Brenton Ladd

Priority effects produced by plant litter result in non-additive competitive effects

Litter may indirectly affect competitive interactions. It is not clear whether these changes are additive or non-additive indirect effects. Non-additivity could result from: (1) changes in biomass allocation patterns by competitors towards organs not directly involved in resource acquisition (e.g., longer hypocotyls); (2) changes in the proportion of different functional groups (e.g., grasses and forbs) that possess different competitive abilities; or (3) through priority effects caused by subtle changes in timing of emergence. We used a combination of field and glasshouse experiments in which Eucalyptus obliqua seedlings were grown either with or without leaf litter (grass litter/eucalypt litter), and with or without competitors. Eucalypt species growing in the field and in pots attained more biomass with litter than without when competitors were absent. Competition substantially decreased the biomass of eucalypt seedlings. Competitive intensity was heavily influenced by litter type and was most intense in the presence of grass litter. Litter produced a small change in patterns of biomass allocation in the competing herbaceous vegetation, and there was a slight (marginally non-significant) indication of a change in the proportion of grasses relative to forbs when litter was present. However, when the integral of competitor biomass over time was used to calculate competitive intensity, the combined effects of the experimental factors (litter and competition) became additive, suggesting that the effect of leaf litter on the timing of germination and establishment in the grasses and forbs, relative to that of Eucalyptus seedlings, was the principal mechanism by which leaf litter altered the interaction strength of the species studied.

The adaptive value of functional and life-history traits across fertility treatments in an annual plant

BACKGROUND AND AIMS Plant functional traits are assumed to be adaptive. As selection acts on individuals and not on traits, interpreting the adaptive value of a trait not may be straightforward. For example, productive leaves are associated with fertile environments. However, it is not clear if productive leaves confer an advantage in these habitats, or if they are an advantage as part of a suite of coordinated traits. METHODS Genotypes of Arabidopsis thaliana were grown in high and low nutrient treatments and low, neutral and high pH treatments. Nutrient availability is reduced in acidic or basic soils relative to neutral pH soils. pH treatments were used to alter the availability of resources rather than the amount of resources. KEY RESULTS Leaf function (specific leaf area, SLA) and life history (size at reproduction, age at reproduction) were variable across genotypes and were plastic. High nutrient availability induced higher SLA and larger size at reproduction. Genotypes that reproduced at large size in high nutrient conditions at neutral pH had the greatest fruit production. SLA was only indirectly related to fruit production through a causal relationship with rosette size; in high nutrient conditions, plants with high SLA were large at reproduction and had higher fruit production. In high nutrient and high pH treatments, plants were large at reproduction, but large size at reproduction was associated with low fecundity. This suggests that large size is adaptive under high nutrient availability. CONCLUSIONS Interpreting the adaptive value of functional traits will sometimes only be possible when these traits are considered as a suite of correlated and coordinated traits. Leaf functional traits may be important in defining adaptive strategies in A. thaliana but only through how they affect plant life history. Finally, manipulating soil pH can be a valuable tool in assessing adaptive plasticity on nutrient gradients.

Carbon isotopic signatures of soil organic matter correlate with leaf area index across woody biomes

Leaf area index (LAI), a measure of canopy density, is a key variable for modelling and understanding primary productivity, and also water use and energy exchange in forest ecosystems. However, LAI varies considerably with phenology and disturbance patterns, so alternative approaches to quantifying stand-level processes should be considered. The carbon isotope composition of soil organic matter (C-13(SOM)) provides a time-integrated, productivity-weighted measure of physiological and stand-level processes, reflecting biomass deposition from seasonal to decadal time scales. Our primary aim was to explore how well LAI correlates with C-13(SOM) across biomes. Using a global data set spanning large environmental gradients in tropical, temperate and boreal forest and woodland, we assess the strength of the correlation between LAI and C-13(SOM); we also assess climatic variables derived from the WorldClim database. We found that LAI was strongly correlated with C-13(SOM), but was also correlated with Mean Temperature of the Wettest Quarter, Mean Precipitation of Warmest Quarter and Annual Solar Radiation across and within biomes.Synthesis. Our results demonstrate that C-13(SOM) values can provide spatially explicit estimates of leaf area index (LAI) and could therefore serve as a surrogate for productivity and water use. While C-13(SOM) has traditionally been used to reconstruct the relative abundance of C-3 versus C-4 species, the results of this study demonstrate that within stable C-3- or C-4-dominated biomes, C-13(SOM) can provide additional insights. The fact that LAI is strongly correlated to C-13(SOM) may allow for a more nuanced interpretation of ecosystem properties of palaeoecosystems based on palaeosol C-13 values.

