Pervasive within-species spatial repulsion among adult tropical trees

Effective integration of drone technology for mapping and managing palm species in the Peruvian Amazon

Remote sensing data could increase the value of tropical forest resources by helping to map economically important species. However, current tools lack precision over large areas, and remain inaccessible to stakeholders. Here, we work with the Protected Areas Authority of Peru to develop and implement precise, landscape-scale, species-level methods to assess the distribution and abundance of economically important arborescent Amazonian palms using field data, visible-spectrum drone imagery and deep learning. We compare the costs and time needed to inventory and develop sustainable fruit harvesting plans in two communities using traditional plot-based and our drone-based methods. Our approach detects individual palms of three species, even when densely clustered (average overall score, 74%), with high accuracy and completeness for Mauritia flexuosa (precision; 99% and recall; 81%). Compared to plot-based methods, our drone-based approach reduces costs per hectare of an inventory of Mauritia flexuosa for a management plan by 99% (USD 5 ha-1 versus USD 411 ha-1), and reduces total operational costs and personnel time to develop a management plan by 23% and 36%, respectively. These findings demonstrate how tailoring technology to the scale and precision required for management, and involvement of stakeholders at all stages, can help expand sustainable management in the tropics.

Integrating conspecifics negative density dependence, successional and evolutionary dynamics: Towards a theory of forest diversity

Tree successional diversity is evident even to casual observers and has a well-understood physiological basis. Various life history trade-offs, driven by interspecific variation in a single trait, help maintain this diversity. Conspecific negative density dependence (CNDD) is also well-documented and reduces tree vital rates independently of succession strategies. The CNDD hypothesis is frequently justified by specialist natural enemies at a separate trophic level. We integrate these processes into an analytical demographic model, spanning short-term plant physiological responses to the dynamics of a large forest mosaic connected to a metacommunity. Surprisingly, multiple trade-offs do not necessarily increase diversity, as suboptimal trait combinations lead to strategies that cannot compete for successional niches, explaining the weak correlation between functional traits and succession position. Succession alone can sustain half of the species in the metacommunity, with diversity increasing linearly with CNDD strength. The steeper increase with larger metacommunities suggests CNDD plays a greater role in tropical forests. However, if each successional type contains multiple equivalent species, CNDD maintains diversity but becomes less effective in promoting successional diversity, consistent with some tropical forests being less successional diverse. Additionally, CNDD enhances the likelihood of successful speciation and shifts life-history trait frequency by affecting more late-successional species.

Synergizing Steric Hindrance and Stacking Interactions To Facilitate the Controlled Assembly of Multiple 41 Metalla-Knots and Pseudo-Solomon Links

In this work, a noncoplanar terphenyl served as a building block to synthesize a novel 3,3'-substituted bipyridyl ligand (L1) which further reacted with binuclear half-sandwich units A/B, giving rise to two aesthetic 41 metalla-knots in high yields via a coordination-driven self-assembly strategy. Furthermore, given the inherent compactness of the 41 metalla-knots, it creates favorable conditions for the emergence of steric repulsion. We focused on progressively introducing nitrogen atoms featuring a lone pair of electrons (LPEs) into ligand L1 to manipulate the balance of H⋅⋅⋅H/LPEs⋅⋅⋅LPEs steric repulsion during the assembly process, ultimately achieving controlled assembly from 41 metalla-knots to the pseudo-Solomon link and then to molecular tweezer-like assembly facilitated by stacking interactions. All the assemblies were well characterized by solution-state NMR techniques, ESI-TOF/MS, and single-crystal X-ray diffraction. The evolutionary process of the topological architectures is equivalent to visualizing the synergistic effect of steric hindrance and stacking interactions on structural assembly, providing a new avenue for achieving the controlled synthesis of different topologies.

Correlated evolution of dispersal traits and habitat preference in the melicgrasses

PREMISE

Seed dispersal is a critical process impacting individual plants and their communities. Plants have evolved numerous strategies and structures to disperse their seeds, but the evolutionary drivers of this diversity remain poorly understood in most lineages. We tested the hypothesis that the evolution of wind dispersal traits within the melicgrasses (Poaceae: Meliceae Link ex Endl.) was correlated with occupation of open and disturbed habitats.

