Bee Research on Green Roofs in Asia, Europe, and North America by Michaela Hofmann and Susanne S. Renner

March 7, 2018 at 5:34 pm

A Personal View, by Michaela Hofmann

When you grow up on a farm, moving into a big city like Munich (with 1.5 million inhabitants) can feel like moving into a concrete desert.  However, only at first glance.

Between building fronts and paved roads, nature has gained a foothold.  But it was only when I began working on urban bees for my doctoral research that I became aware of a huge additional green space in modern cities, namely rooftops.

 Bee Research Green Roofs Asia Europe North America Hofmann Renner

One of the nesting aids that the researchers were trying out on the ground. Such sand heaps (even much smaller ones) would be a huge help for bees. Photo by Michaela Hofmann.

It is now mandatory for many types of buildings to have green roofs, and the aesthetic and climate benefits of this type of new urban habitat are obvious and well-documented.  But are there benefits for wild bees, the topic of my research?

The literature about effects of green roofs on biodiversity is surprisingly limited.  My search for studies about wild bees on green roofs in Asia, Europe and North America revealed that so far, only 35 studies (worldwide) have been carried out, which have identified 236 species that use man-made green roofs as foraging or nesting ground.  For comparison, there are 19,700 known bee species, and Germany alone has over 570 species.

The percentage of cavity-nesting bees on roofs is higher than that on nearby ground, while the percentage of pollen specialists is lower.  Data are almost completely lacking on the reproductive success of bees on green roofs, the effect of roof age on bee diversity, and the genetic or demographic benefits of increased habitat connectivity.

I am hoping that my list of the bee species so far reported on green roofs may help in the selection and implementation of suitable soils, nesting aids, and plantings. One reason for why green roofs are so important for insects, certainly in Germany, is that they receive less fertilizer, fewer pesticides, and fewer herbicides than most other urban and agricultural land.

I think this aspect may make green roofs scientifically interesting spaces to study the relative effects of different factors that contribute to the loss of insect diversity in Central Europe.

Bee species recorded between 1992 and 2017 from green roofs in Asia, Europe, and North America, with key characteristics and open research questions

By Michaela Hofmann* and Susanne S. Renner*
Systematic Botany and Mycology, Faculty of Biology, University of Munich (LMU)
*Joint corresponding authors

Publisher’s Note: The following article was reviewed by and posted on Apidologie 49(1): 00-00. DOI: 10.1007/s13592-017-0555-x on December 19, 2017

Bee Research Green Roofs Asia Europe North America Hofmann Renner

A male Lasioglossum calceatum discovered on green roofs. Photo by Michaela Hofmann.

Abstract

Green roofs, which have become mandatory on new flat-topped buildings in many cities, increase habitat connectivity for wildlife and have contributed to a boom in urban bee keeping.  The ecological benefits or risks of green roofs for wild bees (bee species other than the domesticated honey bee, Apis mellifera), however, have not been comprehensively analyzed.

We therefore reviewed studies on insects caught on green roofs in Asia, Europe, and North America between 1992 and early 2017 and extracted information on wild bees.  The resulting species list includes 236 Apidae identified in 35 studies, with thermophilic species probably overrepresented because roofs provide warm and dry habitats.

The percentage of cavity-nesting bees on roofs is higher than on nearby ground, while the percentage of pollen-specialists is lower.  Data are almost completely lacking on the reproductive success of bees on green roofs, the effect of roof age on bee diversity, and the genetic or demographic benefits of increased habitat connectivity.  Our list of the bee species so far reported on green roofs will help in the selection and implementation of suitable soils, nesting aids, and plantings.

 Bee Research Green Roofs Asia Europe North America Hofmann Renner

Osmia caerulescens recorded on green roofs. Photo by Michaela Hofmann.

INTRODUCTION

The past 20 years have seen a dramatic increase in research on green roofs (reviewed in Bowler et al. 2010; and Blank et al. 2013), which are now mandatory on flat-topped buildings in Switzerland and a few other European countries, and supported by incentives in the United States (Brenneisen 2006; Stutz 2010).  Although there are different types of green roofs, one can generally distinguish between intensive and extensive roof greening.

Intensive green roofs usually have a soil layer of at least 15 cm and sometimes up to 60 cm or more (Mann 1994), while extensive green roofs have only a thin layer of soil (5 -15 cm), supporting mostly mosses, herbs, succulents, and grasses (Gedge and Kadas 2005).  Roofs with shallow soil layers are a difficult growing environment for plants because of moisture stress, severe drought, and full exposure to sun and wind (Schneider and Riedmiller 1992; Dunnett and Kingsbury 2008). On the other hand, extensive roofs require minimal maintenance and can be self-sustaining.

Ecosystem services from green roofs include stormwater management (Getter and Rowe 2008; Berndtsson 2010), moderation of the urban heat island effect (Takebayashi and Moriyama 2007; Tabares-Velasco et al. 2012), lower building temperatures (Oberndorfer et al. 2007), and a role as urban wildlife habitat (for reviews see Fernandez-Canero and Gonzalez-Redondo 2010; Williams et al. 2014; Gonsalves 2016).  An important aspect for the latter role is that green roofs are undisturbed by humans during most of the year, making them quiet habitats with low pesticide loads (Hui and Chan 2011).  They also increase habitat connectivity for certain arthropods (Braaker et al. 2014).

