Tree pruning is done for several reasons: in young trees it is done to create a structure that will support the weight of the fruit, while in mature trees it is done to improve exposure to sunlight and to maintain a balance between vegetative and reproductive functions. Other purposes of pruning include reducing susceptibility or ease of pest and disease control, controlling growth and productivity of older trees through rejuvenating pruning, and reducing miscegenation.
Severe pruning can result in a significant loss of stored energy in plant tissues as carbohydrate-producing parts are removed. In olives, flowering starts in the summer/autumn of the previous year and flower bud differentiation begins in late winter after a period of reduced temperatures. Thus, the number of clusters of flowers is not related to pruning, and does not seem to increase fruit set, which depends on their quality.
After full flowering, there is a massive shedding of flowers and young fruits due to competition for stocks. Trees resume photosynthetic activity after the winter freeze, usually in April. Pruned trees do not necessarily have more energy available for higher fruit set rates, since they invest their resources in restoring photosynthetic capacity. The more severe the pruning, the greater the length of new shoots and the number of leaves per shoot, both of which are critical for the following year’s crop.
In Mediterranean regions and in rainfed orchards, available water limits the vegetative growth of the trees. The olive tree adapts to stress conditions through morphological and structural adaptations that reduce water loss. Pruning increases the root/shoot ratio and enhances the water conditions of the remaining foliage, allowing an increase in shoot length.
Heavy pruning reduces olive yield, but the trees show plasticity and can withstand light to moderate pruning without significant reduction in productivity. In irrigated orchards, pruned trees may face production difficulties compared to non-pruned trees, since leaf area index and radiation are important limiting factors.
The literature often mentions the advantages of pruning, but there is not enough evidence to show an increase in production due to pruning. Severe pruning causes less yield loss when carried out after an ‘on’ year, as the following year would be poor anyway. Conversely, in an ‘off’ year, severe pruning can make the situation worse.
Tightly pruned trees produce larger fruit, probably due to fewer fruits and fewer points of resource absorption. Harvesting can be difficult on unpruned trees due to dense foliage that is conducive to pests and diseases.
In conclusion, light to moderate pruning is beneficial and adaptable for a variety of purposes, while severe pruning should be avoided and performed only after an “on” year.
