Month: August 2011

Are native species inherently superior to non-native species?

The native plant movement is based on the fundamental assumption that native species of plants and animals are inherently superior to non-native species.  The basis of this assumption seems to vary.  Sometimes the explanation offered is as simple as “the non-native doesn’t belong here.”  It’s not clear what that statement means.  Putting it in the best light, it implies that there is some optimal ecology that is best represented by exclusively native species.  A less generous interpretation would be that non-native plant and animal species are the non-human equivalent of illegal immigrants. 

We will examine this claim of the superiority of native species in the context of bees to make the point that nature is complex and cannot be oversimplified by such a sweeping generalization.

Professor Gordon Frankie, our local expert on the bees of the Bay Area, says that native bees are superior pollinators to the European honeybee.  If that were true, we would consider that a legitimate basis for the judgment that, in this case, the native bee is superior to the non-native bee.  However, the evidence available to us suggests that a comparison of the native to the non-native bee is more complicated.

In considering this question, we will focus on agriculture rather than residential gardens, because agriculture is economically more important and for the same reason more is known about the role of bees in agriculture.

Why would native bees be superior pollinators than non-native bees?

We know of two specific examples of native bees that are more effective pollinators of agricultural crops.  Both cases illustrate the pros and cons of native bees as agricultural pollinators.

Bumblebee on Cotoneaster, Albany Bulb

There are some crops—tomatoes, cranberries, blueberries, eggplants, and kiwi fruits—that are effectively pollinated by native bumblebees (Bombus) because of their unique method of pollination.  This method is called “buzz-pollination” or “sonication” and it is described as “an intense vibration, like a tuning fork being struck, pollen gathered from other flowers literally exploded off Bombus.”(1)

Unfortunately, though its pollination technique is superior, other characteristics of the native bumblebee have limited its usefulness in agriculture.  The crops with which it is most effective produce only pollen.  Therefore, the bumblebee must be provided with an alternate source of nectar to fulfill its dietary needs.(2)  

The bumblebee, like most native bees, is solitary.  It does not live in hives like the social European honeybee.  Therefore, it cannot be transported where and when it is needed, as the honeybee can.  An attempt at a high-tech solution to this limitation ended in disaster:  “In the 1990s, a bumblebee species Bombus occidentalis, was made extinct when experimenting breeders mixed species in Europe and shipped queens back to America.  The queens carried with them an exotic disease that Bombus occidentalis has no immunity for.”   Growers of tomatoes are now “forced to resort to less efficient pollinators.”  (Schacker 2008). 

Another example of a native bee that is a superior pollinator of an agricultural crop is the alkali bee which is the most efficient pollinator of alfalfa, a crop that is essential to the dairy and beef industries.  “Alfalfa flowers…keep their sexual parts hidden, under tension like a spring.  Bees must trip the spring to get at the pollen, and in so doing, they are hit on the head—something honey bees are not particularly fond of.  The alkali bees…don’t mind getting hit on the noggin and will happily pollinate a field of alfalfa.”  (Schacker 2008). 

Native bee approaching nest in ground, Albany Bulb

Unfortunately, the alkali bee, like 85% of native bees in the US, nests in the ground, in particular the alkaline soils of the western US for which it is named.  As cropland in the west expanded, the alkali bee was virtually wiped out by plowing up the ground in which it nested.  A leafcutter bee was imported from Canada as a substitute, but a fungus is now infecting its larvae. (Schacker 2008)

These disadvantages of native bees can be compensated for by providing nesting and nectar sources adjacent to croplands.  These hedgerows must be large enough to provide sufficient nesting opportunities and nectar sources. 

However, such hedgerows do not solve all the potential problems of using native bees as pollinators.  Because the bees are resident year around and cannot be transported, they cannot be removed when the crops are sprayed with pesticides.  And the pesticides are very damaging to the bees.  Therefore, a commitment to providing hedgerows for a resident bee population is also a commitment to organic agriculture, i.e., without using pesticides. 

This is not to say that the honeybees aren’t being adversely affected by the use of pesticides in the crops they are pollinating.  The impact of pesticides on  honeybees would be exacerbated if they were resident when pesticides were applied to the crop.  As it is, the honeybee is being affected by the residues of the pesticides on the crops they pollinate.  This is considered one of the primary reasons for Colony Collapse Disorder of commercial honeybees which has been destroying about one-third of commercial honeybee hives in the past few years.

