Understory Ferns Research Articles

A maritime location reduced palynofloral turnover and extirpation across the end Cretaceous boundary interval on the west coast of Canada

A well-preserved suite of ∼163 spore-pollen taxa from a recently discovered K/Pg interval within the maritime Oyster Bay Formation, Vancouver Island, British Columbia, Canada, reveals a pattern of floral turnover across the boundary event with local extirpations of ∼15 % of Cretaceous taxa. Along the margin of the eastern North Pacific, a shift occurred in near-coastal vegetation composition from uppermost Cretaceous diverse fern and bryophyte-dominated communities to Danian conifer-dominated forests with a fern understory. The ‘fern spore spike’ common in other K/Pg records was not detected within the sandstone to mudstone sequence. Spore-pollen assemblages preserved herein align with those of the Continental Margin floristic province. Palm pollen is noteworthy in the studied sections including Arecipites spp. (aff. Arecaceae), Spinizonocolpites spp. (aff. Nypa) and Pandaniidites typicus (aff. Pandanus) suggesting a warm, frost-free, sub-tropical climate prevailed across the K/Pg interval. The presence of numerous endemic spore-pollen taxa is indicative of geographic isolation from the North American Western Interior. Maritime climate buffering along the west coast of North America contributed to microrefugia permitting greater stability in terrestrial plant communities than in continental regions.

Chemical composition of soil carbon is governed by microbial diversity during understory fern removal in subtropical pine forests

Understory vegetation has an important impact on soil organic carbon (SOC) accumulation. However, little is known about how understory vegetation alters soil microbial community composition and how microbial diversity contributes to SOC chemical composition and persistence during subtropical forest restoration. In this study, removal treatments of an understory fern (Dicranopteris dichotoma) were carried out within pine (Pinus massoniana) plantations restored in different years in subtropical China. Soil microbial community composition and microbial diversity were measured using phospholipid fatty acids (PLFAs) biomarkers and high-throughput sequencing, respectively. The chemical composition of SOC was also measured via solid-state 13C nuclear magnetic resonance (13C NMR). Our results showed that fern removal decreased alkyl C by 4.2 % but increased O-alkyl C by 15.6 % on average, leading to a decline of alkyl C/O-alkyl C ratio, suggesting altered chemical composition of SOC and lowered SOC recalcitrance without fern. Fern removal significantly lowered the fungi-to-bacteria ratio, and it also reduced fungal and bacterial diversity. Partial correlation analysis revealed that soil nitrogen availability was a key factor influencing microbial diversity. Bacterial diversity showed a close relationship with the Alkyl C/O-alkyl C ratio following fern removal. Furthermore, the microbial community structure and bacterial diversity were responsible for 18 % and 55 % of the explained variance in the chemical composition of SOC, respectively. Taken together, these analyses jointly suggest that bacterial diversity exerts a greater role than microbial community structure in supporting SOC persistence during understory fern removal. Our study emphasizes the significance of understory ferns in supporting microbial abundance and diversity as a means of altering SOC persistence during subtropical forest restoration.

Understory ferns removal downregulates microbial carbon use efficiency and carbon accrual in previously degraded lands

When reforesting degraded lands, understory ferns can take root and cover the forest floor, which can change the quality and quantity of litter added to soils. However, it is unclear how ferns and the ongoing succession of trees impact soil organic carbon (SOC) dynamics. Here, we established experimental sites in Masson pine (Pinus massoniana) stands for understanding the underlying mechanisms of how ferns affect SOC stock and soil respiration (Rs) in subtropical China. The established three pine stands covered with ferns (Dicranopteris dichotoma (Thunb.) Berhn.) were used to represent a 37-year restoration sequence: two restored sites with vegetation cover (VC) established in 1984 and 2002 (referred to VC-1984 and VC-2002), and an unrestored site (VC-0). In August 2014, two treatments were set i.e., ferns were retained in half area of the sites (“control”), and continuously removed ferns from the other half (“fern removal”) for seven years. Our results showed that fern removal significantly decreased Rs by 25.8% in VC-2002 compared to the control over a three-year period from 2015 to 2018, but did not significantly affect Rs in VC-0 and VC-1984. We found that fern removal decreased fine root biomass by 50.4% in VC-0, 31.4% in VC-2002, and 54.7% in VC-1984 in 2019, with seven-year averaged SOC stocks decreased by 37.2%, 13.9%, and 22.7% in VC-0, VC-2002, and VC-1984, respectively. Moreover, fern removal significantly increased carbon- and nitrogen-degrading enzyme activities and decreased microbial carbon use efficiency, suggesting that fern removal may increase SOC decomposition. Taken together, we concluded that fern removal may increase SOC-derived CO2 efflux counteracting the reduced root respiration in VC-0 and VC-1984 but not in VC-2002, leading to a divergent response of Rs to understory fern removal. Our study emphasizes the necessity of incorporating understory plants regulates SOC decomposition and accumulation in assessing forest recovery effects on soil carbon cycling.

