Densities In Plots Research Articles

Impact of Zinnia elegans Cultivation on the Control Efficacy and Distribution of Aphidius colemani Viereck (Hymenoptera: Braconidae) against Aphis gossypii Glover (Hemiptera: Aphididae) in Cucumber Greenhouses.

This study aimed to evaluate the enhancement of A. gossypii control by A. colemani when Z. elegans was planted as a companion crop in cucumber greenhouses. The density and spatial distribution of A. gossypii and parasitized mummies were investigated across three treatment plots: (1) the simultaneous application of A. colemani and cultivation of Z. elegans (parasitoid-zinnia plot); (2) the application of A. colemani alone (parasitoid plot); and (3) a control plot (no application of both). A. gossypii maintained low densities in the parasitoid-zinnia plots, while its densities in the parasitoid plots initially decreased but rapidly increased thereafter. The spatial distribution patterns of A. gossypii and parasitized mummies showed similar trends across treatments. However, the parasitism rate of A. gossypii exhibited random distribution in parasitoid and control plots, while showing uniform distribution in the parasitoid-zinnia treatment. These results supported the idea that cultivating Z. elegans alongside cucumber could enhance the effectiveness of A. colemani as a biocontrol agent against A. gossypii, highlighting the importance of such companion planting in pest management strategies.

Bottom-up population regulation of Orthotomicus erosus on irrigated and fertilized Pinus eldarica: A comprehensive field study

The Mediterranean pine engraver, Orthotomicus erosus (Wollaston), is a destructive pest that has caused a significant threat to planted pine forests worldwide through feeding on phloem, disrupting sap flow and transmitting phytopathogens. This study investigated the bottom-up effects of different irrigation and fertilization treatments on the mean numbers of O. erosus immature stages (egg, larva and pupa) and adults in the pine forest of western Tehran, Iran. A total of 72 Pinus eldarica Medw. trees were selected in Chitgar Forest Park. The experiment was arranged as a split plot in a randomized complete block design with three replications. The irrigation treatments included non-irrigation, low-irrigation (30 liters of water per month) and high-irrigation (30 liters of water per two weeks) were assigned to main plots. Moreover, fertilizers of nitrogen 100 kg/ha, superphosphate 100 kg/ha and potassium sulfate 65 kg/ha were applied in subplots. Then, the total number of O. erosus life stages was counted under the bark samples (two 10 × 10 cm bark samples) separated from the pine trees. Results showed that irrigation and fertilization significantly affected the mean number of O. erosus from egg to adult stages. Irrigation had a more pronounced effect on the pest population than fertilization. The highest number of different life stages occurred in non-irrigated pines regardless of fertilization. Moreover, fertilizer effects were influenced by irrigation, where high irrigation negatively affected superphosphate + potassium sulfate fertilized pines and significantly increased the mean numbers of different O. erosus life stages compared to low-irrigation treatment. The lowest mean number of egg (11.95 ± 0.17), larva (8.62 ± 0.21), pupa (10.38 ± 0.13) and adult (9.04 ± 0.23) per bark samples occurred in superphosphate + potassium sulfate at low-irrigation plots. Interestingly, nitrogen fertilization increased pest density compared to unfertilized trees. Furthermore, despite the low mean number of different O. erosus life stages in superphosphate + potassium sulfate treatments, the nitrogen combination increased the pest density in both low and high-irrigation plots. These findings highlighted the importance of considering the interaction between irrigation and fertilizer types in the integrated pest management program for O. erosus.