METHODS

To evaluate wind dispersal potential, we collected seed dispersal structures (diaspores) from 24 melicgrass species and measured falling velocity and estimated dispersal distances. Species' affinity for open and disturbed habitats were recorded using georeferenced occurrence records and land cover maps. To test whether habitat preference and dispersal traits were correlated, we used phylogenetically informed multilevel models.

RESULTS

Melicgrasses display several distinct morphologies associated with wind dispersal, suggesting likely convergence. Open habitat taxa had slower-falling diaspores, consistent with increased wind dispersal potential. However, their shorter stature meant that dispersal distances, at a given wind speed, were not higher than those of their forest-occupying relatives. Species with affinities for disturbed sites had slower-falling diaspores and greater wind dispersal distances, largely explained by lighter diaspores.

CONCLUSIONS

Our results are consistent with the hypothesized evolutionary relationship between habitat preference and dispersal strategy. However, phylogenetic inertia and other plant functions (e.g., water conservation) likely shaped dispersal trait evolution in melicgrasses. It remains unclear if dispersal trait changes were precipitated by or predated changing habitat preferences. Nevertheless, our study provides promising results and a framework for disentangling dispersal strategy evolution.

Consequences of Local Conspecific Density Effects for Plant Diversity and Community Dynamics

Conspecific density dependence (CDD) in plant populations is widespread, most likely caused by local-scale biotic interactions, and has potentially important implications for biodiversity, community composition, and ecosystem processes. However, progress in this important area of ecology has been hindered by differing viewpoints on CDD across subfields in ecology, lack of synthesis across CDD-related frameworks, and misunderstandings about how empirical measurements of local CDD fit within the context of broader ecological theories on community assembly and diversity maintenance. Here, we propose a conceptual synthesis of local-scale CDD and its causes, including species-specific antagonistic and mutualistic interactions. First, we compare and clarify different uses of CDD and related concepts across subfields within ecology. We suggest the use of local stabilizing/destabilizing CDD to refer to the scenario where local conspecific density effects are more negative/positive than heterospecific effects. Second, we discuss different mechanisms for local stabilizing and destabilizing CDD, how those mechanisms are interrelated, and how they cut across several fields of study within ecology. Third, we place local stabilizing/destabilizing CDD within the context of broader ecological theories and discuss implications and challenges related to scaling up the effects of local CDD on populations, communities, and metacommunities. The ultimate goal of this synthesis is to provide a conceptual roadmap for researchers studying local CDD and its implications for population and community dynamics.

Joint evolution of mutualistic interactions, pollination, seed dispersal mutualism, and mycorrhizal symbiosis in trees

Mycorrhizal symbiosis, seed dispersal, and pollination are recognized as the most prominent mutualistic interactions in terrestrial ecosystems. However, it remains unclear how these symbiotic relationships have interacted to contribute to current plant diversity. We analyzed evolutionary relationships among mycorrhizal type, seed dispersal mode, and pollination mode in two global databases of 699 (database I) and 10 475 (database II) tree species. Although database II had been estimated from phylogenetic patterns and therefore had lower certainty of the mycorrhizal type than database I, whose mycorrhizal type was determined by direct observation, database II allowed analysis of many more taxa from more regions than database I. We found evidence of joint evolution of all three features in both databases. This result is robust to the effects of both sampling bias and missing taxa. Most arbuscular mycorrhizal-associated trees had endozoochorous (biotic) seed dispersal and biotic pollination, with long dispersal distances, whereas most ectomycorrhizal-associated trees had anemochorous (abiotic) seed dispersal and wind (abiotic) pollination mode, with shorter dispersal distances. These results provide a novel scenario in mutualistic interactions, seed dispersal, pollination, and mycorrhizal symbiosis types, which have jointly evolved and shaped current tree diversity and forest ecosystem world-wide.

