Ponderosa Pine on Tygh Ridge: Succession or Invasion?

Scattered Pine in Tygh  Ridge Grazing Lands

Tygh Ridge is located in North Central Oregon and is part of the Columbia Basin Ecological Province. Much of the land has been continuously tilled and planted with dryland wheat over the past century. This hasn't been conducive for succession (see my last post) or for the land to be anything more than short term grassland.

OSU's ecological profile indicates that the expected vegetation over much of the Columbia Basin habitats would include some shrub cover, but doesn't mention any thing about Ponderosa pine. However, over the last twenty years the pine has established and spread in certain areas on Tygh Ridge.   How could that be?

There are many variables, but here's my take on it.  Most of the change was kicked into motion with the expansion of the Conservation Reserve Program.  In the mid-1980's, the program was expanded in order to protect highly erodible soils such as those on Tygh Ridge. Thousands of acres were taken out of production for wheat and seeded into expansive stands of grass where livestock grazing wasn't allowed.  By the mid-1990s I first started to notice pine trees where I hadn't seen them in the thirty years prior.

There also was funding available for landowners to plant shelter belts and  trees for wildlife habitat.  Perhaps   some of the pine got into the middle of the grasslands by planting, but I'm not convinced about that because the placement of the trees is so random.  It always seems that when humans are involved in something they must have a certain sense of order!

Ponderosa Pine in Idaho Fescue Grassland  on Tygh Ridge

Where did the seed come from? 

The Dalles Ecological Province is a long, thin map unit that covers most of the east slopes of the Cascade Mountains in North Central Oregon, and is adjacent to the Columbia Basin Province. Tygh Ridge lines the northeastern portion edge of The Dalles Province.

The Dalles Province is  forested with Ponderosa Pine, Oregon white Oak, and smaller amounts of Douglas fir. Those who have never been in that part of the world might find the transition, from the forested The Dalles habitat type  to Columbia basin grassland type, abrupt.  Once at the base of the Cascades, the trees don't slowly peter out as they often do in transitional zones, they just cease to exist in the landscape almost as if there is a line that they are forbidden to cross.  That's part of why it's surprising to see so much Ponderosa pine has established 15-20 miles to the east (as a bird flies) in the center of Tygh Ridge!

Since Ponderosa are monoecious, meaning the male and female reproductive structures are both present on the same tree, they have no reason to worry about pollination or how far a pollinator can be drawn in from. Ponderosas have a self contained system to perpetuate their existence, which sometimes makes them seem like nothing more than weeds.  Like weeds they grow in dense thickets that continue to get denser with lack of disturbance.

Boys and Girls Co-habitating. 

 I'm guessing that once the seeds for the rogue Tygh Ridge trees were mature, they got some help with their pilgrimage to the new world.  The distance is too far for mice or rodents to lug the big pine nuts, but it seems birds could do an efficient job of transporting them to their new home.

Clark's Nutcrackers have been known to transport both Ponderosa and whitebark pine seeds . The birds have been thought to be the salvation of the pine through  caching of seed, which in the end leads to greater genetic diversity. However, recent research has followed some of the nutcrackers in their migratory and caching activities and found that sometimes where they bury the seed is either marginal or totally wrong for germination. Or is it?  Perhaps for the whitebark pine that seems to be  a bit more particular about where it grows, but  what about the weedy Ponderosa?  It's successfully grown in a number of habitats for eons.

 When I looked at a sighting map for Clark's nutcracker and laid it over map of The Dalles Ecological Province, I found there have been a few sightings of the nutcrackers there.  Of course, the sighting map didn't show any nutcracker sightings in the adjacent Columbia Basin ecotype. It's likely none have been seen or even looked for there.  However, that doesn't mean they don't go there.  There also are a lot of jays and other corvids that are on less specialized diets that frequent both areas in question.

After spending  probably too much time wondering if the rogue Ponderosa pine trees of the grasslands got there through succession or invasion, I begin to wonder if my question really matters.  I don't have a research proven answer, but that's the neat thing about science because nothing stagnates.  Sometimes scientists work for years to come up with a reasonable hypothesis only to be tormented by someone else who claims to know it all, but really knows nothing.

We likely will never know as much as we would like, but must continue to chase each tidbit of truth we can find, because the natural world isn't going to sit here and stagnate with us..

