The Red River of the North and tributaries experienced the flood of the century in the spring of 1997. Damage was extensive, and 8,000 acres were entered into perpetual floodplain easements. Agencies and producers initially planned extensive reforestation since much of the easement area had been originally forested. A wide assortment of planting stock types and planting designs were used. By the third year of the program, tree planting efforts had diminished due to establishment failures and high costs. Most subsequent easements were seeded with an assortment of native and introduced forbs and grasses. Newly emerged forest cover, estimated at about 5,000 acres, resulted primarily from natural regeneration. Though elevation changes along the Red River are often quite small, slight changes (as little as 10 inches) can result in completely different vegetation. Higher elevations have pure stands of switchgrass and big bluestem. Mid level elevations consist primarily of dense, tall cottonwood stands. Lower elevations are dominated by sedges, reed canarygrass and annuals. These different vegetation zones occur within as little as 6 vertical feet. Other factors influencing vegetation establishment include: time of flooding, duration of flooding, existing ground cover, previous land use, time of grass seeding or tree planting, weed pressure and deer. Though similarities exist in cover types 10 years after the 1997 flood, each property has a unique species mix, health and vigor of current vegetation. To date, it appears natural produces very small dense stands of two to five species. This article is a collection of observations over the past ten years. The many variables within this riparian zone make statistical analysis of reforestation efforts problematic.
Geologic and Hydrologic Setting
The Red River of the North flows north. It forms the boundary between North Dakota and Minnesota flowing across the ancient glacial Lake Agassiz bed. The river gradient of the study area is only 2 centimeters per kilometer. "The Red River tends to pool, with waters spilling out as a shallow lake that can approach (as in 1997) 80 to 100 km. in width." 1
"Whereas most flood models have been based on unidirectional flow of tributaries toward the trunk stream, the youth and immature floodplain development of the Red River's tributaries allows each to spill out their waters over extensive lengths of "divides." This spillage (overland flooding) occurs well in advance of their point of junction with larger or trunk streams." 1
When the southern end of the valley is experiencing warm conditions, melt water is often impeded by the ice still in the northern reaches of the channel. Ice jams, rapid flooding and overland ice flows can shear off vegetation.
The April 1997 flood had the highest water level recorded in the 20th century. At the deepest it was 13.5 feet above flood stage or 35 feet above normal water level. Since 1997, nineteen floods have covered the riparian areas along the Red River, in whole or in part. To complicate a bad situation for local landowners, these floods have been during the growing season (May-Sept.) ten times in the last 10 years. 2
Red River Valley Agricultural History
Prior to 1997, the riparian areas adjacent to the Red River, were cropped to small grains, sugar beets, potatoes, and dry edible beans. The rich valley soils produced abundant crops and a high standard of living for farmers and the agricultural infrastructure. Floods prior to that time occurred mainly in the spring and were an accepted part of agriculture. After flood waters drained away, farmers would clear debris from their fields, with plenty of growing season left to raise bumper crops.
The increasing number of growing season floods changed the economics of agriculture. Where spring floods cost only the fuel to clear flood debris, the summer floods could cost over $1,000 per acre in lost crop inputs. This recurring loss was incentive for many landowners to enroll their most flood-prone land into the Emergency Watershed Protection Program (EWPP), administered by the Natural Resources Conservation Service. Generally, this program requires the cessation of farming on enrolled acres, and the establishment of permanent, perennial vegetation on fields formally in crop in return for an easement payment. Easements on 8,000 acres of Red River cropland were accepted beginning in 1998. Reforestation observations reported in this paper were made across a wide selection of these easement acres every year from 1997 to present.
Riparian Forest Establishment Efforts
Beginning in 1998, conservation plans were developed for individual landowners with EWP easements. Much of the area had been forested before the "plow out" of the 1960s and 1980s and conservation plans were developed with a high proportion of reforestation in an effort to return much of the area to a more "natural" forest cover type. If not planted to trees, most land not planted to trees was seeded to a diverse mix of native and introduced grasses and forbs. Some acres were abandoned and no management applied due to inaccessibility.
