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Precautionary Planning

Precautionary Planning for the Effects of
Climate Change on Forests in the Northeast

(An abridged version of this article by Karl Davies and Michael Mauri was published in the Massachusetts Woodland Steward , Summer 1998).

 If you have a forest management plan, it's likely that a very important, but not necessarily explicit assumption was made in writing your plan.  This assumption is that forest growth and mortality rates will not change significantly over the time period of your plan.  Given the most recent projections of many climatologists, meteorologists and ecologists about climate change resulting from the burning of fossil fuels, this assumption may no longer be warranted (IPCC Working Group II 1996). 

Many climate scientists believe it is likely that damaging storms (ice, snow, wind) will increase in frequency and severity; many forest ecologists believe that winter freeze injury will increase, that insect and disease outbreaks will increase, and that forest fires will also increase.  On the other hand, increased levels of CO2 and precipitation will probably  improve the growth rates of trees that are not affected.  These changes will influence the growth and mortality rates of your forest.  The risk of increased mortality and slower growth due to climate change suggest a need for precautionary planning and better risk management (Gucinski and McKelvey 1992).

It is important that we as landowners, foresters and others concerned about the health and viability of our forests try to understand the dynamics and effects of climate change, and then adjust our forest management plans accordingly.  We need to be thinking both about strategies for 1) adaptation to climate change and air pollution, and 2) mitigation of climate change and air pollution.  This article will try to describe the problem, as well as possible adaptation and mitigation strategies.  

What is Happening to the Weather and Why

Severe storms augmented by the recent El Nino weather pattern have made climate change a reality for many of us.  It's no longer just a theory debated in academic journals, radio talk shows and online newsgroups.  The pattern and its effects are clear.  El Nino events now occur about every 3 years instead of the historical frequency of about every 6 years (Karl et al 1996, Wellington et al 1996), and recent El Nino events are longer and more intense (Climate Diagnostics Center 1998).  

Forest landowners in Northern New England and New York State, plus southern Quebec and Ontario will be dealing with the consequences of the severe January ice storm for decades to come.  The storm caused moderate to severe damages on over 15,000,000 acres.  The Maine Forest Service (1998) estimated damages at roughly $50 per acre in that state.  But they didn't count the future loss of grade value to trees that suffer decay and discoloration resulting from crown damage (Shigo and Larson 1969).  Discounted damages could easily be two or three times the estimated amount.

The January ice storm Up North, as well as the February rain and snowstorms on the West Coast, and the tornadoes Down South, all fit with predicted weather changes resulting from global warming and climate change (Kuemmel 1996).  Increased carbon dioxide and other greenhouse gases allow solar energy to reach the Earth, but they prevent the infrared wavelengths from radiating back into space.  The increased energy is trapped as heat which causes more evaporation from oceans and more respiration from vegetation on the land.  The result is a warmer, wetter and more turbulent climate (Dai et al 1997, Karl and Knight 1998).

A couple of analogies may help in understanding the process.  Carbon dioxide constitutes only about .03% of the atmosphere, but it's a very important .03%.  Because it controls the heat balance of the planet, it's like a little engine driving a very big flywheel (Hemphill 1998).  Another analogy is that carbon dioxide and other greenhouse gases (water vapor, methane, nitrous oxides, USEPA 1998) are like a blanket.  Up until the Industrial Revolution we had two blankets and were very comfortable.  Now we've added another blanket and yet another will be added over the next 40-50 years.

Warming is accentuated close to the equator where the sun's rays are more direct, and where there is less reflectivity in the atmosphere from tiny sulphur and other particles released by burning fossil fuels.  Sulphur particles (also called aerosols) in the northern hemisphere combine with water vapor to form tiny droplets of sulphuric acid which reflect the sun's rays back into space, thereby cooling the oceans and ground below (Wielicki et al 1995, Kuemmel 1996).  The difference between the warmer atmosphere near the equator and the cooler atmosphere further north causes more atmospheric turbulence, with increases in heavy precipitation events and storms (Karl and Knight 1998). 

Computer models have been developed to simulate future global climate change with a doubling of CO2 by 2050 (IPCC Working Group II 1996, Loehle and LeBlanc 1996).  The models are on very large area and time scales, that is, they don't account for regional changes in climate and vegetation, and they don't account very well for transitional climatic changes between now and 2050.

Some data are available for transitional changes in the Northeast, but they have not yet been incorporated into the models.  Researchers have found positive correlations between El Nino events and severe thaw-freeze events in the Northeast (Auclair et al 1996).  These freezes weaken trees and make them more susceptible to subsequent drought stress, insects and diseases.  Severe freezes do more damage to tree root systems in open winters, which are more likely in El Nino years.  El Nino events also bring more precipitation and warmer temperatures to the Northeast, which can manifest as heavy, wet snowstorms and ice storms. 

