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  • Volume 10 Issue 6
    The view near the experiment site: the Gongga Mountains (29°20′–30°20′N, 101°30′–102°15′E, 7556 m a.s.l.), which is located in the southeastern fringe of the Tibetan Plateau in China. The picture was taken on 19 December 2014, when conducting the stem CO2 efflux rate measurement. Photo was taken by Guang Zhao. See Zhao et al. 1001–1011.
      
    Research Articles
    Patrick Addo-Fordjour, Zakaria B. Rahmad, Robyn J. Burnham
    2017, 10 (6): 883-894.
    Abstract ( 71 )   PDF   Save
    Aims Liana research has increased in the past two decades, yet there is still inadequate comparison of liana communities at a cross-continental scale. We compared liana assemblages in tropical forest ecosystems of Ghana and Malaysia, thereby determining patterns and mechanisms that are common or unique to the regions.
    Methods Liana diversity, community structure and taxonomic composition were determined in 60 plots of 40×40 m 2 in three forest types (primary, disturbed secondary, selectively logged) in each biogeographic area. Two traits, climbing mechanisms and dispersal modes were determined for all species and individuals via direct field observation and with published literature. Data were analyzed at biogeographic (using combined forest data) and forest-type levels.
    Important findings Both observed and rarefied–extrapolated species richness of lianas were significantly higher in Ghanaian forests compared to Malaysian forests. In most cases, species diversity indices (Shannon diversity index, Margalef, Fisher's alpha) showed significantly higher liana diversity at Ghanaian forests at biogeographic and forest-type levels. Similarly, Ghanaian forests harbored significantly higher values of liana abundance and basal area than Malaysian forests at both biogeographic and forest-type levels. The taxonomic composition of lianas differed considerably between the two biogeographic areas at all levels, although similarity in composition increased at generic and family levels. Though above-ground biomass of lianas was similar between the two biogeographic regions, variations occurred at forest-type level between the two regions. The two biogeographic areas showed some similarities in assemblages of liana climbing mechanisms. Although more species of lianas were adapted for animal dispersal than other dispersal modes in both countries, the majority of liana individuals in Ghana were wind dispersed whereas the majority of liana individuals in Malaysia were animal dispersed. We speculate that the differences in liana community assemblages between the two biogeographic areas are due to historical and evolutionary processes, as well as climatic variation between the two biogeographic regions.
    Jamir A. Prado-Junior, Ivan Schiavini, Vagner S. Vale, Diego Raymundo, Sergio F. Lopes, Lourens Poorter
    2017, 10 (6): 895-906.
    Abstract ( 73 )   PDF   Save
    Aims Functional traits have emerged as an important tool to evaluate plant performance. However, the environmental conditions and ecological pressures that plants face change with their size, and the relationship between traits and plant performance should therefore be size-dependent, which has rarely been tested.
    Methods Here, we evaluated over a broad range of tree sizes the interspecific relationship between tree growth and mortality and eight functional stem, leaf and seed traits. We did so across 59 tree species in Brazilian dry forests and evaluated whether the relationships found for wet forest types in the literature also hold for dry forests, where water rather than light might limit tree performance.
    Important findings We indeed found a strong size-dependent relationship between demographic rates and functional traits. At small sizes, when trees are in the shaded understory, species with functional trait values that enhance light capture or shade tolerance (i.e. higher maximum adult stature, taller heights, wider crowns, higher seed mass) have higher growth and/or lower mortality rates (MR). This relationship disappears at larger sizes when trees attain better light conditions in the canopy. Drought adaptations play only a role at larger tree sizes; once trees are in the dry and exposed canopy, species with higher wood density (an indicator of cavitation resistance) have lower MRs. Our study shows that both drought and shade adaptations are important in this dry forest, and that the relationships between functional traits and plant performance changes with plant size. Plant size should therefore explicitly be included as an axis of variation in functional analyses, to better understand the relationship between functional traits and demographic rates.
    Tiina Savolainen, Minna-Maarit Kytöviita
    2017, 10 (6): 907-917.
