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What does contemporary Indigenous stewardship look like in urban spaces? We answer this question by exploring Urban ʻĀina, a practice-based Native Hawaiian paradigm that shapes how we engage urban landscapes as Indigenous spaces, revitalizes the expression of Indigenous knowledge, and relies on Indigenous sensibilities to address and respond to modern issues such as food security, ecological degradation, and the climate change crisis. We find that places shaped by Urban ʻĀina practices serve as cultural kīpuka—biocultural refugia where kincentric, reciprocal relationships are honored through the engagement of ancestral knowledge. In Hawaiʻi, efforts to maintain these kincentric relationships continue to be challenged by political, socioeconomic, environmental, psychological, and spiritual disruptions that have their origin in the illegal overthrow of the Hawaiian Kingdom. Our research methodology and the paper’s resulting structure rely on ceremony and the Pewa Framework, which were selected to transport you through our restoration process. This exploration and the sharing of innovative case studies from urban Oʻahu bring breath and the healing power of Indigenous knowledge and ancestral practices to urban spaces, with the aim of transforming contemporary conceptions of urban stewardship. Through our process, we demonstrate how revitalized ancestral practices foster ecological sustainability, restorative justice, biocultural continuity, food sovereignty, regenerative forestry, and community wellbeing in urban spaces.

Tree size shapes forest carbon dynamics and determines how trees interact with their environment, including a changing climate. Here, we conduct the first global analysis of among-site differences in how aboveground biomass stocks and fluxes are distributed with tree size. We analyzed repeat tree censuses from 25 large-scale (4-52 ha) forest plots spanning a broad climatic range over five continents to characterize how aboveground biomass, woody productivity, and woody mortality vary with tree diameter. We examined how the median, dispersion, and skewness of these size-related distributions vary with mean annual temperature and precipitation. In warmer forests, aboveground biomass, woody productivity, and woody mortality were more broadly distributed with respect to tree size. In warmer and wetter forests, aboveground biomass and woody productivity were more right skewed, with a long tail towards large trees. Small trees (1-10 cm diameter) contributed more to productivity and mortality than to biomass, highlighting the importance of including these trees in analyses of forest dynamics. Our findings provide an improved characterization of climate-driven forest differences in the size structure of aboveground biomass and dynamics of that biomass, as well as refined benchmarks for capturing climate influences in vegetation demographic models.

Drought is a prominent feature of Hawaiʻi’s climate. However, it has been over 30 years since the last comprehensive meteorological drought analysis, and recent drying trends have emphasized the need to better understand drought dynamics and multi-sector effects in Hawaiʻi. Here, we provide a comprehensive synthesis of past drought effects in Hawaiʻi that we integrate with geospatial analysis of drought characteristics using a newly developed 100-year (1920–2019) gridded Standardized Precipitation Index (SPI) dataset. The synthesis examines past droughts classified into five categories: Meteorological, agricultural, hydrological, ecological, and socioeconomic drought. Results show that drought duration and magnitude have increased significantly, consistent with trends found in other Pacific Islands. We found that most droughts were associated with El Niño events, and the two worst droughts of the past century were multi-year events occurring in 1998–2002 and 2007–2014. The former event was most severe on the islands of O’ahu and Kaua’i while the latter event was most severe on Hawaiʻi Island. Within islands, we found different spatial patterns depending on leeward versus windward contrasts. Droughts have resulted in over $80 million in agricultural relief since 1996 and have increased wildfire risk, especially during El Niño years. In addition to providing the historical context needed to better understand future drought projections and to develop effective policies and management strategies to protect natural, cultural, hydrological, and agricultural resources, this work provides a framework for conducting drought analyses in other tropical island systems, especially those with a complex topography and strong climatic gradients.

SummaryIntroduced mammalian predators are responsible for the decline and extinction of many native species, with rats (genus Rattus) being among the most widespread and damaging invaders worldwide. In a naturally fragmented landscape, we demonstrate the multi-year effectiveness of snap traps in the removal of Rattus rattus and Rattus exulans from lava-surrounded forest fragments ranging in size from 10 ha. Relative to other studies, we observed low levels of fragment recolonization. Larger rats were the first to be trapped, with the average size of trapped rats decreasing over time. Rat removal led to distinct shifts in the foraging height and location of mongooses and mice, emphasizing the need to focus control efforts on multiple invasive species at once. Furthermore, because of a specially designed trap casing, we observed low non-target capture rates, suggesting that on Hawai‘i and similar islands lacking native rodents the risk of killing non-target species in snap traps may be lower than the application of rodenticides, which have the potential to contaminate food webs. These efforts demonstrate that targeted snap-trapping is an effective removal method for invasive rats in fragmented habitats and that, where used, monitoring of recolonization should be included as part of a comprehensive biodiversity management strategy.

Pantropical variation in soils of the tropical dry forest (TDF) biome is enormously high but has been poorly characterized. To quantify variation in the global distribution of TDF soil physical and chemical properties in relation to climate and geology, we produced a synthesis using 7500 points of data with gridded fields representing lithologic, edaphic, and climatic characteristics. Our analyses reveal that 75 TDF ecoregions across five biogeographic domains (Afrotropical, Australasian, Indo-Malayan, Neotropical, and Oceanian) varied strongly with respect to parent material: sediment (57%), metamorphic (22%), volcanic (13%), and plutonic (7%). TDF ecoregions support remarkably high variability in soil suborders (32), with the Neotropical and Oceanian realms being especially diverse. As a whole, TDF soils trend strongly toward low fertility with strong variation across biogeographic domains. Similarly, the exhibited soil properties marked heterogeneity across biogeographic domains, with soil depth varying by an order of magnitude and total organic C, N, and P pools varying threefold. Organic C and N pool sizes were negatively correlated with mean annual temperature (MAT) and positively correlated with mean annual precipitation (MAP). By contrast, the distribution of soil P pools was positively influenced by both MAT and MAP and likely by soil geochemistry, due to high variations in soil parent material across the biogeographic domains. The results summarized here raise important questions as to how climate and parent material control soil biogeochemical processes in TDFs.

