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. future opportunities for increasing the pro­ duction or forest resources through nutrient management.
INCREASING FOREST PRODUCTIVITY
THROUGH NUTRIENT MANAGEMENT
1
Dean S. DeBell
Principal Silviculturist
U.S.D.A. Forest Service, Olympia, WA
During the past three decades, foresters have learned that tree growth on many forest sites is limited by nutrient deficiencies. We have found it profitable to correct these deficiencies on some site through fertilizer applications. As other s cultural practices become more refined and widely implemented, tree nutrition will become an increasingly important factor affecting forest production. Accordingly, management of nutrients will have much greater significance ,in future forest management decisions and operations than i has today. t
What do we mean by the term "nutrient management"? Its objective is to manipulate and use forest nutrient capital to attain optimum levels of resource production. (For the purpose of this discussion--that goal can be narrowed to in­ creased wood or fiber production.)
Nutrient management involves stsrting Qr modifying cultural practices to conserve, optimize .£!' and nutrient supplies of the forest. the
ConseTVation of nutrient supplies focus­ es on preventing decreases rather than stim­ ulating increases in productivity, and therefore is a bit outside my assigned topic. Nutrient conservation is a very important aspect of nutrient . management , however, and should be a significant con­ sideration in forestry decisions. Harvest­ ing and site preparation practices, in part­ icular, deserve close scrutiny with regard to effects on nutrient supplies as well as effects on other site and soil properties
(Bengtson the
1981).
My paper will discuss the other two aspects of nutrient management: (1) optimizing the use of nutrients and
(2) adding to nutrient supplies of the forest.
In the latter, I'll concentrate on the opportunity for fertilization and its advan­ tages, disadvantages, and interactions with other cultural practices. The potential for use of nitrogen-fixing plants will be men­ tioned briefly. Finally, I'll draw some general conclusions regarding present and lFrom
Increasing c
Proceedings of of the Society t of or s Productivity:
1981
Amer
;)m
Foresters.
51
OPTIMIZING USE OF NUTRIENTS
There are several opportunities for increasing productivity through optimizing use of existing nutrient supplies (native or applied). These approaches might be implemented in lieu of or--as a complement to--nutrient additions. The techniques include practices that: (1) increase availability and uptake of nutrients and
(2) lead to more efficient use of nutrients taken up by forest stands (i.e., greater amounts of merchantable biomass per kilogram of nutrient accumulated). I will illustrate these possibilities with a few selected examples.
Practices for Increasing Nutrient
Availability and Uptake
1. Enhancement of nutrient rates. In forests
2! cycling where natural rates of
�ent cycling limit growth, thinning and other types of cutting may improve the nutrient status of tree crops. Prescribed fire and application of some fertilizers can also increase availability of native nutrients.
2. Control of competing vegetation.
One of the benefits of vegetation control is greater nutrient availability and increased uptake of nutrients by tree crops.
3. Manipulation mycorrhizae.
Foresters have known for some time that mycorrhizae permit trees to exploit native nutrient supplies that otherwise would remain unavailable. Recent studies have suggested that on some sites, especially on those that are har r infertile, the inoculation of tree seedlings with specific mycorrhizae may result in more effective use of nutrient supplies (Ruehle and Marx
1979).
Practices for More Efficient Use of
Accumulated Nutrients
1. Selection.£! species and genotypes.
Substantial differences exist between species and within species in amounts of merchantable biomass producsd per kilogram of nutrient accumulated.
Species differences can be illustrated with data on yield and nutrient accumulation in 40-year-old adjacent stands of red aud jack pine, spruce, and aspen in Minnesota
(Alban et al.
1978).
Bolewood yields varied

from 88 tlha for white spruce to 145 tlha for red pine. Amounts of nutrients accumu­ lated in above- and below-ground biomass during the 40-year period also differed substantially. If bolewood yields are expressed in relation to nutrient content
(kilograms of bolewood t kilograms of nutrients), an index of efficiency of nutrient use by each species is obtained.
The two pines produced nearly twice as much bolewood per kilogra of nitrogen, phosphorus, and potassium accumulated as did aspen or white spruce. In this instance, the highest yielding species (red pine) was also one of the most efficient users of the native nutrient supply.
