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Abstract. Parasitic plants growing on tree branches may be a novel niche and phytoresource for arthropods. The spatial continuity between hosts and their parasites in canopies might provide a homogeneous environment for arthropod communities, but differences in mistletoe leaves and host needles could be exploited by different species of arthropods. Therefore, it is important to determine insect-community assemblages in order to discover the role of parasitic plants as a different habitat for arthropods. Thus, we aim to evaluate the level of similarity between the arthropod community on mistletoe (Viscum album) and that on its two principal pine hosts, Black pine (Pinus nigra) and Scots pine (P. sylvestris), on a Mediterranean mountain. Our results reveal that, irrespective of the species of pine host, V. album has a stable, independent and simple arthropod trophic web, composed mainly of two specialist hemipteran herbivores, Cacopsylla visci (Psyllidae) and Pinalitus viscicola (Miridae), and a hemipteran predator, Anthocoris visci (Anthocoridae). Despite this, the composition of the arthropod communities differed signifi cantly on both host species, with a greater richness and diversity on Scots than Black pine and these differences are not refl ected in the community on mistletoe. Overall, we conclude that, although Viscum album is considered to be a pest of pine, its presence increases the heterogeneity of the forest canopy by providing a novel habitat for a new and specifi c community of arthropods. In addition, this is a new record for and most probably an extension of the southernmost limit of the known geographical distribution of the arthropod community inhabiting V. album.

Indirect interactions emerge among a wide range of herbivores sharing the same plant resource. Consumers usually belong to different trophic guilds, from folivores and sapsuckers to parasitic plants. We propose that mistletoes parasitizing pines could play a key role acting as herbivores on host pines and coming indirectly into competition with other herbivores feeding on the same host. Changes caused by mistletoes on its host have been well studied, but its effects running across trophic webs remain unrevealed. In this study, we investigate the effect of European mistletoe (Viscum album subsp. austriacum) on the host‐feeding herbivores via trait‐mediated indirect interactions (TMIIs) across their shared pine host (Pinus nigra subsp. salzmannii). We performed field and laboratory experiments, and analyzed the net effect of different mistletoe parasite loads on three host‐phytophagous species: the sapsucker Cinara pini (Aphididae), the winter folivore Thaumetopoea pityocampa (Thaumetopoeidae), and the summer folivore Brachyderes sp. (Curculionidae), all being members of different functional feeding groups (FFGs). We summarize the mistletoe–host–herbivore interactions by means of a TMII, where mistletoe parasitism causes non‐trophic links and detrimental indirect interactions on pine‐feeding herbivores across its shared host, suggesting a worsening of host quality as food. These indirect interactions vary according to three parameters. First, the intensity has a non‐proportional relation with parasite load, showing an impact threshold on highly parasitized pines. Second, the movement capacity of insect herbivores determines their response, by decreasing the abundance of herbivores with low movement ability (aphids and pine processionary caterpillars) while altering the behavior (plant selection) of more mobile herbivores (pine weevils). Finally, FFG determines the intensity of mistletoe parasitism effects, folivores being more responsive than sapsuckers. Overall, mistletoe generates non‐trophic interaction linkages in the forest able to modify community structure by becoming a nexus of the entire herbivore community of the pine canopy.

Revegetation is key to achieve the goals of the UN Decade on Ecosystem Restoration. For many situations and plant species, selecting direct seeding or planting can define revegetation success. However, there is no clarity about when one method should be preferred over the other, partly driven by methodological difficulties that preclude avoiding bias during experimentation. To move the debate forward, (1) we propose a systematic review of the studies that compare seeding and planting, including how they have handled bias; and (2) we describe an ongoing experiment that tests different ways to handle bias when comparing seeding with planting.

Fire greatly affects plant and animal biodiversity. There is an extensive body of literature on the effects of fire on insect communities, in which a large variability of responses has been observed. Very few studies, however, have addressed functional responses at the species level, information that would greatly enhance our understanding of the impact of fire at higher organisational levels. The aim of this study is to analyse the short‐term ecological and behavioural responses of the Mediterranean ant Aphaenogaster gibbosa to fire‐induced environmental changes. We compared aspects of the abiotic and biotic environment relevant to this species, as well as differences in colony foraging behaviour, on unburnt and burnt plots in a Mediterranean area that was affected by a wildfire. Our results showed that fire modified plant cover around nests and daily cycles of soil temperature close to the nest. Although there were no significant differences in food quantity, food quality (particularly seed composition) was different between unburnt and burnt plots. In accordance with these environmental changes, we found significant differences in the daily activity rhythms and diet composition of A. gibbosa between unburnt and burnt plots. Overall, these differences did not result in significant changes in overall foraging activity and efficiency, allowing ant colonies to maintain the same food intake regardless of the habitat they occupied. We conclude that A. gibbosa uses behavioural plasticity to modify its foraging strategy in recently burnt environments and thus survive post‐fire conditions.

