Date: 01/30/2009
Intro to Forest Management Guidelines – Forest
Soil Productivity
Curriculum
Primary Author:
Dick Rossman
MN DNR Forestry
6603 Bemidji Ave N
Bemidji MN 56601
218-308-2371
I. Target audience(s)
Logging business owners/employees and forest management professionals
II. Learning Objective(S)/Purpose
The primary objective is to introduce the soil productivity guidelines to a mixed
group of natural resource professionals and logging operators so that the participants
gain understanding of soil productivity issues and guidelines contained in the MN
Site Level Forest Management Guidelines. Information should be sufficient to allow
the participants to read and understand the guidelines themselves and then apply the
guidelines in the field. Presentations should be modified to highlight soil conditions
and productivity issues occurring on the field site being used during the presentation.
Presenters should encourage participant discussion regarding their perspectives and
experiences relating to implementation of soil productivity guidelines.
If the field site being used has been harvested, the discussion should include how the
Forest Management Guidelines have been implemented on the site, focusing on
specific issues related to forest soil productivity.
III. Presentation Outline
The following material is intended to provide you with the content that should be
conveyed to workshop participants at the soil productivity field station. It is NOT
intended to be used as a script to be recited word-for-word. Instead, please use this
outline as a basis for creating your own personalized presentation. It is
recommended that instructors be familiar enough with the material to do the
presentation without having to refer to extensive notes.
Allow approximately 15 to 20 minutes for this discussion. You may not be able to
cover all topics in full during the time allotted.
The topic for this station is forest soil productivity. We will:
1) Do a brief overview of the main issues surrounding soil productivity and forest
management.
2) Take a more in-depth look at what the Guidelines say about managing soil
productivity in the context of harvest operations.
3) Look at how the Forest Soil Productivity Guidelines were used at this site and
talk about whether there were other ways to address soil productivity concerns.
Brief Overview
What is soil productivity?
Soil productivity is defined as the capacity of soil, in its normal
environment, to support plant growth. In forest management we most often
measure this productivity in the volume of trees (fiber) produced on a site.
The goal of the soil productivity guidelines is to maintain or enhance the
productive capacity of our forest soils.
Maintaining soil productivity is critical to sustainable forest management. A
decrease in soil productivity could affect the level of harvesting the forest can
sustain, as well as other forest values, such as the quality of wildlife habitat
and populations, and biodiversity.
What are the desired outcomes of implementing soil productivity guidelines?
The desired outcomes of these guidelines are to:
1) Primarily to maintain forest soils in a condition that favors
regeneration, survival, and long-term growth of forest vegetation (in
our case trees).
2) Increase the awareness and understanding of soil productivity issues
related to forest management.
3) Minimize the forest area occupied by roads, landings, and primary skid
trails infrastructure).
4) Encourage the use of alternative equipment and operating techniques
that avoid or reduce impacts to soils.
-
Reference pages 4&5 of soil productivity rationale
With most soil related issues, preventing negative impacts is more
desirable and less costly than correcting impacts after they have occurred.
What are the issues relating to soil productivity and forest management (timber
harvesting)?
If we are to continue to manage our forests and remove forest products, soil
impacts are nearly impossible to totally eliminate (some soil impacts are
inevitable when operating equipment in the forest). Most guidelines are directed
at avoiding impacts where possible, and minimizing impacts where some impact
is necessary. The second 26 pages in the Yellow section of the Guidebook (Soil
Productivity Rationale) describe and discuss the issues related to soil productivity
and forest management. This section is basically broken into the following topics:
1) The importance of maintaining soil productivity and the desired outcomes of
these guidelines.
2) The issues related to forest management and the physical, chemical, and
biological properties of the soil.
3) Enhancements to soil productivity.
To look at the issues relating to soil productivity and forest management let us look
at the three parameters of: soil physical properties, soil chemical properties, and soil
biological properties. All three of these properties need to be maintained (in good
“health”) in order to have good soil productivity.
1) The main issues relating to soil physical properties are soil compaction, rutting,
and erosion.
2) The main issue relating to soil chemical properties is nutrient management.
3) Soil biological properties include the population of plants and animals that
thrive in a particular soil including: fungi, bacteria, worms, etc. Healthy
populations of these plants and animals are important to healthy soil.