The selection within species of races or genotypes that use nutrients efficiently also has promise and probably bas greater potential for wide application than species selection per se. For example, Blackmon and others (1979) found that ll-year-old cotton­ wood from three sources--Louisiana,
Mississippi, 'and Illinois--produced similar biomass yields on an unfertilized site in northern Mississippi. Total accumulation of nitrogen and potassium, however, differed widely. The Louisiana source was by far the most efficient in nutrient use.
Compared with the Illinois source, it produced sbout 50 percent more biomass per kilogram of nitrogen accumulated and nearly twice as much biomass per kilogram of potassium accumulated. Differences in efficient use of nutrients also exist among genotypes of loblolly pine (Pope 1979) and probably most other species.
2. Selection of management regimes.
On sites .where growth is limited by low fertility, information on stemwood produc­ tion per kilogram of nutrient use could be considered in decisions regarding rotation age, stocking, and other aspects of management regimes. Few data now exist with which we can critically evaluate differences among management alternstives.
Such .data would not be difficult to obtain, and a psper prepared by Switzer and his associates (1976) provides an indication of the magnitude of possible differences.
These authors presented data on nutrient accumulation and dry matter production by poplars grown under three management production regimes. If ratios of to total nitrogen accumulation are calculated from their data, close-spaced, thinned plantations appear to be 15 to 20 percent more efficient in use of nitrogen than are either natural stands or widely spaced, unthinned plantations.
ADDING TO NUTRIENT SUPPLIES
The major possibilities for adding nutrients to forests are fertilization, symbiotic nitrogen fixation, and application of sewage sludge. I will limit my comments to the first two.
Forest Fertilization
Nutrient deficiencies can be remedied by application of fertilizers. Good responses to nitrogen have been obtained in the Douglas-fir forests of the Pacific
Coast (Miller and Fight 1979). Established stands of pine have responded well to nitrogen and phosphorus in the Southeast, and the response of young pine plantations to preplanting applications of phosphorus on some coastal plain soils has been outstanding (Pritchett 1979). The value of wood added in these forests is such that fertilization is considered an attractive investment (Bengtson 1979, Fight and Dutrow
1981). Forest sites in other regions are also deficient in nutrients and other species have responded to application of fertilizers, but estimated financial returns are rarely sufficient to make fertil zation profitable. Specific information on growth response of tree species to various fertilizers and application methods under different site and stand conditions is in re orts of the forest fertilization research cooperatives centered at the University of Florida,
University of Washington, and North
Carolina State University. Much information is also contained in publications from laborat ries of the
Forest Service, industry, and other public agencies and universities throu hout the nation. These reports verify that there is an excellent opportunity to increase timber production through fertilization of species on some sites for some owners.
In the next few paragraphs, I will characterize the fertilization opportunity by examining some of its advantages and limitations. I'll also discuss some of the interactions between fertilizer application
. and other forest management activities. advantages
£!. fertilization.
Flexibility in timing with respect to stand age is one of the principal advantages of fertilizer application. Many other cultural practices must be done within narrow time limits or the opportunity is lost; not so with nitrogen fertilization and some phosphorus fertilization.
Growth increases after applications of nitrogen fertilizer occur within a short (5­ to 10-year) period.. If stands are fertilized a few years before commercial
52

thinning or final harvest, this permits short investment periods and thus increases economic attractiveness.
Labor inputs and administrative costs are low.
When applied by aircraft, fertilizers cause essentially no disturbance to the physical environment.
Positive interactions between fertiliza­ tion and other intensive cultural practices
(e.g., thinning) have been documented (Hall et al. 1980). Also, in some cases, fertili­ zation may substitute for other practices that may be more costly or more disruptive, such as drainage or intensive site preparation.
Some limitations of forest fertilization.
