Oceanic islands have high biodiversity, which is severely threatened by invasive species. Functional traits serve as a framework to investigate invasive-native dynamics, but most studies investigating native-invasive plant functional trait differences on islands focus on live foliage traits, while litter traits remain understudied. It is hypothesized that invasive species produce higher quality litter (e.g., high nutrient content, low tannins and leaf mass per area) than native species, and furthermore, that this high-quality litter decomposes more rapidly, in turn providing a positive feedback that facilitates their expansion. To investigate native vs. invasive plant litter quality in a highly endemic island flora, we conducted a systematic review to synthesize litter trait data from Hawai'i. To account for the extensive heterogeneity that occurs across the Hawaiian Islands, litter trait variability was synthesized with respect to elevation and climate gradients. Litter quality varies extensively across the Hawaiian Islands in native and invasive species. Although invasive plants have higher quality litter than native species overall, species origin accounts for relatively little trait variance, and native and invasive species overlap considerably in litter multivariate trait space. Moreover, intraspecific variation exceeds interspecific variation, highlighting the important role of environmental heterogeneity for widespread species. Climate influences native and invasive litter quality in distinct ways, leading to a reversal in strategy across climate gradients. When controlling for the full direct effects of climate, native and invasive plant litter traits are not significantly different. Climate heterogeneity, more than plant species origin, plays a key role in shaping plant litter trait variation and resource-use strategies at the landscape or archipelago scale. Litter quality could be more commonly sampled as part of the functional syndrome of plants and for a better understanding of how traits differ between native and invasive plants.

Trait-based approaches feature prominently in ecology, providing mechanistic insights into plant interactions with abiotic and biotic factors. Increasingly, traits are used in restoration and conservation to select species with target functions and to monitor performance in restoration settings. Physiological traits are rarely used, despite their clear relevance for restoration in the context of climate change. We provide rationale and guidance for the expanded integration of physiological traits (e.g., metabolic and energy transfer processes, gas exchange, nutrient dynamics, and hydraulics) into restoration to enhance resilience of terrestrial ecosystems to climate change. We identify traits mediating the tolerance of climate stressors, particularly drought, heat, and salinity due to sea level rise. Physiological traits are highly dynamic, within and among species, and this variability can be leveraged to inform species selection and monitoring efforts. Trait variability via phenotypic plasticity and climate stress thresholds offers key insights into plant performance and population stability under climate stress. Trait-based approaches complement existing restoration and conservation strategies, including those based on Indigenous ecological knowledge and resource management. Effective researcher-practitioner collaborations are essential to successfully integrate physiology into ecological restoration. Synthesis and applications. Climate stress is increasing globally, and physiological traits are critical for understanding stress tolerance in plants. Integrating physiology into restoration will contribute to climate resilience, but depends on partnerships between researchers and practitioners and will benefit from increased physiological trait sampling of more species, sites, and traits. Expanded trait coverage will enhance species selection and performance monitoring, improving restoration and species stabilization in a changing climate.

Abstract Biodiversity encompasses species diversity, functional diversity, genetic diversity, and phylogenetic diversity, which are outcomes of evolutionary and ecological processes. These biodiversity components play an important role in shaping ecosystem function and stability in distinct ways. National and international conservation programs have typically considered species diversity, while other dimensions of biodiversity are often neglected in conservation policy. In 2010, the Convention on Biological Diversity (CBD) established the global Strategic Plan for Biodiversity 2011–2020 and Aichi Biodiversity Targets, which aim to halt biodiversity loss, enhancing ecosystem conservation and restoration. To deliver these global strategies and targets, CBD member countries have subsequently developed and implemented national biodiversity conservation action plans. Here, we investigated the use of functional trait‐based approaches in conservation policy at the national level to meet the Aichi Biodiversity Targets. Trait‐based approaches promote functional diversity within communities, supporting ecosystem services and human health and well‐being. We accessed the 5th and 6th National Reports submitted to the CBD over the last 11 years. We found that 26% of the countries incorporate trait‐based approaches in their 5th National Reports, and 33% incorporate trait‐based approaches in the 6th National Reports, highlighting widespread failure to consider functional diversity in decision making. We advocate for a greater focus on functional diversity in conservation policies for better conservation outcomes.