The conclusion of the technical team that developed these Guidelines was that the
soil physical resource is the most susceptible with the most long lasting impacts, and
the soil nutrient budget seem to be next most susceptible. It appears that if we
maintain good soil physical conditions and nutrient budget, then the biological
aspects will take care of themselves (in other words, create habitat and the critters
will come). However, as indicated in the new biomass harvesting guidelines, soil
biology becomes more susceptible to negative impacts as we look at removal of
larger amounts of biomass from forest management sites. Therefore the biomass
harvesting guidelines address certain concerns regarding maintaining healthy soil
biology (see biomass guidelines rationale pages 8-13 and pages 22-24).
A More In-Depth Look at Issues and Guidelines
Soil Physical Properties
Let's expand and look at the soil physical issues, and the guidelines that help
minimize or avoid impacts to soil productivity. As stated before, the main concerns
are with soil compaction, rutting, and erosion.
1. Soil Compaction
Soil compaction is the increase in soil density resulting from loads applied to the
soil surface. The increase in density comes from the reduction or elimination of
the large pore spaces in the soil that are particularly important for water and air
movement and for root growth. The greatest increase in density occurs in the
first few trips over the soil surface. As the soil density (strength) increases from
compaction, the % increase with each successive load becomes less.
Research indicates that the recovery of compacted soils tends to be a long-term rather
than a short-term process (decades rather than a few years). NCFES research in
Minnesota shows no reduction in soil density over a 15-year period on severely
compacted soils.
What are the impacts of compaction?
Reduced aeration, which decreases the respiratory activity of plant roots and their
capacity to supply the plant with adequate moisture and nutrients.
Increased resistance to root penetration.
Increase overland flow due to reduced infiltration.
Reduced biological activity in the soil.
2. Soil Rutting
“Rutting” means the creation of depressions made by the tires of vehicles such as
skidders and trucks, usually under wet soil conditions. Rutting occurs when the
soil strength is not sufficient to support the applied loads. Soil in the bottom of a
rut is compacted. Soils on the sides of the ruts may be compacted as well as
smeared or puddled (soil structure destroyed).
Rutting physically severs roots within the ruts.
Rutting disrupts natural surface drainage by blocking surface flows or diverting
surface flows down the ruts themselves (surface soil water does not flow internally
across ruts or through the compacted soils directly under the rut).
Rutting is an indication that other physical soil impacts may be occurring on a site.
Guidelines Related to Soil Compaction and Rutting
The Guidelines are designed to eliminate or minimize compaction and rutting.
Evaluating the Site (site inventory and evaluation, pages GG10-14)
Refer to soil surveys, verify with on-site evaluation (investigation), look for steep
slopes, indications of poor or inhibited drainage, look at the texture and drainage,
depth to bedrock.
Most counties now have up to date soil surveys. Look at both the soil descriptions
and the soil interpretations in the soil surveys.
The more you know about a site the better job you can do of managing it.
Planning (pages GG 17-21 and TH 6-16)
Plan to conduct activities when soil is likely to be firm enough to support the
equipment being used.
Determine what the preferred operating season might be on a site and plan
accordingly, if operations are planned to occur in a non-preferred season, plan on
alternate strategies to implement in case conditions are such that soil impacts are
likely to occur. (e.g., equipment alternatives, techniques, alternate sites).
Design the activity (timber sale) so that you can minimize infrastructure needed to
do the job.
Share roads and landings where possible with other sites.
Avoid layouts that require a lot of roads or high frequency of major skid
trails (i.e. long narrow site with road down the middle).
Plan for no more that 1-3% of the site occupied by roads and landings.
Plan for a progressive timber harvest where you do not traffic over previously
harvest areas (i.e. back to front); this focuses trails and keeps traffic on existing trails.
Operational Guidelines (GG pages 17-21 and TH pages 13-28)
Conduct an on-site meeting with the operator(s) prior to moving equipment on to
the site. You have made all these plans; now relate them to the operator so that you
understand each other's expectations.
Carry out the plan.
Conduct activities during the identified season, with appropriate equipment.
Use caution when conducting operations during spring breakup, after heavy rains,
and during fall recharge period.
Follow infrastructure development plans.
Develop infrastructure to conform to the following:
No more than 1-3% of the site should be occupied by roads and
landings.
No more than 10-15% of the site should be occupied by primary skid t
rails.
No more than 20-30% of the rest of the site should be trafficked with
low use skid trails (a few passes with equipment).
th
** note error in Guidelines on page 26 of t-harvest: The 4 bullet in “lay
out skid trails” suggests that we are limiting access to the site. This bullet
should read similar to the 4th bullet on TH page 10.
