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The response of plant functional traits to aridity in a tropical dry forest
Abstract
Drylands are experiencing an overall increase in aridity that is predicted to intensify in the future due to climate change. This may cause changes in the structure and functioning of dryland ecosystems, affecting ecosystem services and human well-being. Therefore, detecting early signs of ecosystem change before irreversible damage takes place is important. Thus, here we used a space-for-time substitution approach to study the response of the plant community to aridity in a Tropical dry forest (Caatinga, Brazil), and infer potential consequences of climate change. We assessed plant functional structure using the community weighted mean (CWM) and functional diversity, measured through functional dispersion (FDis), along a 700 km climatic gradient. We studied 13 functional traits, reflecting strategies associated with establishment, defense, regeneration, and dispersal of the most abundant 48 plant species in 113 sampling sites. Spearman correlations were used to test the relation between aridity and single-trait functional metrics. Aridity was a major environmental filter of the plant community functional structure. We found a higher abundance of species with deciduous leaves, zoochorous dispersal, fleshy fruits, chemical defense exudation and spinescence, and crassulacean acid metabolism towards more arid sites, at the expense of species with evergreen and thicker leaves, autochory dispersal, and shrub growth-form. The FDis of leaf type and thickness decreased with aridity, whereas FDis of fruit type, photosynthetic pathway, and defense strategies increased. Our findings provide functional indicators to early detect climate change impacts on Caatinga structure and functioning, to timely adopt preventive measures (e.g. conservation of forest remnants) and restoration actions (e.g. introduction of species with specific functional traits) in this threatened and unique ecosystem.
... The present study was carried out along a regional aridity gradient of 700 km, covering four Brazilian states, namely Alagoas, Ceará, Paraíba, Pernambuco, and Piauí (Figure 1). This gradient overlaps the Caatinga Phytogeographic Domain represented by many vegetation types ranging from semideciduous forests to open vegetation, located in rocky outcrops in driest areas (Fernandes and de Queiroz, 2018), encompassing also local variations in land management (for more details see Oliveira et al., 2020a). The study area has a mean annual temperature of 24 • C (ranging from 21 to 26 • C), average annual precipitation of 680 mm (spanning from 440 to 1,098 mm), and an altitude between 278 and 930 m (Oliveira et al., 2020a). ...
... This gradient overlaps the Caatinga Phytogeographic Domain represented by many vegetation types ranging from semideciduous forests to open vegetation, located in rocky outcrops in driest areas (Fernandes and de Queiroz, 2018), encompassing also local variations in land management (for more details see Oliveira et al., 2020a). The study area has a mean annual temperature of 24 • C (ranging from 21 to 26 • C), average annual precipitation of 680 mm (spanning from 440 to 1,098 mm), and an altitude between 278 and 930 m (Oliveira et al., 2020a). The aridity index varies from 0.27 to 0.69 including mostly semi-arid and humid climates (Oliveira et al., 2020a). ...
... The study area has a mean annual temperature of 24 • C (ranging from 21 to 26 • C), average annual precipitation of 680 mm (spanning from 440 to 1,098 mm), and an altitude between 278 and 930 m (Oliveira et al., 2020a). The aridity index varies from 0.27 to 0.69 including mostly semi-arid and humid climates (Oliveira et al., 2020a). ...
Ecological indicators based on biodiversity metrics are valuable and cost-effective tools to quantify, track and understand the effects of climate change on ecosystems. Studying changes in these indicators along climatic gradients in space is a common approach to infer about potential impacts of climate change over time, overcoming the limitations of lack of sufficiently long time-series data. Here, we studied the response of complementary biodiversity metrics in plants: taxonomic diversity (species richness and Simpson index) and functional diversity (diversity and redundancy) in 113 sampling sites along a spatial aridity gradient (from 0.27 to 0.69 of aridity index-AI) of 700 km in a Tropical dry forest. We found different responses of taxonomic and functional diversity metrics to aridity. Species diversity showed a hump-shaped curve peaking at intermediate levels of aridity between 0.38 and 0.52 AI as an ecotone, probably because it is where most species, from both drier and more mesic environments, still find conditions to co-exist. Functional diversity showed a positive linear relation with increasing aridity, suggesting higher aridity favors drought-adapted species with diverse functional traits. In contrast, redundancy showed a negative linear relation with increasing aridity, indicating that drier sites have few species sharing the same functional traits and resource acquisition strategies. Thus, despite the increase in functional diversity toward drier sites, these communities are less resilient since they are composed of a small number of plant species with unique functions, increasing the chances that the loss of one of such "key species" could lead to the loss of key ecosystem functions. These findings show that the integration of complementary taxonomic and functional diversity metrics, beyond the individual response of each one, is essential for reliably tracking the impacts of climate change on ecosystems. This work also provides support to the use of these biodiversity metrics as ecological indicators of the potential impact of climate change on drylands over time.
... Although some studies have shown an important role of soil fertility in determining plant stoichiometry, published studies have shown inconsistent results (Fang et al., 2019;Fyllas et al., 2009;He et al., 2010;Ordoñez et al., 2009;Xiong et al., 2021). Soil fertility as indexed by the soil C : N ratio had no significant effect on leaf stoichiometry in our analysis, indicating a decoupling of soil and leaf stoichiometry (Delgado-Baquerizo et al., 2017;Elser et al., 2010). Plant-soil interactions may affect whole-plant stoichiometry nonetheless, through effects on C allocation to different tissues. ...
... Plant-soil interactions may affect whole-plant stoichiometry nonetheless, through effects on C allocation to different tissues. Allocation of N to leaves shows stronger homeostasis than in other tissues, possibly as a consequence of the need to maintain the crucial functions of photosynthesis and leaf respiration; the stoichiometry of other tissues may adjust to soil conditions in order to support leaf-level function Delgado-Baquerizo et al., 2017;Zhang et al., 2017). Uncertainty in our soil fertility data may was inevitably introduced due to our reliance on a gridded soil map (Shangguan et al., 2013). ...
Leaf stoichiometric traits are central to ecosystem function and biogeochemical cycling, yet no accepted theory predicts their variation along environmental gradients. Using data in the China Plant Trait Database version 2, we aimed to characterize variation in leaf carbon and nitrogen per unit mass (Cmass, Nmass) and their ratio and to test an eco-evolutionary optimality model for Nmass. Community-mean trait values were related to climate variables by multiple linear regression. Climatic optima and tolerances of major genera were estimated; Pagel's λ was used to quantify phylogenetic controls, and Bayesian phylogenetic linear mixed models to assess the contributions of climate, species identity, and phylogeny. Optimality-based predictions of community-mean Nmass were compared to observed values. All traits showed strong phylogenetic signals. Climate explained only 18 % of C:N ratio variation among species but 45 % among communities, highlighting the role of taxonomic replacement in mediating community-level responses. Geographic distributions of deciduous taxa were separated primarily by moisture and evergreens by temperature. Cmass increased with irradiance but decreased with moisture and temperature. Nmass declined with all three variables. C:N ratio variations were dominated by Nmass. The coefficients relating Nmass to the ratio of maximum carboxylation capacity at 25 ∘C (Vcmax25) and leaf mass per area (Ma) were influenced by leaf area index. The optimality model captured 68 % and 53 % of variation between communities for Vcmax25 and Ma, respectively, and 21 % for Nmass. We conclude that stoichiometric variations along climate gradients are achieved largely by environmental selection among species and clades with different intraspecific trait values. Variations in leaf C:N ratio are mainly determined by Nmass, and optimality-based modelling shows useful predictive ability for community-mean Nmass. These findings should help to improve the representation of C:N coupling in ecosystem models.
... Climate conditions are important controls of how plant traits are expressed (Bussotti et al., 2015;Bjorkman et al., 2018;de Oliveira et al., 2020). For example, changes in temperature have multiple effects on leaf nutrient content (Reich & Oleksyn, 2004), specific leaf area (Rosbakh et al., 2015), and wood density (Swenson & Enquist, 2007), thereby affecting plant production capacity and adaptive strategies (Moles et al., 2014). ...
... For example, changes in temperature have multiple effects on leaf nutrient content (Reich & Oleksyn, 2004), specific leaf area (Rosbakh et al., 2015), and wood density (Swenson & Enquist, 2007), thereby affecting plant production capacity and adaptive strategies (Moles et al., 2014). Precipitation influences many plant traits, such as leaf thickness, leaf size, and leaf moisture content (de Oliveira et al., 2020;Baird et al., 2021). The variability of traits with climatic conditions will likely cause variations in plant flammability, as plant flammability is determined by many functional traits (Schwilk, 2015;Pausas et al., 2017;Alam et al., 2020). ...
Plant flammability is an important driver of wildfires, and flammability itself is determined by several plant functional traits. While many plant traits are influenced by climatic conditions, the interaction between climatic conditions and plant flammability has rarely been investigated.
Here, we explored the relationships among climatic conditions, shoot‐level flammability components, and flammability‐related functional traits for 186 plant species from fire‐prone and nonfire‐prone habitats.
For species originating from nonfire‐prone habitats, those from warmer areas tended to have lower shoot moisture content and larger leaves, and had higher shoot flammability with higher ignitibility, combustibility, and sustainability. Plants in wetter areas tended to have lower shoot flammability with lower combustibility and sustainability due to higher shoot moisture contents. In fire‐prone habitats, shoot flammability was not significantly related to any climatic factor.
Our study suggests that for species originating in nonfire‐prone habitats, climatic conditions have influenced plant flammability by shifting flammability‐related functional traits, including leaf size and shoot moisture content. Climate does not predict shoot flammability in species from fire‐prone habitats; here, fire regimes may have an important role in shaping plant flammability. Understanding these nuances in the determinants of plant flammability is important in an increasingly fire‐prone world.
... Semi-arid and arid environments cover about 40% of the Earth's land surface and are expanding and intensifying as a result of climate change [1,2]. These environments have ecological and environmental problems resulting from vulnerability to water deficit, soil desertification, and frequent, extreme weather [3,4], which affect the productivity and physiological, biochemical, and anatomical responses of plants [5]. ...
... The leaf thickness values for H. brasiletto and P. dulce were similar to the average reported for deciduous species [44] and for species from semi-arid areas [17]. A thin leaf corresponds to a denser and thinner mesophyll, as observed in the anatomical measurements, which does not accumulate large amounts of water (low WC and RWC) and does not have a high foliar maintenance cost [2]. Similarly, a dense leaf indicates that there is a high inversion of dry matter per unit of leaf area that intercepts light [18,44], which decreases the conductance of the mesophyll and affects gas exchange and photosynthetic rate [45]. ...
Semi-arid environments characterized by low rainfall are subject to soil desertification processes. These environments have heterogeneous landscapes with patches of vegetation known as resource islands that are generated by nurse species that delay the desertification process because they increase the availability of water and nutrients in the soil. The study aimed to characterize some foliar physiological, biochemical, and anatomical traits of three nurse tree species that form resource islands in the semi-arid environment of La Guajira, Colombia, i.e., Haematoxylum brasiletto, Pithecellobium dulce, and Pereskia guamacho. The results showed that H. brasiletto and P. dulce have sclerophyllous strategies, are thin (0.2 and 0.23 mm, respectively), and have a high leaf dry matter content (364.8 and 437.47 mg/g). Moreover, both species have a high photochemical performance, reaching Fv/Fm values of 0.84 and 0.82 and PIABS values of 5.84 and 4.42, respectively. These results agree with the OJIP curves and JIP parameters. Both species had a compact leaf with a similar dorsiventral mesophyll. On the other hand, P. guamacho has a typical succulent, equifacial leaf with a 97.78% relative water content and 0.81 mm thickness. This species had the lowest Fv/Fm (0.73) and PIABS (1.16) values and OJIP curve but had the highest energy dissipation value (DIo/RC).
... Therefore, to persist in these areas, taller plants must exhibit greater plasticity in height, resulting in smaller individuals in drier locations. The death of taller plants could result in drastic changes in carbon stocks in the Caatinga, since most of the carbon in a Caatinga SDTF is stored in larger trees (Sampaio & Silva, 2005 studies show that this pattern does not hold in more arid environments (see Akram et al., 2023;Oliveira et al., 2020). Our findings support the latter observations, as species with thicker leaves were more susceptible to a drier future climate. ...
Aim
The Anthropocene climate crisis may shift the distribution range of various species. Global Climate Models predict an increase in temperature and changes in precipitation across the Brazilian tropical semiarid region. Based on the joint analysis of functional traits and plant distribution models, we aim to identify which functional traits define the vulnerability of plants to climate change.
Location
Caatinga, Brazil.
Taxon
Trees-shrub plants.
Methods
We selected 36 species common to at least 25% of the floristic and phytosociological surveys made in the Brazilian semiarid region. We modelled both the current and future spatial distribution of these species and investigated whether functional traits, such as plant height, leaf area, leaf thickness, specific leaf area, stem specific density, and seed size can explain the range shifts of these species.
Results
Models indicate that 58.4% of the species are expected to expand their distribution range in the future. These species tend to be shorter and produce large seeds and thin leaves, which confer higher hydraulic safety and resistance of seeds to prolonged droughts. Meanwhile, 41.6% of the species are expected to reduce their distribution ranges in the future. Most of these are characterized as tall individuals with thick leaves and small seeds.
