de Bie, Kees 
  
4.2 Age of trees, biennial bearing and canopy cover 
The age of mango trees in the surveyed orchards varied from 3-35 years (average 
of 15 years). Two orchards had only trees less than 5 years of age and did not 
produce any fruits. Purseglove (1977) states that mango starts bearing fruit 
around its fifth year and comes to full production at the age of 20. Farmers (33x) 
reported ages of 3.5 to 8 years with a median of 5 years (Figure 4 left). The two 
orchards with an alleged age of less that 5 years were excluded from further 
analysis. Linear, regression with the remaining sites produced the following 
equation (Adj.-R? of 2.596 and a regression coefficient with a non-significant P): 
Ln(Yield+1) = -0.81 + 0.87 * Ln (Tree Age); see Figure 4 middle (n245). 
Mangos have the tendency to biennial fruit bearing and may only produce one 
good crop every 3-4 years depending on weather conditions; they require strongly 
marked seasons and dry weather for flowering and fruiting (Purseglove 1977). The 
pattern of yields over the years was not studied in detail because the reliability of 
information on annual sale proceeds supplied by farmers for 5 individual years 
was considered poor. Instead, estimates of average sale proceeds for the entire 5- 
year period were collected (Figure 4 right). Both sets of yield data are significantly 
related (Adj. -R? of 3296), although the 1993 sale proceeds were on average lower 
than those obtained during the preceding 5 years. In 1993, several sites had a 
relatively good yield (8x) while others produced relatively less (11x); see the 9996 
confidence lines in Figure 4. This qualitative information is coded as 1, 0, and -1 
(relatively good, average, and poor respectively), and used as such during model 
formulation. 
The canopy cover of orchards (including the possible contribution by “other” trees) 
varied from 10 to 95% of the ground surface (median of 75%). The canopy cover 
data are not related to tree age (correlation of 8%) or to yield (Adj.R? of 3%); cover 
data of individual mango trees were not collected. Canopy cover is further 
discussed under ‘Weeding’ (page 9). 
  
  
  
20 E 6 T T T 6 T T 
T ra T T T ] sé 
Regression line with 
9996 confidence lines di. 
  
1 
Ce 
T 
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15r 
   
            
  
  
  
  
  
  
  
  
  
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E = 5 2” o 
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5- 2 = 
$ 8 A ar e 
105 1N : OR. | 
ge @ eo de $ © 0 ee i 
3 4 5 6 7 8 9 0 10 20 30 40 0 2 4 6 
Fruit bearing age of mango (yrs) Age of mango trees Ln(1987-92 Yields + 1) 
Figure 4. Impacts of tree age and biennial bearing on mango yields. 
  
International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B7. Amsterdam 2000. 
327