The goal is to keep the equipment on the existing roads and trails to maximize the area
not impacted by traffic. For example do not travel cross-country with empty skidders
returning for a new load.
Maintain the infrastructure in good condition so that you do not have to create new
roads or trails or widen trails to go around bad spots.
If skid trails do not hold up (resulting in excessive rutting or requiring the need to
create new skid trails) OR if rutting occurs in the general harvest area (outside of primary
skid trails) use alternative operating techniques such as the following:
Shift harvest operations to a stable portion of the site or to a new site.
Use low ground pressure equipment that can operate without rutting.
Use slash on the skid trails as a driving surface and stay on the trails.
Reduce loads carried by logging equipment.
Pack snow or ground cover to enhance freezing.
If alternative operating techniques fail to eliminate rutting, curtail operations
until soil dries out or freezes solidly.
**Note that rutting in wetland areas or wetland sites within the general harvest area is not
covered by the 6” x 300 ft. rule. This guide only applies to roads. On the infrastructure
of the site we talk about “minimizing rutting” and on the remainder of the site (the
general harvest area) the guidelines refer to “avoid rutting” or “avoid repeated rutting”.
Minimizing rutting suggests that there is some tolerance for rutting, and some rutting is
acceptable, but there is no established threshold as to what is too much (except for the 6”
x 300 ft on roads). One of the things that we certainly want to avoid is when a trail gets
so rutted up that the operator creates a new parallel trail, this doubles the footprint.
“Avoid rutting,” suggests a much lower threshold, but again there is no established
amount or depth of rutting that is determined to be too much. The DNR – Division of Forestry
has established a rutting standard for use on state forestry lands (see attached), however this standard has
not yet been adopted as official guidelines.
Relating to biomass harvesting guidelines; most equipment and operations that harvest
biomass are very similar to timber harvesting. One additional guideline related to soil
compaction in the biomass guidelines is on page 25 of forest biomass harvesting chapter.
This guideline recommends “Avoid re-entry into the general harvest area of a site with a
second operation for the purpose of harvesting biomass once regeneration has begun or
planting has been completed”. This guideline was crafted impart to avoid additional
compaction of soil due to additional traffic on a site.
3. Soil Erosion
Soil erosion is the movement of soil particles by wind, water, and gravity, to some
down slope or downstream point.
Erosion is natural, but can be accelerated by human activity, primarily from
increased bare soil exposure.
Soil erosion reduces productivity by removing rich surface soils (as well as
subsoil) and depositing them as sediment on top of down slope soils.
Erosion on roads and trails increases maintenance and may require
reconstruction or relocation, increasing the area impacted by roads and trails.
Key factors influencing the degree of erosion include: soil type, steepness of
slope, volume of water, length of slop (volume, velocity, and distance), and soil
cover.
Guidelines Related to Soil Erosion
Implementing the erosion control measures identified in the FMGs will prevent erosion in
most situations. These guidelines (practices) should be implemented on all sites, not just
those with potential water quality impacts.
Planning
Site investigation and evaluation (same as previously stated) with particular
attention to slope steepness and length and to areas that concentrate runoff such as
ravines or drainages. Avoid these areas when planning road and skid trail
locations.
Use soil surveys to identify the erodibility of the mapped soil units.
Identify any water diversion structures or soil stabilization requirements that
may be appropriate for the site.
Operational Guidelines
Implement water diversion practices and soil stabilization measures as needed.
- reference FR 30-32 including waterbar spacing chart
REMEMBER the keys to reducing erosion are 1) maintain soil cover, and 2) reduce
the velocity, volume, and distance that water can travel.
Soil Chemical Properties (Soil Nutrient Management)
Soil nutrient management involves balancing nutrient inputs with nutrient outputs. A
forest site has a "bank" of nutrients contained within the soil and forest floor, as well as
nutrients tied up in the vegetation that cycle throughout the site. This site may receive
natural inputs of nutrients through atmospheric deposition and geological weathering of
the soil minerals. Nutrients are also removed from a site through natural processes of
leaching and runoff, and through human processes such as the removal of outputs (timber
for example) as they affect the nutrient capital (bank). In Minnesota, we are blessed with
young, relatively rich soils with large reserves of weatherable minerals. Therefore in most
situations the soils are capable of sustaining removals of nutrients from timber harvesting
on a 40-year basis.
