Smith Falls State Park

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Jess Riddle
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Smith Falls State Park

Post by Jess Riddle » Sat Sep 14, 2013 5:11 pm

They say a squirrel could cross the primeval forest from the Atlantic to the Mississippi without touching the ground. Either the squirrels of the primeval forest were a lost species that could fly, or that charming saying ignores a host smaller rivers, blow-downs, and savannahs that added heterogeneity and biodiversity to the pre-European forests. Similarly, the prairie does not stretch as an unbroken sea of grass and forbs from the Mississippi to the Rockies. Eastern deciduous forests follow narrow, steep side river valleys deep into the prairie.

I recently had an opportunity to help out with some research on a disjuct population of quaking aspen trees at Smith Falls State Park in north-central Nebraska. The park and surrounding area are uniquely positioned at the intersection of several major landforms, which allows an unusual mixing of eastern and western flora. To the northwest lies the Pine Ridge; to the south lie the Nebraska sandhills, a sparsely populated region now occupied mostly by low-density rangeland; and the park itself occupies the Niobrara River valley, a tributary of the Missouri River and popular canoeing destination; to the east is a broad swath of rangeland, then hundreds of miles of corn and soybean fields. In addition to that unique setting, cliffs and spring-fed narrow ravines, with slopes often exceeding 45 degrees, create additional cool, moist microclimates.
Looking south from Smith Falls State Park towards the northern edge of the Nebraska Sandhills
Looking south from Smith Falls State Park towards the northern edge of the Nebraska Sandhills
The first hint of the Niobrara valley’s forests, Ponderosa pines grow scattered on the moderate slopes north of the river and on the fridges of the adjacent plateau. They also occupy the upper slopes and ridges of the short, steep southern wall of the valley. That north facing slope and adjacent river terraces contain enough moisture to also support broadleaf trees and closed canopy forest. Bur oak mixes with the pines on the drier slopes, but is absent from the most extreme topographic positions. Lower slopes and ravines contain a broader mix of species with American elms, green ash, eastern hophornbeam, paper birch, and occasionally quaking aspen, oak, and pine. Closer to the river, black walnut, cottonwood, hackberry, and especially box elder become common, and a few basswood grow scattered in the ravine bottoms. On all slope positions and aspects, eastern red cedar is common, sometimes as a dense midstory and sometimes mixed in the overstory. The ponderosa pine, paper birch, quaking aspen, basswood, black walnut, and hophornbeam are all near the edge of their ranges creating a striking mix of species.
The north side of the Niobrara River valley
The north side of the Niobrara River valley
North facing slopes along the Niobrara River in Smith Falls State Park.
North facing slopes along the Niobrara River in Smith Falls State Park.
SmithFallsSP.jpg
Fires sweeping in from the prairies historically maintained the upper slopes as pine or pine-oak savannahs. 100 years of fire suppression has allowed the canopies to close and red cedar to proliferate throughout the area, though trees over 100 years old are still common. Browsing, by both deer and cattle, has altered the forests. Exclosures recently erected by the park have created islands of greater aspen sapling growth and survival, and refuges for large forbs like goldenrod and raspberry.
Outside those exclosures, bedstraw, virginia stickseed, and Pennsylvania pellitory commonly grow underneath the hardwoods. In areas where the park has cleared the red cedars, virginia wild rye and smooth brome form dense ground covers on the slopes and stream terraces respectively. Many prairie species, like big bluestem, grow on the highest ridges while asters and scouring rush grow at the bottom of ravines. Young red cedars form the understory on the drier slopes, and mix with chokecherries and young hophornbeams on the more mesic slopes.
Gorge below Smith Falls
Gorge below Smith Falls
I call the aspens quaking, but much of the literature surrounding the park refers to them as hybrids between quaking aspen and bigtooth aspen, Populus x smithii. As far as I know, that identification is based primarily on the relatively large teeth found in this population. However, the bark color and leaf size are consistent with quaking aspen rather than intermediate between the putative parent species. The other interesting thing about this aspen population is that they are all the same genetic individual. Though there are now about a dozen stands, ranging from two to a couple dozen individuals, scattered along a half mile of river, they spread from a single seed. The stands appear likely to contract still further as snags are common in all of them and browsing and increased competition has severely limited regeneration in recent decades. However, recent clearing of surrounding cedars and a few oaks and the small exclosures may increase regeneration.
Aspens with surrounding woody vegetation cleared away
Aspens with surrounding woody vegetation cleared away
Smith Falls
Smith Falls
I had limited time to measure trees, so I know I did not find the largest individuals of some species, especially red cedar and aspen. Additionally, the nearby Niobrara National Scenic River and Fort Niobrara National Wildlife Refuge likely have larger individuals of some of the locally widespread species like ponderosa pine and green ash. Still, all of these individuals are large for the region. Most of them were at the base of the slopes, but aspen and basswood definitely reached larger sizes in the ravines. Unfortunately, the largest aspens may have recently died, and the tops are dying back in most of the paper birch.
Smith_Falls_SP_measurements.JPG
Jess Riddle