Those who argue that climate change is not really happening, or that it is insignificant, have had their credibility seriously challenged.  Ross Gelbspan (1997) documented that nearly all of the prominent `denialist` researchers were in the employ fossil fuel industry groups.  The debate seems to have turned from whether or not climate change exists to whether the trend will be linear or abrupt and chaotic (Broeker 1995).

What Will Happen to Our Forests?

On the Downside

The Intergovernmental Panel on Climate Change's (IPCC) Climate Change 1995: Working Group III (1996) references computer models of climate change that project forest mortality rates of 30-40% over the next 50 years with a doubling of CO2 rates.  The computer models project that climate-defined species ranges will move northward, but that trees and other plants will not be able to move with them.  The result will be increased mortality. 

The models project that trees will die along the southern boundaries of their ranges because of drought stress and fire, plus more favorable environments for insects and diseases that are normally found further south.  While the degree of expected mortality is disputed (Loehl and LeBlanc 1996), none of the models assume any damages due to increased severity or frequency of storms.  Given the recent ice storm Up North, this may be an unreasonable assumption. 

Neither do the models estimate damages resulting from the other products of burning fossil fuels: sulfur dioxide, nitrogen oxides, ozone or heavy metals.  High levels of pollution can kill trees outright; low levels make them more susceptible to other biotic agents (Skelly 1992).  Pollution also makes trees more susceptible to freeze injury (Sheppard 1994, Gawel et al 1996, Wellburn et al 1997) , which in turn makes them more susceptible to drought stresss and biotic agents (Auclair et al 1996). 

Increased storm damage may result when trees are already structurally weakened by air pollution and/or freeze-drought stress.  Some researchers have attributed part of the severe damage from the recent ice storm to these causes (Hawkes personal communications).  Many of the heavily damaged sugarbushes and maple stands were already under stress from air pollution, freeze injury and insect defoliation.

Wetter soils are one consequence of increased precipitation and warmer temperatures in the Northeast (Karl and Knight 1996).  Wet winter soil conditions limit the time window for logging jobs that require frozen ground.  These conditions are already pushing a transition from chainsaws and rubber-wheeled skidders to tracked harvesters and forwarders, which cause less rutting and soil compaction.  Even with low-impact harvesting systems, there is a risk of increased soil compaction which will lower the long-term productivity of forest soils (Brais 1994). 

In most the Northeast, we already have roughly 20% more precipitation and 5F higher temperatures than we did 100 years ago (Karl et al 1996).  Most of the increases come in late fall, winter and early spring, and most of the increased precipitation comes as heavy precipitation events (Karl and Knight 1998).  Part of the manifestation of these trends will be as more heavy, wet snowstorms (as in December 1996 and April 1997) and more severe ice storms (as in January 1998).

On the Upside

Some parts of the world may benefit from increased levels of CO2 in the atmosphere.  Scandinavian forest researchers project that their northern forests will survive and grow faster while their southern forests will probably suffer increased mortality rates (Talkkari and Hypen 1997).  They project a net benefit.  The same dynamics should hold for boreal forests in Siberia and Canada--unless forest fires offset the increases, and unless wet ground conditons prevent access to the timber.

The combined effects of increased CO2, more precipitation and warmer temperatures should benefit all plants, including trees, in the Northeast.  Some of the excess nitrogen oxides from buring fossil fuels become available to plants in forms that can be beneficial (Aber 1992,  Wright et al 1995).  But agriculture and forestry will suffer from increased levels of tropospheric ozone which is produced when sunlight acts on these nitrogen oxides in the atmosphere (Wellburn et al 1997).   

Hurricanes are less frequent following El Nino winters (O'Brien et al 1996).  Since El Nino winters are now more frequent, this might mean fewer hurricanes overall.  However, this does not appear to be the case (Henderson-Sellers et al 1998).  Apparently there are enough more hurricanes during the non-El Nino years to offset the El Nino year decreases. 

Long-term projections of supply and demand for forest products indicate that global demand could easily exceed supply (IPCC Working Group III 1996), particularly if large-scale climate-related impacts reduce the amounts of marketable timber, wood and pulp.  As an example, the recent ice storm Up North will reduce the supply of northern hardwoods from that area.  Over time, this will result in increased values of northern hardwoods in other parts of their ranges

Losses could also occur in other parts of the world.  The southern Appalachians are currently losing significant areas of timber to the effects of acid precipitation (Institute for Environmental Studies 1998).  This will increase the value of timber in unaffected areas.  Supply and demand mechanisms could increase prices for timber in the Northeast if forest fires destroy large areas of boreal forests in Scandinavia, Siberia or Canada.