However, analysis of data at the time of the GEIS indicated that, on some sites, some
nutrients were being removed by timber harvest at a greater rate than the rate of natural
additions (i.e., the money is going out faster than it is coming in). On mineral soils the
nutrient of most concern was calcium. Other nutrients were seldom lost at greater rates
than additions. Even in most situations where outputs exceeded inputs, the soil’s reserves
easily made up for the difference. However, in some situations the soil reserves are not
sufficient to make up for removals without some strain on the nutrient capital, and these
soils could experience a significant decline in the nutrient budget for the site (nutrient
depletion may become a concern after 2 or 3 rotations).
Specifically, 2 situations where this may occur are on well-drained sandy soils and
shallow soils over bedrock (8" or less of soil) where aspen or other hardwoods are being
harvested. Aspen is specified because it uses and stores a large amount of calcium in the
bole and bark of the tree. Recent research reviewed during the development of the
biomass harvesting guidelines changed some perspectives on this issue as it relates to
biomass harvesting. Specifically:
- Recent researched indicated that we may not be getting the benefit that we once
thought out of retaining slash on dry-low nutrient sites. Nutrients not taken up by
regenerating stands may be leaching out of the system at a similar rate as what
would have been removed during harvest.
- In addition, forest ecologists suggested that plant communities that have evolved
on these dry-low nutrient sites may not be harmed and may even benefit from
removal of some slash. See pages 13-17 in forest biomass chapter.
Other soil situations where nutrient depletion becomes a concern is on deep organic soils
(greater than 24"). These soils have relatively low reserves of potassium and
phosphorous, and rely heavily on atmospheric inputs which may take about 100 years to
restore soil reserves to pre-harvest levels. In this case however, the P and K are stored
mostly in the needles and branches of lowland conifers, so slash management becomes a
key solution to nutrient depletion.
Guidelines Related to Soil Nutrient Management
Site investigation and Planning:
Look at the site to see if it falls into one of the nutrient sensitive categories:
1. Well drained sandy soils with aspen or other hardwoods, OR
2. Shallow to bedrock soils with aspen or other hardwoods OR
3. Deep organic soils. In the case of biomass “ombrotrophic”.
If the site falls into category 1 or 2, plan to use one or preferably more of the
following strategies:
Convert the site to a species that stores fewer nutrients in the bolewood
and bark such as red or jack pine.
Retain or redistribute the slash on the site.
- If redistributing slash during un-frozen seasons, care should be
taken to stay on established trails rather than trafficking fresh areas
of the site (leave slash in small piles along trails if need be).
Increased trafficking of new parts of the site may be worse than not
redistributing the slash.
Avoid full tree harvest.
Add nutrients to the site (fertilize).
Avoid shortened rotations, and in fact consider extending rotations if
practical.
For organic soils (3 above), consider the same options except for conversion.
Operational Guidelines
Carry out the selected strategy (s) from above.
Favor dispersed slash on all sites where practical and silviculturally
appropriate. (It may not be needed on all sites, but it will not hurt.)
Topics to discuss regarding the application of Forest Soil Productivity Guidelines on
the training site you are currently on:
What are the soil productivity concerns on this site?
What soil types, drainage, steep slopes, etc. might influence the activity either good or
bad? Talk about any operational concerns.
Do the soils on this site fit into one of the categories identified as having nutrient
concerns?
Look for operability concerns and ways to resolve them (equipment, seasonal
restriction, etc.).
Look for erosion concerns (soils type, slope, etc.).
Look at infrastructure layout.
(This part of the presentation will vary from site to site. Instructors will be provided
with specific information for each field site before the sessions begin).
IV. Discussion Questions
These questions should encourage discussion and be worked into the instructor’s
presentation.
a. Does this site (indicating the site being used during presentation) fall into
one of the site conditions that kick in nutrient conservation measures listed
on page ____ of TH guidelines? What about pages 22& 23 of biomass
harvesting guidelines? If so, or if not, how/why. What actions would you
take on this site related to nutrient conservation?
b. Can you relate experiences were you used these nutrient conservation
measures?
c. Are there any equipment operation concerns on this site from a soil
perspective? What would the preferred season of operations be?
d. If operating conditions were not ‘perfect” what measures would you take
to minimize impacts?
e. How would you lay out this site? What operating strategies would you
have related to soil productivity?
f. What about back to front logging? Does it apply here? Benefits?
V. Frequently Asked Questions
These are common questions about the topic that may be asked by workshop
participants, and suggested answers that instructors can use in formulating their
responses.
a. Isn’t soil compaction a short-term concern in MN due to freezing and
thawing?
