Too Much Biodiversity is Bad News for Wildlife

Finding the optimal diversity of plant species will encourage more wildlife, including beneficial insects.

Finding the optimal diversity of plant species will encourage more wildlife, including beneficial insects.

Native plants offer the gardener an overwhelming array of benefits, but they are not without controversy. Despite all the evidence that landscaping with more native plants is healthier for people and for wildlife, some gardeners seem intent on attacking the whole notion.

Mention the concept of “biodiversity“, on the other hand, and you will find nearly uniform support. Biodiversity is so obviously a good thing – like Mom and apple pie – that no one could possibly be opposed to it. Right?

While biodiversity can be a (very) good thing, like any good thing too much of it can be bad.

For example, when we introduce a new invasive plant to a forest we are (temporarily) increasing the biodiversity of that forest: more species exist in the forest than did before, but this is clearly not a good thing.

Large groupings of host plants, like milkweed, are more likely to attract and support bees and butterflies.

Too much of a good thing can also be a problem, even in a native plant landscape. Attempting to plant too many different kinds of native plants in your garden or landscape can often be counterproductive, and here is why: over-diversification.

No matter where you live, there are probably many thousands of species of plants that are native to your county or state. Hike a mile or two through a nearby wild forest or prairie and you will likely spot hundreds of species of native plants.

But few gardeners own yards the size of a state, county, forest, or prairie. Most gardens are measured in the hundreds, maybe thousands, of square feet instead. And for the native plant enthusiasts tending these smaller parcels trying to squeeze in hundreds or thousands – or even dozens – of different species of native plants can be a mistake.

Every type of wildlife has certain habitat needs. This can be a type of ground cover, or a certain plant. Wildlife will use their senses, like smell or sight, to locate these habitat needs and if you dilute them too much in your landscape you run the risk of failing to support the insects or birds you intend to attract.

A study of gardens in England published in 2007 concluded, in part: “Entire gardens, or large parts thereof, given over to individual land-cover types, with different gardens providing coverage of different types, would be ecologically more valuable.”

In other words, it is ideal if each gardener treats their own garden as a single type of community because the network of different gardeners (with different community types) throughout a city or town provides the right amount and scale of diversity.

Planting three purple milkweed plants in a garden might attract some Monarch butterflies, but planting three dozen of them is much more likely to do so. Planting one or two turtlehead plants might attract a Baltimore checkerspot butterfly, but planting a hundred square feet of turtlehead is much more likely to be an attractant.

Large groupings of plants are attractive to people and to wildlife.

It may seem unnatural to entertain the idea of planting fewer species of native plants, but it makes sense once you think it through. An acre of prairie might contain 75 to 100 different species of native plants, but any given square foot within that acre might contain just six or eight species. We are still aiming for biodiversity, but now we are paying attention to the scale at which that biodiversity exists.

If you are gardening in a small area (hundreds or thousands of square feet) there is only so much variety you can offer to wildlife before you become self-defeating. In a four hundred square-foot garden, you should not aim to be all things to all animals: the haphazard plant shopping model (“three of these”, five of those, one of that”) just won’t cut it if your goal is to have your yard function at its ecological optimum.

Here are three steps to optimize your biodiversity:

  1. Decide your habitat type. Don’t try to cram canopy trees and an urban meadow both onto a small residential lot: pick your habitat type, then stick to it.
  2. Pick your plant palette. Chose a handful (maybe a dozen, no more) of plants that are locally native and that are well-suited to your soil type, shade conditions, etc.
  3. Plant a lot of plants. Remember the prairie example I mentioned earlier? It had six to eight plants per square foot, so don’t be afraid to plant your native plants densely. No more leaving 18 or 24 inches between plants in a wildlife garden!

Don’t be afraid that by specializing in a particular type of habitat, or that strongly emphasizing only a few species of plants, that your garden will be boring.  As far as wildlife are concerned, nothing could be more appealing.

© 2012, Vincent Vizachero. All rights reserved. This article is the property of Native Plants and Wildlife Gardens. We have received many requests to reprint our work. Our policy is that you are free to use a short excerpt which must give proper credit to the author, and must include a link back to the original post on our site. Please use the contact form above if you have any questions.

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Comments

  1. Laura Thomas says

    I am so guilty of this. Even though I know better, I want it all. Sometimes at the expense of aesthetic and now ecological integrity. A fantastic dose of reality check.