Context Fire is increasing in intensity and frequency, leading to novel fire regimes in many regions. For oceanic islands of volcanic origin, endemic plants have evolved in the context of lava-ignited fires.Aims Responses to fire were investigated in four endemic (Nototrichium humile, Hibiscus brackenridgei subsp. mokuleianus, Gossypium tomentosum, and Erythrina sandwicensis) and one invasive (Leucaena leucocephala) plant species in Hawai'i. Because conservation efforts commonly rely on juvenile stages, which are predicted to be particularly vulnerable to fire, we tested fire resprouting in saplings.Methods Sapling resprouting was tested using experimental methods. Saplings were burned using a fire torch, and resprouting was monitored for 30 days. Proportion of plants resprouting and the timing of resprouting were the metrics of fire tolerance.Key results Resprouting rates were high in four of the species (65-95%). The endemic E. sandwicensis was the only species that failed to resprout. The timing of resprouting varied among species, with the invasive species resprouting faster than the endemics.Conclusions Saplings demonstrated surprisingly high tolerance to the fire treatments, indicating potential for these early stages to withstand fire. The invasive species resprouted faster than the endemics, which could contribute to competitive displacement in burned sites. At least one native Hawaiian plant species potentially lacks fire tolerance completely at the sapling stage.Implications Sapling fire tolerance informs restoration actions that rely on out-plantings into fire-prone sites. Scaling up these results requires additional species testing and fire treatments to mimic contemporary fires.

Offshore islets are features of archipelagos and coastal continental regions. Because of their small size, they can be considered microcosms for studies of island biogeography and community assembly. The Hawaiian Islands include at least 54 islets, which provide safe habitat for nesting seabirds and monk seals due to the absence of mammalian predators and laws restricting human activity. Because the Hawaiian islets are uninhabited by people, they offer unique opportunities to examine community dynamics in relatively undisturbed habitats. M & amacr;nana Islet, also known as Rabbit Island, is a 25.5-hectare islet located off Kaup & omacr; Beach in Waim & amacr;nalo, O'ahu Island, that has been designated a Seabird Sanctuary by the state of Hawai'i. European rabbits (Oryctolagus cuniculus) were introduced to M & amacr;nana in the 1880s for food and game but were eradicated by 1985 through a state-initiated hunting and poisoning program. Across a nearly 80-yr period (1927-2008), spanning rabbit habitation and eradication, the vegetation of M & amacr;nana has been surveyed or reported 21 times, providing a longitudinal record of plant diversity on the islet. To extend this record, a new vegetation survey was conducted in 2023, replicating previous methods. Rabbits had devastating effects on the vegetation of M & amacr;nana, which then increased in plant species richness after rabbit eradication. The most recent surveys have detected an increase in nonnative species, highlighting biological invasion as an ongoing threat to these islet habitats. In the most recent survey, a total of 43 plant species were detected, including seven new records, six of which are non-native. How these patterns in species richness correspond to measures of diversity based on abundance and evenness remains unclear. Additional restoration of M & amacr;nana Islet may increase native biodiversity, supporting nesting seabirds and ensuring these diverse coastal islets persist in the future.

