Soil Fertility Gradient Research Articles

Increasing plant species diversity and extreme species turnover accompany declining soil fertility along a long‐term chronosequence in a biodiversity hotspot

Summary Long‐term soil chronosequences provide natural soil fertility gradients that can be used to explore linkages between soils and plant community composition and diversity. Well‐studied forested soil chronosequences have revealed that local (α) plant diversity increases with greater soil age and declining fertility, but corresponding changes in species turnover and beta (β) diversity have not been explored, particularly in extremely species‐rich regions. We quantified changes in plant species diversity and community composition, and identified the edaphic drivers of these changes, along a >2‐million year retrogressive dune chronosequence in the south‐west Australia biodiversity hotspot. We found greater plant species diversity across all growth forms as soil development proceeded and concentrations of soil nutrients, particularly phosphorus (P), diminished to extremely low levels (surface soil total P concentrations of 6 mg P kg−1). Despite the high plant α diversity on older nutrient‐impoverished soils, species turnover across the chronosequence was exceptionally high when all growth forms were considered (mean of 1% of species shared between the youngest and oldest soils), and there was complete turnover of woody species along the chronosequence. Such extreme species turnover across the chronosequence reflected large changes in soil chemical properties. In addition, β diversity within individual chronosequence stages increased with declining soil fertility. Shrubs remained the dominant and most speciose growth form throughout the chronosequence. Synthesis. The large increase in plant α diversity and the extreme species turnover associated with declining soil fertility highlight the central role of soil properties in driving plant community assembly during long‐term ecosystem development, previously only reported from comparatively species‐poor regions. Our finding that plant β diversity increased with declining soil fertility points to a novel mechanism whereby extremely low soil fertility, rather than high productivity, promotes high β diversity. These results suggest that the interaction of an exceptionally diverse plant species pool and nutrient‐impoverished soils provides the basis for the maintenance of such high β diversity at extremely low soil fertility.

Soil fertility gradients shape the agrobiodiversity of Amazonian homegardens

The importance of homegardens for the conservation of agrobiodiversity, the maintenance of farm ecosystem processes, and the economic and food security of rural populations worldwide is increasingly recognized. While biophysical and socio-economic conditions are considered to influence homegarden management, and affect their ecological and societal relevance, little is known about how variation in soil properties affects these agroecosystems. By combining soil data with extensive botanical inventories, we investigated how farmers’ use and management of soil variation results in differences in the structure, diversity and the floristic composition of homegardens in Central Amazonia. We sampled 70 homegardens located along the gradient from low-fertility Ferralsols to Amazonian Dark Earths (ADE), i.e., fertile anthropogenic soils created by pre-Columbian populations at least 500 years ago. Our results show that several characteristics of homegardens are significantly influenced by variation in soil texture and fertility. While differences in soil texture are due to natural soil variation, observed heterogeneity in soil fertility was largely the result of pre-Columbian and modern soil transformations. Homegardens on sandier soils tended to be more diverse in plant species and to have more individual plants; homegardens on more fertile soils tended to have fewer trees and palms, more herbs, shrubs and climbers, and a higher total number of species and landraces; variation in soil fertility was significantly related to differences in the composition of species and landraces. Our results show that farmers’ use of natural and anthropogenic variation in soil properties influences agrobiodiversity patterns in homegardens. Pre-Columbian and modern soil enrichment increases soil heterogeneity in the landscape, resulting in strong soil fertility gradients that shape the agrobiodiversity of current Amazonian homegardens.

Intervenção mecânica e gesso agrícola para mitigar o gradiente vertical de cátions sob sistema de plantio direto

