Publications

About half of the world's tropical peatlands occur in Southeast (SE) Asia, where they serve as a major carbon (C) sink. Nearly 80% of natural peatlands in this region have been deforested and drained, with the majority under plantations and agriculture. This conversion increases peat oxidation which contributes to rapid C loss to the atmosphere as greenhouse gas emissions and increases their vulnerability to fires which generate regional smoke haze that has severe impacts on human health. Attempts at restoring these systems to mitigate environmental problems have had limited success. We review the current understanding of intact and degraded peatlands in SE Asia to help develop a way forward in restoring these ecosystems. As such, we critically examine them in terms of their biodiversity, C storage, hydrology and nutrients, paying attention to both above‐ground and below‐ground subsystems. We then propose an approach for better management and restoration of degraded peatlands that involves explicit consideration of multiple interacting ecological factors and the involvement of local communities who rely on converted peatlands for their livelihood. We make the case that as processes leading to peatland development involve modification of both above‐ground and below‐ground subsystems, an integrated approach that explicitly recognizes both subsystems and their interactions is key to successful tropical peatland management and restoration. Synthesis and applications . Gaining a better understanding of not just carbon stores and their changes during peat degradation, but also an in‐depth understanding of the biota, nutrient dynamics, hydrology and biotic and abiotic feedbacks, is key to developing better solutions for the management and restoration of peatlands in Southeast Asia. Through the application of science‐ and nature‐based solutions that recognize the interactions among the above‐ground and below‐ground subsystems, and taking into account the livelihood needs of local people, we propose a way to mitigate the ongoing environmental damage that is occurring in these iconic and unique ecosystems.

There has been much recent interest in understanding how abiotic factors such as light, nutrients, and soil moisture affect the composition and biomass of lichen communities. Meanwhile, whether and how ground layer vegetation such as bryophytes and shrubs also influence lichen communities have received much less attention, particularly regarding how these effects vary across environmental gradients. In this study, we used a long‐term (19‐year) biodiversity manipulation experiment to assess the importance of feather moss and ericaceous dwarf shrub removals on the composition and diversity (assessed via metabarcoding) and biomass (assessed via PLFA markers) of terricolous lichen communities along a 5000‐year boreal forest post‐fire chronosequence in northern Sweden. Overall, our results showed that shrub removals had a greater impact than moss removals on the biomass and composition of lichen communities. Shrub removals increased lichen alpha‐diversity while decreasing lichen beta‐diversity. This is mainly because, although the number of lichen species increased in the absence of shrubs, lichen communities were strongly dominated by Cladonia spp. However, the effects of shrub removals were context‐dependent, with greater effects observed in older ecosystems. Our results highlight that shrubs had a greater impact than moss in shaping terricolous lichen communities in boreal forests, with increasing effects from young ecosystems to older ones. We conclude that the foreseen expansion of vascular plants such as ericaceous shrubs into high latitude regions will probably have negative consequences on lichen cover, but that these effects will be dependent on the environmental context.

Summary Invasive herbivores can strongly affect ecosystems by reducing or removing native plant species, and early in primary successions they could have enduring consequences for plant community assembly and ecosystem functioning, although this has seldom been explored. Invasive brushtail possums ( Trichosurus vulpecula ) browse from ground levels to forest canopies in New Zealand, including on plant species common early in primary succession. We used exclosures (fenced on the top as well as the sides) and corresponding control plots to study effects of brushtail possums on primary successions on bare landslide surfaces in the South Island of New Zealand. We then conducted repeated measurements of the plant community over 11 years and at the end also quantified soil abiotic and biotic properties. Above‐ground, plant biomass increased from close to zero to > 1000 g dry mass m −2 after 11 years in both exclosures and control plots, with significantly more biomass of the N 2 ‐fixing tree Carmichaelia odorata in the controls. Brushtail possums reduced the biomass in the control plots of small‐stature grasses and sedges in the first 3 years. Plant species richness was greater in control than exclosure plots throughout the experiment. Below‐ground, soil carbon and nitrogen concentrations and the biomass of all major soil microbial groups were significantly greater in the control than exclosure plots, although soil nematode abundances were not. Below‐ground effects could be attributed to the greater biomass of Carmichaelia in control plots. Synthesis . Our study shows that an invasive herbivore exerted strong effects on the rate and trajectory of primary succession by altering plant community assembly. Herbivore exclusion resulted in reduced biomass of a key N 2 ‐fixing tree that drives forest development, with important below‐ground consequences. These results support a view that restoration of ecosystems needs to consider the consequences of altering plant community structure before removing invasive herbivores.