Coastal dune plants provide critical ecosystem and cultural services, which are severely threatened by ongoing climate change and sea-level rise. Coastal habitats account for a disproportionate extent of land on islands, emphasizing the importance of these ecosystems for island biodiversity. We investigated salinity tolerance in a diverse pool of 19 native and invasive plant species from Hawaiʻi’s coastal dunes for insights into their vulnerability to sea-level rise. Salinity tolerance was investigated experimentally in seedling and juveniles by treating plants with artificial seawater for 3 weeks, followed by a 2-week freshwater recovery period. For mechanistic insights, stomatal conductance and leaf chlorophyll content were measured before, during, and after seawater treatment. Salinity tolerance was highly variable among species. The least tolerant species experienced 100

Cannabis sativa L. is an annual flowering herb of Eurasian origin that has long been associated with humans. Domesticated independently at multiple locations at different times for different purposes (food, fiber, and medicine), these long-standing human associations have influenced its distribution. However, changing environmental conditions and climatic fluctuations have also contributed to the distribution of the species and define where it is optimally cultivated. Here we explore the shifts in distribution that C. sativa may have experienced in the past and explore the likely shifts in the future. Modeling under paleoclimatic scenarios shows niche expansion and contraction in Eurasia through the timepoints examined. Temperature and precipitation variables and soil variable data were combined for species distribution modeling in the present day and showed high and improved predictive ability together as opposed to when examined in isolation. The five most important variables explaining ~65% of the total variation were soil organic carbon content (ORCDRC), pH index measured in water solution (PHIHOX), annual mean temperature (BIO-1), mean temperature of the coldest quarter (BIO-11) and soil organic carbon density (OCDENS) (AUC = 0.934). Climate model projections where efforts are made to curb emissions (RCP45/SSP245) and the business as usual (RCP85/SSP585) models were evaluated. Under projected future climate scenarios, shifts worldwide are predicted with a loss of ~43% in suitability areas with scores above 0.4 observed by 2050 and continued but reduced rates of loss by 2070. Changes in habitat range have large implications for the conservation of wild relatives as well as for the cultivation of Cannabis as the industry moves toward outdoor cultivation practices.

Islands host unique biodiversity that faces threats from global change. Understanding plant reproduction is vital to conserve and restore island ecosystems, in turn ensuring stable population dynamics and preserving biodiversity. Dubautia menziesii (Asteraceae) is a common shrub endemic to the alpine and subalpine ecosystem of Haleakala volcano on Maui. The purpose of this study is to: (i) characterize the breeding system of D. menziesii, (ii) identify its main pollinators, (iii) determine how plant isolation affects seed set and seed parasitism, and (iv) estimate the abundance of D. menziesii and its flower resources in the habitat. Hand pollination treatments were conducted to assess seed set and determine the breeding system. Flower-visiting insects were observed, to identify pollinators. The impact of isolation was assessed by analyzing seed set and seed predation at varying distances from the nearest flowering neighbor. Species abundance was estimated using belt transects and plotless sampling. Dubautia menziesii is self-incompatible and requires outcrossing to set seeds (66 % seed set for outcrossed flowers vs. 3 % for manually self-pollinated and bagged unmanipulated flowers). The most frequent flower visitors were endemic Hylaeus bees (44 %), and non-native honeybees (34 %), followed by Nysius spp. seed bugs (15.9 %). Isolation had no significant effect on either seed set or seed predation at 2 sites. The relative dominance of D. menziesii at high elevations on Haleakala suggests it plays an important role in maintaining insect populations and may benefit other plants with which it shares floral visitors, such as the Haleakala silversword.

Comparing the functional traits of co‐occurring native and invasive plant species can offer insight regarding mechanisms of invasion. Previous studies have failed to reach a consensus, indicating that the extent of trait differences between native and invasives might depend on the environmental context and on the spatial grain of the analysis. Here we evaluate the scale‐dependency of native–invader trait comparisons within the Hawaiian Archipelago, a globally important region of high endemicity and high invasibility. We evaluated trait (e.g. gas exchange, leaf nutrient concentration, specific leaf area) differences locally and regionally (i.e. within and across islands) and found that while invasives are more resource acquisitive at the regional scale, native–invader differences are highly idiosyncratic at localized scales, varying both in direction and magnitude within islands. Our findings clarify how region‐wide species comparisons may fail to characterize interactions happening at local scales, thereby misleading or obscuring the mechanisms underlying invasion.