RESUMO O gesso agrícola tem sido apontado como melhorador das características químicas do solo em profundidade porque favorece a movimentação de alguns nutrientes para camadas inferiores do solo. Porém, questiona-se a efetividade dessa prática como ferramenta para uma melhor distribuição de alguns nutrientes no perfil de solos de textura argilosa e em áreas de plantio direto já consolidado. Objetivou-se avaliar o impacto de doses de gesso agrícola e de uma única intervenção mecânica (aração + duas gradagens) efetuada somente na instalação do experimento sobre o gradiente de distribuição de alguns nutrientes no perfil do solo. Doses de 0 t ha-1, 2 t ha-1, 4 t ha-1 e 6 t ha-1 de gesso agrícola foram aplicadas a lanço, nos estádios iniciais de desenvolvimento da aveia branca. Foram efetuados quatro cultivos da sucessão soja/milho e aveia como planta de cobertura de inverno. O manejo de solo com uma única operação de aração e gradagem, em áreas há vários anos sob sistema de plantio direto, não minimiza o gradiente de fertilidade do solo. Para esse solo com teor de argila acima de 70 %, o gesso foi pouco eficiente em promover a mobilidade vertical de cátions aos 36 meses após sua aplicação, sendo os efeitos limitados aos primeiros 0,10 m de profundidade, diferentemente do observado para o ânion S-SO42-.

Regional growth decline of sugar maple (Acer saccharum) and its potential causes

Sugar maple (Acer saccharum Marsh) has experienced poor vigor, regeneration failure, and elevated mortality across much of its range, but there has been relatively little attention to its growth rates. Based on a well‐replicated dendrochronological network of range‐centered populations in the Adirondack Mountains (USA), which encompassed a wide gradient of soil fertility, we observed that the majority of sugar maple trees exhibited negative growth trends in the last several decades, regardless of age, diameter, or soil fertility. Such growth patterns were unexpected, given recent warming and increased moisture availability, as well as reduced acidic deposition, which should have favored growth. Mean basal area increment was greater on base‐rich soils, but these stands also experienced sharp reductions in growth. Growth sensitivity of sugar maple to temperature and precipitation was non‐stationary during the last century, with overall weaker relationships than expected. Given the favorable competitive status and age structure of the Adirondack sugar maple populations sampled, evidence of widespread growth reductions raises concern over this ecologically and economically important tree. Further study will be needed to establish whether growth declines of sugar maple are occurring more widely across its range.

Reproductive response to nitrogen and phosphorus fertilization along the Hawaiian archipelago's natural soil fertility gradient.

Nitrogen (N) and phosphorus (P) are the most important nutrients involved in plant reproduction and typically the most limiting in terrestrial ecosystems. The natural soil fertility gradient of the Hawaiian archipelago, in which younger islands are N limited and older islands are P limited, provides a model system to examine questions regarding allocation of nutrients. Using fertilized plots (+N or +P) at the extreme sites of the Hawaiian archipelago, vegetative productivity (e.g., net primary productivity, growth, and litterfall) and foliar nutrient responses have previously been studied for the dominant canopy tree, Metrosideros polymorpha. Here, we investigated whether the reproductive response of M. polymorpha mirrors the previously found vegetative productivity and foliar nutrient responses, by quantifying: (1) inflorescence and seed productivity, and (2) nutrient concentration of reproductive structures. Fertilization with N and P did not significantly affect the productivity of inflorescences or seeds, or seed viability at either site. However, nutrient concentrations increased after fertilization; %P increased in inflorescences in the +P treatment at the P-limited site. Seeds and inflorescences generally contained higher nutrient concentrations than leaves at both sites. Unlike foliar data, reproductive strategies of M. polymorpha differed depending on soil nutrient limitation with emphasis on quality (higher seed viability/greater nutrient concentrations) at the P-limited site. We suggest that in response to P additions M. polymorpha employs a nutrient conservation strategy for its inflorescences and an investment strategy for its seeds. Examining N and P simultaneously challenges a basic assumption that reproductive allocation follows a similar pattern to the often measured aboveground productivity.

