More than meets the eye

©iStockphoto.com/skodonnellDuring the last two decades, various environmental groups have been claiming that turfgrass, while a green carpet of grass, is devoid of biodiversity and should be replaced with native plants or other, more diverse systems. The term “green desert” is commonly used to emphasize this lack of diversity. As a biologist, I take issue with the idea that deserts are devoid of living things, let alone diversity. I contend that our urban turfgrass systems, whether lawns, athletic fields or golf courses, are also surprisingly diverse.

Too many people believe that biodiversity is strictly related to the large things that they can see – birds, mammals, frogs, trees, shrubs and flowers. I can’t think of any park that doesn’t emphasize these plants and animals in their construction, informational brochures and nature walks. While these organisms are an important part of these ecosystems, the real biodiversity is found in the Lilliputian scale: Entomologists will point out that there are more species of insects, spiders, mites, millipedes, centipedes and crustaceans in these habitats than any other group.

While I can agree to this (being an entomologist), other biologists are pointing out that there is even more biodiversity at an even smaller microscopic scale – bacteria, fungi, nematodes, protozoa, etc.

Recently developed genetic techniques that allow us to mass-extract DNA from soil, water, wood, etc., and identify unique organisms, indicate there are hundreds of thousands of these microscopic organisms, most of which haven’t been properly identified and described.

It’s appearing that the small things in our world are the real contributors to biodiversity (distinct groups and species of genetic material).


Turf's Diversity
So, how diverse is a turfgrass stand? One would think that most turf stands are really a monoculture of grasses. Technically, this is correct (as long as you have eliminated the broadleaf weeds, though their seeds remain in the system).

But if we look at the species and gene level, most turf stands consist of a mix of grass species (even a planting of PennEagle bentgrass or Tiffdarf Bermuda on a golf green will soon contain Poa annua), and even where a single species has been planted, the seed supplier has often blended several cultivars to provide greater genetic diversity that can deal with environmental conditions.

Whether sodded, seeded or sprigged, over time, turf stands segregate out (you see patches of turf that have different color, texture and uprightness) and other grass species can become established. So, turf stands are definitely not as biodiverse as a natural prairie or forest stand, but they are not monocultures of a single genome either. If the turf is considered as a part of an urban and suburban landscape, adding turf to all the trees, shrubs, perennials and annual flowers that are used, managed urban landscapes are actually turning out to be more biodiverse than nearby “natural stands.”

I’ve even claimed that most turf stands are actually miniature “rain forests.” Turf is constantly renewing its foliage and roots. Turf often has a daily dew event (the equivalent of rain that keeps the humidity high), but what is interesting is that this “rain” also has some nutrients in it. Turf often is subjected to wet and dry seasons and it can respond like the trees in a rain forest (going dormant, reproducing at specific times of the year, producing protective chemicals at different times of the year, etc.). Why are rain forests so diverse? Productivity.

They produce a lot of organic matter that is utilized by a complex web of consumers and decomposers which are also fed upon by predators, parasites and diseases. Turf produces a lot of organic matter (recent studies are showing that it is a pretty good carbon sink), which is then eaten by consumers and decomposers, which are themselves then eaten by predators, parasites and diseases.

Arthropod Biodiversity in Turf
Most turf managers would likely be able to only list half dozen arthropods that inhabit turfgrass systems. As you would likely guess, these are arthropods that commonly reach pest status – white grubs, cutworms, sod webworms, billbugs and chinch bugs. In reality, there are thousands of other arthropods that inhabit turf stands and most of these never reach pest status.

Many would state that this claimed arthropod diversity is mere conjecture, but recent studies in Quebec, New York, Pennsylvania and Ohio are finally showing the true magnitude of arthropod diversity in managed turf.

As part of a project to determine if lawn turf could be managed without pesticides, Sophie Rochfort, a graduate student at Laval University at the time of the study, surveyed the pests and other arthropods in lawns that received: 1) standard care (e.g., regular herbicide, insecticide and fertilizer applications); 2) an Integrated Pest Management program (e.g., pesticides only after sampling determined a need, plus regular fertilizer applications); 3) an ecological management program (corn gluten meal plus organic fertilizer and bio-herbicides); and 4) control plots that only received fertilizer applications.

These plots were sampled on a regular basis using pitfall traps (cups placed within the plots that trap any little critter crawling through the turf). During the three years of the study, there were no significant differences – in terms of total numbers of arthropods – between the treatments. Numbers captured ranged from 450 arthropods per trap during the growing season (June through August) down to 50 to 100 arthropods per trap in October and November.

