Tuesday, March 27, 2012

To mow or not to mow- that is the question

This post follows the recent thread about habitat fragmentation and managing your backyard with an eye towards the organisms that live there.  Just a brief recap on the issue: through intense urbanization and its sprawl large pieces of intact landscape  (forests, meadows, wetlands) have become less common.  This leaves thousands of small patches of wild land across the landscape, which means: our backyards are the ecosystem, the ecosystem is our backyard.  Our backyards have therefore become places relied on by wildlife (bugs, birds, trees, bacteria, worms, fox, coyotes, etc) and our management actions (mowing, planting, cutting, spraying, gardening, bee keeping, etc) affect their survival.

The commonly cultivated and manicured lawn is an intensely managed landscape that does little to boost the vitality of our backyard ecosystem.  If you compare the ecological processes of a manicured lawn to those of a forest or a meadow (termed 'non human-managed ecosystem' in the table) you will see some stark differences.

Manicured lawn
Non human-managed ecosystem
Nope.  Mowed grass does not flower.  No pollen= no food for pollinating insects. 
Yes. Most plants flower and their flowers produce pollen.  Pollen is food for animals and pollination is needed to produce the seeds for next year’s plants. 
Erosion control
Not really.  Unblocked water falls hard on a lawn and kicks up pieces of soil.  Water is then quickly shed from a lawn taking soil and nutrients with it.
Yes.  Plants slow the speed of falling water.  Once slowed it can percolate into the soil. 
Wildlife habitat
Not really.  There are no hiding places or food sources in a lawn.
Yes. Trees, shrubs, and herbs in a variety of heights and densities creates diverse habitat
Water filtration
Not really.  If water is shed it does not enter the soil where filtration happens.
Yes. Water enters the soil where soil microorganisms and plant roots clean it.

Pollution control
Nope.  Quick moving erosive water caries away excess fertilizer, acids from the rain, and household nasties (detergents, oils, cleaning supplies).
Yes.  Thick living soil can accept pollutants.  The living parts of the soil- roots, bacteria, fungus, and insects- can metabolize these pollutants and render them harmless.  
Oxygen production
Not really.  Lawns don’t contain much biomass (the amount of carbon).  Biomass is the direct product of respiration, where (in plants), carbon dioxide exchanged for gaseous oxygen.  Lawns don't make a lot of oxygen compared to a forest.
Yes.  Most non-managed systems contain more biomass than a lawn and therefor have produced wonderful, glorious, breathable oxygen.

This table could go on and on- obviously there are many ecological differences between our manicured lawns and non human-managed ecosystems.  Remembering that our backyards are the ecosystem we will see that the simple act of keeping a manicured lawn is preventing some pretty important ecological processes from occurring.      

So now what?  What can you do with your lawn?  What are the options?  Thankfully, gardeners, landscape designers, conservationists and permaculturalists across the country have begun to question the manicured lawn paradigm.  The goal is not to abandon backyard management, but instead, to manage our backyards in such a way that allows them to carry out ecological processes. The Mianus River Gorge Preserve in Westchester County has published this, which aids landowners in the conversion of their lawns into meadows.  For those of us don't have a large enough backyard to create a full blown meadow what are some other tools?  Ecosystem gardening is a neat way to incorporate ecological principals in your own backyard.  Also, the well known bird conservation group The Audubon Society has for a long time educated the public about backyard ecosystems.  On their website is this neat interactive drawing of a healthy lawn.  Alternatives to lawns differ from region to region, place to place, town to town.  Remember, the examples I have included in this paragraph are just jumping off points and they are meant to be modified to fit your backyard and your desires.  It is not necessary to have a backyard that looks like a jungle or a prairie- the goal of this post is to help landowners understand the natural processes occurring in their backyards and how they affect the organisms living there.  Simply cutting your grass less often would make a difference to the organisms that live in your backyard.     

What about unwanted organisms like ticks and poison ivy?  It is possible to choose an lawn alternative that protects you and your family from undesirable plants and animals. To avoid ticks, keep your recreation (gardening, game of catch) away from tick hot spots such as stone walls, leaf piles and dark, humid forest edges.  Also, by spreading a 3 foot mulch barrier between the nearby woodlot and your living/working area you can protect yourself from ticks.  

Mulch barrier: a landscaping tool to prevent ticks
The 100%, hands down, no foolin' best method to protect yourself from ticks is to check your body for them and be aware of your health.  Likewise, the best way to protect yourselves from poison ivy is to recognize and avoid it.  If desired, it can be removed from your backyard by hand (hands covered in gloves, that is).

Backyard management- to mow or not to mow? 


Chris said...

“… the goal of this post is to help landowners understand the natural processes occurring in their backyards and how they affect the organisms living there.”

