117
pollinators, while a large number of staples rely on wind- or self-pollination. For
this reason, perennials’ yields may be more susceptible to the vagaries of weather
that influence the behaviour of animal pollinators (Garibaldi et al. 2011).
Our analysis (Fig. 10.2a) indicates that for individual countries in eastern and
southern Africa the tested crops with the least stable yields vary, depending on the
country. Of the 68 country–crop combinations that we analysed, however, while 21
combinations involved perennial crops (31%) and the remainder were for annuals,
only 2 of the 20 least stable country–crop combinations involved perennial species
(10%), suggesting that perennial crops overall display more stable production characteristics than annuals (see also Table 10.1). This is supported by an analysis of
absolute deviations in transformed year-on-year yield changes that averages results
across nations and crops, where overall deviations are lower for perennials than
annuals (Fig. 10.2b). Our current analysis does not further explore the reasons for
this stability; but, in some cases, it may reflect greater investments in production for
what are sometimes valuable perennial commodities rather than intrinsic differences in their stability compared to annuals.
As expected, based on different production ecologies, individual country profiles
of crops (Fig. 10.2a) indicate that directions in yield change for any particular yearto- year interval vary depending on the crop. This raises the prospect of actively
designing compensatory crop combinations, where crops with different responses
are deliberately combined to support resilience to variable seasonal conditions. To
explore this issue further, we took the two countries with the highest number of
crops, Kenya (N = 8) and Tanzania (N = 10) and, for each crop–crop combination in
each nation, regressed transformed fractional year-on-year yield changes against
each other. The results demonstrated that most comparisons had positive associations (40 of all comparisons, summing for both countries), indicating that yields for
a pair of crops increase or decrease in the same direction over tested yearly intervals. However, in 33 cases the association was negative, indicating that yield for one
member of a pair of crops increased and yield for the other decreased over yearly
intervals.
The majority of positive associations indicates that most crops respond similarly
to climatic conditions for a particular season; but the negative associations also
indicate the possibilities for deliberate planning of compensatory crop combinations on a country-specific basis. Applying an initial probability test to regressions
of paired comparisons only revealed a few to be of statistical significance (P ≤ 0.05)
(Fig. 10.3); but, in the case of Tanzania, the one significant negative correlation
observed was for an annual-perennial crop pair (potato–coffee, Fig. 10.3b). This
raises the prospect that perennial crops could have a particularly important role in
defining compensatory crop combinations. A more complete analysis would, however, compare a wider range of countries and crops. In addition, it would explore
weather data over the time period to try and identify the causal factors behind yield
changes for specific crops, to establish the mechanisms involved and possible stabilising responses on an individual crop basis.
Because of the caveats associated with the use of FAOSTAT data sets for such
analyses (Dawson et al. 2018a), alternative across-species crop production data sets
10 Delivering Perennial New and Orphan Crops for Resilient and Nutritious Farming…
pollinators, while a large number of staples rely on wind- or self-pollination. For
this reason, perennials’ yields may be more susceptible to the vagaries of weather
that influence the behaviour of animal pollinators (Garibaldi et al. 2011).
Our analysis (Fig. 10.2a) indicates that for individual countries in eastern and
southern Africa the tested crops with the least stable yields vary, depending on the
country. Of the 68 country–crop combinations that we analysed, however, while 21
combinations involved perennial crops (31%) and the remainder were for annuals,
only 2 of the 20 least stable country–crop combinations involved perennial species
(10%), suggesting that perennial crops overall display more stable production characteristics than annuals (see also Table 10.1). This is supported by an analysis of
absolute deviations in transformed year-on-year yield changes that averages results
across nations and crops, where overall deviations are lower for perennials than
annuals (Fig. 10.2b). Our current analysis does not further explore the reasons for
this stability; but, in some cases, it may reflect greater investments in production for
what are sometimes valuable perennial commodities rather than intrinsic differences in their stability compared to annuals.
As expected, based on different production ecologies, individual country profiles
of crops (Fig. 10.2a) indicate that directions in yield change for any particular yearto- year interval vary depending on the crop. This raises the prospect of actively
designing compensatory crop combinations, where crops with different responses
are deliberately combined to support resilience to variable seasonal conditions. To
explore this issue further, we took the two countries with the highest number of
crops, Kenya (N = 8) and Tanzania (N = 10) and, for each crop–crop combination in
each nation, regressed transformed fractional year-on-year yield changes against
each other. The results demonstrated that most comparisons had positive associations (40 of all comparisons, summing for both countries), indicating that yields for
a pair of crops increase or decrease in the same direction over tested yearly intervals. However, in 33 cases the association was negative, indicating that yield for one
member of a pair of crops increased and yield for the other decreased over yearly
intervals.
The majority of positive associations indicates that most crops respond similarly
to climatic conditions for a particular season; but the negative associations also
indicate the possibilities for deliberate planning of compensatory crop combinations on a country-specific basis. Applying an initial probability test to regressions
of paired comparisons only revealed a few to be of statistical significance (P ≤ 0.05)
(Fig. 10.3); but, in the case of Tanzania, the one significant negative correlation
observed was for an annual-perennial crop pair (potato–coffee, Fig. 10.3b). This
raises the prospect that perennial crops could have a particularly important role in
defining compensatory crop combinations. A more complete analysis would, however, compare a wider range of countries and crops. In addition, it would explore
weather data over the time period to try and identify the causal factors behind yield
changes for specific crops, to establish the mechanisms involved and possible stabilising responses on an individual crop basis.
Because of the caveats associated with the use of FAOSTAT data sets for such
analyses (Dawson et al. 2018a), alternative across-species crop production data sets
10 Delivering Perennial New and Orphan Crops for Resilient and Nutritious Farming…