ForestClim-Bioclimatic variables for microclimate temperatures of European forests.

Microclimate research gained renewed interest over the last decade and its importance for many ecological processes is increasingly being recognized. Consequently, the call for high-resolution microclimatic temperature grids across broad spatial extents is becoming more pressing to improve ecological models. Here, we provide a new set of open-access bioclimatic variables for microclimate temperatures of European forests at 25 × 25 m2 resolution.

ForestTemp - Sub-canopy microclimate temperatures of European forests.

Ecological research heavily relies on coarse-gridded climate data based on standardized temperature measurements recorded at 2 m height in open landscapes. However, many organisms experience environmental conditions that differ substantially from those captured by these macroclimatic (i.e. free air) temperature grids. In forests, the tree canopy functions as a thermal insulator and buffers sub-canopy microclimatic conditions, thereby affecting biological and ecological processes. To improve the assessment of climatic conditions and climate-change-related impacts on forest-floor biodiversity and functioning, high-resolution temperature grids reflecting forest microclimates are thus urgently needed. Combining more than 1200 time series of in situ near-surface forest temperature with topographical, biological and macroclimatic variables in a machine learning model, we predicted the mean monthly offset between sub-canopy temperature at 15 cm above the surface and free-air temperature over the period 2000-2020 at a spatial resolution of 25 m across Europe. This offset was used to evaluate the difference between microclimate and macroclimate across space and seasons and finally enabled us to calculate mean annual and monthly temperatures for European forest understories. We found that sub-canopy air temperatures differ substantially from free-air temperatures, being on average 2.1°C (standard deviation ± 1.6°C) lower in summer and 2.0°C higher (±0.7°C) in winter across Europe. Additionally, our high-resolution maps expose considerable microclimatic variation within landscapes, not captured by the gridded macroclimatic products. The provided forest sub-canopy temperature maps will enable future research to model below-canopy biological processes and patterns, as well as species distributions more accurately.

Specialized fungal parasites reduce fitness of their lichen hosts.

Background and aims: Understanding to what extent parasites affect host fitness is a focus of research on ecological interactions. Fungal parasites usually affect the functions of vascular plants. However, parasitic interactions comprising effects of fungal parasites on the fitness of lichen hosts are less well known. This study assesses the effects of the abundance of two highly specialized gall-forming fungi on growth of their two respective lichen hosts and tests whether these fungal parasites reduce lichen fitness. Methods: The relative biomass and thallus area growth rates, and change in specific thallus mass of Lobaria pulmonaria and L. scrobiculata were compared between lichens with and without galls of the lichenicolous fungi Plectocarpon lichenum and P. scrobiculatae, cultivated in a growth chamber for 14 d. By estimating the thallus area occupied by the galls, it was also assessed whether growth rates varied with effective photosynthetic lichen surface area. Key results: Plectocarpon galls significantly reduced relative growth rates of the lichen hosts. Growth rates decreased with increasing cover of parasitic galls. The presence of Plectocarpon-galls per se, not the reduced photosynthetic thallus surface due to gall induction, reduced relative growth rates in infected hosts. Specific thallus mass in the hosts changed in species-specific ways. Conclusions: This study shows that specialized fungal parasites can reduce lichen fitness by reducing their growth rates. Higher parasite fitness correlated with lower host fitness, supporting the view that these associations are antagonistic. By reducing hosts' growth rates, these parasites in their symptomatic life stage may affect important lichen functions. This fungal parasite-lichen study widens the knowledge on the ecological effects of parasitism on autotrophic hosts and expands our understanding of parasitic interactions across overlooked taxonomic groups.

Variation in the reproductive strategy of a lichenized fungus along a climatic gradient.

Background and aims: Onset of reproduction and reproductive allocation patterns are key components of plant reproductive strategies. Life history theory predicts that plants in adverse environments for juvenile performance start reproduction at smaller sizes and exhibit higher reproductive allocation compared to their counterparts in favourable environments. Life history theory will gain in generality if its predictions are shown to apply to a broad range of organisms and modes of reproduction. This study tested whether the asexual reproductive strategy of a lichenized fungus changed along a climatic gradient. Methods: The variation in threshold size for asexual reproduction and asexual reproductive allocation of the lichen Lobarina scrobiculata was assessed in 18 populations (9665 individuals) along a climatic gradient spanning 800 km in latitude in Southern Europe. Using generalized linear models and standardized major axis regressions, the allometric relationships and the associated variation in climatic factors according to the changes in the threshold size for reproduction and reproductive allocation patterns were assessed. Key Results: The onset of reproduction was size-dependent and the reproductive allocation increased with individual size. Both the threshold size for reproduction and the reproductive allocation varied along the rainfall gradient. A lower threshold size for reproduction and higher reproductive allocation in drier, adverse locations were found. Therefore, populations in drier locations fitted the predictions of life history theory for sexually reproducing organisms in adverse environments for juvenile performance. Conclusions: This study highlights the applicability of the life history theory to fungi and to modes of reproduction other than sexual reproduction. Based on the intraspecific variation in the asexual reproductive strategy of a fungal organism with climatic factors, these findings expand the scope of life history theory predictions and increase our understanding of life history diversity and reproductive strategies across environments.

