Fires in the face of climate change: Indicators of fire disturbance in heath areas - Inference from military training lands.

Global warming significantly affects the frequency and intensity of wildfires in many fire-prone areas of the world and fire disturbance regimes are changing rapidly. Alongside this, controlled burning is often considered or implemented as an alternative method for nature protection. Here, we studied the post-fire secondary succession in dry heath habitat located in military training grounds to recognise the impact of fire on the effectiveness and rate of ecosystem recovery. We focus particularly on identifying indicator species for a given successional phase of Central European dry heath habitats and assessing their value for dating the last fire disturbance. The research involved 60 vegetation patches (plots of 25 m2), which were assigned to four post-fire age classes, namely: 1-5 years (Class A), 6-10 years (Class B), 11-15 years (Class C), and >15 years (Class D). In each study plot, species diversity and coverage of lichens, bryophytes and vascular plants were examined in addition to the physicochemical properties of the soil substrate. Cryptogams and vascular plants clearly differ in terms of the secondary succession pattern; specific sets of cryptogams correspond well to particular post-fire classes and are therefore good determinants of the post-fire succession stage. Spontaneous succession of plant vegetation eventually leads to complete recovery of the heath in a relatively short time. Nevertheless, great vegetation dynamics in the first years after a fire disturbance may result in seemingly different directions of succession. Post-fire classes did not differ noticeably in terms of soil properties, it follows that the effects of fire on soil conditions are negligible; though, a significant upward trend was observed for exchangeable form of K throughout the succession process. Our results indicate that sporadic fires reduce the undesirable overgrowth of heathlands or psamophilous grasslands and generally have a little negative side-effect on the ecosystem. The revealed succession patterns and defined sets of species characteristic for subsequent post-fire age classes are applicable to dating fire disturbances, regardless of whether the fire was planned or spontaneous.

Environmental drivers of ground-floor bryophytes diversity in temperate forests.

Bryophytes play important role in forest ecosystem functioning and their distribution and diversity are driven by numerous environmental factors. The aim of the present study was to bring new insights in deeper understanding of terrestrial bryophytes diversity in temperate forests, as well as to determine the environmental factors which have predominant influence on ground-floor bryophytes. The survey was conducted in Fruska Gora Mountain (Serbia) across seven forest sites where ground-bryophytes were sampled. Soil moisture, temperature, and pH were measured as soil characteristics, while herbaceous cover, litter cover, stream distance, number of trees and shrubs were used as characteristics of stand structure. Species richness, Shannon diversity index, and evenness index were used as diversity measures. Generalised linear model and canonical correspondence analysis (CCA) were used to test the influence of environmental variables on bryophyte diversity. Litter cover was the most important explanatory variable, followed by soil moisture, stream distance and tree number, respectively. Overall, the stand structure was found to have a greater impact on ground-floor bryophyte diversity compared to soil characteristics. Identification of the most significant ecological factors affecting the diversity and distribution of bryophytes in forest ecosystems is of great importance in forest ecology with the aim of defining adequate management methods to preserve the biodiversity of forests, with particular emphasis on endangered and rare bryophyte species.

Warming enhances dominance of vascular plants over cryptogams across northern wetlands.

Climate warming causes profound effects on structure and function of wetland ecosystem, thus affecting regional and global hydrological cycles and carbon budgets. However, how wetland plants respond to warming is still poorly understood. Here, we synthesized observations from 273 independent sites to explore responses of northern wetland plants to warming. Our results show that warming enhances biomass accumulation for vascular plants including shrubs and graminoids, whereas it reduces biomass accumulation for cryptogams including moss and lichen. This divergent response of vascular plants and cryptogams is particularly pronounced in the high latitudes where permafrost prevails. As warming continues, this divergent response is amplified, however, the reduction in cryptogams is more drastic. Warming leads to declined surface soil moisture and lowered water table, thereby shifting wetlands from a wet system dominated by cryptogams to a drier system with increased cover of vascular plants. Under a high-emission scenario of Shared Socioeconomic Pathways (SSP5), a 4.7-5.1°C mean global temperature rise will cause more than fivefold loss of cryptogams compared with current climate. As cryptogams are largely concentrated at northern high latitudes, where warming will likely be greater than the projected global mean, modification in wetland plant composition and major reduction in cryptogams are expected to occur even much earlier than 2100.

Trees as net sinks for methane (CH4 ) and nitrous oxide (N2 O) in the lowland tropical rain forest on volcanic Réunion Island.

Trees are known to emit methane (CH4 ) and nitrous oxide (N2 O), with tropical wetland trees being considerable CH4 sources. Little is known about CH4 and especially N2 O exchange of trees growing in tropical rain forests under nonflooded conditions. We determined CH4 and N2 O exchange of stems of six dominant tree species, cryptogamic stem covers, soils and volcanic surfaces at the start of the rainy season in a 400-yr-old tropical lowland rain forest situated on a basaltic lava flow (Réunion Island). We aimed to understand the unknown role in greenhouse gas fluxes of these atypical tropical rain forests on basaltic lava flows. The stems studied were net sinks for atmospheric CH4 and N2 O, as were cryptogams, which seemed to be co-responsible for the stem uptake. In contrast with more commonly studied rain forests, the soil and previously unexplored volcanic surfaces consumed CH4 . Their N2 O fluxes were negligible. Greenhouse gas uptake potential by trees and cryptogams constitutes a novel and unique finding, thus showing that plants can serve not only as emitters, but also as consumers of CH4 and N2 O. The volcanic tropical lowland rain forest appears to be an important CH4 sink, as well as a possible N2 O sink.

