Do you reap what you sow? Temporal dynamics of insect-relevant floral characteristics of flower strip mixtures

Abstract

The implementation of flower strips in agroecosystems is an effective measure to counteract the loss of biodiversity and enhance ecosystem services. Positive effects of flower strips on their main target group, flower-visiting insects, are assumed to be mediated by plant species composition and its associated floral characteristics (e.g., species richness and floral trait diversity). However, comprehensive studies investigating the establishment success and maintenance of different flower strip mixtures over time remain scarce. Therefore, we studied the performance of four different flower strip mixtures (two annual and two perennial) in a field experiment at three distinct study sites over three consecutive years. Here, we assessed their potential benefits in supporting flower visitors by evaluating the temporal dynamics of plant community composition and six insect-relevant floral characteristics. Moreover, we examined the impact of weed invasion on flower strips and how realized mixture performance under field conditions deviates from expected mixture performance. We found that both perennial flower strip mixtures undergo a significant community shift due to compositional changes in sown plant species after the year of sowing, strongly affecting mixture performance over time. Furthermore, deviation from expected mixture performance in both annual mixtures was largely explained by weed invasion, whereas in perennial mixtures, deviation was mainly caused by community changes in sown plant species (e.g., disproportional dominance of single species). The mixture with the highest initially sown species richness (PERENNIAL 51) outperformed all other mixtures after the year of sowing regarding taxonomic (species richness and Shannon diversity) as well functional floral characteristics (functional diversity and redundancy). Overall, we conclude that such mixtures (e.g., PERENNIAL 51) probably enhance the ability to support a diverse and abundant community of flower-visiting insects over several years and under varying site conditions, likely reflecting greater stability under environmental stressors such as drought and weed invasion.