Fire frequency effects on plant community characteristics in the Great Basin and Mojave deserts of North America

BackgroundWildfire regimes are changing dramatically across North American deserts with the spread of invasive grasses. Invasive grass fire cycles in historically fire-resistant deserts are resulting in larger and more frequent wildfire. This study experimentally compared how single and repeat fires influence invasive grass-dominated plant fuels in the Great Basin, a semi-arid, cold desert, and the Mojave, a hyper-arid desert. Both study sites had identical study designs. In the summer of 2011, we experimentally burned half of each experimental block, the other half remaining as an unburned control. Half of the burned plots were reburned 5 years later to simulate increasing burn frequency. We estimated non-woody plant biomass, cover, and density in plots from 2017 to 2020.ResultsBiomass did not vary between sites, but there was higher plant cover and lower plant density at the Mojave site than at the Great Basin site. Plant biomass, density, and cover varied significantly across the years, with stronger annual fluctuations in the Great Basin. At both desert sites, fire increased plant density and biomass but had no effect on the cover. The effect of fire on plant cover varied significantly between years for both deserts but was greater in the Great Basin than in the Mojave site. Repeat fires did not amplify initial fire effects.ConclusionsThe results suggest that in general annual fluctuations in fine fuel production and fluctuations in response to fire were more apparent at the Great Basin site than at the Mojave site, with no immediate compounding effect of repeat fires at either site.

Spatial distribution of soil organic carbon and its response to forest growth and soil layer in Cunninghamia lanceolata plantations in mid-subtropical China

To investigate the effects of stand age and soil layer on the temporal and spatial distribution of soil organic carbon (SOC) in Cunninghamia lanceolata plantations, five experimental plots and 15 soil sampling sites were established in five stands of different ages (3, 6, 9, 15, and 25 years) in Huitong, Hunan Province. Tree diameter at breast height, tree height, canopy density and elevation in sample plots, and soil organic carbon concentrations (SOCC), soil enzyme activity, soil pH, and soil bulk density at 0–15, 15–30, 30–45 cm soil layers were measured during stand development. The change in SOC distribution with stand age and soil layer, and soil enzyme activity were investigated using ANOVA, LSD test, and inter-subject effect test and simulation analysis. The results showed that the SOC distribution in Cunninghamia lanceolata plantations had spatiotemporal heterogeneity and surface aggregation. The SOC increased with increasing stand age and decreased with increasing soil depth. Furthermore, SOCC and SOC density (SOCD) were strongly correlated with environmental factors; however, the interaction between forest growth and soil layer reduced the variation of SOC distribution. Forest growth and soil enzyme activity were important factors that affect the temporal and spatial distribution of SOC. Therefore, the management measures to promote the growth of the plantation and improve soil enzyme activity can enhance the SOC storage capacity from the angle of balancing ecological and economic benefits, and contribute to the achievement of the goal of “carbon neutrality”.

Forest Carbon Density Estimation Using Tree Species Diversity and Stand Spatial Structure Indices

The forest spatial structure and diversity of tree species, as the important evaluation indicators of forest quality, are key factors affecting forest carbon storage. To analyze the impacts of biodiversity indices and stand spatial structure on forest carbon density, five tree diversity indices were calculated from three aspects of richness, diversity and evenness, and three indices (Reineke’s stand density index, Hegyi’s competition index and Simple mingling degree) were calculated from stand spatial structure. The relationships between these eight indices and forest carbon density were explored using the Structural Equation Model (SEM). Then, these eight indices were used as characteristic variables to predict the aboveground carbon density of trees (abbreviated as forest carbon density) in the sample plots of the National Forest Resources Continuous Inventory (NFCI) in Shaoguan City in 2017. Multiple Linear Regression (MLR) and four typical machine learning models of Random Forest (RF), Tree-based Piecewise Linear Model (M5P), Artificial Neural Network (ANN) and Support Vector Regression (SVR) were used to predict the forest carbon density. The results show that: (1) Based on the analysis results of the structural equation model (SED), the species diversity and forest stand spatial structure have greater impacts on carbon density. (2) The R2 of all the five prediction models is greater than 0.6, among which the random forest model is the highest. (3) Based on the calculation results of optimal model of RF, the mean forest carbon density of Shaoguan city in 2017 was 43.176 tC/ha. The forest carbon density can be accurately estimated based on the species diversity index and stand spatial structure with machine learning algorithms. Therefore, a new method for the prediction of forest carbon density and carbon storage using species diversity indices and stand spatial structure can be explored. By analyzing the impacts of different biodiversity indices and stand spatial structure on forest carbon density, a scientific reference for the making of management measures for increasing forest carbon sinks and reducing emissions can be provided.