Biocrust-forming mosses mitigate the negative impacts of increasing aridity on ecosystem multifunctionality in drylands.

The increase in aridity predicted with climate change will have a negative impact on the multiple functions and services (multifunctionality) provided by dryland ecosystems worldwide. In these ecosystems, soil communities dominated by mosses, lichens and cyanobacteria (biocrusts) play a key role in supporting multifunctionality. However, whether biocrusts can buffer the negative impacts of aridity on important biogeochemical processes controlling carbon (C), nitrogen (N), and phosphorus (P) pools and fluxes remains largely unknown. Here, we conducted an empirical study, using samples from three continents (North America, Europe and Australia), to evaluate how the increase in aridity predicted by climate change will alter the capacity of biocrust-forming mosses to modulate multiple ecosystem processes related to C, N and P cycles. Compared with soil surfaces lacking biocrusts, biocrust-forming mosses enhanced multiple functions related to C, N and P cycling and storage in semiarid and arid, but not in humid and dry-subhumid, environments. Most importantly, we found that the relative positive effects of biocrust-forming mosses on multifunctionality compared with bare soil increased with increasing aridity. These results were mediated by plant cover and the positive effects exerted by biocrust-forming mosses on the abundance of soil bacteria and fungi. Our findings provide strong evidence that the maintenance of biocrusts is crucial to buffer negative effects of climate change on multifunctionality in global drylands.

Trends and concepts in fern classification.

BACKGROUND AND AIMS: Throughout the history of fern classification, familial and generic concepts have been highly labile. Many classifications and evolutionary schemes have been proposed during the last two centuries, reflecting different interpretations of the available evidence. Knowledge of fern structure and life histories has increased through time, providing more evidence on which to base ideas of possible relationships, and classification has changed accordingly. This paper reviews previous classifications of ferns and presents ideas on how to achieve a more stable consensus. SCOPE: An historical overview is provided from the first to the most recent fern classifications, from which conclusions are drawn on past changes and future trends. The problematic concept of family in ferns is discussed, with a particular focus on how this has changed over time. The history of molecular studies and the most recent findings are also presented. KEY RESULTS: Fern classification generally shows a trend from highly artificial, based on an interpretation of a few extrinsic characters, via natural classifications derived from a multitude of intrinsic characters, towards more evolutionary circumscriptions of groups that do not in general align well with the distribution of these previously used characters. It also shows a progression from a few broad family concepts to systems that recognized many more narrowly and highly controversially circumscribed families; currently, the number of families recognized is stabilizing somewhere between these extremes. Placement of many genera was uncertain until the arrival of molecular phylogenetics, which has rapidly been improving our understanding of fern relationships. As a collective category, the so-called 'fern allies' (e.g. Lycopodiales, Psilotaceae, Equisetaceae) were unsurprisingly found to be polyphyletic, and the term should be abandoned. Lycopodiaceae, Selaginellaceae and Isoëtaceae form a clade (the lycopods) that is sister to all other vascular plants, whereas the whisk ferns (Psilotaceae), often included in the lycopods or believed to be associated with the first vascular plants, are sister to Ophioglossaceae and thus belong to the fern clade. The horsetails (Equisetaceae) are also members of the fern clade (sometimes inappropriately called 'monilophytes'), but, within that clade, their placement is still uncertain. Leptosporangiate ferns are better understood, although deep relationships within this group are still unresolved. Earlier, almost all leptosporangiate ferns were placed in a single family (Polypodiaceae or Dennstaedtiaceae), but these families have been redefined to narrower more natural entities. CONCLUSIONS: Concluding this paper, a classification is presented based on our current understanding of relationships of fern and lycopod clades. Major changes in our understanding of these families are highlighted, illustrating issues of classification in relation to convergent evolution and false homologies. Problems with the current classification and groups that still need study are pointed out. A summary phylogenetic tree is also presented. A new classification in which Aspleniaceae, Cyatheaceae, Polypodiaceae and Schizaeaceae are expanded in comparison with the most recent classifications is presented, which is a modification of those proposed by Smith et al. (2006, 2008) and Christenhusz et al. (2011). These classifications are now finding a wider acceptance and use, and even though a few amendments are made based on recently published results from molecular analyses, we have aimed for a stable family and generic classification of ferns.

Cryptogamic Biomass in Pannonic Acidic Sand Steppes Subject to Changing Land-Use.