    Abstract ( 57 )   PDF   Save
    Aims Competition has been shown to modify the niche breadth of coexisting species, but within-species interactions have received little attention. Establishing small juvenile individuals and established, larger, sexually reproducing adult individuals represent two life-history stages within species. We investigated the nitrogen and carbon resource use of adult and juvenile individuals and similarity of symbiotic fungal community composition in these two plant life stages. We used the plant Solidago virgaurea growing in a simplified system in the low Arctic as model species.
    Methods Isotopic signatures (foliar δ 15 N and foliar δ 13 C) were analysed to characterize nitrogen acquisition and water-use efficiency of the plants. Symbiotic root fungal community composition was estimated by cloning and sequencing small subunit ribosomal RNA gene.
    Important findings The isotopic signatures differed significantly between the life stages, indicating that the establishing juvenile cohort used relatively more amino acids or gained N through mycorrhizal symbiosis in comparison to the established adult plants. Symbiotic fungal communities did not differ between the two plant cohorts suggesting a possibility that the plants shared the same mycorrhizal network. We conclude that competition-mediated differences in plant resource use may create niche differentiation between the two life-history stages and enable them to coexist.
    Claire E. Wainwright, John M. Dwyer, Richard J. Hobbs, Margaret M. Mayfield
    2017, 10 (6): 918-926.
    Abstract ( 42 )   PDF   Save
    Aims Despite acknowledgement that interactions among native and exotic species are important for determining the structure and diversity of novel communities, directed experiments using multiple exotics from the same system are rare. Recent observational studies have highlighted distinct ways that exotic species interface with resident natives across invaded communities. The correlative nature of these studies, however, has provided few details about the mechanisms driving distinct interaction outcomes within the same communities. Our aim was to determine how three exotic annual plant species with distinct relationships with local plant diversity impact the performance of a co-occurring native annual in the York gum–jam woodlands of Western Australia.
    Methods We grew species in experimental communities in growth chambers at varying total planting densities to assess how interaction outcomes varied among natives and exotics across a gradient of competition intensity. We measured a variety of performance responses, including survival, biomass and population-level and individual-level reproductive investment.
    Important findings Overall, the effects of interspecific versus intraspecific competition on performance varied with the identity and density of exotic competitors. The exploitative exotic grass Bromus madritensis was dominant in polyculture, whereas the diminutive grass Pentameris airoides conferred weak intraspecific competition and interspecific facilitation on native Waitzia nitida. The exotic broadleaf forb, Hypochaeris glabra, suppressed growth and survival of W. nitida, while W. nitida had weakly negative, neutral or positive effects on all exotics. These outcomes highlight the complexity of interactions impacting the diversity, stability and structure of novel plant communities. As few of these communities contain a single exotic species, understanding the competitive dynamics occurring in diverse novel communities is critical for their conservation and restoration.
    Antonio I. Arroyo, Yolanda Pueyo, Ramón Reiné, Maria Luz Giner, Concepción L. Alados
    2017, 10 (6): 927-936.
    Abstract ( 48 )   PDF   Save
    Aims Seed bank strongly influences composition and structure of aboveground vegetation. Little attention has been paid to the role of allelopathy driving soil seed bank dynamics, even though allelochemicals released by allelopathic plants might determine whether a species can or cannot germinate from the soil seed bank and, therefore, to co-exist in the neighborhood of the allelopathic species. Hence, the effects of allelopathic plants on community organization through the effects of allelochemicals on soil seed bank remain largely unknown. In this study, we assessed spatial heterogeneities in soil seed bank caused by the presence of allelopathic plants, and evaluated allelopathic effects on seed bank germination and seedling mortality.
    Methods We examined the effects of the allelopathic shrub Artemisia herba-alba Asso on the spatial structure (in terms of species richness and seed density) of the soil seed bank of a semi-arid ecosystem in NE Spain. Specifically, we evaluated seed bank richness and density at three microsites: under the canopy of A. herba-alba individuals, under the canopy of Salsola vermiculata L. (a non-allelopathic shrub) individuals, and in bare soil. In addition, we assessed the effects of aqueous extract of A. herba-alba on soil seed bank germination (seedling emergence and emergence timing) and seedling mortality.