Unlike most native bees, the European honeybee does not hibernate.  It is therefore available year around to be transported where and when it is needed.  Most native bees hibernate, but not necessarily at the same time.  Different species of native bees hibernate at different times and are therefore available for pollination at different times. 

Most native bees are more selective in their pollination than the European honeybee which is an extreme generalist:  “honeybees have the greatest pollen dietary range…of any known pollinator.” Although there are “only a handful of well-documented cases in North America of truly monolectic bees [a bee that visits only one kind of flower]” (Buchmann 1996), the flower preferences of native bees are narrower than that of the European honeybee.  While some native bees may prefer native plants, honeybees are willing to pollinate both native and non-native plants.  This is important because virtually all of our agricultural crops are non-native.

Native bees are not inherently superior to non-native bees

Honeybee hives, USDA photo

In summary, the European honeybee has several important advantages over native bees as pollinators of agricultural crops:

  • Because the honeybee is a social bee that lives in hives, it can:
    • Be transported where and when it is needed
    • Be removed from the agricultural crop when it is sprayed with pesticides
    • Does not need to be provided with nesting space and an alternate food supply
  • The honeybee is available for pollination services year around because it does not hibernate.
  • The honeybee pollinates a wider range of flowers than most native bees.

While native bees may be more efficient pollinators of residential gardens, there are a number of disadvantages to using native bees for agricultural pollination.  Although many of these obstacles can be overcome with greater use of resources, we cannot agree with the assumption of native plant advocates that native bees are inherently superior to the non-native European honeybee.  As with all sweeping generalizations, the truth is usually more complicated because nature is complex and man’s understanding of it is limited.

(1) Schacker, Michael, A Spring without Bees, Lyons Press, Guilford, Conn, 2008.

(2) Buchmann, S, and Nabhan, G, The Forgotten Pollinators, Island Press, 1996

“Museumification” of our parks separates children from nature

The Berkeley Meadow

We recently published an article about the Berkeley Meadow, a 72-acre fenced pen for native plants and animals.  In response, one of our readers alerted us to a video cartoon about the Berkeley Meadow which we recommend to you.  “Grandpa Takes the Kids to the Plant Zoo” captures the absurdity of this “restoration” project.

The sentiments expressed by the children in this video remind us of an article published in 2004 about similar restoration projects in Chicago and San Francisco.  “Urban Park Restoration and the ‘Museumification’ of Nature” was written by Dr. Paul Gobster after he visited the Bay Area as a visiting professor at UC Berkeley, collaborating with colleagues in landscape architecture.

Dr. Gobster is a social scientist with the US Forest Service, stationed in the Chicago area and the editor of a book* about the restoration movement there.  The restorations in Chicago are similar to those in the San Francisco Bay Area because both places were primarily grassland prior to the arrival of Europeans.   Restorations in both areas therefore require the destruction of most trees.  In the Chicago area, many of the trees are native because of the natural succession of grassland to shrubland and finally to forest.  The fires of Native Americans that sustained the grassland were stopped at the time of settlement.

In “Museumification,” Dr. Gobster expresses his opinion of the restorations in the San Francisco Bay Area and in Chicago:

“…it is my contention that little headway has been made in exploiting the key role urban parks might have in strengthening the ties between nature and culture.  To the contrary, some current attempts at ecological restoration in urban parks may distance people from the experience of nature even further than did earlier naturalistic designs, leading to a form of detached observation not unlike what one might experience in a museum.  Instead of providing a bridge between nature and the city…park restoration can lock nature inside the gates of paradise and leave people on the outside looking in.”

Dr. Gobster is particularly concerned about the impact of “museumification” of parks on children who should be the primary beneficiaries of our parks.  Their earliest experiences with nature may foster a lifelong interest in nature or an alienation from it.

“The wild and weedy nature that existed in many of these urban park areas prior to restoration provided [a setting for unstructured play]…Now displaced by a more ecologically diverse yet more fragile nature, these kinds of activities are discouraged just as they are in more manicured park settings.  Children are much less likely to attain satisfying nature experiences through passive forms of interaction and thus may be disproportionately affected by such changes.  The result of this museumification is that we are creating a significant gap in the spectrum of nature experiences available to urban children precisely at the nearby places where children stand the best chances for getting acquainted with nature.  Thus while striving to achieve authenticity in the restoration of ecosystems we may be sacrificing the authenticity of children’s nature experiences.”