Since plantings would occur in highly productive crop fields, site preparation was thought to be easy. Planting conservation grade seedlings and transplants via machine would have been no different than past tree plantings. Conservation staff envisioned many acres of new riparian forest within several years.
In addition to machine planting with conservation grade rooted stock, agency personnel in cooperation with landowners attempted other methods of reforestation. Unrooted cuttings of cottonwood and willow were planted in both the fall and the spring when stock was dormant. Additionally, hand planting in areas too wet for machinery was attempted in both the fall and the spring.
Direct seeding of basswood, bur oak, green ash, hackberry, birch, chokecherry, false indigo, and ironwood was attempted on two properties. one site was no-till drilled into clean soybean stubble. The other property was broadcast seeded into a worked site. Both seedings were in the fall after leaf drop. Species used were determined by native species observed around the planting sites and by availability of seed. Seed was dewinged and processed, as necessary, by the Bismarck Plant Materials Center (PMC) staff. Seed was planted in early November on both sites.
The drilled site was planted with the PMC native grass seed drill and a specialty large seed drill. The other site was seeded using a broadcast fertilizer spreader followed by a light harrow and packer. Seeding rates were determined to provide at least 10,000 emerged seedlings the first spring after planting. The high seeding rate was based on observations of natural regeneration stocking rates and the realization that traditional plantings of 300-500 trees per acre often turned into weed patches.
Riparian Forest Planting Results
Reforestation results were not as expected. only about 25 acres of the several hundred acres planted materialized into a riparian forest. All other sites, including all the variety of planting methods and materials was unsuccessful. A few plants may have survived a year or two, but the few remnants that are still there today do not indicate a successful planting. To aid future riparian restoration efforts, the following observations may be helpful. These observations were along the Red River of the North. Other stream systems or locations with higher precipitation may have different results.
Rooted planting stock
- Cost of traditional machine planting and program cost limitations restricted the planned density to about 400 trees per acre. Even if all plants had survived, this may not have been stocked heavy enough to fully capture the site.
- Some sites were exposed to repeated growing season floods that killed young trees whose tops were not above the flood waters.
- All sites were exposed to extreme deer pressure. Unusual circumstances may have allowed trees on the two successful machine planted sites the time necessary to grow past deer. Deer often walk down a row of planted stock browsing the tops of every tree.
- Weed pressure was very intense. Weed control efforts fell along two extremes, no weed control and too much weed control.
- On sites with no weed control, Canadian thistle, quack grass, smooth bromegrass and/or reed canary grass overtook the site within 1-2 years. If the site was elevated enough to escape some of the subsequent flooding, the weed pressure killed much of the young stock that initially established.
- Some landowners elected to use extensive tillage as the weed control method. Though the weeds were controlled diligently, the 3-4 tillage operations each year for the first 3-4 years damaged or removed 60-70% of the planted stock. once tillage ceased, the sites were overrun with thistle and quack grass. Tillage reduce stocking to only 30-40 trees per acre. Not enough trees remained to shade out the weeds.
- Traditionally planted stock was never able to become established, except on two sites where landowners diligently utilized tillage and or herbicides to control weeds. Tree canopies have grown together providing 70-80% canopy cover by summer of 2008.
Hand planted and unrooted stock
- Few plants survived. Soils may have been part of the problem. Clay content was so high that it was nearly impossible to close a hand planting trench. Another factor may have been the small number of trees planted. once found by deer, the few plants could easily have been nipped off in a single evening.
- The unrooted cuttings may have failed because stock may have been too short to reach a growing season water table. Though the site may flood 10 feet deep, there are still times of the year when the water table could be 3-4 feet below the surface.