Responses of bud banks and shoot density to experimental drought along an aridity gradient in temperate grasslands

Abstract Climate change is expected to increase the magnitude and frequency of extreme drought in most grassland ecosystems. Exploring the responses of below‐ground bud banks and their relationships with above‐ground plant structure and drought is need to explain how climate change will impact grassland ecosystems. However, studies on the response of community‐scale bud and shoot densities to experimental drought along an aridity gradient are rare. We experimentally removed 66% of growing season precipitation for 4 years in three temperate grasslands that spanned an aridity gradient in northern China. We quantified the legacy effects of drought on grass, forb and total community below‐ground bud density, above‐ground shoot density and the ratio of bud to shoot density 1 year following treatment. Below‐ground bud density was lowest at the highest aridity site for the entire community, while above‐ground shoot density was highest at the medium aridity site. Below‐ground bud and above‐ground shoot densities were the lowest at the high aridity site for grasses but the highest for forbs at this site. Bud:shoot ratios decreased with increasing aridity for grasses, yet remained constant for forbs along the aridity gradient. Below‐ground bud density in drought plots remained lower than controls a year following drought at each site. Experimental drought did not alter the below‐ground bud bank for grasses but decreased forb bud banks across sites. Experimental drought had little legacy effects on above‐ground shoot density and bud:shoot ratios for grasses, forbs and the total community at each site. Our results suggest that grass and forb bud banks can differ in their responses to both multi‐year drought along an aridity gradient, and that bud limitation for shoot generation may increase as grasslands get drier. Bud bank responses to climate will impact plant community functioning and resilience. Thus, incorporating bud bank dynamics will improve projections of grassland ecosystems under future climate change. Read the free Plain Language Summary for this article on the Journal blog.

Undersowing oats with clovers supports pollinators and suppresses arable weeds without reducing yields

Abstract Sustainable food production requires agriculture to conserve biodiversity and facilitate ecosystem services to maintain productivity levels while reducing inputs detrimental to ecosystem functioning. Increasing within‐field vegetation diversity by legume intercropping seems promising to facilitate cropping system multi‐functionality. Effects of intercropping with legumes on biodiversity‐mediated ecosystem services such as pollination or natural pest control are, however, not sufficiently understood. Using 26 observation plots in a paired field design, we studied the effects of undersowing oats with a mixture of three annual clovers across different aspects of cropping system multi‐functionality. We investigated 16 below‐ and above‐ground ecosystem service indicators related to soil mineral nitrogen, arable weed control, pollination, disease and pest pressures, natural pest control and crop yield. We found lower arable weed cover, higher flower cover and pollinator densities as well as decreased root‐feeding nematode densities in intercropped observation plots compared with the non‐intercropped controls. However, intercropping decreased spider activity densities and oat yield nitrogen content. Root diseases, pest damages, natural pest control and crop yield were not affected by intercropping. The biomass of undersown clovers was positively related with the differences in flower cover and pollinator densities, and negatively related with the differences in arable weed cover between the intercropped and the control treatment. Synthesis and applications: We demonstrate that undersowing annual clovers suppresses arable weeds and simultaneously support pollinators without reducing crop yields or taking land out of arable production. Undersown plant mixtures should, however, be tailored to support a wider spectrum of pollinators and benefit natural pest control to support a higher level of overall cropping system multi‐functionality.