Fire regime, soil fertility and growth form interact to shape fire and growth traits in two co-occurring Banksia species

Inter- and intra-specific comparisons were made between several co-occurring populations of two Banksia species growing in Eastern Australian dry sclerophyll open woodland that experiences a grass-fueled surface-fire regime. The two species differ in life-history from a short basal resprouter (B. Neoanglica) to a tall fire-survivor (B. integrifolia). Growth (LMA = leaf mass per unit mass area), persistence (bark thickness) and recruitment (serotiny) traits were determined across independent gradients in soil fertility and fire frequency. Trait correlations for the two species showed distinct patterns, from each other and across environments, with the resprouter having higher LMA and infructescence retention but lower bark thickness. However, there were no consistent intra-specific patterns with variation in fire and soil nutrients. LMA only varied in B. integrifolia with soil fertility, and fire frequency had no effect on either species. Relative bark thickness varied with plant size but not among sites. There was a trend of increasing pyriscence with fire in B. neoanglica and with lower nutrients soils but not in B. integrifolia. Clearly the two species respond differently to variability in nutrients and fire. Nevertheless, growth form appears to be the strongest determinant of both growth (LMA) and fire traits (thicker bark; pyriscence) in these co-existing Banksia species.

Application of the Bait-Lamina Method to Measure the Feeding Activity of Soil Fauna in Temperate Forests

The aim of the study was to compare the feeding activity of soil fauna in seven temperate forests with the application of the bait-lamina method. Seven types of temperate forests located throughout Poland (East-Central Europe) were tested, ranging from dry pine forest with a typical poor quality soil to eutrophic riparian fresh deciduous forest. Each forest type was represented by five stands and all stands altogether represented natural gradient of soil fertility, texture and vegetation diversity. Despite clear diversification between the studied forest types according to a range of soil physicochemical properties and vegetation characteristics in addition to applying recommended measurement conditions for the method, we determined that the feeding activity of soil fauna did not differ between forest types. The activity of soil fauna did not depend on site botanical characteristics or any soil physical or chemical features, indicating that the bait lamina method was useless in measuring the feeding activity of soil fauna in temperate forest soils. Differences in the feeding activity of soil fauna might result from other environmental factors that influence soil fauna feeding activity in forest stands that were not measured here, i.e., soil temperature and humidity. The differences could also be attributable to the attractiveness of the bait substrate to soil fauna, which may be different in various soil conditions.

Morphological and physiological traits of aquatic macrophytes respond to water chemistry in the Amazon Basin: an example of the genus Montrichardia Crueg (Araceae)

Species composition and occurrence of aquatic macrophytes in the Amazon Basin are associated with the hydrology and geomorphology of the catchment area. Nonetheless, the distribution of the Neotropical genus Montrichardia in the Amazon floodplains remains unclear. Three taxa of the genus were described: Montrichardia linifera (Arr.) Schott (ML), associated with nutrient-rich rivers; Montrichardia arborescens (L.) Schott (MA) and M. arborescens var. aculeata (G. Mey.) Engl., growing in nutrient-poor rivers. We hypothesize that different taxa can be discriminated according to variation in density, morphology, physiology, and biomass along environmental gradients of water characteristics and soil fertility. Samples of 55 populations of Montrichardia were taken in rivers with contrasting water types in the Amazon Basin along a gradient of declining soil fertility from Western to Eastern Amazonia spanning about 2,500 km. Local phenotypic variations and discriminant analysis separated ML and MA with MA as subset of MA. Water chemistry influenced the distribution of taxa. The nutritional soil gradient at the basin level clearly explained the distribution of ML, but not that of MA. The distribution pattern of ML was similar to that of tree species in the Amazon Basin, with higher density in West Amazon.

Phylogenetic structure of arbuscular mycorrhizal community shifts in response to increasing soil fertility

Understanding the underlying mechanisms driving responses of belowground communities to increasing soil fertility will facilitate predictions of ecosystem responses to anthropogenic eutrophication of terrestrial systems. We studied the impact of fertilization of an alpine meadow on arbuscular mycorrhizal (AM) fungi, a group of root-associated microorganisms that are important in maintaining sustainable ecosystems. Species and phylogenetic composition of AM fungal communities in soils were compared across a soil fertility gradient generated by 8 years of combined nitrogen and phosphorus fertilization. Phylogenetic patterns were used to infer the ecological processes structuring the fungal communities. We identified 37 AM fungal virtual taxa, mostly in the genus Glomus. High fertilizer treatments caused a dramatic loss of Glomus species, but a significant increase in genus richness and a shift towards dominance of the lineage of Diversispora. AM fungal communities were phylogenetically clustered in unfertilized soil, random in the low fertilizer treatment and over-dispersed in the high fertilizer treatments, suggesting that the primary ecological process structuring communities shifted from environmental filtering (selection by host plants and fungal niches) to a stochastic process and finally to competitive exclusion across the fertilization gradient. Our findings elucidate the community shifts associated with increased soil fertility, and suggest that high fertilizer inputs may change the dominant ecological processes responsible for the assembly of AM fungal communities towards increased competition as photosynthate from host plants becomes an increasingly limited resource.