Precautionary Planning


Use of the precautionary principle has been advocated by the insurance industry which has been outspoken about the risks associated with climate change (UNEP Insurance Initiative 1996).  The precautionary principle simply advocates taking steps toward adaptation and mitigation now in order to avoid losses in the future--even when the exact probability of future losses is unknown.

Insurers and others concerned about climate change believe that we need to adapt our activities to reduce the risks from storms and other risks resulting from climate change.  Some foresters are starting to think along these lines, particularly in Great Britain and Northern Europe where there have been very significant storm-related damages to forests.  Several levels of response/adaptation have been proposed. 

The most extreme response is what are called `preemptive salvage cuts.`  These cuts are designed to realize whatever value there is the forest before it suffers a catastrophic loss--as in the recent ice storm Up North, or as in a hurricane or tornado.  Much of the value in the trees that were heavily damaged by the ice storm will be lost because of the narrow time window between the event and warm weather which will bring insects and infections to the damaged trees. 

There are other factors which operate against successful salvage operations under these circumstances. There is danger associated with harvesting trees with broken branches still hung up in the crowns, plus many branches on the forest floor.  Loggers who don't have mechanized harvesters with protective cabs are at risk of severe injuries.  Most loggers have existing contractual obligations that they must honor, and are therefore not free to quickly move to salvage operations.  Sawmills have limited capacities and markets for product.

Less extreme than preemptive salvage cuttings would be thinnings and selective harvests to remove those trees that would be most susceptible to storm damage. For example, red pines are susceptible to ice and snow damage because their thick needles and flexible branches hold the snow/ice without breaking.  This causes the stems to break or uproot.  White pines under the same circumstances just lose some of their branches.  Red maples are more likely to suffer ice and snow damages than red oaks because their wood is not as strong.

Trees of any species with forked crowns are especially at risk because forks are weaker than single stems.  Heavy ice and snow loads will often break off one or both forks.  Trees on wet soils are at risk of uprooting under the weight of wet snow and ice because their root systems are shallow.  This problem also occurs on normally well-drained soils which happen to be saturated at the time when the heavy snow or ice storm hits.

Arborists and foresters have written about how different species react to different kinds of extreme weather.  Illinois arborists developed a table of species resistance and resilience to ice damage (Hauer et al 1994).  The Harvard Forest in Petersham has a computer model that indicates forest susceptibility to hurricane damage according to species, height and site topography (Foster 1988).  Some species are resistant or resilient to ice and snow, but susceptible to high wind.  This is a complicated subject that requires sophisticated analysis (Davies in progress).

Some forest managers have suggested shorter rotations to reduce the time that trees are at risk of climate-related damages (IPCC Working Group II 1996).  Others have suggested a shift to uneven-aged silviculture to reduce the proportion of older trees which would be more at risk.  Older trees are at greater risk of thaw-freeze and drought injury (Auclair 1996 and 1997).  Short rotation and uneven-aged management could have ancillary benefits of increased rates of value growth (Davies 1991 and 1996).  Other ancillary benefits from these and other adaptation strategies could include increased biodiversity and forest health.

A more moderate approach would be to improve access roads to facilitate salvage operations in the event of a severe storm or insect/disease outbreak.  This would make salvage cuttings easier and therefore more attractive to loggers.  Better access roads and trails would also facilitate visual monitoring of the forest for signs of infestation or disease.  Monitoring by remote sensing (satellites) is becoming more available and less expensive and can be used for the same purposes (Lenz et al 1995). 

In any case, good inventory data are needed.  While it may be difficult to plan for the next 10-20 years, it's still necessary to gather good inventory data and to monitor for changes in rates of growth or incidence of disease or infestation.  Good inventory data can also indicate stands that may be more susceptible to storm damage.

You may want to upgrade your inventory to include some permanent sample points so that you can keep better track of growth and mortality rates.  This means identifying the centers of sample points with permanent markers and measuring tree diameters to the tenth of an inch.  It's a simple matter to go back and remeasure trees to compare the actual growth rates with the growth rates projected from historical trends. 


The insurance industry has been hurt by serious financial losses over the past two decades due to hurricanes, floods and other storm-related events.  There is debate as to whether the increase in damages is the result of more frequent and severe storms--or more people and higher property values in at-risk areas--or some combination of these factors (Changnon et al 1997). 

