Forest Productivity as Related to Slash Burning and Other rorest Practices ._,
DeanS. DeBell
ABSTRACT
_
slash burning:
Three aspects of forest productivity are impon:mt in ma.t::ing decisions on
(1) The risk of losing the accumulated production in adjacent stands was
the initial impetus for burning slash in the Douglas-fir region, and hazard reduc::ion
remains
an
impon:mt consideration today.
(2) The production of
the :1ext timber crop
depends on many factors, but there are few general conclusions that em be made :lbout
the effecrs of burning.
(3) Lirtle definitive information is available concerning long-term
soil productivity. Existing knowledge arid experience should be synthesized to develop
an
improved framework for deC.sion making, and practitioners must be increasingly
analytical in a pplying various slash reduction practices. A technology dev elopmenr effort
initiated jointly by research and management organizations is suggested to enhance
understanding of productivity and provide site-specific guidelines and standards for
managed forest.
Forest productivity is a consideration in many decisions related to slash burning:
whether to burn or not to burn; when and how to burn; whether to choose an
alternative approach for treating residues or just do nothing. The purpose of this
paper is to discuss concerns and needs with respect to forest productivity, as
well as comment on the strength of the present knowledge base and offer
suggestions on how we might improve it Many of my remarks are not limited
to slash burning: they pertain to effects of management practices in general, as
related to forest productivity.
Forest productivity is a broad subject and includes the quantity and quality
of all products and services of the forest-timber, wildlife, fish, water, air, and
recreation. All these uses are important In this paper, however, I will limit my
remarks to timber management, and discuss productivity in terms of the capacity
of forest sites to produce crops of merchantable trees. If this capacity is
maintained or enhanced, maximum flexibility is retained in management op­
tions to manipulate tree cover and thereby affect habitat and conditions related
to production of other goods and services.
Three rather different aspects of forest productivity are important when
considering slash burning decisions:
1. The Accumulated P!oduction in Adjacent Stands. The risk of
349
losing the
DeBell
accumulated timber in surrounding forested areas was the initial impetus for
burning slash in the Douglas-fir (Pseudotsuga mensiesiz) region. Fire control
organizations and effective methods for reducing hazards (and thus risk of
timber losses) were essential prerequisites to development of forestry in the
northwestern United States. Over the years many things have changed­
transportation systems, utilization standards, amounts of residue, and air quality
regulations that restrict when and how we bum. We must ask, and continue to
ask, which risk is greater. that of increased losses of accumulated production
resulting from wildfire if slash in a unit is not burned, or losses of accumulated
production associated with escaped fire if sla$h is burned?
Such questions cannot be readily answered by designing experiments. Never­
theless, judgments are made and answers are inferred from the decades of
experience and records available in fire control divisions of forest management
organizations. The answers inferred by fuel specialists differ for various situa­
tions, and rightly so. There may be an opportunity, however, to derive better
answers through a cooperative, systematic evaluation of past records and past
experience of several organizations. As a result of extensive wildfires in the
Pacific Northwest in recent years, such an evaluation may be more informative
today than it could have been several years ago.
2. Productivity of the Next Timber Crop. There are many influences on the
establishment and growth-and thus productivity-of the next stand on a
cutover area Some of these factors may be affected or manipulated by
prescnbed fire. Some management options will be created by slash burning;
others will be destroyed. Decisions, therefore, are made in light of whether the
new stand will be established from advance reproduction, natural seeding, or
planting; whether dwarf mistletoe or animal problems are associated with
residual vegetation and slash; whether
uch residue will aid or hinder' the
establishment and growth of young trees on different sites; and whether other
options such as herbicides are available to reduce existing or developing
competition from noncrop vegetation. Also to be considered is whether the
immediate effects of burning on levels of available nutrients and microbial
populations in the forest floor and mineral soil are beneficial or detrimental.
Existing information on the most critical factors involved in productivity of
the next stand seems adequate for reasonable slash burning decisions. This does
not mean that more information will not improve decisions; certainly it will.
Furthermore, there is a need to syntliesize existing knowledge and develop
general guidelines for its use in slash burning decisions.
3. Long-Term Soil (or Site) Productivity. What are the effects of slash
burning on the sustained capacity of a site to produce timber crops? How do
various protocols for burning affect the organic and mineral horizons of the
soils, especially as reflected in tree growth? How does burning affect develop­
mental patterns of natrual as well as manipulated or introduced populations of
noncrop plants? These noncrop plants may alter moisture regimes, fix atmos­
pheric nitrogen, affect soil acidity, or otherwise influence the amounts, distribu­
tion, and availability of various nutrients and moisture in the soil. Moreover,
350
Forest Productivity
as
Related to Slash Burning
how do effects of burning compare with effects of other slash reduction
practices? We have little definite evidence re garding long-term effects-either
positive or negative----on growth of subsequent tree crops. We therefore cannot
intentionally select alternative slash treatment practices to meet specific long­
term needs on different sites.