Since these traps are about one-tenth of a square foot, these numbers would equate to 500 to 4,500 arthropods per square foot, or 4,500 to 40,500 arthropods per square yard. These numbers are certainly comparable to temperate forest and prairie habitats.

But, what about diversity? You can have a lot of arthropods, but if they are all the same species, then you have low diversity. In Rochfort’s study, she found that mites accounted for 23 percent to 42 percent of the totals trapped; ants were 38 percent to 51 percent; carabids (ground beetles) were 2 percent to 6 percent; staphylinids (rove beetles) were 5 percent; millipeds were 4 percent to 9 percent; centipedes were 1 percent to 2 percent; plant bugs were 0.3 percent to 2 percent; and weevils were 0.3 percent to 1 percent. The problem is that these are large groups and don’t tell us about the total biodiversity. So, Rochfort looked at two important groups which are commonly used in biodiversity studies – the springtails (Collembola) and the ground beetles (Carabidae).

Study Results
The springtails had to be sampled using a different technique (a Berlese funnel in which a plug of the turf and underlying soil is placed in a funnel and a light is placed overhead to drive down the arthropods into preservative below). In this study, 21 species representing 17 genera and nine families were found. This is comparable to published studies of springtail diversity in tall grass prairies (27 species in Michigan and Illinois) and dry grasslands (23 species in Austria), but is considerably lower than what is in forest habitats (75 species in Vancouver temperate forests). So, turf is comparable in springtail species richness as other grass-covered habitats.

An analysis of the ground beetles found in the pitfall traps revealed 17 species representing 10 genera and seven tribes. Each turf area had slightly different abundances of the primary species. What was surprising was the fact that many of these ground beetles were seed eaters, but predatory groups were also prominent. Studies from analogous habitats (urban-rural gradients) have found from 21 to 77 species (mainly European studies), so the Quebec numbers would appear to be a bit low, but are likely close to what is found in comparable habitats.

In Ohio, Dan Digman and I undertook a “non-target” study where we looked at the potential non-target effects of new insecticide categories on lawn turf arthropods. To perform these studies, like Rochfort’s studies, we had to take periodic cores out of the turf and extracted those using Berlese funnels. Without going into all the details about the minimal effects of the pesticide applications, the bottom line was that we found incredible numbers of arthropods in the turf.

Sampling in 2002 and 2003, the primarily Kentucky bluegrass lawns (which received broadleaf weed control and normal fertilizations) yielded: 73.9 percent mites, 18.6 percent springtails, 4 percent ground beetles (larvae and adults), 1.7 percent diplurans (little primitive, blind insects), 0.5 percent spiders, 0.5 percent bees, wasps and ants, 0.4 percent thrips, 0.3 percent true bugs and 0.2 percent flies.

Now, you’ll probably say that having more than 70 percent of the arthropods being mites is not very diverse. Not true. Mites range from primary turf feeders (e.g., clover mites and winter grain mites are only two such mites), decomposers (something has to eat the grass clippings and grass blades and stems that die naturally), fungivores (eating the molds and fungi that are in the thatch), predators (some eat other insects; mites and one group even eats nematodes), to parasites (some feed on the blood of other arthropods and some feed on the blood of animals – chiggers and ticks).

In fact, we estimated that nearly half of the mites we recovered may be new species and most species are poorly known, biologically. There are probably 100 to 300 different mite species in this sampling.

We also saw considerable diversity among the other arthropod groups, even though they were not necessarily numerous.

When you multiply the numbers, we found between 21,000 and 45,000 arthropods per square meter of turf. So not only is there considerable biodiversity, there are incredible numbers of individuals present.

Dan Peck, with Cornell University, has also completed a study on the non-target effects of turfgrass insecticides on the fauna found in turfgrass lawns in upstate New York. In his studies, he found the following arthropods: 67.8 percent mites, 17.5 percent springtails, 6.5 percent bees, wasps, ants, 3.6 percent true bugs, 1.1 percent thrips, 0.8 percent flies, 1.1 percent beetles (adults plus larvae). Does this look familiar? Indeed, Peck found nearly the same groupings in the same proportions that we found in Ohio.

His calculated numbers also yielded between 20,000 and 50,000 arthropods per square meter of turf.

Conclusions
Turf is not a green desert. It is actually a largely unexplored environment. There are likely hundreds of new species of animals that will be found, but most of these are mites and  they are very small.

It is easy to see, identify and count birds, mammals, frogs and the other animals that most biologists count in their biodiversity studies, but the real biodiversity is on a microscopic scale.
 

The author is professor of urban landscape entomology at Ohio State University.