Birgit Nordt, Isabell Hensen, Solveig Franziska Bucher, Martin Freiberg, Richard B. Primack, Albert-Dieter Stevens, Aletta Bonn, Christian Wirth, Desiree Jakubka, Carolin Plos, Maria Sporbert, Christine Römermann

Four phenological stages observed on common peony (Paeonia officinalis) by the PhenObs network

Across the globe, climate change is altering the timing of biological events, especially leaf out, flowering, fruiting, and leaf senescence. These changes have important implications for how ecosystems function and how species interact. Much of the botanical research on biological timing, also known as phenology, particularly on leaf out in spring and leaf senescence in autumn, has been conducted on tree and shrub species. Far less is known about how herbaceous wildflowers respond to climate change, even though they represent the majority of plant diversity. To fill this gap, we established an international network of botanical gardens to monitor wildflower phenology using a standard methodology that is suitable for a wide range of growth forms. The goal is to help predict effects of a warming climate on wildflower phenology and ecologically related animal species such as the insects that pollinate their flowers and the birds that eat their fruits. 

In our paper, we present the new PhenObs initiative –  a group of botanical gardens acting as a global phenological observation network for wildflowers. We will also gather additional data on plant traits and site conditions. We will use the results to answer the following questions:

A.     How does climate change affect the phenology of leaf out, flowering, fruiting, and leaf senescence for a wide range of wildflower species.

B.     How does a plant’s characteristics, such as plant height, the leaf size, and the habitat where it grows, affect its phenology?

C.     As wildflowers change their phenology due to climate change, how will that affect their ecological relationships with other species? For example, if a species is now flowering earlier in the spring than in the past, will that affect its ability to be pollinated by a specialized pollinator?

In this first paper of the network, we report on a two-year study involving 199 wildflower species at four German botanical gardens. Based on our experiences so far, we propose a simple scoring system to monitor just three vegetative stages (“initial growth”, “leaves unfolding” and “senescence”) and two reproductive stages (“flowers open” and “ripe fruits”) to fully capture wildflower phenology. We provide an illustrated monitoring protocol as a supplement to the manuscript.

Read the article in full here.