Publications

Most biological invasion literature—including syntheses and meta-analyses and the resulting theory—is reported from temperate regions, drawing only minimally from the tropics except for some island systems. The lack of attention to invasions in the tropics results from and reinforces the assumption that tropical ecosystems, and especially the continental tropics, are more resistant to invasions. We have critically assessed biological invasions in the tropics and compared them with temperate regions, finding relatively weak evidence that tropical and temperate regions differ in their invasibility and in the traits that determine invader success and impacts. Propagule pressure and the traits that promote adaptation to disturbances (e.g., high fecundity or fast growth rates) are generally favorable to invasions in both tropical and temperate regions. We emphasize the urgent need for greater investment and regional cooperation in the study, prevention, and management of biological invasions in the tropics.

Some of the most species-rich plant communities occur on ancient, strongly weathered soils, whereas those on recently developed soils tend to be less diverse. Mechanisms underlying this well-known pattern, however, remain unresolved. Here, we present a conceptual model describing alternative mechanisms by which pedogenesis (the process of soil formation) might drive plant diversity. We suggest that long-term soil chronosequences offer great, yet largely untapped, potential as ‘natural experiments’ to determine edaphic controls over plant diversity. Finally, we discuss how our conceptual model can be evaluated quantitatively using structural equation modeling to advance multivariate theories about the determinants of local plant diversity. This should help us to understand broader-scale diversity patterns, such as the latitudinal gradient of plant diversity.

Degraded tropical peatlands lack tree cover and are often subject to seasonal flooding and repeated burning. These harsh environments for tree seedlings to survive and grow are therefore challenging to revegetate. Knowledge on species performance from previous plantings represents an important evidence base to help guide future tropical peat swamp forest (TPSF) restoration efforts. We conducted a systematic review of the survival and growth of tree species planted in degraded peatlands across Southeast Asia to examine (1) species differences, (2) the impact of seedling and site treatments on survival and growth and (3) the potential use of plant functional traits to predict seedling survival and growth rates. Planted seedling monitoring data were compiled through a systematic review of journal articles, conference proceedings, reports, theses and unpublished datasets. In total, 94 study‐sites were included, spanning three decades from 1988 to 2019, and including 141 indigenous peatland tree and palm species. Accounting for variable planting numbers and monitoring durations, we analysed three measures of survival and growth: (1) final survival weighted by the number of seedlings planted, (2) half‐life, that is, duration until 50% mortality and (3) relative growth rates (RGR) corrected for initial planting height of seedlings. Average final survival was 62% and half‐life was 33 months across all species, sites and treatments. Species differed significantly in survival and half‐life. Seedling and site treatments had small effects with the strongest being higher survival of mycorrhizal fungi inoculated seedlings; lower survival, half‐life and RGR when shading seedlings; and lower RGR and higher survival when fertilising seedlings. Leaf nutrient and wood density traits predicted TPSF species survival, but not half‐life and RGR. RGR and half‐life were negatively correlated, meaning that slower growing species survived for longer. Synthesis and applications . To advance tropical peat swamp reforestation requires expanding the number and replication of species planted and testing treatments by adopting control vs. treatment experimental designs. Species selection should involve slower growing species (e.g. Lophopetalum rigidum, Alstonia spatulata, Madhuca motleyana ) that survive for longer and explore screening species based on functional traits associated with nutrient acquisition, flooding tolerance and recovery from fire.

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Lichens and bryophytes are abundant primary producers in high latitude and high elevation ecosystems, and they play an important role in ecosystem processes such as decomposition and nutrient cycling. Despite their importance, little is known about the decomposability of lichens and bryophytes either among or within species, at the whole community level, or how this decomposability is affected by their functional traits. Here, we studied decomposability of lichens and bryophytes at the community‐level and individual species‐level (using 21 species and genera) collected from an elevational gradient in alpine Norway. In order to isolate the elevation effect on litter quality, we used a standardized laboratory bioassay to measure decomposability. In contrast to our expectations, we found that community‐level decomposability of lichens and bryophytes increased with elevation and thus decreasing temperature. In contrast, phosphorus release from the litter decreased with elevation while nitrogen release was unresponsive. Decomposability was explained by nutrient concentrations, litter pH and primary producer group identity (lichens versus bryophytes) at both the individual species and community levels. Species turnover (changes in species composition and abundance) was the main driver of decomposability across elevation at the community level, despite some of the traits explaining decomposability showing high intraspecific variability. Our study highlights the importance of among‐species variation in determining lichen and bryophyte decomposability. Further, the higher decomposability that we found for higher elevations suggests that global warming might result in a shift towards slower decomposable lichen and bryophyte species.