Backyard Succession:  The Jungle Bed

Succession is an often discussed topic of plant ecologists.  However, it is seldom considered by gardeners because they just plain don't have the time to sit back and let it happen.  Gardeners are busy ones.  They carefully tend their plants and continually are buying some new and sexy strain of hybridized horticultural variety that will move their garden toward their internalized vision.  Backyard succession can look sort of messy, so it doesn't appeal to many hard core gardeners. 

What Is Ecological Succession?

In a nutshell, ecological succession is the observed change of structure (herbaceous or woody) and species presence through time.  It's a concept that has always fascinated me as I've wondered how much impact we have on succession as we go about doing our good deeds.  

When we built our house in the Southern Black Hills eleven years ago, I put in one large bed where the soil was sandy, rocky, and thin.  Since the bed is on the south side of the house and has such poor soil, it tends to be very dry.  Initially, I had no idea what would grow in such a harsh site, but figured whatever I discovered that would grow there would be easier than lawn.  

A few years after planting some aspen and chokecherry in the bed we dubbed it with the name of" the jungle bed."  The jungle bed has done well by being mostly on its own and has taken off on its own path of succession.  It's been my own classroom to observe ecological succession.

The Jungle Bed in May 2013.

Jungle Bed, September 2004

I was so new to gardening in this part of the country when the jungle bed came to be.  In spite of going to all of local resources like SDSU Extension, Master Gardeners, and the Garden Club I never really got a good feel for what it was like to garden in the Black Hills or found a plan that suited me, so I decided to experiment.

First I went and got a package of wildflower seed.  I was in full realization that most of the seed in such a mix wasn't native, but I also made sure that the mix didn't have seeds from the more aggressive naturalized plants like ox-eye daisy or dame's rocket.  The next spring we transplanted some aspen and chokecherry that we dug up at some friend's house over on the Limestone.  The Limestone is quite a bit higher in elevation than where our house is, so it was a bit of a gamble, but one that worked out.

Everything that was planted in the jungle bed in the spring of 2003 grew well, but the poor plants had a hard time keeping ahead of the browsing deer.  I initially tried the conventional gardening practice of pulling out the grass and clover that inevitably started growing in the jungle bed, but after the first couple of years things got way out of hand, so I stopped. That's when the backyard succession really began.

In 2005, we built a permanent fence around the jungle garden because the deer continued to be a problem.  Their continuous dining was leaving all of the plants looking deformed and stunted.  The fence further helped succession by releasing some of the plants we had yet to realize were there.  When we dug up the aspen and chokecherry we must have also gotten some root runners of prairie rose and once the deer were gone the roses really took off.

A Haven for Birds

The only plants that I've tried to be aggressive about keeping out of the jungle bed are white campion (Silene pratensis), field bindweed (Convoluvulus arvensis), and Canada thistle (Cirsium arvense). All of these weedy plants spread aggressively once established.

Once the area was fenced and the aspen began to get larger, there's been another wildlife problem affecting them.  We have a lot of woodpeckers in the area that  peel the bark off the larger aspen stems, in the early spring, trying to get at the sugary sap for energy.  They often will strip the bark off all the way around  the main trunk killing the entire top of the tree.

Woodpecker Damage

   At first this bothered me because it gave the trees a really ugly look to be cut off mid trunk, but then I looked at it from a different perspective.  Aspen require some disturbance in order to stay healthy.  They're clonal so they continually are sending up sprouts from the roots. Killing the tops of the trees stimulates the growth from the roots.  The relationship between the aspen and the woodpeckers indicates two species that are taking care of their own needs while benefiting another in the process.  It's a sustainable situation for both species!

I recently did an early spring crawl through the jungle bed to find and destroy white campion and bindweed.   It was amazing to see some of the good native plants that have found their way into the jungle garden over the last ten years with no help at all from me.

The yearly cover of deteriorating leaves dropped by the aspen and chokecherry has really improved the soil by adding an organic component and increasing moisture retention.  Because of the improvement in the soil I now have healthy stands of native plants like  starry false Solomon seal (Maienthemum stellatum), meadow-rue (Thalictrum sp.) and sedge (Carex sp.).  All of these plants are generally adapted to much moister habitats than the rock pile I started with eleven years ago.

If you give them a chance, they will come.

Starry False Solomon Seal

 

Sedge

Meadow-rue