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1. Successional gradients are ubiquitous in nature, yet few studies have systematically examined the evolutionary origins of taxa that specialize at different successional stages. Here we quantify successional habitat specialization in Neotropical forest trees and evaluate its evolutionary lability along a precipitation gradient. Theoretically, successional habitat specialization should be more evolutionarily conserved in wet forests than in dry forests due to more extreme microenvironmental differentiation between early and late-successional stages in wet forest. 2. We applied a robust multinomial classification model to samples of primary and secondary forest trees from 14 Neotropical lowland forest sites spanning a precipitation gradient from 788 to 4000 mm annual rainfall, identifying species that are old-growth specialists and secondary forest specialists in each site. We constructed phylogenies for the classified taxa at each site and for the entire set of classified taxa and tested whether successional habitat specialization is phylogenetically conserved. We further investigated differences in the functional traits of species specializing in secondary vs. old-growth forest along the precipitation gradient, expecting different trait associations with secondary forest specialists in wet vs. dry forests since water availability is more limiting in dry forests and light availability more limiting in wet forests. 3. Successional habitat specialization is non-randomly distributed in the angiosperm phylogeny, with a tendency towards phylogenetic conservatism overall and a trend towards stronger conservatism in wet forests than in dry forests. However, the specialists come from all the major branches of the angiosperm phylogeny, and very few functional traits showed any consistent relationships with successional habitat specialization in either wet or dry forests. 4. Synthesis. The niche conservatism evident in the habitat specialization of Neotropical trees suggests a role for radiation into different successional habitats in the evolution of species-rich genera, though the diversity of functional traits that lead to success in different successional habitats complicates analyses at the community scale. Examining the distribution of particular lineages with respect to successional gradients may provide more insight into the role of successional habitat specialization in the evolution of species-rich taxa.

Aims Pioneer tree species such as Betula pendula and Pinus sylvestris encroach soils contaminated with heavy metals (HMs). This is facilitated by ectomycorrhizal fungi colonizing tree roots. Thus, we evaluated the ectomycorrhizal fungal (EMF) communities of B. pendula and P. sylvestris growing in HM-contaminated soils compared to non-contaminated soils. We also studied the effect of HMs and soil properties on EMF communities and soil fungal biomass. Methods Roots of B. pendula and P. sylvestris were collected from three HM-contaminated sites and from two non-contaminated sites located in Poland. EMF species were identified using DNA barcoding. Soil fungal biomass was determined by soil ergosterol. Results B. pendula and P. sylvestris growing in HM-contaminated soils had similar EMF communities, where Scleroderma , Rhizopogon and Russula as well as ectomycorrhizae of the long-distance exploration type dominated. Among all of the examined soil factors studied, toxicity index (TI Total ) was the most significant factor shaping the composition of EMF communities. Despite significant differences in the structure of the EMF communities of trees growing in HM-contaminated sites compared to control sites, no differences in overall diversity were observed. Conclusions Only well-adapted EMF species can survive toxic conditions and form ectomycorrhizal symbiosis with encroaching trees facilitating the forest succession on contaminated soils.

Frequent earthquakes, monsoon torrential rains and typhoons cause severe landslides and soil erosion in Taiwan. Hibiscus taiwanensis, Macaranga tanarius, and Mallotus paniculatus are major pioneer tree species appearing on landslide-scarred areas. Thus, these species can be used to restore the self-sustaining native vegetation on forest landslides, to control erosion, and to stabilize slope. However, their growth performance, root traits and biomechanical properties have not been well characterized. In this study, root system and root traits were investigated using the excavation method, and biomechanical tests were performed to determine the uprooting resistance, root tensile strength and Young’s modulus of 1-year-old Hibiscus taiwanensis, Macaranga tanarius, and Mallotus paniculatus seedlings. The results reveal that relative to H. taiwanensis, M. tanarius and M. paniculatus seedlings had significantly larger root collar diameter, longer taproot length, higher root biomass, higher root density, higher root length density, heavier root mass, larger external root surface area, higher root tissue density, larger root volume, longer total root length, and a higher root tip number. Additionally, the height of M. paniculatus seedlings was significantly higher than those of H. taiwanensis and M. tanarius. Furthermore, the uprooting resistance and root tensile strength of M. paniculatus seedlings was significantly higher than those of H. taiwanensis and M. tanarius. Young’s modulus of M. paniculatus and M. tanarius seedlings was also significantly higher than that of H. taiwanensis. These growth characteristics and biomechanical properties demonstrate M. paniculatus and M. tanarius are superior than H. taiwanensis, considering growth performance, root anchorage capability, tensile strength and Young’s modulus. Taken as a whole, the rank order for species selection of these pioneer species for reforestation comes as: M. paniculatus M. tanarius H. taiwanensis. These results, along with knowledge on vegetation dynamics following landslides, allow us to better evaluate the effect of selective removal management of pioneer species on the resilience and sustainability of landslides.

