Belowground legacies of Pinus contorta invasion and removal result in multiple mechanisms of invasional meltdown.

Plant invasions can change soil biota and nutrients in ways that drive subsequent plant communities, particularly when co-invading with belowground mutualists such as ectomycorrhizal fungi. These effects can persist following removal of the invasive plant and, combined with effects of removal per se, influence subsequent plant communities and ecosystem functioning. We used field observations and a soil bioassay with multiple plant species to determine the belowground effects and post-removal legacy caused by invasion of the non-native tree Pinus contorta into a native plant community. Pinus facilitated ectomycorrhizal infection of the co-occurring invasive tree, Pseudotsuga menziesii, but not conspecific Pinus (which always had ectomycorrhizas) nor the native pioneer Kunzea ericoides (which never had ectomycorrhizas). Pinus also caused a major shift in soil nutrient cycling as indicated by increased bacterial dominance, NO3-N (17-fold increase) and available phosphorus (3.2-fold increase) in soils, which in turn promoted increased growth of graminoids. These results parallel field observations, where Pinus removal is associated with invasion by non-native grasses and herbs, and suggest that legacies of Pinus on soil nutrient cycling thus indirectly promote invasion of other non-native plant species. Our findings demonstrate that multi-trophic belowground legacies are an important but hitherto largely unconsidered factor in plant community reassembly following invasive plant removal.

Plasticity in above- and belowground resource acquisition traits in response to single and multiple environmental factors in three tree species.

Functional trait plasticity is a major component of plant adjustment to environmental stresses. Here, we explore how multiple local environmental gradients in resources required by plants (light, water, and nutrients) and soil disturbance together influence the direction and amplitude of intraspecific changes in leaf and fine root traits that facilitate capture of these resources. We measured population-level analogous above- and belowground traits related to resource acquisition, i.e. "specific leaf area"-"specific root length" (SLA-SRL), and leaf and root N, P, and dry matter content (DMC), on three dominant understory tree species with contrasting carbon and nutrient economics across 15 plots in a temperate forest influenced by burrowing seabirds. We observed similar responses of the three species to the same single environmental influences, but partially species-specific responses to combinations of influences. The strength of intraspecific above- and belowground trait responses appeared unrelated to species resource acquisition strategy. Finally, most analogous leaf and root traits (SLA vs. SRL, and leaf versus root P and DMC) were controlled by contrasting environmental influences. The decoupled responses of above- and belowground traits to these multiple environmental factors together with partially species-specific adjustments suggest complex responses of plant communities to environmental changes, and potentially contrasting feedbacks of plant traits with ecosystem properties. We demonstrate that despite the growing evidence for broadly consistent resource-acquisition strategies at the whole plant level among species, plants also show partially decoupled, finely tuned strategies between above- and belowground parts at the intraspecific level in response to their environment. This decoupling within species suggests a need for many species-centred ecological theories on how plants respond to their environments (e.g. competitive/stress-tolerant/ruderal and response-effect trait frameworks) to be adapted to account for distinct plant-environment interactions among distinct individuals of the same species and parts of the same individual.

A megafauna's microfauna: gastrointestinal parasites of New Zealand's extinct moa (Aves: Dinornithiformes).

WE PERFORM THE FIRST MULTIDISCIPLINARY STUDY OF PARASITES FROM AN EXTINCT MEGAFAUNAL CLADE USING COPROLITES FROM THE NEW ZEALAND MOA (AVES: Dinornithiformes). Ancient DNA and microscopic analyses of 84 coprolites deposited by four moa species (South Island giant moa, Dinornis robustus; little bush moa, Anomalopteryx didiformis; heavy-footed moa, Pachyornis elephantopus; and upland moa, Megalapteryx didinus) reveal an array of gastrointestinal parasites including coccidians (Cryptosporidium and members of the suborder Eimeriorina), nematodes (Heterakoidea, Trichostrongylidae, Trichinellidae) and a trematode (Echinostomida). Parasite eggs were most prevalent and diverse in coprolites from lowland sites, where multiple sympatric moa species occurred and host density was therefore probably higher. Morphological and phylogenetic evidence supports a possible vicariant Gondwanan origin for some of the moa parasites. The discovery of apparently host-specific parasite taxa suggests paleoparasitological studies of megafauna coprolites may provide useful case-studies of coextinction.

Soil-mediated indirect impacts of an invasive predator on plant growth.

While several studies have shown that invasive plant effects on soil biota influence subsequent plant performance, corresponding studies on how invasive animals affect plants through influencing soil biota are lacking. This is despite the fact that invasive animals often indirectly alter the below-ground subsystem. We studied 18 offshore islands in northern New Zealand, half of which have been invaded by rats that are predators of seabirds and severely reduce their densities, and half of which remain non-invaded; invasion of rats thwarts seabird transfer of resources from ocean to land. We used soil from each island in a glasshouse experiment involving soil sterilization treatments to determine whether rat invasion indirectly influences plant growth through the abiotic pathway (by impairing seabird-driven inputs to soil) or the biotic pathway (by altering the soil community). Rat invasion greatly impaired plant growth but entirely through the abiotic pathway. Plant growth was unaffected by the soil community or its response to invasion, meaning that the responses of plants and soil biota to invasion are decoupled. Our results provide experimental evidence for the powerful indirect effects that predator-instigated cascades can exert on plant and ecosystem productivity, with implications for the restoration of island ecosystems by predator removal.