Litterfall as a niche construction process in a northern hardwood forest

Northern hardwood forests can exhibit considerable temporal stability in their species composition, which litterfall may help to maintain by modifying the soil environment to create an ecological inheritance. We evaluated the evidence for this niche‐construction perspective by carrying out a spatially explicit analysis of redistribution of calcium (Ca), magnesium (Mg), and potassium (K) via leaf litterfall of the six dominant tree species in a temperate forest in northwest Connecticut, USA. We combined stem maps with litterfall measurements to fit models of leaf litterfall for individual species, and we chemically analyzed leaves, surface soil extractions, and unweathered soil particles.Analysis of elemental oxides in unweathered soil particles suggested that species did not differ in ability to gain access to rock‐bound nutrients. Nevertheless, species had a significant effect on quantity of Ca cycled in litter—the two calcicoles (species with affinity for calcium‐rich soils) occurred most commonly on the richest soils, and the Ca concentration in their senescent leaves increased sharply across the soil fertility gradient. No species effects on Mg or K redistribution were seen. Litter dispersal distances cut across calcium affinities: e.g., of the four calcifuges (plants with affinity for acidic soils) two had distant litter dispersal (modal dispersal distance ≥ 4 m) and two had close litter dispersal (modal dispersal distance < 0.3 m). Dispersal distance was associated with leaf size: the three species with the smallest leaves had the most concentrated litterfall shadows. One of these, eastern hemlock, has a recognized ability to exclude other species in part by creating an acidic low‐nutrient soil environment. Overall, the ability of trees to generate soil conditions that were aligned with their own resource use was expressed most clearly in the calcium content of their leaves. We concluded that tree‐environment interactions at the site displayed several of the criteria for niche construction.

Integrated soil fertility management in sub-Saharan Africa: unravelling local adaptation

Abstract. Intensification of smallholder agriculture in sub-Saharan Africa is necessary to address rural poverty and natural resource degradation. Integrated soil fertility management (ISFM) is a means to enhance crop productivity while maximizing the agronomic efficiency (AE) of applied inputs, and can thus contribute to sustainable intensification. ISFM consists of a set of best practices, preferably used in combination, including the use of appropriate germplasm, the appropriate use of fertilizer and of organic resources, and good agronomic practices. The large variability in soil fertility conditions within smallholder farms is also recognized within ISFM, including soils with constraints beyond those addressed by fertilizer and organic inputs. The variable biophysical environments that characterize smallholder farming systems have profound effects on crop productivity and AE, and targeted application of agro-inputs and management practices is necessary to enhance AE. Further, management decisions depend on the farmer's resource endowments and production objectives. In this paper we discuss the "local adaptation" component of ISFM and how this can be conceptualized within an ISFM framework, backstopped by analysis of AE at plot and farm level. At plot level, a set of four constraints to maximum AE is discussed in relation to "local adaptation": soil acidity, secondary nutrient and micronutrient (SMN) deficiencies, physical constraints, and drought stress. In each of these cases, examples are presented whereby amendments and/or practices addressing these have a significantly positive impact on fertilizer AE, including mechanistic principles underlying these effects. While the impact of such amendments and/or practices is easily understood for some practices (e.g. the application of SMNs where these are limiting), for others, more complex processes influence AE (e.g. water harvesting under varying rainfall conditions). At farm scale, adjusting fertilizer applications to within-farm soil fertility gradients has the potential to increase AE compared with blanket recommendations, in particular where fertility gradients are strong. In the final section, "local adaption" is discussed in relation to scale issues and decision support tools are evaluated as a means to create a better understanding of complexity at farm level and to communicate appropriate scenarios for allocating agro-inputs and management practices within heterogeneous farming environments.