Understanding how environmental adaptations mediate plant and ecosystem responses becomes increasingly important under accelerating global environmental change. Multi-stemmed trees, for example, differ in form and function from single-stemmed trees and may possess physiological advantages that allow for persistence during stressful climatic events such as extended drought. Following the worst drought in Hawaii in a century, we examined patterns of stem abundance and turnover in a Hawaiian lowland dry forest (LDF) and a montane wet forest (MWF) to investigate how multi-stemmed trees might influence site persistence, and how stem abundance and turnover relate to key functional traits. We found stem abundance and multi-stemmed trees to be an important component for climate resilience within the LDF. The LDF had higher relative abundance of multi-stemmed trees, stem abundance, and mean stem abundance compared to a reference MWF. Within the LDF, multi-stemmed trees had higher relative stem abundance (i.e., percent composition of stems to the total number of stems in the LDF) and higher estimated aboveground carbon than single-stemmed trees. Stem abundance varied among species and tree size classes. Stem turnover (i.e., change in stem abundance between five-year censuses) varied among species and tree size classes and species mean stem turnover was correlated with mean species stem abundance per tree. At the plot level, stem abundance per tree is also a predictor of survival, though mortality did not differ between multiple- and single-stemmed trees. Lastly, species with higher mean stem abundance per tree tended to have traits associated with a higher light-saturated photosynthetic rate, suggesting greater productivity in periods with higher water supply. Identifying the traits that allow species and forest communities to persist in dry environments or respond to disturbance is useful for forecasting ecological climate resilience or potential for restoration in tropical dry forests.

E ulu ē E ulu kini o ke Akua Ulu a‘e ‘o Kāne me Kanaloa Ulu ka ‘Ōhi‘a a lau ka wai Ka ‘Ie‘ie Ulu a‘e ke Akua a noho i kona kahu Eia ka wai lā He wai ola E ola ia‘u i ke kumu E ola i ke po‘o, ke po‘o pua‘a E ola i ka pae, ka paepae E ola i nā haumana, nā haumana a pau ‘Eli‘eli kapu, ‘eli‘eli noa In this Pule Ho‘oulu (prayer for inspiration), we are calling ourselves and you, the reader, to embrace growth and perpetuation of life’s many sacred manifestations, to honour the guardians of our places and the sources of our knowledge, and affirm the profound responsibility that is conservation management. This chant initiates the process of kuahu, an altar of Native Hawaiian spiritual practice within Hālau ‘Ōhi‘a, a ritual-based stewardship program in Hawai‘i led by Kumu (master teacher, a primary holder and source of knowledge for the community) Kekuhi Kealiikanakaoleohaililani. This paper outlines how the kuahu process has advanced learner capacity to embrace the many sacred dimensions of resource stewardship, thereby transforming conservation biology, and related conservation practices, through Indigenous perspectives. We examine themes evoked during the kuahu process at scales spanning the universal, the regional, and the personal. In doing so, we describe how kuahu practice can serve as a coparticipant, catalyst, and portal to sacred conservation, allowing learners to engage and grow more personal relationships with the environment, our communities, and ourselves.

Metrosideros polymorpha Gaud. (‘ōhi‘a) is the most abundant native forest tree in Hawai‘i and a keystone species of cultural, ecological, and economic importance. ‘Ōhi‘a forests, particularly on Hawaiʻi Island, are being severely impacted by Rapid ‘Ōhi‘a Death (ROD), which is caused by the fungal pathogens Ceratocystis lukuohia and C. huliohia. ROD is characterized by branch dieback, crown wilting, and mortality. Initial disease resistance screening of four varieties of M. polymorpha with C. lukuohia demonstrated that varieties may differ in susceptibility. Several survivors of field or screening-based infections still exist, providing strong impetus for the establishment of the ‘Ōhiʻa Disease Resistance Program (ʻŌDRP). Here, we outline a framework for guiding the ʻŌDRP throughout the process of identifying and developing ROD resistance in M. polymorpha and, possibly, all Hawaiian Metrosideros species. Core ʻŌDRP projects include: (1) evaluating and operationalizing methods for greenhouse-based production and screening of test plants; (2) greenhouse screening of seedlings and rooted cuttings sampled from native Metrosideros throughout Hawaiʻi; (3) establishing field trials to validate results from greenhouse assays; (4) understanding environmental and genetic drivers of resistance to characterize the durability of resistance to ROD; (5) developing remote sensing and molecular methods to rapidly detect ROD-resistant individuals; and (6) conducting breeding trials to improve the degree and durability of ROD resistance. Ultimately, the ʻŌDRP seeks to produce ROD-resistant material for the perpetuation of M. polymorpha across Hawai‘i, with the goal of preserving the ecology, culture, and communities that are dependent on this tree species.