Indirect effects of invasive predators on litter decomposition and nutrient resorption on seabird-dominated islands.

Despite recent interest in the ecosystem impacts of invasive aboveground organisms, most work in this area has focused on effects of invasive plants, and the effects of invasive herbivores and predators remain poorly understood. We studied 18 forested, offshore islands in northern New Zealand. Nine of these host high densities of burrowing seabirds that serve as ecosystem drivers by transporting nutrients from the ocean to land. The other nine have been invaded over the past 50-150 years by rat species introduced from Europe which serve as predators of seabird eggs and chicks and severely reduce their densities. We collected fully expanded leaves and fresh leaf litter from invaded and uninvaded islands for each of 12 perennial plant species that represent a wide spectrum of life forms from ground dwelling to emergent canopy species. We found that, across these species, invasion by rats significantly reduced nitrogen (N) but not phosphorus (P) concentrations of foliage and litter, promoted N but not P resorption from leaves before litter fall, and reduced the release of N but not P from decomposing litter. Rat invasion also negatively affected litter decomposability but had no overall effects on litter quality variables other than N. Our results provide evidence that rat invasion causes more conservative cycling of N but not P through foliage and litter and limitation of ecological processes by N but not P. We found few instances in which the effects of rat invasion on response variables varied significantly across plant species, meaning that invasion had similar effects for species that varied greatly in growth form and foliar and litter quality. Further, correlation analyses across the 12 species showed that foliar and litter quality traits were poor predictors of how invasion effects on resorption and decomposition variables varied among species. Our results show that the effects of invasive predators on native prey can have substantial indirect effects on variables relevant for ecosystem functioning. These types of effects are probably widespread, especially given the role of seabirds in improving soil fertility in many coastal ecosystems worldwide and the wide global distribution of predators of seabirds.

Aboveground and belowground effects of single-tree removals in New Zealand rain forest.

There has been considerable recent interest in how human-induced species loss affects community and ecosystem properties. These effects are particularly apparent when a commercially valuable species is harvested from an ecosystem, such as occurs through single-tree harvesting or selective logging of desired timber species in natural forests. In New Zealand mixed-species rain forests, single-tree harvesting of the emergent gymnosperm Dacrydium cupressinum, or rimu, has been widespread. This harvesting has been contentious in part because of possible ecological impacts of Dacrydium removal on the remainder of the forest, but many of these effects remain unexplored. We identified an area where an unintended 40-year "removal experiment" had been set up that involved selective extraction of individual Dacrydium trees. We measured aboveground and belowground variables at set distances from both individual live trees and stumps of trees harvested 40 years ago. Live trees had effects both above and below ground by affecting diversity and cover of several components of the vegetation (usually negatively), promoting soil C sequestration, enhancing ratios of soil C:P and N:P, and affecting community structure of soil microflora. These effects extended to 8 m from the tree base and were likely caused by poor-quality litter and humus produced by the trees. Measurements for the stumps revealed strong legacy effects of prior presence of trees on some properties (e.g., cover by understory herbs and ferns, soil C sequestration, soil C:P and N:P ratios), but not others (e.g., soil fungal biomass, soil N concentration). These results suggest that the legacy of prior presence of Dacrydium may remain for several decades or centuries, and certainly well over 40 years. They also demonstrate that, while large Dacrydium individuals (and their removal) may have important effects in their immediate proximity, within a forest, these effects should only be important in localized patches containing high densities of large trees. Finally, this study emphasizes that deliberate extraction of a particular tree species from a forest can exert influences both above and below ground if the removed species has a different functional role than that of the other plant species present.

Above- and below-ground impacts of introduced predators in seabird-dominated island ecosystems.

Predators often exert multi-trophic cascading effects in terrestrial ecosystems. However, how such predation may indirectly impact interactions between above- and below-ground biota is poorly understood, despite the functional importance of these interactions. Comparison of rat-free and rat-invaded offshore islands in New Zealand revealed that predation of seabirds by introduced rats reduced forest soil fertility by disrupting sea-to-land nutrient transport by seabirds, and that fertility reduction in turn led to wide-ranging cascading effects on belowground organisms and the ecosystem processes they drive. Our data further suggest that some effects on the belowground food web were attributable to changes in aboveground plant nutrients and biomass, which were themselves related to reduced soil disturbance and fertility on invaded islands. These results demonstrate that, by disrupting across-ecosystem nutrient subsidies, predators can indirectly induce strong shifts in both above- and below-ground biota via multiple pathways, and in doing so, act as major ecosystem drivers.

Island biology and ecosystem functioning in epiphytic soil communities.

Although island attributes such as size and accessibility to colonizing organisms can influence community structure, the consequences of these for ecosystem functioning are little understood. A study of the suspended soils of spatially discrete epiphytes or treetop "islands" in the canopies of New Zealand rainforest trees revealed that different components of the decomposer community responded either positively or negatively to island size, as well as to the tree species that the islands occurred in. This in turn led to important differences between islands in the rates of ecosystem processes driven by the decomposer biota. This system serves as a model for better understanding how attributes of both real and habitat islands may affect key ecosystem functions through determining the community structure of organisms that drive these functions.