    Important findings We found that seed bank richness and density were higher under shrub canopy than they were in bare soil. A. herba-alba and S. vermiculata microsites had similar seed bank richness. However, seed bank density was higher under A. herba-alba because of the high abundance of A. herba-alba seeds. Aqueous extract reduced seedling emergence from the seed bank by 50%, and affected mortality of some emerged seedlings. On the other hand, aqueous extract did not influence the emergence timing of seedlings. We conclude that, although the presence of allelopathic plants does not cause relevant changes in seed bank structure relative to similar non-allelopathic shrubs, their presence can actually result in a reduction of seedling emergence from the seed bank, which leads to low plant species richness and density nearby. To our knowledge, this is the first study to examine the effect of an allelopathic plant on the structure and germination in an entire soil seed bank.
    Gabriela Aparecida de Oliveira Coelho, Marcela de Castro Nunes Santos Terra, Hisaias de Souza Almeida, Eduardo van den Berg
    2017, 10 (6): 937-948.
    Abstract ( 62 )   PDF   Save
    Aims The diversity and structure of forest edges are a central issue in ecology. However, most studies have focused on anthropogenic forest edges, being natural ones least understood. We studied the communities of shrubs and trees in natural edges of gallery forests with the main goal of learning what are the main factors that shape the structure and diversity of these natural sharp ecotones.
    Methods We evaluated 10 gallery forest sites, allocating in each of them three 15×20 m plots. The plots were laid out in relatively rectilinear stretches of forest edges, respecting a minimal distance of 10 m between each plot. As they are permanent plots and meant to study eventual fluctuations in the forest–grasslands limits, we allocated the plots with their longest side parallel to the forest edge and covering perpendicularly 5 m of the grassland and 10 m of forest. Inside the plots we identified, mapped and measured all shrub and tree individuals with diameter at breast height (DBH) ≥ 1cm.
    Important findings Although many differences exist among the communities in terms of density and basal area, all of them were highly dense and had relatively low basal areas. In addition, both the number of individuals and the basal area increased rapidly towards the forest interior. Our results also revealed that the edge communities are composed mainly by small individuals that demand a great amount of light. Both the vertical stratification and the proportion of the functional groups are similar among the sites yet change quickly in the first 10 m of the forest edge. However, the floristic similarities were low among the communities mainly due to the species turnover within each area. Therefore, although the overall structure is constant in the studied edges, the low floristic similarity among them possibly indicates that the species within the same functional groups are substituting each other across the sites. Despite older and seemingly stable, our results showed the gallery forest edges are quite similar to the anthropogenic edges or recent clearings. This points out that, independent of the age, those characteristics are possibly permanent in edges.
    James R. Biggs, Dawn M. VanLeeuwen, Jerry L. Holechek, Sherri L. Sherwood, Raul Valdez
    2017, 10 (6): 949-957.
    Abstract ( 69 )   PDF   Save
    Aims Recognizing ungulate browsing thresholds between viable and declining aspen (Populus tremuloides Michx.) stands are critical to ensuring long-term persistence of this biologically important plant community. Studies have shown declines in vigor and regeneration when as few as 30% of current annual twigs are browsed while other studies have shown higher limits. Although the effects of ungulate herbivory are of concern in aspen forests, few studies have assessed browsing effects following wildfire and few criteria exist for determining potential effects of ungulate browsing on aspen forests following wildfire. We evaluated the effects of ungulate abundance and foraging intensity on regenerating aspen 1 to 6 years post-fire and assessed the use of abundance and foraging intensity indicators in predicting impacts to regenerating aspen. Rocky Mountain elk (Cervus elaphus nelson) was the primary ungulate in the study area.
    Methods The study area was located within the 17 500 ha Cerro Grande Fire burn area in the Jemez Mountains, New Mexico, USA. We used percent aspen twigs browsed and pellet-group counts to evaluate relationships between these indicators and aspen patch structure (height, size). We collected data in randomly generated 3 × 33 m plots 5–6 years post-fire. We also established 4 fenced exclosures (25 × 55 m and 3.3 m in height) with paired unfenced plots 1-year post-fire to monitor aspen regeneration. Each spring, we recorded percent browsed twigs from the previous fall through the early spring period which coincided with the highest ungulate use period within the study area. We assessed associations between percent twigs browsed and pellet-group density and patch size and height of aspen using Spearman's correlation coefficients.