Lack of host specificity leads to independent assortment of dipterocarps and ectomycorrhizal fungi across a soil fertility gradient

Plants interact with a diversity of microorganisms, and there is often concordance in their community structures. Because most community-level studies are observational, it is unclear if such concordance arises because of host specificity, in which microorganisms or plants limit each other's occurrence. Using a reciprocal transplant experiment, we tested the hypothesis that host specificity between trees and ectomycorrhizal fungi determines patterns of tree and fungal soil specialisation. Seedlings of 13 dipterocarp species with contrasting soil specialisationswereseeded into plots crossing soil type and canopy openness. Ectomycorrhizalcolonists were identified by DNA sequencing. After 2.5years, we found no evidence of host specificity. Rather, soil environment was the primary determinant of ectomycorrhizal diversity and composition on seedlings. Despite their close symbiosis, our results show that ectomycorrhizal fungi and tree communities in this Bornean rain forest assembleindependently of host-specific interactions, raising questions about howmutualism shapes the realised niche.

American beech and sugar maple sapling relative abundance and growth are not modified by light availability following partial and total canopy disturbances

Studies have reported divergent results on the effect of soil fertility and canopy opening on understory density and growth of sugar maple (AS; Acer saccharum Marsh.) and American beech (FG; Fagus grandifolia Ehrh.). The main objective of this study was to evaluate the effect of a gradient of canopy opening and soil fertility on the density and growth of AS and FG saplings in southwestern Quebec, Canada. We investigated 56 stands containing both AS and FG that were subjected to different disturbance history types (DHTs) (UF, unmanaged forest; PC, partial cut; and CC, clearcut) on various soil types. AS and FG absolute and relative sapling density varied greatly among the 56 stands; however, no significant effects of DHT, soil nutrient availability, or their interaction were found. Both species responded positively in terms of radial growth to canopy openings, with FG growth being slightly better than AS growth in PC stands compared with other canopy treatments. Contrary to our hypothesis, AS did not show significantly higher growth than FG following clear-cutting. These results do not support the idea that AS abundance and growth could be promoted by increasing the intensity of the canopy opening during harvest, at least on the generally acidic and base-poor soils that were investigated.

Isolating the effects of precipitation, soil conditions, and litter quality on leaf litter decomposition in lowland tropical forests

Global change drivers such as climate change influence decomposition by altering extrinsic site conditions and intrinsic litter traits. This study aimed to quantify the relative importance of these two pathways for litter decomposition in tropical forests. The effects of soil nutrient availability, mean annual precipitation (MAP), and leaf litter chemistry on decomposition were isolated by measuring mass loss of leaf litter from 10 tropical tree species transplanted to 19 sites along independent gradients of soil fertility and precipitation in Panama. Across species, litter nitrogen (N) content ranged from 7.1 to 13 mg N g−1 and phosphorus (P) from 0.077 to 0.56 mg P g−1. Across sites, soil N content ranged from 1.7 to 5.5 g N kg−1, soil P from 77 to 1500 mg P kg−1, and MAP from 1900 to 2700 mm. Variation in leaf litter mass loss was explained largely by litter species identity (55 %). Site only explained a small, but significant, amount of variance (6.5 %); soil C:N ratio explained this response. Notably, neither litter nutrient content nor MAP were significant predictors of litter decomposition. Changes in tree species composition may influence decomposition rates more than changes to site conditions.

Biotic homogenisation and differentiation along a habitat gradient resulting from the ageing of managed beech stands