But the message of this post is that lawns are harmful. In fact, lawns are a serious environmental concern only where they are a large proportion of a watershed, and when lawn chemicals are used improperly. Although poorly managed lawns can be a source of nutrient and chemical pollution to waterways, in rural settings this source is dwarfed by runoff from agricultural land. It is therefore misleading to suggest that reducing lawn size will result in meaningful water quality improvement.

Lawns have important and complicated ecological roles. Lawns green up in spring a month before native woody vegetation, and stay green in the fall a month or more after native deciduous vegetation has senesced. They therefore fix atmospheric carbon and assimilate soil nutrients into biomass about 30% longer than native vegetation with potentially positive environmental effects. Lawns are responsible for creating many miles of important edge habitat where they meet forest and shrubland. Lawns are a habitat used by many native mammals, birds, reptiles, amphibians, and invertebrates. Healthy New England lawns typically include two dozen species of plants that flower and provide pollen and/or nectar for insects (even many grasses are well adapted to flower successfully in mowed lawns).

Many people consider those who tend large, well-maintained lawns to be doing a community service by beautifying the landscape. Large, sunny yards lower the humidity and thereby reduce the number of mosquitoes and other flies near dwellings compared to taller vegetation. Lawns are an important cultural component of communities in the northeastern US, and are a non-threatening introduction to the outdoors for kids and nature-challenged adults.

Our environmental arguments will be effective only when they are fair, balanced, and scientifically accurate.

Tate Bushell said...

Chris has raised some good points. Lawns do become more of an issue as their relative percentage of the watershed increases. They do become more of an issue when landowners misuse/ overuse fertilizers. Yes, agricultural land is a huge source of run off fertilizers. From where I am writing and living, many people keep large lawns and fertilizers are commonly used. There are not very many (in fact I don't know of any) large agricultural operations in the area, so I don't think I was misleading my readers to point out that lawns can't perform ecological processes like a forest or meadow.
I wasn't aware that New England lawns typically include two dozen plants that flower and provide pollen and/or nectar for insects. Can you please supply me with a list of these species? I am more familiar with birds than I am with native lawn grasses so I can say with confidence that the native birds that find our lawns suitable as habitat are the species that have generally thrived along side human development. I doubt it is the lawn that is really supporting them. Jays, crows, robin, titmouse, chickadees, finches, nuthatch, sparrows, etc are extremely common in the east. It could be said that although lawns act as habitat for extremely common birds with wide distributions and a variety of acceptable home site characteristics (cities, city parks, downtowns, forests, agricultural land, etc.) they likely do very little for birds of conservation concern. Thanks for the comments.

Charlie Hohn said...

It may be my CA bias but I have to disagree here. Most things are harmless in a small quantity. Lans aren't really an issue in Salisbury, VT, it is true, but in vast areas of the country, they take up massive areas of land and create ecological wastelands. And, the argument that 'X is ok because Y is worse' just doesn't sit well with me. People can only do so much about farming practices, but they have total control over their lawn (unless an evil HOA is present).

I don't see animals using lawns. I just don't (I'm not talking about hayfields, just mowed lawns). I honestly question the accuracy of the statement about co2 fixation. Where is it going? Lawns don't build upward of time and create a negligible litter layer. Where is the CO2 going? I'm sure they sequester some but compared to wetlands or the ocean, again, miniscule.

Lawns may produce less mosquitos than some habitat types but I've seen them breed in sprinkler wells, old tires, and puddles. Mosquito abundance isn't useful as a reason to have a lawn. It has been used as an excuse to drain wetlands but as we know that has caused a host of other problems while yielding questionable results. The best thing we can do to manage mosquitos in urban/suburban areas is get rid of old tires, buckets, anything that can trap water.

Beautifying is totally subjective. I find lawns ugly, honestly.

I'm not saying we shouldn't have ANY lawns, they are fine for playing soccer, but I find them massively overused and a waste. This isn't even getting into the MASSIVE water issues associated with lawns in vast parts of the US including probably half the population of the country, definitely hundreds of millions of people. You don;'t think displacement of native veg and agriculture with HUNDREDS OF MILLIONS of lawns is a bad thing?

Ok, just my rant for the day.

Charlie Hohn said...

also there may be 2 dozen species of plant in a lawn (I've seen much less but now I am curious and will look) but it is the same 2 dozen species over the entire country if not world.

Chris said...

Thanks Tate and Charlie for your responses, which focus on critical areas of this topic. Lawns are an established part of the landscape in many parts of the Eastern and Midwestern US, but are barely sustainable in some other parts of the country. Diverting substantial amounts of water to irrigate lawns usually has negative environmental effects, and defending lawns in semi-arid areas is a losing proposition.

