Posts tagged ‘woods’

Two videos: Natural disturbance-based silviculture and restoring late-successional structure

Back in June 2009, someone named Tom posted a great question about applying the Dauerwald concept in Minnesota.  In a nutshell, the Dauerwald approach involves intensive management designed to maintain a high diversity of tree species and ages.  This approach can be attractive to those interested in active management but less comfortable with more extensive harvests such as clearcuts or shelterwood treatments.

This month we feature a two-part video response to Tom’s question and the ensuing discussion from Tony D’Amato, silviculturist at the University of Minnesota’s Department of Forest Resources.  Tony’s first video addresses the concept of natural disturbance-based silviculture.  His second video addresses a somewhat related concept, of active management to restore late-successional structure. Tony discusses how ecological forestry can complement other approaches like production forestry and multiple use sustained yield forestry on the landscape.

Ecological forestry: Natural disturbance-based silviculture


Ecological forestry: Restoring late-successional forest structure


Your turn

How does (or doesn’t) ecological forestry fit into your woodland plans?  Why or why not?  Leave a comment below or add to the initial discussion begun by Tom.

November 10, 2009 at 6:05 am Leave a comment

Poem of the month: Woods


I wish to grow dumber,
to slip deep into woods that grow blinder
with each step I take,
until the fingers let go of their numbers
and the hands are finally ignorant as paws.
Unable to count the petals,
I will not know who loves me,
who loves me not.
Nothing to remember,
nothing to forgive,
I will stumble into the juice of the berry, the shag of bark,
I will be dense and happy as fur.

— Noelle Oxenhandler

Noelle Oxenhandler’s most recent book is The Eros of Parenthood. (Source)

October 12, 2009 at 8:45 am Leave a comment

Emerald ash borer and your Minnesota woodlands

A few months ago, we heard from a frustrated reader.  Noting the abundant info about emerald ash borer (EAB) in urban environments, he could find almost nothing on managing ash in woodland stands.  Philip Potyondy created this video to begin to answer that question.

The video has four sections:

  • First Extension’s Jeff Hahn reviews basic EAB biology, dispersal, and impacts on host trees.
  • Second, Keith Jacobson of the MN DNR’s Utilization & Marketing unit briefly reviews markets for ash wood in Minnesota.
  • Third, we head to the woods for brief comments from Paul Dickson, president of the Minnesota Association of Consulting Foresters.
  • We close with a summary of research and management recommendations for woodland ash stands from Extension’s Angela Gupta.

Special thanks to Jeff Hahn, Keith Jacobson, Paul Dickson, and Angela Gupta for their contributions to this video.  You can learn much more about EAB in Minnesota at the UMN Extension EAB page.

What are you doing to prepare your woods for EAB?  Leave a comment to let us know.

October 12, 2009 at 8:02 am 5 comments

Northern Minnesota phenology report: October 2009

By John Latimer, KAXE Radio, Grand Rapids

Fall color from Oberg Mtn. Allison Eklund photo.

Fall color from Oberg Mtn. Allison Eklund photo.

The arrival of fall is best announced by the leaves of the trees turning color. For many years it was assumed that these colors were in the leaves from the beginning and that as the tree prepared for winter it stopped producing chlorophyll and the intrinsic colors were revealed. Recent studies have shown that the colors are not in the leaves and must be produced by the tree.

From an evolutionary perspective simply turning color would be a waste of energy because the pigments produced are lost when the leaves fall. There must be a reason why the trees would invest in the color change. Two theories have emerged as possible explanations.

One theory is that the color is a signal to insects to stay away. Many insects approach trees in the fall to lay their eggs and in the spring these eggs will hatch and begin an attack on the tree. There is some evidence that insects avoid the most colorful trees. The trees with the brightest colors will self select because they will experience the least insult from pests. Ultimately these trees should come to dominate the forest. That they don’t is the source of much conjecture.

The problem is that some trees do not turn color in the fall. Rather they just drop their leaves while still green. Scientists that support this protectionist theory contend that there is always going to be some natural variation within the plant community. Research indicates that those trees under the greatest pressure were the ones that evolved to have the brightest colors.

Jack pine needles about to drop in fall. Esagor photo.

Jack pine needles about to drop in fall. Esagor photo.

Other scientists have noted, especially here in the far north, that by the time trees begin to turn color the majority of their insect pests have perished.  Where then is the pressure to turn color for defense? They contend that the trees turn color to mitigate the effects of sunlight on the leaf as it shuts down.