Conclusion
Species with traits that confer resistance to drought are likely to increase distribution towards the coast and to areas where the Caatinga borders with other domains. Also, these species with low height, thin leaves and large seeds may expand their distribution to the slopes and plateaus. The retraction of taller plants and with thicker leaves may have profound implications for the structure and functioning of Brazilian semiarid ecosystems, given their role in ecosystem processes and carbon cycle. Retractions can result in a reduction in the number of local species, which will impact regional biodiversity.
... Favoring certain traits led to a reduction in functional divergence, which could be related to a niche reduction something connected with a decrease in the ecosystem productivity and services (Mason et al. 2005;Ding et al. 2012). Our patent nding in the case of zoochorous species is probably conditioned by the fact that the richness of this group of species is high compared to other SDTF where no changes in the functional diversity of this dispersal syndrome has been detected (de Oliveira et al. 2020;Silva et al. 2020). This suggests that the ltering of species is dependent on the local conditions and, mainly, of the evolutive history of the forests (Valenta et al. 2018). ...
Although chronic disturbance is widely recognized as a main driver in the loss of diversity of tropical forests, their consequences in other attributes of the diversity such as functional dimensions still need to be clarified, especially in those traits associated with the dispersal process of plants. Here, we evaluated the effects of chronic disturbance on the community functional traits of a seasonally dry tropical forest, and their potential effects on the frugivores community. We characterized eight traits related to seed dispersal and calculated the community weight mean and functional diversity indices for trees and the whole woody community. We used generalized linear models to evaluate the effects of the disturbance on the community weight mean, functional diversity, and the abundance and diversity of fruits as resources for wildlife. Our results revealed that, the dominance of plants with costly fruiting species was reduced with disturbance. The functional richness and divergence were reduced with the disturbance, mainly in the qualitative traits. Finally, the availability of resources was slightly different between groups of dispersers, observing a general pattern of reduction in the availability and richness of fruits with the disturbance. Our results suggest that the changes in vegetation richness and abundance are not random but the result of filtering on traits related to dispersal costs and their subsequent ability to withstand environmental stress. The observed changes in vegetation have a direct effect on the availability of resources for frugivorous species, which in the medium term can generate a cascading effect on the ecosystem.
... As mudanças de temperatura no ambiente estão relacionadas à eficiência de algumas espécies de plantas, principalmente cactos e bromélias, conhecido como metabolismo ácido da crassuláceas (CAM), estratégia comum em regiões Áridas e Semiáridas; as plantas CAM fecham seus estômatos durante o dia para evitar perdas de água e abri-los durante a noite, permitindo absorção de CO2 e fixação de carbono (OLIVEIRA et al., 2020;SANTOS et al., 2012) Também, observou-se um padrão distinto nos dados, onde na área II, no mês de fevereiro, houve maior desprendimento de CO2 no período diurno quando a temperatura do solo se apresentou maior (Figura 6B). Como a região Semiárida apresenta variabilidade climática é possível as taxas de CO2 oscilem nos diferentes turnos, portanto, cabe então, investigar as variações ao longo dos períodos (FERREIRA et al., 2018). ...
O CO2 medido do solo é a atividade microbiana provido de diversos processos biogeoquímicos e sua investigação pode responder sobre os fatores associados a condição ambiental na Caatinga. Desse modo, o objetivo desta pesquisa foi avaliar as emissões de CO2 do solo em dois ambientes de Caatinga, comparando com os condicionantes ambientais do solo e do clima, no Semiárido de Alagoas. A atividade microbiana foi avaliada pelo CO2 liberado do solo, onde foi absorvido por uma solução de KOH. Foi instalado pluviômetro para obter índices de precipitação e a leituras de temperatura do solo a 10 cm da superfície. Foram avaliados o conteúdo de água, teores de carbono e matéria orgânica do solo. A maior emissão de CO2 do solo nas duas áreas avaliadas ocorreram no período noturno, em virtude da temperatura do solo apresentar-se mais amena; A liberação de CO2 apresenta variável, em decorrência das propriedades do solo, clima e vegetação; O carbono e a matéria orgânica do solo apresentaram valores elevados nas áreas de Caatinga, demonstrando grande atividade biogeoquímica e de ciclagem de nutrientes; Recomenda-se que estudos futuros sobre cinética de CO2 sejam realizados, de modo a comparar valores e compreender mais a fundo a dinâmica do ambiente.
... Understanding these phenomena in sink-source dynamics helps understand carbon stocks in ecosystems (Nosetto et al., 2020). Furthermore, in dry forest areas, like Caatinga, there is a multispecific floristic composition, which in conjunction with the different metabolisms (e.g., C3, C4 and CAM), drives biophysical resources and carbon use by plants (Jardim et al., 2022;Merrick et al., 2019;Oliveira et al., 2020). ...
Hostile climatic conditions, including high water deficit in the soil-atmosphere system characterize regions with arid and semi-arid climates. Local landscapes with climates of low rainfall and relative humidity, and high air temperature, such as regions of sub-humid, semi-arid, and arid zones, cover approximately 45.4% of the entire land surface of the planet, to which the biomes with dry forests occupy a total area of 1079 × 104 km2. Thus, this review aims to quantify the processes and changes in energy, water, and carbon fluxes and their interactions with the surfaces of terrestrial ecosystems of Caatinga and cacti in semi-arid environments. Studies report that forests in arid and semi-arid environments show resilience to local diversity, prominent in the interrelationship of species, which favors the survival of individuals with changes in the ecological niche. One of the main modifications in land use and land occupation in dryland landscapes is the implementation of agriculture. There is evidence that poor land use can negatively affect soil carbon stocks. Furthermore, carbon and energy fluxes in terrestrial ecosystems undergo significant changes with the removal of native vegetation. Therefore, the damage caused by deforestation can cause severe problems in the energy and carbon balance, compromising species' survival. Finally, we emphasize that crassulacean acid metabolism plants can be an alternative in places with serious environmental degradation problems.
... También, la selección de este tipo de coloración garantiza el aumento en la calidad de la recompensa para los frugívoros, ya que la biosíntesis de las moléculas que determinan las coloraciones de rojos a naranjas (antocianinas y carotenos) está regulada por carbohidratos y lípidos (Camara & Brangeon, 1981;Solfanelli et al., 2006). Adicionalmente, las frutas con pulpas carnosas son importantes en la dieta de muchas aves, en particular en ecosistemas secos tropicales con una producción altamente variable y dependiente de las condiciones climáticas (de Oliveira et al., 2020). De esta manera, la covarianza entre los rasgos perceptibles (color) y los no perceptibles (valor nutricional) permite utilizar señales visuales como indicadores de mejores recompensas (Valido et al., 2011). ...
Introducción:
La frugivoría es un proceso ecológico determinante para la estructuración y regeneración de los bosques. En los trópicos, donde la diversidad de plantas y animales frugívoros es alta, las relaciones interespecíficas son complejas y requieren estudio.
Objetivo:
Identificar las especies de plantas ecológicamente importantes en dos redes de interacción, y el papel de los rasgos funcionales de los frutos en esas interacciones en un bosque seco.
Métodos:
Recolectamos 10 frutos por planta de 10 plantas de cada especie de interés en un bosque seco colombiano, calculamos el índice de importancia de las plantas a partir de la relevancia de aves y mamíferos frugívoros en la estructura de las redes. Esta relevancia se relaciona directamente con el potencial del animal como dispersor efectivo de semillas. Utilizamos modelos lineales generalizados para estimar el tamaño, color, estrato, y tipo de pulpa, en el índice.
Resultados:
Las plantas más importantes son especies de los géneros Miconia, Ficus, Cecropia, Bursera, Casearia y Trichilia, también identificadas como recursos importantes para los frugívoros de los trópicos en otros estudios. Las plantas con frutos carnosos, rojos y de menor tamaño son los mejores para dispersores de semillas. El índice de importancia de las plantas tiene alta variación; esto sugiere que un conjunto de especies frugívoras beneficiadas por cada especie de planta tiene una contribución diferenciada en procesos ecológicos derivados de la dispersión de semillas.
Conclusiones:
Programas de restauración para este tipo de bosque tropical seco debería incluir una variedad de plantas, incluyendo especies con frutos pequeños, rojos y carnosos.
... Plant species from the non-invaded environment are extremely adapted to some conditions, such as low soil fertility, low litterfall, and high soil temperature on the soil surface. Some of these factors are also important to break down the native seed's dormancy [49][50][51]. To date, the invaded environment has promoted changes in litter deposition and decomposition in a tropical Cambisol. ...
Cryptostegia madagascariensis is an invasive plant species that covers 11% of the Brazilian northeastern territory, but its role on the litter trait in tropical ecosystems remains unclear. Here, we analyzed and compared the litter deposition, litter nutrient content, soil organic matter, and the litter decay rate from invaded and non-invaded environments by C. madagascariensis at a tropical Cambisol. The PCA analysis revealed that litter deposition, litter quality, and soil organic matter were correlated with the invaded environment. We grew plant species in greenhouse conditions to obtain a standard litter material to use in our litter bags in field conditions. We found that litter decay rate was higher in the invaded environment than in the non-invaded one. Our results suggest that C. madagascariensis changes litter traits in tropical ecosystems that in turn create negative plant–soil feedback to the native species by creating a physical barrier on soil surface and to promote its own rhizosphere.
... At the tropics, litter layer is scars due to year-round decomposition, high vegetation variation, seasonality, and plant growth strategies (e.g., some plant species lose their leaves during dry periods) de Oliveira et al. 2020;Kothandaraman et al. 2020;Raj and Jhariya 2021). Plant litter is also directly connected to net primary production (e.g., due to their losses for herbivory and litterfall). ...
In this chapter, the soil ecosystem is introduced as a multiphase system that (i) acts as habitat for a wide diversity of soil organisms and (ii) varies at both spatial and temporal scale. The soil formation varies according to a combination of geological factors and biological process (e.g., here included the influence of mankind) that result in an almost infinite variation in soil-forming factors. Basically, five forming factors are defined as the most important factors. These forming factors are parent material, climate, topography, time, and the activity of soil organisms (e.g., plant roots, insects, microorganisms, human influence, etc.). Considering the wide range of soil properties, i.e., physical, chemical, and biochemical variables, in this chapter we focused only on describing the most important and significant properties to soil organisms, such as soil organic carbon, soil pH, soil aggregation, and moisture. Finally, when considering the tremendous variety of soil types, the need for soil ecologist to recognize this variation must be considered to avoid stresses. Especially, if the student is considering both spatial and temporal variation into soil ecosystem. In view of this, it is important that soil ecologist must consider both soil biota and soil ecosystem characterization.
... At the tropics, litter layer is scars due to year-round decomposition, high vegetation variation, seasonality, and plant growth strategies (e.g., some plant species lose their leaves during dry periods) de Oliveira et al. 2020;Kothandaraman et al. 2020;Raj and Jhariya 2021). Plant litter is also directly connected to net primary production (e.g., due to their losses for herbivory and litterfall). ...
This chapter explores how natural and invaded ecosystem provide habitat and energy supply for the entire soil food web, how biological invasion changes habitat of the soil organisms, and two study cases considering invasive plant species (Cryptostegia madagascariensis and Prosopis juliflora) from tropical zones. Natural ecosystem is defined as a community of biotic and abiotic entities that naturally occurs in a specific range, while biological invasion defines the spread and dominance of any organisms in a new range. These two concepts are strongly linked to each other in moist and dry tropical ecosystems, and in some cases, they create a war condition (by antagonism) that affects the entire soil food web. Natural ecosystem can provide a wide range of physical, chemical, and biological processes that promotes the entire soil food web, while invasive organisms just change the habitat for their own benefit.
... At the tropics, litter layer is scars due to year-round decomposition, high vegetation variation, seasonality, and plant growth strategies (e.g., some plant species lose their leaves during dry periods) de Oliveira et al. 2020;Kothandaraman et al. 2020;Raj and Jhariya 2021). Plant litter is also directly connected to net primary production (e.g., due to their losses for herbivory and litterfall). ...
Previously, the soil ecosystem acting as habitat and food resource for soil organisms and the living soil and its wide variety of groups were introduced. This chapter will introduce the functional role of soil organisms on significant ecological processes, such as soil nutrient availability, biological control, soil structure, herbivory, symbiosis, and plant growth. Ecosystem engineers, litter transformers, predators, herbivores, symbionts, microregulators, decomposers, and prokaryotic transformers are essential for the soil ecosystem functioning because they promote services that provide habitat and food resource for the entire soil food web (e.g., including the primary producers). Basically, soil organisms are living individuals which live into soil ecosystem (e.g., by creating nests and galleries), and they have key role in increasing nutrient cycling, plant growth, soil structure, and plant resistance to abiotic and biotic stresses in tropical ecosystems. They can increase plant growth (e.g., by symbiotic relationships helping plants to uptake N, P, and micronutrients), litter deposition (e.g., by increasing the production of phytohormones to start leaf senescence processes), nutrient cycling (e.g., by increasing litter transformation and soil organic matter decomposition), and soil food web (e.g., by promoting a wide range of functional groups, and controlling the dominance of potential pathogen groups).KeywordsBiological control promoted by soil organismsPlant growthSymbionts in tropical ecosystemsSoil nutrient availabilityStructuring soil profiles
... At the tropics, litter layer is scars due to year-round decomposition, high vegetation variation, seasonality, and plant growth strategies (e.g., some plant species lose their leaves during dry periods) de Oliveira et al. 2020;Kothandaraman et al. 2020;Raj and Jhariya 2021). Plant litter is also directly connected to net primary production (e.g., due to their losses for herbivory and litterfall). ...