Intraspecific life history variation in contrasting habitats: Insights from an obligate symbiotic organism.

PREMISE OF THE STUDY: Life history theory predicts that plants in unfavorable habitats for juvenile growth and survival will commence reproduction at smaller sizes and exhibit higher reproductive allocations than those in favorable habitats. The scope of life history theory will increase if these predictions apply to a broad range of organisms. Populations of organisms in contrasting habitats may experience different demographic rates. Thus, we compared the demography and life history traits of a lichen species in contrasting habitats. METHODS: We compared the abundance, growth, mortality, and reproductive strategy (threshold size for reproduction and reproductive allometry) of epiphytic and saxicolous populations of the asexually reproducing lichen Lobarina scrobiculata in two oak forests in central Spain. KEY RESULTS: The growth rates of saxicolous individuals were two times faster than those of epiphytic individuals. Epiphytic specimens exhibited a smaller threshold size for reproduction and a higher reproductive allocation than their saxicolous counterparts. The populations hosted by trees were two times larger than those on rocks (13,788 vs. 6629 individuals, respectively). The mortality rate did not vary between habitats. CONCLUSIONS: Our results demonstrate that contrasting habitats selected for differences in the demography and life history traits of a lichen species. Consistent with life history theory predictions, in the habitat with slower growth, L. scrobiculata started to reproduce at a smaller size and its reproductive allocation was higher. This study extends the scope of life history theory and improves our understanding of life history patterns and variations in overlooked taxa such as lichens.

The role of fungal parasites in tri-trophic interactions involving lichens and lichen-feeding snails.

Lichens are hosts for a variety of lichenicolous fungi. By investigating two lichens with specialized parasites, we will test the hypothesis that these parasites reduce lichen fitness by increasing the palatability of their respective hosts. The palatability of Lobarina scrobiculata and Lobaria pulmonaria with or without galls of the lichenicolous fungi, Plectocarpon scrobiculatae and P. lichenum, respectively, were quantified in a feeding-preference experiment with grazing snails (Cepaea hortensis). We repeated the experiment for pairs with or without gall in which the carbon-based secondary compounds (CBSCs) had been reduced nondestructively by acetone rinsing. Lichens with galls had lower concentration of CBSCs than those without, but this contrast disappeared after acetone rinsing. In the lichen high in nitrogen (N) (the cyanolichen L. scrobiculata), the grazing was low, and the snails did not discriminate between specimens with and without Plectocarpon-galls. In L. pulmonaria low in N (green algae as main photobiont), the parasite reduced the lichen C : N ratio and the snails strongly preferred specimens with Plectocarpon-galls, regardless of whether CBSC concentration had been reduced or not. In conclusion, some lichen parasites can indirectly reduce lichen fitness by increasing its palatability and thus the grazing pressure from snails, whereas other parasites do not affect grazing preferences.

Environmental factors that drive the distribution and abundance of a threatened cyanolichen in Southern Europe: a multi-scale approach.

PREMISE OF THE STUDY: High-quality information about threatened species is required to prevent current global biodiversity losses. Lichens are important components of forest biodiversity and help to maintain ecosystem functioning. The epiphytic cyanolichen Lobarina scrobiculata is red-listed in Europe and North America, but knowledge of its ecology and distribution in Southern Europe is scarce. METHODS: We used a multispatial scale design to investigate the effects of macroclimate, forest structure, tree features, and microhabitat on the occurrence, abundance, spatial distribution, and performance of Lobarina scrobiculata in the Iberian Peninsula at plot and tree scales. Generalized linear models and mixed models were used for analysis. KEY RESULTS: We recorded ca 14000 individuals of the threatened species Lobarina scrobiculata from 22 populations in the Iberian Peninsula. Our results suggest that L. scrobiculata thrives mainly in oak forests with highly variable annual precipitation levels. At the plot scale, the L. scrobiculata abundance increased with annual precipitation and tree density (habitat quantity). At the tree scale, our models highlighted the importance of tree size and bark roughness (habitat quality) as the main drivers of species occurrence and abundance. We detected a marked spatial pattern on tree trunks, i.e., L. scrobiculata occurred preferentially on north-facing surfaces and close to the ground where humidity is higher. CONCLUSIONS: By integrating multiscale modeling, we analyzed a unique large dataset and these results are essential for understanding the ecology of this threatened cyanolichen. There is an urgent need to preserve the forests that this species currently inhabits as well as potential colonization sites.

"Land-sparing benefits biodiversity while land-sharing benefits ecosystem services": Stakeholders' perspectives on biodiversity conservation strategies in boreal forests.

