Proper site selection for Fraser fir Christmas trees involves consideration of a wide number of factors that can influence the ultimate success of production. Many Fraser fir growers continue to incur costs for poor site selection decisions made years ago. The decision to set a particular field affects all subsequent management activities for the trees on that site, for good or worse. Natural fertility of the soil will determine both the quality of tree growth and the cost of fertility management. Aspect (the direction a field faces) and elevation can influence the incidence of several pests. Site factors including clay content of soils, soil depth to an impervious layer or rock, and water drainage patterns across a field can predispose Fraser fir to infection by Phytophthora root rot. While certain management activities can off-set the negative impacts of a poor or marginal site, the cost of production and the time involved in finishing trees will usually increase compared to better sites. By considering a full range of site factors, many problems can be avoided, delayed, or reduced in the site selection process.
One grower concern overwhelms all others in regard to site selection of Fraser fir and many other Christmas tree species: avoiding any factor that might increase the likelihood of developing Phytophtora root rot (PRR). Development of PRR depends on the interaction of the pathogen, Phytophthora cinnamomi, the host, and the environment. PRR can only occur where the fungus has been introduced, but it spreads with water, soil, and farm equipment. As a soil-borne disease, PRR is nearly impossible to control and will remain in the soil for years if not decades to come. Fraser fir has no resistance to the disease. Fungicides are a short-term solution that often fail to penetrate the root zone. Landscape features, soil hydrology (movement of water through the soil), and human activity all can influence development and spread of the disease. While the disease may be more likely to develop on a poor site, a “good” site with perfect soils can be overwhelmed in a flood or an extremely wet season. Proper site selection can improve the odds of harvesting a healthy crop but provides no guarantee. For more information on this disease, read the following: Management of Phytophthora Root Rot in Fraser Fir Christmas Trees.
The Fraser Fir Task Force: In 1998, NC State University administrators brought together an interdisciplinary task force to address industry concerns over declining site productivity and the loss of farmland to PRR. The task force implemented Fraser fir seedling nursery and field surveys over the following two years.
The nursery survey identified Phytophthora in approximately 1-2% of seedlings sampled from 31 nurseries. That small percentage found in one year of production became an alarming number when the cumulative effect of decades of annual planting were considered. A very small risk of infection could become a near certainty over time. Results from this nursery survey helped the NC Christmas tree industry transition away from bare root seedlings to less risky soil-less container-grown plugs.
The Fraser Fir Task Force field survey included over 250 sites across the North Carolina mountain region. Elevation, aspect, soil fertility, soil type, depth of soil, tree growth, and disease incidence were assessed at every site. Data provided a clearer understanding of nutrient status across the industry. However, the most critical information related to factors most commonly linked to development of PRR. Sites with shallow soils and subsoils with higher clay content provided the highest correlation to incidence of disease. Task force results have influenced the following discussion of optimal site selection for Fraser fir.
Elevation and Aspect
Elevation and aspect are often used to define the suitability of a site for Fraser fir, particularly in regard to the climate and soil. As a rule of thumb, growers in some counties used a 3,000 foot bottom threshold, but widespread production in other counties occurs at much lower elevations. However, either extreme in elevation present problems. Very cold, exposed high-elevation sites (ridges and peaks above 4,500 feet) and very warm low-elevation sites (south-facing slopes below 2,500 feet) adversely affect Fraser fir root growth, bud set and foliage quality. At either climatic extreme, the period of time that tree roots function may be limited.
Climate and temperature also control the formation of soil on a site. Organic matter decays and minerals weather faster on warmer sites. Lower elevations and southern aspects generally have less organic matter in the topsoil and more clay in the subsoil than higher elevations or northern aspects. At elevations above 3,400 feet, dark, loam soils can be found at any aspect. As elevation drops below 3,000 feet, aspect becomes more important. At 2,400 feet, a south-facing slope may have too much clay in the subsoil predisposing the site to PRR spread. The north face of the same ridge will have a less-weathered, loamy subsoil that drains better. Aspect will have a greater influence on steeper slopes than on level ground.
After experiencing PRR-related mortality at low-elevation clayey sites, some growers have shifted their production to high elevation farms. While they reduced their risk of root rot, they did not eliminate it. The same factors that predispose a low elevation site to disease are still present -- they are simply less widespread. Also, these growers incurred a different set of site-related problems. High elevation climate can be severe. Trees are at greater risk of being whipped by strong winds, beaten by hail, or pruned by late spring freezes. Well-drained high-elevation soils can become excessively dry during droughts. High-elevation organic soils have different fertility issues that require individualized management. These potential problems are not insurmountable and do not take the land out of Christmas tree production as PRR would, but can increase production costs and rotation length.