In the previous chapter, the tropical soil types and their forming factors and inner physicochemical properties were introduced. The next issue to be considered is the living soil that is constituted by a wide diversity of soil organisms. Also, the soil biota classification based on their body size and taxonomic and functional groups is introduced within this chapter. The soil ecologists must consider the structure of the soil food web and the ecosystem services provided by soil organisms into tropical ecosystems. Basically, soil organisms are both above- and belowground individuals which might be living in soil ecosystem. They are difficult to understand and to study because of their vast diversity of taxonomic groups. In tropical ecosystem, soil organisms build a complex soil food web which provides ecosystem services (e.g., soil organic matter formation, nutrient cycling, bioturbation, and control of pests and diseases). Finally, this chapter will introduce the relationships among soil organisms and how do they are influenced by environmental disturbances.KeywordsDiversity of soil organismsMacrofaunaMesofaunaMicrobiotaSoil food web
... At the tropics, litter layer is scars due to year-round decomposition, high vegetation variation, seasonality, and plant growth strategies (e.g., some plant species lose their leaves during dry periods) de Oliveira et al. 2020;Kothandaraman et al. 2020;Raj and Jhariya 2021). Plant litter is also directly connected to net primary production (e.g., due to their losses for herbivory and litterfall). ...
This textbook explores the complex nature of soil biological communities and their environments, and covers deserts, rainforests, seasonal tropical forests, dry deciduous forests, and island environments in the tropical zone. It provides essential information on soil biology concepts, ecological processes, plant-soil feedback, trophic structure, and land use effects on soil’s biological properties. The book also offers an updated approach to soil biota and microbiota and their interactions with plants that regulate the structures and functions of tropical ecosystems. Uniquely, it addresses island environments and natural disasters, shedding new light on soil organisms recovering tropical ecosystem functions. Further topics include ecological processes, plant-soil interactions, trophic communities, molecular approaches, and land use, making the book a valuable asset for students, educators and researchers engaged in the Environmental Sciences, Biodiversity and Conservation, Soil Ecology, Soil Biology, Ecology, Zoology, and Soil Biota Classification using classical and molecular tools. © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2022.
... At the tropics, litter layer is scars due to year-round decomposition, high vegetation variation, seasonality, and plant growth strategies (e.g., some plant species lose their leaves during dry periods) de Oliveira et al. 2020;Kothandaraman et al. 2020;Raj and Jhariya 2021). Plant litter is also directly connected to net primary production (e.g., due to their losses for herbivory and litterfall). ...
This chapter explores current knowledge used to study the trophic structure and the soil biological communities at the tropics. Trophic structure is defined by the complex of various feeding levels (e.g., producers, decomposers, herbivores, etc.) into an entire community, while the soil biological communities represent the wide range of soil organisms (e.g., roots, insects, nematodes, bacteria, fungi, etc.) that live in soil profile. These two concepts are strongly linked to each other. Trophic groups can influence decomposition, aboveground herbivory, net primary production, and nutrient cycling. It has been recognized that roots are an important driver of soil biological communities and most recently have soil ecologists started describing the effects of root exudates on soil biota diversity and community composition. This chapter examines some of the many ways that root exudates, plant biomass production, and litter may influence trophic structure and soil biological communities, and these changes may in turn feedback to affect the soil ecosystem at the tropics.KeywordsTrophic groupsAutotrophsHeterotrophsRoot exudatesNet primary production
... At the tropics, litter layer is scars due to year-round decomposition, high vegetation variation, seasonality, and plant growth strategies (e.g., some plant species lose their leaves during dry periods) de Oliveira et al. 2020;Kothandaraman et al. 2020;Raj and Jhariya 2021). Plant litter is also directly connected to net primary production (e.g., due to their losses for herbivory and litterfall). ...
This chapter explores how land uses and soil contamination in dry tropical ecosystems must affect soil organisms’ community composition. Land use is defined by the complex of vegetation type, soil management, and aftercare practices commonly used in agroecosystems, while the soil contamination defines the input level of exotic compounds in soil ecosystem that must affect organism’ fitness, reproduction, and behavior. These two concepts are strongly linked to each other in dry tropical ecosystem, and in some cases, they interact in the production with negative effects on the entire soil food web. Conventional farming system can negatively influence soil food web overtime by reducing soil organic matter contents. On the other hand, organic farming systems may improve soil organisms’ community composition by improving both habitat and resources availability. It has been recognized that organic residues are important drivers of soil biological communities. This chapter examines some of the many ways that soil contamination can be studied by using soil organisms as bioindicators.KeywordsAgroecosystemsConventional farming systemsDegraded ecosystemsOrganic farming systemsSoil food web
... At the tropics, litter layer is scars due to year-round decomposition, high vegetation variation, seasonality, and plant growth strategies (e.g., some plant species lose their leaves during dry periods) de Oliveira et al. 2020;Kothandaraman et al. 2020;Raj and Jhariya 2021). Plant litter is also directly connected to net primary production (e.g., due to their losses for herbivory and litterfall). ...
In this chapter, the natural disaster concept is introduced as the main influencer of soil ecosystem structure and functioning. At the tropics, there are several natural disaster types, but in this chapter our aim is to present some related aspects of fire events, landslides, and hurricanes and their influence on soil abiotic and biotic traits. These natural disasters are formed through the human activities, urban growth, nature of soils (geology, morphology, and topography), and climate conditions. In this chapter, we focused only on describing the most important and significative effects of natural disasters on soil ecosystem, such as plant community structure, soil organic matter, and N:P stoichiometry. In view of this, it is important that soil ecologist must consider the characterization of both soil abiotic and biotic traits.KeywordsFireHurricanesLandslidesSoil ecosystemSoil food web
... At the tropics, litter layer is scars due to year-round decomposition, high vegetation variation, seasonality, and plant growth strategies (e.g., some plant species lose their leaves during dry periods) de Oliveira et al. 2020;Kothandaraman et al. 2020;Raj and Jhariya 2021). Plant litter is also directly connected to net primary production (e.g., due to their losses for herbivory and litterfall). ...
A feedback is an event that occurs when the output of an organism metabolism (e.g., litter deposition by the natural process of plant senescence) is used as input back into the soil food web as an energy resource for other organism (e.g., litter transformers – Scarabaeidae and Spirobolida) as part of a chain of cause and effect. This chapter will introduce the main differences between feedback and interaction into soil ecology and soil biology. Primary producers may alter soil ecosystem through litter deposition, rootability, and rhizodeposition. In turns, soil organisms are influenced to act as herbivores (e.g., when feeding the fresh plant tissues), decomposers (e.g., when decomposing the dead plant tissues), and symbionts (e.g., when colonizing the roots through arbuscules and root nodules formation). Here, we will examine the various pathways that primary producers influence soil properties, the plant-arthropod interactions, and soil organisms influence primary producers. Plant-soil feedback over long timescales appears to be important drivers of soil sustainability or soil disturbance levels.KeywordsPrimary producers as soil conditionersPositive plant-soil feedbackNegative plant-soil feedbackPlant-arthropod interactionsSoil sustainability
... Relationships between chemical and morphological traits across a range of plant species have been rarely investigated (but see, e.g., [20,23,24]). Disentangling these relationships may improve our understanding of how plants adapt to the various challenges of climate change [25]. ...
Plants show an extraordinary diversity in chemical composition and are characterized by different functional traits. However, relationships between the foliar primary and specialized metabolism in terms of metabolite numbers and composition as well as links with the leaf economics spectrum have rarely been explored. We investigated these relationships in leaves of 20 woody species from the Mediterranean region grown as saplings in a common garden, using a comparative ecometabolomics approach that included (semi-)polar primary and specialized metabolites. Our analyses revealed significant positive correlations between both the numbers and relative composition of primary and specialized metabolites. The leaf metabolomes were highly species-specific but in addition showed some phylogenetic imprints. Moreover, metabolomes of deciduous species were distinct from those of evergreens. Significant relationships were found between the primary metabolome and nitrogen content and carbon/nitrogen ratio, important traits of the leaf economics spectrum, ranging from acquisitive (mostly deciduous) to conservative (evergreen) leaves. A comprehensive understanding of various leaf traits and their coordination in different plant species may facilitate our understanding of plant functioning in ecosystems. Chemodiversity is thereby an important component of biodiversity.
In an epoch of rapid environmental change, understanding and predicting how biodiversity will respond to a changing climate is an urgent challenge. Since we seldom have sufficient long‐term biological data to use the past to anticipate the future, spatial climate–biotic relationships are often used as a proxy for predicting biotic responses to climate change over time. These ‘space‐for‐time substitutions’ (SFTS) have become near ubiquitous in global change biology, but with different subfields largely developing methods in isolation. We review how climate‐focussed SFTS are used in four subfields of ecology and evolution, each focussed on a different type of biotic variable – population phenotypes, population genotypes, species' distributions, and ecological communities. We then examine the similarities and differences between subfields in terms of methods, limitations and opportunities. While SFTS are used for a wide range of applications, two main approaches are applied across the four subfields: spatial in situ gradient methods and transplant experiments. We find that SFTS methods share common limitations relating to ( i ) the causality of identified spatial climate–biotic relationships and ( ii ) the transferability of these relationships, i.e. whether climate–biotic relationships observed over space are equivalent to those occurring over time. Moreover, despite widespread application of SFTS in climate change research, key assumptions remain largely untested. We highlight opportunities to enhance the robustness of SFTS by addressing key assumptions and limitations, with a particular emphasis on where approaches could be shared between the four subfields.
Beyond the local abundance of species, their functional trait distinctiveness is now recognized as a key driver of community dynamics and ecosystem functioning. Yet, since the functional distinctiveness of a species is always relative to a given species pool, a species distinct at regional scale might not necessarily be distinct at local or community scale, and reciprocally. To assess the importance of scale (i.e. the definition of a species pool) when quantifying the functional distinctiveness of species, and how it might distort the ecological conclusions derived from it, we quantified trait distinctiveness of 1350 plant species at regional, local and community scales over ca 88 000 grassland plots in France. We measured differences in functional distinctiveness of species between regional (mainland France), local (10 × 10 km cell) and community (10 × 10 m plot) scale, and tested the influence of environmental predictors (climate and nitrogen input) and contexts (environmental distinctiveness, frequency and heterogeneity) on these variations. In line with theoretical expectations, we found large variation in functional distinctiveness (in particular between regional and community scales) for many species, with a general tendency of lower distinctiveness at smaller scales. We also showed that nitrogen input – a key aspect of high land use intensity – and environmental frequency partly explained the differences between local and regional scale only. These results suggest the role played by environmental filtering on species distinctiveness at local scale, but the determinant of distinctiveness variations at community scale still need to be elucidated. Our study provides robust empirical evidence that measures of ecological originality are strongly scale‐dependent. We urge ecologists to carefully consider the scale at which they measure distinctiveness, as ignoring scale dependencies could lead to biased (or even entirely wrong) conclusions when not considered at the scale of interest for the respective research question.
Plant functional strategies are well-established for low- and high-stress environments, such as rainforests and deserts. However, in environments with low- and high-stress level fluctuation within years, the relationship between plant functional strategies and their spatial distribution is still poorly understood. We aimed to answer: what are the relationships between above- and below-ground traits in the largest seasonally dry tropical forest in the Americas? Do the studied species form detectable groups from the functional perspective? If detectable, do functional groups present distinct spatial distributions across the domain, mediated by spatial heterogeneity of aridity? We sampled a range of 16 above- and below-ground traits from the 20 most common native tree species. We performed a PCA to understand the species' main coordinated trade-offs, a k-mean analysis to test for functional groups, and a Ripley's-K analysis followed by a GLS model to test spatial functional groups distribution through the aridity gradient. We found five coordinated trade-offs representing different aspects of the conservative-acquisitive strategy continuum. Drought-tolerance and avoidance mechanisms seem linked to the conservative-acquisitive gradient, where water storage is positively correlated with acquisitive strategies. Different from other seasonally dry regions, acquisitive strategies are not limited by aridity. The presence of short-term water storage traits might buffer rainfall fluctuations, allowing acquisitive species to occupy more arid regions. This study sheds new light on the functional complexity of species from Americas seasonally dry tropical forests, for the first time including the relationship of its below- and above-ground traits.