Grasshopper abundance and offtake increase after prescribed fire in semi-arid grassland

Background Fire modulates herbivore dynamics in open ecosystems. While extensive work demonstrates the interaction between fire and vertebrate grazers, less research describes how grasshopper herbivory dynamics respond to fire. Aim We examined how fire increased grass crude protein content and increased the density of and offtake by grasshoppers relative to unburned mixed-grass prairie. Methods We deployed grasshopper exclusion cages to determine grasshopper offtake of aboveground plant biomass, counted grasshopper abundance throughout the study period, and measured crude protein content of aboveground grass biomass. Key results Offtake and density were higher in burned versus unburned plots. Burned plot grasshopper density increased over time, with greater rates of increase in recently burned plots, while density remained constant in unburned locations. Conclusions We present a potential mechanism by which fire interacts with grasshoppers in open ecosystems. It is likely that greater grasshopper offtake and density in recently-burned plots is at least partially attributable to higher crude protein content, as grass in these plots has a much higher proportion of recent growth after fire removed senesced material. Implications Grasshopper herbivory likely acts as a multiplier of livestock herbivory in burned rangeland. Restoring fire regimes can balance direct negative effects of heating against nutritional benefits.

Plant Functional Trait Responses to Dolomite and Limestone Karst Forests in Southwest China

Southwest China is distributed with the largest area of limestone and dolomite karst landscapes in the world, and its ecological environment is very fragile; the problem of rock desertification is particularly prominent. Karst lithological differences make habitats and soil heterogeneity more complex, and vegetation has developed certain morphological and physiological structural characteristics to adapt to these special environments, which will most likely lead to differentiation in vegetation functional characteristics, such as seed size, wood density, life type and flowering time, thus affecting the number and growth of seedlings and young trees and the future succession potential of forest stands in karst-vegetation restoration. Therefore, it is important to understand the differences in species composition and the functional characteristics of dolomite and limestone karst forests. Over a 2-year period, we investigated a total of 3170 individuals from 123 species and analyzed the relationship between the species compositions and the functional characteristics of two karst-forest areas with different lithology (i.e., limestone and dolomite karst). It was found that the average number of species with medium-diameter seeds and medium wood density in dolomite plots was obviously greater than the average number of species in limestone plots, but this reached no significant difference. However, with the gradual restoration of each forest, the height and carbon sequestration capacity of the trees began to diverge, with the relative abundance of species with tall trees and high wood density being significantly higher in limestone plots than in dolomite plots. The species richness of evergreen trees was significantly higher in the limestone plots than in the dolomite plots. There was no significant difference in the relative species richness of flowering plants in the two karst-forest areas during spring–summer and winter–spring seasons; however, the species richness of flowering plants in the limestone karst forests was significantly higher than that of flowering plants in the dolomite karst forests during summer and autumn seasons. These significant traits were very closely related to the species richness of the understory plants. Further insight into the temporal aspects of karst-forest succession is needed to grasp how functional traits affect the restorations of different lithological karst forests to their primary states.

Soil seed bank distribution and restoration potential in the vegetation of Buska Mountain range, Hamar district, southwestern Ethiopia

The seed banks are vital components for the reestablishment of degraded lands since they are used to predict the future coverage of vegetation and allow for the implementation of appropriate conservation measures in a particular area. The study was conducted in the Buska Mountains of the Hamar area in south-western Ethiopia and determined the composition, density and vertical distribution of soil seed banks under various land-use systems and soil layers. A total of 96 soil samples were involved in the study; four land-use types (grassland, forest, scrub and bare ground). Three distinct soil layers from each plot (0–3 cm, 3–6 cm, 6–9 cm depths) were sampled. Jaccard's Similarity Coefficient was applied to evaluate the correspondence between different land-use types and soil layers. One-way ANOVA was used to compute species density and composition respectively within land-use systems along with the seed bank and above ground vegetation. Fifty six (56) species within 27 plant families and 50 genera were recorded. Twenty percent of the species was contributed by Asteraceae followed by Poaceae (16%). Herbaceous growth forms were the most dominant in the area, contributing about 78.6%. The total seedling density in the study plots was 8171 seedlings/m2. Jaccard's Similarity Coefficient is relatively higher (0.52) between grassland and scrub, while the forest and bare land had the least amount of similarity (0.22). There was seen a higher similarity of species between the first and second soil layers and a decreasing density with soil depth. A substantial difference between the aboveground species and seed bank was recorded in the area. The lower resemblance between the standing vegetation and the seed bank infers a lower overall restoration potential and suggests other alternative regeneration mechanisms such as seedling plantation of priority indigenous plant species and avoiding anthropogenic disturbances.