Physical dormancy in seeds can challenge restoration efforts where scarification conditions for optimal germination and seedling vigor are unknown. For species that occur along wide environmental gradients, optimal scarification conditions may also differ by seed source. We examined intraspecific variation in optimal scarification conditions for germination and seedling performance in koa (Acacia koa), which occurs across a wide range of environmental conditions. To evaluate scarification responses, we recorded imbibition percentage, germination percentage, germination time, seedling abnormalities, early mortality, seedling growth, and seedling survivorship. From these, we developed a scarification index (SI) that integrates these measures simultaneously. We hypothesized that seeds from lower elevation sources exposed to higher temperatures would have harder seed coats and would require more intense scarification treatments. To test this hypothesis, we repeatedly exposed seeds to hot water differing in temperature and time until seeds imbibed. Supporting the hypothesis, seeds from lower elevation sources generally required more intense scarification, although we found substantial variation among sources. Koa seeds germinated in about a week following imbibition. Boiling seeds (i.e., maintaining at 100°C) was effective for imbibing seeds but it also substantially reduced germination percentages. Repeated exposure to 90 to 100°C water did not reduce germination percentage but decreased seedling performance and increased early mortality. No seeds remained unimbibed after six attempts of boiling germinated whereas seeds remaining unimbibed after 15 attempts of exposure to 90 to 100°C water showed high germination percentages. Abnormalities in seedling development were rare but increased with treatment intensity. Exposure to 100°C water for 1 min overall generated the best SI values but the best treatment differed by elevation, and the treatment with the best SI was rarely predicted from the highest germination percentages. Seeds that imbibed without any treatment germinated at the same level as manually filed seeds but produced poor seedling quality. Variation in mother tree environments along an elevational gradient can lead to differences in seed coat characteristics, which may explain differing responses to treatments. Scarification treatments affected processes beyond imbibition and germination and using an index like SI may improve efficiency by identifying optimal scarification treatments while reducing seed waste.

Forest litter inputs to soil can stimulate the decomposition of older soil organic matter (SOM) via a priming effect (PE). The magnitude and underlying mechanisms driving PE are poorly understood, with especially little know about how litter quality and site conditions affect PE in situ. Further, very few studies have examined PE in tropical and subtropical soils. Here, we established low and high elevation sites (600 vs. 1,400 m a.s.l.) in the subtropical Wuyishan National Park, China, that differed with respect to mean annual temperature (MAT; ∆MAT = 4.2°C), vegetation, soil texture and soil moisture. We conducted a 1‐year field incubation study at these two sites to compare PE induced by adding low‐ and high‐quality ¹³C‐labelled leaf litter to soils. At the low elevation site, additions of high‐quality (low C/N) litter caused a PE that was 140% greater than the PE observed following additions of low‐quality (high C/N) litter. In contrast, we saw no significant differences in PE between litter types at the high elevation site, perhaps because PE was not limited by substrate quality at this cooler, finer textured and higher soil moisture coniferous site. In addition, we found a negative relationship between home‐field advantage (HFA) for litter decomposition and PE, indicating that specialized litter decomposer community driving HFA may not accelerate SOM decomposition via PE in the same way. In line with our observed strong relationship between PE and the efficiency of priming (PE size per unit of mineralized litter C), PEs induced by the high‐ and low‐quality litters were directed to microbial phosphorus (P) mining rather than nitrogen (N) mining. This interpretation aligns with observed increases in the activity of P acquiring extracellular enzymes, often described as phosphatases (P‐tases), as well as the positive relationship between the PE, P‐tase activity and the activity of C acquiring extracellular enzymes. Overall, this PE study across two contrasting sites highlights the important role of site characteristics and litter quality in regulating PE size. Further, we suggest that MAT may be a dominant driver of soil priming, through both the direct effects of litter quantity on labile substrate supply and the indirect effects of litter quality changes on downstream decomposer communities. A free Plain Language Summary can be found within the Supporting Information of this article.

Symbiotic nitrogen (N)-fixing trees can provide large quantities of new N to ecosystems, but only if they are sufficiently abundant. The overall abundance and latitudinal abundance distributions of N-fixing trees are well characterised in the Americas, but less well outside the Americas. Here, we characterised the abundance of N-fixing trees in a network of forest plots spanning five continents, ~5,000 tree species and ~4 million trees. The majority of the plots (86%) were in America or Asia. In addition, we examined whether the observed pattern of abundance of N-fixing trees was correlated with mean annual temperature and precipitation. Outside the tropics, N-fixing trees were consistently rare in the forest plots we examined. Within the tropics, N-fixing trees were abundant in American but not Asian forest plots (~7% versus ~1% of basal area and stems). This disparity was not explained by mean annual temperature or precipitation. Our finding of low N-fixing tree abundance in the Asian tropics casts some doubt on recent high estimates of N fixation rates in this region, which do not account for disparities in N-fixing tree abundance between the Asian and American tropics. Synthesis. Inputs of nitrogen to forests depend on symbiotic nitrogen fixation, which is constrained by the abundance of N-fixing trees. By analysing a large dataset of ~4 million trees, we found that N-fixing trees were consistently rare in the Asian tropics as well as across higher latitudes in Asia, America and Europe. The rarity of N-fixing trees in the Asian tropics compared with the American tropics might stem from lower intrinsic N limitation in Asian tropical forests, although direct support for any mechanism is lacking. The paucity of N-fixing trees throughout Asian forests suggests that N inputs to the Asian tropics might be lower than previously thought.