Data, meta data and R-scripts for results in 'Mosses modify effects of warmer and wetter conditions on tree seedlings at the alpine treeline'. 3 years of tree seedling survival data and final growth data from warming experiment with sites along a precipitation gradient. Sites are at/above treeline. Seedlings were transplanted into 3 different moss species. Growing season soil moisture and temperature data. See publication for further details on methods (Lett et all 2020 Global Change Biology, doc: 10.1111/gcb.15256). <br><br>

Summary 1. Functional trait diversity can reveal mechanisms of species coexistence in plant communities. Few studies have tested whether functional diversity for foliar traits related to resource‐use strategy increases or decreases with declining soil phosphorus (P) in forest communities. 2. We quantified tree basal area and four foliar functional traits (i.e. nitrogen (N), phosphorus (P), thickness and tissue density) for all woody species along the c . 120 000 year Franz Josef soil chronosequence in cool temperate rain forest, where strong shifts occur in light and soil nutrient availability (i.e. total soil P declines from 805 to 100 mg kg −1 ). We combined the abundance and trait data in functional diversity indices to quantify trait convergence and divergence, in an effort to determine whether mechanisms of coexistence change with soil fertility. 3. Relationships between species trait means and total soil N and P were examined using multiple regression, with and without weighting of species abundances. We used Rao’s quadratic entropy to quantify functional diversity at the plot scale, then compared this with random expectation, using a null model that randomizes abundances across species within plots. Taxonomic diversity was measured using Simpson’s Diversity. Relationships between functional and taxonomic diversity and total soil P were examined using jackknife linear regression. 4. Leaf N and P declined and leaf thickness and density increased monotonically with declining total soil P along the sequence; these relationships were unaffected by abundance weighting of species in the analyses. Inclusion of total soil N did not improve predictions of trait means. All measures of diversity calculated from presence/absence data were unrelated to total soil N and P. There was no evidence for a relationship between Rao values using quantitative abundances and total soil P. However, there was a strong positive relationship between Rao, expressed relative to random expectation, and total soil P, indicating trait convergence of dominant species as soil P declined. 5. Synthesis: Our results demonstrate that at high fertility locally dominant species differ in resource‐use strategy, but as soil fertility declines over the long term, dominant species increasingly converge on a resource‐retentive strategy. This suggests that differentiation in resource‐use strategy is required for coexistence at high‐fertility but not in low‐fertility ecosystems.

The rate and scale of human-driven changes can exert profound impacts on ecosystems, the species that make them up and the services they provide that sustain humanity. Given the speed at which these changes are occurring, one of society's major challenges is to coexist within ecosystems and to manage ecosystem services in a sustainable way. The effect of possible scenarios of global change on ecosystem services can be explored using ecosystem models. Such models should adequately represent ecosystem processes above and below the soil surface (aboveground and belowground) and the interactions between them. We explore possibilities to include such interactions into ecosystem models at scales that range from global to local. At the regional to global scale we suggest to expand the plant functional type concept (aggregating plants into groups according to their physiological attributes) to include functional types of aboveground–belowground interactions. At the scale of discrete plant communities, process-based and organism-oriented models could be combined into “hybrid approaches” that include organism-oriented mechanistic representation of a limited number of trophic interactions in an otherwise process-oriented approach. Under global change the density and activity of organisms determining the processes may change non-linearly and therefore explicit knowledge of the organisms and their responses should ideally be included. At the individual plant scale a common organism-based conceptual model of aboveground–belowground interactions has emerged. This conceptual model facilitates the formulation of research questions to guide experiments aiming to identify patterns that are common within, but differ between, ecosystem types and biomes. Such experiments inform modelling approaches at larger scales. Future ecosystem models should better include this evolving knowledge of common patterns of aboveground–belowground interactions. Improved ecosystem models are necessary tools to reduce the uncertainty in the information that assists us in the sustainable management of our environment in a changing world.

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Litterfall reflects forest productivity and is an important pathway of nutrient cycling in forests. We quantified litter quantity, nutrient concentrations, and decomposability for 22 permanently marked plots that included gradients of altitude (a range of 320-780 m), soil nutrients and past disturbance in a cool temperate evergreen montane rain forest in the western South Island of New Zealand. For each plot we quantified total fine litterfall and sorted it into components over a 2-year period, and for each of four widespread tree species in each plot (when present) we measured litter nitrogen (N) and phosphorus (P) concentrations, litter decomposability, and the release of litter N and P during decomposition. Total fine litterfall (mean 2.96 Mg ha -1 year -1 ) was low compared with other similar montane forests in New Zealand and elsewhere, and it declined with altitude and increasing successional stage of the plots. However, litterfall of four widespread tree species was unrelated to successional stage and that of only one was related to altitude. Further, neither total fine litterfall nor that of these four species was related to soil N or P concentrations with one exception. For the four species we found substantial variation among plots in litter N and P concentrations (up to 16-fold for N, 57-fold for P), litter decomposability, and the release of N and P during decomposition. Despite this, these variables were only rarely correlated with altitude, successional status, or soil nutrient concentrations across plots. Our results suggest that within-species variability in litterfall, nutrient concentrations, and decomposability are likely to be substantial in systems that have a high level of spatial variability because of recurrent large disturbances, and this has potentially important implications for the cycling of carbon, N and P, at the landscape scale.