The entire photosynthetic process must be shut down in the fall. The tree needs to carefully dismantle the chemicals used in the process, nitrogen, and phosphorus among others will be maintained in the tree to be used again in the spring. All this housekeeping requires energy that comes from photosynthesis, yet this is the process that is shutting down.

Leaves cannot use all the energy striking their surfaces in the fall and the excess can cause damage. Anthocyanins, those molecules that cause leaves to turn red, act as a sunscreen allowing the leaf to get its work done without destroying the chemicals the tree is trying to extract.

Scientists produced trees in the laboratory that were unable to produce the colors associated with fall. While these trees prospered in the greenhouse they were unable to ship nutrients to the tree for storage in the fall. This supports the sunscreen theory, but the sunscreen is only present in those trees that produce anthocyanins. The trees that turn yellow manufacture a chemical called carotenoid and this has no effect on sunlight. Currently they are arguing that there is another, as yet undiscovered, chemical doing the screening.

So it goes, the two sides concede that the other may be partly correct. Possibly the leaves turning color may accomplish more than one task. I am just glad that they do turn color in the fall. Whatever the reason it is a time of stunning beauty.

John Latimer is well known throughout northern Minnesota for his phenology work. He appears weekly on KAXE radio in Grand Rapids, and audio and twitter archives are available here. His work is a frequent feature on MyMinnesotaWoods.  This article also appeared in the Duluth Senior Reporter.  It is printed with the author’s permission.

October 5, 2009 at 9:01 am 3 comments

Updated content on Minnesota Land Economics

[I thought this message might be of interest to some of our readers:]

Dear Colleague:

Three new things at Minnesota Land Economics:

1. 2009 assessor estimates of land values. Please be careful. From the site:
“In 2009, the Minnesota Legislature created several new classifications for agricultural and timber land in the state. On Minnesota Land Economics, the reclassifications are handled by treating post-2008 land valuation data in a separate section. If you select “2009 and onward” on the attributes page, you will be presented with the new valuation classifications. These changes resulted in valuation data that is not directly comparable for that reported in previous years. In some counties, the currently reported numbers aren’t even close to the previous year. Many of the inconsistencies are expected to be resolved by the time the final 2009 Mini Abstract is posted here in December. In the meantime, please be careful with the 2009 numbers!”

2. Forest Productivity Index (FPI) now available for twenty counties. Details by clicking “Read more” on the Soils Data section.

3. Graphs! On most data report pages, you’ll see a “chart-it” or “plot-it” link. Histograms, scatter plots. On the fly!

As always, please let me know if you experience any problems with Minnesota Land Economics–and thanks for your continued kind words about the service we provide.

Steven J. Taff, Department of Applied Economics, University of Minnesota

Check out the updated content at Minnesota Land Economics now.

August 17, 2009 at 11:07 am Leave a comment

MyMinnesotaWoods is on Facebook

Last week we created a new MyMinnesotaWoods Facebook page.  If you’re on Facebook, and if you like what we do, visit the page and become a fan.

Why Facebook?  One of our primary goals is to reach and engage new people interested in the care and management of Minnesota woodlands.

In Minnesota and nationally, the woodland owner population is aging.  A new, younger generation will soon assume control of much of the woodlands on which rural wood products industry depends. When new landowners go looking for information, we want them to find reliable, accurate information through

So check us out on Facebook! New MyMinnesotaWoods Facebook page.

August 5, 2009 at 9:28 am Leave a comment

Minnesota forest insect & disease updates

Just a quick post in case you missed it: The Minnesota DNR, Division of Forestry has published the June 2009 Forest Insect & Disease Newsletter (PDF).  This is by far the best source of timely, quality information on insect and disease issues in the Minnesota woods. This summer’s issue includes a play-by-play of the discovery of emerald ash borer in the Twin Cities this spring.

The list of articles from the June 2009 issue is below.