Impact of Tillage Intensity on Planosol Bulk Density, Pore Size Distribution, and Water Capacity in Faba Bean Cultivation

Tillage systems affect many properties of soil, such as soil bulk density, porosity, pore distribution, and soil water capacity. However, the effect of reduced tillage (RT) on faba bean cultivation requires wider analysis. We carried out our investigations at Vytautas Magnus University, Agriculture Academy (Lithuania), as part of a long-term field experiment. The aim was to determine the effect of tillage intensity on soil bulk density, pore distribution and soil water capacity in faba bean cultivation. Five tillage systems were used: deep (DP) and shallow (SP) ploughing, deep cultivation (DC) (chiselling), shallow cultivation (SC) (disking), and no tillage (NT). The results showed that the soil bulk density in NT plots was somewhat higher in upper (0–10 cm) and less in deeper (15–20 cm and 30–35 cm) soil layers compared to DP. The distribution of soil pores depended more on the sampling depth than on tillage. In RT and NT plots, the number of meso-pores was often higher, and that of micro-pores was lower than in ploughed plots. In the upper (0–5 cm) soil layer, the highest water capacity was established in NT, and in deeper layers, this was found in RT plots compared to DP. The density of soil mainly affected the volume of micro-and-macro-pores and water capacity.

Growth dominance and growth efficiency in response to thinning treatments in Chinese fir plantations with long-term spacing trials

Growth dominance is a relatively new, simple, quantitative metric of within stand resource partitioning, while growth efficiency can be used to quantify the efficiency of resource use at both stand and tree level. We examined long-term silvicultural experiments in Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) to characterize how growth dominance and stand growth efficiency in stands thinned from below develop with age, cumulative thinning intensities, residual density, and planting density. Results showed that growth dominance in unthinned plots increased with increasing age, while stand growth efficiency displayed the reverse pattern. Both of them were not significantly different between planting densities, which indicates that the efficiency of resource use and relative growth of Chinese fir was always proportional to its size, even in dense stands. Thinning improved the relative growth of larger trees and decreased stand growth efficiency. When the dense plots were thinned to the next lower initial planting density, the growth dominance of the thinned plots were higher than that of the unthinned plots, and stand growth efficiency of the thinned plots were lower than the respective unthinned plots. When plots with different planting densities were thinned to the same stand density, growth dominance increased with cumulative thinning intensities, while stand growth efficiency showed the reverse pattern. Growth dominance was positively correlated with the growth efficiency difference between smaller and larger trees in both unthinned and thinned plots, while negatively correlated with stand growth efficiency.

Quantification Model of Residual Biomass in Citrus Uprooting

In this paper, the aerial biomass of citrus plantations in Spain was evaluated using destructive methods. Before cutting down the trees, their geometric variables were measured: trunk diameter at 10 cm from the ground (Dt), trunk perimeter at 10 cm from the ground (Pm), mean crown diameter (Dc), canopy height (Hc), and maximum crown height (Hmax). After geometric characterization of the tree, it was felled. This was performed with a chainsaw about 10 cm above the ground. After cutting down, trees with and without leaves were weighed, and biomass variables such as moisture, calorific value, elemental composition, and proximate analysis were measured. The predictive models obtained showed an r2 of 0.78. According to our analysis, in plantations in Spain, where the average plantation pattern is 4 × 4 m, the amount of carbon stored in a plot is 15 t of C per hectare. If leaves and wood are counted, the energy density in citrus plots can be estimated at 900 MJ/tree. However, if only wood is included in the calculation, the accumulated energy per tree is 750.3 MJ/tree, which represents 5.6 × 105 MJ/ha.