A comparative ecophysiological study of two forest understory ferns (Dryopteris marginalis and Polystichum acrostichoides) during summer drought and excessive heat

A comparative ecophysiological study of two forest understory ferns (Dryopteris marginalis and Polystichum acrostichoides) during summer drought and excessive heat

Understory ferns promote the restoration of soil microbial diversity and function in previously degraded lands

Microorganisms facilitate the recovery of previously degraded soils, such as degraded lands experiencing vegetation restoration and understory expansion, through vital soil functions like nutrient cycling and decomposing organic matter. Despite the role of microorganisms in recovery, little is known about the effects of the process on microbial diversity and function. Here, we performed an understory fern, Dicranopteris dichotoma (Thunb.) Berhn removal treatments nested within three Masson pine (Pinus massoniana L.) plantations with different restoration years in subtropical China. Three ferns treatments including no ferns cover, with ferns cover, and the ferns removal treatments were established to assess the impact of the ferns on soil microbial diversity and function during revegetation and drivers of observed changes. We combined high-throughput sequencing, network structure modeling, and function prediction of soil bacterial and fungal communities to determine microbial diversity and functions. Our results showed that soil bacterial and fungal diversity increased with restoration time. Understory ferns significantly increased soil microbial diversity in the un-restored land but the effect became smaller in two restored sites. Understory ferns significantly increased the relative abundance of bacterial phyla Proteobacteria and Acidobacteria, but decreased that of Chloroflexi and Firmicutes. Furthermore, the presence of ferns increased the abundance of Basidiomycota, but increased the abundance of Ascomycota. Co-occurrence network analysis revealed that the presence of ferns leads to more complex of bacterial networks with more connections, nodes, average degrees, betweenness, and degrees. The functional predictions indicate that aerobic chemoheterotrophy, chemoheterotrophy, and nitrogen fixation functional groups play key roles in the nutrient cycling of soils with ferns cover. The bacterial and fungal community compositions were strongly affected by revegetation and understory ferns as litter biomass and soil nitrogen were identified as the key environmental factors. Our study highlights the role of understory in facilitating microbial diversity and function recovery during degraded lands restoration.

Responses of tree seedlings to understory filtering by the recalcitrant fern layer in a subtropical forest.

The recalcitrant understory fern layer is an important ecological filter for seedling regeneration, yet how the fern layer influences seedling regeneration dynamics remains unclear. Here we transplanted 576 seedlings of four dominant tree species, Castanopsis fargesii, Lithocarpus glaber, Schima superba and Hovenia acerba, to the treatments of Diplopterygium glaucum retention and removal under an evergreen broad-leaved forest in eastern China. We monitored the survival, growth and biomass data of these seedlings for 28 months, and then used generalized linear mixed models to evaluate the treatment effects on seedling survival, growth, biomass and root-shoot ratio. Our results showed that fern retention significantly inhibited the seedling establishment of all four species. During the seedling development stage, the seedling relative growth rate of L. glaber decreased under fern retention, which was not the case for the other three species. Root-shootratio of C. fargesii and L. glaber increased significantly under fern retention. Our findings provide new evidence of the filtering effect of a recalcitrant fern understory. Notably, we observed that the response of tree seedlings to the recalcitrant fern understory was more sensitive in the establishment stage. Finally, our work highlights that the filtering effect of the recalcitrant fern understory changes depending on the regeneration stages, and that shade-tolerant species, C. fargesii and L. glaber were even more affected by fern disturbed habitats, suggesting that effective management should attempt to curb forest fern outbreaks, thus unblocking forest recruitment.

