Thursday, September 13, 2012

Pondering Pollination

We all know that bees are an important part of our landscape. They provide pollination services to our agricultural sector worth billions of dollars each year; a study by the University of California, Berkeley calculated that the economic value of pollination from wild, free-living bees in California alone is $937 million to $2.4 billion per year[1].
However, crisis looms as bee colony numbers are dropping due to habitat loss, disease and pesticide use. Intensive, monoculture agriculture tends to reduce bee numbers due to the removal of natural habitats where bees would normally feed and nest. For example, pollen from wild flowers found in forests and grasslands provides the proteins and nutrients that bees need to grow and develop[2]. Further, beehive colonies, which farmers introduce for their pollination services, have been experiencing extremely high losses worldwide[3] and in some cases, beekeepers have reported losing 30 – 90 % of their hives. The most likely cause of this so-called ‘colony collapse disorder’ is a virus which is spread by parasitic Varroa mites, originally native to Asia. The mites pass deformed wing virus (DWV) on when they feed on honey bees, but a particularly deadly strain of DWV appears to have become dominant, causing it to become “one of the most widely distributed and contagious insect viruses on the planet”[4].
So what can farmers do to improve the number of pollinating bees on their land? One answer lies in the protection of native bee habitats, such as trees within neighboring forest patches and agroforestry systems. Tropical forests provide habitat to a diverse range of native pollinator species including bees, yet they are being destroyed at an alarming rate; figures from the Food and Agricultural Organization of the UN (FAO) estimate that from 2000 to 2005, 10.4 million hectares of tropical forest were permanently destroyed each year[5]. Furthermore the FAO deforestation estimates are in fact lower than actuality due to the fact that forest degradation is not accurately estimated. So, in truth, the loss of forest habitat is significantly higher. Research has shown that plantation forests, which often contain non-native tree species and tend to be low in biodiversity, do not provide the same variety or abundance of native bee species, and therefore have a far weaker effect on crop production than do native forests[6].
As well as the protection of native forests that surround agricultural lands, maintaining diverse agroforestry systems can provide a solution to pollinator problems for crops such as cacao and coffee, which flourish under a canopy of shade trees. The main pollinators of cacao are midges, which need a wide range of plant species and decaying matter on the ground as well as a humid environment, in order to flourish[7]. Cacao is strictly dependent on insects for pollination, so maintaining a good habitat for its pollinating midges is extremely important for ensuring good yields. Leaving leaf litter and rotting fruit on the ground provides the necessary breeding ground for midges, but if farmers remove this litter layer, then having diverse forest remnants close to cacao farms helps to support their populations[8].
For coffee, bees are the main pollinator, and have been found to increase in abundance (the number of bees) and species richness (the number of different bee species) the closer a farm is to native forest[9] as well as when coffee is grown under a canopy of shade. Of further benefit to farmers, research has shown that when coffee farms are located close to native forest patches they can have higher coffee quality and quantity[10]. In addition, shade coffee farms have been found to support native bee populations which then pollinate native trees in surrounding forest patches, thereby preserving the genetic diversity of these forest remnants[11].
The California native bee species Bombus vosnesenskii, the yellow-faced bumble bee, forages on almond flowers that are located right next to rangelands habitat. (Alexandra Maria-Klein photo)
    It is clear that in today’s industrialized agricultural landscape, the preservation of a diverse matrix of native forest and grassland habitats is essential for the conservation of our important pollinator species, which provide such a valuable ecosystem service. Crops such as cacao and coffee, which flourish under a canopy of shade, can therefore enhance pollinator numbers by being grown as diverse agroforestry systems. Aside from providing pollinator habitat, the benefits of agroforestry systems are numerous, including watershed protection, reduced soil erosion and maintenance of soil fertility. For these and many other reasons, agroforestry is promoted as a more sustainable method of production.

Martin Noponen, International Forest Carbon Project Manager

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