    Important findings Mean percent twigs browsed and ungulate pellet-group density across the burn area was ≤31% and 1 pellet-group 100 sq m-1, respectively. Patch size and height decreased with increasing browsing and pellet-group density 5–6 years post-fire. However, mean aspen heights were approaching or exceeding a minimum browsing level of 2 m and, therefore, ungulate browsing did not appear sufficient to cause significant impacts to aspen across the burn area. We observed a positive correlation between pellet-group density and twig browsing suggesting that one or both measures could be used to assess potential effects of browsing on regenerating aspen following fire.
    Jonathan Ilunga Muledi, David Bauman, Thomas Drouet, Jason Vleminckx, Arnaud Jacobs, Jean Lejoly, Pierre Meerts, Mylor Ngoy Shutcha
    2017, 10 (6): 958-969.
    Abstract ( 75 )   PDF   Save
    Aims Relationships between local habitat heterogeneity and tree communities in miombo woodlands have been very little studied. While some studies have addressed this topic at broad scales and based on few environmental parameters, this study aims at (i) detecting fine-scale habitats (≤10 ha) on the basis of a detailed characterisation of soil explicitly considering past anthropogenic disturbances, and an exhaustive census of the tree community, and at (ii) searching for indicator tree species corresponding to the resulting habitats.
    Methods The study was carried out in the miombo woodland of Mikembo Forest Reserve, Upper Katanga, The Democratic Republic of the Congo. A complete census of the tree community was conducted in a 10-ha forest dynamics plot comprising 160 adjacent quadrats of 25 × 25 m, with a total of 4604 trees (diameter at breast height> 10 cm). Thirty-six physicochemical soil parameters were measured. Studying the frequency distribution of soil charcoal content allowed identifying local signature of past human agriculture in the soil. Two strategies were used to define habitats: (i) a combination of principal component analysis (PCA) on soil variables and Ward clustering and (ii) multivariate regression trees (MRT) to search for key soil parameters allowing the best prediction of species composition. Tree-habitat associations were tested by means of a robust statistical framework combining the IndVal index and torus randomisations.
    Important findings The forest contained 82 tree species and a significant proportion of wet miombo species (e.g. Marquesia macroura). We detected a strong east–west edaphic gradient driven by soil texture; most chemical soil parameters followed this pattern. Five habitats were identified based on soil factors and floristic composition. Nine indicator species of these habitats were found. The key soil factors discriminating habitats were total calcium, available forms of phosphorus and clay content. Even though past agricultural practices were successfully detected in soils, they did not display any significant influence neither on habitat differentiation nor on the associated tree communities. Based on an unprecedented large number of soil parameters, fine-scale soil heterogeneity and niche partitioning were shown to contribute to the variability of the floristic composition in this forest. Our results indicated that considering the most variable environmental parameters, as in PCA, is a poor manner for defining habitats. In contrast, combining MRT with the IndVal index and torus randomisation has proved to be a much more robust and sensitive approach to highlight tree-habitat associations at this scale. The common dichotomous viewpoint of considering deterministic and neutral effects as acting at broad and fine scales, respectively, is not confirmed when measuring suitable environmental variables, even in a case where the physical environment does not exhibit strong heterogeneity.
    Zhaochen Zhang, Michael J. Papaik, Xugao Wang, Zhanqing Hao, Ji Ye, Fei Lin, Zuoqiang Yuan
    2017, 10 (6): 970-980.
    Abstract ( 58 )   PDF   Save
    Aims Understanding the controls influencing tree growth is central to forest ecology. Although many factors such as tree size, neighborhood competition and environmental variables, have been proposed as being important in explaining patterns of tree growth, but their relative contributions are still subject to debate. We aimed to examine the relative importance of tree size, local abiotic conditions and the density and identity of neighbors on tree growth in an old-growth temperate forest in northeast China.
    Methods We used linear mixed models with data from a 25 ha (500 × 500 m) broad-leaved Korean pine (Pinus koraiensis) mixed forest permanent plot to examine the relative importance of these local drivers on tree growth at three organizational levels (community, guild and species). Subplot was included as a random effect to account for spatial autocorrelation in growth of trees located within the same subplot, and species was included as a random effect to account for variation among species in growth.