While there has been much interest in the relationships between traits of primary producers and composition of associated invertebrate consumer communities, our knowledge is largely based on studies from vascular plants, while other types of functionally important producers, such as lichens, have rarely been considered. To address how physiological traits of lichens drive community composition of invertebrates, we collected thalli from 27 lichen species from southern Norway and quantified the communities of associated springtails, mites, and nematodes. For each lichen species, we measured key physiological thallus traits and determined whether invertebrate communities were correlated with these traits. We also explored whether invertebrate communities differed among lichen groups, categorized according to nitrogen‐fixing ability, growth form, and substratum. Lichen traits explained up to 39% of the variation in abundances of major invertebrate groups. For many invertebrate groups, abundance was positively correlated with lichen N and P concentrations, N:P ratio, and the percentage of water content on saturation (WC), but had few relationships with concentrations of carbon‐based secondary compounds. Diversity and taxonomic richness of invertebrate groups were sometimes also correlated with lichen N and N:P ratios. Nitrogen‐fixing lichens showed higher abundance and diversity of some invertebrate groups than did non‐N‐fixing lichens. However, this emerged in part because most N‐fixing lichens have a foliose growth form that benefits invertebrates, through improving the microclimate, independently of N concentration. Furthermore, invertebrate communities associated with terricolous lichens were determined more by their close proximity to the soil invertebrate pool than by lichen traits. Overall, our results reveal that differences between lichen species have a large impact on the invertebrate communities that live among the thalli. Different invertebrate groups show contrasting responses to traits that are indicative of thallus quality (nutrient concentrations), and thallus growth form is often an important determinant of the invertebrate community. Given the large diversity of lichen traits and growth forms that occur in many ecosystems, lichen–invertebrate communities may be an important contributor to overall community diversity in boreal forests.

New Zealand's offshore and outlying islands have long been a focus of conservation biology as sites of local endemism and as last refuges for many species. During the c. 730 years since New Zealand has been settled by people, mammalian predators have invaded many islands and caused local and global extinctions. New Zealand has led international efforts in island restoration. By the late 1980s, translocations of threatened birds to predator-free islands were well under way to safeguard against extinction. Non-native herbivores and predators, such as goats and cats, had been eradicated from some islands. A significant development in island restoration in the mid-1980s was the eradication of rats from small forested islands. This eradication technology has been refined and currently at least 65 islands, including large and remote Campbell (11 216 ha) and Raoul (2938 ha) Islands, have been successfully cleared of rats. Many of New Zealand's offshore islands, especially those without predatory mammals, are home to large numbers of breeding seabirds. Seabirds influence ecosystem processes on islands by enhancing soil fertility and through soil disturbance by burrowing. Predators, especially rats, alter ecosystem processes and cause population reductions or extinctions of native animals and plants. Islands have been promoted as touchstones of a primaeval New Zealand, but we are now increasingly aware that most islands have been substantially modified since human settlement of New Zealand. Archaeological and palaeoecological investigations, together with the acknowledgement that many islands have been important mahinga kai (sources of food) for Māori, have all led to a better understanding of how people have modified these islands. Restoration technology may have vaulted ahead of our ability to predict the ecosystem consequences of its application on islands. However, research is now being directed to help make better decisions about restoration and management of islands, decisions that take account of island history and key drivers of island ecosystem functioning.