Farmers have always "read the lay of the land" to determine good sites for their crops. This is especially important for Fraser fir, where small changes in soil drainage can make a big difference in the development of PRR. Landscapes (visually presented in topographical maps) range between concave areas that collect water and convex areas that shed water. Look for and avoid planting any hollows, gullies, ravines, or dips that indicate intermittent streams or drainage areas. Changes in vegetation can indicate changes in soil type or drainage and can be a useful tool in reading landscape. Rushes often indicate wet areas. Patches of green grass in winter also reflect wet areas that do not freeze.
Note any depressions or sunken areas on slopes that historically are the result of earth-slides or tree-falls. These small areas will have subsoil at the surface and poorer drainage than surrounding soils. Buildup at the lower edge of one of these areas can function like a dam to hold back or inhibit water drainage. Any of these micro-sites can become future Phytophthora problem areas.
While evaluating the landscape, it is also important to note any tree lines that will create shade along the edges of fields. Tree borders or other landscape features that restrict air flow will increase humidity and aggravate diseases like grey mold (Botrytis shoot blight) or pests such as hemlock rust mite. The same features can hinder the drainage of cold air from lower portions of a field making the site more susceptible to frost injury. Slope changes, concave areas or dips, ravines or hollers, streams, and bottomland all have the potential to be a frost pocket. Be sure to consider landscape features beyond the property line that may impact your fields.
Slope and Drainage
Slope and water drainage must be considered carefully when selecting a site. Most Fraser fir in North Carolina are planted on sloping land because it drains better than flat land. Water moves slowly out of flat land which can remain saturated long enough for Phytophthora root rot to get started. However, sloping land does not guarantee a good site for Fraser fir, nor is flat land always bad.
The position of a site in relation to water flow is critical. Flat land can be well drained on a mountain top or be very wet at the foot of a slope where water collects from the watershed above it. Sloping land near the bottom of any hill, close to surface water, or above any feature that cuts or compacts soil can have a higher water table and be slower to drain than unimpeded slopes. It is also important to remember that water drainage occurs both along the grade of the slope and internally in the pore space of the soil. A good site must be well drained in both ways.
Avoid severe slopes within the site being considered for Christmas trees. Steep slopes are difficult to work. A tree will have to grow an extra year or two to have the horizontal space to produce a uniform whorl of bottom branches. Further, many trees grown on steep slopes have uneven budset from side-to-side in response to uneven light levels. Resulting variation in growth and tree density can be enough to reduce trees’ marketable grade and add additional time to field rotations as growers work to correct defects. Gentle to moderate slopes tend not to have these problems.
Soil characteristics for a potential site must be evaluated thoroughly not just for nutrient status but also for soil physical properties. Many growers take a surface soil sample (0-4 inches) for nutrient analysis. Additional deeper samples of 4-8 inches or even 12-20 inches will indicate what trees have to draw on during periods of moisture stress. Soil reports provide a good indication of the amount and type(s) of lime and fertilizer needed to provide optimum fertility for Fraser fir growth. Multiple nutrient deficiencies, toxicities, or pH imbalances should be "red flags" for selecting that site. The process of collecting soil samples also provides a good indication of topsoil color, texture (amount of sand, silt, and clay), and compaction. While there is no "right" topsoil, darker, loamy, and less compacted soils generally are good.
For a more thorough discussion on taking soil samples and interpreting their results read Soil Testing and Interpretation of Results for Christmas Tree Plantations.
Simply looking at the surface soils is not enough, however. Using a shovel or preferably a soil auger, determine the depth of topsoil and subsoil. Mountain soils will vary from 20 to 60 inches to bedrock. Deeper soils will generally provide more water and nutrients during dry periods and provide a greater depth of aerated soils during the wet periods than will shallow soils. Shallow topsoils will not sustain more intensive site preparation or tillage practices that can result in either erosion or compaction. As stated earlier, the soil survey conducted by the NC State University Fraser Fir Task Force in 1999-2000 showed a very strong link between the incidence of Phytophthora root rot and the presence of shallow soils.
By looking at the soil profile you should get an indication of water drainage, depth of the root zone, and some of the tillage options that are feasible on that site. The ease with which the hole is dug can tell you how much rock is present and how compacted the soil is. Pay particular attention to any hard layer which could inhibit the drainage of surface soils such as a plow pan or clay layer. Examine the structure of the subsoil. A soil with small clods or a granular structure will have more pore space and air for optimum root growth than a blockier, more clayey soil. If the subsoil has a tight clayey structure, no amount of tillage, subsoiling, or amendments will alter it over the life of a ten-year crop rotation of Fraser fir. If a soil has been compacted, it can require decades to regain pore space and internal drainage.