Disturbance decreases genotypic diversity by reducing colonization: Implications for disturbance-diversity feedbacks.

One objective of eco-evolutionary dynamics is to understand how the interplay between ecology and evolution on contemporary timescales contributes to the maintenance of biodiversity. Disturbance is an ecological process that can alter species diversity through both ecological and evolutionary effects on colonization and extinction dynamics. While analogous mechanisms likely operate among genotypes within a population, empirical evidence demonstrating the relationship between disturbance and genotypic diversity remains limited. We experimentally tested how disturbance altered the colonization (gain) and extinction (loss) of genets within a population of the marine angiosperm Zostera marina (eelgrass). In a 2-year field experiment conducted in northern California, we mimicked grazing disturbance by migratory geese by clipping leaves at varying frequencies during the winter months. Surprisingly, we found the greatest rates of new colonization in the absence of disturbance and that clipping had negligible effects on extinction. We hypothesize that genet extinction was not driven by selective mortality from clipping or from any stochastic loss resulting from the reduced shoot densities in clipped plots. We also hypothesize that increased flowering effort and facilitation within and among clones drove the increased colonization of new genets in the undisturbed treatment. This balance between colonization and extinction resulted in a negative relationship between clipping frequency and net changes in genotypic richness. We interpret our results in light of prior work showing that genotypic diversity increased resistance to grazing disturbance. We suggest that both directions of a feedback between disturbance and diversity occur in this system with consequences for the maintenance of eelgrass genotypic diversity.

GREEN MANURES AND NPK FERTILIZER APPLICATIONS EFFECT ON ORGANIC CARBON POOL, SOIL PHYSICAL PROPERTIES AND CUCUMBER PRODUCTION

Deterioration of soil physical properties and organic matter depletion resulting from continuous cultivation of tropical sandy loam soils, even with the regular applications of inorganic fertilizers is common. To regenerate the soil organic matter and maintain soil structural and hydraulic properties for crop production, the effects of different legumes green manures and NPK chemical fertilizer were evaluated after a 3-year field experiments at the University of Port Harcourt, Teaching and Research Farm (2018 – 2021). Treatments were: 5 tons ha-1Centrocema (Ce5), 5 tons ha-1 Gliricidia (Gl5), 5 tons ha-1Calapogonium (Ca5), NPK 20:10:10 (NPK) and the Control, arranged in a Randomized Complete Block Design (RCBD), in 5 replications. Results showed that three annual applications of Centrocema, Gliricidia, and Calapogonium increased soil organic carbon pool at the 0-30 cm topsoil, and reduced the bulk densities by 8.5%, 4.1%, and 7.0%, respectively, compared to the NPK fertilizer and control. The increased in bulk density in untreated plots led to decrease in water stable aggregates, low water holding capacity and low yield of cucumber crop. Green manures applications increased soil organic carbon pool, improved topsoil physical properties and cucumber yield, while NPK chemical fertilizer had negative effects on these properties.

Effects of strawberry resistance and genotypic diversity on aphids and their natural enemies

Ecological theory hypothesizes that plant trait diversity may be as important as the presence of specific functional traits (e.g., resistance) for the herbivore and predator communities within a population. We used experimental populations of wild woodland strawberry (Fragaria vesca) to test whether the degree of plant genotypic diversity and/or the existence of specific resistance traits play a role in the host plant’s community structure specifically, the community of generalist and specialist aphids and their natural enemies. In 2019, we studied the aphid abundance and relative predator abundance in an experimental field site in Alnarp, Southern Sweden; the field consisted of plots planted with combinations of 20 different wild strawberry genotypes. These strawberry genotypes were previously identified as either susceptible to or resistant against the herbivorous beetle (Galerucella tenella). Two aphid species, Chaetosiphon fragaefolii (specialist) and the exotic Aphis gossypii (generalist) were found in the plots and of the two species A. gossypii was dominant. The abundance of the specialist aphid (C. fragaefolii) was highest in susceptible plots with high genotypic diversity, while the generalist (A. gossypii) was highest in plots with a mix of resistant and susceptible plants with high genotypic diversity. Anthocorid predators, developed significantly higher population densities in strawberry plots with high genotypic diversity. Overall, predator abundance showed a positive correlation with aphid abundance. These results show that the specific functional trait of resistance as well as plant diversity affected aphids. Knowledge about these effects can be important factors to consider when designing strawberry plantings less susceptible to aphids.

