1,721,079 research outputs found
Invasion drives plant diversity loss through competition and ecosystem modification
No full text1. Although invasive plants increasingly contribute to the current biodiversity crisis, the mechanisms through which they impact native communities are still poorly understood. Community ecology theory has emphasized direct competitive displacement over common resources, but invasion-driven ecosystem modifications, such as altered soil pH, might also have consequences for plant diversity. However, the relative importance of ecosystem modification compared to direct resource competition has rarely been tested.
2. Here we studied the invasive vine Vincetoxicum rossicum across invaded meadows in southern Ontario, Canada. In each meadow site, we quantified: 1) the strength of impact on the resident plant community, 2) the potential for competition with resident species (as the degree of niche-dissimilarity and competitive superiority to the residents based on their functional traits), and 3) the amount of ecosystem modification related to invasion.
3. We found that impacts on plant biodiversity were more negative where the invader had greater potential to competitively displace species (because it had a similar niche as the residents or was competitively superior), but also where it strongly altered soil N pools, moisture and pH.
4. Synthesis. Our case study suggests that, while competition is undoubtedly an important driver of invasion impact, ecosystem modifications can have cascading effects on plant communities, thereby magnifying the impacts of biological invasions
Biophysical Drivers of Tree Crop Performance in Shade Agroforestry Systems: The Case of Coffee in Costa Rica
Full text linkAgroforestry production methods present one option for addressing growing concerns about the long term sustainability of intensive coffee production techniques. A study was designed to compare the effects of fertilization and shading from two leguminous species, Erythrina poeppigiana and Chloroleucon eurycyclum, on coffee grown at a Costa Rican research site. Coffee below biannually pruned, conventionally fertilized Erythrina exhibited the highest photosynthetic performance under both low and high light levels as well as greater biomass and higher N concentration. Soil P did not affect coffee performance, although shade trees on sites with higher soil P fixed more N compared to trees grown on low P sites, most of which were not found to be fixing. Results suggest shade mechanisms are the most important drivers of coffee adaptation in coffee agroforestry systems, though proper soil nutrient management and legume species pairing also appear to augment coffee response to microclimate conditions.MAS
Farmer Advice Network Ties as Predictors of Organizational Leadership
No full textIncreasingly, more farmers are turning to agroforestry, or the integration of trees with agriculture, to diversify their livelihoods while contributing to environmental sustainability. Despite the prominence of farmer groups in the diffusion of agroforestry, few studies have examined predictors of organizational leadership in these groups. By applying social exchange theory and principles of leadership theory, this study used social network analysis to investigate agroforestry advice ties between members of a farmer group in the Ayeyarwady delta region of Myanmar. Advice-seeking ties were found to be influential in predicting leadership status. Actors who received more advice requests and had more frequent interactions through these requests were more likely to be organizational leaders. Also, actors with more ties to elicit and provide advice were more likely to report higher levels of socio-cultural well-being. Study findings suggest farmer groups are well-suited to serve as learning and resource platforms for the adoption of agroforestry.M.A
Root Ecology for Sustainable Agroecosystems: Intraspecific Variation in a Pan-Tropical Tree Crop
No full textAgroecosystems that rely on higher levels of biodiversity and fewer inputs to sustain both crop production and ecosystem function require a dramatic shift away from a one-size-fits-all approach to management. Notably, this means that phenotypic expression of plants on farms cannot be assumed constant, as biotic and abiotic conditions in low-input, biodiverse agroecosystems are complex. To accurately assess and predict plant and ecosystem function in these agroecosystems, we require a more robust understanding of the drivers and consequences of intraspecific variation in plants. This includes root systems, which are arguably understudied but have a critical role in resource acquisition and use. To this end, I carried out research on the root systems of an economically important and widely cultivated tree crop,Ph.D
Nutrient Availability in the Rhizosphere of Coffee: Shade-tree and Fertilization Effects
Full text linkShade tree incorporation is beneficial in coffee cropping systems under sub-optimal conditions. This study was performed in lowland Costa Rica, at a 12-year-old experimental coffee farm. The main objective was to compare the effect of a nitrogen fixing shade tree, Erythrina poeppigiana, on nutrient availability in the rhizosphere of coffee under conventional fertilization. Accumulation of nutrients (mineral N, available P, and exchangeable base cations) in rhizosphere relative to bulk soil was greater under shade than full sun. Low nitrate availability in rhizosphere soil of full sun coffee was explained by root-induced acidification relative to bulk soil, as abundance of ammonia-oxidizing bacteria (AOB), which mediate nitrification, were positively correlated with pH. Organic fertilization enhanced AOB abundance and altered soil bacterial community structure relative to conventional fertilization. This study indicates clear effects of shade-tree presence on nutrient availability at the micro-scale, management of which is critical for stability of coffee agroforestry systems.MAS
Biophysical Drivers of Tree Crop Performance in Shade Agroforestry Systems: The Case of Coffee in Costa Rica
No full textAgroforestry production methods present one option for addressing growing concerns about the long term sustainability of intensive coffee production techniques. A study was designed to compare the effects of fertilization and shading from two leguminous species, Erythrina poeppigiana and Chloroleucon eurycyclum, on coffee grown at a Costa Rican research site. Coffee below biannually pruned, conventionally fertilized Erythrina exhibited the highest photosynthetic performance under both low and high light levels as well as greater biomass and higher N concentration. Soil P did not affect coffee performance, although shade trees on sites with higher soil P fixed more N compared to trees grown on low P sites, most of which were not found to be fixing. Results suggest shade mechanisms are the most important drivers of coffee adaptation in coffee agroforestry systems, though proper soil nutrient management and legume species pairing also appear to augment coffee response to microclimate conditions.MAS
Beyond Yield Alone: Functional Traits of Regionally Adapted Daucus carota (carrot) Varieties on Organic Farms
Full text linkWhile agronomic traits have been widely studied, crop functional trait expression and variation among regionally and broadly adapted seeds have not. I measured 14 above- and below-ground functional traits in six varieties of Daucus carota (carrot) grown at ten organic farms across Canada to test whether seed regionality corresponds to differential expression of functional traits. Environmental conditions at the farm level over varietal difference explained variation in trait expression. Leaf traits trade off in patterns predicted by the Leaf Economics Spectrum. Environmentally-patterned variation in trait expression differed between varieties. Regionally adapted varieties expressed higher resource acquisitive traits when grown outside their local region, and while hybrid varieties performed more consistently between sites, hybrids expressed higher resource acquisitive traits when grown in western regions. By testing trait tradeoffs between varieties, this research addresses a knowledge gap regarding the ecological consequences of crop functional trait expression, with implications for multiple end users.M.Sc
Development Interventions and Agricultural Adaptation in a Changing Environment: A Social Network Analysis of Farmer Knowledge Transfer in Ghana
Full text linkFormal social ties play an important role in agricultural knowledge exchange, particularly in developing-country agriculture with high exposure to development interventions. However, little is known about informal agrarian knowledge transfer in such an institutional agricultural information landscape and the consequences in terms of smallholder farm management in regions undergoing environmental change. Using a social network approach, I chart the structure of agrarian knowledge networks in six communities which have been differentially exposed to agriculture development intervention in the Brong Ahafo and Ashanti regions of Ghana. Farmer network size, density and composition were distinctly variable, with development project affiliated and male farmers tending toward larger networks and engaging in more diverse agricultural production. Furthermore, agriculture-related knowledge sources were dependent on the type of crop species produced. As promotion of diverse agriculture systems continues as a response to environmental change, understanding such social and agroecological complexities will be important for effective agriculture interventions.M.A
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
- …