Lawns are never hotspots for diversity of animals or plants, and are usually not a good place to look for rare species. But neither are they monocultures. Two dozen plant species is not an outrageous claim for an individual lawn, and those species vary greatly from one region to the next. Unfortunately, many of those species are not native – they are classic introduced weeds. So a very strong argument can be made that lawns do little to increase native diversity, and in fact encourage introduced species. But if we are just counting species, I think that at least six species of grass are common in my Vermont lawn: annual and Kentucky bluegrass, bentgrass, tall fescue, perennial ryegrass, and crabgrass. I think there are a couple more. Some of these are more or less native. Non-grass species present include:

White clover Trifolium repens
Gill over the ground Glecoma hederacea
Dandelion Taraxacum officianale
Plantain Plantago major
Wild garlic Allium vineale
Blue violet Viola papilionacea
Speedwell Veronica sp.
Hawkweed Hieracium aurantiacum
Winter rocket Barbarea vulgaris
Pineapple weed Matricaria discoidea
Mouse eared chickweed Cerastium arvense
Common chickweed Stellaria media
American brooklime Veronica Americana
Dooryard knotweed Polygonum arenastrum
Northern white violet Viola pallens
Daisy Leucanthemum vulgare
Canada thistle Cirsium arvense (it just won’t die)
Some damn sedge

These are just the plants that can survive mowing and that I can recall without stepping outside (or checking to see if their names have changed since I learned them decades ago). It doesn’t include the mosses that persist in shady places. Along the edges where things can grow taller, other grasses and sedges and another few dozen species of herbs are present. That is the famous ecotone that commonly supports more species than the communities on either side of it.

Although these many herbs have some ecological effect, the ecological function of the lawn itself is dominated by grasses. Grasses have that strange adaptation (to grazing) that allows the leaves to be cropped short and continue to grow from the bases. The often minimal aboveground biomass is countered by a disproportionate (compared to other plant types) allocation to roots. Extensive production of roots produces the erosion resistant turf, and constant turnover of fine roots adds substantially to soil organic matter. Lawns don’t look like much biomass, but if the grass is growing well (and if you don’t collect and remove the clippings), carbon is constantly being sequestered in the soil. Deep prairie soils were made, not invaded, by grasses. Nonetheless, a mature forest has a lot more carbon stored both above and below ground than a lawn, and letting a lawn succeed to forest is a good way to transfer some CO2 out of the atmosphere. However, if all the lawns in New England were allowed to revert to forest, the effect on atmospheric CO2 would probably be undetectable (but the croquet industry would collapse).

And the mosquitoes would definitely be worse. On sunny days in bug season, I can usually work in the lawn or garden without being bothered by mosquitoes. But one step into the more humid woods and I am attacked. Yesterday the fire department rushed in to extinguish a small fire spreading through the dry leaves in the woods behind my neighbor’s house. If spring is going to be warmer and drier in coming decades, I will keep mowing my little green fire break. A house in the woods could be a dangerous and buggy place to live.

Charlie Hohn said...

I do admit that it would be fun to catalog the diversity in my lawn (perhaps with iNaturalist) and see what pops up. Even though I dislike lawns, it would be an interesting element of suburban nature.

Carbon sequestration of grass via root penetration is an interesting topic, though I wonder how deep the roots of lawns go. I guess it depends on the species of plant. As for runoff - what I learned in Pittsburgh (which admittedly is different, as the lawns we looked at had compacted clay soil, whereas many other areas have sand)... was that lawns didn't shed as much runoff as pavement, but much more than intact woodland ecosystems (or patches of buckthorn for that matter), native plant gardens, or food gardens. The compacted, short-cut lawns of the golf course shed almost as water during a thunderstorm as a parking lot. Lawns also cause a lot of problems when they are plopped onto the edges of rivers and lakes, where they damage the riparian buffer.

I could buy the argument that in rural New England the lawns mowed around houses are totally harmless and may in some ways increase diversity. I guess I was more thinking of Pound Ridge, NY, which based on the photos Tate posted earlier seemed to have quite a bit of light sprawl in wooded areas, and this is exactly where reducing lawn coverage (maybe instead going with a transitional zone with thinned, managed trees) could do a lot of good. It's also best not to have lots of trees dangling over the house where they could fall on the roof and cause damage.

As for mosquitos, isn't the issue more the exposure to wind than the presence/absence of lawn? I guess there are more bugs in the woods. They don't bother me all that much. If I get west nile it will probably be while camping or something anyway. I wish there were more bats around, though.

The idea of needing fire clearance in Vermont is a bit alarming... though I also look forward to hearing if any red/pitch pine pops up in any of the fire areas. What an odd year.

Unknown said...

Around Pittsburgh Pennsylvania, where I live, I see too many McMansions with very few or no trees around them in semi-rural areas. Regular mowing to maintain a huge lawn around their house (often 5-10 acres or more) seems to be mostly a relic of traditions from the past. Mosquitoes are not a big issue around here. I am puzzled why more developers and homeowners don't plant large shade trees closer to their houses -- the forest and can cool peak temperatures by 5-10 degrees, reduce summer air conditioning bills, and make your yard a more pleasant place to be on hot summer days.

-Paul Heckbert