Nevertheless, insurers and others concerned about climate change believe we should immediately reduce the levels of greenhouse gas emissions.  The recent conference in Kyoto, Japan was about negotiating international agreements on emissions and  implementing regulations.  The political issues associated with reductions in emissions are complex and explosive.  Although progress was made in these negotiations, there remains a very long way to go.

Some foresters, ecologists and climatologists have advocated planting more trees to sequester carbon dioxide from the atmosphere and to substitute for fossil fuels (Marland and Schlamadinger 1997, Watson et al 1996).  Unfortunately, research has shown that even massive efforts at reforestation and substitution would have only marginal effects on the amount of carbon in the atmosphere.  The oceans sequester more carbon, and in both cases nearly all the sequestered carbon eventually cycles back into the atmosphere due to biological activity, death and decay. 

Until recently, it was thought that carbon dioxide had a `half-life` of about 100 years, that is, carbon released by the burning of fossil fuels would stay in the atmosphere this long before half of it was absorbed by vegetation or the oceans.  Now this concept has come under attack with the realization that excess carbon will just `slosh` back and forth between `reservoirs` (atmosphere, biomass, oceans) for the foreseeable future (Tans 1997).  In other words, the genie is out of the bottle and can't be put back in.  

From this perspective, the only effective mitigation strategy would be to move away from fossil fuels and toward renewable energy sources, including biomass/wood.  The idea would be to limit releases of more carbon from the fossil fuel `reservoirs.`  But even if we were to stop using fossil fuels entirely, the flywheel will keep on turning.  The extra blankets will stay in place.  Any success with mitigation measures would not be manifested until well into the next century.

Other Considerations

Part of the difficulty in forecasting climate change and its effects on forests is the unpredictability of what are called feedback mechanisms (IPCC Working Group II 1996).   Positive feedback mechanisms accelerate the rate of change, while negative feedback mechanisms retard it.  Feedback mechanisms can interact with the primary movement and each other in unforeseeable ways 

The principle positive feedback mechanisms associated with climate change are more carbon from fires resulting from droughts, more carbon and methane from warming tundra and boreal forests, and more carbon from warmer ocean waters.  Another very important positive feedback mechanism is increased water vapor in the atmosphere from more evaporation from oceans and transpiration from vegetation.  Water vapor is itself a very powerful greenhouse gas.

Negative feedback mechanisms would include increased cloudiness (and resulting cooling) in northern latitudes from increased evaporation and transpiration, and increased absorption of carbon by vegetation under warmer growing conditions.  Less ice in the polar regions may allow more carbon absorption by polar oceans.

If positive feedback mechanisms start to kick in, such as last year's increased forest burning in Indonesia and the Amazon, the rate of CO2 increase will accelerate.  All the scenarios in the computer simulations could happen sooner than projected. 

Although the trend is toward wetter and warmer conditions in the Northeast, it is possible that we could have a severe drought.  Extremes of all sorts are expected with climate change (Keummel 1996).  Severe droughts would stress trees and make them more susceptible to dieback, insects and disease attacks.

Some researchers think that the effects of climate change will be much worse than the models predict if the climate goes into a non-linear, rapid rate of change.  The climate could get much warmer much faster, or it could quickly go in just the opposite direction.  If warming significantly alters the circulation of major ocean currents, there could be a `flip` to a much colder climate in northern regions (Broeker 1995).

Other researchers take a longer view of geologic history and see the current climate changes as a positive trend away from the generally glacial climates of the past two million years (Crowley 1996).  These researchers point out that all the carbon, sulfur, nitrogen and other elements present in fossil fuel reservoirs today came from fixation of atmospheric gases by ancient trees and other vegetation, and that putting these gases back into the atmosphere by burning fossil fuels may take us back to a pre-glacial Garden of Eden. 

However, these same researchers caution that there are some very important differences between our present climate trends and those of the pre-glacial past.  Also, the rate of climate change is apparently much greater now than it ever has been in the past.  Therefore, a continuation of the present trends could entail some very unpleasant transition climates between the present and any return to the Garden of Eden.

Sidebar 1:  Things to Do Now on Your Woodlot

The first thing to do is review your inventory and management plan with your forester.  If good data inventory data are lacking, you should consider upgrading them.  If your management plan is about to expire, you might want to have a new one done sooner rather than later.  If your plan is a recent one, you should review it with your forester, and consider possible modifications.

For instance, if you own significant volumes of older, mature timber, you should consider preemptive salvage operations.  Large, old trees are least likely to survive stress events.  Decisions about cutting such timber should be influenced by the species, size and quality of the timber.  Large, non-grade hardwoods and softwoods are likely to be growing slowly in value anyway--and therefore ready to harvest for economic reasons.  Small and medium-sized grade hardwoods are more likely to adapt to changing conditions.  Medium-sized grade hardwoods are likely to be growing rapidly in value--and therefore more likely to be worth holding onto.  See Davies (1991, 1996).