----
The uncertainty �te-specificity of response are a major limitation. With few exceptions, there is financial risk involved in a plying fertilizer at any single location. For large industrial or public owners, the average responses are sufficient to carry the investment. But the situation is more risky for small private landowners. Such risks can be reduced with refinements in fertilization prescriptions. This will require improve­ ments in diagnostic techniques for assess­ ing nutrient de£ieieneiea and alao greater understanding of the relation of stand characteristics and other site and soil factors to response. Some of the recent approaches developed by workers associated with the various research cooperatives
(e.g., Fi her and Garbett 1980; Ballard and
Lea 1981; Shumway and Atkinson 1978) appear promising. Better prescriptions are essential if the fertilization opportunity is to be extended to the small private owners who control nearly 60 percent of our commercial forest land.
Large outlays of cash are needed. And-­ again--this limitation affects the small private owner most.
Energy inputs are high. Fertilization can result in a net gain in energy (Miller and Fight 1979), but inputs of energy associated with nitrogen fertilization dwarf those of most other silvicultural practices; and net energy from other practices usually exceeds that associated with fertilizer applications. The practical consequence of this limitation depends on future supplies and cost of energy and the related effects on avail­
Most studies have shown that recovery of fertilizer nutrients by timber crops is generally less than that reported for agricultural crops (Ballard 1980). Forest fertilization might therefore be regarded by some as a waste of energy or fertilizer that is needed or could be used more effectively elsewhere.
Interactions
Fertilization and cultural
1. Control of growing stock. thinning practices. are the major opportunities we have to manipulate growth in established conifer stands. Application of either of these practices commonly has a favorable effect on the other. In general, individual trees in thinned stands respond more to fertilizer than trees in unthinned stands. But total stand growth depends on stocking as well as individual tree growth; therefore, total volume response in thinned stands may be more or less than that in unthinned st nds.
Recent analyses have suggested that growth response of Douglas-fir (Strand and
DeBell 1979) and also loblolly pine
(Ballard and Lea 1981) to nitrogen fertilization is curvilinearly related to growing-stock level. Total stand volume response is lowest in both poorly stocked and excessively stocked stands. We also know that accelerated growth caused by fertilization will increase basal area; it follows then that repeated applications of fertilizer may eventually result in stand densities that are less favorable for response. Therefore, periodic thinning may be required to maintain stands in a stocking or basal area range that is responsive to fertilizer application. If thinning is not a feature of management regimes, growth gains obtainable through repeated app lications of nitrogen throughout a rotation may be substantially lower than if stands are thinned.
Fertilization may enhance potential gains from thinning. Nitrogen fertiliza­ tion can foster a more rapid re-occupation of the site. Also, nitrogen applications have overcome or compensated for growth reductions associated with "thinning shock" in Douglas-fir (Hall et al. 1980) and perhaps could do so with other species. preparation. 2. Site It is much more difficult to make general statements about interactions between fertilization and site preparation. Responses to fertilizer on prepared sites may be less than, equal to, or more than fertilizer responses on unprepared sites. The nature of this interaction depends on the severity of vegetative competition, native nutrient levels, and how the particular site preparation method affects both. If vegeta­ tive competition is severe, site preparation may be a prerequisite for fertilizer response. But where competition is minimal, fertilizer may give greater growth
53

gains than preparation and, in such cases, might substitute for the latter.
3. Drainage. Applications of phosphorus fertIlizer have improved growth on many wet sites in the southeastern coastal plain. In some instances, fertilizer has produced growth increases comparable to those obtained with improved drainage (Pritchett
1979).
These findings have led to the suggestion that, at least on some sites, fertilization might reduce the need for drainage (Langdon and McKee
1981). O n the other hand, combination of drainage and fertilizer application may be even better if maximum timber production is desired.
4. improvement. Since nutritional limitations are increasingly important, it seems logical to include some nutrient­ related criteria in genetic selection pro­ grams. There_ are at least three considera­ tions of potential significance: (a) growth on unamended or infertile 80ils, (b) response to applied nutrients, and (c) efficiency of nutrient use (i.e., merchantable biomass per kilogram of nutrient accumulated.
These considerations are not necessarily mutually exclusive. At the present time, one of the items may seem more important than the others, and this may differ with region, species, and ownership or management objectives. Consid­ ering the long-range nature of tree improve­ ment programs, it seems prudent to retain flexibility in future options. We can do this by evaluating both growth and nutrient use of genetic mate s-on-unamended, amended, and, in some cases, on infertile sites.
