Platitudes and Plants
A recent article that I found compelling and posted on Facebook that was originally posted on Huffington Post has me thinking very seriously about the subject of native plants.
It posited the idea that the same plants are planted in similar climates the world over. It was an opinion piece that decried the lack of diversity that imperils native fauna by the lack of native flora. Here is the link to the story:
‘Just Because It’ll Grow in Your Yard Doesn’t Mean You Should Plant It’ -Lisa Novick
Native plants is a term bandied about by well meaning people, it has real practical applications and it is so much more complicated than politically correct buzz words. As with any idea it is subject to both narrow and broad interpretation but to really make an informed opinion I think there should be some background information. I’m not going to espouse an opinion that is right or wrong. Rather, I will give you perameters that I hope will help you as gardeners make up your own mind. At Xera we have our own interpretation of the term and I will describe our philosophy that shapes what we choose to grow and promote.
Vocabulary- Words shape the garden
For a more comprehensive understanding of where plants grow and why there are a group of vocabulary words that I think are useful. Once they are combined they can give the gardener a clearer picture of how to view native plants.
Edaphic- Soil and the composition of soil- this greatly influence the plant community that resides there. I.E. Scree- loose rocky soil. Clay- tightly compacted particles with a heavy silica component. Soils can range from poor nutrient content (Sand) to high nutrient content (humus). Plants are greatly influenced by edaphic conditions. A striking example of this is found in serpentine soils of Southern Oregon. These soils are high in toxic heavy elements such as zinc and nickle. In this environment- where serpentine conditions rise to the surface it can abruptly influence plant communities. Plants not adapted to this stop abruptly and a whole new adapted community dominates. This is a severe example of edaphic adaptation but it makes an important example.
Mesic- Soil conditions with a positive influx of moisture. Plants can also be described as mesic and those rely on a continuous supply of moisture and are less adapted to dry conditions. Mesic designated plants often have lush, foliage with little adaptation to drought. As an example the foliage of mesic plants has little ability to inhibit moisture loss through transpiration. A majority of shade plants are mesic. Plants that are shielded from direct sunlight put more energy into photosynthesis and less into structure that limits moisture loss. They often lose moisture at the same rate they accrue it. These are the plants that require constant summer irrigation in our gardens. Think of native ferns and native Bleeding Heart (Dicentra formosa).
*Transpiration- The loss of moisture through plant foliage.
Hydric-These are soils that are predisposed to seasonal or continuous water inundation. This can be stagnant (anaerobic ) and/or temporarily inundated. Riparian zones- along water ways typify this description. For instance the plants in these areas are primarily mesic in nature. Two species in Western Oregon that typify Hydric soils are the beloved blue Camas (Cammasia quamash) and Oregon Ash (Fraxinus latifolia).
*Riparian- Wetlands adjacent to rivers and streams.
Xeric- An environment that is starved for moisture. Xeric also describes the adaptation of plants to deal with a continuous moisture loss. Xeric plants may employ a variety of ways to limit this. Hair on leaves, waxy leaves, succulent foliage, leaves held perpendicular to the sun are examples of adaptations of Xeric plants that interrupts the loss of moisture. In Western Oregon xeric conditions are often found on south facing hillsides. It can also occur in urban areas adjacent to asphalt- which is taking the idea one step further.
What can be tricky is that many (most?) plants do not adhere to one or the other, Xeric or Mesic they all have their own adaptation. But by describing the extremes you get a better idea of how they work. And how they can work for you.
Biome- A region of similar climate and conditions that harbors like flora in a continuous zone. It is defined by conterminous precipitation, temperatures, and soils.
Ecotone- The margins between two biomes- a transition zone. For instance the boundary between a forest and a grassland. This may be abrupt- in several tens of feet or gradual, many miles. Differing soil conditions (edaphic), moisture, exposure, elevation, or latitude can drive this change.
These words can give you a rudimentary description of the places where plants grow. Just saying that a native plant will grow in any situation is horribly flawed. Now most people do not really mean to simplify it into one category- and yet you often see “native plant” gardens with species from all different biomes jammed together into one space. It really is a problem that people are not educated to understand the different circumstances that each plant requires. For instance a Biome can extend far beyond our political borders. The Willamette Valley which receives between 35-50″ inches of rain on average and low temperatures annually between 10º and 20ºF is not discrete. The same situation occurs at higher elevations though out Californias mountains. Gradually rising in elevation as you move south. These areas have surprisingly similar flora. Douglas Fir (Pseudotsuga menziesii) Ponderosa (Pinus ponderosa) Oregon White Oak (Quercus garryana) and Western Dogwood (Cornus nutallii) repeatedly show up in this continuous biome south to the lower third of California. In fact Douglas Fir extends as far south as central Mexico at very high elevations. (It is thought that Mexico is the paleo origin of this species that is so iconic of the Pacific Northwest).
Plants Are on the Move
We may think of the range of plants as permanent- and in a humans lifetime their ranges don’t really extend that dramatically. In the course of natures timeline this is far from the case. In reality species are in nearly constant movement increasing their range in one direction, withdrawing in another- driven by the change in climate that has waxed and waned with the ice ages and interstadials (warm periods between ice ages).
During the cold dry periods of the ice age in Western Oregon species of trees that now dominate the highest elevations of the Cascades dominated all of the lower elevations of our state. At the glacial maxima 11,000 BP the Willamette Valley was a vast forest of Tsuga mertensiana (Mountain Hemlock), Picea englemannii (Engleman’s Spruce), Pinus contorta var. murrayana (Lodgepole Pine)- a current assemblage of flora that now occurs at Government Camp at 4800’+ on the slopes of Mt. Hood. The question this poses is are these locally native plants if only separated by a few thousand years?
The Right Plant in the Right Place
So, if you take the time to learn the correct biome where a plant occurs you will successfully grow many native plants. As an example Ribes sanguineum (Flowering Currant) is a plant of the forest margin ecotone. It thrives on the borders of woods. Luckily it can take full sun as well- to which it has been committed in untold blasting hot landscapes. But forest margins are where it thrives. Trilliums such as Trillium ovatum which decorates the woodlands in early spring is clearly a mesic plant – but it avoids the heat of summer by going safely dormant.
At Xera we have taken a broad approach to native plants. Instead of confining them to their specific political boundaries we try to embrace the whole extension of their occurrence in a biome. To extend that further we seek out plants in similar biomes throughout the world. That is not all of what we grow but its an overall important component. And as we like to say, native plants are great, especially if you know what to do with them.