Cryptogams, often neglected in vegetation dynamics studies, compose a large part of biomass and contribute to the biodiversity of sandy grasslands. Since the work of Verseghy (1970s), their productivity has not been analyzed in Hungary. We studied the lichen and bryophyte dynamics (hereinafter called cryptogams) at two Eastern Hungarian dry sandy grassland sites. The sites of Corynephorus canescens and of Festuca vaginata dominance, respectively, belonging to the community Festuco vaginatae-Corynephoretum have been monitored. We aimed at (1) quantifying the diversity and biomass of the cryptogamic communities; (2) exploring the cryptogamic response to management changes; and (3) studying the effect of experimental management (fencing) on the cryptogamic assemblages. The sites have been compared in 2013 and 2018, respectively. Forty microplots per site per management have been analyzed in both years. Samples of lichens and bryophytes were hand-sorted, dried and then measured. Fencing has led to increased biomass of cryptogams within a few years. Lichens in general benefited comparatively more from exclosure than bryophytes. The increase in lichen biomass (especially that of Cladonia rangiformis) is clearly due to the over 10-year absence of grazing. The only lichen favored by moderate grazing is the legally protected C. magyarica. Short spells of low-intensity grazing can promote the species richness of cryptogams in the community.

Assessing the present levels of 137Cs in the remote ecosystem of Bjornoya (South Svalbard).

The remoteness and small size of Bjornoya (S Svalbard) make the island one of the most unreachable places in the Arctic. Limited accessibility contributes to still-existing knowledge gap on isotope accumulation in compartments of its ecosystem. Therefore, in this study we aimed to investigate the current concentration of 137Cs in the terrestrial samples of vascular plants, cryptogams, and soil collected on Bjornoya in 2021. The measured average activity of 137Cs in bryophytes was 56.5 Bq kg-1, lichens 27.6 Bq kg-1, vascular plants 7.26 Bq kg-1, and soil 9.63 Bq kg-1. In the case of bryophytes, 137Cs activity was negatively correlated with δ15N. Our results suggest that bird guano was the main source of nitrogen and 137Cs for vascular plants. For bryophytes, significantly lower values of δ15N than in vascular plants suggests that this group is more sensitive to atmospheric N intake, with fallout being the main source of 137Cs.

Physiological Plasticity as a Strategy to Cope with Harsh Climatic Conditions: Ecophysiological Meta-Analysis of the Cosmopolitan Moss Ceratodon purpureus in the Southern Hemisphere.

Determining the physiological tolerance ranges of species is necessary to comprehend the limits of their responsiveness under strong abiotic pressures. For this purpose, the cosmopolitan moss Ceratodon purpureus (Hedw.) Brid. is a good model due to its wide geographical distribution throughout different biomes and habitats. In order to disentangle how this species copes with stresses such as extreme temperatures and high radiation, we designed a meta-analysis by including the main photosynthetic traits obtained by gas exchange measurements in three contrasting habitats from the Southern Hemisphere. Our findings highlight that traits such as respiration homeostasis, modulation of the photosynthetic efficiency, adjustment of the optimal temperature, and switching between shade and sun-adapted forms, which are crucial in determining the responsiveness of this species. In fact, these ecophysiological traits are in concordance with the climatic particularities of each habitat. Furthermore, the photosynthetic trends found in our study point out how different Livingston Island (Maritime Antarctica) and Granite Harbour (Continental Antarctica) are for plant life, while the population from the Succulent Karoo Desert (South Africa) shares traits with both Antarctic regions. Altogether, the study highlights the high resilience of C. purpureus under abrupt climate changes and opens new perspectives about the wide spectrum of physiological responses of cryptogams to cope with climate change scenarios.

Patterns and drivers of cryptogam and vascular plant diversity in glacier forelands.

Vascular and nonvascular plants are affected by environmental factors determining their distribution and shaping their diversity and cover. Despite the cryptogam commonness in Arctic communities, previous studies have often focused on limited number of factors and their impact on only selected species of vascular plants or cryptogams. Our study aimed to investigate in detail the differences in species diversity and cover of cryptogams and vascular plants in the glacier forelands and mature tundra on Svalbard. Furthermore, we determined the biotic and abiotic factors that affected diversity, cover and distribution of cryptogam and vascular plant species. In 2017, we established 201 plots in eight locations (each including habitat type of foreland and mature tundra) and surveyed species abundance, sampled soils and environmental data. Results revealed that diversity and cover of analysed groups differed significantly between locations and habitat types, except for cryptogam cover in mature tundra in terms of location. Distance to the glacier terminus, slope, soil conductivity, nutrient content, and clay content impacted both plant groups' diversity. In contrast, distance to the glacier terminus, nutrient content and soil pH affected their cover. In addition, for cryptogam diversity and cover, foreland location and vascular plant cover were also important, while for vascular plant cover time elapsed after glacier retreat was significant. Distribution of both groups' species in forelands was associated with time elapsed after glacier retreat, soil pH, and nutrient contents. Soil texture and distance to the glacier terminus additionally influenced cryptogam distribution. The positive impact of vascular plants on cryptogam diversity and cover indicates complex relationships between these groups, even in forelands' relatively simple communities. As the cryptogam diversity in the polar areas is high but still largely unknown, future studies on species ecology and climate change impact on vegetation should consider both vascular plants and cryptogams and interactions between these groups.