Evaluation of Host Resistance, Hydrated Lime, and Weed Control to Manage Clubroot in Canola

Plasmodiophora brassicae Wor. is a soilborne parasite causing clubroot of canola (Brassica napus L.), a serious disease managed mostly by planting clubroot-resistant (CR) cultivars. Recently, new pathotypes of P. brassicae have emerged that overcome resistance, highlighting the need for a greater understanding of resistance stewardship and an integrated approach to clubroot management. Replicated field experiments were conducted in Edmonton, AB, in 2018 and 2019, to evaluate the effect of lime application and weed management on clubroot severity, crop yield and various growth parameters in clubroot-susceptible (CS) and CR canola cultivars. P. brassicae resting spore densities were also monitored by quantitative PCR for each treatment. When hydrated lime was applied to increase the soil pH from initial values of 5.2–5.5 to 7.2, clubroot severity decreased by 34–36% in the CS canola cultivar, while seed yield increased by 70–98%. The application of hydrated lime also resulted in resting spore densities that were 48–80% lower, relative to untreated controls, in plots where the CS cultivar was grown. Lime application or management of weeds did not significantly affect spore densities in plots with the CR cultivar. The results from the field trial suggest that the application of hydrated lime may be a useful strategy to manage clubroot, when used in combination with genetic resistance to reduce disease pressure.

Changes in the direction of the diversity–productivity relationship over 15 years of stand development in a planted temperate forest

Abstract Experiments manipulating diversity in both forests and grasslands have often observed a positive diversity–productivity relationship (DPR) which tends to strengthen during plant community development. This pattern is generally attributed to an increase in niche complementarity or facilitation. Most analyses do not examine species dominance and density, which also change over time. Moreover, how neighbourhood‐scale interactions among tree species affect the DPR is not well‐understood. We analysed growth and mortality data from the Simplex experiment, a part of the BIOTREE tree diversity experiment. Simplex consists of 36 plots each planted with four common and commercially important tree species to create a gradient of tree species evenness at two tree densities (6667 and 3556 trees ha−1). We test whether: (a) the effect of evenness on total above‐ground biomass productivity increase with stand development (year), (b) the effect of evenness on productivity is stronger in dense plots; and (c) intraspecific competition from neighbours negatively affect the growth of dominant species more strongly compared to co‐dominant species, and whether this negative effect is stronger in denser plots. The direction of DPR was initially negative because the fast‐growing long‐lived pioneer Douglas fir (Pseudotsuga menziesii [Mirb.] Franco) dominated. However, with time, shade‐tolerant Norway spruce (Picea abies [L.] Karst.) and European beech (Fagus sylvatica L.) increased in abundance (by biomass), and the relationship between evenness and biomass increment changed from negative to positive in high‐density plots. Neighbourhood analyses revealed that for Douglas fir and Norway spruce, conspecifics reduced individual growth rates across density levels and years. Synthesis. We observed a shift in the diversity–productivity relationship over 15 years in our experiment. Over time, increasing intraspecific competition limited the increment of the abundant Douglas fir in uneven plots, and a persistent increase in the abundance (by biomass) of shade‐tolerant Norway spruce and European beech in even plots led to a higher community biomass increment, which led to a positive DPR. Emergence of a positive DPR in temperate forest plantations requires significant time and is importantly promoted by diversity at the neighbourhood scale (intimate mixtures) as well as higher density planting.