Understanding the processes driving biodiversity changes in forest communities helps to better evaluate sustainable forest management methods and their effects on forest ecosystems. This, in turn, is crucial for the appropriate management of protected areas, in particular those covered under the European protection program Natura 2000. Two datasets from the Polish Eastern Carpathians collected in the 1970s and 2000s were compared to analyse the temporal and spatial changes in the species composition of beech forests in a habitat gradient of soil moisture, acidity and fertility. We found that species favouring fertile and alkaline soils, with low ability for vegetative propagation and without a persistent seed bank became less frequent, whilst frequency of good competitors tolerant to lower soil pH and fertility with a persistent seed bank and a capacity for dispersing seeds over long distances increased. Herb layer vegetation on poor and rich soils became less similar in the past 30years, though two opposite processes occurred. In poor habitats, the biotic differentiation of herb layer vegetation prevailed, whilst biotic homogenisation was more important in fertile habitats. It is suggested that the ageing of the managed beech stands might have contributed to these changes through the accumulation of litter, top soil acidification and the lowering of the concentration of nutrients as well as due to altered disturbance regimes in older stands. The observed relationships between biotic homogenisation/differentiation and the habitat gradient indicate that differences in soil conditions not only shape the spatial pattern of the forest vegetation, but also the spatial and temporal patterns of changes in vegetation composition resulting from the ageing of tree stands. Our results also suggest that in spite of continuous management the studied beech forests have only slightly changed in their specific species composition. Moreover, the ageing of tree stands did not necessarily generate better conditions for the conservation of the species richness of herbaceous plants, at least those species that are considered a measure of naturalness in beech forests.

Changes in fungal communities along a boreal forest soil fertility gradient.

Boreal forests harbour diverse fungal communities with decisive roles in decomposition and plant nutrition. Although changes in boreal plant communities along gradients in soil acidity and nitrogen (N) availability are well described, less is known about how fungal taxonomic and functional groups respond to soil fertility factors. We analysed fungal communities in humus and litter from 25 Swedish old-growth forests, ranging from N-rich Picea abies stands to acidic and N-poor Pinus sylvestris stands. 454-pyrosequencing of ITS2 amplicons was used to analyse community composition, and biomass was estimated by ergosterol analysis. Fungal community composition was significantly related to soil fertility at the levels of species, genera/orders and functional groups. Ascomycetes dominated in less fertile forests, whereas basidiomycetes increased in abundance in more fertile forests, both in litter and humus. The relative abundance of mycorrhizal fungi in the humus layer remained high even in the most fertile soils. Tolerance to acidity and nitrogen deficiency seems to be of greater importance than plant carbon (C) allocation patterns in determining responses of fungal communities to soil fertility, in old-growth boreal forests.

Variation in Canopy Litterfall Along a Precipitation and Soil Fertility Gradient in a Panamanian Lower Montane Forest

AbstractFertilization experiments in tropical forests have shown that litterfall increases in response to the addition of one or more soil nutrients. However, the relationship between soil nutrient availability and litterfall is poorly defined along natural soil fertility gradients, especially in tropical montane forests. Here, we measured litterfall for two years in five lower montane 1‐ha plots spanning a soil fertility and precipitation gradient in lower montane forest at Fortuna, Panama. Litterfall was also measured in a concurrent nitrogen fertilization experiment at one site. Repeated‐measures ANOVA was used to test for site (or treatment), year, and season effects on vegetative, reproductive and total litterfall. We predicted that total litterfall, and the ratio of reproductive to leaf litterfall, would increase with nutrient availability along the fertility gradient, and in response to nitrogen addition. We found that total annual litterfall varied substantially among 1‐ha plots (4.78 Mg/ha/yr to 7.96 Mg/ha/yr), and all but the most aseasonal plot showed significant seasonality in litterfall. However, litterfall accumulation did not track soil nutrient availability; instead forest growing on relatively infertile soil, but dominated by an ectomycorrhizal tree species, had the highest total litterfall accumulation. In the fertilization plots, significantly more total litter fell in nitrogen addition relative to control plots, but this increase in response to nitrogen (13%) was small compared to variation observed among 1‐ha plots. These results suggest that while litterfall at Fortuna is nutrient‐limited, compositional and functional turnover along the fertility gradient obscure any direct relationship between soil resource availability and canopy productivity.

