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on the safety net provided by natural ecosystems in terms of food
security and sustained access to fuel, medicinal products, con-
struction materials and protection from natural hazards such as
storms and floods (MA, 2005). With the number of IAS in ter-
restrial ecosystems expected to increase, these impacts are likely
to worsen and hamper efforts to meet the growing demands for
food (FAO, 2008). In addition, they will likely be exacerbated
further by climate change (Pyke
et al
., 2008).
Alien invasive weeds and pathogens are estimated to be respon-
sible for about 8.5% and 7.5% in yield reduction, respectively,
equivalent to US$24 billion and US$21 billion of a crop value of
US$267 billion (USBC, 2001; Pimentel
et al
., 2004; Rossman,
2009). Different estimates range from US$1.1–US$55 billion
in losses every year, corresponding to annual losses of 0.4%
(OTA, 1993) to 17% (Pimentel
et al
., 2004; 2005; Rossman,
2009). This does not include increased expenses for more me-
chanical or pesticide weed control or losses from invasive in-
sects (about 5%) or diseases of livestock.
The spread of invasive species frequently occurs in the provi-
sion of humanitarian emergency food aid. Lower sanitary and
phytosanitary standards apply to food aid, particularly emer-
gency food aid, so it may not be surprising that the introduc-
tion and spread of potentially invasive species would follow
the distribution of emergency relief. For example:
The grey leaf spot (
Circosporda zeae-maydis
) is thought to
have been introduced into Africa via US food aid shipments
of maize during the 1980’s (Ward
et al
., 1999). It has subse-
quently spread into all the main maize-growing areas of Afri-
ca, and its effect on yields has been such that it is now argued
to pose a serious threat to food security (Rangi, 2004).
The parthenium weed (
Parthenium hysterophorus
) from Mex-
ico arrived in Africa through grain shipments for famine re-
lief to Ethiopia, where it has earned a local indigenous name
which translates to “no crop” (Chenje and Katerere, 2006).
Therefore, the spread of plant pests, weeds and animal dis-
eases across physical and political boundaries threatens food
security and represents a global public “bad” that links all
countries and all regions.
Current and future global food crises may also
facilitate the spread of invasive species