Long-term Studies of Annual Variation in Growth and Reproduction of the Understory Fern Steiropteris deltoidea in a Hurricane-prone Rainforest in Puerto Rico

Two long-term studies were conducted in a rainforest in Puerto Rico that included measurements of leaf and plant functional traits of the common fern species Steiropteris deltoidea. A Fern Demography study (1993-2009) compared annual variation and effects of a category 3 hurricane (Georges, 1998) on fertile and sterile leaf traits. A second long-term study (2003-2019), the Canopy Trimming Experiment, evaluated annual variation in growth and reproduction of S. deltoidea in response to two experimentally simulated and one category 4 hurricane (Maria, 2017). In the Fern Demography study, differences between fertile and sterile leaf production rates and plant leaf count of S. deltoidea were significant while leaf lengths and lifespans did not differ between leaf types. Fertile (but not sterile) leaf production increased three-fold after Hurricane Georges but declined 10-fold by the end of the study. Leaf lifespans of cohorts emerging before and in the three years after Hurricane Georges were significantly shortened by tree and debris fall. Elevated production of fertile leaves and increased plant leaf counts followed the two simulated hurricanes of the Canopy Trimming experiment and two natural hurricanes. Steiropteris deltoidea exhibits a level of interannual flexibility in some growth and reproductive traits in response to a changed understory environment that suggests it may be a good indicator species for evaluating microhabitat hurricane effects. Although S. deltoidea exhibited resilience, predicted increases in frequency and magnitude of hurricanes in response to climate change may test the limits of life history strategies of rainforest understory ferns.

Cunninghamia lanceolata and understory ferns had positive rhizosphere effects on the temperature sensitivity of soil microbial respiration in a subtropical forest

Rhizosphere processes play a critical role in soil organic carbon (SOC) cycling that is primarily regulated by temperature. Understanding the response of rhizospheric SOC decomposition to global warming, which is called temperature sensitivity (Q10), is pivotal for predicting the feedback of SOC cycling to global warming. However, the rhizosphere effects (REs) on Q10 and their underlying mechanisms in forest ecosystems remain unclear. Here, the REs on Q10 for Cunninghamia lanceolata and three understory ferns (e.g., Woodwardia japonica, Parathelypteris glanduligera and Microlepia marginata) in a subtropical forest were explored using a novel incubation procedure with periodically changing temperatures based on the mean annual temperature. Our results showed that the positive REs on Q10 were observed for all plant species, which ranged from 33% to 88%, and P. glanduligera exhibited higher REs on Q10 than C. lanceolata. The positive REs on Q10 were associated with the rhizospheric nitrogen (N) availability and microbial properties. The REs on N component (i.e., the REs on total N, NH4+ and NO3− along the first PCA axis), which is the most important driver, had a positive direct effect on the REs on Q10. Furthermore, the rhizospheric microbial biomass and the REs on microbial residues were also positively related to the REs on Q10. Overall, these findings highlight that plant-covered soils have high risks of C emissions under planetary warming, underscore the importance of root-soil interactions for accurately predicting SOC dynamics and reveal that rhizospheric nutrients and microbial properties drive the feedback of the root-associated SOC cycle to global warming.

Searching for a nearest living equivalent for Bennettitales: a promising extinct plant group for stomatal proxy reconstructions of Mesozoic pCO2

ABSTRACT To understand Earth´s climate variability and improve predictions of future climate change, studying past climates is an important avenue to explore. A previously published record of pCO2, across the Triassic–Jurassic boundary (TJB, ~201 Ma) of East Greenland, showed that Bennettitales (Anamozamites and Pterophyllum) responded in parallel to the empirically proven pCO2-responders Ginkgoales, reducing their stomatal densities by half across the TJB, indicating a transient doubling of pCO2. The abundance of fossil Bennettitales in Mesozoic strata and natural history museum collections worldwide offers enormous potential for further stomatal proxy pCO2 reconstructions, but a suitable nearest living equivalent (NLE) should ideally first be identified for this extinct plant group. Using specimens from herbarium collections, three species of cycads, historically considered the best NLE, were tested for pCO2 response, as well as two species of tree ferns, grown in experimental growth chambers. None responded to changes in pCO2, and were consequently rejected as NLEs. Finally, two species of ferns were selected from the literature, and produced very similar pCO2 compared to Ginkgoales. However, these understory ferns are not appropriate NLEs for Bennettitales due to differences in habitat and a distant evolutionary relationship. Future work should test additional plant groups, in particular seed plants such as basal angiosperms and Gnetales, for suitability as NLE for Bennettitales in pCO2 reconstructions, for example through biogeochemical fingerprinting using infrared microspectroscopy. Until an appropriate NLE is identified, Bennettitales pCO2 can be reconstructed based on cross-calibration of stomatal densities with those of co-occurring pCO2 responders, such as Ginkgoales.