Children discovering nature. NPS photo

In “Grandpa Takes the Kids to the Plant Zoo,” we see that the kids are uninterested in looking at the plants on the other side of the fence.  They ask Grandpa to take them elsewhere so they can play.  Grandpa must also ask them not to touch the few plants within reach because they have been sprayed with herbicides.  The park is not accessible to the kids because it is behind a fence and it has also been sprayed with herbicides, so it’s not a safe place for them to play.  In the East Bay Regional Park District, for example, herbicide use in its restoration projects (AKA “resource management”) increased 300% in 2009.  Herbicides had not been sprayed in the Serpentine Prairie prior to 2009, when it was fenced for “restoration.”  Now it is sprayed with herbicides, mowed, planted, and is due for periodic prescribed burns to prevent its succession to shrubs and subsequently to oak woodland.

When we alienate children from nature, we jeopardize the future of our parks.  If parks are not viewed as useful places, they will not enjoy the support needed to sustain them.  And if nature is not viewed as valuable, we undermine the public’s support for preservation of the environment.  As adults debate the merits of native plant restorations, they should keep in mind the needs of children because the future of our public lands is in their hands and children are unable to speak for themselves in the public policy arena. 

* Gobster & Hull, eds., Restoring Nature, Washington DC, Island Press, 2000

“Mulch Madness” and other restoration mistakes

Thanks to Professor Gordon Frankie (UC Berkeley), we have learned a lot about the bees in the Bay Area.  He has been studying our bees for over 20 years and has made a wealth of interesting information available on his website.

Native bee (Anthrophora urbana) approaching nest in ground at Albany Bulb

Unlike the European honeybee, our native bees are usually solitary.  That is, they do not live in social colonies such as the hives of the European honeybee.   Most (60-70%) California native bees live in small nests in the ground.  Although they may produce enough honey to feed their own young, they don’t store an excess of honey like the honeybee.

Professor Frankie has identified one of the biggest challenges to native bees in urban gardens, “Mulch Madness.” 

“[If] you happen to be one of the many ground-nesting bees that looks for garden sites for digging small tunnels where you will lay your eggs in individually-made brood cells that you will provision with pollen and some nectar, [you have a new problem in urban gardens]…Something has happened in recent years to those favored bare dirt sites that makes your task much harder and oftentimes impossible.  MULCH MADNESS has arrived and has become a highly promoted ‘eco-friendly’ method for suppressing weeds, conserving water, and unknowingly discouraging ground-nesting bees!”

Anyone who is familiar with native plant restorations knows that most are covered in a thick layer of mulch.  When tree removals are required for a restoration, the mulch is usually composed of the chips of the trees that have been cut down.  The projects of UC Berkeley for which UC is applying for FEMA funding (based on its claim that the clear-cutting of all non-native trees will reduce fire hazards) say specifically that the clear-cut areas will be covered with 24 inches of mulch composed of the chips of the destroyed trees.

The UC Berkeley projects also claim that native vegetation will return to these clear-cut areas without being planted, based on an assumption that the seeds of native plants are dormant in the soil.  One wonders how these seeds would be able to germinate when covered with 24 inches of mulch, or how the sprouts could penetrate it.  Their proposal contains the fanciful suggestion that squirrels will plant the acorns of oaks in the mulch, which may be true of the oaks, but is an unlikely scenario for the many other native plants and trees which UC claims will populate their “restorations” without being planted.

Accommodating bees in native plant restorations

In the unlikely event that native plants would emerge from this tomb of mulch, they won’t find a population of bees to pollinate them in the future because bees will not be able to populate these projects:  “bees will not dig through a thick layer of mulch.”  Frankie suggests that “about 50% of your garden be left in bare dirt for the bees and other organisms.”  Studies indicate that it will take between 10 and 15 years for 24 inches of mulch to decompose.

Native plant restorations also require the use of herbicides.  A particularly toxic herbicide, Garlon, is used to kill the roots of the non-native trees after they have been cut down.  If the stump isn’t sprayed with this herbicide immediately, the tree will resprout.  The plans for the UC Berkeley projects say that retreatment with this herbicide is required twice per year for 10 years.  Although insecticides are considered one of the primary reasons why bee populations are declining in the United States, less is known about the effect of herbicides on bees and other insects, because testing of these chemicals is minimal. Some scientists believe that all pesticides (both insecticides and herbicides) are more harmful to bees and other animals than we presently know.*  Professor Frankie recommends against the use of all “synthetic chemicals” in a garden in which bees are welcome.

