Migrating through the Merriam Mountains

By Frank Landis, Chairperson, Conservation Committee 

I'm still mulling over the issue of plant migration, and since I'm writing this in the middle of August as a break from working on the Newland Sierra EIR, I figured it was worth a column combining the two. This may get messy. 

The Newland Sierra project does affect plant migration pathways.  The property, which is in the Merriam Mountains north of Escondido, just west of I-15 and just north of Deer Springs Road, is a bit of a biological black hole, as in no SDNHM Plant Atlas or Bird Atlas data, although there are CNDDB data and what the developer and others have reported. Still, the Merriam Mountains are considered valuable because they're a big block of undeveloped land with links to other undeveloped blocks of land. As such, this area is both a core habitat area for plants and animals, and a key link between three wildlife corridors.

Unfortunately, the Newland Sierra project intends to expand Deer Springs Road from two lanes to six lanes, and to dissect the southern half of the project site into multiple small undeveloped patches (the development looks a bit like an octopus).  This is problematic for the small patches, since they're mostly chaparral.  As we have seen in the canyons in San Diego, small, isolated chaparral areas tend to lose their fire followers over time, and Merriam Mountains has some old chaparral dominated by fire followers like chamise.  While most of us have trouble mustering tears for old chamise dying away, I'm not at all sure what will replace the chamise in these small areas if they die without a fire.  While Newland Sierra claims to be saving these areas, if the dominant plants die out and the vegetation changes radically, was it saved?  Connectivity matters.

The bigger problem is that the wildlife corridor to the east has to go under I-15.  There are three culverts under the highway by the Merriam Mountains, but the biggest (and most used) culvert is on the south side of Deer Springs Road, across the road from Newland Sierra. The road expansion and all the south-side development basically disconnects the northern half of the Merriam Mountains, with their two wildlife corridors to the west and northwest, from the southeast corridor on the east side of I-15. That's a big problem, but I won't be commenting on it for CNPSSD, because CNPS doesn't talk about wildlife corridors.

Why don't we talk about wildlife corridors? Because we are a science based organization, and because we don't know enough about how much plants depend on wildlife corridors to migrate. This sounds nonsensical, but here's the question: how do plants migrate?

We don't know, and that's a problem. Obviously there's a lot of science out there, but it's dispersed among many sources. Plants tend to get dispersed as seeds or spores (with the occasional willow getting washed downstream and replanting itself). We do know that some seeds travel by gravity (meaning they roll downhill).  Some are dispersed by animals, either eating them (berries), or as nuts that are stored by animals without being eaten, or as burs that cling to feathers or fur, or as seeds with elaiosomes carried by ants (acacias), or by being carried and buried by gophers and squirrels, and by force (pods that pop seeds). Some spores and tiny seeds float on the wind and water, and some are expelled from the mother plant by force. While it's obvious that gravity-dispersed seeds aren't going to move by themselves through a freeway culvert, when we deal with animal-dispersed seeds its much less clear. For example, we also don't whether things like manzanita seeds will be hauled by rats and mice through wildlife crossings to be buried and cached on the other side. Nor do we know whether Summer Holly (Comarostaphylis diversifolia) and Engelmann Oak (Quercus engelmannii) are carried by mammals through wildlife crossings. Perhaps they depend on scrub jays and mockingbirds to fly across the freeways instead? While I can speculate, I can't say for sure, and speculating that plants need wildlife undercrossings won't stop a road from being widened. This is true even if we're trying to preserve the summer hollies and Engelmann oaks that live on the Newland Sierra property, and these plants are supposed to be protected by the upcoming North County MSCP.

This gets more generally to the problem of plant migration and assisted migration. We know so little functional information that it's impossible to say how necessary it is for humans to move and plant seeds of each species, let alone populations of each species.  Can we get away with making freeway undercrossings more hospitable for deer mice lugging manzanita and summer holly seeds and for squirrels carrying acorns? Or is it more appropriate for us to collect the seeds and replant them where we think the next generation needs to grow? It's not a simple question.

Of course, it gets more complicated. One complication is the specialist help that some plants require. While I don't think it's possible to plant manzanitas where there aren't deer mice to cache their seeds, things get a lot weirder when we're talking about plants like mistletoes, which disperse best with phainopeplas, birds that specialize in eating mistletoe berries and pooping the seeds out on branches. If we care about mistletoe migration, we have to make sure both that phainopeplas fly the migration route while carrying precious mistletoe seeds, and that there's a suitable mistletoe host plants waiting for them to defecate upon. Migration gets even more complicated with other parasitic plants, some of which, like snow plant (Sarcodes sanguinea) parasitize specific ectomycorrhizal fungi (Rhizopogon ellenae in the case of snow plant).  While some fungi produce mushrooms and other aboveground structures that throw spores into the wind and migrate thusly, others produce truffle-type underground fruiting bodies that have to be consumed by animals and moved in animal guts.

This is not to say that whole communities have to move in lockstep, as if the plants are part of some great community-machine. Plants, like humans, make communities where they settle, based on whatever is there. Some are so specialized that they can only survive with their partners, others are less picky, and none of this necessarily affects whether a plant is common or rare. So far as I know, it's okay to make new ecosystems using migrants, although as an ardent CNPSer, I'm going to insist that those communities be made with California native plants. At least in California. At least for now.

And there's another level of complexity: most plant species are not genetically uniform, not crowds of clones. When we talk about assisting plants to migrate north to deal with climate change, it may sound intuitively obvious that we should move southern, heat-adapted plants north to mate with their northern, less-adapted kin. However, back in the last ice age it wasn't so obvious. Back then, the northern plants were the trailblazers colonizing the raw landscapes left behind by the retreating glaciers. Sure, 10,000 years or more has passed, but are the northern populations of some species more pioneering than southern populations? Perhaps, and if so, we don't want to swamp out that pioneering genome with a bunch of southern stay-at-homes. Also, some plant species are more heat tolerant than others are. Not everything needs to migrate to survive climate change. Creosote might do just as well where it is. Which plants need to move? It's hard to say. Stress testing a plant is tricky, especially since plant durability varies with age, and seedlings tend to be more delicate than adults. Does this matter? It might, because if we're going to spend the effort trying to help them migrate, they should survive the process.

Unfortunately, the point of this long and twisted presentation is that we can't depend on science to answer all our questions before we have to decide whether to help a species migrate or not.  Science can help a lot, but if we wait for all the answers before acting, try to let the data make decisions for us, then we're simply betting that the plants will survive without any help from us at all, because we'll never have all the answers we want. That's a big bet to make, especially for familiar coastal species like Torrey pines which have no parkland pathways up the coast for them to colonize, due to a century of urbanization.

In the meantime, I've got to figure out if I want to argue that plants need to be able to move under freeways and across roads without getting run over. It might sound weird, just as making a deer mouse/summer holly seed undercrossing sounds weird.  But until we decide if and how we're going to help plants migrate, then we've got to make it easier for the mice, the jays, the mockingbirds, the coyotes, the phainopeplas, and everything else, to move the native plants instead.