Fossil pinnae, sporangia, and spores of Osmunda from the Eocene of South China and their implications for biogeography and paleoecology

AbstractThe genus Osmunda L. contains approximately 10 extant species widely distributed in tropical and temperate regions, with the greatest concentration of species in East and Southeast Asia. Osmunda is characterized by dimorphic or commonly hemidimorphic fronds with dimorphic pinnae. Its geological history has been traced back to the Triassic. Most records of the genus are based on rhizomes and rarely on pinnae bearing sporangia and spores. Here, we describe fossil pinnae, sporangia, and spores of Osmunda lignitum (Giebel) Stur recovered from the middle Eocene of the Changchang Formation in the Changchang Basin, Hainan Island and the Youganwo Formation in the Maoming Basin, Guangdong, South China. The fossils closely resemble the extant Osmunda banksiifolia (C. Presl) Kuhn of the subgenus Plenasium on the basis of their morphological and anatomical structures. The present occurrence of O. lignitum indicates subg. Plenasium flourished and extended from the high latitude regions such as Northeast China to the low latitude areas of South China during the middle Eocene. Large numbers of specimens described here also indicate that Osmunda was the dominant understory fern element beneath mixed evergreen broad‐leaf angiosperm and gymnosperm forests living in a warm and humid environment.

Effects of a recalcitrant understory fern layer in an enclosed tropical restoration experiment

Establishing mixed-species tree plantings and fencing them to protect seedlings from herbivory is a valuable strategy for reconnecting forest fragments separated by agropastoral lands. However, fencing may provide exotic plants with the escape from herbivory required to invade the understory of planted communities. Here we take advantage of such a situation to ask how the identity of planted species and the resulting canopy cover influenced invasion success by the Asian swordtail fern (Nephrolepis brownii Desv. Nephrolepidaceae) in a 13-year-old tropical restoration experiment. Through a seed addition experiment, we also evaluated the effects the ferns had on recruiting seedlings. We found that the invasion was most acute in the unplanted control plots where canopy cover was consistently scarce. Frond density correlated negatively with canopy cover, though most of the variance in the model is explained by the design of our experiment (r2m = .161, r2c = .460). Between planting treatments that differed in the dispersal mode of the planted trees, the wind-dispersed treatment had higher fern density and longer fronds than the animal-dispersed treatment. The animal-dispersed treatment had the highest recruiting species richness, which was negatively correlated with fern density (r2 = .748). The seed addition experiment confirmed that mortality rates increased where frond density was higher (F1,41 = 7.159, p = .011) and germination rates were lowered for the smaller-seeded species (F1,42 = 13.2, p = .002). To prevent recalcitrant understory layers from establishing in plantings in the future, we recommend: (1) establishing larger plantings or expanding existing ones to minimize edge effects (particularly light filtration), (2) supplementing young plantings with additional seedlings to prevent canopy gaps from forming, and (3) planting an assemblage of species that cover the full forest strata and have consistently full tree-canopies.

Understory ferns alter soil carbon chemistry and increase carbon storage during reforestation with native pine on previously degraded sites

Reforestation with native species and resulting understory succession can exert important influences on soil organic matter (SOM) storage and chemistry, but a mechanistic understanding of these effects is lacking. We studied different aged Masson pine (Pinus massoniana L.) plantations with and without the understory fern, Dicranopteris dichotoma (Thunb.) Berhn., in subtropical China to assess how SOM over a 30 year sequence of pine growth and fern expansion. To do this, we measured total SOM, lignin-derived phenols, soil carbon (total C and 13C), soil nitrogen (total N and 15N), and soil microbial community composition via phospholipid fatty acid (PLFA) analyses. We found that the accumulation of newly-formed SOM outweighed decomposition of old SOM, with the majority of this increase being derived from fern detrital inputs. Where ferns were present, ferns contributed 54–61% of total soil C storage in surface (0–10 cm depth) soils, which was 62–91% higher than pre-reforestation soil C storage. We found that the abundance of lignin-derived compounds was lower in fern dominated soils, perhaps because soils under ferns supported more soil fungi, the primary decomposers of the lignin in soil. Fern soils also showed higher ratios of syringyls to vanillyls and decreased δ13C values, an indicator that ferns altered the composition of SOM at the molecular level while contributing significantly to SOM accumulation. Reforestation especially when accompanied by fern expansion also improved soil N and phosphorus (P) status, with observed declines in soil δ15N in fern dominated soils aligning with increased nutrient retention and observed increases in soil C storage. Our study highlights the potentially important role of understory ferns in mediating SOM chemistry and soil C storage during ecosystem recovery.