If you own significant volumes of red pine or red maple, you should consider cutting now to minimize the risk of ice and snow damage.  If you own significant volumes of hemlock, you should check to see if it's infested with the hemlock adelgid, which is moving further north as temperatures rise (Evans et al 1996).  If you own significant volumes of white ash, you should check rates of growth and mortality.  Ash decline is thought to be the result of drought stress in the 1960's followed by severe thaw-freeze events in the 1980's (Woodcock et al 1993), particularly on certain sites (Woodcock et al 1997).  Harvest older trees on high-risk sites.

Risk of ice and snow damage is mostly a function of the surface area of small branches and needles (Hauer et al 1994), and the strength of branches and stems.  Here's a rough risk continuum for species commonly found in the Northeast:

High:  red pine, red maple, white birch (especially younger trees)

High-Medium:  yellow birch, black birch, sugar maple, black cherry (especially trees with big forks)

Medium:  white pine, hemlock, spruce, fir

Medium-Low:  red oak, black oak, white oak

Low: white ash, hickory, butternut, walnut (unless trees have big forks)

If you are planning any kind of cutting operation, you should carefully consider the timing of it.  Since our winters are becoming shorter, warmer and wetter, ground conditions might be better in the summer.  Most sawmills have added kiln drying facilities in recent years.  This means the risk of lumber staining in hot weather is much less than it used to be and that summer log and lumber prices are better now than they were just a few years ago. 

Regardless of the season for cutting operations, you might want to consider adding restrictive clauses in your bid prospectus and contract concerning acceptable ground conditions and equipment systems.  You might also want to be flexible about payment schedules so that adverse weather and ground conditions don't force loggers to have too much of their money tied up in sales that they can't access.  

You might also want to get some estimates for access road improvements.  Even if you don't want to do the work now, you should know what it might cost.  Remember that better access roads not only facilitate salvage operations, they also improve access for fire suppression and increase recreational values.

If you're thinking of planting fast-growing trees of southern provenance in anticipation of warmer temperatures, you might want to hold off until more research has been done on the adaptability of these species to our transitional climate, particularly thaw-freeze events.  If you're thinking of planting trees of more northern provenance you should still carefully consider the microclimates on your property to minimize the risk of winter and spring freeze injury (Davies 1990).

Sidebar 2:  Possible Further Actions

The first thing is to learn more about climate change.  Read what you can and discuss what you learn with your family and friends.  Ask your local library to set up a special shelf on climate change.  Make a list of Internet sites on climate change.  Speak to your elected representatives about your concerns.  Talk to your forester about climate change.  If he/she doesn't want to think about climate change, find another forester who does.

If you want to go further, you might want to consider taking more direct action.  Write to fossil fuel industry associations to demand that they insure and indemnify forest landowners against increases in mortality above historical rates.  If they're so sure that their `denialist` scientists are right about climate change being a hoax, the fossil fuel industries should gladly accept this challenge. 

Buy stock in forest product companies and use your authority as an owner to demand that forest products industries exercise the precautionary principle by joining with the insurance industry to demand a reduction in fossil fuel emissions.  Write to company executives to say that if they don't do this, and simultaneously take precautionary actions to adapt to climate change on company lands, that you will sell your stock and tell all your friends and associates to do the same.

Write to your elected representatives to ask that they sponsor legislation taking away all subsidies, tax credits and tax deductions for the fossil fuel industries.  These government giveaways are estimated at well over $50 billion per year (Hwang 1995).  Without these giveaways to the fossil fuel industries, renewable energy sources would be much more competitive.  If the renewable energy industries had been receiving these same subsidies all along, we would have much less of a climate change problem now.


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Wright, RF, JGM Roelofs, M Bredemeiier, K Blanck, AW Boxman, BA Emmett, P Gundersen, H Hultberg, OJ Kjonaas, F Moldan, A Tietema, N van Breemen, HFG van Dijk.  1995.  NITREX: responses of coniferous forest ecosystems to experimentally changed depostion of nitrogen.  Forest Ecology and Management 71:163-169.


Bernd Kuemmel Home Page:

Canadian Forest Service Fact Sheets on Climate Change: http://www.nofc.forestry. ca/climate/factsht/factse.html

Climate Action Network:

Climate Diagnostics Center Current State of the Tropical Pacific:

El Nino-Southern Oscillation (ENSO) Home Page:

Global Change:

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April 1998