Search Results (17)

Niche complementarity is suggested to be a main driver of productivity overyielding in diverse environments due to enhanced resource use efficiency and reduced competition. Here, we combined multiple different approaches to demonstrate that niche overlap is the most likely cause to explain a lack of overyielding of three tree species when grown in different species combinations. First, in an experimental planting we found no relationship between productivity and species diversity for leaf, wood, or root production (no slope was significantly different from zero), suggesting a lack of niche differences among species. Second, data extracted from the United States Department of Agriculture Forest Inventory and Analysis revealed that the species do not significantly co-occur in natural stands (p = 0.4065) as would be expected if coexistence was common across their entire range. Third, we compared trait differences among our species and found that they are not significantly different in multi-dimensional trait space (p = 0.1724). By combining multiple analytical approaches, we provide evidence of potential niche overlap that precludes coexistence and a positive diversity–productivity relationship between these three tree species. Full article

Increased tree species diversity can promote forest production by reducing intra-specific competition and promoting an efficient unitization of resources. However, questions remain on whether and how mixed stands affect the dynamics of intra–annual xylem formation in trees, especially in subtropical forests. In this study, we randomly selected 18 trees from a monoculture of 63-year-old Masson pine (Pinus massoniana) growing in pure stands and mixed them with 39-year-old Castanopsis hystrix in Pinxiang, southern China. A total of 828 microcores were collected biweekly throughout the growing season from 2022 to 2023 to monitor the intra-annual xylem formation. Cell production started in early March and ended in late December and lasted about 281 to 284 days. Xylem phenology was similar between mixed and pure stands. During both seasons, the Masson pine in mixed stands showed higher xylem production and growth rates than those in pure stands. The Masson pine in mixed stands produced 45–51 cells in 2022 (growth rate of 0.22 cells day⁻¹) and 35–41 cells in 2023 (0.17 cells day⁻¹). Growth rate, and not growth seasons, determined the superior xylem growth in the mixed stands. Our study shows that after 39 years of management, Masson pine and C. hystrix unevenly aged mixed stands have a significant positive mixing effect on Masson pine xylem cell production, which demonstrates that monitoring intra-annual xylem growth dynamics can be an important tool to evaluate the effect of species composition and reveal the mechanisms to promote tree growth behind the mixing effect. Full article

The global shortage of high-quality forage has significantly constrained the development of animal husbandry. Leveraging the complementary effects of forage rapeseed and hairy vetch intercropping can enhance forage yield and quality; however, the underlying mechanisms of overyielding in forage rapeseed–hairy vetch intercropping systems remain unclear. Over two years of field experiments, three cropping systems—rapeseed sole cropping, hairy vetch sole cropping, and rapeseed–hairy vetch intercropping—were investigated to assess the effects of intercropping on root and stem morphology, canopy light distribution, leaf photosynthetic physiology, and nitrogen metabolism. Our results demonstrated that intercropping increased forage biomass and crude protein yield by 14.3–20.0% and 30.7–92.8%, respectively, compared to sole cropping. Intercropping significantly enhanced root biomass, increasing lateral root biomass by 81% compared to rapeseed sole cropping. It also improved stem anatomical traits, including the cortex area (58.8–80.7%), cortex thickness (25.1–38.3%), number of vascular bundles (18.0–37.3%), vascular bundle length (17.8–18.4%), vascular bundle perimeter (6.7–18.7%), vascular bundle area (34.6–63.9%), and stem breaking strength (25.7–76.6%). Additionally, intercropping optimized vertical canopy light interception, reduced the activity of antioxidant enzymes (CAT, POD, SOD) and reactive oxygen species (ROS) accumulation, and enhanced the activities of glutamine synthetase and nitrate reductase, stomatal traits, and photosynthetic rates in the leaves of both crops. Structural equation modeling revealed that, in the intercropping system, improved population lodging resistance directly promoted nitrogen metabolism and leaf photosynthetic rates, ultimately increasing population biomass. In summary, rapeseed–hairy vetch intercropping improved canopy light distribution, strengthened rapeseed stem anatomy and root penetration, and enhanced population lodging resistance, leaf photosynthetic physiology, and nitrogen metabolism, thereby boosting forage biomass and quality. The supportive role of rapeseed in the intercropping system elucidates the overyielding mechanisms of rapeseed–hairy vetch intercropping, offering a theoretical framework for optimizing forage production systems worldwide. Full article

