Teaming with Microbes: A Gardener's Guide to the Soil Food Web

Wow. This is like finding out there's a southern hemisphere.

Until I read this book, most of what little soil science and "chemistry" (e.g. over simplified "N-Ph-P" and how-to-alter-your-pH advice) that I had hodge-podged together over the years floated around my mind in scatter-shot unlinked fragments. A lot of it I took more on faith than real understanding, and I also often didn't know what-to-do-1st to start to help heal the problems in my disturbed soils.

Now I know why: most of that soil chemistry is more accurately the processes and products of soil microbiology, and there's nothing mystical or disconnected about it.

I think most of us have been mentally messed-over by the petro-chem hort gardening industries (see the advertisers behind every popular gardening magazine today), but also, a lot of knowledge about soil microbiology is relatively new information too (increased microscopic power in the 90's is what changed this). So while intuitively, we knew that plants, soils and nutrient cycles were more like a super-clever elegant symphony than disparate fields of study, this is the only book that has succeeded in substantiating, factually explaining and pulling-it-all together for me. Which, btw, also means the authors must be really good writers.

If that weren't enough, starting at about page 52 (with a peek ahead at chapter 12), I suddenly started to recognize and then re-interpret dozens of soils / landscapes (old-growth forest -> shittiest dead zones) I've been in, with a new clarity about why (given the criteria of a soil microbiology POV) their plant communities were what they were too! :D That's cool!

There's too much essential and excellent advice in this book to try to sum up, but here's one bone for native plant gardeners: LEAF MULCH. Specifically, dry, brown and aged. Apply it on top of the soil (not into the soil: applying into the soil encourages bacteria more than fungi: which would be fine for annuals and veggies). Why? That mulch will feed and encourage networks of fungi that native plant perennials and woodies NEED to uptake nutrients in at the root level (rhizosphere) below. You can take that on faith or, if you'd rather actually know what's going or to see a lot more excellent advice, read this book! :) It's in circulation at the Toronto Public Library, or buy it. This one's worth it.

Growing trees.

An excellent article about Toronto's urban forest by LEAF's Todd Irvine appeared last Sunday in the Toronto Star. Excerpted from greenTOpia: Towards a Sustainable Toronto Vol.3

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"Carolinian Canada" is a big place. A lot of plants are actually very regionally specific. For example Redbud is only really native down near Point Pelee, and Winged Sumach only occurs in Norfolk and Prince Edward Counties. Ever tried to find which tree and shrub species are really indigenous to your region? Check out Forest Gene Conservation Association's list of trees and shrubs native to the Toronto area / eco-district 7E4. Also see this site for native trees and shrubs elsewhere in South-central Ontario.

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We're not just growing plants, we're growing soils and the biota who live there. This is especially important in urban and suburban areas where so much of our soil-life has been heavily disturbed and destroyed. In past few years we've started to clue-in to the necessary role of mycorrhiza fungi in tree health. Check out Mycorrhizae: Unsung Heros of Forest Health from the Ontario Arborist.

Garlic Mustard: Negative impact on hardwood trees, seedlings, mycorrhiza & rare West Virginia White butterflies

A Perspective on the Ecological Ramifications Of Garlic Mustard
by Donald A. Sutherland - Biodiversity Section of the OMNR

“The garlic mustard/sugar maple relationship would give Norway maple an additional competitive advantage, particularly in the ravines of Toronto and other riparian areas of southern Ontario where garlic mustard is abundant. Garlic mustard could reduce or eliminate the soil mycorrhizae necessary for the survival of sugar maple seedlings and thereby give a competitive advantage to Norway maple. I have no idea whether Norway maple seedlings are similarly dependent on soil mycorrhizae for their survival, but both exotic, Norway maple and garlic mustard have presumably evolved together. Norway maple produces abundant seed with high viability rates and is tolerant of air pollution such that it has already a competitive advantage over the native Sugar Maple in urban and near-urban areas. In more native forest situations, a loss of sugar maple could in the long term have grave implications for forest song birds which are dependent on the many sugar maple-obligate invertebrate species which feed on the maple. Many forest lepidopteran species, for example Bruce's Spanworm, are largely dependent on sugar maple and the loss of these species (and particularly their larvae) could considerably reduce available food for forest birds and their nestlings.