The impacts of soil compaction along skid trails (haul roads) on the growth of seedlings were monitored during the first growing season in a mature deciduous stand in the Hyrcanian forests, northern Iran. Two native pioneer tree species, alder (Alnus subcordata C.A.M.) and maple (Acer velutinum Boiss.), were seeded within and beside the upslope and downslope tracks of two differently aligned skid trails: (1) flat skid trail (STF) and (2) skid trail with transversal (lateral) slope (STTS). Following a 5-month growth period, seedlings were measured for germination percentage, root length, above-ground stem height and root-to-stem ratio. Germination percentages of both species were unaffected by soil compaction, but mean root length of seedlings on control plots was significantly greater than those on plots disturbed by skidding operations. Seedlings developed longer roots in the track edge than the track centre positions although other growth parameters did not differ significantly. Seedling height was slightly greater on all tracks than on control plots, probably in response to increased light exposure of the seedlings after removal of overstorey along the skid trails. Maple and alder seedlings grown on undisturbed control areas with dense canopies generally produced deeper main roots and lower plant heights. Both species confirmed their value as pioneer trees in forest restoration by successfully establishing when seeded on disturbed and compacted ground.

Aim To examine whether the tree flora of the Atlantic forest of northeastern Brazil has experienced detectable taxonomic homogenization via the proliferation of native pioneer species in response to habitat loss and fragmentation. Location Biotic homogenization (BH) was examined across the Atlantic forest of northeast Brazil, i.e. a 56,000 km² piece of tropical forest and a distinct centre of species endemism in South America. Methods We assessed a dataset consisting of 5122 tree records and compared the similarity of tree floras from 12 semi-natural sub-regions of the Atlantic forest between two time periods: pre-1980 (plant records between 1902 and 1980), and post-1980 (between 1981 and 2006). To understand the mechanisms leading to BH (1) tree floras were ordered (via non-metric multidimensional scaling - NMDS) by date (pre/post 1980) based on species occurrence and frequency, (2) NMDS axes were regressed against the proportion of those species that increased their occurrence post-1980 (i.e. the winner species), and (3) patterns of geographic distribution and frequency of particular life-history traits were examined across winner species and a control group. Results Tree floras across the Atlantic forest became c. 20-40% more similar to each other post-1980, but patterns of species similarity were also influenced by between-plot geographical distance. NMDS ordination clearly segregated pre- and post-1980 floras with a clear signal of floristic convergence. Furthermore, winner tree species were largely composed of short-lived and small-seeded pioneer species that exhibit wide geographic distributions. Main conclusions Our results suggest that tropical forest biotas are susceptible to taxonomic homogenization (i.e. increasing levels of similarity) in the context of severe human-disturbance via the proliferation of particular groups of native species comprised mainly by ecologically-plastic, generalist species. We are thus extending the concept of homogenization to address and highlight a pervasive biological shift in the structure of tropical forest communities currently taking place across hyper-fragmented landscapes.

Lomatia hirsuta (Lam.) Diels is a pioneer tree species that develops after wildfires, and in advanced successional stages, it is often found as a secondary species in Patagonian forests. However, in El Manso Valley, Province of Río Negro in Western Argentina, L. hirsuta forms mature pure stands, originated from stump shoots. The wood is very attractive for its colourful appearance and beautiful grain. Nevertheless, these forests are not managed for timber production, they are mostly strong thinned for grazing, and the wood is mainly used as firewood. The objective of this study was to evaluate the possibility to improve quality wood production in stands through silvicultural interventions in a sustainable way. Samples have been carried out in stands of different developmental stages. We evaluated the state and quality of the trees, and their growth has been studied by means of trunk analysis. The results indicate that there is significant potential to improve the production of quality wood in dense stands by thinning to release crop trees. Thinning should start in young stands. It also became apparent that forest management is first necessary to stabilise these nearly unattended forests.