Arid and semiarid environments are characterized by low water availability (e.g., in soil and atmosphere), high air temperature, and irregularity in the spatio-temporal distribution of rainfall. In addition to the economic and environmental consequences, drought also causes physiological damage to crops and compromises their survival in ecosystems. The removal of vegetation is responsible for altering the energy exchange of heat and water in natural ecosystems and agricultural areas. The fluxes of CO2 are also changed, and environments with characteristics of sinks, which can be sources of CO2 after anthropic disturbances. These changes can be measured through methods such as sap flow, eddy covariance, remote sensing, and energy balance. Despite the relevance of each method mentioned above, there are limitations in their applications that must be respected. Thus, this review aims to quantify the processes and changes of energy fluxes, CO2, and their interactions with the surfaces of terrestrial ecosystems in dry environments. Studies report that the use of methods that integrate data from climate monitoring towers and remote sensing products helps to improve the accuracy of the determination of energy fluxes on a global scale, also helping to reduce the dissimilarity of results obtained individually. Through the collection of works in the literature, it is reported that several areas of the Brazilian Caatinga biome, which is a Seasonally Dry Tropical Forest have been suffering from changes in land use and land cover. Similar fluxes of sensible heat in areas with cacti and Caatinga can be observed in studies. On the other hand, one of the variables influenced mainly by air temperature is net radiation. In dry forest areas, woody species can store large amounts of carbon in their biomass above and belowground. The use of cacti can modify the local carbon budget when using tree crops together. Therefore, the study highlights the complexity and severity of land degradation and changes in CO2, water, and energy fluxes in dry environments with areas of forest, grassland, and cacti. Vegetation energy balance is also a critical factor, as these simulations are helpful for use in forecasting weather or climate change. We also highlight the need for more studies that address environmental conservation techniques and cactus in the conservation of degraded areas.
Understanding the spatial distribution of plant diversity and its drivers are major challenges in biogeography and conservation biology. Integrating multiple facets of biodiversity (e.g., taxonomic, phylogenetic, and functional biodiversity) may advance our understanding on how community assembly processes drive the distribution of biodiversity. In this study, plant communities in 60 sampling plots in desert ecosystems were investigated. The effects of local environment and spatial factors on the species, functional, and phylogenetic α- and β-diversity (including turnover and nestedness components) of desert plant communities were investigated. The results showed that functional and phylogenetic α-diversity were negatively correlated with species richness, and were significantly positively correlated with each other. Environmental filtering mainly influenced species richness and Rao quadratic entropy; phylogenetic α-diversity was mainly influenced by dispersal limitation. Species and phylogenetic β-diversity were mainly consisted of turnover component. The functional β-diversity and its turnover component were mainly influenced by environmental factors, while dispersal limitation dominantly effected species and phylogenetic β-diversity and their turnover component of species and phylogenetic β-diversity. Soil organic carbon and soil pH significantly influenced different dimensions of α-diversity, and soil moisture, salinity, organic carbon, and total nitrogen significantly influenced different dimensions of α- and β-diversity and their components. Overall, it appeared that the relative influence of environmental and spatial factors on taxonomic, functional, and phylogenetic diversity differed at the α and β scales. Quantifying α- and β-diversity at different biodiversity dimensions can help researchers to more accurately assess patterns of diversity and community assembly.
The Caatinga is a tropical dry forest. Rational exploitation of Caatinga wood resources consists of sustainable forest management under coppice systems. Therefore, the recovery of the timber stock for the next cycle will depend on the regrowth and survival capacity of the exploited species, as well as on the future structure of the forest. The objective of this work was to characterize the survival, structure, and diversity of Caatinga submitted to coppicing under sustainable forest management comparing pre- and post-harvest conditions. Permanent plots were installed in a Caatinga in the municipality of Floresta-PE, Brazil, in 2013, and measured 2 years after clearcutting. Height and circumference at the base (CAB) of the stumps and shoots were obtained for two situations: pre-cut (grouping by live and dead stumps) and (ii) post-cut (shoots on only live stumps). In addition, all individual shrub-tree species (CAB ≥ 4 cm) not included in the post-cut situation were identified, measured (CAB and height total) and tagged as persisting (6 cm ≤ CAB) or growing (6 < CAB ≤ 4 cm) in 2015. The survival and mortality of the stumps were quantified, as well as changes in the horizontal structure and floristic diversity. There was a decrease in the number of species 2 years after cutting, mainly due to the loss of Croton rhamnifolius H. B. K. and Sapium glandulatum (Vell.) Pax and predominance of Cenostigma bracteosum (Tul.) E. Gagnon & G. P. Lewis, Aspidosperma pyrifolium Mart., and Cnidoscolus quercifolius Pohl., resulting in a greater number of individuals of a few species. The outstanding regrowth capacity of these three species indicates that the forest remnant under study may eventually consist of populations with a predominance of species capable of coppicing.
The invasive Cryptostegia madagascariensis occupies riparian areas covered by tropical Cambisols throughout the North-eastern Brazil however litter is known regarding its ability to impact litter inputs, and ecosystem processes. This study aimed to characterize the effects of the invader on the litter deposition, soil physical-chemical properties, litter nutrient content, and the litter decay rate in a Tropical Cambisol. Comparisons of native and invaded environments showed that C. madagascariensis alters the quantity of litter deposition during both dry and rainy seasons. In contrast to native species, C. madagascariensis litterfall displayed litter seasonal variation (rainy vs. dry season), however invaded sites had higher litter biomass compared to native sites. C. madagascariensis litter was enriched in soil organic matter, N, P, and K contents as compared to the native litter. Compared to native environments, invaded ones had significantly decreased soil temperature and soil water content. Results suggest that C. madagascariensis enhances litter and N, P, and K availability in ways that have potential to impact soil ecosystem in the Tropical Cambisols from Caatinga ecoregion, Brazil.
Understanding and predicting the impact of global change drivers on biodiversity, the basis of the delivery of goods and services to humans, is a critical task in the Anthropocene Era. This has led to the development of international monitoring networks and frameworks to evaluate changes in biodiversity, the Essential Biodiversity Variables, though still somewhat ineffective. Biodiversity drivers have changed their relative importance in time and space, e.g. due to policies to combat air pollution, the increasing nitrogen pollution or climate change. Hence, to monitor their impact on biodiversity in space and time, we need appropriate Biodiversity Change Indicators and Surrogates, measured through distinct metrics. In this chapter, we propose a conceptual model to select the most cost-effective metrics of biodiversity-change based on both the type and intensity of the drivers that limit or impact biodiversity, and the nature of the Essential Biodiversity Variables which may be affected in each case. We propose ecophysiology-based metrics for low intensity limiting/impacting drivers, affecting organisms’ individual performance; trait-based metrics for medium intensity drivers, affecting the ecological performance of sensitive species before tolerant ones, changing species abundance and community functional traits; taxonomic-based metrics for high driver intensities which may culminate in species loss. We further discuss the utility of remote sensing data to measure some of these indicators or surrogates, allowing to upscale and/or generalize spatial and temporal information.
1.- The fast–slow plant economics spectrum predicts that because of evolutionary and biophysical constraints, different plant organs must be coordinated to converge in a unique ecological strategy within a continuum that shifts from fast to slow resource acquisition and conservation. Therefore, along a gradient of aridity, taxa with different strategies will be expected to be successful because selection pressures for slow resource acquisition become stronger as the environment becomes drier. In extremely arid and seasonal environments, however, a slow strategy may become disadvantageous because slow traits are costly to maintain. Additionally, as the availability of water decreases, selection pressures increase, reducing the variation in ecological strategies.
2.- Using shrub assemblages along an aridity gradient in the Atacama Desert, we test the hypothesis that selection pressures imposed by hyper aridity act simultaneously on the variation and coordination of trait attributes, leading to an inverse pattern in the fast–slow plant economics spectrum, where strategies shift from slow to fast as the environment becomes drier.
3.- We established 20 to 22 plots at each of four sites along the gradient to estimate plant community structure and functional variation. For all species recorded we quantified a set of leaf, stem and, root traits.
4.- Results revealed an inverse pattern of the fast–slow economics spectrum for leaf and stem traits, but not for root traits; that is, as aridity further increased, aboveground traits exhibited a shift from a slow to a fast strategy with some level of coordination. Belowground traits, however, did not shift accordingly with our prediction, rather they showed more complex pattern of shift and coordination with aboveground traits along the gradient. We also found that trait variation showed an idiosyncratic pattern of variation along the gradient, indicating that ecological strategies are driven by local processes within sites.
5.-Synthesis: Our results increase our understanding of the fast–slow plant economics spectrum by showing that environmental gradients, as well as local processes, can simultaneously shape different below‐ and above‐ground resource acquisition strategies in extremely poor resource environments.
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Our aims were to quantify and map the plant sub regions of the the Caatinga, that covers 844,453 km² and is the largest block of seasonally dry forest in South America. We performed spatial analyses of the largest dataset of woody plant distributions in this region assembled to date (of 2,666 shrub and tree species; 260 localities), compared these distributions with the current phytogeographic regionalizations, and investigated the potential environmental drivers of the floristic patterns in these sub regions. Phytogeographical regions were identified using quantitative analyses of species turnover calculated as Simpson dissimilarity index. We applied an interpolation method to map NMDS axes of compositional variation over the entire extent of the Caatinga, and then classified the compositional dissimilarity according to the number of biogeographical sub regions identified a priori using k-means analysis. We used multinomial logistic regression models to investigate the influence of contemporary climatic productivity, topographic complexity, soil characteristics, climate stability since the last glacial maximum, and the human footprint in explaining the identified sub regions. We identified nine spatially cohesive biogeographical sub regions. Current productivity, as indicated by an aridity index, was the only explanatory variable retained in the best model, explaining nearly half of the floristic variability between sub regions. The highest rates of endemism within the Caatinga were in the Core and Periphery Chapada Diamantina sub regions. Our findings suggest that the topographic complexity, soil variation, and human footprint in the Caatinga act on woody plant distributions at local scales and not as determinants of broad floristic patterns. The lack of effect of climatic stability since the last glacial maximum probably results from the fact that a single measure of climatic stability does not adequately capture the highly dynamic climatic shifts the region suffered during the Pleistocene. There was limited overlap between our results and previous Caatinga classifications.
This book provides in-depth information on Caatinga’s geographical boundaries and ecological systems, including plants, insects, fishes, amphibians, reptiles, birds, and mammals. It also discusses the major threats to the region’s socio-ecological systems and includes chapters on climate change and fast and large-scale land-use changes, as well as slow and small-scale changes, also known as chronic human disturbances. Subsequent chapters address sustainable agriculture, conservation systems, and sustainable development. Lastly, the book proposes 10 major actions that could enable the transformation of Caatinga into a place where people and nature can thrive together.
“I consider this book an excellent example of how scientists worldwide can mobilize their efforts to propose sound solutions for one of the biggest challenges of modern times, i.e., how to protect the world’s natural ecosystems while improving human well-being. I am sure this book will inspire more research and conservation action in the region and perhaps encourage other groups of scientists to produce similar syntheses about their regions.”
Russell Mittermeier, Ph.D. Executive Vice-Chair, Conservation International
The effects of human disturbance on biodiversity can be mediated by environmental conditions, such as water availability, climate and nutrients. In general, disturbed, dry or nutrient-depleted soils areas tend to have lower taxonomic diversity. However, little is known about how these environmental conditions affect functional composition and intraspecific variability in tropical dry forests. We studied a Seasonally Dry Tropical Forest (SDTF) under chronic anthropogenic disturbance (CAD) along rainfall and soil nutrient gradients to understand how these factors influence the taxonomic and functional composition. Specifically we evaluated two aspects of CAD, wood extraction and livestock pressure (goat and cattle grazing), along soil fertility and rainfall gradients on shrub and tree traits, considering species turnover and intraspecific variability. In addition, we also tested how the traits of eight populations of the most frequent species are affected by wood extraction, livestock pressure, rainfall and soil fertility. In general, although CAD and environmental gradients affected each trait of the most widespread species differently, the most abundant species also had a greater variation of traits. Considering species turnover, wood extraction is associated to species with smaller leaf area and lower investment in leaf mass, probably due to indirect effects of this disturbance type on the vegetation, i.e., the removal of branches and woody debris clears the vegetation, favouring species that minimize water loss. Livestock pressure, on the other hand, affected intraspecific variation: the herbivory caused by goats and cattle promoted individuals which invest more in wood density and leaf mass. In this case, the change of functional composition observed is a direct effect of the disturbance, such as the decrease of palatable plant abundance by goat and cattle herbivory. In synthesis, CAD, rainfall and soil fertility can affect trait distribution at community and species levels, which can have significant implications for the ecosystem functioning of SDTF under increasing levels of disturbance, climate change and soil nutrient depletion.
A Caatinga é um dos biomas brasileiros no qual se registram os maiores índices de degradação, associada, principalmente, à supressão da vegetação para produção energética e prática da agricultura de subsistência, ocasionando interferências na ciclagem de nutrientes. O objetivo do trabalho foi quantificar e analisar quimicamente a deposição de serapilheira em um fragmento de Caatinga, localizado no município de Pombal - PB. Foi coletada mensalmente, durante 12 meses, e separada em diferentes frações (folhas, estruturas reprodutivas, galhos e miscelânea) toda serapilheira depositada em coletores de 1,0 m2 de área, distribuídas de forma sistemática. Os nutrientes analisados foram N, P, K, Ca e Mg. A deposição anual de serapilheira foi de 3.785,67 kg ha-1, composta predominantemente da fração folha com 70,2%, seguida pela fração estruturas reprodutivas com 18,3%. Os teores de nutrientes na serapilheira seguiram a ordem Ca>N>K>Mg>P. O teor de nutrientes nas frações varia em função do tempo e há evidências de sua relação com a precipitação pluviométrica. A deposição da serapilheira coincidiu com o período de sazonalidade da Caatinga.
