The common agents of disease that affect adult honey bees include fungi, bacteria, protozoa, viruses, parasites and poisons. The gross symptoms displayed by affected adult bees are very similar, whatever the cause, making it difficult to ascertain the causes without microscopic identification of microorganisms or chemical analysis of poisons.[91] Since 2006, colony losses from colony collapse disorder (CCD) have been increasing across the world, although the causes of the syndrome are unknown.[92][93] In the U.S., commercial beekeepers have been increasing the number of hives to deal with higher rates of attrition.[94]
A large array of interactive physical, chemical, biological and human processes lead to what we define in this report as land degradation (Johnson and Lewis 2007138). The biological productivity, ecological integrity (which encompasses both functional and structural attributes of ecosystems) or the human value (which includes any benefit that people get from the land) of a given territory can deteriorate as the result of processes triggered at scales that range from a single furrow (e.g., water erosion under cultivation) to the landscape level (e.g., salinisation through raising groundwater levels under irrigation). While pressures leading to land degradation are often exerted on specific components of the land systems (i.e., soils, water, biota), once degradation processes start, other components become affected through cascading and interactive effects. For example, different pressures and degradation processes can have convergent effects, as can be the case of overgrazing leading to wind erosion, landscape drainage resulting in wetland drying, and warming causing more frequent burning; all of which can independently lead to reductions of the soil organic matter (SOM) pools as a second-order process. Still, the reduction of organic matter pools is also a first-order process triggered directly by the effects of rising temperatures (Crowther et al. 2016139) as well as other climate changes such as precipitation shifts (Viscarra Rossel et al. 2014140). Beyond this complexity, a practical assessment of the major land degradation processes helps to reveal and categorise the multiple pathways in which climate change exerts a degradation pressure (Table 4.1).
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