Soil color can be a useful tool in determining the suitability of a site for Christmas tree production.
Dark topsoils have more organic matter than light topsoils. Darker subsoils (brown or red) are usually more fertile than light-colored subsoils (yellow or white) and will often have greater capacity to hold nutrients. Over the life of a Christmas tree crop, this can represent very different needs for lime and fertilizer as well as the magnatude of nutrient problems that occur. Dark soils will still have nutrient deficiencies that require regular soil sampling to identify.
Take note of any gray spots in the subsoil. Grey color in clays indicates prolonged water saturation and, very likely, a high water table. Some slopes will have channels of grey-mottled soil at intervals across a field. These are points where water moves through the soil like a subsurface stream. Grey mottling is a strong precursor for Phytophthora root rot.
When examining a reddish soil, do not assume that the color indicates a high clay content. Red color more correctly indicates iron content without directly corresponding to the amount of clay in the soil. Some reddish subsoils are very well-drained while others are poorly-drained clays. If a soil is moist, you can estimate clay content by squeezing a ribbon between your thumb and fingers. Clayey soils will make a longer and smoother ribbon than loamy soils. Of course, your county soil survey can provide a much more exact estimation of soil texture.
County Soil Survey
It is helpful to back up visual observations of soil and landscape with the descriptions from your county soil survey. Online versions of the soil survey are available as well as printed copies. Find your field location on the soil maps. Note the changes in soil type that occur within the site. Soil types often follow changes in aspect and/or slope. Note the range in clay content. Those areas in a field that represent the high end of clay content could be more problematic. Read each soil class description, paying particular note to the different management guidelines for each type. The level of disturbance that a soil can sustain at a particular slope will vary widely for different soil types. Fraser fir is much more sensitive to changes in clay content and moisture than the major crops discussed in most soil surveys.
Before 2005, NC county soil surveys were periodically updated and printed in a rotating cycle. Now, updated soil surveys are available online from the USDA Natural Resource Conservation Service. The interactive website can be very informative once you learn how to use it. Working from interactive satellite maps you can view your property and overlay different types of soil and site information. To get started, go to the USDA's Soil Survey.
Farmers have always used existing vegetation as a tool to evaluate the suitability of a site for a crop. Broom sedge is an indicator of low pH and/or low phosphorus. Rushes and sedges can indicate wet areas in a field that could be a problem. Old apple trees can harbor other species of Phytophthora root rot that can kill newly planted Fraser fir. However, problems at old apple orchards have generally declined over time unlike the root rot disease from Phytophthora cinnamomi, which remains in the soil permanently.
When evaluating the soils and landscape of a site it is important to also look for existing or potential pest problems.
There is a visible record of vegetation at almost any time of year whether it is growing, blooming, going to seed, or merely a weathered skeleton of last year’s growth. Of course, most herbaceous weeds, shrubs, and trees will be most easy to identify in late summer or fall when they have gone to seed. A record of dominant and problem weeds made during site inspection can be used to direct future weed management strategies. In fact, growers will often target certain perennial problems that can be treated more aggressively during site preparation in the absence of Christmas trees.
Tree of heaven is a noxious invasive weed that deserves special attention when considering a site for Christmas trees. While the tree is a nuisance itself, it is a favorite host of Spotted Lanternfly, a new invasive insect pest currently spreading into neighboring Virginia. By killing the host tree before the insect arrives in NC, Christmas tree growers may keep the new insect out of their fields. For identification and life cycle information of the Spotted Lanternfly, view the Spotted Lanternfly publication from NCDA&CS Plant Industry Division.
White grubs are an occassional pest of Christmas trees that can be found and identified during the site selection process. They are most easy to find in old pastures in summer and fall. Recommended monitoring involves sifting through soil from five holes of approximately one cubic foot each from across a field. Checking old pastures prior to planting can allow a grower to implement a control strategy before transplants are damaged during their first year. For more information on identifying and controlling white grubs, read Grubs & Other Root Feeding Pests.
Another pest that can occasionally damage new plantings is the pales weevil. If mature pines are being harvested close-by the summer or fall before Christmas trees are to be set, a migration of weevils can occur. The weevils will feed on the stems of Christmas trees of all sizes, but can girdle and kill young trees.
These scenarios indicate that even during initial site evaluation, pest management is a critical concern.
All site factors that contribute to optimal Fraser fir growth must be met in a particular location. However, several farm management issues should be considered as well. The site should fit the intended scale of production. Farm equipment, particularly tractors with tree planting machines or sprayers, must be able to function for the field size, turnout areas, and terrain. Farm location, road accessibility, and harvest season access are critical to keeping production costs low. The cost of additional road construction can be a major ongoing expense and drawback for some sites. Thieves may be attracted to multiple access points or limited visibility that can make equipment and tree theft easy. It might be a useful exercise to consider a new site from a thief’s perspective.If neighbors live close to the property line, pesticide use or other activities can become points of conflict. Growers have maintained buffers or planted screens just to keep the peace. Making investments to address any of these management factors could be justified for a good production site, but they can tip the balance against sites with marginal soils or landscape features.