Culcita remberi sp. nov., an Understory Fern of Cyatheales from the Miocene of Northern Idaho

Premise of research. Excavations at the Clarkia fossil beds in northern Idaho have recovered numerous exceptionally well-preserved plant fossils over the past 45 years. We report on a compression fossil of a fertile frond from a tree fern found at the Emerald Creek locality.Methodology. Intact leaf material was liberated from the substrate by wetting with hydrofluoric acid followed by submersion in a water bath. The lamina was preserved between sheets of acetate and photographed, and fertile pinnules with sporangia were mounted on aluminum stubs and imaged with scanning electron microscopy. Spores were released from sporangia after incubation in Schulz’s solution and treatment with KOH.Pivotal results. The specimen is similar to members of several extant fern lineages, including Hymenophyllaceae, Dennstaedtiaceae, and the tree fern order Cyatheales. It shares with these groups the possession of oblong, marginal sori, although the sori of the specimen are most similar to the cup-shaped sori of Dennstaedtiaceae and the bivalvate sori of Culcitaceae. The fossil also has sporangia, each with a complete, uninterrupted, oblique annulus, which is strongly associated with Culcitaceae.Conclusions. On the basis of its overall lamina morphology and details of the sori and especially the sporangia, we conclude that this specimen belongs to an extinct species of the monogeneric tree fern family Culcitaceae. The occurrence of a tree fern in the temperate plant community of the Miocene Clarkia locality is unexpected but not incompatible with the habitat preferences of this genus, as the two extant species of Culcita are found in montane altitudes and temperate forests elsewhere in the world.

The role of bilberry and Alpine lady-fern in soil formation within the Carpathian subalpine spruce forest stands

The effect of the understory vegetation in the spruce forests of the upper montane belt on soil properties was investigated. Three types of understory vegetation were included: dominant Alpine lady fern, dominant bilberry or a mix of the two species. All studied soils were derived from sandstone, had acidic soil reactions, were located under similar physiographic conditions and have been populated by coniferous forests with similar to today's understory species for more than thousand years. The effect of Alpine lady fern on soil organic matter accumulation and quality as well as the amount of total Fe and Al and the share of different forms of these elements (linked to humus, amorphous inorganic, silicate and non-silicate crystalline) in the total Fe and Al were compared to the effect of bilberry on the aforementioned soil features. This work aimed to assess if the understory vegetation effect was strong enough to influence pedogenic processes taking place in the soils. The main differences between the studied soil properties were related to organic matter transformation and Fe and Al mobility. They were caused by a different susceptibility of Alpine fern lady and bilberry plant residues to the decomposition. In the soils with bilberry dominance, there were greater amounts of less decomposed organic matter accumulated than in soils with Alpine lady fern dominance in which organic matter was characterised by a high humification degree, large CH/CF ratios and significantly lower C/N ratios. Bilberry in the understory caused the increased Fe and Al mobility. Therefore in soils under bilberry podsolization processes and spodic horizon formation occurred that was indicated by the values of Fe and Al mobility indices. In soils under Alpine lady fern influence, these indices values were lower and the podzolisation processes were not intensive enough to form spodic horizons. In these soils, regardless of the condition favouring podsolization (low pH, spruce forest), the mobility of Fe and Al was slowed. The presence of Alpine lady fern as a dominant understory species resulted in a decrease in solubility of metallo-organic complexes, probably because of the quicker oxidisation of litter then in soils under bilberry. The sites with a mix of Alpine lady fern and bilberry turned out to be in a transitional phase, which with time would probably change to bilberry or fern understory. The ecological role of the studied soils resulting from accumulation of inorganic amorphous Fe, which takes part in anion sorption, thus limiting leaching, was also emphasized.