& Key message Parasitism by mistletoe increases the cover and diversity of herbaceous vegetation under the host tree and attracts the activity of rabbits in comparison to control trees. Thus, the effects on forest community go beyond the parasitized tree. & Context Mistletoes are a diverse group of aerial hemiparasitic plants and are considered keystone species in forest ecosystems around the world. They produce nutrient-enriched litter, which exerts a substantial effect on soil-nutrient concentration, and the enriched nutrient patch alters the vegetation at the site as well as the associated fauna. & Aims Our goal is to ascertain whether mistletoe (Viscum album) parasitism of pine forest of a Mediterranean mountain favors herbaceous vegetation and attracts mammalian herbivores. & Methods We recorded in Sierra de Baza (SE Spain) the composition of the herbaceous vegetation under pines with and without mistletoe parasitism, and estimated the rabbit activity at the same sites by collecting their excrements. & Results An effect on herbaceous vegetation, especially in grasses belonging to the family Poaceae, was reflected in a notable increase in soil cover, species richness, and species diversity beneath parasitized pines with respect to unparasitized ones. As a consequence, parasitized pines attract the activity of rabbits, as shown by a fivefold quantity of excrement with respect to control ones. & Conclusion Parasitism by mistletoe, by creating patches of greater nutrient availability under the host canopy, extends its effects beyond the host tree to other members of the forest community, such as herbaceous plants and associated herbivorous animals, which in turn contribute to environmental heterogeneity with their activity.

1. The colonisation of a new habitat by a community is led by deterministic and stochastic processes at different spatio‐temporal scales. Parasitic plants, such as mistletoe, represent a new habitat within forest canopy that is free to be colonised by many organisms. 2. This study investigates how ecological factors operating at forest and plant scales drive changes in both specialist (mistletoe‐dwelling) and tourist (transient visitors) arthropod communities inhabiting European mistletoe, Viscum album subsp. austriacum, in a Mediterranean pine forest. The influence of elevation along a broad elevational gradient was tested by sampling arthropod communities dwelling in mistletoe plants and host pine branches and the effects of mistletoe plant size, distances to other mistletoes, and temporal variation in arthropod assemblages inhabiting mistletoes. 3. The diversity of the specialist community remained constant along the elevational gradient and over the summer period, while the tourist and pine‐dwelling arthropod communities showed species turnover. Larger mistletoes were occupied by more species and individuals, whereas more isolated mistletoes presented the same equilibrium point as the more aggregated ones. Thus, mistletoe size is key to the composition of the arthropod community. 4. In conclusion, this study's findings indicate contrasting assembly rules for specialised and tourist arthropod communities associated with mistletoe. The specialist community was highly stable and followed a deterministic trophic sequence of colonisation as the assemblage rule: first, colonisation by the main specialist herbivore, Cacopsylla visci, and, second, by its predator Anthocoris visci. Meanwhile, the tourist community, being a subset of the arthropod assemblage of the pine, acts independent of mistletoe presence.

Providing fruit, nectar, leaves and litter, mistletoes represent important resources for many organisms, linking above-ground patterns with below-ground processes. Here, we explore how mistletoe litter affects arthropod availability, especially those taxa preferentially consumed by ground-feeding insectivorous birds, a group that has undergone widespread declines. We estimated the influence of mistletoe on arthropod occurrence by sampling arthropod communities beneath infected and uninfected trees with pit-fall traps. Then, we experimentally isolated direct effects of mistletoe litter on arthropods with a litterbag study. Soil arthropod communities beneath infected trees had consistently greater abundance and biomasstotal arthropods and the subset of arthropods preferentially consumed by ground-foraging insectivorescompared to otherwise comparable uninfected trees. Arthropods showed a weak response to litter addition, with maximum abundances recorded from bags with low mistletoe litter, significantly lower abundances associated with higher mistletoe fractions and pure tree litter (after 5 months). Our findings confirm that mistletoe occurrence has a significant positive impact on arthropod availability, especially on those preferred by ground-foraging bird insectivores. However, only a minor part of this impact is due to the direct, short-term effects of mistletoe litter, which suggests that additional mistletoe-mediated effects (e.g. local changes in structural or microclimatic factors, cumulative effects over multiple years) play significant roles. By altering arthropod assemblages within leaf litter and increasing the heterogeneity of resource availability on forest floors, mistletoe plays an important role in improving habitat quality for declining insectivores.