Further, roads collect and move surface water. Sometimes it is muddy and contaminated with the spores of PRR brought in from another site. Without careful planning and ditch construction, runoff will flow into a tree field. This creates ideal conditions for PRR to become established below a road. This is especially true of wider public roads that produce more surface runoff than a typical farm road. Too often, this occurs at the top of a field where disease can spread downhill and kill a swath of trees. To avoid this, runoff must be directed away from Fraser fir production areas to field borders. Proper water management may require a large rock-lined ditch to handle storm water. For roads to be an asset, growers must carefully consider their influence on water movement and plan accordingly.
Presence of a public road above a Christmas tree field should be considered a serious strike against using that site for Fraser fir production. Look for drainage culverts that collect water from ditches on the other side of a road. Consider how water may flow into the field from any hills or dips in the road above a site. Do not plant trees in draws or drainages that collect runoff from a road. Trees planted in those locations will die.
For additional information, review related articles in the road construction section of the NC State University Christmas tree portal.
Even farms that are good sites for Fraser fir will have areas that are not suitable for Christmas tree production. Many of these non-crop areas can still be vitally important for very specific uses.
The edges of some wet or concave areas can be used as roads or harvest staging areas. They might require draining or filling to be used in all seasons. Be sure to review water quality regulations before altering any streambanks. The Natural Resource Conservation Service can provide guidance in using marginal areas and constructing stream buffers.
Some shady hollows may be suitable for tree storage yards, particularly northern aspects that are close to water. Flat areas at the bottom of long north-facing slopes can also be used as storage areas. These water and air drainage areas can often be 10 to 20 degrees cooler than surrounding areas.
Of course, larger areas of flat land that are not suitable for Fraser fir may be ideal for other crops and could provide an opportunity for diversification. Small areas could be used for other purposes such as or beneficial insect or wildlife food plots.
Critical Tools for Fraser Fir Site Evaluation
- County soil survey
- Soil test report
- Soil sampling tube and bucket to take soil samples and soil sample boxes
- Soil auger or shovel to evaluate subsoil
- Shovel to sample for grubs
Site selection for Fraser fir production must involve consideration of a wide range of factors. Each site will have a unique mix of strengths and weaknesses. Factors that contribute to Phytophthora root rot are of primary concern, but production and business management issues must also be considered.
- Elevations between 2,500 and 4,000 feet provide a target range where optimum climate and soil conditions can be found. Higher elevation sites have exposure and accessibility problems. Lower elevation sites may have tight soils with too much clay and be too hot for optimum Fraser fir growth.
- Aspect (the direction which a field faces) is particularly important on low-elevation sites. South- and southwest-facing sites have higher soil temperatures and often a higher clay content than other aspects at the same elevation. On marginal sites, southern aspects may aggravate survival and growth problems.
- Landscape or topography can indicate small changes in drainage that can predispose an area to Phytophthora root rot. Drainage areas, dips, or depressions in fields should not be planted in Fraser fir. Changes in aspect, slope, or vegetation can indicate changes in soil type. Also note shaded areas and potential frost pockets.
- Moderate slopes do not guarantee a good site. Well-drained sites depend on both good internal soil drainage and movement of water down the slope. Look beyond slope to soil characteristics and landscape position.
- Soil testing provides vital information for current nutrient status and corrective nutrient applications needed to optimize growth.
- Depth of topsoil and subsoil can indicate much about the productivity of a site. Shallow soils (20 inches or less to bedrock) have less water and nutrients during droughts, too much water during wet spells, and no reserve of topsoil to compensate for erosion or compaction.
- By examining the soil profile with a soil auger, you can identify potential rockiness, plow pans, clay layers, or drainage problems. If there are major problems in the subsoil, no amount of tillage, subsoiling, or fertilizer will improve the site for the entire rotation of a crop of Fraser fir Christmas trees.
- Soil color can identify certain site characteristics. Dark subsoils tend to be more fertile than light subsoils. Grey mottling indicates poor drainage. Red color indicates iron, not clay (but clay soils can also contain iron).
- Use maps and soil class descriptions in the county soil survey to confirm field observations.
- Look at the site with pest management in mind and monitor for weeds and grubs.
- Business, logistics, and management factors must be considered in selecting a site, but Fraser fir growth factors are paramount.
Publication date: Jan. 1, 2004
Revised: April 1, 2020
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