Conversion of native terrestrial ecosystems in Hawai‘i to novel grazing systems: a review

The remote oceanic islands of Hawai‘i exemplify the transformative effects that non-native herbivorous mammals can bring to isolated terrestrial ecosystems. We reviewed published literature containing systematically collected, analyzed, and peer-reviewed original data specifically addressing direct effects of non-native hoofed mammals (ungulates) on terrestrial ecosystems, and indirect effects and interactions on ecosystem processes in Hawai‘i. The effects of ungulates on native vegetation and ecosystems were addressed in 58 original studies and mostly showed strong short-term regeneration of dominant native trees and understory ferns after ungulate removal, but unassisted recovery was dependent on the extent of previous degradation. Ungulates were associated with herbivory, bark-stripping, disturbance by hoof action, soil erosion, enhanced nutrient cycling from the interaction of herbivory and grasses, and increased pyrogenicity and competition between native plants and pasture grasses. No studies demonstrated that ungulates benefitted native ecosystems except in short-term fire-risk reduction. However, non-native plants became problematic and continued to proliferate after release from herbivory, including at least 11 species of non-native pasture grasses that had become established prior to ungulate removal. Competition from non-native grasses inhibited native species regeneration where degradation was extensive. These processes have created novel grazing systems which, in some cases, have irreversibly altered Hawaii’s terrestrial ecology. Non-native plant control and outplanting of rarer native species will be necessary for recovery where degradation has been extensive. Lack of unassisted recovery in some locations should not be construed as a reason to not attempt restoration of other ecosystems.

The biostratigraphy and sedimentary environments of the Lower Cretaceous section, Malaya Kheta structural-facies region, West Siberia

The biostratigraphic study of the Low Cretaceous sediments of the Middle Messoyakha swell (Malaya Kheta region) distinguished 12 biostratons based on biofossil data and thus confirmed Boreal Berriassian, Valanginian, and Lower Hauterivian strata. The genetic types of the sediments were determined by lithofacies and biofacies analyses. In the deposit, the Bazhenovo and Kulomzino horizons (Berriassian to basal Valanginian) consist of relatively deep-water marine, shallow-water marine, and coastal-continental facies that displace one another along the strike. The Tara and Ust’-Balyk horizons (middle Lower Valanginian to Lower Hauterivian) are composed of shallow-water marine facies. Paleontological data suggest a low-hilled island covered with conifer-gingko forests with fern understory in the place of the Middle Messoyakha swell in the Berriassian Age.

In the right place at the right time: habitat representation in protected areas of South American Nothofagus-dominated plants after a dispersal constrained climate change scenario.

In order to assess the effects of climate change in temperate rainforest plants in southern South America in terms of habitat size, representation in protected areas, considering also if the expected impacts are similar for dominant trees and understory plant species, we used niche modeling constrained by species migration on 118 plant species, considering two groups of dominant trees and two groups of understory ferns. Representation in protected areas included Chilean national protected areas, private protected areas, and priority areas planned for future reserves, with two thresholds for minimum representation at the country level: 10% and 17%. With a 10% representation threshold, national protected areas currently represent only 50% of the assessed species. Private reserves are important since they increase up to 66% the species representation level. Besides, 97% of the evaluated species may achieve the minimum representation target only if the proposed priority areas were included. With the climate change scenario representation levels slightly increase to 53%, 69%, and 99%, respectively, to the categories previously mentioned. Thus, the current location of all the representation categories is useful for overcoming climate change by 2050. Climate change impacts on habitat size and representation of dominant trees in protected areas are not applicable to understory plants, highlighting the importance of assessing these effects with a larger number of species. Although climate change will modify the habitat size of plant species in South American temperate rainforests, it will have no significant impact in terms of the number of species adequately represented in Chile, where the implementation of the proposed reserves is vital to accomplish the present and future minimum representation. Our results also show the importance of using migration dispersal constraints to develop more realistic future habitat maps from climate change predictions.