Increased Coral Larval Supply Enhances Recruitment for Coral and Fish Habitat Restoration

Loss of foundation reef-corals is eroding the viability of reef communities and ecosystem function in many regions globally. Coral populations are naturally resilient but when breeding corals decline, larval supply becomes limiting and natural recruitment is insufficient for maintaining or restoring depleted populations. Passive management approaches are important but in some regions they are proving inadequate for protecting reefs, therefore active additional intervention and effective coral restoration techniques are needed. Coral spawning events produce trillions of embryos that can be used for mass larval rearing and settlement on degraded but recoverable reef areas. We supplied 4.6 million Acropora tenuis larvae contained in fine mesh enclosures in situ on three degraded reef plots in the northwestern Philippines during a five day settlement period to initiate restoration. Initial mean larval settlement was very high (210.2 ± 86.4 spat per tile) on natural coral skeleton settlement tiles in the larval-enhanced plots, whereas no larvae settled on tiles in control plots. High mortality occurred during early post-settlement life stages as expected, however, juvenile coral survivorship stabilised once colonies had grown into visible-sized recruits on the reef by 10 months. Most recruits survived and grew rapidly, resulting in significantly increased rates of coral recruitment and density in larval-enhanced plots. After two years growth, mean colony size reached 11.1 ± 0.61 cm mean diameter, and colonies larger than 13 cm mean diameter were gravid and spawned, the fastest growth to reproductive size recorded for broadcast spawning corals. After three years, mean colony size reached 17 ± 1.7 cm mean diameter, with a mean density of 5.7 ± 1.25 colonies per m–2, and most colonies were sexually reproductive. Coral cover increased significantly in larval plots compared with control plots, primarily from A. tenuis recruitment and growth. Total production cost for each of the 220 colonies within the restored breeding population after three years was United States $17.80 per colony. A small but significant increase in fish abundance occurred in larval plots in 2018, with higher abundance of pomacentrids and corallivore chaetodontids coinciding with growth of A. tenuis colonies. In addition, innovative techniques for capturing coral spawn slicks and larval culture in pools in situ were successfully developed that can be scaled-up for mass production of larvae on reefs in future. These results confirm that enhancing larval supply significantly increases settlement and coral recruitment on reefs, enabling rapid re-establishment of breeding coral populations and enhancing fish abundance, even on degraded reef areas.

Exclusion netting affects apple arthropod communities

Exclusion cages can quantitatively demonstrate the value of natural enemies and the biological control services they provide. Currently, in Washington State, enclosing orchards in netting is being evaluated as a pest control method, but these enclosures may also serve as an exclusion cage to natural enemies, thereby disrupting biological control. To test the effects of net enclosures on apple arthropod communities, we conducted a two-year study comparing apple herbivore, predator, and parasitoid densities in caged and uncaged plots (both receiving insecticides) to an untreated check. Effects on the various groups were influenced by size and motility. Densities of larger motile arthropods, including codling moth (Cydia pomonella (L.)), chrysopids, and syrphids, were lower in the caged plots, demonstrating exclusion. Woolly apple aphid (Eriosoma lanigerum (Hausmann)) and its parasitoid Aphelinus mali (Haldeman) densities in the caged plots were over 100-fold greater and 5-fold greater, respectively, than the other treatments. European earwig (Forficula auricularia (L.)), a generalist predator, was more abundant in the caged plots in 2016 but not in 2017. Spider mites were more abundant in the cage treatments for both years, while predatory mites had higher densities in the cages in 2017 only. These outcomes show that net enclosures change the composition of apple arthropod communities through exclusion of certain herbivores and natural enemies. In the case of some pest herbivores (e.g., codling moth), this exclusion is beneficial, but in the case of predators, it is detrimental. This study further demonstrated that exclusion of only part of the natural enemy complex may be sufficient to cause herbivore outbreaks.