Phylogenetic relatedness within Neotropical fern communities increases with soil fertility

AbstractAimTo examine the relative importance of gradients in soil fertility and rainfall for the phylogenetic structure of Neotropical forest fern communities, and to quantify how much the results are affected by phylogenetic resolution.LocationTropical lowland forests in Brazil (central Amazonia) and Panama (the Panama canal watershed).MethodsWe inventoried local fern communities at a total of 87 sites to model how their species richness and phylogenetic relatedness varied along gradients in soil fertility and rainfall. We produced a time‐calibrated species‐level molecular phylogeny of ferns, and quantified the phylogenetic relatedness of species within local communities using Faith's phylogenetic diversity (PD) and mean phylogenetic diversity (MPD). Calculations were compared for phylogenies resolved to the species and genus levels.Results(1) We found significant and consistent effects of soil nutrient status on local phylogenetic community structure in both regions. In contrast, phylogenetic structure showed only a weak or no relationship with rainfall. (2) In both regions, MPD declined with increasing soil fertility, which means that fern communities on poor soils consisted, on average, of less closely related lineages than fern communities on rich soils. (3) Different fern genera were over‐represented in different sections of the soil nutrient gradient. (4) Qualitatively similar results were obtained whether phylogenies were resolved to the species or the genus level.Main conclusionsOur results highlight the importance of edaphic variation in structuring plant communities over evolutionary time‐scales. Within the tropical forests studied, the effects of soil variation on local phylogenetic community structure seem to outweigh those of climate. Several fern genera show strong edaphic niche conservatism to either poor or rich soils, whereas many other genera have radiated to span a rather broad edaphic range. PD‐based measures are so dominated by deep relationships that genus‐level phylogenies are sufficient to investigate these patterns in tropical fern communities.

Resilience Assessment of Lowland Plantations Using an Ecosystem Modeling Approach

As afforestation programs of former farmlands take hold in Taiwan to achieve a variety of ecological and socio-economic values, it is becoming necessary to define best forest management. Hence, we simulated mixed stands of Cinnamomum camphora and Fraxinus griffithii planted through a gradient of soil fertility and varying camphor/ash density ratios, but maintaining a fixed total stand density of 1500 trees ha−1. Total stand productivity was slightly lower in mixed stands than the combination of both monocultures in rich and poor sites. Maximum negative yield surpluses for 50-year old stands were 7 Mg ha−1 and 6 Mg ha−1 for rich and poor sites with a 1:1 camphor laurel/ash ratios. Maximum stand woody biomass in rich sites was reached in camphor laurel monocultures (120 Mg ha−1) and in poor sites for Himalayan ash monocultures (58 Mg ha−1). However, for medium-quality sites, a small yield surplus (11 Mg ha−1) was estimated coinciding with a maximum stand woody biomass of 95 Mg ha−1 for a 1:1 camphor laurel/ash density ratio. From an ecological resilience point of view, rotation length was more important than stand composition. Long rotations (100 years) could improve soil conditions in poor sites. In rich sites, short rotations (50 years) should be avoided to reduce risks or fertility loss.

The linkages between photosynthesis, productivity, growth and biomass in lowland Amazonian forests

Understanding the relationship between photosynthesis, net primary productivity and growth in forest ecosystems is key to understanding how these ecosystems will respond to global anthropogenic change, yet the linkages among these components are rarely explored in detail. We provide the first comprehensive description of the productivity, respiration and carbon allocation of contrasting lowland Amazonian forests spanning gradients in seasonal water deficit and soil fertility. Using the largest data set assembled to date, ten sites in three countries all studied with a standardized methodology, we find that (i) gross primary productivity (GPP) has a simple relationship with seasonal water deficit, but that (ii) site-to-site variations in GPP have little power in explaining site-to-site spatial variations in net primary productivity (NPP) or growth because of concomitant changes in carbon use efficiency (CUE), and conversely, the woody growth rate of a tropical forest is a very poor proxy for its productivity. Moreover, (iii) spatial patterns of biomass are much more driven by patterns of residence times (i.e. tree mortality rates) than by spatial variation in productivity or tree growth. Current theory and models of tropical forest carbon cycling under projected scenarios of global atmospheric change can benefit from advancing beyond a focus on GPP. By improving our understanding of poorly understood processes such as CUE, NPP allocation and biomass turnover times, we can provide more complete and mechanistic approaches to linking climate and tropical forest carbon cycling.