Because of this lack of knowledge as well as overriding considerations of air
quality, operational efficiency, and more immediate productivity concerns,
long-term considerations have not had much influence on slash burning
decisions. Nor is it clear that they should. Although one would expect high
intensity fires occurring on short cycles to reduce long-term productivity on
some sites, historical records of fire and tree growth in the Douglas-fir region
·
and in managed forests in other pans of the world provide no bases for alarm.
Harvest residue from subsequent rotations in managed stands is expected to be
much less than residue left today following harvest of even the most sound
timber in natural stands. Prescribed fire-if needed and used after harvest of
managed stands-will be of lower intensity and shorter duration, and thus less
likely to have negative effects on long-term productivity than do natural fires
or curren t slash burns.
I believe our concemwith respect to the present lack of informationregarding
·
long-term productivity is mainly one of opportunities forgone rather than
potentially serious site degradation on the vast majority of commercial forest
lands. Presumably opportunities exist to do things better-whether by use,
restriction, or modific:J.tion of present practices for burning.
General Needs
Improved Toolsfor Decision Making
Few general statements and conclusions exist regarding effects of slash
burning on matters pertaining to the next crop-whether the effect in question
is plant succession, tree seedling establishment, pest control, or stand yield. Lack
of defmite answers may be attributed to one or both of the following:
(1) The
positive or negative effects of slash burning are of minimal importance com­
pared with other influences on forest productivity. (2) Effects of slash burning
are important, but they are also strongly interrelated with other factors, thus
making general statements about slash burning not only difficult but inap­
propriate.
I suspect that both possibilities are operative in different situations.
Moreover, they illustrate a need for better understanding of what determines
productivity at different sites throughout the Douglas-fir region. Thus I believe
our first priority is to synthesize existing information and develop a general
decision-making framework. Attempts to do so would not only improve current
decisions but would also identify the areas where additional data are most
ne ded, and thus increase the effectiveness of research and development efforts.
351
DeBell
The forthcoming book on pres.."'ibed fire by Walstad et al. (in press) will no
doubt provide some of the needed synthesis; so do existing models. Models or
decision-aiding tools of any kind need to be validated, however, and they need
to be used with a good understanding of their assumptions and limitations.
Fundamental Research on Forest Productivity
Research on forest productivity in the Douglas-fir region has mostly been of
two kinds:
(1) empirical attempts to estimate or predict potential stand produc­
(2) basic studies of underlying processes
tivity over a wide range of sites, and
at a few sites. The predictive work focused initially on development of soil-site
equations, and more recently on habitat or plant association relationships. This
work and process-level work at a few locations have not provided, and are not
likely to provide, the information needed to understand what specifically limits
productivity at different sites. Nor will this kind of work tell us how the effects
of such limiting factors might be lessened through management efforts. The
network of fertilizer trials established tliioughout the Douglas-fir region by the
University ofWashington' sRegionalForestNutritionResearch Project probab­
ly comes closest to providing a vision of the kind of information needed-albeit
in a limited empirical manner for only one productivity factor and one manage­
ment alternative for affecting it Studies that are more comprehensive--in both
depth and breadth-than those now conducted will be needed if we are to
understand and manipulate the processes controlling site productivity.
Analytical Forestry Practitioners
The technical capabilities of practicing silviculturists and other forestry
specialists have increased greatly during the past fiftee n to twenty years. Such
advances are due in part to widespread opportunities for midcareer training and
also to the increased recognition given to such jobs in various organizations. As
forest management becomes more intensive and more complex, practitioners
must become increasingly analytical and critical in their decisions and applica­
tions of various forest practices, including slash burning. Whether the issue at
hand involves the need to reduce residue, create more planting spots, or leave
large woody debris, foresters need to question both the traditional procedures
and the recently advocated changes in them. Practitioners must ask: What is the
evidence for or against the need for such_a practice? What other advantages and
disadvantages are associated with this approach or that one? What other alter­
natives exist, and how might they affect productivity?
An Approach for Meeting Technology Needs
Comments made earlier in this paper indicate a need for improved tools to
evaluate or predict effects of slash burning on productivity of the next stand;
moreover, we have a limited body of scientific knowledge regarding burning
and long-term site productivity. How can we develop site-specific technology
352
Forest Productivity as Related to Slash Burning
related to productivity for decisions on slash burning and other forest practices? A few months ago, the station director at the P.acific Northwest
Research Station of the USDA Forest Service appointed a task force to look into the long-term site productivity issue on federal forest lands and make recommendations for the station's research program. Inasmuch as the productivity concerns regarding slash burning are essentially a subset of the broader issue of effects of manage­
ment practices on forest productivity, I think the general conclusions of the task force are applicable. Members agreed that the productivity issue spanned the spectrum from basic research to operations, and that successful development and application of useful technology would require the pooling of human and financial resources of research and management organizations. The task force therefore recommended that the station director, the regional forester of the Pacific Northwest Region of the Forest Service, and the state director for Oregon
and WashingtOn of the Bureau of Land Management set up a cooperative
organization to carry out a comprehensive technology development program.
...
The structural framework of the proposed program consists of three tiers:
1. Primary Research Sites in Major Ecosystems. Alternative management
strategies would be compared; and effects on forest growth, soil properties and
processes, and other factors related to productivity would be examined in
fundamental srudies, many conducted at the process level. Research organiza­
tions would have the primary responsibility for work in this tier.