Would native plant restorations benefit from more bees?

The restorations with which we are familiar in the San Francisco Bay Area are often unsuccessful.  That is, they are not usually populated by native plants unless they have been intensively planted, weeded, and irrigated.  Few managers of public lands have the resources for such intensive gardening.  UC Berkeley has been clear-cutting non-native trees on its properties for about 10 years, so we can visit some of those areas to see the results of such projects.  They are now weedy messes, as shown in this photograph.

Results of clear-cutting non-native trees, UC Berkeley project

The use of heavy mulches and herbicides in native plant restorations raises these questions:    Would using less mulch and herbicide attract more bees?  Would more bees benefit the native plants?  Would restorations be more successful if they were more attractive places for bees?  We don’t claim to know the answers to these questions.  However, we don’t think that the managers of these projects know the answers either.

Would scientific methods produce more successful native plant restorations?

What the managers of these projects call “adaptive management,” we call “trial-and-error.”  There is no science involved in these projects.  Control areas are not set up to test questions such as “Will a more bee-friendly environment benefit our projects?”    We think a more methodical approach to these efforts would be less wasteful and more successful.  If we could see more success, perhaps we would be less opposed to what seems like the needless destruction of non-native trees.  As it is, the consistently poor results do not justify the destruction that we witness.

* Schacker, Michael, A Spring without Bees, Lyons Press, Guilford, Connecticut, 2008.

Nature is resilient, animals can adapt to change

We are always puzzled by the widespread belief amongst native plant advocates that native animals are dependent upon native plants and the corollary argument that non-native plants are invasive because they have no predators.  We suspect that one of many reasons for this assumption is a lack of understanding about evolution.  That is, if you believe that animals are unable to adapt to new plant species, then you probably assume that the new plant species are not useful nor are they prey to native animals.  

The Gallup Poll tracks the opinions of Americans regarding evolution.  In 2010 a surprisingly small percentage of Americans (16%) believed in the evolution of man unguided by God.  Even amongst those who believe in evolution, it is often seen as an historical process that moves too slowly to be perceived.  Science has only recently found living examples of on-going evolution:

“A growing appreciation that organic evolution, like mountain building, is an ongoing rather than simply historical process has stimulated an infusion of evolutionary thinking into mainstream ecology.”(1)

The Soapberry Bug

Soapberry bug on balloon vine. Scott Carroll, UC Davis

The soapberry bug (Jadera haematoloma) is an example of a native insect that has changed genetically in less than 100 generations over a period of 20 to 50 years in response to a new non-native plant host. 

The soapberry bug is named for the plant upon which it depends for both food and reproduction, the Sapindaceae family (‘Soapberry’ family).  In southern Florida, the native host plant of the soapberry bug was the balloon vine (Cardiospermum corindum).  As its name suggests, its seed is large and round.  The soapberry bug that feeds on that seed has a large jaw–up to about 70% of its body length–that enables it to get the seed into its mouth. 

In the 1950s a new member of the Sapindaceae family of plants was introduced to southern Florida, the Chinese flametree (Koelrueleria elegans) as an ornamental.  Its seed is much smaller than the seed of the balloon vine.  The soapberry bug quickly made a transition to its new host and over time it evolved several adaptations to it.  The jaw of the soapberry bug that feeds on the flametree is much smaller, as little as 50% of its body length. 

The life cycle of the soapberry bug has also changed and is better suited to the brief, simultaneous availability of seeds of its new host, the flametree:  “The flametree-specialized race [of soapberry bug] has a briefer development time (and thus an earlier age at first reproduction), greater fecundity, and exhibits greater expenditure of effort towards reproduction than the balloon vine race of J. haematoloma from which they originated.”(2)

In south Florida, the soapberry bug now has two genetically distinct races that are suited to their specific hosts–one native, one not.  The original race has not changed where its host is the native balloon vine.  The soapberry bug is not very mobile, so these two populations are physically separated.  This is an example of increased genetic biodiversity in response to an introduced plant. 

There are 400 genera and 1,500 species of plants in the Sapindaceae family all over the world(3), so we should not be surprised to find many other examples in the scientific literature of insect hosts that are adapted to them, whether they are native or introduced plants, as well as differences in those insects that are suited to the specific plants and/or their locations.  The soapberry bug isn’t an isolated example of an insect that has rapidly evolved to adapt to new hosts.  On the other hand, science cautions us against generalizing to all insects. 