Direct seeding, drilled site
- This appeared to be a cost effective, easy-to-apply method of tree and shrub establishment. Cost of seed and labor was about one third the cost of traditional machine planting. Additionally, stocking rates were 25 times higher, which should have led to rapid site capture and canopy closure. once the site was prepared, all that was necessary was load the prepared seed into the drill and drive.
- Though drilled, the 6 row spacing and mixture of seed in each row should have caused the stand to look like a forest, rather than a plantation, quite quickly.
- In May 2000 following the fall seeding, just over 10,000 seedlings per acre were counted of the species seeded. No basswood, birch, or aspen germinated, which is understandable after learning more about those species. This reforestation method appeared successful early in the spring of 2000.
- Canadian thistle and marsh elder overran the site by late summer. Boxelder started seeding in from the adjacent forest.
- Deer kept all species, except false indigo, browsed to the top of the dense Canadian thistle cover for 3 years.
- Planted species continued to decline over the next 3 years, primarily from deer browse, weed pressure, and dense stocking of volunteer boxelder.
- Nine years later very few of the trees seeded on the site are present. The most prevalent, though not very numerous, are chokecherry and false indigo. There is some question regarding how much of the chokecherry was from the drilled seeds or how much was spread by animals from neighboring native stands.
- Thistles and marsh elder have diminished. Quack grass patches have expanded. Nearly half the area has boxelder that has grown past deer browse heights. The site is mostly forested, but with very few of the species drilled.
Direct seeding broadcast seeded site
- There was adequate emergence the first spring after planting. Thistles, annual grasses and docks were extensive on this site for 2 years following tree seeding. The landowner was concerned about the weeds on the tree planting site as well as the surrounding grass planting. In an effort to control weeds, the entire contract was sprayed with broadleaf herbicides. All emerged seedlings, as well as the broadleaf weeds were killed.
- Weed pressure continued for the next 2-3 years (years 4-6 of the contract), but expanding grasses kept weeds mostly in check. Ten years after the initial planting, volunteer trees are returning to the direct seeding site, but they are less than 2 feet tall.
- Volunteer trees on the remainder of the contract acreage range from 2 to 8 feet tall.
Natural regeneration of riparian forest
- Initially, natural regeneration was not a consideration, except to fill in between the planted stock. This philosophy only worked on the two sites where the planted rooted stock survived through diligent weed control. (The volunteer trees and shrubs emerged after the planted stock was established and weed control stopped, due to difficulty in maneuvering between the rapidly growing trees.)
- In the Red River Valley, all fields converting to perennial vegetation experienced an initial dense stand of weeds, primarily Canadian thistle.
- Areas seeded to a diverse mix of grasses and forbs seemed to have reduced weed pressure the first year or two after planting.
- Nearly 5,000 acres of naturally regenerated riparian forest is becoming established on both the sites seeded to grasses and forbs, on sites where rooted woody material was planted and died and on abandoned fields where nothing had been done.
- Primary regenerating species are eastern cottonwood, boxelder, green ash, and American elm. Some stands of volunteer trees have exceeded 60,000 stems per acre. Traces of other species such as chokecherry, Siberian elm, basswood, and bur oak are to be found when adjacent to seed sources.
- There is much diversity from site to site. Species concentrations occur in pure, to nearly pure stands of one or occasionally two species. The result is a mosaic of forest types. Never has a uniform "blend" of native riparian species been observed. See Tree Species Occurrence chart.
- Expansion of vegetation types can occur quite rapidly. Witness the expansion of the sand bar willow and cordgrass over 2 years as shown in view 4-2006 and view 4-2008.
- Elevation differences as little as 2 meters can affect the ability of a site to recruit and maintain a forest cover. View 3 shows the effect of elevation changes. The very lowest sites along the river (Not visible, behind and to the left in view 3.) have continuously drowned out, even though they have dense stands of newly emerged cottonwoods and boxelders after each flood event. The growing season floods entirely cover the plants and kill them.