Mixed stands of tree species with complementary traits can modulate stand growth and timber quality. At the Fengshushan Forest Farm, mixtures of Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) with Liquidambar formosana Hance, Schima superba Gardner & Champ., Elaeocarpus sylvestris (Lour.) Poir., Cinnamomum camphora (L.) Presl, and Chinese fir monoculture were established. Differences in stand growth and timber quality among these mixtures were assessed and a test was conducted to evaluate the factors influencing the mixture effects. The average diameter at breast height, tree height, stand volume, and individual tree annual increment of mixtures generally exceeded those of Chinese fir monocultures but not necessarily those of broad-leaved monocultures. When the net interaction between species was complementary, overyielding in mixtures occurred (RP_fir,bl > 0), which was influenced significantly by stand density, soil properties, and timber quality. The timber quality and wood production of Chinese fir were enhanced by mixture with some broad-leaved species, with reduced slenderness and knottiness in mixtures, and notable increases in medium- (average outturn rates of 56.13%) and large-diameter (11.71%) timber in C. lanceolata/C. camphora mixture. The growth and timber quality of Chinese fir are largely promoted when grown mixed with broad-leaved species. Overyielding at the stand level occurs where Chinese fir compensates for the underperformance of broad-leaved trees. Full article

The bare row spacing between young jujube trees reduces resource use efficiency. Planting cotton between rows of jujubes can improve the efficiency of light, heat, water, and temperature resources. However, it is not clear how many rows of cotton between the jujube rows would be the most suitable pattern. A field study with different cropping systems was performed to investigate the land equivalent ratio (LER), the competition of cotton to jujube, and the sustainability index. The treatments included (1) monoculture jujube, (2) monoculture cotton, (3) jujube intercropped with two rows of cotton (J/C2), (4) jujube intercropped with four rows of cotton (J/C4), and (5) jujube intercropped with six rows of cotton (J/C6). The results showed that the LER under the J/C2, J/C4, and J/C6 systems were 1.17, 1.30, and 1.28, respectively. The LER and total yield were higher under J/C2 than under the J/C4 and J/C6 treatments. The overyielding rate of cotton was increased, while those of jujube were decreased with increasing rows of cotton. The competition between cotton to jujube was less than 0. The net, complementarity, selection effect, and sustainability index were significantly higher under J/C4 and J/C6 than under J/C2, with J/C4, showing stronger net effects. Both complementarity and selection effects contributed to the intercropping yield advantages. Comprehensively considering yield, economic efficiency, sustainability index, land use efficiency, and net effect, J/C4 is one of the most productive and sustainable planting patterns of jujube–cotton intercropping system in southern Xinjiang, which is the more ideal pattern in arid and semi-arid regions. Full article

Forest productivity (FP) depends not only on tree species diversity but also on functional traits, stand structure, and environmental factors; however, causation and relative importance remain controversial. The effects of tree species diversity (species richness), trait community-weighted mean (CWM), forest structure (forest density and maximum DBH), and environmental factors (soil nutrients and elevation) on larch (Larix principis-rupprechtii Mayr) forests’ productivity were investigated, and the relative importance of each factor in determining productivity was quantified. Our results showed that stand structure and functional traits had significant positive effects on the basal area increment (BAI) of larch stands (p < 0.05) and were more important than tree diversity and environmental factors in explaining BAI variations. The contribution ratio of each influencing factor was as follows: stand structure (59%), functional composition (30%), environmental factors (9%), and species diversity (SD) (2%). The biomass ratio hypothesis was more important than the niche complementarity hypothesis in explaining the relationship between species diversity and productivity. The structural equation model showed that environmental factors did not directly affect the BAI in larch forests but indirectly affected the BAI through tree diversity and stand structure. Therefore, in larch forests with low species richness, it is more important to adjust stand structure to maintain overyielding while also considering the influence of environmental factors. Full article

The amount of PM bound by tree canopies depends on leaf traits, but also the leaf area available, both of which are dependent on tree identity. We investigated four species (Acer platanoides L., Tilia cordata Mill., Quercus robur L., Carpinus betulus L.) grown in monocultures and in two and four species polycultures. The amount of PM on the leaves of these species was determined by washing and fractionation of the PM into PM_2.5, PM₁₀ and PM₁₀₀ size classes using a filtering method. The leaf area index was estimated by litter collection. The amount of PM_2.5 per m² leaf area was significantly higher in T. cordata compared to Q. robur and A. platanoides, and in C. betulus compared to A. platanoides. The leaf area index in monocultures was similar for all species except T. cordata which was considerably lower. Overyielding of LAI was shown in the two species polyculture of T. cordata and A. platanoides, and also in the four species polyculture. In polyculture, higher amounts of PM were determined in the two species polyculture of Q. robur and C. betulus and also in the four species polyculture. The result show that both tree identity and mixture influence the amount of PM in the canopy, and this is related to tree leaf traits, and also to overyielding of LAI in the polyculture. Full article

