Introduction

Respectful pruning relies on understanding two physiological features of grapevines, as described below, and then transferring this knowledge to pruning operations. These grapevine features are distinct from those of other woody species due to its liana nature, which influences its specific wood characteristics and vascular system.

• Wound healing: the grapevine's natural healing process involves sealing off cuts to prevent dehydration and infection, forming a dry necrotic area known as a desiccation cone. When pruning cuts are made too close to living vascular structures that are necessary for maintaining sap flow in the future, the desiccation cone can disrupt this pathway¹. Thus, it is important to minimise the size of pruning wounds and maintain a sufficient distance from the vine's perennial structures (trunk, arms and spurs).
• Vascular structure: the grapevine's vascular system is composed of two longitudinal alignments along parallel axes (orthostichy), dividing the stem into two relatively independent halves². Given this, to avoid disrupting the sap flow³, pruning cuts should be made on one side of the vine's trunk, arm or spur, and cuts on opposite sides should be minimised to prevent decreased xylem conductance and premature structural aging^{4 5 6}.

In this context, although empirical observations support the importance of following respectful pruning principles, there is still very little systematic research validating their effectiveness. To enhance our knowledge on this topic, we established comparison plots in two newly planted vineyards. These plots, free from the influence of previous pruning practices, constitute a useful study case that, from our point of view, can also be informative for pruning in adult vineyards.

Experimental Setup

We studied two vineyards planted in 2019 with Tempranillo on Richter 110 rootstock in northern Spain. Vineyard #1 is located in Murieta, Navarra, while Vineyard #2 is situated in El Cortijo, La Rioja. Both vineyards have a Mediterranean climate, with Vineyard #1 being slightly cooler and wetter than Vineyard #2. Vineyard #1 used a drip irrigation system, whereas Vineyard #2 had no irrigation. More information on their characteristics can be found in Galar-Martínez et al. (2024)⁷.

The vineyards were trained using a spur-pruned bilateral cordon system with the same training schedule, as detailed in Figure 1. In each vineyard, three pruning styles were compared using a completely randomised design with three blocks. These pruning styles involved different degrees of compliance with the principles of respectful pruning described in the previous section.

• RESP, pruning cuts were always made leaving a portion of internode wood ≥ 1.5 times the diameter of the cut, choosing the preferential sap flow path, positioning wounds on the same side to compartmentalise their effects.
• AGGR, no stubs were left at cane shortening and very flat cuts were made for cane removal, without maintaining even the crown buds, and, when possible, the non-preferential sap flow path was followed.
• WIN, the common practices used by wine growers in the area were applied (representing an intermediate style between RESP and AGGR), leaving internode wood 0.7-1.0 times the diameter of the cut and not applying specific criteria for sap flow path.

These three pruning styles were applied at five stages of the training process (Dec 2019, May 2020, Dec 2020, Dec 2021 and Dec 2022), as shown in Figures 1 and 2.

Although it is difficult to evaluate the implication of pruning structures, plant growth can serve as a useful surrogate for assessing overall vine status. Thus, to evaluate the effects of the different pruning styles, we measured annual and accumulated vegetative growth. During the winter season, the number and diameter of canes were recorded. These measurements were then used to calculate the mean and total cane cross-sectional area (CCSA) for each vine. Pruning weight was also measured, considering it complementary to CCSA. When green pruning was performed (years 2021 and 2022), the weight of the shoots removed was also determined. All data were statistically analysed using ANOVA.

Results

Figure 3 demonstrates a significant effect of pruning style on vine vegetative development, as observed in cumulative shoot growth measured as cane cross-sectional area (CCSA) and spring and winter pruning weight. Vines pruned according to the RESP style consistently exhibited higher growth values across these three indicators compared to the AGGR and WIN styles. These differences were nearly always statistically significant, except for total CCSA and green pruning weight in one of the vineyards, where the same trend was observed, although it was not statistically significant. In contrast, no differences were found between AGGR and WIN styles for any growth variable.

Figure 3. Accumulated vegetative growth for the three pruning styles in the two plots. Cane cross-sectional area (top) and green (middle) and winter (bottom) pruning weight.

The differences in growth should not be interpreted as positive or negative from a grower’s perspective during the training period. Rather, they serve as surrogate indicators of vine physiological status. In this context, we should interpret greater growth as reflecting a better vine status, suggesting that vines under the RESP style are in a more favourable condition.

It is also worth mentioning that no significant differences between AGGR and WIN styles were observed under our experimental conditions. These pruning styles had minimal differences in sap flow management between them, differing primarily in the stub length in shoot cuts. Thus, we can hypothesise that, under the study conditions, maintaining the sap flow pathway plays a more significant role than stub length in grapevine development during the initial years. Similarly, the fact that the differences were more pronounced in the less vigorous vineyard indicates that the negative effects of not adhering to respectful pruning principles become apparent earlier in less vigorous conditions, although such effects could appear in more vigorous vineyards over time.

In summary, our results demonstrate that respectful pruning, while emphasising the importance of sap flow and minimising unnecessary cuts, can be an effective strategy for maintaining optimal vine health and could contribute to mitigating vine decline. Lastly, we would like to highlight that, while these findings are based on young vines, the principles of respectful pruning are equally applicable to spur and cane structures in adult vineyards. While the evidence obtained in our study cannot be directly transferred to adult vineyards, we hope our ongoing trials will provide concrete results in a few years time.

Acknowledgements: This work was carried out within the EFA324/19 VITES QUALITAS and EFA033/01 VITRES projects, which are both part of POCTEFA, a European cross-border cooperation programme created to promote the sustainable development of the border area between Spain, France and Andorra (POCTEFA 2014-2020 and POCTEFA 2021-2027). These projects were co-financed (65 %) by the European Regional Development Fund (ERDF) through the Interreg V-A Spain-France-Andorra programme.