How to Replicate the Functions and Biodiversity of a Threatened Tree Species? The Case of Fraxinus excelsior in Britain

Microclimates hold the key to spatial forest planning under climate change: Cyanolichens in temperate rainforest

There is deepening interest in how microclimatic refugia can reduce species threat, if suitable climatic conditions are maintained locally, despite global climate change. Microclimates are a particularly important consideration in topographically heterogeneous landscapes, while in some habitats, such as forests and woodlands, microclimates are also extremely labile and affected by management practices that could consequently be used to offset climate change impact. This study explored a conservation priority guild-cyanolichen epiphytes in temperate rainforest-quantifying the niche response to macroclimate, and landscape or woodland stand structures that determine the microclimate. Based on epiphyte survey in a core region of European temperate rainforest (western Scotland), a 'random forest' machine-learning model confirmed a strong cyanolichen response to summer dryness, as well as the effects of distance to running water, topographic heatload and tree species identity, which modify the local moisture regime and/or lichen growth rates. By quantifying this response to macroclimate, landscape and stand structures, it was possible to estimate an extent to which woodland may be expanded in the future, to offset a negative effect of increasing summer dryness projected through to the 2080s. Using current policy as a yardstick, sufficient woodland expansion could be delivered relatively quickly for median impacted sites, but with times to woodland delivery extending over 10, 20 and 25 years for sites at the 75th, 90th and 95th percentiles of cyanolichen decline. Furthermore, the extent of new woodland required, and delivery times, increase almost threefold on average, as new woodland becomes distributed over wider riparian zones. These contrasting implications emphasize an urgent need for afforestation that achieves targeted spatial planning responsive to microclimates as refugia.

Emerging Fungal Threats to Plants and Animals Challenge Agriculture and Ecosystem Resilience

While fungi can make positive contributions to ecosystems and agro-ecosystems, for example, in mycorrhizal associations, they can also have devastating impacts as pathogens of plants and animals. In undisturbed ecosystems, most such negative interactions will be limited through the coevolution of fungi with their hosts. In this article, we explore what happens when pathogenic fungi spread beyond their natural ecological range and become invasive on naïve hosts in new ecosystems. We will see that such invasive pathogens have been problematic to humans and their domesticated plant and animal species throughout history, and we will discuss some of the most pressing fungal threats of today.

A role for the asexual spores in infection of Fraxinus excelsior by the ash-dieback fungus Hymenoscyphus fraxineus

The invasive pathogen, ash dieback fungus Hymenoscyphus fraxineus, is spreading rapidly across Europe. It shows high levels of outcrossing and limited population structure, even at the epidemic front. The anamorphic (asexual) form produces prolific conidia, thought to function solely as spermatia (male gametes), facilitating gene flow between sympatric strains. Here, we show that conidia are capable of germination on ash leaves and in vitro, and can infect seedlings via leaves or soil. In leaves, germlings form structures resembling fruiting bodies. Additionally, H. fraxineus colonises ash debris and grows in soil in the absence of ash tissues. We propose an amended life-cycle in which wind-dispersed, insect-vectored or water-spread conidia infect ash and may sporulate in planta, as well as in forest debris. This amplifies inoculum levels of different strains in ash stands. In combination with their function as spermatia, conidia thus act to maximise gene flow between sympatric strains, including those originally present at low inoculum. Such mixing increases evolutionary potential, as well as enhancing the likelihood of gene introgression from closely-related strains or assimilation of further genetic diversity from parental Asian populations. This scenario increases the adaptability of H. fraxineus to new climates and, indeed, onto new host species.