lunes, 15 de mayo de 2017

Globally, small and medium farms (≤50 ha) produce 51–77% of nearly all commodities and nutrients


Information about the global structure of agriculture and nutrient production and its diversity is essential  to improve present understanding of national food production patterns, agricultural livelihoods, and food chains, and  their linkages to land use and their associated ecosystems services. Here we provide a plausible breakdown of global  agricultural  and  nutrient  production  by  farm  size,  and  also  study  the  associations  between  farm  size,  agricultural   diversity, and nutrient production. This analysis is crucial to design interventions that might be appropriately targeted  to promote healthy diets and ecosystems in the face of population growth, urbanisation, and climate change. 

We  used  existing  spatially-explicit  global  datasets  to  estimate  the  production  levels  of  41  major  crops,   seven livestock, and 14 aquaculture and fish products. From overall production estimates, we estimated the production  of vitamin A, vitamin B₁₂, folate, iron, zinc, calcium, calories, and protein. We also estimated the relative contribution  of farms of different sizes to the production of different agricultural commodities and associated nutrients, as well as  how  the  diversity  of  food  production  based  on  the  number  of  different  products  grown  per  geographic  pixel  and   distribution of products within this pixel (Shannon diversity index [ H ]) changes with different farm sizes.

Globally,  small  and  medium  farms  (≤50  ha)  produce  51–77%  of  nearly  all  commodities  and  nutrients   examined here. However, important regional differences exist. Large farms (>50 ha) dominate production in North  America, South America, and Australia and New Zealand. In these regions, large farms contribute between 75% and  100% of all cereal, livestock, and fruit production, and the pattern is similar for other commodity groups. By contrast,  small  farms  (≤20  ha)  produce  more  than  75%  of  most  food  commodities  in   Sub-Saharan  Africa,   Southeast  Asia,   South Asia, and China. In Europe,  West Asia and  North Africa, and  Central America, medium-size farms (20–50 ha)  also contribute substantially to the production of most food commodities. Very small farms (≤2 ha) are important and  have local significance in  Sub-Saharan Africa,  Southeast Asia, and  South Asia, where they contribute to about 30% of  most food commodities. The majority of vegetables (81%), roots and tubers (72%), pulses (67%), fruits (66%), fish  and livestock products (60%), and cereals (56%) are produced in diverse landscapes ( H >1·5). Similarly, the majority  of  global  micronutrients  (53–81%)  and  protein  (57%)  are  also  produced  in  more  diverse  agricultural  landscapes   ( H >1·5).  By  contrast,  the  majority  of  sugar  (73%)  and  oil  crops  (57%)  are  produced  in  less  diverse  ones  ( H ≤ 1·5),  which  also  account  for  the  majority  of  global  calorie  production  (56%).  The  diversity  of  agricultural  and  nutrient   production diminishes as farm size increases. However, areas of the world with higher agricultural diversity produce  more nutrients, irrespective of farm size.

Our results show that farm size and diversity of agricultural production vary substantially across regions and  are  key  structural  determinants  of  food  and  nutrient  production  that  need  to  be  considered  in  plans  to  meet  social,   economic, and environmental targets. At the global level, both small and large farms have key roles in food and nutrition  security. Efforts to maintain production diversity as farm sizes increase seem to be necessary to maintain the production of  diverse nutrients and viable, multifunctional, sustainable landscapes. 

domingo, 7 de mayo de 2017

Trade-Offs Between Plant Growth and Defense Agains
Insect Herbivory: An Emerging Mechanistic Synthesis

Costs of defense are central to our understanding of interactions between organisms and their environment, and defensive phenotypes of plants have long been considered to be constrained by trade-offs that reflect the allocation of limiting resources. Recent advances in uncovering signal transduction networks have revealed that defense trade-offs are often the result of regulatory “decisions” by the plant, enabling it to fine-tune its phenotype in response to diverse environmental challenges. We place these results in the context of classic studies in ecology and evolutionary biology, and propose a unifying framework for growth–defense trade-offs as a means to study the plant’s allocation of limiting resources. Pervasive physiological costs constrain the upper limit to growth and defense traits, but the diversity of selective pres- sures on plants often favors negative correlations at intermediate trait levels. Despite the ubiquity of underlying costs of defense, the current challenge is using physiological and molecular approaches to predict the conditions where they manifest as detectable trade-offs.