Garlic mustard is already posing a serious problem for one of the province's SAR butterfly species. The West Virginia White, currently a special concern species in Ontario, is a relatively widespread but uncommon forest butterfly throughout its eastern North American range. The larval host of the West Virginia White is a native member of the mustard family, called toothwort. Increasingly, West Virginia White is being observed nectaring on the closely-related, early-flowering garlic mustard; however, not only is garlic mustard a common source of nectar for the butterfly, but the West Virginia White is preferentially laying its eggs on the exotic mustard. The eggs hatch, but the mustard is evidently unpalatable to the maturing larvae and the butterfly larvae don't survive beyond their first instar - thus garlic mustard is effectively an ecological cul-de-sac for the West Virginia White. Never abundant, the West Virginia White has recently been placed among the ranks of globally rare taxa by NatureServe, largely thanks to problems with garlic mustard.

There is often the perception that some exotic species are benign. Exotic species are never benign they only appear so because their impacts haven’t yet been recognized.”

Please also see:

• Invasive Plant Suppresses the Growth of Native Tree Seedlings by Disrupting Below ground Mutualisms. Stinson KA, Campbell SA, Powell JR, Wolfe BE, Callaway RM, et al. (2006) PLoS Biol 4(5): e140
• Invasive species harms native hardwoods by killing soil fungus - Steve Bradt, Harvard University, Apr 26/06 “Find is first to identify specific mechanism by which invasive plants harm native species”
• Garlic Mustard photos & information: Global Invasive Species Database – ISSG – Garlic Mustard

• For more information please see other Garlic Mustard, mycorrhiza or invasive plant resources posted on this blog.

Garlic Mustard - killing trees by changing soils' microbial communities?

Phytotoxic chemicals produced by A. petiolata may interfere with growth of native species, potentially through inhibition of mycorrhizal activity - Vaughn and Berhow, 1999.

"Garlic Mustard Alliaria petiolata infestations shift microbial community structure by increasing the population of free-living nitrogen fixing bacteria. As garlic mustard is currently invading forests at high rates there is a concern that changes in microbial community structure will alter nutrient availability or competitive dynamics of aboveground biomass and alter nutrient dynamics of North American forests." Possible shifts of microbial community structure in temperate forests of central Illinois ...the adverse effects of an invasive species, Alliaria petiolata, on pine plantation stands.

For more information please see other Garlic Mustard, mycorrhiza or invasive plant resources posted on this blog.

Here's a good, relatively local & easy to understand Garlic Mustard Fact Sheet from the Fletcher Wildlife Garden in Ottawa.

Since we're talking about tree health & beneficial mycorrhizal fungi...

Case for inoculating urban trees with a diversity of beneficial mycorrhizal fungi:

"Urban trees, in particular, are subject to many environmental stresses. Many harmful chemicals are deposited on the trees and directly on the soil, and the ground they are growing on is typically heavily compacted. Also, let's face it, they don't exactly grow on great quality soil. Furthermore, young tree seedlings and sapling growing in nurseries are typically fertilized, which further eliminates many beneficial mycorrhizal fungi. Some of our preliminary research in the cities of Guelph and Toronto shows that trees in streetscapes are heavily infected by mycorrhizal fungi (a good thing), but fungal diversity is very low (not a good thing). Many species normally associated with these trees in forests have become extinct from urban environments.

In a recent field-trial we tried to bring back some of these fungal species. We inoculated black maples with a cocktail of mycorrhizal fungi to see if this would improve their growth. During the first year, there was no sign that inoculation helped at all. All trees were similar is size and overall health, and we began re-evaluating our story. But then came the big summer drought of 1998. This placed a lot of stress on our experimental trees, and right now, the inoculated trees are the only ones that have survived. This suggests that things may be fine during normal years, but that this diversity of fungi may be important during years with extremes in climate. As climate is expected to be less predictable in the coming years, mycorrhizal inoculations may prove to be more necessary."

Excerpt - Mycorrhizae Research Information Dr. John Klironomos, University of Guelph

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Care about Toronto's urban trees? Visit LEAF and Urban Forestry Services.

You might also like Trees of the Carolinian Forest by Gerry Waldron