Reforestation with native species and resulting understory succession can exert important influences on soil organic matter (SOM) storage and chemistry, but a mechanistic understanding of these effects is lacking. We studied different aged Masson pine (Pinus massoniana L.) plantations with and without the understory fern, Dicranopteris dichotoma (Thunb.) Berhn., in subtropical China to assess how SOM over a 30 year sequence of pine growth and fern expansion. To do this, we measured total SOM, lignin-derived phenols, soil carbon (total C and 13C), soil nitrogen (total N and 15N), and soil microbial community composition via phospholipid fatty acid (PLFA) analyses. We found that the accumulation of newly-formed SOM outweighed decomposition of old SOM, with the majority of this increase being derived from fern detrital inputs. Where ferns were present, ferns contributed 54–61% of total soil C storage in surface (0–10 cm depth) soils, which was 62–91% higher than pre-reforestation soil C storage. We found that the abundance of lignin-derived compounds was lower in fern dominated soils, perhaps because soils under ferns supported more soil fungi, the primary decomposers of the lignin in soil. Fern soils also showed higher ratios of syringyls to vanillyls and decreased δ13C values, an indicator that ferns altered the composition of SOM at the molecular level while contributing significantly to SOM accumulation. Reforestation especially when accompanied by fern expansion also improved soil N and phosphorus (P) status, with observed declines in soil δ15N in fern dominated soils aligning with increased nutrient retention and observed increases in soil C storage. Our study highlights the potentially important role of understory ferns in mediating SOM chemistry and soil C storage during ecosystem recovery.

Invasive species alter hydrologic processes at watershed scales, with impacts to biodiversity and the supporting ecosystem services. This effect is aggravated by climate change. Here, we integrated modelled hydrologic data, remote sensing products, climate data, and linear mixed integer optimization (MIP) to identify stewardship actions across space and time that can reduce the impact of invasive species. The study area is the windward coast of Hawai'i Island (USA) across which non-native strawberry guava occurrence varies from extremely dense stands in lower watershed reaches, to low densities in upper watershed forests. We focused on the removal of strawberry guava, an invader that exerts significant impacts on watershed condition. MIP analyses spatially optimized the assignment of effective management actions to increase water yield, generate revenue from enhanced freshwater services, and income from removed biomass. The hydrological benefit of removing guava, often marginal when considered in isolation, was financially quantified, and single- and multiobjective MIP formulations were then developed over a 10-year planning horizon. Optimization resulted in $2.27 million USD benefit over the planning horizon using a payment-for-ecosystem-services scheme. That value jumped to $4.67 million when allowing work schedules with overnight camping to reduce costs. Pareto frontiers of weighted pairs of management goals showed the benefit of clustering treatments over space and time to improve financial efficiency. Values of improved land-water natural capital using payment-for-ecosystem-services schemes are provided for several combinations of spatial, temporal, economical, and ecosystem services flows.

Arbuscular mycorrhizal (AM) and ectomycorrhizal (EcM) associations are critical for host-tree performance. However, how mycorrhizal associations correlate with the latitudinal tree beta-diversity remains untested. Using a global dataset of 45 forest plots representing 2,804,270 trees across 3840 species, we test how AM and EcM trees contribute to total beta-diversity and its components (turnover and nestedness) of all trees. We find AM rather than EcM trees predominantly contribute to decreasing total beta-diversity and turnover and increasing nestedness with increasing latitude, probably because wide distributions of EcM trees do not generate strong compositional differences among localities. Environmental variables, especially temperature and precipitation, are strongly correlated with beta-diversity patterns for both AM trees and all trees rather than EcM trees. Results support our hypotheses that latitudinal beta-diversity patterns and environmental effects on these patterns are highly dependent on mycorrhizal types. Our findings highlight the importance of AM-dominated forests for conserving global forest biodiversity., The relationship of mycorrhizal associations with latitudinal gradients in tree beta-diversity is unexplored. Using a global dataset approach, this study examines how trees with arbuscular mycorrhizal and ectomycorrhizal associations contribute to latitudinal beta-diversity patterns and the environmental controls of these patterns.

Mycorrhizae alter global patterns of CO2 fertilization, carbon storage, and elemental cycling, yet knowledge of their global distributions is currently limited by the availability of forest inventory data. Here, we show that maps of tree-mycorrhizal associations (hereafter “mycorrhizal maps”) can be improved by the novel technology of imaging spectroscopy because mycorrhizal signatures propagate up from plant roots to impact forest canopy chemistry. We analyzed measurements from 143 airborne imaging spectroscopy surveys over 112,975 individual trees collected across 13 years. Results show remarkable accuracy in capturing ground truth observations of mycorrhizal associations from canopy signals across disparate landscapes (R2 = 0.92, p

Drought is a growing threat to hydrological, ecological, agricultural, and socio-cultural systems of the tropics, especially tropical islands of the Pacific where severe droughts can compromise food and water security. Overcoming barriers to knowledge sharing between land managers and researchers is a critical cross-sector strategy for engaging and mitigating or adapting to drought. Here we describe the establishment and functioning of the Pacific Drought Knowledge Exchange (PDKE), which provides users with easier access to: (1) sector- and geography-specific climate information; (2) better and more comprehensive information; (3) improved technical assistance; and (4) a more collaborative information-transfer environment through participation in knowledge co-production. We focus on our collaborative work with managers of important tropical dryland ecosystems from three distinct geographies to pilot the collaborative development of climate change, climate variability, and drought “portfolios” featuring site-specific historical and forecasted future information. This information was then used to collaboratively produce factsheets that partners used to: (i) better understand past and projected climate for specific management units; (ii) integrate new climate knowledge into management planning; and (iii) support climate-focused educational and outreach efforts. This pilot effort demonstrates the successful application of climate-focused co-production in dry tropical landscapes.