Para avaliar a deposição da serapilheira e as frações folhas, galhos, estruturas reprodutivas e miscelânea em área da Caatinga Nativa, bem como, verificar a interferência de variáveis climáticas, desenvolveu-se um estudo em uma microbacia experimental localizada no Município de Iguatu, Ceará, Brasil. A produção de serapilheira foi coletada mensalmente, entre os meses de abril de 2013 a março de 2014. Para a quantificação da serapilheira depositada sobre o solo da Caatinga, foram instaladas 20 caixas coletoras na área estudada, construídas de madeira, com dimensões de 1,0 m x 1,0 m x 0,2 m. Separando-se em seguida as frações de folhas, estruturas reprodutivas, galhos e miscelânea. A produção de folhas apresentou uma estreita relação com o regime pluviométrico, sendo seu ápice logo após a quadra chuvosa, enquanto a produção de estruturas reprodutivas foi determinada pelas espécies. A produção da serapilheira foi estimada em 4.038,79 kg ha-1, a fração folha apresentou maior contribuição com 1.268,57 kg ha-1. A maior deposição ocorreu na estação seca, onde a floresta Caatinga perde sua folhagem como estratégia de adaptação as condições climáticas semiáridas. A serapilheira estocada apresentou maior acúmulo no período seco (verão) onde a fração folha apresentou o maior acúmulo.
Drylands are home to more than 38% of the total global population and are one of the most sensitive areas to climate change and human activities1, 2. Projecting the areal change in drylands is essential for taking early action to prevent the aggravation of global desertification3, 4. However, dryland expansion has been underestimated in the Fifth Coupled Model Intercomparison Project (CMIP5) simulations5 considering the past 58 years (1948–2005). Here, using historical data to bias-correct CMIP5 projections, we show an increase in dryland expansion rate resulting in the drylands covering half of the global land surface by the end of this century. Dryland area, projected under representative concentration pathways (RCPs) RCP8.5 and RCP4.5, will increase by 23% and 11%, respectively, relative to 1961–1990 baseline, equalling 56% and 50%, respectively, of total land surface. Such an expansion of drylands would lead to reduced carbon sequestration and enhanced regional warming6, 7, resulting in warming trends over the present drylands that are double those over humid regions. The increasing aridity, enhanced warming and rapidly growing human population will exacerbate the risk of land degradation and desertification in the near future in the drylands of developing countries, where 78% of dryland expansion and 50% of the population growth will occur under RCP8.5.
Para avaliar a deposição e a taxa de decomposição da serapilheira em área da Caatinga, bem como, verificar a interferência de variáveis climáticas, desenvolveu-se um estudo em quatro microbacias localizadas no município de Iguatu, Ceará, Brasil. A produção de serapilheira era coletada mensalmente (mai/2007 a set/2008) em 20 caixas de 1,0 m2, separando-se em seguida as frações: folhas, estruturas reprodutivas, galhos e miscelânea. Coletou-se, trimestralmente, a serapilheira circunscrita sob um quadrado de ferro de (0,5 m x 0,5 m), estimando-se em seguida a serapilheira armazenada sobre o solo; a massa seca de serapilheira foi obtida pela secagem em estufa a 70ºC até peso constante. Foram coletadas amostras de solo (0-15 cm) para se obter a umidade. Observou-se que entre as espécies arbustivo-arbóreas, apenas duas (Aspidosperma pyrifolium Mart. e Croton sonderianus Muell. Arg.) representam mais de 50% da população e a cobertura vegetal é determinada pelo estrato herbáceo, já que apresenta um número bem maior de plantas. A produção de folhas apresentou uma estreita relação com o regime pluviométrico, sendo seu ápice logo após a quadra chuvosa, enquanto a produção de estruturas reprodutivas foi determinada pelas espécies. A deposição da serapilheira apresentou caráter sazonal com uma produtividade de 2.855,42 kg ha-1, e picos de produção imediatamente posterior a quadra chuvosa. Já a decomposição da serapilheira mostrou-se relativamente lenta, com uma taxa de decomposição (K) inferior a 1.
Global plant trait studies have revealed fundamental trade-offs in plant resource economics. We evaluated such trait trade-offs during secondary succession in two species-rich tropical ecosystems that contrast in precipitation: dry deciduous and wet evergreen forests of Mexico. Species turnover with succession in dry forest largely relates to increasing water availability and in wet forest to decreasing light availability. We hypothesized that while functional trait trade-offs are similar in the two forest systems, the successful plant strategies in these communities will be different, as contrasting filters affect species turnover. Research was carried out in 15 dry secondary forest sites (5-63 years after abandonment) and in 17 wet secondary forest sites (
We used a functional trait‐based approach to assess the impacts of aridity and shrub encroachment on the functional structure of Mediterranean dryland communities (functional diversity ( FD ) and community‐weighted mean trait values ( CWM )), and to evaluate how these functional attributes ultimately affect multifunctionality (i.e. the provision of several ecosystem functions simultaneously).
Shrub encroachment (the increase in the abundance/cover of shrubs) is a major land cover change that is taking place in grasslands worldwide. Studies conducted on drylands have reported positive or negative impacts of shrub encroachment depending on the functions and the traits of the sprouting or nonsprouting shrub species considered.
FD and CWM were equally important as drivers of multifunctionality responses to both aridity and shrub encroachment. Size traits (e.g. vegetative height or lateral spread) and leaf traits (e.g. specific leaf area and leaf dry matter content) captured the effect of shrub encroachment on multifunctionality with a relative high accuracy ( r ² = 0.63). FD also improved the resistance of multifunctionality along the aridity gradient studied.
Maintaining and enhancing FD in plant communities may help to buffer negative effects of ongoing global environmental change on dryland multifunctionality.
Predicting ecosystem responses to global change is a major challenge in ecology. A critical step in that challenge is to understand how changing environmental conditions influence processes across levels of ecological organization. While direct scaling from individual to ecosystem dynamics can lead to robust and mechanistic predictions, new approaches are needed to appropriately translate questions through the community level. Species invasion, loss, and turnover all necessitate this scaling through community processes, but predicting how such changes may influence ecosystem function is notoriously difficult. We suggest that community-level dynamics can be incorporated into scaling predictions using a trait-based response–effect framework that differentiates the community response to environmental change (predicted by response traits) and the effect of that change on ecosystem processes (predicted by effect traits). We develop a response-and-effect functional framework, concentrating on how the relationships among species' response, effect, and abundance can lead to general predictions concerning the magnitude and direction of the influence of environmental change on function. We then detail several key research directions needed to better scale the effects of environmental change through the community level. These include (1) effect and response trait characterization, (2) linkages between response-and-effect traits, (3) the importance of species interactions on trait expression, and (4) incorporation of feedbacks across multiple temporal scales. Increasing rates of extinction and invasion that are modifying communities worldwide make such a research agenda imperative.
The production of litter and the consequent liberation of nutrients is considered as one of the most important processes of energy transfer in ecosystems, and its knowledge is basic for the management and conservation of natural and artificial forests. Nutrient cycling research in the Caatinga is scarce; this study analyzes the dynamics of the litterfall in Caatinga shrub-trees at Seridó Ecological Station-RN. The deciduous material was collected monthly in 30 wooden litter traps for one year, oven-dried, separated into leaves, bark and branches, reproductive structures and miscellany, and then weighed. After twelve months the Caatinga deposited 2068.55 kg ha-1 of deciduous material; 79.90% was leaves, 9.27% was branches and bark, 7.91% was miscellany and 2.92% was reproductive structures. The deposition peak of reproductive material occurred in March, while for the other fractions it happened in May, which coincided with the beginning of the dry season during the studied period. Deposition was reduced during the time of low precipitation (July-December) and increased after the rains of January, showing a marked seasonal pattern.
Plant functional traits are the features (morphological, physiological, phenological) that represent ecological strategies and determine how plants respond to environmental factors, affect other trophic levels and influence ecosystem properties. Variation in plant functional traits, and trait syndromes, has proven useful for tackling many important ecological questions at a range of scales, giving rise to a demand for standardised ways to measure ecologically meaningful plant traits. This line of research has been among the most fruitful avenues for understanding ecological and evolutionary patterns and processes. It also has the potential both to build a predictive set of local, regional and global relationships between plants and environment and to quantify a wide range of natural and human-driven processes, including changes in biodiversity, the impacts of species invasions, alterations in biogeochemical processes and vegetation–atmosphere interactions. The importance of these topics dictates the urgent need for more and better data, and increases the value of standardised protocols for quantifying trait variation of different species, in particular for traits with power to predict plant- and ecosystem-level processes, and for traits that can be measured relatively easily. Updated and expanded from the widely used previous version, this handbook retains the focus on clearly presented, widely applicable, step-by-step recipes, with a minimum of text on theory, and not only includes updated methods for the traits previously covered, but also introduces many new protocols for further traits. This new handbook has a better balance between whole-plant traits, leaf traits, root and stem traits and regenerative traits, and puts particular emphasis on traits important for predicting species’ effects on key ecosystem properties. We hope this new handbook becomes a standard companion in local and global efforts to learn about the responses and impacts of different plant species with respect to environmental changes in the present, past and future.
Foram estudadas plantas ornitófilas em uma área de caatinga da Reserva Particular do Patrimônio Natural Cantidiano Valgueiro (8º36'00" S e 38º34'5" W) em Pernambuco, Nordeste do Brasil, no período de julho de 2002 a junho de 2003. Oito espécies ornitófilas foram registradas no período de estudo, distribuídas em sete gêneros e cinco famílias. Cactaceae foi a família com maior número de espécies polinizadas por beija-flores, sendo representada por três espécies, seguida de Bromeliaceae, com duas espécies. Foram registradas espécies em floração durante todo o ano. Com exceção de Bromelia laciniosa Mart. ex Schult. f. e Neoglaziovia variegata (Arruda) Mez (Bromeliaceae), todas as demais espécies tiveram pico de floração no período seco. Metade das espécies ornitófilas da comunidade estudada apresentou hábito herbáceo. A maioria das espécies apresentou flores vermelhas (62,5%), sendo o tipo tubo registrado em todas as espécies. O comprimento médio do tubo da corola foi 20,2 ± 5,6 mm, a concentração de açúcares no néctar variou de 18% a 33,5% e o volume de 22 a 41 µL. Cinco espécies de beija-flores foram registradas visitando as flores da comunidade estudada, das quais apenas uma foi residente. Chlorostilbon aureoventris (d'Orbigny & Lafresnaye, 1838), devido ao seu comportamento e freqüência de visita, foi considerada como a espécie dominante da comunidade. Comparações com estudos semelhantes evidenciaram que o número de espécies de plantas ornitófilas que floresceram no período de estudo na Reserva foi expressivamente menor do que o encontrado em estudos em remanescentes de Mata Atlântica e áreas neotropicais em geral. Além disso, uma espécie de Trochilinae, e não de Phaethornithinae, atuou como organizadora da comunidade.
Although the potential for increased temperature is the primary and best-studied aspect of anthropogenic climate change, altered rainfall patterns, increased storm intensity, and more severe droughts are also predicted in most climate-change scenarios. We altered experimentally the rainfall regime in a native tallgrass prairie in northeastern Kansas and assessed leaf-level physiological activity and plant growth responses for C3 and C4 plant species. Our primary objective was to contrast the importance of reductions in rainfall quantity (30% smaller rain events, no change in rainfall pattern) with an altered, more extreme distribution of rainfall (no reduction in total growing-season quantity, 50% increased inter-rainfall dry intervals) for these dominant species from the two main plant functional groups (C4 grasses, C3 forbs) present in many grasslands. Leaf water potential (wl), net photosynthetic carbon gain ( ), specific leaf mass, leaf C : N ratio, growth rate ACO2 for Andropogon gerardii (C4 grass) and Solidago canadensis (C3 forb), vegetative and flowering stem densities, and canopy light penetration for grass and forb assemblages were intensively monitored during the 1999 growing season in a long-term rainfall manipulation study at the Konza Prairie Biological Station. Soil water content at 0-30 cm depth was more variable in response to the altered rainfall distribution compared to the reduced-quantity treatment. In S. canadensis ,, gs (stomatal conductance), A : Ci (leaf stomatal (CO2)), ACO2 and A : E (estimated leaf transpiration rate) were positively correlated with soil water content, but no rela- tionship was seen for A. gerardii, indicating that even though this dominant grass species has most of its roots in the upper 30 cm of the soil, A. gerardii was buffered physiologically from increased resource variability. There were few significant responses in growth parameters in either grasses or forbs, but canopy light pen- etration increased with both rainfall treatments. We concluded (1) that the temporal variability in rainfall inputs can have as much impact on soil moisture as simple reductions in rainfall quantities with no change in temporal distribution, (2) that responses of A. gerardii and S. canadensis to altered rainfall distributions were not consistent with common views of soil resource partitioning between shallow-rooted grasses and deep-rooted forbs, and (3) that altered rainfall patterns may have the potential to offset elevated CO2 impacts on grassland vegetation.