Answer- research shows soil compaction to be more of long term
issues mitigated in decades rather than years. Even in MN we have a
long-term study that is looking at soil compaction that shows little if
any recovery after 15yrs of compaction (this study is the long-term
soil productivity study [LTSPS] sponsored by the USFS research
center.
b. Why the concern about rutting, can’t we just fix them by smoothing out
the ruts when operations are done?
Answer - No, you can make them look less objectionable, and
perhaps redirect some surface runoff, but the internal damage to the
soil in not corrected by smoothing. It will take time or expensive
methods such as chisel plowing to correct physical impacts such as
rutting.
c. Why the difference between the timber harvest guidelines and the biomass
guidelines when it comes to slash retention on dry sandy sites?
Answer- Research since the time to the FMGs being published and
the development of biomass guidelines indicated that we were not
getting the benefit that we thought form the retention of slash on
these dry sandy sites. It has been hypothesized that retained
nutrients in slash was being moved off site from leaching and runoff
and not being utilized by the new stand. In addition and perhaps
more significantly, ecologists believe that the plant species that have
adapted to these dry low nutrient sites may not be able to compete as
well if we continually retain slash – in other words they are better
able to compete in the dry, low nutrient situation, and perhaps
removing slash emulates wildfires that originally established these
communities.
VI. Group Activity / Case Studies
If appropriate, include one or more suggested activities for the group.
1) The obvious activity here is to dig a hole and look at what the soil conditions
are on the site and relate this to guideline applications. If the site is variable, dig a
couple of holes and compare differences such as drainage or texture.
2) An alternative is to have a copy of the soils info that is available on the internet
or soil survey available for the site and discuss what info the participants can get
from various sources to help determine soil conditions on the site. The new online soil surveys provide nice site-specific information that is user friendly.
VII. Resources
List any additional resources that may be useful for instructors and
participants. Include links to internet-based materials.
2005 version of Site-Level Forest Management Guidelines
GEIS on Minnesota Timber Harvesting and Forest Management in
Minnesota 1992 – Forest Soils Technical paper.
 An Update of: Forest soils. A Technical Paper for a
Generic Environmental Impact Statement on Timber Harvesting
and Forest Management in Minnesota. 28 December 2004,
David F. Grigal, Forestry/Soils Consulting, Roseville, MN 55113
 Tools to Minimize the Impacts of Energy Wood Harvesting on the
Environment and Soil Productivity in Minnesota. Anna L. Robertson,
Michael A. Kilgore, and Alan R. Ek, December 2008. Staff Paper Series No.
200, Department of Forest Resources, University of MN
 Local soils survey or NRCS expertise
VIII. Handouts
List or include copies of any handouts that should be provided or modified for
the specific workshop location.
a. Copy of soils info obtained from soil survey specific to the site
IX. Facility, field site or other presentation needs
Identify important characteristics of the primary facility where the program will
be based (room size, seating arrangement, ability to move tables, tables to
write on, projection capabilities needed, computing capability). As
appropriate, list the field site needs (characteristics, materials, products)
and/or other presentation requirements
a. About any field site will work for this discussion. However, best
discussions may occur on sites with some topography, variable soil types
or presence of small wetlands that will allow for greater discussion.
b. Presenter should bring a tile spade or shovel to dig a shallow pit
c. Be prepared to discuss the local soil conditions by reading the local soil
survey for the field site.
X. Other
A thorough understanding of the Guidelines is an important component of developing
and facilitating discussion. It is more important to have an understanding of the
Guidelines than to have a background in soils.
Before the workshop, instructors should review the following sections of the Forest
Management Guidelines. (Note: These are not the only places where forest soil
productivity guidelines appear, but they include all the major recommendations.)







Forest Soil Productivity (Part 2, “Rationale for Guidelines,” second 26 pages in
the yellow section).
“Conducting a Site Inventory” (General Guidelines, pp. 10-15 in the green
section).
“Incorporating Sustainability into Forest Management Plans” (General
Guidelines, pp. 17-21 in the green section).
Forest Roads: “Considerations” and “Design Outcomes to Maintain Soil
Productivity” (Roads Guidelines, pp. 7-10 in the red section).
Timber Harvest: “Considerations” and “Design Outcomes to Maintain Soil
Productivity” (Timber Harvest Guidelines, pp. 6-10 in the blue section).
Timber Harvest: “Planning & Design” (Timber Harvest Guidelines, pp. 10-16
in the light blue section).
Timber Harvest: “Operational Activities” (Timber Harvest Guidelines, pp.2031 in the light blue section).