  • Emerald ash borer found in Minnesota
    • Play-by-play
    • Updated firewood restrictions in on state land
  • Another cool and protracted spring
    • Winter injury of Colorado blue spruce
    • Two-lined chestnut borers
    • Forest tent caterpillars are at it again
    • Oak anthracnose
    • Ash plant bug and ash anthracnose
    • Bumper crop of seeds
    • Summer shorts
  • Heads-up
    • Approved firewood vendor applications now
      need to be renewed
    • Tick-borne diseases
  • Publications
    • Trees and Shrubs of Minnesota
    • IPM for Home Apple Growers
  • Feature Article
    • Wolves in sheep’s clothing: Outbreaks of
      previously obscure native forest
  • Handy and helpful websites for Forest Health

Read it now: June 2009 Forest Insect & Disease Newsletter (PDF)

July 23, 2009 at 8:41 am 2 comments

Small Ownerships: Overview

In addition to limited access to cost-sharing, owners of smaller parcels can be faced with significant forest management challenges. Windstorms, insect outbreaks, and diseases can affect woodlands regardless of boundaries. On smaller parcels though, the costs of treatments to reduce impacts can be prohibitively high. This can lead to less treatment, which can lead to worse outbreaks in the long run.

Continue Reading April 4, 2008 at 4:27 am Leave a comment

How woodland trees grow

This post includes information about how site, climate, tree characteristics, and shade tolerance affect the growth and vigor of trees.

Effect of site characteristics
Site characteristics that affect tree growth include soil depth, texture, moisture, and fertility, along with topography.

On the whole, deep soils are better for tree growth than shallow soils because they potentially have a greater nutrient supply and water-holding capacity.

Soil texture refers to the size of soil particles.  Particles are classified by size (from smallest to largest) as clay, silt, and sand. Different soils have different proportions of each particle size.  Sandy soils absorb water quickly, but also lose it quickly to drainage.  Clay soils have a large water-holding capacity but absorb water slowly and hold it so tightly that much absorbed water is not available for plant use.

Soil fertility is based largely on the type of parent material from which the soil originated.  On the whole, fine-textured (clay) and medium-textured (silt) soils have a greater nutrient supply than coarse-textured (sandy) soils. Read more about Soils and Landscapes of Minnesota.

Forested slope near Lanesboro MN. Click for a better view.

Flickr photo by esagor. Click for original.

Topography affects tree growth largely because of its influence on soil depth and moisture availability.  Because gravity pulls soil particles and water downhill, soil depth, nutrient supply, and water supply usually are greater on bottomlands, lower slopes and benches than on steep slopes and ridge tops.

Aspect also influences the amount of sunlight and soil moisture available to trees.  In Minnesota, slopes that face north and east tend to be cooler and moister than slopes that face south and west.  These effects become exaggerated as the steepness of the slope increases.

Effect of climate
Length of the frost-free growing season, cold temperature extremes, precipitation amount, and duration of droughts are some of the elements of the climate that influence tree growth.

Native trees have evolved in our climate and are adapted to it. When we attempt to import trees from the south, they often cannot survive the winters, are damaged by late spring or early fall frosts, or find the growing season too short to consistently produce viable seed.

In prairie regions, rainfall is not evenly distributed over the growing season and prolonged summer droughts combined with factors such as wildfire limit tree survival and growth.  Some tree species will grow in dry, wet, or other tough conditions, but may need supplemental watering, mulching, or weed control, especially when young.

Effect of tree characteristics
A tree’s crown size, genetics, and ability to tolerate shade and competition from other plants all influence how well it will grow in different environments.

Large, healthy red oak crown.  Click for a better view.
Columnar crown in red oak. Click for a better view.
Large, healthy crown (left) and small, columnar crown (right) in Minnesota red oak. Flickr photos by esagor. Click for originals.

The most important aspect of crown form is the live crown ratio.  The live crown ratio of a tree is the percentage of the total tree height that has live branches on it.  The optimal live crown ratio varies by species and tree age.   If trees are too crowded and the crown is too small, the tree will grow slowly.  If the crown is too large, the amount of usable wood in the main stem will be reduced (knots tend to reduce the value of harvested logs).

Live crown ratios apply primarily to coniferous trees.  For hardwoods, the more important measures are crown position and spread.   The image below illustrates the different crown positions.  The dominant tree in the center has the optimal crown position (above its competitors) as well as a wide spread, allowing it to capture a lot of sunlight for growth.  The two codominant trees, on the other hand, have narrower crowns.  The intermediate and suppressed trees are under heavy competition and have inferior crown positions.

An illustration of different crown classes. Source: Woodland Stewardship: A guide for Midwestern Landowners.

Note: One widespread misconception is that small, stunted trees will bounce back and thrive after partial harvests. In many cases this is not true. Trees that have been stunted and suppressed, with poor form, often will continue to grow slowly and will not improve appreciably. During partial harvests, it’s crucial that you leave some large, dominant trees in the stand.