Plant diversity is known to influence ecosystem functioning, but the strength and direction of this relationship vary considerably among studies, most of which have a short duration. In communities with long‐lived species, such as forests, traits of individual trees change from seedlings to maturity, and the environment in which trees grow also continually changes through stand development and forest succession. We argue that interactions between these individual and community‐level effects over time will alter biodiversity‐ecosystem functioning (BEF) relationships, likely explaining at least part of the reported variation in BEF effects among studies. We outline a series of mechanisms through which temporal changes at the tree and stand levels can alter BEF relationships and illustrate these processes using data from the long‐term Satakunta forest diversity experiments in Finland. We argue that long‐term forest diversity experiments are essential to robustly characterize temporal dynamics emerging from the complex interplay between plant functional traits and environmental conditions over time. These experiments can provide critical insights for predicting the consequences of biodiversity loss on ecosystem functioning and service provisioning over time.

Despite representing a fraction of the global terrestrial surface area, oceanic islands are disproportionately diverse in species, resulting from high rates of endemicity. Island plants are thought to share a unique phenotype-referred to as an island syndrome-which is thought to be driven by convergent evolution in response to selection by shared abiotic and biotic factors. One aspect of the island plant syndrome that has received relatively little research focus is that island plants are expected to have converged on conservative resource use associated with slow growth rates and weak competitive abilities. Here we tested whether native, woody Hawaiian plant species are phenotypically distinct-with more resource-conservative leaf traits-compared to a globally distributed sample of continental species. Using an archipelago-wide trait data set, we detected that on average, native Hawaiian species had lower leaf nutrient concentrations overall, and lower nutrient concentrations at high leaf mass per area, but no other phenotypic differences compared with continental plants. There was also considerable overlap in the trait spaces of native Hawaiian species and continental species. Our findings indicate that an island plant syndrome for leaf traits is not present in the Hawaiian flora, and that island species can demonstrate extensive variation in their resource-use strategies, on a scale that is comparable with that of continental species worldwide.

Island plants are predicted to have weak or absent defenses as part of the island plant syndrome. Evidence supporting the weak island defense prediction stems largely from observations of intense damage from invasive mammalian herbivores on islands. However, this evidence is misleading because most oceanic island plants have not evolved with native mammalian herbivores, and so should not have evolved defenses against them. In contrast, many islands have been home to other native vertebrate megafaunal herbivores, including flightless birds, tortoises, and turtles, many of which are now extinct or rare and therefore easy to overlook as agents of selection for island plant defenses. We review the evidence that island megaherbivores have selected for spinescence in island plants, supplementing published data with new estimates of spinescence for island floras varying in historical legacies of megafaunal herbivores. While the proportions of spinescent species are generally low, there are many spinescent island plants, likely functioning in defense against extant herbivores or persisting as defense anachronisms, no longer functioning due to the losses of native island megaherbivores. Future research exploring the evolvability of spinescence, including rates of losses or gains as herbivory selection pressure shifts, will be particularly enlightening for assessing island plant defenses in response to complex and variable historical legacies of megafaunal herbivory.

Plant functional strategies change considerably as plants develop, driven by intraindividual variability in anatomical, morphological, physiological and architectural traits. Developmental trait variation arises through the complex interplay among genetically regulated phase change (i.e. ontogeny), increases in plant age and size, and phenotypic plasticity to changing environmental conditions. Although spatial drivers of intraspecific trait variation have received extensive research attention, developmentally driven intraspecific trait variation is largely overlooked, despite widespread occurrence. Ontogenetic trait variation is genetically regulated, leads to dramatic changes in plant phenotypes and evolves in response to predictable changes in environmental conditions as plants develop. Evidence has accumulated to support a general shift from fast to slow relative growth rates and from shade to sun leaves as plants develop from the highly competitive but shady juvenile niche to the stressful adult niche in the systems studied to date. Nonetheless, there are major gaps in our knowledge due to examination of only a few environmental factors selecting for the evolution of ontogenetic trajectories, variability in how ontogeny is assigned, biogeographic sampling biases on trees in temperate biomes, dependencies on a few broadly sampled leaf morphological traits and a lack of longitudinal studies that track ontogeny within individuals. Filling these gaps will enhance our understanding of plant functional ecology and provide a framework for predicting the effects of global change threats that target specific ontogenetic stages. Read the free Plain Language Summary for this article on the Journal blog.