The evolution of competitive strategies in annual plants

Annual plants are common in disturbed habitats. It is frequently assumed that because these habitats often have low-plant density, competition is not important in shaping the ecological strategies of annual plants. We test for competitive strategies in genotypes of the short-lived annual plant Arabidopsis thaliana. Genotypes were grown in treatments with or without conspecific competitors. We measured size at reproduction and fitness (fruit production) at final development. We estimated competitive ability in each genotype at first reproduction (the ability to maintain size in the presence of competitors) and at final development (the ability to maintain fruit production in the presence of competitors). Genotypes showed relatively high competitive ability measured as fruit production at final development, but most genotypes had low competitive ability measured as size at reproduction. Our results suggest that competition has been important in the evolution of strategies in these genotypes but vegetative size is not a strong predictor of competitive ability. Rather, competitive ability is determined by the capacity to reproduce efficiently in the presence of competitors. The competitive strategies expressed across these genotypes suggest that competition has been a selective force in these plants, and that a fast life history is not equivalent to an “r-strategy.”

Optimal allocation of resources in response to shading and neighbours in the heteroblastic species, Acacia implexa

BACKGROUND AND AIMS Heteroblasty is an encompassing term referring to ontogenetic changes in the plant shoot. A shaded environment is known to affect the process of heteroblastic development; however, it is not known whether crowded or high density growing conditions can also alter heteroblasty. Compound leaves of the shade-intolerant Acacia implexa allocate less biomass per unit photosynthetic area than transitional leaves or phyllodes and it is hypothesized that this trait will convey an advantage in a crowded environment. Compound leaves also have larger photosynthetic capture area - a trait known to be advantageous in shade. This studied tested the hypothesis that more compound leaves will be developed under shade and crowded environments. Furthermore, this species should undergo optimal allocation of biomass to shoots and roots given shaded and crowded environments. METHODS A full factorial design of irradiance (high and low) and density levels (high, medium and low) on three populations sourced from varying rainfall regions (high, medium and low) was established under controlled glasshouse conditions. Traits measured include the number of nodes expressing a compound leaf, biomass allocation to shoots and roots, and growth traits. Key Results A higher number of nodes expressed a compound leaf under low irradiance and in high density treatments; however, there were no significant interactions across treatments. Phenotypes strongly associated with the shade avoidance syndrome were developed under low irradiance; however, this was not observed under high density. There was no significant difference in relative growth rates across light treatments, but growth was significantly slower in a crowded environment. Conclusions Heteroblastic development in Acacia can be altered by shade and crowded environments. In this experiment, light was clearly the most limiting factor to growth in a shaded environment; however, in a crowded environment there were additional limiting resources to growth.

How are soil carbon and tropical biodiversity related

This article discusses how biological conservation can benefit from an understanding of soil carbon. Protecting natural areas not only safeguards the biota but also curtails atmospheric carbon emissions. Opportunities for funding biological conservation could potentially be greater if soil carbon content is considered. In this article current knowledge concerning the magnitude and vulnerability of soil carbon stocks is reviewed and the relationship of these stocks to biological conservation values is explored. Looking at two relatively well-studied tropical regions we find that 15 of 21 animal species of conservation concern in the Virunga Landscape (Central Africa), and nine of ten such species in the Federal District of Brazil (Central Brazil), rely on carbon-rich habitats (alluvial and/or wetlands). At national scales, densities of species, endemics and threatened taxa (plants, mammals, birds, reptiles, amphibians and fish) show positive and significant relations with mean soil carbon content in all but two cases (threatened amphibians and threatened fish). Of more than 1000 threatened species in 37 selected tropical nations, 85% rely on carbon-rich habitats. This tendency is observed in plants, mammals, reptiles, amphibians and crustaceans, while birds appear more evenly distributed. Research to clarify and explore these relationships is needed. Soil carbon offers major opportunities for conservation.