Biodiversity conservation and economic profit from forests can be combined by various land-sparing and land-sharing approaches. Using a semi-structured survey, we evaluated support for scenarios representing contrasting conservation strategies in a managed boreal forest landscape. Land-sparing approaches were supported by the conservation organisation, regional administrations and the forest company, mainly motivated by the benefit for biodiversity based on ecological theory. Land-sharing approaches were supported by one recreational organisation, some municipalities and the forest owners' association, mainly motivated by the delivery of ecosystem services. Stakeholder groups using certain ecosystem services had motivations that we related to an anthropocentric mindset, while others focused more on species conservation, which can be related both to an anthropocentric or an ecocentric mindsets. Forest conservation planning should consider stakeholders' preferences to handle land-use conflicts. Since reaching consensus among multiple stakeholders seems unfeasible, a combination of land-sparing and land-sharing approaches is probably the best compromise.

High-resolution data are necessary to understand the effects of climate on plant population dynamics of a forest herb.

Climate is assumed to strongly influence species distribution and abundance. Although the performance of many organisms is influenced by the climate in their immediate proximity, the climate data used to model their distributions often have a coarse spatial resolution. This is problematic because the local climate experienced by individuals might deviate substantially from the regional average. This problem is likely to be particularly important for sessile organisms like plants and in environments where small-scale variation in climate is large. To quantify the effect of local temperature on vital rates and population growth rates, we used temperature values measured at the local scale (in situ logger measures) and integral projection models with demographic data from 37 populations of the forest herb Lathyrus vernus across a wide latitudinal gradient in Sweden. To assess how the spatial resolution of temperature data influences assessments of climate effects, we compared effects from models using local data with models using regionally aggregated temperature data at several spatial resolutions (≥1 km). Using local temperature data, we found that spring frost reduced the asymptotic population growth rate in the first of two annual transitions and influenced survival in both transitions. Only one of the four regional estimates showed a similar negative effect of spring frost on population growth rate. Our results for a perennial forest herb show that analyses using regionally aggregated data often fail to identify the effects of climate on population dynamics. This emphasizes the importance of using organism-relevant estimates of climate when examining effects on individual performance and population dynamics, as well as when modeling species distributions. For sessile organisms that experience the environment over small spatial scales, this will require climate data at high spatial resolutions.

Intraspecific variation influences performance of moss transplants along microclimate gradients.

Identifying the environmental drivers of population dynamics is crucial to predict changes in species abundances and distributions under climate change. Populations of the same species might differ in their responses as a result of intraspecific variation. Yet the importance of such differences remains largely unexplored. We examined the responses of latitudinally distant populations of the forest moss Hylocomiastrum umbratum along microclimate gradients in Sweden. We transplanted moss mats from southern and northern populations to 30 sites with contrasting microclimates (i.e., replicated field common gardens) within a forest landscape, and recorded growth and survival of individual shoots over 3 yr. To evaluate the importance of intraspecific variation in responses to environmental factors, we assessed effects of the interactions between population origin and microclimate drivers on growth and survival. Effects on overall performance of transplanted populations were estimated using the product of survival and growth. We found differences between southern and northern populations in the response to summer temperature and snowmelt date in one of three yearly transitions. In this year, southern populations performed better in warm, southern-like conditions than in cold, northern-like conditions; and the reverse pattern was true for northern populations. Survival of all populations decreased with evaporation, consistent with the high hydric demands and poikilohydric nature of mosses. Our results are consistent with population adaptation to local climate, and suggest that intraspecific variation among populations can have important effects on the response of species to microclimate drivers. These findings highlight the need to account for differential responses in predictions of species abundance and distribution under climate change.

Contrasting Environmental Drivers Determine Biodiversity Patterns in Epiphytic Lichen Communities along a European Gradient.

Assessing the ecological impacts of environmental change on biological communities requires knowledge of the factors driving the spatial patterns of the three diversity facets along extensive environmental gradients. We quantified the taxonomic (TD), functional (FD), and phylogenetic diversity (PD) of lichen epiphytic communities in 23 beech forests along Europe to examine their response to environmental variation (climate, habitat quality, spatial predictors) at a continental geographic scale. We selected six traits related to the climatic conditions in forest ecosystems, the water-use strategy and the nutrient uptake, and we built a phylogenetic tree based on four molecular markers. FD and climate determined TD and PD, with spatial variables also affecting PD. The three diversity facets were primarily shaped by distinct critical predictors, with the temperature diurnal range affecting FD and PD, and precipitation of the wettest month determining TD. Our results emphasize the value of FD for explaining part of TD and PD variation in lichen communities at a broad geographic scale, while highlighting that these diversity facets provide complementary information about the communities' response under changing environmental conditions. Furthermore, traits such as growth form, photobiont type, and reproductive strategy mediated the response of lichen communities to abiotic factors emerging as useful indicators of macroclimatic variations.