Bringing together leaf trait data spanning 2,548 species and 175 sites we describe, for the first time at global scale, a universal spectrum of leaf economics consisting of key chemical, structural and physiological properties. The spectrum runs from quick to slow return on investments of nutrients and dry mass in leaves, and operates largely independently of growth form, plant functional type or biome. Categories along the spectrum would, in general, describe leaf economic variation at the global scale better than plant functional types, because functional types overlap substantially in their leaf traits. Overall, modulation of leaf traits and trait relationships by climate is surprisingly modest, although some striking and significant patterns can be seen. Reliable quantification of the leaf economics spectrum and its interaction with climate will prove valuable for modelling nutrient fluxes and vegetation boundaries under changing land-use and climate.
1. Habitat filtering (HF, trait convergence) and niche differentiation (ND, trait divergence) are known to impact upon plant community structure. Both processes integrate individual responses to the abiotic environment and biotic interactions. Thus, it is difficult to clearly identify the underlying abiotic and biotic factors that ultimately impact community structure by looking at community-level patterns of trait divergence or convergence alone.
2. We used a functional trait-based and multiscale approach to assess how biotic interactions and aridity determine the functional structure of semi-arid shrublands sampled along a large aridity gradient in Spain. At the regional scale, we investigated functional differences among species (axes of specialization) to identify important traits for community assembly. At the community scale, we evaluated the relative impact of HF and ND on community structure using a null model approach. Finally, at the plant neighbourhood scale, we evaluated the impact of biotic interactions on community structure by investigating the spatial patterns of trait aggregation.
3. The shrub species surveyed can be separated along four axes of specialization based on their above-ground architecture and leaf morphology. Our community scale analysis suggested that the functional structure of semi-arid communities was clearly non-random, HF and ND acting independently on different traits to determine community structure along the aridity gradient. At the plant neighbourhood scale, the spatial distribution of species was also clearly not random, suggesting that competition and facilitation impacted on the observed changes in the functional diversity of shrubland communities along the aridity gradient.
4. Synthesis: Our results demonstrated that HF and ND acted simultaneously on independent traits to jointly determine community structure. Most importantly, our multiscale approach suggested that competition and facilitation interplayed with aridity to determine this structure. Competition appeared to be constant along the aridity gradient and explained the high functional diversity observed in semi-arid shrublands. Facilitation affected subordinate and rare species and, thus, may act to enhance the biodiversity of these ecosystems. Finally, the framework employed in our study allows moving forward from the examination of patterns to the development of mechanistic trait-based approaches to study plant community assembly.
Dispersal-viewed as the departure of a diaspore (eg. seed or fruit) from the parent plant-is examined in terms of mechanisms, advantages (eg. in connection with escape from parental influence, and colonization), and patterns of production (eg. geographical aspects, seasonality, and intraspecific variation).-P.J.Jarvis
The implicit hydrologic dimensions of international efforts to mitigate climate change, specifically potential impacts of the Clean Development Mechanism-Afforestation/Reforestation (CDM-AR) provisions of the Kyoto Protocol (KP) on global, regional and local water cycles, are examined. The global impact of the redistribution of water use driven by agriculture and land use change, of which CDM-AR can be a contributing factor, is a major component of ongoing global change and climate change processes. If converted to forest, large areas deemed suitable for CDM-AR would exhibit increases in actual evapotranspiration (AET) and/or decreases in runoff. Almost 20% (144 Mha) of all suitable land showed little or no impact on runoff and another 28% (210 Mha) showed only moderate impact. About 27% (200 Mha) was in the highest impact class, exhibiting an 80–100% decrease in runoff, and prevalent in drier areas (based on Aridity Index (AI)), the semi-arid tropics, and in conversion from grasslands and subsistence agriculture. Significant impacts on local hydrologic cycles were evident, however large impacts were not predicted at regional or global scale due primarily to the current limit on carbon offset projects under the Kyoto Protocol. Predicted decreases in runoff ranged from 54% in drier areas to less than 15% in more humid areas, based on four case studies located across a range of biophysical conditions and project scenarios in Ecuador and Bolivia. Factors other than climate, e.g. upstream/ downstream position, were shown to be important in evaluating off-site impacts. This study demonstrates that it will become increasingly important to consider implications on local to regional water resources, and how the hydrologic dimension of CDM-AR impacts on issues of sustainability, local communities, and food security.
1. Indices quantifying the functional aspect of biodiversity are essential in understanding relationships between biodiversity, ecosystem functioning and environmental constraints. Many indices of functional diversity have been published but we lack consensus about what indices quantify, how redundant they are and which ones are recommended.
2. This study aims to build a typology of functional diversity indices from artificial data sets encompassing various community structures (different assembly rules, various species richness levels) and to identify a set of independent indices able to discriminate community assembly rules.
3. Our results confirm that indices can be divided into three main categories, each of these corresponding to one aspect of functional diversity: functional richness, functional evenness and functional divergence. Most published indices are highly correlated and quantify functional richness while quadratic entropy (Q) represents a mix between functional richness and functional divergence. Conversely, two indices (FEve and FDiv respectively quantifying functional evenness and functional divergence) are rather independent to all the others. The power analysis revealed that some indices efficiently detect assembly rules while others performed poorly.
4. To accurately assess functional diversity and establish its relationships with ecosystem functioning and environmental constraints, we recommend investigating each functional component separately with the appropriate index. Guidelines are provided to help choosing appropriate indices given the issue being investigated.
5. This study demonstrates that functional diversity indices have the potential to reveal the processes that structure biological communities. Combined with complementary methods (phylogenetic and taxonomic diversity), the multifaceted framework of functional diversity will help improve our understanding of how biodiversity interacts with ecosystem processes and environmental constraints.
Seasonal variations in CAM performance of sunexposed and partially shaded populations of Bromelia humilis were measured under natural conditions in a semi-arid region in northern Venezuela. The sun population consisted of smaller plants, with lower chlorophyll and total nitrogen contents per unit leaf area compared with plants from the partial-shade population. During the dry season CAM activity, assessed as nocturnal acid accumulation, was higher in the partial-shade population. Acid accumulation was stimulated by irrigation in both populations within 24 h after treatment. Daily changes in concentration of soluble sugars were opposite to leaf acidity indicating their role as carbon source for acid synthesis during the night. The change in nocturnal sugar concentration was always more than the amount required for acid accumulation, suggesting other carbohydrate-consuming processes such as transportation of sugars out of the leaf. CAM activity was higher during the rainy season, and differences between populations were smaller. At the end of the rainy season reduction of CAM activity caused by drought was first detected in the sun population. Measured ratios of glucan/soluble sugar show a higher proportion of readily utilizable sugars during periods of active CAM and growth. Under conditions of continuous high light intensity and air temperature leading to all year round high potential evaporation in semiarid tropical regions, fully exposed populations of B. humilis show a pronounced reduction of metabolic activity. Partial shade favours growth and CAM activity in this constitutive CAM species. It is concluded that water stress, and not light intensity, is the predominant limiting factor for growth of this species under natural conditions.
We developed interpolated climate surfaces for global land areas (excluding Antarctica) at a spatial resolution of 30 arc s (often referred to as 1-km spatial resolution). The climate elements considered were monthly precipitation and mean, minimum, and maximum temperature. Input data were gathered from a variety of sources and, where possible, were restricted to records from the 1950-2000 period. We used the thin-plate smoothing spline algorithm implemented in the ANUSPLIN package for interpolation, using latitude, longitude, and elevation as independent variables. We quantified uncertainty arising from the input data and the interpolation by mapping weather station density, elevation bias in the weather stations, and elevation variation within grid cells and through data partitioning and cross validation. Elevation bias tended to be negative (stations lower than expected) at high latitudes but positive in the tropics. Uncertainty is highest in mountainous and in poorly sampled areas. Data partitioning showed high uncertainty of the surfaces on isolated islands, e.g. in the Pacific. Aggregating the elevation and climate data to 10 arc min resolution showed an enormous variation within grid cells, illustrating the value of high-resolution surfaces. A comparison with an existing data set at 10 arc min resolution showed overall agreement, but with significant variation in some regions. A comparison with two high-resolution data sets for the United States also identified areas with large local differences, particularly in mountainous areas. Compared to previous global climatologies, ours has the following advantages: the data are at a higher spatial resolution (400 times greater or more); more weather station records were used; improved elevation data were used; and more information about spatial patterns of uncertainty in the data is available. Owing to the overall low density of available climate stations, our surfaces do not capture of all variation that may occur at a resolution of 1 km, particularly of precipitation in mountainous areas. In future work, such variation might be captured through knowledge-based methods and inclusion of additional co-variates, particularly layers obtained through remote sensing.
Worldwide decomposition rates depend both on climate and the legacy of plant functional traits as litter quality. To quantify the degree to which functional differentiation among species affects their litter decomposition rates, we brought together leaf trait and litter mass loss data for 818 species from 66 decomposition experiments on six continents. We show that: (i) the magnitude of species-driven differences is much larger than previously thought and greater than climate-driven variation; (ii) the decomposability of a species' litter is consistently correlated with that species' ecological strategy within different ecosystems globally, representing a new connection between whole plant carbon strategy and biogeochemical cycling. This connection between plant strategies and decomposability is crucial for both understanding vegetation-soil feedbacks, and for improving forecasts of the global carbon cycle.
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Premise of the study:
Seedling establishment and early survivorship are crucial steps for the regeneration of plant populations because both have long-lasting effects on plant population dynamics. For species recruiting through facilitation, species-specific facilitative effects might affect early fitness, an overlooked aspect in studies of facilitation considering groups of nurse species. •
Methods:
We experimentally evaluated the roles of 10 nurse species and open space on the early performance of the columnar cactus Neobuxbaumia mezcalaensis. We measured establishment, survivorship, and growth of individuals over 3 years. Moreover, to study an extended period of the ontogeny of the interaction between this cactus and its nurse plants, we also monitored survivorship and growth rates of individuals between 3 to 12 cm tall during a 3-year period. •
Key results:
Neobuxbaumia mezcalaensis performance varied significantly among nurse species, and only six yielded positive effects on early fitness. Densely canopied plants were the best nurses for this cactus. However, even among densely canopied species, some produced negative effects on the early fitness of N. mezcalaensis, indicating that similar nurse plants may elicit either facilitative or interference effects on beneficiary species. •
Conclusions:
Our results emphasize the importance of species-specific facilitative interactions in the crucial early stages in the life cycle of N. mezcalaensis and how different nurse species modify the effect of seed-rain and contribute significantly to the population dynamics of the species.
Assessing the effects of environmental constraints on community structure often relies on methods that consider changes in species functional traits in response to environmental processes. Various indices have been proposed to measure relevant aspects of community trait composition from different viewpoints and perspectives. Among these, the 'community-weighted mean trait value' (CWM) and the Rao coefficient have been widely used in ecological research for summarizing different facets of functional composition and diversity. Analyzing changes in functional diversity of bee communities along a post-fire successional gradient in southern Switzerland we show that these two measures may be used to describe two complementary aspects of community structure, such as the mean and the dispersion of functional traits within a given species assemblage. While CWM can be adequately used to summarize shifts in mean trait values within communities due to environmental selection for certain functional traits, the Rao coefficient can be effectively applied to analyze patterns of trait convergence or divergence compared to a random expectation.
Managing ecosystems to ensure the provision of multiple ecosystem services is a key challenge for applied ecology. Functional traits are receiving increasing attention as the main ecological attributes by which different organisms and biological communities influence ecosystem services through their effects on underlying ecosystem processes. Here we synthesize concepts and empirical evidence on linkages between functional traits and ecosystem services across different trophic levels. Most of the 247 studies reviewed considered plants and soil invertebrates, but quantitative trait–service associations have been documented for a range of organisms and ecosystems, illustrating the wide applicability of the trait approach. Within each trophic level, specific processes are affected by a combination of traits while particular key traits are simultaneously involved in the control of multiple processes. These multiple associations between traits and ecosystem processes can help to identify predictable trait–service clusters that depend on several trophic levels, such as clusters of traits of plants and soil organisms that underlie nutrient cycling, herbivory, and fodder and fibre production. We propose that the assessment of trait–service clusters will represent a crucial step in ecosystem service monitoring and in balancing the delivery of multiple, and sometimes conflicting, services in ecosystem management.