Competition intensity at local versus regional spatial scales

Studies of competition intensity over natural (i.e. topographic) gradients often contradict the results from studies where artificial (i.e. fertilizer) gradients have been used. Why should the type of gradient matter? To explore the possibilities, we performed experiments to measure competition intensity experienced by tree seedlings from grass competitors across a natural resource gradient, and simultaneously across artificial soil nutrient (fertiliser) gradients. We measured various functional traits (i.e. specific leaf area, leaf area, leaf nitrogen content, delta(15)N, delta(13)C, RGR) to gain mechanistic insight into the nature of competition across these gradients. Competition intensity increased with increasing resource availability, unequivocally at the local scale (i.e. with fertilizer application) but not at the regional scale (i.e. across the natural productivity gradient). Our measurements of plant traits were generally consistent with measurements of competition intensity, and demonstrate that competition occurs even when resource levels are low. Competition mainly acted to reduce the growth of Eucalyptus seedlings. Functional (physiological) traits in the Eucalyptus seedlings were not strongly affected by competitors, with the possible exception of delta(15)N, which may effectively integrate information on soil nutrient, moisture and leaf processes.

Carbon accrual rates, vegetation and nutrient dynamics in a regularly burned coppice woodland in Germany

Historically, large areas of forest in Europe were managed as coppice woodland to produce wood‐based fuel for the smelting industry. We hypothesized that this practice produced a legacy effect on current forest ecosystem properties. Specifically, we hypothesized that the historical form of coppicing may have produced a legacy of elevated stocks of soil organic carbon (SOC), nutrients and black carbon (BC) in soil as fire was routinely used in coppiced woodland to clear land. We further hypothesized that these changes in soil properties would result in increased biodiversity. To test these hypotheses, we sampled the surface soil (0–5, 5–10 and 10–20 cm) from a chronosequence of forest sites found in the Siegerland (Germany) that had been coppiced and burned 1, 2, 3.5, 6, 8, 11 and 17 years before present. Mature beech and spruce forests (i.e., >60 years) were also sampled as reference sites: to provide a hint of what might occur in the absence of human intervention. We measured stocks of SOC, BC, NO3‐N, P, K, Mg, as well as cation exchange and water‐holding capacity, and we mapped plant composition to calculate species richness and evenness. The results showed that coppicing in combination with burning soil and litter improved soil nutrient availability, enhanced biodiversity and increased SOC stocks. The SOC stocks and biodiversity were increased by a factor of three relative to those in the mature beech and spruce forests. This study shows that traditional coppicing practice may facilitate net C accrual rates of 20 t ha−1 yr−1 and maintain high biodiversity, indicating that aspects of traditional practice could be applied in current forest management to foster biodiversity and to mitigate climate change.

REDD+ en Latinoamérica: el caso de Perú

SUMMARY The question of how developing countries like Peru can participate effectively in the REDD+ (reducing emissions from deforestation and forest degradation) policy initiative of the United Nations has been the focus of considerable debate recently. The aim of this study was to detect the main challenges associated with monitoring deforestation and forest degradation and also to analyze the policy challenges associated with implementing REDD in Peru. To participate effectively in this process, it is essential that the Peruvian national government formulates a national response since it is unlikely that provincial agencies managing natural resources will be able to develop the necessary expertise to carry out effective monitoring, reporting and verification, and because the underlying factors driving deforestation will require a large investment and a coordinated response at the country level.

Using Knowledge of Plant Persistence Traits to Optimize Strategies for Post-Mine Ecological Restoration on the Peruvian Altiplano

The Peruvian Altiplano is an important center of mining activity. As a key hotspot for endemic biodiversity in Peru, it also has conservation value. Thus, ecological restoration strategies need to be developed to ensure that mining impacts on these biodiversity values are minimized. As a step toward this larger objective, we measured the composition of the soil seed bank on the Peruvian Altiplano and compared it with the standing vegetation in different plant communities. We calculated evolved persistence traits to evaluate the suitability of topsoil removal, storage, and redeployment as an ecological restoration strategy for the Peruvian Altiplano. The comparison demonstrates low similarities (Sorensen Index for sites A: 0.15, B:0.27, C:0.11, and D:0.12) between the seed bank and the standing vegetation. The flora of the germinable soil seed bank is dominated by ephemeral species. Meanwhile, the standing flora contains a higher percentage of perennial species, many of which invest in the capacity to persist via resprouting from underground storage organs. It is clear that the well-established restoration technique of topsoil removal, storage, and redeployment needs to be tested and will probably need modification to be an effective strategy for the Peruvian Altiplano. The required modifications are relatively straightforward and would ensure that this low-cost and effective restoration technique could be applied to good effect on the Peruvian Altiplano.