    Important findings Tree size was typically the most important predictor of growth, followed by neighborhood competition and then soil nutrients. The correlation of tree size to growth varied from strongly positive for large trees and medium trees to slightly positive for small trees. The effect of neighborhood competition on growth showed weak negative density dependence as indicated by slightly negative effect of total basal area of neighbors and the proportion of conspecific neighbors. Environmental factors influenced growth of very common species, smaller tree-size classes and shade-tolerant species. We concluded that the relative importance of variables driving patterns of tree growth varied greatly among tree size classes, shade tolerance and abundance classes in this temperate forest. These results provide critical information for future studies of forest dynamics and offer insight into forest management in this region.
    Alrun Siebenkäs, Jens Schumacher, Christiane Roscher
    2017, 10 (6): 981-993.
    Abstract ( 56 )   PDF   Save
    Aims Functional trait differences among species are thought to be a prerequisite for niche differentiation. Plant traits are known to vary plastically in response to environmental conditions and different plant neighbours. However, it is not clear to which extent the direction and magnitude of trait variation differ among species representing different growth forms or varying dominance in different environments and how this trait variation affects community-level trait dissimilarity.
    Methods In a field experiment, we studied shoot and leaf traits of eight perennial grassland species assigned to two functional groups (grasses vs. forbs) and varying in growth stature (small vs. tall) in monocultures, two- and four-species mixtures that were exposed to two levels of light (shaded vs. full light) and nutrient availability (fertilized vs. non-fertilized) to address this gap of knowledge.
    Important findings Fertilization increased leaf greenness and specific leaf area (SLA) as well as tissue nitrogen concentrations. Under shading, changes in morphological and physiological light-acquisition traits as well as increased nitrogen and decreased carbon concentrations in plant tissue indicated larger efforts to acquire light and carbon limitation of plant growth. Similar changes in light-acquisition traits as observed under shading and decreasing shoot biomass also revealed an accelerated carbon limitation at higher species richness (SR) irrespective of the external manipulation of light and nutrient supply. Overall, the direction of trait variation in response to resource availability (shade, fertilization) and SR did not differ between functional groups or growth statures. The magnitude of variation in several traits at different resource availability, however, was larger in grasses than in forbs as well as in small-statured than in tall-statured species. In general, dominant species in terms of aboveground biomass production had taller shoots with higher carbon and lower nitrogen concentrations and allocated less biomass into leaves than subordinates. The expression of leaf traits of dominants (lower SLA and higher leaf greenness than subordinates) indicated their competitive advantage in light acquisition. Shading, as well as fertilization, accentuated trait differences between dominants and subordinates. Fertilization increased community-level dissimilarity in tissue nitrogen concentrations due to differential responses of functional groups and growth statures. However, resource supply did not alter community-level dissimilarity in other traits. Our study shows that a varying extent of trait variation of species belonging to different functional groups or growth statures and varying in their ability to achieve dominance may modulate community-level trait dissimilarity at different resource availability. These results emphasize the importance to consider the context-dependency of trait-based approaches.
    Arvind Bhatt, Prakash Chandra Phondani, Shyam S. Phartyal, Andrea Santo, David Gallacher
    2017, 10 (6): 994-1000.
    Abstract ( 84 )   PDF   Save
    Aims To determine if the germination response of desert plant species to a period of aerial storage in field conditions (i.e. mature seeds that remain attached to the parent plant) is comparable to seeds harvested at maturity and stored in ambient laboratory conditions, to better understand the role of aerial seed bank in the germination ecology of desert plants, using one annual and two perennial species.
    Methods Seeds of three desert plants (Anastatica hierochuntica, Blepharis ciliaris and Scrophularia deserti) that matured in June 2014, were collected from wild plants in June and November 2014, and germinated under two photoperiods (0, 12 hours light) and three thermoperiods (night/day temperatures of 15/25, 20/30 and 25/35°C).