Mediterranean drylands are particularly vulnerable to predicted increases in aridity which are expected to have negative consequences for biodiversity. To understand the effects of climate change on ecosystems, a framework for the selection of indicators based on the essential biodiversity variables (EBV) was proposed. In this framework, a functional approach has been suggested because functional traits have shown to be sensitive to small-scale environmental changes. Additionally, functional traits are also associated with ecosystem-limiting processes. In this context, we used ants as ecological indicators, as they are functionally important and respond in a measurable way to environmental changes. We identify which biodiversity-based indicators (e.g., taxonomic, single-trait and multi-trait indices) help track changes in Mediterranean drylands; for this, we used a space-for-time substitution climatic gradient in the western Mediterranean. Ants were sampled along an aridity gradient and identified to species level. Four continuous and seven categorical traits were measured or retrieved from literature. Continuous traits included Weber’s length, which is indicative for body length, head length, eye length and femur length; categorical traits were diet, behavioral dominance, daily activity, nest preference, mound presence, worker polymorphism and foraging strategy. We calculated taxonomic, functional structure and single- and multi-trait functional diversity indices and correlated them with aridity. We found that ant taxonomic and multi-trait functional diversity were maintained along the aridity gradient. Despite maintenance of species and functional diversity along the gradient, ant functional structure responded to aridity with increases in mean trait values of Weber’s length, eye length and femur length in the drier part of the gradient. Under wetter conditions, we found the highest proportion of ants with a seed-based diet, reflecting a potential increase in resource quantity. We observed a change in foraging strategy from group to individual as aridity increased. In conclusion, with a space-for-time substitution climatic gradient, this study shows the potential role of aridity as an environmental driver of ant trait values. These results highlight the value of ants and functional traits as indicators to track the effects of climate change on ecosystems. Finally, this study represents a starting point to monitor important species traits in the context of EBV and to use them as indicators to track the effects of aridity on Mediterranean dryland ecosystems.
Species abundance data is essential to understand ecosystems structure and functioning and to support species and habitat conservation. However, most regional to global databases provide only presence or presence/ab-sence data. The main aim of this paper is to develop a methodology to estimate plant species abundances from a presence/absence database using as a case-study the largest and one of the most diverse tropical dry forest of the world-the understudied Caatinga vegetation, that dominates in the drylands of Brazil. Plant data missed abundance estimations and derived from different sources, with uneven sampling efforts over space and time. Starting from the raw data, we considered only the presence records of terrestrial plant individuals identified to the species-level. Afterwards, we applied the re-sampling method to estimate species abundances thus obtaining database DB1. To deal with the uneven sampling effort along the study area and increase information reliability, we filtered DB1 in two ways: (i) we excluded re-sampling units with a lower sampling effort and produced the Database DB2; (ii) we excluded low occurrence species and build the Database DB3. The reliability of the databases was compared by calculating a measure of their completeness. DB1 had 789 species over 323 sampling units, DB2 retained 530 species distributed in 38 sampling units, and DB3 retained 48 species over 113 sampling units. In DB1 and DB2, despite the different number of species considered, the percentage of exotic (7%), en-demism (14%), woody (44%), climber (12%), and herbaceous species (45%) was similar. DB3 included only native species (no exotic species) and displayed a higher percentage of endemism (29%) and woody species (79%), and a lower proportion of herbaceous species (21%) than DB1 and DB2. The databases obtained provide an important basis to improve Caatinga ecological knowledge and conservation: we suggest the use of DB2 to support conservation strategies, and of DB3 to support ecosystem structure and functioning studies. Moreover, the re-sampling methodology proposed to estimate plant abundances from presence data, dealing with uneven sampling efforts across large areas and over time, provides an important tool that may be used to obtain abundance data, often essential to the development of plant-based indicators of ecosystem structure and functioning , and to support conservation studies.
Thresholds of aridity
Increasing aridity due to climate change is expected to affect multiple ecosystem structural and functional attributes in global drylands, which cover ∼45% of the terrestrial globe. Berdugo et al. show that increasing aridity promotes thresholds on the structure and functioning of drylands (see the Perspective by Hirota and Oliveira). Their database includes 20 variables summarizing multiple aspects and levels of ecological organization. They found evidence for a series of abrupt ecological events occurring sequentially in three phases, culminating with a shift to low-cover ecosystems that are nutrient- and species-poor at high aridity values. They estimate that more than 20% of land surface will cross at least one of the thresholds by 2100, which can potentially lead to widespread land degradation and desertification worldwide.
Science , this issue p. 787 ; see also p. 739
The spatial and temporal changes in annual and seasonal aridity, the shift of land from one arid class to another and the effect of this shift on different landuses in Iran during 1951–2016 have been assessed in this study. The monthly rainfall data of global precipitation climatology center (GPCC), and the monthly mean temperature and potential evapotranspiration (PET) data of climate research unit (CRU) having a spatial resolution of 0.5° were used for this purpose. The novelty of the study is the assessment of the significance in the shift of arid land between 1951 and 1980 and 1987–2016. Besides, the association of rainfall and temperature with aridity in different arid zones were assessed to understand the driving factors of the shift of arid lands. The results revealed an increase in annual and seasonal aridity in Iran, which caused expansion of arid land. The most remarkable changes include conversion of 4.84% semi-arid land to arid land due to an increase in annual aridity, shift of 4.84% arid land to hyper-arid during summer and 6.45% semi-arid land to arid during winter. However, only the expansion of semi-arid land to dry-subhumid land was found statistically significant. Analysis of results revealed different contributions of rainfall and temperature in the expansion of different classes of arid lands. The decrease in rainfall was the cause of the increasing aridity in the arid and semi-arid region, while the increasing temperature was found to play a major role in increasing aridity in the humid region. The overlapping of landuse map on aridity shift map revealed that the rangelands and farmlands in the north and the northwest were more affected by the expansion of aridity which might have severe consequences on agricultural production and food security of the country.
Biodiversity encompasses multiple attributes such as the richness and abundance of species (taxonomic diversity), the presence of different evolutionary lineages (phylogenetic diversity), and the variety of growth forms and resource use strategies (functional diversity). These biodiversity attributes do not necessarily relate to each other and may have contrasting effects on ecosystem functioning. However, how they simultaneously influence the provision of multiple ecosystem functions related to carbon, nitrogen, and phosphorus cycling (multifunctionality) remains unknown. We evaluated the effects of the taxonomic, phylogenetic, and functional attributes of dominant (mass ratio effects) and subordinate (richness effect) plant species on the multifunctionality of 123 drylands from six continents. Our results highlight the importance of the phylogenetic and functional attributes of subordinate species as key drivers of multifunctionality. In addition to a higher taxonomic richness, we found that simultaneously increasing the richness of early diverging lineages and the functional redundancy between species increased multifunctionality. In contrast, the richness of most recent evolutionary lineages and the functional and phylogenetic attributes of dominant plant species (mass ratio effects) were weakly correlated with multifunctionality. However, they were important drivers of individual nutrient cycles. By identifying which biodiversity attributes contribute the most to multifunctionality, our results can guide restoration efforts aiming to maximize either multifunctionality or particular nutrient cycles, a critical step to combat dryland desertification worldwide.
Drylands are vital ecosystems which cover almost 47% of the Earth's surface, hosting 39% of the global population. Dryland areas are highly sensitive to climatic changes and substantial impacts are foreseen under a warming climate. Many studies have examined the evolution of drylands in the future highlighting the need for improved capability of climate models to simulate aridity. The present study takes advantage of new higher resolution climate projections by the HadGEM3A Atmosphere Global Climate Model using prescribed time varying SSTs and sea ice, provided by a range of CMIP5 climate models under RCP8.5. The aim of the higher resolution models is to examine the benefit of the improved representation of atmospheric processes in the dryland research and to see where these results lie in the range of results from previous studies using the original CMIP5 ensemble. The transient response of aridity from the recent past until the end of the 21st century was examined as well as the expansion of global drylands under specific levels of global warming (1.5 °C, 2 °C and 4 °C). Dryland changes were further assessed at the watershed level for a number of major global river basins to discuss implications on hydrological changes and land degradation. The areal coverage of drylands could increase by an additional 7% of the global land surface by 2100 under high end climate change. At a 4 °C warmer world above pre-industrial, 11.2% of global land area is projected to shift towards drier types and 4.24% to wetter. At the same level of warming the number of humans projected to live in drylands varies between 3.3 and 5.2 billion, depending on the socioeconomic developments. By keeping global warming levels to 1.5 °C, up to 1.9 billion people could avoid living in drylands compared to a 4 °C warmer world of low environmental concern.
Studies to date suggest that most of the native vegetation in the Caatinga has remained relatively intact. In this chapter we have combined information from fire hotspots, roads, and land-use changes to demonstrate that at least 63.3% of the Caatinga is composed of anthropogenic ecosystems. Human impact is higher in the humid and more productive ecoregions (e.g., Brejos and São Francisco-Gurgéia) than in those ecoregions with very dry climates and nutrient-poor soils (e.g., Dunas do São Francisco and Raso da Catarina). The future of the Caatinga’s unique biota is conditional on how societies will protect and restore the native ecosystems. We suggest that an urgent conservation program for the Caatinga should be structured around four quantitative targets: (a) zero species loss; (b) zero natural ecosystem loss; (b) all large and mid-size natural ecosystem patches formally protected; and (c) all protected areas connected through conservation corridors composed of a mix of natural and anthropogenic ecosystems. The second and third actions are the most urgent and need to be implemented as soon as possible. The first and fourth actions are long-term ones that will require building capacity at the local level to design and execute sound conservation development programs.
Aridity acts as a strong environmental filter to plants, limiting major ecosystem processes. Climate change models predict an overall increase of aridity in drylands. This could lead to changes in plant communities, particularly in the dominance and range of plant functional traits, which largely determine ecosystem functioning. However, to study how changes in aridity may affect plant functional metrics, a critical decision needs to be taken: the choice of the functional traits to be studied. Previous studies related plant functional traits and aridity, however mostly focusing on a single facet of functional diversity and primarily on perennial species. Hence, the response of plant traits to aridity quantifying different functional metrics at the whole-community level (considering also annual species) is not well established in drylands.
• Lichens have been used to efficiently track major drivers of global change from the local to regional scale since the beginning of the industrial revolution (sulphur dioxide) to the present (nitrogen deposition and climate change). Currently, the challenge is to universalize monitoring methodologies to compare global change drivers’ simultaneous and independent effects on ecosystems and to assess the efficacy of mitigation measures.
• Because two protocols are now used at a continental scale North America (US) and Europe (EU), it is timely to investigate the compatibility of the interpretation of their outcomes. For the first time, we present an analytical framework to compare the interpretation of data sets coming from these methods utilizing broadly accepted biodiversity metrics, featuring a paired data set from the US Pacific Northwest.
• The methodologies yielded highly similar interpretation trends between response metrics: taxonomic diversity, functional diversity and community composition shifts in response to two major drivers of global change (nitrogen deposition and climate). A framework was designed to incorporate surrogates of species richness (the most commonly used empirical trend in taxonomic diversity), shifts in species composition (compositional turnover) and metrics of functional diversity (link between community shifts to effects and ecosystem structure and functioning). These metrics are essential to more thoroughly comprehend biodiversity response to global change. Its inclusion in this framework enables future cross-continental analysis of lichen biodiversity change from North America and Europe in response to global change. Future works should focus on developing independent metrics for response to global change drivers, namely climate and pollution, taking us one step closer to a lichen-based global ecological indicator.
Despite growing evidence of changes in plant functional traits (FT) along environmental gradients, the way they shape species niches (i.e. how they alternatively influence the limits, width and environmental optimums of species niche) remains only partially understood. Thus, Species Distribution Models were developed and evaluated using distribution data from the Spanish Forest Inventory for 21of the most common Mediterranean woody species, and used to derive different environmental characteristics of species niche, which were then correlated against species-specific values of 14 FT and combinations of relatively orthogonal FT. Species leaf traits, and in particular Specific Leaf Area (SLA), were highly correlated with species niche characteristics regarding aridity (especially with the more arid limit). Hydraulic traits, i.e. the water potential at which a species loses 50% of xylem hydraulic conductivity due to cavitation (PLC50), and species hydraulic safety margins (SM), were better correlated with species aridity niche optimums. Overall, the best model fits, particularly regarding species’ optimum and maximum aridity limit, were obtained when SLA and hydraulic traits (either PLC50 or SM) were used in combination. The study shows how in the Mediterranean region a single trait may be able to explain broad differences in species distributions, but also that the coordination of relatively independent traits achieves a more accurate representation of their environmental limits, particularly at the dry end of the species’ range. The approach used in this study relies on the physiological limits of a species and, to a certain extent, on the mechanisms behind them, adding robustness and accuracy to predict species distribution and mortality under climate change scenarios.
Little is known about the role of plant functional diversity for ecosystem-level carbon (C) fluxes. To fill this knowledge gap, we translocated monoliths hosting communities with four and 16 sown species from a long-term grassland biodiversity experiment (‘The Jena Experiment’) into a controlled environment facility for ecosystem research (Ecotron). This allowed quantifying the effects of plant diversity on ecosystem C fluxes as well as three parameters of C uptake efficiency (water and nitrogen use efficiencies and apparent quantum yield). By combining data on ecosystem C fluxes with vegetation structure and functional trait-based predictors, we found that increasing plant species and functional diversity led to higher gross and net ecosystem C uptake rates. Path analyses and light response curves unravelled the diversity of leaf nitrogen concentration in the canopy as a key functional predictor of C fluxes, either directly or indirectly via LAI and aboveground biomass.