In this chapter, we describe current understanding of and identify research gaps on how invasive species directly, and indirectly, affect ecosystem processes. Specifically, we focus on how invasive species can alter the terrestrial carbon, nitrogen, and hydrologic cycles and how changes to these terrestrial cycles cascade to affect water quantity and quality. While invasive species may alter other ecosystem processes, we focus on these due to their importance to policy, to the public, and to their likely interaction with climate change effects. For example, carbon sequestration and surface water supply originating from forests and grasslands (Caldwell et al. 2014) are important policy and public concerns, and drought frequency and intensity will likely increase with climate change (Vose et al. 2016a). Our goal is to draw generalizations rather than provide details on invasive species effects on a case-by-case basis. We do, however, provide case studies for illustration and draw linkages with other chapters that provide detailed coverage to disturbance regimes (Chap. 5) and types and mechanisms of ecological impact caused by invasive insects (Chap. 2).

ForestGEO is a network of scientists and long-term forest dynamics plots (FDPs) spanning the Earth's major forest types. ForestGEO's mission is to advance understanding of the diversity and dynamics of forests and to strengthen global capacity for forest science research. ForestGEO is unique among forest plot networks in its large-scale plot dimensions, censusing of all stems ≥1 cm in diameter, inclusion of tropical, temperate and boreal forests, and investigation of additional biotic (e.g., arthropods) and abiotic (e.g., soils) drivers, which together provide a holistic view of forest functioning. The 71 FDPs in 27 countries include approximately 7.33 million living trees and about 12,000 species, representing 20% of the world's known tree diversity. With >1300 published papers, ForestGEO researchers have made significant contributions in two fundamental areas: species coexistence and diversity, and ecosystem functioning. Specifically, defining the major biotic and abiotic controls on the distribution and coexistence of species and functional types and on variation in species' demography has led to improved understanding of how the multiple dimensions of forest diversity are structured across space and time and how this diversity relates to the processes controlling the role of forests in the Earth system. Nevertheless, knowledge gaps remain that impede our ability to predict how forest diversity and function will respond to climate change and other stressors. Meeting these global research challenges requires major advances in standardizing taxonomy of tropical species, resolving the main drivers of forest dynamics, and integrating plot-based ground and remote sensing observations to scale up estimates of forest diversity and function, coupled with improved predictive models. However, they cannot be met without greater financial commitment to sustain the long-term research of ForestGEO and other forest plot networks, greatly expanded scientific capacity across the world's forested nations, and increased collaboration and integration among research networks and disciplines addressing forest science.

Although precious health and wellbeing benefits can result from investments into urban green and blue infrastructure, access to these benefits is uneven. Surprisingly little is known about the conditions, programmes, policies and practices that support more equitable access to, influence over and governance of urban nature by diverse cosmopolitan communities. Based on our experiences applying a model from Hawaiʻi in New York City (NYC), we describe how sacred relationships with nature enhance the stewardship capacity of natural resource professionals and community members, with profound impacts on how people interact with urban landscapes and seascapes. By engaging in traditional rituals and adapting rituals for new settings, communities and managers can collaboratively work to cultivate and express personal connections to place, which can enhance equitable access to urban nature.

Drought is a prominent feature of Hawaii's climate, however, the biological, ecological, cultural, and socioeconomic impacts of drought in Hawaii are not well understood. This paper provides a comp...

Despite growing understanding of how rising temperatures affect carbon cycling, the impact of long-term and whole forest warming on the suite of essential and potentially limiting nutrients remains understudied, particularly for elements other than N and P. Whole ecosystem warming experiments are limited, environmental gradients are often confounded by variation in factors other than temperature, and few studies have been conducted in the tropics. We examined litterfall, live foliar nutrient content, foliar nutrient resorption efficiency (NRE), nutrient return, and foliar nutrient use efficiency (NUE) of total litterfall and live foliage of two dominant trees to test hypotheses about how increasing mean annual temperature (MAT) impacts the availability and ecological stoichiometry of C, N, P, K, Ca, Mg, Mn, Fe, Zn, and Cu in tropical montane wet forests located along a 5.2°C gradient in Hawaii. Live foliage responded to increasing MAT with increased N and K concentrations, decreased C and Mn concentrations, and no detectable change in P concentration or in foliar NRE. Increases in MAT increased nutrient return via litterfall for N, K, Mg, and Zn and foliar NUE for Mn and Cu, while decreasing nutrient return for Cu and foliar NUE for K. The N:P of litterfall and live foliage increased with MAT, while there was no detectable effect of MAT on C:P. The ratio of live foliar N or P to base cations and micronutrients was variable across elements and species. Increased MAT resulted in declining N:K and P:K for one species, while only P:K declined for the other. N:Ca and N:Mn increased with MAT for both species, while N:Mg increased for one and P:Mn increased for the other species. Overall, results from this study suggest that rising MAT in tropical montane wet forest: (i) increases plant productivity and the cycling and availability of N, K, Mg, and Zn; (ii) decreases the cycling and availability of Mn and Cu; (iii) has little direct effect on P, Ca or Fe; and (iv) affects ecological stoichiometry in ways that may exacerbate P-as well as other base cation and micronutrient - limitations to tropical montane forest productivity.