  2. says

    I’ve been thinking about this for my front yard, which I’m still wary about turning into a mini prairie. I know that the key is to put in shortgrass prairie plants that sorta look like lawn, this means, in a way, a monoculture. I also think that simplicity in design may also ease neighborhood views into acceptance more readily, vs. just going all Victorian color palate or something. thanks for this.
    Benjamin Vogt recently posted..Of Cats and Fall

  3. says

    A great article. This point really needs to be made more in native forums. Not only does the “one of everything” approach have limited wildlife value, but it creates chaotic gardens that turn people off from native plants. Native gardens have a real problem now: we enthusiasts have created too many sloppy imitations of nature. The current aesthetic is–I would argue–too anti-design.

    We must seduce people into loving native plants by showing they are drop dead gorgeous and relevant in a typical suburban yard. One of the best ways we can improve the aesthetic experience of natives is to mass them. Massing gives them legibility and power.

    A great topic!

  4. says

    Great piece, Vincent! Thank you. I agree with you on both the community ecology level and on the design level. As Thomas Rainer says in his comment above, if we use a more limited palette of native plants and mass them, they begin to look like what people expect a garden to look like. That helps with the conventional aesthetic. I tell my clients to think of of half a dozen plants they love and build a garden around those, not many dozens. As you say, pick a community type, and within it, pick your favorite few plants of each strata of that community (trees, vines, shrubs, grasses, wildflowers). Look at the natural communities around us; they develop with keystone species, and the relationships they have with other species.
    Susan J. Tweit recently posted..Giving Thanks for Hospice

  5. Kevin Songer says

    Good article, Vincent. As part of our Green Roof studies we’ve focused many times on biodiversity. From my perspective there is incomplete and less incomplete biodiversity. Sometimes we get stuck thinking in terms of Genus and Species. Species biodiversity may not be as attractive to pollinators and wildlife as Family biodiversity. I love studying glade and prairie type ecosystems where the biodiversity across a year is so very high at the Family level. Now my brain is trained to think in terms of plant Families we drive down the road or walk through the forests. Living by the 10-20-30 rule where no more than 10% of my created landscape is the same Species, no than 20% the same Genus and 30% the same Family we have created small, 1000 SF rooftops with 50 or more plant Families represented, and hundreds of Genus and Species. They are alive with life, both plant and animal. I liken it to a Chinese buffet. The moer choices the better, especially the many different types of sushi rolls on small plates. Great article! Kevin

  6. says

    Well done Vincent! Although I can be very guilty of wanting to have some of everything, I agree that’s not always productive. Since I ripped my entire garden out this summer because it had gotten overrun with too many invasives, I’m in the process of trying to choose very carefully the direction I want my garden to take as I start planting this spring. I’m going to concentrate on butterflies and add lots of host plants and nectar from early spring through late fall.
    Carole Sevilla Brown recently posted..The 5 Pillars of Ecosystem Gardening

  7. DeAnna says

    Thank you for the practical information that I will apply to my small garden! I’m gardening for the butterfly in a very small space, in the yard of a mobile home lot, that’s a small space!
    I LOVE the pic of the Tuberosa plants & I’m going to add to my existing patch until it looks like the pic, it is beautiful & stunning! I see the logic of planting densely, as it provides cover for the various insects, etc. This simple change in my butterfly garden will make a huge difference! Please stop by my page to see my butterfly garden at :https://www.facebook.com/MyButterflyGarden

Trackbacks

  1. [...] Remember – a healthy plant community isn’t always about lots and lots of variety of the … You need a few good workhorses to be the backbone of of a healthy and happy plant community.  Next time you are taking a walk around a lake or stream, pay attention to what species you see growing there. Chances are you will see a few species repeated over and over again than a new species everywhere you look. Try to mimic these natural patterns in your own landscape.I’m sure there are many other great species for drier shorelines as well – these are just a few that seem to work well on Wisconsin shorelines. [...]

  2. [...] Simple ~  It’s tempting to buy one of everything when you go plant shopping, but it’s much more effective from both a garden design and a habitat creation perspective to choose several species of  plants and then use them in multiples. Cluster plants of the same species together in groups of 3+ plants. Not only will this maximum their visual impact, the groupings will also be more attractive to wildlife. [...]

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