Developing perennial wildflower strips for use in Mediterranean orchard systems

Abstract

To support sustainable food production and the delivery of ecosystem services through ecological intensification, wildflower strips have become a popular strategy. Despite their success in temperate orchard systems, they remain understudied in Mediterranean ecosystems, which poses a significant barrier to uptake. In order to further promote their adoption, seed mixes must be optimised for commercial orchard systems and for the Mediterranean climate. Plant species should be selected for their consistent performance, whilst the availability of resources for ecosystem service providers determines the quality of the wildflower strip. In this study, the suitability of 12 native perennial forbs and two tussock-forming grass species for wildflower strips in commercial Citrus orchards was assessed over a 3-year period. Distinct resources for natural enemies according to the different plant growth stages were used an indicator of wildflower strip quality. The wildflower strips were managed under two different cutting strategies: (i) standard management, in which wildflower strips were cut once annually in February, and (ii) active management, in which wildflower strips were cut two additional times each year. The establishment and success of the sown species were compared. The influence of wildflower strips and their management on plant species richness, community structure, and the provision of resources was compared with a control treatment, in which alleyways were managed conventionally by cutting any naturally occurring vegetation to a height of ≤5 cm, four to five times annual. For the first time, the performance of native perennial plant species has been assessed in Mediterranean orchard systems and a seed mix developed for targeting pest regulation services. The wildflower strips were successful in increasing plant species richness and the available resources expected to support natural enemies. However, only wildflower strips managed with cutting once annually enhanced vegetation cover relative to the control, whilst extending the flowering period. This study therefore provides crucial tools for the further development of sustainable approaches to food production in Mediterranean orchard systems.

Keywords: Citrus; ecosystem services; habitat management; mowing; orange orchards; plant provided resource.

FIGURE 1

Schematic diagram of a 0.5 ha experimental plot, consisting of eight rows of orange trees and seven alleyways. Wildflower strips were established in alternate alleyways. Black dashed lines delimit the surveying areas.

FIGURE 2

Mean species richness between (a) the three treatments; control, standard management wildflower treatment (SMWT) and active management wildflower treatment (AMWT), summed across Years and (b) study years, 1 (2017), 2 (2018) and 3 (2019), summed across treatments. Error bars represent ±1 SEM. Superscripts represent significant differences (Tukey's pairwise contrasts; p < .05).

FIGURE 3

Biplot with 10 indicator species based on the negative binomial latent variable model (boral). The points correspond to site indices. Points are coloured to visualise community separation according to treatment, where control are light blue triangles, standard management wildflower treatment (SMWT) are dark blue circles, and active management wildflower treatment (AMWT) are green rhombi.

FIGURE 4

Percentage cover scores of sown species in response to management (standard management wildflower treatment: SMWT or active management wildflower treatment: AMWT) across the 3‐year study. The coefficients from mvabund model are plotted; no difference from the mean is white, an increase is green and a decrease is pink. The scale represents the mean change in the response from the predictor and therefore denotes the magnitude of the response, with the sign indicating direction.

FIGURE 5

Mean height of vegetation in the alleyways between rows of Citrus trees in response to management: control and establishing wildflower strips EWS during Year 1, (a) and control and standard management wildflower treatment (SMWT) and active management wildflower treatment (AMWT) during Years 2 and 3, (b) Structural heterogeneity of the alleyway vegetation, calculated as the coefficient of variation of height, in response to management: control and EWS during Year 1, (c) and control and SMWT and AMWT during Years 2 and 3, (d) Where box represents the interquartile range and the notch indicates the 95% confidence interval about the median.

FIGURE 6

Plant resource index (%) by resource class, bare ground, leaf litter, vegetative forbs, vegetative grasses, budding forbs, budding grasses, flowering forbs, flowering grasses, dehiscent forbs and dehiscent grasses (irrespective of being sown/unsown) between treatments during (a) the establishment Year 1 (2017), (b) Year 2 (2018) and (c) Year 3 (2019). Error bars represent ±1 SEM. Superscripts denote significant differences in the plant resource index between treatments (Tukey's pairwise contrasts; p < .05).

FIGURE A1

Location of the three orchards in relation to (a) the Iberian Peninsula and (b) the province of Huelva, south‐west Spain.

FIGURE A2

Treatment plots; (a) control treatment, managed conventionally by cutting throughout the season to keep the vegetation low; (b) standard management wildflower treatment, cut once annually, allowed to grow tall and complex; (c) active management wildflower treatment, cut three times annually to approximately 10 cm to encourage spillover of natural enemies onto the crop.