Of the many arthropods living on green roofs, bees stand out because of their role as pollinators and because urban beekeepers tend to find bee keeping “restorative and empowering” (Moore and Cost 2013).  While urban bee keeping has led to an increase of the density of honey bees in cities, the past 50 years have seen a decline in the abundance of wild bee species, attributed mostly to habitat loss and pesticides (Goulson et al. 2008), although data on change in bee abundances in urban spaces over time are scarce.  Wild bees, most of which are solitary bees, are expected to benefit from the newly created habitat on green roofs because they may be able to forage both on the ground and on green roofs, and thermophilic species might also find nesting opportunities on green roofs.

Surprisingly, however, the effects of green roofs on the diversity and abundance of wild bees in cities have received little attention despite repeated calls for bee-targeted green roof research (Zurbuchen and Müller 2012; Witt 2016).  We here provide the first list of bee species recorded from green roofs, summarize key ecological traits of these bees, and point to important open questions about the role of green roofs as habitat for solitary bees.

Bee Research Green Roofs Asia Europe North America Hofmann Renner

A female Bombus sylvarum, found on green roofs in France. Photo by Michaela Hofmann.

Online Supporting Materials

Download the 26-page Hofmann-Renner 2017 Bee Research on Green Roofs PDF of Online Supporting Materials, Tables S1 (Table S1: Overview of green roof (= GR) studies involving wild bee species assessment-), S2 (Table S2: Alphabetical list of species reported on green roofs), and References.

 Bee Research Green Roofs Asia Europe North America Hofmann Renner
More Info

For more information and to read the entire study, you may purchase the Bee species recorded between 1992 and 2017 from green roofs in Asia, Europe, and North America, with key characteristics and open research questions PDF on Apidologie for $39.95, or contact the authors below.


~ Michaela Hofmann and Susanne S. Renner, 
Systematic Botany and Mycology, Faculty of Biology, University of Munich (LMU)

Our research focuses on the systematics, phylogenetics, and evolution of plants and fungi, especially their adaptation to biotic and abiotic factors. Methods brought to bear on these questions range from light and electron microscopy to molecular cytogenetics, field work, and next generation sequencing of entire genomes to study them comparatively.

Contact Michaela Hofmann, Systematic Botany and Mycology, Faculty of Biology, University of Munich (LMU), 80638, Munich, Germany at: michaela.hofmann@campus.lmu.de.

Contact Professor Dr. Susanne Renner, Faculty of Biology, University of Munich (LMU) at: renner@lmu.de.

Watch the Greenroofs & Walls of the World Virtual Summit 2015 Video: “Biodiversity in the Sky – How Green Roofs Can Be Designed as Wild Life Refuges” Keynote by Stephan Brenneisen

October 13, 2016 at 10:18 am

We’ve come to the end of releasing all of the awesome 23 videos from the 30+ speakers who participated at our third Greenroofs & Walls of the World Virtual Summit 2015 ~ Connecting the Planet with Living Architecture: People, Projects & Design, and we’re finishing up with the wonderful Keynote “Biodiversity in the Sky – How Green Roofs Can Be Designed as Wild Life Refuges” by Dr. Stephan Brenneisen, shown above or seen on our VS2015 Virtual Summit 2015 playlist on our GreenroofsTV channel on YouTube.

In his video, Stephan addresses habitat issues and: What kind of species can benefit from greenroofs? What kind of ecosystem is a greenroof? What kind of greenroof design is beneficial for urban wild life? Plus, he provides a background on the status of greenroofs in Switzerland/Basel and talks about the size of greenroofs and metapopulation aspects.

Virtual Summit 2015 Video Biodiversity in the Sky Stephan Brenneisen

If you attended the Virtual Summit 2015 and watched Stephan’s video presentation then, you will have noticed a couple of times where the audio overlapped, which was distracting.  While we couldn’t fix it at the time he sent it to us, we have corrected all of the audio now and his “Biodiversity in the Sky – How Green Roofs Can Be Designed as Wild Life Refuges” is truly fantastic, packed with tons of information on a variety of Stephan’s research in Switzerland on 16 test sites in the Basel area.

Virtual Summit 2015 Video Biodiversity in the Sky Stephan Brenneisen

Biodiversity was a leading topic at the Virtual Summit 2015 and, appropriately, Dr. Stephan Brenneisen is a greenroof and biodiversity expert who leads the Green Roof Competence Center at Zurich University of Applied Sciences (ZHAW) in Wädenswil, Switzerland.  As everyone knows who has heard him speak, the soft-spoken yet highly engaging Swiss researcher is renown the world over for his detailed studies of birds – in particular lapwings (Vanellus vanellus) – beetles (hundreds), and others insects on vegetated roofs – and he has made many friends along the way for his passion, belief, and promotion of designing a better living roof to encourage biodiversity.