Soils of the Andean highlands are under threat from cropping system intensification. Improved forage-based fallows offer great promise to address this issue, but research is needed to better understand the potential of species mixtures vs. monocultures to support multiple farmer objectives, especially forage production and soil conservation. We used a pot study to quantify above- and belowground biomass production as well as the total N uptake of grass–legume pairs between five grasses: (1) oat (Avena sativa), (2) ryegrass (Lolium multiflorum), (3) festulolium (Lolium × Festuca genera), (4) brome grass (Bromus catharticus), and (5) orchard grass (Dactylis glomerata), and four legumes: (1) vetch (Vicia dasycarpa), (2) red clover (Trifolium pratense), (3) black medic (Medicago lupulina), and (4) alfalfa (Medicago sativa) relative to the performance of each species in monoculture within two soils from the central Peruvian Andes. Grass–legume bicultures demonstrated significant overyielding, producing 65% and 28% more total dry biomass and total N uptake on average than monocultures. Aboveground biomass of bicultures was significantly influenced by the species of legume present, while belowground biomass was more affected by the grass species in the mixture. When evaluating the growth of each species separately, our findings indicate that overyielding was driven more by the enhanced growth of grasses relative to legumes. Our findings indicate that combining key functional groups (e.g., grass and legume, annual and perennial) offers great promise for developing improved fallows for supporting soil health and productivity in Andean agroecosystems. Full article

(1,2) In this theoretical study, we apply MesoFON, a field-calibrated individual-based model of mangrove forest dynamics, and its Lotka–Volterra interpretations to address two questions: (a) Do the dynamics of two identical red mangrove species that compete for light resources and avoid inter-specific competition by lateral crown displacement follow the predictions of classical competition theory or resource competition theory? (b) Which mechanisms drive the dynamics in the presence of inter-specific crown plasticity when local competition is combined with global or with localized seed dispersal? (3) In qualitative support of classical competition theory, the two species can stably coexist within MesoFON. However, the total standing stock at equilibrium matched the carrying capacity of the single species. Therefore, a “non-overyielding” Lotka–Volterra model rather than the classic one approximated best the observed behavior. Mechanistically, inter-specific crown plasticity moved heterospecific trees apart and pushed conspecifics together. Despite local competition, the community exhibited mean-field dynamics with global dispersal. In comparison, localized dispersal slowed down the dynamics by diminishing the strength of intra-/inter-specific competition and their difference due to a restriction in the competitive race to the mean-field that prevails between conspecific clusters. (4) As the outcome in field-calibrated IBMs is mediated by the competition for resources, we conclude that classical competition mechanisms can override those of resource competition, and more species are likely to successfully coexist within communities. Full article

In Mediterranean environments, with mild winters and dry summers, peas are planted in autumn or early winter to profit from winter rain and to avoid terminal drought and high summer temperatures. The root parasitic weed broomrape (Orobanche crenata) appears as a major limiting factor under these conditions. To address such specific growing conditions and associated constraints, targeted breeding is needed. We present here recent achievements in the development of pea lines arising from a wide hybridization program incorporating resistance to broomrape and to powdery mildew (Erysiphe pisi) from landraces and wild relatives. Their adaption to autumn sowings under Mediterranean rain fed conditions, and their agronomic performance and resistance to prevailing diseases is compared with those of check cultivars in a multi-environment field test with nine trials performed over three seasons. HA-GGE biplots were a powerful tool for comparison among accessions in terms of performance and stability for each trait assessed. Like this, breeding lines NS22, NS34, NS8, NS39, NS35, NS21 and NS83 over-yielded all check cultivars. Grain yield was strongly affected by broomrape infection, with little influence of powdery mildew and ascochyta blight. All breeding lines studied showed high to moderate resistance to broomrape, whereas all check cultivars were severely infected. Broomrape infection was not correlated with days to flowering, whereas powdery mildew infection was favored by long cycles. Broomrape infection was enhanced by mild winter temperatures before flowering and spring rain, whereas high spring temperatures hampered broomrape development. Full article

Grassland mixtures hold the potential for increasing biomass and productivity. In a field experiment, monocultures and mixtures of eight white clover (Trifolium repens L.) genotypes and perennial ryegrass (Lolium perenne L.) were analyzed over three years (2015, 2016, and 2018) for their species-specific aboveground and belowground biomass. Roots were analyzed by Fourier transform infrared (FTIR) spectroscopy to identify species-specific root mass, vertical distribution, and belowground relative yield total (RYT). Aboveground biomass decreased strongly from 2015 to 2018. Aboveground and belowground RYT were always significantly higher than one. Aboveground biomass overyielded in 2016 and 2018 compared to monocultures. Monocultures of perennial ryegrass displayed a significantly higher proportion of roots in shallow soil layers than white clover in two of the three examined years. In mixtures, these differences in vertical root distribution between both species were not present and perennial ryegrass, and white clover occupied similar vertical niches in 2015 and 2016. Interestingly, in the dry year 2018, white clover had a higher proportion of roots in shallow soil layers than perennial ryegrass in mixtures. Full article

