My favorite tree (at least right now)

I'm a huge fan of American yellowwood (Cladrastis kentuckea). A US native with smooth silvery bark like a beach, lovely yellow fall color, and right now, this:

Big clusters of dangling, fragrant white flowers almost like a wisteria. Sadly, though, not everyone has the same experience with this tree. Mr. McGregor's Daughter just posted pictures of her tree, and they look pretty sad. I'm not sure what the difference is: She's in Northern Illinois, I'm in Central Michigan, both zone 5. Here the show tends to be this impressive every other year, but she says her's hasn't flower in 5 years! This particular tree is sheltered by a big building, but there are lots of them around campus, and they all look amazing. Any theories?

Dame's rocket

The wildflowers along my daily ride into work are, once again, outdoing the best gardeners. Here are a couple shots of the sheets of dames rocket (Hesperis matronalis) making parts of the woods lovely (and incredibly fragrant) right now.

Before I gets lots of angry comments: Yes, I know it isn't native. I also can see it is far from forming a monoculture, as there are lots of other plants in these stands that it is getting along with just fine, and I've only seen it in large numbers in disturbed, road-side areas like this. I'm certainly not going to spread it to areas where it isn't already growing, but I don't see any harm in enjoying its beauty.

More on invasive species

I've been reading about invasive plants. In my post about purple loosestrife, I promised more about invasive plants which actually have been shown to have significant negative effects on native species.

Easier said than done.

I though I had hit what I was looking for when I found a paper titled Ecology and ecosystem impacts of common buckthorn (Rhamnus cathartica): a review The paper starts elucidating why it is so successful: Shade tolerance, rapid growth, high photosynthetic rates, etc etc. Sounds great. But when it gets to showing how it hurts native plants, it all sort of falls apart – even though the authors clearly WANT common buckthorn to be a bad guy. Allow me to quote:

“Although the surveys and removal experiements do not definitively implicate R. catharica in the decline of native species, and the controlled experiments under individual R. cathartica threes did not show detrimental effects on understory plants, it is quite likely that R. cathartica thickets have negative effects on native species in North America.”

Which I translate as:
“All the evidence shows it really isn't a problem, but we bet it is bad anyhow. Just because.”

I could keep plowing through other species, but I decided to get a bird's eye view of the issues of non-native species, so I read the book Invasion Biology by Mark A Davis (Not to be confused with another -- much less reputable -- book by the same title by David Theodoropoulos). It's aimed at a professional academic audience (professors, grad students) but is very readable, and pretty interesting.
Basically, they say that there is good evidence of serious damage caused to native species by non-native predators and diseases – eg: emerald ash borer, dutch elm disease – especially on islands and small lakes, which ecosystems tend to be more fragile. But most non-native plant species are off the hook (which makes the practice of introducing new non-native predator insects to control non-native plants even more suspicious... let's import something very likely to be a problem to control something which most likely isn't a problem!)
There are plant species which cause significant damage --  not by out-competing native species, but by changing the environment. The best example (actually the only example I've been able to track down so far) are the European grasses in the genus Bromus which changing parts of the Western US. They are much more flammable than native species so areas they have invaded burn more frequently, causing enormous impacts on the entire ecosystem. So some non-native species are bad. Some non-native plants are bad. But my impression from all the reading I've been doing is that in most cases, people have simply seen a non-native species outside of cultivation and ASSUMED it must be doing damage even though indepth studies rarely support that assumption.
So... as a gardener and someone who cares about the environment, what do I do with this? First, I'm certainly not going to support organizations that spend large amounts of time and money trying to eradicate invasive species unless they have very good evidence that it is actually worth it. Pollution, urban sprawl, and global warming are issues I'd much rather spend time and money fighting against. And in my garden? I'll still avoid planting species with the potential to invade natural areas – no one is arguing that invasive species are a GOOD thing – but honestly (and I know this is going to make people mad...), I'm not going to make it the priority I used to. It looks like the carbon dioxide my car emits driving to the nursery to buy the Iris pseudacorus is way more damaging than the presence of that non-native species in my garden.

The Loosestrife Drama

One of my goals in ths project is to present information from hard-core academic literature in simple, everyday language. So it is my great pleasure to present to you today the great Loosestrife debate, as a play, in one act.

Rawinski and Malecki (1984):  Purple Loosestrife is taking over! AHHH!! STOP IT!!! HORRIBLE PURPLE WEED!!!!

Government, environmental groups, people in general: Dude! It is purple and evil! (run about trying to kill purple loosestrife. Spend tons of money. Introduce non-native beetles to eat it. Generally go nuts.)

Hager and McCoy (1998):  Umm... People? Have you actually READ Rawinski and Malecki's paper? It sucks. Basically, they just decided to hate on loosestrife because it is so purple and they noticed it everywhere.

Government, environmental groups, people in general: Lalalalala! I can't HEAR you! (keep spending lots of money trying to kill purple loosestrife)

Anderson (1995), Farnsworth and Ellis (2001), Houlan and Findlay (2004) : (Do a lot of actual research to see if loosestrife is hurting anything) Um... People? Like, Hager and McCoy were right, this loosestrife stuff doesn't seem to be that big of a deal. It just sits there being purple.

Government, environmental groups, people in general: Lalalala! I can't HEAR you! (keep spending lots of money trying to kill loosestrife)

Okay, so I'm being silly, but I started reading about purple loose strife because I wanted to use it as an example of what, exactly, invasive plants do to native species in areas they invade. Surprisingly (to me anyway), in the case of purple loosestrife, the answer seems to be... just about nothing. That's not the whole story – many other invasive species do a lot of damage (more about that in a future post) but it is shocking that so much money and time has been invested in killing purple loosestrife without good evidence that it is worth it. No less than three non-native species of insects have been introduced to the US just to eat the loosestrife. And what if those beetles start eating some other native plant as well?

The lesson I'm taking away from this is: While no invasive plant is good, many aren't all that damaging, and we need to make sure we invest the limited resources we have to save the environment on the issues and species that matter the most -- not just the ones which are easy to notice because they have bright purple flowers.

(Photo: from Urtica on flickr.)

Introducing The Natives Project

Beyond feeling vaguely virtuous when I plant something labeled 'native' and vaguely guilty when I hear a plant I love may be invasive, I've basically ignored the issues of native and invasive plants as a gardener. Partly because I'm afraid I'll have to stop growing some of my favorite plants, partly because it quickly becomes confusing.

What even makes a plant 'native' for my garden? Native to the US? Native to Michigan? Native to the Great Lakes Region? What about those (fabulous) new echinacea? Man-made hybrids between two species native to the Eastern US, neither of which would have grown in the woodland that was my yard before it become part of an ailing industrial city. Native? Non-native? Synthetic abomination? Just plain lovely so who cares?

Same with invasive species... Should I stop planting my beloved cardoons because they are an invasive weed in California? They can't make it through a winter here, but who knows, maybe the seeds could.

And what about plants for wild life habitate? Is native always better? What about the  non-native crab apples loaded with fruit that native song birds love?

There are so many issues to consider and questions to answer, but I've decided I can't ignore these issues any longer. Environmental stewardship is important to me: I ride my bicycle instead of driving, bring my own bags to the grocery store -- I ought to be informed on this significant environmental issue.

So I'm going to figure it out -- here, on this blog. I'm going to be reading everything I can find on the subject, thinking about it, talking to people who seem knowledgeable, and blogging about it all here. Hopefully, comments and questions from you, my readers, will help expand the discussion along the way, and we'll all come out at the end with a clearer understanding of the issues involved.