Must we continue to bring in exotics?

A couple weeks back I posted about a collaborative research project that I am involved with to identify seed sources of two Mediterranean fir species (Turkish fir and Trojan fir) for use as Christmas trees in various locations around the country.   The post prompted a question from Monta Zengerle who asked, “Must we continue to bring in exotics to satisfy the nursery trade?”  Since our intended purpose is Christmas trees and people move plants around the world for purposes other than nursery stock, I’ve broadened the question to “Must we continue to bring in exotics?” for this discussion.

Not all exotic species introductions are man caused.  This dock washed ashore in Oregon following the Japanese tsunami carrying all kinds of critters with it.

The answer, of course, is “No.”  As human beings the only things we absolutely have to do are eat, sleep, and breathe.  But the reality is much of the food and fiber production around the world, as well as our amenity plantings, are based on exotics plants.  Human agricultural history is largely the story of plant importation and subsequent breeding.  As Thomas Jefferson famously observed, “The greatest service which can be rendered any country is to add a useful plant to its culture.”  However, it is doubtful that Jefferson considered kudzu or purple loosetrife could be among those plants added to our culture.  Today we have a different understanding and realize that along with the economic benefits of plant exploration and importation comes the possibility of unintended and serious ecological consequences.  And we’ve realized this for some time. People that deal with plant introductions on a regular basis talk about ecological errors and economic errors.  If we allow importation of a plant that later turns out to be ‘bad actor’, we’ve made an ecologically harmful decision; if we ban a useful plant that ultimately would have turned out to be non-invasive, we’ve suffered an economic loss.  Fortunately, only a small percentage of exotic species become naturalized and only small percentage of naturalized species become invasive.   The underlying challenge is we cannot predict with 100% certainty which plants will be invasive in a new environment and which won’t.  Ecologists are working on it and we can certainly begin to judge the invasive potential of new introductions.  In the meantime, we are left with the imperfect calculation of whether the potential economic upside outweighs any potential environmental risk.

‘Top-work’ on noble fir in Oregon to maintain a single terminal leader.  Turkish fir typically require less top-work.

So let’s look at our current project as a case study.  What’s the upside?  Christmas tree growers in the U.S. produce roughly 20 million trees annually.  That’s a potential economic impact of hundreds of millions of dollars and seasonal and full-time employment for workers on over 13,000 farms from North Carolina to Washington State.  A major issue for growers in virtually all of the principle growing regions is phytophthora root rot.  Previous work at Oregon State University indicates that Turkish fir is highly resistant to this pathogen.  By identifying seed sources with phytophthora resistance and superior Christmas tree characteristics (tree form, needle color, post-harvest needle retention), we will enable growers to continue or expand production and give consumers an additional choice for their holiday tree.

Native noble fir (left) is highly susceptible to root rot. Turkish fir (right) is much more resistant.

What’s the down side?  As I mentioned, predicting invasiveness is difficult.  That said, firs have several characteristics that make them unlikely invaders.  Most firs have a relatively long juvenility period (age before they produce seed) which means they have a long period between generations.  Secondly, most fir species produce seed crops sporadically as opposed to producing heavy seed crops year after year.  Ecologically, firs are pretty wim
py; growing best on moisture, well-drained sites and unlikely to aggressively colonize disturbed areas.  Lastly, the best predictor of invasiveness is invasiveness – a plant that has become invasive in one location is a candidate to become a repeat offender in a similar environment.  Among conifers, the greatest issues with invasives have been pines (genus Pinus), in the southern hemisphere.  In fact, all of the documented cases of invasives in the pine family (Pinaceae) are Pinus species; none were Abies.  Based on all this, the likelihood of Turkish fir or Trojan fir becoming ecological problems appears very small, while the potential to add a useful plant to our culture is clear.

Exotic giant sequoias at Hoyt arboretum, Portland, OR.

Richardson, D.M. and Rejmánek. 2004. Conifers as invasive aliens: a global survey and predictive framework. Diversity and Distributions 10:321-331.

How Can Natives and Exotics Possibly Coexist?

Natives vs. exotics. We’ve heard that before haven’t we Bert?  Well, here’s an interesting little nugget published recently in the journal Ecology Letters.  Exotics and natives are different, and their differences allow them to coexist.  In this study exotics were superior to natives in terms of growth, but were fed upon more by herbivores.  Interesting.   Of course there are lots of different types of exotics and natives, but the plants that these researchers looked at had been living together for about 200 years.  I think that’s something that the invasive extremists and apologists consistently forget – until relatively recently the average person didn’t spend that much time thinking about native or exotic, and yet the world never turned into a desert and neither the natives nor the exotics disappeared.  I’m not saying we shouldn’t think about native vs. exotic differences at all, just that sometimes we concentrate on this distinction too much. Plants tend to be able to fend for themselves.

Are natives the answer? Revisited

I started to leave a comment on Linda’s Friday post regarding Seattle Public Utilities proposed building codes regarding “Healthy Landscapes” but decided I’d weigh in with a regular post.  Linda honed in on the 75% native requirement but there are lots of things to make one scratch their heads in the proposed codes.

Existing invasive plant species shall be removed and no invasive species planted.
No mention of how invasive plants shall be removed.  Heavy-duty herbicides? Armies of school children forced into slave labor? Slow-moving ground-fire? Goats?