Many monoculture forests have been converted to mixed-species forests in Europe over the last decades. The main reasons for this conversion were probably to increase productivity, including timber production, and enhance other ecosystem services, such as conservation of biodiversity and other nature values. This study was done by synthesizing results from studies carried out in Dutch mixed forests compared with monoculture stands and evaluating them in the perspective of the current theory. Then we explored possible mechanisms of higher productivity in mixed stands, in relation to the combination of species, stand age and soil fertility, and discussed possible consequences of forest management. The study covered five two-species mixtures and their corresponding monoculture stands from using long-term permanent forest plots over multiple decades as well as two inventories (around 2003 and 2013) across the entire Netherlands. These forest plot data were used together with empirical models at total stand level, species level and tree level. Overyielding in Douglas-fir–beech and pine–oak mixtures was maintained over time, probably owing to the intensive thinning and was achieved on the poorer soils. However, this overyielding was not always driven by fast-growing light-demanding species. On individual tree level, intra-specific competition was not necessarily stronger than inter-specific competition and this competitive reduction was less seen at lower soil fertility and dependent on species mixtures. Moreover, size-asymmetric competition for light was more associated with tree basal area growth than size-symmetric competition for soil resources. Overall, this study suggests a substantial potential of species mixing for increasing productivity and implies developing forest management strategies to convert monospecific forests to mixed-species forests that consider the complementarity in resource acquisition of tree species. Full article

The research on mixed-species forestry has rapidly increased in recent decades because there is a growing interest in these types of stands for environmental reasons. Their positive influence on ecosystem biodiversity, stability and resilience, as well as their role in the new challenge brought up by the adaptation to global change, have been the object of many research works. However, the economic implications of mixed-species forest management have not deserved the same attention. The objective of this work is to study the effect of species interactions on productivity, and to economically assess this effect. This research is focused on the analysis of financial return and risk in even aged mixed stands of Pinus sylvestris and Fagus sylvatica in Northern Spain. Growth and yield projections for monospecific and mixed stands of Scots pine and European beech were made by means of a previous model developed from a set of the Spanish National Forest Inventory plots in the region of Navarre. Data from yield tables for both species were used. The effect of species proportion on total stand yield was assessed and transgressive overyielding was found for some mixing ratios. A data series on average stumpage price for both species in Spain over a 29-year period was compiled and the joint probability distribution of price data was used to generate 500 price scenarios. Different management alternatives based on species proportion and rotation age were considered and evaluated in terms of profitability and risk. Some management recommendations can be derived from the results obtained, which point at an optimum mixing ratio from 30% to 40% Scots pine and 70% to 60% European beech. Full article

An increasing amount of research is focusing on comparing productivity in monospecific versus mixed stands, although it is difficult to reach a general consensus as mixing effects differ both in sign (over-yielding or under-yielding) and magnitude depending on species composition as well as on site and stand conditions. While long-term experimental plots provide the best option for disentangling the mixing effects, these datasets are not available for all the existing mixtures nor do they cover large gradients of site factors. The objective of this study was to evaluate the effects and uncertainties of tree species mixing on the productivity of Scots pine–European beech stands along the gradient of site conditions in Europe, using models developed from National and Regional Forest Inventory data. We found a positive effect of pine on beech basal area growth, which was slightly greater for the more humid sites. In contrast, beech negatively affected pine basal area growth, although the effects switched to positive in the more humid sites. However, the uncertainty analysis revealed that the effect on pine at mid- and more humid sites was not-significant. Our results agree with studies developed from a European transect of temporal triplets in the same pine–beech mixtures, confirming the suitability of these datasets and methodology for evaluating mixing effects at large scale. Full article

Pine-spruce forests are one of the commonest mixed forest types in Europe and both tree species are very important for wood supply. This study summarized nine European studies with Scots pine and Norway spruce where a mixed-species stand and both monocultures were located in an experimental set-up. Overyielding (where growth of a mixed stand was greater than the average of both monocultures) was relatively common and often ranged between 0% and 30%, but could also be negative at individual study sites. Each individual site demonstrated consistent patterns of the mixing effect over different measurement periods. Transgressive overyielding (where the mixed-species stand was more productive than either of the monocultures) was found at three study sites, while a monoculture was more productive on the other sites. Large variation between study sites indicated that the existing experiments do not fully represent the extensive region where this mixed pine-spruce forest can occur. Pooled increment data displayed a negative influence of latitude and stand age on the mixing effect of those tree species in forests younger than 70 years. Full article