Just one meter higher on the landscape, cottonwoods, willows, boxelders, ash and other species established immediately after the flood water receded and grew tall enough to stick above subsequent growing season floods. (Tallest plants, left side of view 3) In places, some of these plants are 6 meters tall.
Higher on the landscape (Center background of view 3) the grasses were more robust, limiting the amount of bare soil available for the dispersed seed, but tree recruitment is still occurring. These upper elevation trees grew tall enough the first few years after sprouting to survive the 2006 flood event which was only 2.6 feet less than the record 1997 flood.
Further uphill from the river (Lower right foreground view 3) are newly established, one to two-year old, cottonwoods. It is anticipated that the moist and productive soils of the upper elevations will eventually become a cottonwood forest, though increased grass competition may slow forest establishment.
Most sites are becoming fully stocked with riparian forest species however they are still susceptible to fire or severe ice shearing. These riparian trees should be resistant to fire damage in another 10-20 years. Local landowners have observed ice flows completely shearing off 20-30 year old stands of riparian forest so there is still a threat to successful establishment for several years.
- Be patient. There is a riparian forest waiting to happen, if we let it. It will take time.
- Cessation of cropping is all that is necessary to initiate riparian reforestation on most sites.
- Plan for, and be happy with, early successional plant species such as willow, cottonwood and boxelder. Avoid spending money to plant later successional plants such as bur oak, basswood, hackberry. Early successional species will take over the planted trees, even if they survived the weed pressure and flood waters of establishment.
- Weeds will be a fact of life, initially. Make sure landowners are aware of this.
- Direct seeding still has potential, but site selection, site preparation and weed management for the first 3 years will need improvement.
- Lower elevations may remain weed patches until protracted years of low water allow trees to survive subsequent flood events.
- The riparian sites will continue to be a mosaic, with dense single species stands, areas of grass, and areas of annual weeds.
- Between flooding, ice shearing, and deer, there is nothing to be gained from trying to plant rooted stock. Deep flood waters and moving ice sheets preclude any tree protection efforts necessary for rooted stock survival.
- Initially, newly reforested areas will experience rapid cover changes as the local hydrologic, seed sources and wildlife determine what type of forest will establish on which site.
- Elevation changes of less than a meter can greatly impact species occurrence and vigor.
- Be patient.
The Red River of the North riparian area is a dynamic, ever changing environment, with unique hydrologic conditions. These unique conditions require conservationists to rethink traditional tree planting efforts. It forces conservationists to think in broader time frames - decades and centuries rather than years or the period of time between government farm bills. Reforestation in this river system is occurring at a rapid rate, but it's happening in spite of our tree planting efforts, not because of them. Ten years of observation have shown that best intentions and previous tree planting and management experiences are often thwarted. Occasionally, something worked. Over the past decade knowledge of riparian reforestation has increased. Every trip to a revegetation site shows something new that must be incorporated into the knowledge base of reforestation recommendations. The short answer to riparian forest revegetation efforts is: Be patient. Allow Mother Nature to do her thing. When given the opportunity, prepare sites to increase the likelihood of successful natural regeneration. Be patient.
Numerous people from a wide assortment of state, federal, university, county and local agencies have assisted in gathering data, contacting landowners, maintaining records and critiquing results. In particular, this study would not have happened without the assistance of the local Natural Resources Conservation Service and soil conservation district staff in Walsh, Pembina and Grand Forks Counties and the Watershed Planning staff in Bismarck, North Dakota. A special thanks to the landowners who put up with numerous interviews, and dozens of government employees tromping all over their properties.
By Craig Stange, Forester; Dwight Tober, Plant Material Specialist; Natural Resources Conservation Service, Bismarck, North Dakota, December 2008
1 Schwert, Donald P, 2003, "A Geologist's Perspective on the Red River of the North: History, Geography, and Planning/Management Issues", Department of Geosciences, North Dakota State University
2 United States Geological Survey Stream Gauging Station, Drayton, North Dakota, 1997