A growing body of evidence shows that aboveground and belowground communities and processes are intrinsically linked, and that feedbacks between these subsystems have important implications for community structure and ecosystem functioning. Almost all studies on this topic have been carried out from an empirical perspective and in specific ecological settings or contexts. Belowground interactions operate at different spatial and temporal scales. Due to the relatively low mobility and high survival of organisms in the soil, plants have longer lasting legacy effects belowground than aboveground. Our current challenge is to understand how aboveground–belowground biotic interactions operate across spatial and temporal scales, and how they depend on, as well as influence, the abiotic environment. Because empirical capacities are too limited to explore all possible combinations of interactions and environmental settings, we explore where and how they can be supported by theoretical approaches to develop testable predictions and to generalise empirical results. We review four key areas where a combined aboveground–belowground approach offers perspectives for enhancing ecological understanding, namely succession, agro-ecosystems, biological invasions and global change impacts on ecosystems. In plant succession, differences in scales between aboveground and belowground biota, as well as between species interactions and ecosystem processes, have important implications for the rate and direction of community change. Aboveground as well as belowground interactions either enhance or reduce rates of plant species replacement. Moreover, the outcomes of the interactions depend on abiotic conditions and plant life history characteristics, which may vary with successional position. We exemplify where translation of the current conceptual succession models into more predictive models can help targeting empirical studies and generalising their results. Then, we discuss how understanding succession may help to enhance managing arable crops, grasslands and invasive plants, as well as provide insights into the effects of global change on community re-organisation and ecosystem processes.

The ‘home‐field advantage (HFA) hypothesis’ predicts that plant litter is decomposed faster than expected in the vicinity of the plant where it originates from (i.e. its ‘home’) relative to some other location (i.e. ‘away’) because of the presence of specialized decomposers. Despite growing evidence for the widespread occurrence HFA effects, what drives HFA is not understood as its strength appears highly variable and context‐dependent. Our work advances current knowledge about HFA effects by testing under what conditions HFA is most important. Using published data on mass loss from 125 reciprocal litter transplants from 35 studies, we evaluated if HFA effects were modulated by macroclimate, litter quality traits, and the dissimilarity between ‘home’ and ‘away’ of both the quality of reciprocally exchanged litters and plant community type. Our results confirmed the occurrence of an overall, worldwide, HFA effect on decomposition with on average 7.5% faster decomposition at home. However, there was considerable variation in the strength and direction (sometimes opposite to expectations) of these effects. While macroclimate and average litter quality had weak or no impact on HFA effects, home‐field effects became stronger (regardless of the direction) when the quality of ‘home’ and ‘away’ litters became more dissimilar (e.g. had a greater dissimilarity in N:P ratio; F 1,42 = 6.39, p = 0.015). Further, home‐field effects were determined by the degree of difference between the types of dominant plant species in the ‘home’ versus ‘away’ communities (F 2,105 = 4.03, p = 0.021). We conclude that home‐field advantage is not restricted to particular litter types or climate zones, and that the dissimilarity in plant communities and litter quality between the ‘home’ and ‘away’ locations, are the most significant drivers of home‐field effects.

In the long-term absence of disturbance, ecosystems often enter a decline or retrogressive phase which leads to reductions in primary productivity, plant biomass, nutrient cycling and foliar quality. However, the consequences of ecosystem retrogression for higher trophic levels such as herbivores and predators, are less clear. Using a post-fire forested island-chronosequence across which retrogression occurs, we show that nutrient availability strongly controls invertebrate herbivore biomass when predators are few, but that there is a switch from bottom-up to top-down control when predators are common. This trophic flip in herbivore control probably arises because invertebrate predators respond to alternative energy channels from the adjacent aquatic matrix, which were independent of plant biomass. Our results suggest that effects of nutrient limitation, following ecosystem retrogression, on trophic cascades are modified by independent variation in predator abundance, which requires a more holistic approach to trophic ecology to better understand herbivore effects on plant communities.

No abstract is provided for this article.