We offer our readers three sources of information, depending upon their scientific knowledge.  The National Public Radio story about soapberry bug evolution is addressed to the layman.  At the opposite extreme, the citation in our footnotes is addressed to scientists with expertise in genetics.  The middle ground, from which we drew most heavily, is a website about soapberry bugs. 

Cheerful conclusion

As we often do, we conclude cheerfully that nature is remarkably resilient.  Although nature is less fragile than native plant advocates believe it to be, we don’t take that as an invitation to abuse it.  We treat nature with respect, and that includes taking care of what is here, whether it is native or non-native.  

(1) Carroll, Scott P., et. al., “Genetic architecture of adaptive differentiation in evolving host races of the soapberry bug, Jadera haematoloma,” Genetica, 112-113: 257-272, 2001

The Bees of Berkeley

Gordon Frankie is a Professor in the Department of Environmental Science, Policy and Management at UC Berkeley.  He has been studying the preferences of bees in northern California for over 20 years.  In 2002 he published an article in Fremontia, the journal of the California Native Plant Society, reporting on the preliminary results of his study.*

First, a word about the methods used in his study.  His research team visited the residential gardens of north Berkeley and Albany twice per week for three years, 1999 to 2002.  In the first stage of the study, the team identified the plants that were being visited by bees.  In the third year, they focused on counting the number of visits made to the identified “bee plants” by each species of bee.

The plants of Berkeley

Frankie’s team reports having identified 600-700 different varieties of non-native plants in the study area.  Native plants were defined as those that occur historically only in northern California.  Only 50 species of native plants were identified in the study area.

The bees of Berkeley

Frankie was surprised by the diversity of the bee population found by his research team.  They report having identified 74 different species of bees (updated on his website to 81).  Of those, only two were non-native bees (the European honeybee and the leaf cutting alfalfa bee).  Putting these numbers into perspective, there are approximately 1,600 species of bees in California and about 4,000 known to occur in the U.S.  Frankie reported that the population of European honeybees in the study area has declined significantly in the past 10 to 15 years.

What do the bees of Berkeley want?

The bees were observed visiting a small number of the total number of flowering plants available to them.  Only 72 species of flowering plants were visited by bees often enough to be counted by this study as “bee plants,” about 10% of the total number of flowering plants available to them.  Fifty-three of the “bee plants” were non-native and 19 were natives. 

Native bumblebee on non-native cotoneaster, Albany Bulb, Albany, California

While the bees of Berkeley are using a higher percentage of the available native plants (38%) than they are of non-native plants (8%), the percentage of non-native plants they are using is nearly 75% of all the flowers they are using.   Clearly, the non-native plants are important to the bees of Berkeley.

Frankie explains that many non-native plants are not useful to bees because they have been cultivated for looks, rather than for the nectar and pollen needed by the bees.  However, on his website, he updates his research with some strong recommendations to include both natives and non-natives in our gardens both for the benefit of the bees and the benefit of native plants.

Non-native plants extend the blooming period in our gardens, which provides food to the bees for a longer period of time:

“California native [plants] tend to flower in early spring and summer, while non-native ornamentals bloom mainly in late summer to fall, so a combination of both would be ideal for attracting the highest potential density of bees.”

Also, when our gardens attract more bees, all the plants in our gardens benefit from their pollination services, which will also benefit the native plants in our gardens:

“If your priority is a healthy garden, it makes good ecological sense to consider your plants’ bee-attractiveness, rather than focusing exclusively on whether one hundred percent of your plants are natives.  Even if your priority is to have a native garden, it can be highly advantageous to include even a couple of exotic plants on the basis of their bee-attractiveness.  The bees they attract will help your natives thrive.”

Frankie reminds us that the bees don’t care about the nativity of the plants that they use. 

“Insects and other wild animals make no distinction between weeds and plants we put in our gardens.  From the perspective of the bee, any plant that provides quality pollen and nectar is attractive.  For the short period they are in bloom, weeds such as dandelions and white clover provide bees with good sources of pollen and nectar.”

Opening our minds to the benefits of non-native plants

The bees of Berkeley remind us that the obsession with native plants is a human hang up that is not shared by animals.  They consider the nativity of the plants that are useful to them to be irrelevant.  So should we. 

* Gordon Frankie, et al, “Bees in Berkeley,” Fremontia, July/October 2002