Insect-plant interactions are less well studied than other types of herbivory on islands, precluding a comprehensive understanding of the evolutionary ecology of these interactions. Declines in native island plants and insects call for urgent attention to characterize these species' interactions for their conservation and to better understand evolution in these unique, insular ecosystems. In Hawai'i, the Kamehameha butterfly (Vanessa tameamea) is one of only two native butterflies, and larvae are specialists on native urticaceous plants. Using a no-choice bioassay, we investigated performance of V. tameamea reared from egg hatching through eclosion on four native urticaceous host plants, Boehmeria grandis, Pipturus albidus, Touchardia latifolia, and Touchardia oahuensis, and one exotic urticaceous species, Cecropia obtusifolia. Performance varied significantly among the plant diets, with V. tameamea performing best on P. albidus and T. oahuensis among the performance metrics of survival, pupal and adult body mass, and development time. Larval responses to the exotic host plant C. obtusifolia varied among populations, with O'ahu caterpillars successfully completing development on it, but Hawai'i Island caterpillars rejecting it completely, suggesting a geographic mosaic for this novel species interaction. Characterization of a suite of nutritive and defensive plant traits revealed significant variability among plant species, but patterns did not align well with V. tameamea performance rankings, making it difficult to identify key drivers of host plant quality. Future work examining additional plant traits under natural conditions would provide new insights, contributing critical ecological information to conserve this charismatic island species. The endemic Hawaiian Kamehameha butterfly is a specialist on Urticaceous host plants. Yet, caterpillar performance varies significantly among 4 native and 1 non-native host plant. Potential defense and nutritive traits also vary among host plant species, but are not consistent with performance rankings, highlighting this as future research need.image

BACKGROUND AND AIMS:Islands, with their long coastlines and increased vulnerability to sea level rise, offer compelling opportunities to investigate the salinity tolerance of coastal plants. Seeds are generally more vulnerable than other plant stages to increased stressors. The aim of this study was to characterize salinity tolerance during germination across a diverse pool of 21 species from 14 plant families found in coastal communities throughout the Hawaiian Islands in order to increase our general understanding of coastal plant ecology for conservation and restoration. METHODS:Seeds of each species were exposed to unfiltered/untreated seawater (35 ppt total salinity) and two salinity treatments (10 and 20 ppt) in which the seawater was diluted with distilled water, and germination percent and timing were compared to seeds in a distilled water control. Non-germinated seeds were then tested for recovery germination. We quantified and compared germination percent, time and recovery among species and across salinity levels and tested for heterogeneity related to seed size, dormancy class, habit and threatened status. KEY RESULTS:Although salinity tolerance varied considerably among species, salinity exposure generally reduced and delayed germination. The greatest effects were detected at higher salinity levels. Recovery germination overall was higher for seeds that had been exposed to higher salinity. None of the factors we explored emerged as predictors of salinity tolerance except seed mass, which tended to enhance germination at higher salinity. CONCLUSIONS:Species responses to salinity exposure indicate high vulnerability of coastal systems to increased salinity stress, and variability among species could lead to shifts in community assembly and composition under sea level rise. These results can help guide coastal ecosystem conservation and restoration management decisions in the face of climate change.