Molecular-level carbon traits underlie the multidimensional fine root economics space

Carbon influences the evolution and functioning of plants and their roots. Previous work examining a small number of commonly measured root traits has revealed a global multidimensionality of the resource economics traits in fine roots considering carbon as primary currency but without considering the diversity of carbon-related traits. To address this knowledge gap, we use data from 66 tree species from a tropical forest to illustrate that root economics space co-varies with a novel molecular-level traits space based on nuclear magnetic resonance. Thinner fine roots exhibit higher proportions of carbohydrates and lower diversity of molecular carbon than thicker roots. Mass-denser fine roots have more lignin and aromatic carbon compounds but less bioactive carbon compounds than lighter roots. Thus, the transition from thin to thick fine roots implies a shift in the root carbon economy from 'do-it-yourself' soil exploration to collaboration with mycorrhizal fungi, while the shift from light to dense fine roots emphasizes a shift from acquisitive to conservative root strategy. We reveal a previously undocumented role of molecular-level carbon traits that potentially undergird the multidimensional root economics space. This finding offers new molecular insight into the diversity of root form and function, which is fundamental to our understanding of plant evolution, species coexistence and adaptations to heterogeneous environments.

Species and structural diversity of trees at the structural type level

BACKGROUND

Species and structural diversity are important for understanding the formation of forest communities, key ecological processes, and improving forest ecological functions and services, but their spatial characteristics have received little attention. Based on the spatial relationships among neighbouring trees, we proposed to divide trees within a structural unit into 15 structural types, and used the univariate distributions of the uniform angle index (W), mingling (M), and dominance (U), along with four common species diversity indices, to analyse the diversity of structural types in natural forests near the Tropic of Cancer.

RESULTS

Only a portion of clumped class maintained aggregation, most exhibited a random pattern. Species mixture increased exponentially across distribution classes, and abundance and richness exhibited an initial increase followed by a slight decrease. The distribution patterns of mixture classes varied from highly clustered to random, and M distributions gradually shifted from an inverted J-shaped curve to a J-shaped curve. Abundance and richness exhibited an exponential distribution, whereas the Shannon-Wiener index increased linearly. The W distribution of differentiation classes approximated a normal distribution, whereas M distributions exhibited a J shape. The U distribution of each structure type was approximately 0.2.

CONCLUSIONS

These results reveal the species and structural diversity characteristics of trees at the structural type level and expand our knowledge of forest biodiversity. The new method proposed here should significantly contribute to biodiversity monitoring efforts in terrestrial ecosystems, and suggests that higher standards for the simulation and reconstruction of stand structure, as well as thinning in near-natural forests, is warranted.

Multi-ecosystem services differently affected by over-canopy and understory nitrogen additions in a typical subtropical forest

Obtaining a holistic understanding of the impacts of atmospheric nitrogen deposition on multiple ecosystem services of forest is essential for developing comprehensive and sustainable strategies, particularly in heavy N deposition regions such as subtropical China. However, such impacts remain incompletely understood, with most previous studies focus on individual ecosystem function or service via understory N addition experiments. To address this knowledge gap, we quantified the effects of over-canopy and understory N additions on multiple ecosystem services based on a 7-year large-scale field experiment in a typical subtropical forest. Our results showed continued over-canopy N addition with 50 kg ha-1  year-1 over a period of 4-7 years significantly increased plant nutrient retention, but did not affect the services of soil nutrient accumulation, water yield, C sequestration (in plants and soil), or oxygen release. There were trade-offs between the soil and plant on providing the services of nutrient accumulation/retention and C sequestration under over-canopy N addition. However, without uptake and retention of tree canopy, the trade-off between soil and plant were more weaken under the understory N addition with 50 kg ha-1  year-1 , and their relationships were even synergetic under the understory N addition with 25 kg ha-1  year-1 . The results suggest that understory N addition cannot accurately simulate the effects of atmospheric N deposition on multiple services, along with mutual relationships. Interestingly, the services of plant N, P retention, and C sequestration exhibited a synergetic increase under the over-canopy N addition but a decrease under the understory N addition. Our results also found tree layer plays a primary role in providing plant nutrient retention service and is sensitive to atmospheric N deposition. Further studies are needed to investigate the generalized effects of forest canopy processes on alleviating the threaten of global change factors in different forest ecosystems.