Nineteen woody species growing in the semi-arid region of northeastern Brazil were examined to evaluate the relationship between wood density and their vegetative and reproductive phenophases. Wood density varied between 0.29 g/cm3 and 0.83 g/cm3, and these values were inversely related to the quantity of water stored at saturation. The six species that initiated vegetative and/or reproductive phenophases during the dry season had low wood densities (<0.55 g/cm3) and were able to store large quantities of water (110–271% of the dry weight of the wood). Leaf fall in these species occurred during the transition period between the rainy and the dry season, and it occurred earlier than in species with denser wood. Leaf flush among low wood density species was positively related to the photoperiod. Species with high wood densities, on the other hand, were strongly dependent on rainfall for leaf flush, flowering, and fruiting, as they are able to store only limited quantities of water in their trunks; leaf fall in these species occurred during the dry season. These results point to a strong correlation between wood density and phenology among the species studied.
This study describes the fruiting phenology of woody plants and their dispersal syndromes in caatinga
(semi-arid region in the northeast of Brazil). The fruiting phenology of 42 species with different dispersal modes and
life-forms was followed over a period of 1 y. Animal dispersal was the most commonly observed dispersal mode (36%),
followed by anemochory (33%), ballistic dispersal (19%) and barochory (12%). Overall, a greater number of species
fruited during the rainy season. Zoochorous species were the most representative in the rainy season, whereas
anemochorous species predominated during the dry season. Five different life-forms were observed, and the occurrence of
dispersal modes was discussed for each of them. In the caatinga plant community studied the patterns of life-forms,
fruiting phenology and seed dispersal syndromes were similar to other tropical seasonal ecosystems.
Seed dispersal and establishment are critical stages for plants in arid environments, where vegetation is spatially organized in patches with suitable and unsuitable sites for establishment. Theoretical studies suggest that the ability of vegetation to self-organize in patchy spatial patterns is a critical property for plant survival in arid environments, and is a consequence of a scale-dependent feedback between plants and resource availability. Field observations show that plants of arid environments evolved towards short dispersal distance (proxichory) and that the investment in reproduction increases along an aridity gradient. Here, we investigated how plant dispersal strategies affect spatial organization and associated scale-dependent feedback in arid ecosystems. We addressed this research question using a model where the spatio-temporal vegetation patterns were driven by scale-dependent feedbacks between plants and soil water availability. In the model, water availability limited vegetation growth, seed production and establishment ability. Seed dispersal was modelled with an integrodifferential equation that mimicked important plant dispersal characteristics (i.e. fecundity, mean dispersal distance and establishment ability). Results showed that, when the investment in fecundity was relatively high, short seed dispersal helped maintaining higher mean biomass in the system, improving the vegetation efficiency in water use. However, higher fecundity induced a large cost, and high mean biomass could be sustained only with high establishment ability. Considering low establishment ability, intermediate fecundity was more efficient than low fecundity in maintaining high plant biomass under the most arid conditions. Consistently, plant dispersal strategies that maintained more biomass were related to a vegetation spatial organization that allowed the most efficient soil water redistribution, through the strengthening of the scale-dependent feedback. The efficient dispersal strategies and spatial patterns in the model are commonly observed in plants of arid environments. Thus, dispersal strategies in arid environments might contribute to a favourable spatial organization and associated scale-dependent feedback.
1 In water-limited environments, the availability of water and nutrients to plants depends on environmental conditions, sizes and shapes of their root systems, and root competition. The goal of this study was to predict root system sizes and shapes for different plant growth forms using data on above-ground plant sizes, climate and soil texture. 2 A new data set of > 1300 records of root system sizes for individual plants was collected from the literature for deserts, scrublands, grasslands and savannas with ≤ 1000 mm mean annual precipitation (MAP). Maximum rooting depths, maximum lateral root spreads and their ratios were measured. 3 Root system sizes differed among growth forms and increased with above-ground size: annuals < perennial forbs = grasses < semi-shrubs < shrubs < trees. Stem succulents were as shallowly rooted as annuals but had lateral root spreads similar to shrubs. 4 Absolute rooting depths increased with MAP in all growth forms except shrubs and trees, but were not strongly related to potential evapotranspiration (PET). Except in trees, root systems tended to be shallower and wider in dry and hot climates and deeper and narrower in cold and wet climates. Shrubs were more shallowly rooted under climates with summer than winter precipitation regimes. 5 Relative to above-ground plant sizes, root system sizes decreased with increasing PET for all growth forms, but decreased with increasing MAP only for herbaceous plants. Thus relative rooting depths tended to increase with aridity, although absolute rooting depths decreased with aridity. 6 Using an independent data set of 20 test locations, rooting depths were predicted from MAP using regression models for three broad growth forms. The models suc-ceeded in explaining 62% of the observed variance in median rooting depths. 7 Based on the data analysed here, Walter's two-layer model of soil depth partitioning between woody and herbaceous plants appears to be most appropriate in drier regimes (< 500 mm MAP) and in systems with substantial winter precipitation.
The phenology of 19 species of plants was followed for two years at Serra Talhada, Pernambuco State, Northeastern Brazil. Ten plants of each species were monitored biweekly. All plants had a complete canopy cover from February (well established rainy season) until May‐June (just after rains ceased), and all but a few individuals, belonging to six species, were leafless in October‐November (peak of the dry season). Leaf fall and flush, flowering, and fruiting were almost continuous in the community throughout both the years, but they peaked at different periods. The peak of leaf flush preceded the rainy season, spurred by occasional rains, followed by flowering early in the rainy season, and then fruiting. Leaf fall became more pronounced after the rainy season. The species covered a whole range of deciduousness, from those which retained their leaves throughout both years to those which were leafless during 6–7 months each year. This was mostly due to the capacity of leaf retention after the onset of the dry season. Autochoric and zoochoric species produced fruits mostly during the rainy season and anemochoric species during the dry period. The patterns of flowering and fruiting were complex. One species did not produce flowers or fruits in either year; five produced flowers and fruits in one year only and two others produced flowers in both years but fruits in only one. Most of the other species had high intraspecific synchrony and produced flowers for a shorter period than fruits.
RESUMEN
A fenologia de 19 espécies de plantas foi acompanhada por dois anos, em Serra Talhada, PE. Dez plantas de cada espécie foram observadas a intervalos de duas semanas. Todas as plantas tinham a copa completa de fevereiro (estação chuvosa bem estabelecida) a maio—junho (logo após o término das chuvas) e todas, com exceção de poucos individuos pertencentes a seis especies, estavam sem foihas em outubro–novembro (auge da estação seca). Queda e formação de folhas novas, floração e frutificação foram quase continuas na comunidade, durante 0s dois anos, mas com picos em períodos diferentes. 0 pic0 de formação de folhas precedeu a estação chuvosa, impulsionado por chuvas esporádicas, seguido do de floração, no início da estação de chuvas, e depois pelo de frutificação. Queda de folhas foi mais pronunciada depois do período chuvoso. As espécies cobriram toda ma gama de caducifolia, desde as que mantiveram as folhas durante 0s dois anos ás que ficaram defoliadas durante 6–7 meses cada ano. Isto deveuse, principalmente, ás suas capacidades de reter folhas ao longo da estação sea. Espécies autoóricas e zoocóricas produziram frutos principalmente no período chuvoso e as espécies anemocóricas no período seco. Os padrões de floração e frutificação foram complexos. Uma espécie não produziu flores ou frutos nos dois anos, cinco produziram flores e frutos apenas em um dos anos e duas outras, em urn dos anos, produziram flores que não se desenvolveram em frutos. A maioria das outras espécies teve alta sincronia intra‐específica e produziu flores por urn período mais curto que frutos.
1 It is useful to distinguish between the immediate effects of species richness on ecosystems and those which become apparent on a longer time scale, described here as filter and founder effects.
2 Relationships between plant diversity and ecosystem properties can be explored by classifying component species into three categories – dominants, subordinates and transients. Dominants recur in particular vegetation types, are relatively large, exhibit coarse‐grained foraging for resources and, as individual species, make a substantial contribution to the plant biomass. Subordinates also show high fidelity of association with particular vegetation types but they are smaller in stature, forage on a more restricted scale and tend to occupy microhabitats delimited by the architecture and phenology of their associated dominants. Transients comprise a heterogeneous assortment of species of low abundance and persistence; a high proportion are juveniles of species that occur as dominants or subordinates in neighbouring ecosystems.
3 A ‘mass ratio’ theory proposes that immediate controls are in proportion to inputs to primary production, are determined to an overwhelming extent by the traits and functional diversity of the dominant plants and are relatively insensitive to the richness of subordinates and transients. Recent experiments support the mass ratio hypothesis and the conclusion of Huston (1997) that claims of immediate benefits of high species richness to ecosystem functions arise from misinterpretation of data.
4 Attribution of immediate control to dominants does not exclude subordinates and transients from involvement in the determination of ecosystem function and sustainability. Both are suspected to play a crucial, if intermittent, role by influencing the recruitment of dominants. Some subordinates may act as a filter influencing regeneration by dominants following major perturbations.
5 Transients originate from the seed rain and seed banks and provide an index of the pool of potential dominants and subordinates at specific sites. Where the landscape carousel operates against a background of declining diversity in the reservoir of colonizing transients, we may predict that a progressive loss of ecosystem functions will arise from the decline in the precision with which dominants can engage in the re‐assembly and relocation of ecosystems.
Both theoretical arguments and empirical evidence suggests that herbivory in general and mammalian winter herbivory in particular is important in arctic–alpine ecosystems. Although knowledge of the effect of herbivores on specific plants and communities is quite extensive, little is known about the relative impact of large and small vertebrate herbivores and how it might vary among different habitats. To address this key issue, we established exclosures with two different mesh sizes in forest and nearby tundra at three different sites in four contrasting locations in the forest–tundra ecotone in northernmost Sweden and Norway. Plant community composition was recorded annually in three permanent plots within each exclosure and an unfenced control. Local densities of vertebrate herbivores were estimated in spring and autumn from 1998 to 2002.
1) The concept of plant functional type proposes that species can be grouped according to common responses to the environment and.or common effects on ecosystem processes. However, the knowledge of relationships between traits associated with the response of plants to environmental factors such as resources and disturbances( response traits), and traits that determine effects of plants on ecosystem function(effect traits), such as biogeochemical cycling or propensity to disturbance, remains rudimentary.
2) We present a framework using concepts and results from community ecology, ecosystem ecology and evolutionary biology to provide this linkage. Ecosystem functioning is the end result of the operation of multiple environmental filters in a heirarchy of scales which, by selecting individuals with appropriate responses, result in assemblages with varying trait composition. Functional linkages and trade-offs among traits, each of which relates to one or several processes, determine whether or not filtering by different factors gives a match, and whether ecosystem effects can easily be deduced from knowledge of the filters.
3) To illustrate this framework we analyse a set of key environmental factors and ecosystem processes. While traits associated with response to nutrient gradients strongly overlapped with those determining net primary production, little direct overlap was found between response to fire and flammability
4) We hypothesise that these patterns reflect general trends. Responses to resource availability would be determined by traits that also involved in biogeochemical cycling because both these responses and effects are driven by the trade-off between acquisition and conservation. On the other hand, regeneration and demographic traits associated with with response to disturbance, which are known to have little connection with adult traits involved in plant ecophysiology, would be of little relevance to ecosystem processes.
5) This framework is likely to be broadly applicable, although caution must to exercised to use trait linkages and trade-offs appropriate to the scale, environmental conditions and evolutionary context. It may direct the selection of plant functional types for vegetation models at a range of scales, and help with the design of experimental studies of relationships between plant diversity and ecosystem properties.
We have experimentally tested under natural conditions the cost and inducibility of thorns in Hormathophylla spinosa (Cruciferae), a shrub heavily damaged by ungulates. We first excluded ungulates from 40 shrubs, 20 in each of 2 years(1992 and 1998), to test for a negative phenotypic correlation between thorn density and seed production. Next we removed thorns from 20 protected shrubs to compare seed production in thornless shrubs versus control plants(also excluded from ungulates). Finally, we monitored the change in thorn production for three years in the 1998 ungulate-exclusion experiment to test whether plants growing in a herbivore-free environment would then reduce thorn production. Thorns seem to be phenotypically costly for H.spinosa , since a negative correlation with percent fruit set was found in both years, and thorn removal in the second experiment enhanced seed production. In addition, thorn density significantly decreased from the first to the second and third years in shrubs excluded from ungualtes in the 1998 experiments. These results suggest that throns are an induced defense in H.spinosa.
A new framework for measuring functional diversity (FD) from multiple traits has recently been proposed. This framework was mostly limited to quantitative traits without missing values and to situations in which there are more species than traits, although the authors had suggested a way to extend their framework to other trait types. The main purpose of this note is to further develop this suggestion. We describe a highly flexible distance-based framework to measure different facets of FD in multidimensional trait space from any distance or dissimilarity measure, any number of traits, and from different trait types (i.e., quantitative, semi-quantitative, and qualitative). This new approach allows for missing trait values and the weighting of individual traits. We also present a new multidimensional FD index, called functional dispersion (FDis), which is closely related to Rao's quadratic entropy. FDis is the multivariate analogue of the weighted mean absolute deviation (MAD), in which the weights are species relative abundances. For unweighted presence-absence data, FDis can be used for a formal statistical test of differences in FD. We provide the "FD" R language package to easily implement our distance-based FD framework.