conversely, I. cylindrica failed to establish in soil B regardless of treatment, due to dominance of the weed Sorghum halepense. Soil B included creeping rhizomes of S. halepense, and vigorous growth from rhizomes is likely a major reason for its predominance. S. halepense seedlings germinated in both soils, but were successfully eradicated when weeded at less than 1 month of age. Thus, for successful revegetation, land managers should use soil that does not contain creeping rhizomes of S. halepense. If rhizomes are not present, hand weeding twice a year for 2 years is sufficient for establishment of I. cylindrica.

     

Loss of flower bud vigour in the Mediterranean shrub,Cistus albidus L. at advanced developmental stages

To better understand aging in perennials, age‐related changes in the physiology of leaves and flower buds of the Mediterranean shrub, Cistus albidus L. were evaluated. Two groups of different ages (5 and 10 years old), both at advanced developmental stages but of similar size, were compared. Total plant biomass, biomass produced per apical meristem and levels of cytokinins, abscisic acid and jasmonic acid in leaves and flower buds, as well as flower production, were measured. No differences in plant size, vegetative growth rates and levels of phytohormones in leaves were observed between 5‐ and 10‐year‐old plants. However, they showed significant differences in flower bud development; the older plants having reduced vigour, with 29.6% of flowers reaching anthesis compared to 52.5% in the younger plants. Furthermore, endogenous concentrations of zeatin and abscisic acid in flower buds at stage I (start of flower organ formation) were 61% and 41%, respectively, smaller in 10‐ than in 5‐year‐old plants. At stage II (with all flower organs formed), zeatin and abscisic acid concentrations decreased by ca. 90% and 80%, respectively, but differences between age groups were still evident (60% and 29% for zeatin and abscisic acid, respectively). Jasmonic acid levels in flower buds decreased by 80% from stage I to II, but did not differ between age groups. Despite reductions in flower bud vigour, total number of flowers per individual was not significantly different between age groups, so that an age‐related loss in reproductive vigour at the organ level did not lead to a decrease in flower production at the whole plant level.     

华南地区花镜植物资源筛选评价及应用研究

为营造物种多样、季相丰富、景观优美的生态经济型花镜,筛选出一批适合于华南地区花镜景观营造的植物种类,并采用层次分析法进行综合评价。结果表明,适合华南地区花镜景观营造的植物305种,隶属于84科221属,主要有爵床科（Acanthaceae）、豆科（Fabaceae）、菊科（Asteraceae）、石蒜科（Amaryllidaceae）等,小乔木、灌木、草本和藤本植物分别有16、127、134和28种;乡土植物100种,占32.79%,外来植物205种,占67.21%。综合评价分析表明,Ⅰ级、Ⅱ级和Ⅲ级花镜植物分别有148、151和6种;层次分析表明,前景植物、中景植物和背景植物分别有106、162和157种;季节分析表明,春、夏、秋和冬季植物分别有216、232、195和128种。这表明可用于华南地区花镜景观营造的灌木和草本植物资源丰富,应用形式多样。     

Plant species richness under

Exotic pine plantations constitute a significant landscape feature in the North Island of New Zealand but their conservation value for native plant species is not often documented. Pine stem density, height and basal area of nine plantations of Pinus radiata ranging in age from 6 to 67 years in Kinleith Forest was determined. Pines reached heights of 60 m, and stand basal areas up to 183 ± 14 m(2)ha(-1). The abundance of woody shrubs, tree ferns and ground ferns was assessed in each stand. Understorey composition of shrubs and ferns was reflected on the first two axes of DCA ordinations and correlated with the age of the pines. Adventive shrubs predominated in stands < 20 years old. Light-demanding native shrubs with bird dispersed fruits predominated in older stands, with more shade-tolerant species in the oldest site. Species richness increased rapidly in the first 11 years, but thereafter more slowly. Twelve native shrub species and 22 ferns were recorded from the most diverse stands. Richness and species composition were related to stand age, and probably also to topographical heterogeneity and aspect. Tree ferns reached densities of 2000—2500 ha(-1) and basal areas of 20—30 m(2)ha(-1) in the older stands. Initially the tree fern population was strongly dominated by Dicksonia squarrosa, which comprised 84% of individuals overall. Five species were present by 29 years. The faster growing Cynthea medullaris and C. smithii achieved greater heights than the Dicksonia spp., and their relative biomass was greatest in the oldest stands.     

Non-native and native shrubs have differing impacts on species diversity and composition of associated plant communities

The spread of non-native plants has been depicted as a serious threat to biodiversity. However, it remains unclear whether the indigenousness of the invading plant plays a marked role for the ecological consequences of an invasion as few studies have compared the ecological impacts of non-native shrubs with structurally or functionally comparable native shrubs. We studied patches of introduced and native shrubs to assess whether there are general differences in plant species composition or biomass between patches formed by non-native versus native shrubs. The indigenousness of the shrub (non-native vs. native) did not explain the variation in soil nutrients, neither the production of shoot biomass or allocation of growth to different parts of the shoot. The amount of light reaching ground level did not differ between patches of a non-native and a native shrub. However, species richness and biomass of herbaceous plants were lower in patches of non-native than native shrubs and the amount of litter was higher below non-native than native shrubs. Our results suggest that the indigenousness of the patch-forming plant may be an important factor for the diversity and composition of associated herbaceous vegetation. Based on our results, resource availability (light and nutrients) is not a sufficient explanation for the negative effects of non-native shrubs on plant communities. Further research is needed to investigate whether alternative explanations, such as the novelty of the toxic compounds produced by non-native plants, can explain the differences we observed.     

Effectiveness of short‐tongued bees as pollinators of apparently ornithophilous New Zealand mistletoes

Abstract The flowers of two species of threatened New Zealand mistletoes (Peraxilla tetrapetala and Peraxilla colensoi, Loranthaceae) have explosive buds that do not open unless force is applied by birds or two species of native short‐tongued bees. Opened flowers are visited by a variety of birds and insects. Although both species of Peraxilla conform to a pollination syndrome of ornithophily, bees may be effective alternative pollinators. We investigated the effectiveness of bees and birds as pollinators of P. colensoi at one site and P. tetrapetala at two sites in the South Island. Bees and other insects outnumbered birds as flower visitors at all three sites. By excluding birds with wire cages, we showed that two bee species regularly open flowers of P. tetrapetala, but only rarely open flowers of P. colensoi. Few pollen grains were deposited when either birds or bees opened buds, so opening buds was not by itself sufficient for adequate pollination. Instead, pollen continued to accumulate over the next 6 or 7 days, even inside cages that excluded birds. Both populations of P. tetrapetala were regularly pollen‐limited, but in different ways. At Ohau, opened flowers gained enough pollen to produce seeds, but many buds were not opened and hence failed to set seed. In contrast, at Craigieburn, nearly all buds were opened, but many of these did not receive enough pollen. These results demonstrate that native bees can partially replace birds as pollinators of mistletoes, despite their apparent ornithophilous syndrome. Ongoing reductions in New Zealand forest bird numbers means that the service bees provide may be important for the long‐term future of these plants.