Shade tolerance
Shade tolerance refers to a tree species’ ability to thrive under low light conditions.  Tree species differ with respect to their tolerance for shade and competition.  Trees that are very shade tolerant will reproduce and grow beneath a dense canopy.  Trees that are very intolerant will survive only in openings that receive direct sunlight.  Shade tolerance can change with tree age.  The table below shows the shade tolerance classification for selected Minnesota tree species.

Very Tolerant balsam fir, ironwood, sugar maple

Tolerant American basswood, black spruce, northern white cedar, white spruce

Intermediate American elm, bitternut hickory, eastern white pine, green ash, northern red oak, red maple, shagbark hickory, sycamore, white ash, white oak, yellow birch

Intolerant black ash, black cherry, black walnut, butternut, paper birch, red pine, silver maple

Very Intolerant black willow, eastern cottonwood, eastern red cedar, jack pine, quaking aspen, tamarack

(Table adapted from Silvics of North America)

Why is all of this important? Forest ecologists and land managers depend heavily on knowledge of site characteristics and which tree species will perform best on a site. For more information about Minnesota’s native plant communities, visit the MN DNR’s Ecological Classification Systems page.

April 18, 2007 at 10:38 am Leave a comment

How forests grow

Forests are dynamic ecosystems—they’re always growing and changing.  Patterns of forest succession are relatively predictable within given site conditions, but highly variable from site to site.  For instance, in the sub-boreal forests of northeastern Minnesota, widespread aspen and birch forests are being invaded by native spruce and fir trees.  Over time as the short-lived aspens and birches die, shade-tolerant conifers will take over.  This process is readily visible driving along Highway 61 along Lake Superior’s north shore.

However, many factors can affect the process of forest succession.  Variation in climate, soils, seed sources, natural disturbance, and wildlife populations can all affect a forest’s succession.

Blowdown in Boundary Waters wilderness, 1999

1999 BWCA blowdown. Flickr photo by esagor. Click for original.

Natural disturbance
Natural disturbances such as windstorms and severe wildfire can kill most or all existing vegetation on a site.  Although windstorms and wildfires may appear to have similar effects, they in fact have very different impacts on the forest.  Windstorms tend to destroy the mature trees in the canopy and “release” existing seedlings in the understory, which then thrive and quickly replace the pre-disturbance stand.  Severe wildfire, on the other hand, tends to kill both mature trees and understory seedlings.

These two different natural disturbances therefore lead to very different future forests.

Just as different natural disturbances have different effects on the forest, different forest management activities allow foresters to carefully modify the condition of a stand.  In fact, applied forest ecology is the basis of modern forest management.  Planting trees, harvesting some or all of the trees on a site, burning, and direct seeding are only a few of the ways that foresters manage the process of forest development or succession.

White spruce under jack pine, Brainerd MN. Click for a better view.

White spruce thriving under aging Brainerd, MN hardwoods. Flickr photo by esagor. Click for original.

Forest succession
Shortly after a major disturbance like a severe wildfire or clearcut, an early successional forest will become established.  Whether planted or naturally regenerated, early successional stands are densely populated with seedlings early in their development.  Picture a dense “doghair” aspen stand or a thick red pine plantation.

Early successional stands provide unique and important wildlife habitat.  Several common game species, including white-tailed deer and ruffed grouse, depend on early successional forests for food, cover, or both.

Over time, as individual trees grow larger, competition for growing space intensifies.  During this process, some species will self-thin, with more competitive trees taking over growing space and less competitive trees dying out.

Other species, however, will not self-thin.  If grown in pure (single-species) stands, these species will stagnate and become unhealthy and vulnerable to insects, disease, or windthrow.  A common example in Minnesota is the unthinned red pine plantation.

If not left stagnant for too long, these stagnant stands can be reinvigorated through careful thinning or stand improvement operations.  By increasing the growing space available to the best trees on the site, thinning can greatly improve the stand’s vigor, resilience, and value, both for wildlife habitat and potentially for financial returns.  Read more about thinnings in our thinning and stand improvement post.

In the absence of major disturbance, as stands age individual or small groups of trees will die and fall.  These small gaps tend to be invaded by shade-tolerant species.  Over a very long time period, these shade-tolerant species will continue to invade and come to dominate the stand.  The resulting stand will include trees of a variety of species and a variety of ages.  This type of forest is known as an old-growth forest.

April 18, 2007 at 10:18 am Leave a comment

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