Although biocultural stewardship models have been written about widely, especially in Indigenous and rural communities, the practice of applying them in multicultural, urban environments has rarely been explored. We have yet to realize the full potential of kinship-linked, place-based stewardship models in highly diverse and densely populated urban settings. Here we explore how the concept of biocultural stewardship can be applied to a cosmopolitan, urban setting. To do this, we draw upon our experiences as participants and leaders in collaborative projects in New York and Hawaiʻi to consider how diverse knowledge systems and colearning engagements can strengthen a community of practice and enrich our stewardship efforts. Our collaborative projects include stewardship trainings based in a Native Hawaiian perspective (Hālau ʻŌhiʻa) that were adapted for New York City stewardship practitioners (Learning from Place) and subsequently inspired the creation of a New York City-based community of practice (Stewardship Salons). We identify various meanings in diverse practices of stewardship and the ways in which these concepts travel across different geographical contexts and culturally distinct communities. We stress that the meanings and practices resulting from such an integration are important because they shape the conceptualization of resources, their management, and the rights and responsibilities people have for stewardship of their places. We conclude that a biocultural approach to stewardship can help reorient stewardship practices in any context, including urban ones. A shift toward biocultural stewardship can have many positive effects for urban environmental stewardship, but also for much broader applications related to cultivating sustainability and well-being on a planet undergoing rapid environmental, social, and climate change.

The application of functional traits to predict and explain plant species’ distributions and vital rates has been a major direction in functional ecology for decades, yet numerous physiological traits have not yet been incorporated into the approach. Using commonly measured traits such as leaf mass per area (LMA) and wood density (WD), and additional traits related to water transport, gas exchange and resource economics, including leaf vein, stomatal and wilting traits, we tested hypotheses for Hawaiian wet montane and lowland dry forests (MWF and LDF, respectively): (1) Forests would differ in a wide range of traits as expected from contrasting adaptation; (2) trait values would be more convergent among dry than wet forest species due to the stronger environmental filtering; (3) traits would be intercorrelated within “modules” supporting given functions; (4) relative growth rate (RGR) and mortality rate (m) would correlate with a number of specific traits; with (5) stronger relationships when stratifying by tree size; and (6) RGR and m can be strongly explained from trait‐based models. The MWF species’ traits were associated with adaptation to high soil moisture and nutrient supply and greater shade tolerance, whereas the LDF species’ traits were associated with drought tolerance. Thus, on average, MWF species achieved higher maximum heights than LDF species and had leaves with larger epidermal cells, higher maximum stomatal conductance and CO2 assimilation rate, lower vein lengths per area, higher saturated water content and greater shrinkage when dry, lower dry matter content, higher phosphorus concentration, lower nitrogen to phosphorus ratio, high chlorophyll to nitrogen ratio, high carbon isotope discrimination, high stomatal conductance to nitrogen ratio, less negative turgor loss point and lower WD. Functional traits were more variable in the MWF than LDF, were correlated within modules, and predicted species’ RGR and m across forests, with stronger relationships when stratifying by tree size. Models based on multiple traits predicted vital rates across forests (R2 = 0.70–0.72; p

How warming affects the magnitude of CO2 fluxes within the soil profile remains an important question, with implications for modeling the response of ecosystem carbon balance to changing climate. Information on belowground responses to warming is especially limited for the tropics and subtropics because the majority of manipulative studies have been conducted in temperate and boreal regions. We examined how artificial warming affected CO2 gas production and exchange across soil profiles in a replicated mesocosms experiment relying on heavily weathered subtropical soils and planted with Chinese fir (Cunninghamia lanceolata). Half of 2 × 2 m mesocosms (5 replications) was heated with cables buried at a 10 cm depth, which increased temperature in the whole soil profile by 4.5, 3.6 and 2.5 °C at 15, 30 and 60 cm soil depths, respectively. Using a combination of chamber-based and concentration gradient method (CGM) approaches, we found that warming increased soil CO2 efflux across the whole profile by 40%. Changes were unevenly distributed across soil depth: mean CO2 production rate decreased from 0.74 to 0.67 μmol CO2 m−2 s−1 in topsoils (0–15 cm depth) whereas it increased from 0.26 to 0.73 μmol CO2 m−2 s−1 in subsoils (15–60 cm depth). Warming reduced moisture more strongly in subsurface than surface soils and increased subsoil soluble N concentrations as well as fine root turnover, in line with previous temperate and boreal warming studies. This consistency indicates that overall responses of subtropical forests to warming may be similar to forests in higher latitudes.

© 2018, The Author(s). Survival rates of large trees determine forest biomass dynamics. Survival rates of small trees have been linked to mechanisms that maintain biodiversity across tropical forests. How species survival rates change with size offers insight into the links between biodiversity and ecosystem function across tropical forests. We tested patterns of size-dependent tree survival across the tropics using data from 1,781 species and over 2 million individuals to assess whether tropical forests can be characterized by size-dependent life-history survival strategies. We found that species were classifiable into four ‘survival modes’ that explain life-history variation that shapes carbon cycling and the relative abundance within forests. Frequently collected functional traits, such as wood density, leaf mass per area and seed mass, were not generally predictive of the survival modes of species. Mean annual temperature and cumulative water deficit predicted the proportion of biomass of survival modes, indicating important links between evolutionary strategies, climate and carbon cycling. The application of survival modes in demographic simulations predicted biomass change across forest sites. Our results reveal globally identifiable size-dependent survival strategies that differ across diverse systems in a consistent way. The abundance of survival modes and interaction with climate ultimately determine forest structure, carbon storage in biomass and future forest trajectories.