Island floras are diverse with exceptionally high rates of endemicity, and they are also severely threatened. Invasive plants are widespread on islands, but whether islands are particularly susceptible to invasion or island species are more vulnerable to displacement, or both, remains unclear. As part of the “island plant syndrome,” it has been predicted that island plants have convergently evolved conservative resource use, slow growth rates, and weak competitive abilities in response to moderate climates and the presumed absence of competition in communities with relatively low species richness. Yet, functional trait approaches have provided mixed evidence to support this prediction, and direct tests of competition as neighbour effects on plant performance are lacking. Considering the extensive environmental heterogeneity that exists within islands and among islands, it seems more likely that diverse functional strategies, spanning conservative to acquisitive, have evolved in island plants. Furthermore, assessing island plant syndrome predictions through comparisons with invasive species, which are nonrandom subsets of continental plants, is a flawed approach. Future studies that compare functional strategies of native island versus native continental plants and direct tests for competition between native and invasive island plants within the local scale at which competition occurs, and that consider non‐additivities with other simultaneous global threats, are urgently needed to conserve these biodiversity hotspots.

Soil organic matter contributes to productivity in terrestrial ecosystems and contains more carbon than is found in the atmosphere. Yet, there is little understanding of soil organic carbon (SOC) sequestration processes during tropical forest succession, particularly after land abandonment from agriculture practices.Here, we used vegetation and environmental data from two large-scale surveys covering a total landscape area of 20,000 ha in Southeast Asia to investigate the effects of plant species diversity, functional trait diversity, phylogenetic diversity, above-ground biomass and environmental factors on SOC sequestration during forest succession.We found that functional trait diversity plays an important role in determining SOC sequestration across successional trajectories. Increases in SOC carbon storage were associated with indirect positive effects of species diversity and succession age via functional trait diversity, but phylogenetic diversity and above-ground biomass showed no significant relationship with SOC stock. Furthermore, the effects of soil properties and functional trait diversity on SOC carbon storage shift across elevation.Synthesis. Our results suggest that reforestation and restoration management practices that implement a trait-based approach by combining long-lived and short-lived species (conservative and acquisitive traits) to increase plant functional diversity could enhance SOC sequestration for climate change mitigation and adaptation efforts, as well as accelerate recovery of healthy soils.

As the most remote archipelago in the world, the Hawaiian Islands are home to a highly endemic and disharmonic biota that has fascinated biologists for centuries. Forests are the dominant terrestrial biome in Hawai'i, spanning complex, heterogeneous climates across substrates that vary tremendously in age, soil structure, and nutrient availability. Species richness is low in Hawaiian forests compared to other tropical forests, as a consequence of dispersal limitation from continents and adaptive radiations in only some lineages, and forests are dominated by the widespread Metrosideros species complex. Low species richness provides a relatively tractable model system for studies of community assembly, local adaptation, and species interactions. Moreover, Hawaiian forests provide insights into predicted patterns of evolution on islands, revealing that while some evidence supports "island syndromes," there are exceptions to them all. For example, Hawaiian plants are not as a whole less defended against herbivores, less dispersible, more conservative in resource use, or more slowgrowing than their continental relatives. Clearly, more work is needed to understand the drivers, sources, and constraints on phenotypic variation among Hawaiian species, including both widespread and rare species, and to understand the role of this variation for ecological and evolutionary processes, which will further contribute to conservation of this unique biota. Today, Hawaiian forests are among the most threatened globally. Resource management failures - the proliferation of non-native species in particular - have led to devastating declines in native taxa and resulted in dominance by novel species assemblages. Conservation and restoration of Hawaiian forests now rely on managing threats including climate change, ongoing species introductions, novel pathogens, lost mutualists, and altered ecosystem dynamics through the use of diverse tools and strategies grounded in basic ecological, evolutionary, and biocultural principles. The future of Hawaiian forests thus depends on the synthesis of ecological and evolutionary research, which will continue to inform future conservation and restoration practices.