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Bart Bouricius
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Re: Smith Falls State Park

Post by Bart Bouricius » Sun Sep 15, 2013 8:46 am

Many years ago I used to ride my bike in the Sand Hills when going to College in Nebraska, but I recently spent some time in Bolivia in communities next to the Noel Kempf Mercado National Park where there are large areas of Savannah, which, though they have a fascinating and unique ecology, are now thought to be mostly the result of relatively recent human intervention with set fires to produce rangeland. I wonder what the extent of the Prarie was before Native Americans moved into the Western midwest, and what impact they had on the forest - prarie landscape? Possibly someone familiar with the quatenary science of the area would know.

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Will Blozan
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Re: Smith Falls State Park

Post by Will Blozan » Sun Sep 15, 2013 9:02 am

Jess,

Thanks for the wonderful and informative introduction to the western ecotone of species we are so familiar with. I love to see the "strange" mixes (pondy and walnut?!?) whenever I can. Your keen observation allows for a clear mental image which is supported by your photos.

Any thoughts on the dieback in aspen and birch?

Will

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Josh Kelly
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Re: Smith Falls State Park

Post by Josh Kelly » Sun Sep 15, 2013 10:02 am

Jess,

Fantastic report. I think you could put together a number of your site reports into an impressive, useful, and popular (among naturalists) document/book.

Bart,

Speculating about a pre-human time in the prairies of North America is interesting. Knowing that humans have been on those prairies for at least 12,000 years and very likely over 16,000 years puts human arrival firmly in the Pleistocene when the climate was much colder and likely drier than it is today. Nebraska would likely have been a boreal grassland populated by mega-herbivores - mastodons for example - and meg carnivores - cave bear, saber-toothed cat, and dire wolf to go along with all of our extant carnivores. It takes some effort just to imagine the scene.

Because people arrived in the Pleistocene, I doubt there is an analog to what is going on in today's prairies and pyro-genic forests of North America. 100 year, fire-free periods have probably been extremely rare in any one patch of prairie in the Holocene. There may have been some analogs in glacial minimums during the Pleistocene, and yet, most of the prairie grasses benefit from fire, so fire ecology has been in place on Earth since before humans were even dragging their knuckles. Understanding the evolution of plant adaptations to fire is an area of interest of mine in the field of paleo-botany. Anyone have any good reading on the subject to suggest?

Josh

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Jess Riddle
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Re: Smith Falls State Park

Post by Jess Riddle » Sun Sep 15, 2013 4:27 pm

Will,

Thanks for the kind words. It's nice to know the efforts appreciated.

I was wondering about the dieback as well. The obvious factor is the extreme drought last summer. However, I think that may be only a partial explanation, because many of the snags and dead tops have already lost all their fine branches. Age/size may also be a factor for these typically short lived species, but some of the dead aspen are small relative to surrounding individuals. So I'm not sure what the whole story is.

Jess

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Chris
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Re: Smith Falls State Park

Post by Chris » Sun Sep 22, 2013 12:23 pm

Very nice. Since I visited that area like 5 years ago, I thought the Niobrara River was a really special place. I would add that the north face slopes also have many springs/seeps making it especially moist because the river has cut through the sand hill into the underlying sandstone/shales. At that contact, groundwater is forces out.

As far as fire, downstream at the TNC's Niobrara Valley Preserve they had a major one last year, killing large numbers of trees. It will be interesting to see how the place responds (I am wondering if the Aspen will do what Aspen does further in the west in response to fire....... big growth until shaded out by slower growing trees later).

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