2. Administrative Studies on Benchmark Soils. Comparisons of alternative
management treatments would be replicated on major soils or soil groups
throughout the Pacific Northwest These comparisons would be installed and
measured by nonresearch people, and would provide the key data for developing
the site specificity needed in standards and guidelines for managing forest and
soil productivity. R esearchers would participate in design, analysis, and inter­
pretation of such comparisons, thus providing linkage to work at primary
research sites. Eventually the administrative study sites would provide the
research opportunities needed to effectively evaluate concepts developed in the
fundamental studies over a broader range of environments.
3. Monitoring ofOperational Units. A monitoring system is legally required
to track performance on federal forest land. The task force therefore proposed
that monitoring efforts be linked by design and some common measurements
to the former two tiers, and thereby provide a data bank for validation and
refmement of standards and guidelines for productivity management
Work in all three tiers was envisioned as providing data and examples for
modeling efforts and technology transfer. The task force also suggested sup­
plementary work involving retrospective analyses of existing stands and older
studies designed for other purposes.
Although this cooperative framework was initially proposed in response to
a federal land management issue, I believe the general approach could be
extended to aid and involve owners and managers of private, industrial, and state
forest lands.
353
DeBell
Conclusion
Recent discussions of forest productivity in the Pacific Northwest-whether
related to slash burning or other forest practices--have commonly focused on
the possibility of negative impacts. Some discussions have implied a need to
maintain the processes occUrring in unmanaged mature or old-growth forests,
and some have advocated a philosophy of "minimal disnrrbance." Although
such views have importance and validity on some sites and in some management
strategies, it seems that many people, especially the lay public, have an incom­
plete, unrealistic piclllre regarding the vast majority of land managed for
commercial timber production. Opportunities for enhancing productivity-the
possibilities for manipulating productivity factors in young, domesticated
forests--have been neglected. This lack of balance is particularly disconcerting
because it adds confusion to other public land issues, and it de...'Teases the
likelihood of sotmd decisions.
As professional resource
managerS' and scientists, we need to encourage
balance in discussions and information distributed regardingmanagement prac­
tices and forest productivity. It would be well to remind ourselves and the lay
public that the most productive commercial forests throughout the world are on
sites that many people would consider "unnatural"; on most of them, past
dislllrbances and present manipulations are far greater than those typically
encountered in the Douglas-frr region. Examples include the extremely produc­
tive stands of exotic conifers in Australia and New Zealand, and the Eucalyptus
and Pinusplantations throughout the tropics and subtropics. Closer to home, we
have blown that plantings of native pines established in old agricullllral fields
of the Southeast have been substantially more productive than plantations
established on comparable, minimally disturbed cutover forest sites. Recent
evidence suggests that a similar situation eXists with Douglas-fir in the Pacific
Northwest, though the total area of such abandoned farmlands is obviously
much smaller.
It is also appropriate to recognize that some of these successes have met with
serious problems during their development and that such difficulties have been
overcome. In South Australia, for example, high yields of radiata pine in the
first rotation were followed by reduced growth in the second rotation on some
sites. Intensive research pinpointed the cause of this second-rotation decline: in
essence, exotic paslllre grasses not even present in Australia during estab­
lishment of the frrst rotation were aggressively competing with second-rotation
pines on droughty, nutrient-poor sandy soils. This situation no doubt was
worsened by nitrogen losses when heavy slash from the first rotation was
burned. Weed control techniques alone have more than offset the decline
problem, however. When weed control has been combined with more judicious
burning and/or nutrient amendments, growth in the second rotation has ex­
ceeded that of the frrst rotation on such sites.
Compared with such examples of plantation culnrre elsewhere, intensive
forest management in the Pacific Northwest is still in the adolescent phase.
354
Forest Productivitv
as
Related to Slash Burning
Forest management in this region has advanced tremendously during the last
twenty-five yem, and we have numerous advantages in basic resource.s and
existing knowledge to aid and guide future developmenL Our large and produc­
tive forest land base M.s the capacity to meet regional needs for various goods
and services as well as supply wood and fiber for other markets. To fully r
ze
the region's potential, however, we need a better understanding of what con­
tributes to productivity on different sites and what management practices are
most effective. Such improvemenrs in our knowledge base seem unlikely unless
researchers and managers together initiate the long-term efforts required. This
then is the primary need and major challenge with respect to forest productivity.
Will we meet it? That is, will our generation leave a legacy of information? And
a legacy of long-term plots from which answers to present and future questions
can
be obtained? Or will foresters.-:some decades hence-be in the same
situation we are in today, asking similar questions about effecrs of various
management practices on forest productivity?
Literature Cited
J. D. Walstad, S. R. Radosevich. and D. V. Sandberg (eds.) Narural and prescribed fire
in Pacific Northwest forests. Oregon State University Press, Corvallis. In press.
In: Hanley, Donald P.; Kammenga, Jerr.v J.; Oliver,
Chadwick D., eds. The burning decision: regional
perspectives on slash. Seattle: University of
Washington.
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