75% of all new plantings will be native to Western Washington.
So where did 75% come from?  Sounds like a number that was pulled out of the air.  How is 75% defined?  75% of plants? 75% of the area?  And how does this foster “Healthy Landscapes”?  If I have a 2 acre landscape and plant an acre and half of salal or Oregon grape I’ve met the requirement of 75% but have I increased species diversity or structural diversity or contributed to a “Healthy Landscape”?

A vegetation plan must be submitted for review.
By whom?  What happens if they (whoever ‘they’ are) don’t like it?

Existing native plant species shall be protected whenever possible.
Sounds reasonable but what about existing non-invasive non-natives?  Could a homeowner be required to cut down a 40-year-old red maple?

And on and on we could go.  Let me state clearly, I’m not against native plants.  Quite the opposite – I grew up in western Washington and have a passion for PNW plants since my high school days.  Since moving to Michigan I’ve written articles and given talks promoting natives here as well.

Nonetheless, I think many in the native plant movement hurt their cause by parroting the same old lines without ever critically thinking about what they’re saying.  Repeating a lie often enough times does not make it the truth.

Let’s critically look at some of the reasons for planting natives according to the Washington State Native Plant Society:

Native plants are adapted to our climate of wet winters and dry summers.
True. But so are lots of non-natives.  Adaptedness is a function of the environment in which plants have evolved; whether it’s native or exotic.  There are many climates around the world that are similar to the PNW and can produce similarly adapted plants.

Require less water than most non-natives once they are established.
Once again, adaptations such as drought tolerance are a function of the climate under which plants evolved.  There are many exotic species that are more drought hardy than western Washington natives and likely to use less water.

Resist native pests and diseases better.
Sometimes. But unfortunately the days of worrying only about native pests are in the distant past.  Exotic pests are here and they are here to stay.  Dutch elm disease, white pine blister rust, emerald ash borer, chestnut blight, Japanese beetle, the list of exotic pests is long and getting longer.  Native does not mean pest-free.

Improve water quality by needing less fertilizer and no pesticides.
OK, here’s where I get confused.  The reasoning in Doug Tallamy’s book, Bringing Nature Home, is that native insects don’t feed on exotic plants, therefore if we plant exotics, native food pyramids will collapse and it will be the end of life as we know it.  So… if native insects won’t feed on exotic plants, why would exotics require more pesticide use?

Save resources and encourage a sense of Stewardship.
Ok, now maybe we’re getting somewhere.  Not sure why stewardship is capitalized here but if they mean a ‘sense of place’ or a ‘connection to the natural environment’ then I can buy it.  Many native activists, including Tallamy, run away from this argument – apparently it doesn’t sound scientific enough – but it’s one of the best we have.  Washington state has some of the most incredible plants anywhere.  They should be celebrated and promoted and planted.  In my mind, the biggest reason for planting natives – along with carefully selected non-natives – is to increase overall biodiversity.  When I mention biodiversity I am speaking broadly; species diversity, structural diversity, age-class diversity, and landscape diversity.  When we look to the future we have no idea what lies ahead. We don’t know what new, exotic diseases or insects are looming on the horizon. Most of us expect climate will change but no one can say with certainty how.  Plants cannot evolve as fast as climate will change or as fast as new pest will be introduced. The only way to deal with this uncertainly is to spread the risk through diversity – this includes natives, exotics, and even interspecific hybrids.

Invasives! Natives! No, wait, biodynamics

Just had to get your attention there.  We’ve had a great discussion over native and nonnative plants over the last few weeks.  I’m going to completely switch gears and move on to another topic  – biodynamics.

If you’re not familiar with this term, let me refer you to my online column here.  Biodynamics is a set of agricultural practices based on a belief system, not science, but is an increasingly popular approach, especially in the wine industry.  (You can read a discussion of biodynamics in the vineyard in The Skeptical Inquirer here.  This article is engaging as well as accurate – my column is pretty dry by comparison.)

Biodynamics is steeped in mysticism and includes special preparations that are used to treat soils and plants.  Preparation 500, for example, is created by mixing water with manure that has been packed into a cow’s horn and buried for a set amount of time.  Other preparations are more gruesome, requiring a stag’s bladder or cow’s intestine.  A whole certification process has emerged in support of these practices.

While it may be easy to dismiss these practices, it turns out that biodynamic farms or vineyards are generally healthier than conventional systems.  Does this prove a mystical force at work?  Not at all.  Biodynamic systems are also organic – using all of those good practices (low or no till, reduced pesticides, reduced fertilizers, polyculture, etc.) that have been demonstrated to be effective over decades of research.  When comparisons are made between biodynamic and conventional systems, the impact of organic practices are hidden.

The few scientific studies that have compared biodynamic to organic systems – in other words, specifically testing the effectiveness of special preparations – have found no repeatable, significant differences.

Why do I even care about this?  Well, it’s because it’s pseudoscience.  It’s a practice that takes on the mantle of science, but doesn’t stand up to repeated scienific testing.  Belief systems can’t be tested – even the inventor of biodynamics asserted that his methods were “true and correct unto themselves” and didn’t need to be tested.

Apparently simply being organic isn’t sexy enough anymore.