The capacity to forecast climate and land-use driven changes to runoff, soil erosion and sediment transport in the tropics is hindered by a lack of long-term data sets and model study systems. To address these issues we utilized three watersheds characterized by similar shape, geology, soils, vegetation cover, and land use arranged across a 900 mm gradient in mean annual rainfall (MAR). Using this space-for-time design, we quantified suspended sediment (SS) and particulate organic carbon (POC) export over 18 months to examine how large-scale climate trends (MAR) affect sediment supply and delivery patterns (hysteresis) in tropical watersheds. Average daily SS yield ranged from 0.128 to 0.618 t km− 2 while average daily POC ranged from 0.002 to 0.018 t km− 2. For the largest storm events, we found that sediment delivery exhibited similar clockwise hysteresis patterns among the watersheds, with no significant differences in the similarity function between watershed pairs, indicating that: (1) in-stream and near-stream sediment sources drive sediment flux; and (2) the shape and timing of hysteresis is not affected by MAR. With declining MAR, the ratio of runoff to baseflow and inter-storm length between pulse events both increased. Despite increases in daily rainfall and the number of days with large rainfall events increasing with MAR, there was a decline in daily SS yield possibly due to the exhaustion of sediment supply by frequent runoff events in high MAR watersheds. By contrast, mean daily POC yield increased with increasing MAR, possibly as a result of increased soil organic matter decomposition, greater biomass, or increased carbon availability in higher MAR watersheds. We compared results to modeled values using the Load Estimator (LOADEST) FORTRAN model, confirming the negative relationship between MAR and sediment yield. However, because of its dependency on mean daily flow, LOADEST tended to under predict sediment yield, a result of its poor ability to capture the high variability in tropical streamflow. Taken together, results indicate that declines in MAR can have contrasting effects on hydrological processes in tropical watersheds, with consequences for instream ecology, downstream water users, and nearshore habitat.

Fine and coarse woody debris (WD), or woody necromass, serves a multitude of functions in forests including: essential habitat for countless vertebrate, arthropod and microbial species; substrate for regenerating plants, for example as nurse logs; a dominant carbon source for heterotrophs; and both a sink and source for essential nutrients (Harmon et al. 1986; Palace et al. 2012). Further, as WD decomposes, resulting fragments and microbial byproducts of the decay process provide a major source of organic matter for soils (Magnusson et al. 2016). Finally, WD can account for up to 20% of carbon storage in forests (Harmon et al. 1986; Palace et al. 2012), with an important role in biosphere -atmosphere CO2 exchange.

Global change such as climate warming and nitrogen (N) deposition is likely to alter terrestrial carbon (C) cycling, including soil respiration (Rs), the largest CO 2 source from soils to the atmosphere. To examine the effects of warming, N addition and their interactions on Rs, we conducted a two-way factorial soil warming (control, 5 °C warming) and N addition (control, 40 and 80 kg N ha −1 yr −1 ) mesocosm experiment in subtropical China. We measured Rs and nutrient availability. We found warming alone increased Rs by 15%, but warming plus high N addition treatment appeared to have offsetting effects as these plots were not significantly different from unheated and unfertilized controls. Warming alone increased soil available phosphorus (P) but availability declined in response to warming plus N additions. N additions alone had no effect on Rs in this study. Our results suggest that future increases in N deposition could mitigate warming-increased Rs in P-limited and relatively N-saturated subtropical forest ecosystems.

Non-native species invasions, growing human populations, and climate change are central ecological concerns in tropical island communities. The combination of these threats have led to losses of native biota, altered hydrological and ecosystem processes, and reduced ecosystem services. These threats pose complex problems to often underfunded management entities. We developed a watershed decision support tool (WDST) for the windward coast of Hawai‘i Island aimed at prioritizing catchments for invasive species removal and native forest protection from non-native species invasions. Using the Ecosystem Management Decision Support (EMDS) system, we integrated spatial data from four sources: (i) native and invasive species coverage; (ii) modeled water yield; (iii) treatment cost and efficacy; and (iv) native species conservation value. We used a distributed hydrology model (DHSVM) to estimate catchment-level (∼90 ha) water yield under six climate and non-native species invasion scenarios to identify where (1) invasive species removal and (2) protection from invasion would have the greatest benefit to increasing or maintaining native biodiversity and hydrologic functioning. The hydrology model predicted a 30% decline (386 Gl yr−1) in total water yield under a drier future climate (20% reduction in rainfall), with an additional 2% reduction when catchments were fully invaded by non-native species. Increased temperatures had a small compensatory effect on water yield. The WDST identified 6.3% of the study area as high priority for invasive species removal, based on characteristics of large hydrological response to the removal treatment (concentrated in high rainfall areas), high quality road or trail access, and high conservation value. High protection priority from invasive species (5.9% by area) occurred in higher elevation catchments, near the upper range of strawberry guava (the main invasive species), where water yield was most sensitive to invasion. Climate change scenarios had little influence on the spatial distribution of priority scores despite large changes in overall water yield. In contrast, priority scores were sensitive to very high variation in treatment costs, which were influenced largely by travel times to catchments via road and trail networks. This last finding suggests that future management feasibility will hinge on improvements to road and trail networks, or development of alternative management strategies that reduce travel costs and time.

Maintaining tree diversity Negative interaction among plant species is known as conspecific negative density dependence (CNDD). This ecological pattern is thought to maintain higher species diversity in the tropics. LaManna et al. tested this hypothesis by comparing how tree species diversity changes with the intensity of local biotic interactions in tropical and temperate latitudes (see the Perspective by Comita). Stronger local specialized biotic interactions seem to prevent erosion of biodiversity in tropical forests, not only by limiting populations of common species, but also by strongly stabilizing populations of rare species, which tend to show higher CNDD in the tropics. Science , this issue p. 1389 ; see also p. 1328