Neogene palynological assemblages in the west slope of Songliao Basin and their geological implications

Abundant palynological fossils are found from the drill core in the west slope of Songliao Basin, the first full coring borehole that drilled throughout the Neogene. Two Palynological assemblages are recognized according to their vertical distributions, i.e., the late early Miocene-middle Miocene assemblage from the Da’an Formation named as Caryapollenites simplex-Momipites coryloides-Celtispollenites sp.-Tsugaepollenites igniculus, and the late Miocene-early Pliocene assemblage from the Taikang Formation named as Artemisiaepollenites minor-Betulaceoipollenites sp.-Carpinipites sp.-Polypodiace aesporites sp. On the basis of the composition of each assemblage, we infer that the climate was warm-temperate to sub-tropic during the late early Miocene-middle Miocene and the vegetation was mainly deciduous broadleaved forest and subordinate coniferous and broad-leaved mixed forest with few understory ferns, and probably some shallow fresh water wetlands. The climate then turned cooler and drier in the late Miocene-early Pliocene, represented by the development of xerophytic herbs and temperate plants, although the canopy of the forest remained relatively stable. The results significantly improve the understanding of the Cenozoic palynostratigraphy in the Songliao Basin, and provide new data for both stratigraphical correlation and paleovegetational and paleoclimatical analysis in adjacent area.

The understory fern Dicranopteris dichotoma facilitates the overstory Eucalyptus trees in subtropical plantations

Plant–plant interactions are important not only for understanding biodiversity maintenance and plant community assembly but also for forest conservation and management. However, our knowledge about how plant species of different functional groups interact in forests is limited. For example, understory removal is thought to enhance tree growth in subtropical plantations but such enhancement has not been experimentally confirmed. In the present study, we conducted an understory removal experiment combined with nutrient addition to examine how the understory fern Dicranopteris dichotoma interacts with overstory Eucalyptus trees and how fertilization affects that interaction in subtropical plantations. Our results demonstrate that the understory fern D. dichotoma facilitates the overstory Eucalyptus trees and that the facilitative effect is enhanced by nutrient addition. In addition to illustrating the complex interactions among plant functional groups and the importance of plant traits in predicting plant–plant interactions, our findings counter the traditional view that understory ferns primarily compete with trees for resources in subtropical Eucalyptus plantations. This information should help in the development of sustainable management practices.

Understory fern community structure, growth and spore production responses to a large-scale hurricane experiment in a Puerto Rico rainforest

Ferns are abundant in most rainforest understories yet their responses to hurricanes have not been well-studied. Fern community structure, growth and spore production were monitored for two years before and five years after a large-scale experiment that simulated two key components of severe hurricane disturbance: canopy openness and debris deposition. The canopy was opened by cutting branches above 3m and the fallen leaf and woody debris was either added to or removed from the forest floor resulting in four treatments that were replicated three times in a factorial design. Of the 16 fern species observed during the experiment 12 were present before treatments were applied. All but two of the 16 species had densities <250ha−1; Thelypteris deltoidea (2258ha−1) and Cyathea borinquena (1521ha−1) were by far the most common ferns. Under simulated hurricane conditions (open canopy and debris deposition) abundance levels for both T. deltoidea and C. borinquena were highly resilient and returned to pre-disturbance conditions within three years; therefore the resident (non-pioneer) fern species continued to dominate after disturbance. However, several other variables had increasing or decreasing responses that had not returned to pre-treatment levels by the fifth and final year of the experiment. Four pioneer species appeared in low abundance almost immediately after the canopy was opened, including three native species that spread via spore germination and the invasive Nephrolepis brownii that spread by runners. Debris deposition resulted in high mortality for 7 of 12 fern species, with C. borinquena among the species little affected and increases in recruitment following mortality of T. deltoidea under open canopy. Individuals of both T. deltoidea and C. borinquena responded to higher light levels with growth spurts reflected in up to two- to three-fold increases in leaf production and emergence of longer leaves. Spore production rates for both T. deltoidea and C. borinquena had been low in the undisturbed pre-treatment forest, but more than doubled in the years that followed canopy opening. Hurricane impacts to this tropical forest alter the fern community by (1) debris deposition burying individuals and initially reducing some population sizes, and (2) canopy openness overwhelming the negative effects of debris deposition and stimulating growth and reproduction that can last ⩾5years. Changes resulting from hurricane disturbance that affect the fern-dominated herbaceous layer may ultimately influence structure and function of the long-term understory plant community and consequently the habitat of litter- and soil-dwelling organisms.