    Important findings Seeds of B. ciliaris and S. deserti had significantly higher germination percentages when harvested and stored for five months, compared to being stored in the aerial seed bank. Germination percentages of these two species increased with decreasing temperature and in the presence of light. These results indicate that these species use a combination of aerial and soil seed banks to maintain a percentage of viable seeds through favourable germination periods. Germination percentages of A. hierochuntica were high under all tested circumstances, indicating that this species relies mainly on the aerial seed bank to maintain a percentage of viable seeds through favourable germination periods. This study shows that the population survival strategies of an aerial seed bank are species–specific. These results have practical implications for conservation and habitat restoration for these species, and also for their propagation since early collection of mature fruits and ex situ storage will result in greater germination percentages of some species.
    Guang Zhao, Gangcai Liu, Wanze Zhu, Jixia Zhao, Xuemei Wang, Yaoyao Wang, Min Jia
    2017, 10 (6): 1001-1011.
    Abstract ( 54 )   PDF   Save
    Aims Despite the importance of stem CO2 efflux (E s) in ecosystem carbon cycling and energy balance, little is known about temporal variation in the temperature coefficient (Q 10) and sapwood nitrogen concentrations ([N]) and their intrinsic links with E s. The objectives of this study were: (i) to examine the response of E s to temperature in a subalpine region and (ii) to explore the influence of stem diameter and [N] on E s. Also, we will test the hypothesis that (i) E s in trees has thermal acclimation and (ii) E s will be well correlated with diameter at breast height (DBH) and [N].
    Methods Here, a horizontally oriented soil chamber technique was applied to measure E s of Abies fabri in two subalpine forest stands in Southwestern China from May to December 2014. We also examined the variability in E s, Q 10 and [N] in trees and monitored the relationship between temperature, [N], DBH and E s .
    Important findings During the measurement period, E s showed an apparent seasonal trend, following the change in air temperature, increasing from May and peaking in July, then continuously decreasing until December. The mean E s for the growing and dormant seasons were 1.45 and 0.25 μmol·m ?2 ·s-1, respectively, and E s in the mature forest was significantly higher than in the immature forest. The area-based E s was positively correlated with DBH and sapwood width (SW), while volume-based E s showed negative relationship with DBH and SW. Across the five diameter classes, 69.8–89.0% of the variation in E s could be explained by air temperature. The temperature sensitivity (Q 10) of E s ranged from 2.98 to 5.61 during the measurement period, with a higher Q 10 appearing in the growing season than in the dormant season. There was a significant linear relationship (P < 0.01) between [N] and E s (expressed based on two different units). Additionally, exponential models of E s against [N] and air temperature were applied to estimate E s .
    Eva Castells, Maria Morante, Sandra Saura-Mas, Anabel Blasco-Moreno
    2017, 10 (6): 1012-1021.
    Abstract ( 58 )   PDF   Save
    Aims Plant secondary metabolites have been traditionally recognized as key traits regulating plant-herbivore assemblages. However, the ecological relevance of secondary metabolites as resistance mechanisms in comparison to other plant attributes, including physical, morphological or ecological traits, has been recently questioned. We aim to evaluate the role of chemical defenses, plant size and the presence of insect competitors on driving the differences in herbivory damage under natural conditions.
    Methods We performed a replicated field study on the herbivore community associated with four Senecio species (S. lividus, S. vulgaris, S. inaequidens and S. pterophorus) during a full-reproductive season in Montseny Natural Park (Catalonia, NE Spain). Pyrrolizidine alkaloids (PAs), the most characteristic chemical defenses of Senecio due to their toxic effects on herbivores, were analyzed by gas chromatography. Individual plant size was estimated by the number of flower heads produced over the entire reproductive season. We used linear mixed models to explore the relationships between total PA concentrations, plant size and herbivory levels.
    Important findings PA concentrations were not related to the natural guild of herbivores within any plant species or insect type. Moreover, no significant interactions were found between insect species sharing the same host plants. In contrast, herbivore abundance was positively related to plant size in S. vulgaris, S. lividus and S. inaequidens. We found no evidence that PAs confer an increased plant resistance against herbivores in Senecio. Our study supports the hypothesis that plant chemical defenses have a secondary role in determining plant-herbivore assemblages in comparison to other plant traits under the complexity of natural conditions.
Impact Factor
1.833
5 year Impact Factor
2.299
Editors-in-Chief
Wen-Hao Zhang
Bernhard Schmid