Background/Aims The European larch is a pioneer tree and a valuable economic resource in subalpine ecosystems, thus playing crucial roles to ecosystem services and human activities. However, their ectomycorrhizal fungal community remains unknown in high altitudinal natural habitats. Here, we explore the mycobiont diversity of Larix decidua var. decidua between naturally rejuvenated and adult trees, compare ectomycorrhizal colonization patterns in geographically disjunct areas within the Alps of South Tyrol, Italy, characterized by distinct climatic conditions, and explore turnover rates across various seasons. Methods Our approach combines morphotyping of mycorrhized root tips with molecular analysis. Particular effort was given to monitor both ectomycorrhizal host-specialist and -generalist fungi. Results Both adult and young trees show a 100% mycorrhization rate, with a total diversity of 68 ectomycorrhizal species. The ectomycorrhizal composition is dominated by typical host specialists of larch trees (e.g., Lactarius porninsis , Russula laricina , Suillus cavipes , S. grevillei , S. viscidus ), which are widely distributed across sites. A rich diversity of host generalists was also detected. The composition of rare species within a habitat was comparatively consistent during one sampling campaign, but exhibited significant differences among individual sampling campaigns. The ectomycorrhizal compositions were only weakly correlated with distinct climatic conditions and tree ages. However, species richness and diversity, particularly of generalist fungi, was consistently higher in warmer, drier sites compared to cooler, more humid ones. Conclusions This study suggests potential mycobiont community shifts across climatic conditions with significant implications for the adaptability and resilience of subalpine forests in the face of climate change.

The Janzen–Connell (JC) hypothesis provides a conceptual framework for explaining the maintenance of tree diversity in tropical forests. Its central tenet—that recruits experience high mortality near conspecifics and at high densities—assumes a degree of host specialization in interactions between plants and natural enemies. Studies confirming JC effects have focused primarily on spatial distributions of seedlings and saplings, leaving major knowledge gaps regarding the fate of seeds in soil and the specificity of the soilborne fungi that are their most important antagonists. Here we use a common garden experiment in a lowland tropical forest in Panama to show that communities of seed-infecting fungi are structured predominantly by plant species, with only minor influences of factors such as local soil type, forest characteristics, or time in soil (1–12 months). Inoculation experiments confirmed that fungi affected seed viability and germination in a host-specific manner and that effects on seed viability preceded seedling emergence. Seeds are critical components of reproduction for tropical trees, and the factors influencing their persistence, survival, and germination shape the populations of seedlings and saplings on which current perspectives regarding forest dynamics are based. Together these findings bring seed dynamics to light in the context of the JC hypothesis, implicating them directly in the processes that have emerged as critical for diversity maintenance in species-rich tropical forests.

Recent collection efforts along the Brazilian coast revealed a Haliclona species preliminarily identified as a likely new species. However, sequencing of the 28S rRNA C-Region, a barcode marker in sponges, showed its high genetic similarity with a Haliclona sp. from Hawaiʻi (GenBank MW016137–MW016139). We applied an integrated morphological and molecular assessment, which allowed us to identify both Brazilian and Hawaiian specimens as H. ( Reniera ) laubenfelsi , a species with an Indo-Pacific distribution. We postulate this species to be exotic both in the Brazilian coast and in Hawaiʻi. Our evidence is based on the arrival of the species in Brazil after 2001, being first registered next to an international port. In turn, the species is distributed discontinuously in Hawaiʻi, being mainly restricted to sheltered bays and vicinities of ports, showing a predilection for anthropogenic substrates, which strengthen the hypothesis of its exotic origin. Recent collections in Hawaiʻi (2016–2018) failed to find this species in natural habitats, though it was an abundant pioneer species in Autonomous Reef Monitoring Structures. Its capacity to colonize artificial substrata may indicate either a cryptobenthic nature or an invasive potential. We highlight the need of monitoring its abundance, spatial distribution, and biotic interactions along the Brazilian coast to assess its potential environmental impacts. The full morphological description, and the molecular sequences we provided certainly will speed up the identification of this species, allowing to track its range extension.

The humid highlands of the Galapagos are the islands’ most biologically productive regions and a key habitat for endemic animal and plant species. These areas are crucial for the region’s food security and for the control of invasive plants, but little is known about the spatial distribution of its land cover. We generated a baseline high-resolution land cover map of the agricultural zones and their surrounding protected areas. We combined the high spatial resolution of PlanetScope images with the high spectral resolution of Sentinel-2 images in an object-based classification using a RandomForest algorithm. We used images collected with an unmanned aerial vehicle (UAV) to verify and validate our classified map. Despite the astounding diversity and heterogeneity of the highland landscape, our classification yielded useful results (overall Kappa: 0.7, R2: 0.69) and revealed that across all four inhabited islands, invasive plants cover the largest fraction (28.5%) of the agricultural area, followed by pastures (22.3%), native vegetation (18.6%), food crops (18.3%), and mixed forest and pioneer plants (11.6%). Our results are consistent with historical trajectories of colonization and abandonment of the highlands. The produced dataset is designed to suit the needs of practitioners of both conservation and agriculture and aims to foster collaboration between the two areas.