Functional gene approaches have been used to better understand the roles of microbes in driving forest soil nitrogen (N) cycling rates and bioavailability. Ammonia oxidation is a rate limiting step in nitrification, and is a key area for understanding environmental constraints on N availability in forests. We studied how increasing temperature affects the role of ammonia oxidizing archaea (AOA) and bacteria (AOB) in soil N cycling and availability by using a highly constrained natural mean annual temperature (MAT) elevation gradient in a tropical montane wet forest. We found that net nitrate (NO3- ) bioavailability is positively related to MAT (r2 = 0.79, P = 0.0033), and AOA DNA abundance is positively related to both NO3- availability (r2 = 0.34, P = 0.0071) and MAT (r2 = 0.34, P

Animals often increase their fitness by moving across space in response to temporal variation in habitat quality and resource availability, and as a result of intra and inter-specific interactions. The long-term persistence of populations and even whole species depends on the collective patterns of individual movements, yet animal movements have been poorly studied at the landscape level. We quantified movement behavior within four native species of Hawaiian forest birds in a complex lava-fragmented landscape: Hawai‛i ‘Amakihi (Chlorodrepanis virens), ‘Oma‘o (Myadestes obscurus), ‘Apapane (Himatione sanguinea), and ‘I‘iwi (Drepanis coccinea). We evaluated the relative importance of six potential intrinsic and extrinsic drivers of movement behavior and patch fidelity: 1) forest fragment size, 2) the presence or absence of invasive rats (Rattus sp.), 3) season, 4) species, 5) age, and 6) sex. The study was conducted across a landscape of 34 forest fragments varying in size from 0.07 to 12.37 ha, of which 16 had rats removed using a treatment-control design. We found the largest movements in the nectivorous ‘Apapane and ‘I‘iwi, intermediate levels in the generalist Hawai‛i ‘Amakihi, and shortest average movement for the ‘Oma‘o, a frugivore. We found evidence for larger patch sizes increasing patch fidelity only in the ‘Oma‘o, and an effect of rat-removal increasing patch fidelity of Hawai‛i ‘Amakihi only after two years of rat-removal. Greater movement during the non-breeding season was observed in all species, and season was an important factor in explaining higher patch fidelity in the breeding season for ‘Apapane and ‘I‘iwi. Sex was important in explaining patch fidelity in ‘Oma‘o only, with males showing higher patch fidelity. Our results provide new insights into how these native Hawaiian species will respond to a changing environment, including habitat fragmentation and changing distribution of threats from climate change. This article is protected by copyright. All rights reserved.

Mean annual temperature (MAT) is an influential climate factor affecting the bioavailability of growth‐limiting nutrients nitrogen (N) and phosphorus (P). In tropical montane wet forests, warmer MAT drives higher N bioavailability, while patterns of P availability are inconsistent across MAT. Two important nutrient acquisition strategies, fine root proliferation into bulk soil and root association with arbuscular mycorrhizal fungi, are dependent on C availability to the plant via primary production. The case study presented here tests whether variation in bulk soil N bioavailability across a tropical montane wet forest elevation gradient (5.2°C MAT range) influences (a) morphology fine root proliferation into soil patches with elevated N, P, and N+P relative to background soil and (b) arbuscular mycorrhizal fungal (AMF) colonization of fine roots in patches. We created a fully factorial fertilized root ingrowth core design (N, P, N+P, unfertilized control) representing soil patches with elevated N and P bioavailability relative to background bulk soil. Our results show that percent AMF colonization of roots increased with MAT (r 2 = .19, p = .004), but did not respond to fertilization treatments. Fine root length (FRL), a proxy for root foraging, increased with MAT in N+P‐fertilized patches only (p = .02), while other fine root morphological parameters did not respond to the gradient or fertilized patches. We conclude that in N‐rich, fine root elongation into areas with elevated N and P declines while AMF abundance increases with MAT. These results indicate a tradeoff between P acquisition strategies occurring with changing N bioavailability, which may be influenced by higher C availability with warmer MAT., Rising mean annual temperature (MAT) is predicted to increase the availability of inorganic nitrogen (IN) for biological use via impacts on rates of biogeochemical cycling, and with implications for plant N and phosphorus (P) acquisition. We found that fine root proliferation into N+P‐fertilized microsites declined across a natural temperature and soil‐IN gradient, while fine root mycorrhizal colonization increased across the gradient, with no effect of fertilization treatment. We conclude that in this tropical montane forest, plants may prioritize a mycorrhizal nutrient acquisition strategy over fine root proliferation in high MAT/N bioavailability conditions as a compensatory P acquisition strategy.

Nonnative, invasive feral pigs (Sus scrofa) modify habitats by disturbing soils and vegetation, which can alter biogeochemical processes. Soil microbial communities drive nutrient cycling and therefore also play important roles in shaping ecosystem structure and function, but the responses of soil microbes to nonnative ungulate removal remains poorly studied. We examined changes in the soil bacterial community over a ~25 year chronosequence of feral pig removal in tropical montane wet forests on the Island of Hawai’i. We extracted bacterial eDNA from soil samples collected inside and outside of ungulate exclosures along this chronosequence and sequenced the eDNA using the Illumina platform. We found that ungulate removal increased diversity of soil bacteria, with diversity scores positively correlated with time since removal. While functional and phylogenetic diversity were not significantly different between pig present and pig removed soils, soil bulk density, which decreases following the removal of feral pigs, was a useful predictor of dissimilarity among sites and correlated to changes in functional diversity. Additionally, increases in soil porosity, potassium, and calcium were correlated to increases in functional diversity. Finally, sites with greater mean annual temperatures were shown to have higher scores of both functional and phylogenetic diversity. As such, we conclude that feral pigs influence overall bacterial community diversity directly while influencing functional diversity indirectly through alterations to soil structure and nutrients. Comparatively, phylogenetic differences between communities are better explained by mean annual temperature as a climatic predictor of community dissimilarity.