The flower strip dilemma (FSD): An overlooked challenge in nature conservation and a possible first step towards a solution by combining different aged flower strips

Abstract

Perennial flower strips on high-yield soils may lose most of their flowering aspect during aging. This creates a dilemma, referred to herein as flower strip dilemma (FSD): On the one hand the number of pollinating and non-pollinating insects increases during the short-term aging of flower strips, on the other hand, perennial flower strips of a certain age often become grass dominated and are therefore less attractive to many species. Thus, the question arises when there is the most appropriate time to create a new flowering strip to support as many species as possible. To find a way out of the described dilemma, we focused on carabid beetles in two different aged types of flower strips. Many ground beetle species (carabids) are important pest antagonists in intensively cultivated farmland and can be promoted by flower strips. The creation of combined wildflower strips, consisting of wildflower strips of different ages, might be a measure to compensate the loss of species richness and abundance during flower strip aging. To study the impact of combined wildflower strips on non-pollinating insects, we recorded carabid beetles as a model guild in one- and three-year-old wildflower strips as well as in combined wildflower strips, and examined the results regarding species richness, abundance and functional traits. We show that combined wildflower strips increase the richness of carabid beetle species significantly beyond simple aging effects. Furthermore, the dominating functional traits of carabids differ with the type of flower strip: In combined wildflower strips significantly more macropteric and herbivorous carabid species were found, as well as carabids with imaginal hibernation. The study shows that the creation of combined wildflower strips can increase species richness in carabids by buffering possible negative effects in either young or old flower strips regarding their specific attractiveness for different species or guilds respectively. As a recommendation, farmers should create at least part of their flower strips in combination, so that a greater effect on increasing biodiversity can be achieved. Further investigations should make suggestions for how long a flower strip should exist according to different taxa to make the problem of the FSD more visible.