Aramis and I were very pleased for Stephan’s participation in the 2015 Virtual Summit, and always enjoy his company when we see him in real life.  He’s a great greenroof colleague – and is so genuine.  I’m sure you’ll highly enjoy his video!

Dr. Stephan Brenneisen

Virtual Summit 2015 Video Biodiversity in the Sky Stephan Brenneisen

Basel, Switzerland. Dr. Stephan Brenneisen conducts research and advises on green roof policies and designs as the head of the Green Roof Competence Center at Zurich University of Applied Sciences.

A member of the collective UG LAB, he is a true leader and pioneer in the green roof field for over 15 years, Stephan has opened many doors in the green roof world and challenged how we think of green roof biodiversity. Continuously without fail, he has demonstrated his ingenuity and critical thinking about ecosystems, urban greening, substrates and how we interact in our world. A well known international speaker and a true educator he is dedicated to sharing his knowledge through teaching, writing and cutting edge research. He also has created a successful model for policy and green roof implementation in Basel and Zurich and is constantly creating new green solutions for improving our urban habitats.

Stephan did his PhD Geograph studies on how different green roof substrate depths influence biodiversity and continues to actively promote the design of green roofs for biodiversity.

Virtual Summit 2015 Video Biodiversity in the Sky Stephan Brenneisen

Read about our Keynote “Biodiversity in the Sky – How Green Roofs Can Be Designed as Wild Life Refuges” by Stephan Brenneisen video’s 5 Key Learning Objectives which I identified for participants of the Virtual Summit 2015.

Virtual Summit 2015 Video Biodiversity in the Sky Stephan Brenneisen

Next week I’ll conclude this series with my short “Greenroofs.com Closing Address.”  As always, we welcome your input and suggestions to make our Greenroofs & Walls of the World Virtual Summit 2017 more accessible, interactive, and a just better all around global social media experience!

~ Happy watching,

Linda S. Velazquez, ASLA, LEEP AP, GRP
Greenroofs.com Publisher

~ Also enjoy these released videos available now from our Greenroofs & Walls of the World Virtual Summit 2015 ~ Connecting the Planet with Living Architecture: People, Projects & Design:

“Small Scale Green Roofs” by Dusty Gedge and John Little.

“Social Healing with Greening” Panel – Part 2 with Patrick Carey and Darius Jones.

 “Social Healing with Greening” Panel – Part 1 with Patrick Carey, Peter Ensign, and George Irwin.

“Urban and Social Needs of Green” by Marc Grañén.

“Soil Ecological Processes on Green Roofs: Research and Observation Meet Theory and Intuition” by Christine Thuring.

“Greening the World Inside and Outside” by Mark Paul.

“The Great Green Roof Review” by Jenny Hill and Terry McGlade.

“Pollinators on the Parapets” by Angie Durhman.

“Using a Climate and Ecological Template Approach for Plant Selection for Extensive Green Roofs” by Ed Snodgrass.

“Beyond Extensive and Intensive: Defining the Comprehensive Green Roof” by Molly Meyer.

“Greenwalls in Middle Earth” by Graham Cleary.

“Green Roofs to New Cities” Keynote by Dr. Diana Balmori.

“Biosolar Roofs” by Nathalie Baumann and Dusty Gedge.

“Versatile Living Walls & Roofs: International Applications for Agriculture, Energy Conservation, Pollution Attenuation, and Aesthetics” by Dr. Bob Cameron.

“Greening Rooftops in Alberta: People, Place + Projects” by Kerry Ross.

“Stewardship of Rooftop Ecosystems” by Michael Furbish, Brad Garner, and Dr. Whitney Griffin.

“The Development of Revolutionary Large Scale Vegetated Infrastructure Projects in Latin America and the Foundation of a New Industry” by Pablo Atuesta.

“Two Extremes in Waterwise Design from Denver, Colorado and Athens, Greece” by Andrew Clements and Karla Dakin.

“From Passive House to the Cold North—How Vegetative Envelope Components Impact Buildings Panel Session with Dr. Bob Cameron, Dr. Allen Lee, Dr. Karen Liu, and Chris Wark.”

A Higher Purpose – Benefits to Human Health and Education through Green Roofing by Elizabeth Hart.

“A Green Building Should Look Green, Which Means Hairy! Dr. Ken Yeang Keynote Interview by Linda Velazquez.”

The Greenroofs.com 2014 Top 10 List of Hot Trends in Greenroof & Greenwall Design + a Look into 2015″ by Linda Velazquez and Haven Kiers.

Greenroofs.com’s VS2015 Opening Address from Linda Velazquez.”

Promos:

The Greenroofs & Walls of the World Virtual Summit 2015 Speakers.

Invitation to the Greenroofs & Walls of the World Virtual Summit 2015.

VIRTUAL SUMMIT 2015 teaser from Groncol.

Small Scale Green Roofs at the Virtual Summit by Dusty Gedge and John Little.