Use of Nitrogen-Fixing Plants
Nitrogen is the element that most commonly limits growth of forests, and uncertainties associated with the energy crisis have led to renewed interest in use of nitrogen-fixing plants in forestry as in agriculture (Gordon et al.
1979).
The potential of this approach can be illustrated with a Douglas-fir--red alder plantation located on a low quality, nitrogen-deficient site in southwest
Washington. The planting is in the Yacolt
Burn area of the Wind River Experimental
Forest where red alder was interplanted in a 4-year-old Douglas-fir plantation. When the plantation was about 30 years old, growth of Douglas-fir and nitrogen and organic mstter in the soil were greater in the mixed stand than in the surrounding plantation retained as pure Douglas-fir
(T arrant and Miller
1963).
At age 48,
54 heights of dominant Douglas-fir trees averaged 20 percent taller in the mixed stand than in the pure stand-and total volume of the mixed stand waS nearly twice that of the pure stand (Miller and
Murray 1978).
There are other examples of successes with nitrogen-fixing plants in forestry
(Haines and DeBell 1979). These include: understory mixtures of autumn olive with black walnut, legumes with sycamore; or lupines with Monterey pine, Scots pine, or
Norway spruce. Nitrogen-fixing plants may also provide auxiliary benefits--such as control of weeds or soil-borne diseases. On some forest sites, use of nitrogen-fixing plants may provide a better option than application of synthetic nitrogen fertilizers for long-term improvements in soil productivity.
CLOSING THOUGHTS
There is no question that there are many opportunities for increasing productivity through nutrient management. Neither is there much doubt that nutrient management will have much greater significance in the future than it has today.
Application of fertilizers is the most dramatic--and in some instances, the only practical--way to increase productivity.
Some outstanding gains have been achieved.
Present opportunities for profitable appli­ cations, however, are confined primarily to large industrial and public holdings in the
Pacific Northwest and in the Southeast.
For this reason and other reasons, fertilizer application shQuld not dominate our future attentions in nutrient management--at least not to the extent that other approaches are neglected. Some of the other nutrient management opportunities may have far wider application--and some may have more lasting impacts--than fertilizer amendments. These alternative approaches can also provide added flexibility and diversity in nutrient management options. Today we may not have the necessary information to fully imple­ ment some of the alternative or supplemen­ tary approaches--but neither can we profit­ ably fertilize moar-of our commercial forest land.
----
Several years ago the concept of inte­ grated pest management was introduced in forest protection circles. Today it has proven value, and I believe a comparable approach to nutrient management has equal merit. We need to develop an integrated and diversified technology for manipulat­ ing forest nutrient capital. This should include:
(1) conservation measures to

minimize losses, (2) procedures to optimize use of nutrients, and (3) alternative methods for adding to existing nutrient supplies.
With such understanding and technology, foresters could selectively implement those nutrient management tactics (or combinations thereof) that would optimize achievement of management goals. Such goals include both attaining sustaining high levels of forest productivity.
LI"n:RATURE Cln:D
Alban, D. H., D. A. Perala, and B. E.
Schlaegel. 1978. Biomass and nutrient distribution in aspen, pine, and spruce stands on the same soil type in Minne­ sota. Can. J. For. Res. 8:290-299.
Ballard, R. 1980. The means to excellence through nutrient amendment, p. 159-200. p.
Weyerhaeuser Sci. Symposium 1:
Plantations--The shape of
Perry (eds.). 1979. forests. For. Res. Lab., Oreg.
Univ., Corvallis. 501 p.
Haines, S. G., and D. S. DeBell. of nitrogen-fixing species to maintain productivity of
279-303.
Forest the future.
Weyerhaeuser Co., Tacoma, WA.
Ballard, R., and R. Lea. 1981. analysis for predicting quantitative fertilizer response: the importance of stsnd and site variables to the interpretation. Proceedings:
World Congress, Kyoto, Japan.
224 p.
Foliar
XVII IUFRO
Paper presented at combined meeting of Working
Parties Sl.02.0l and Sl.02.08.
Bengtson, G. W. 1979. Forest fertiliza­ tion in the United States: Progress and
Outlook. J. For. 78:222-229.
Bengtson, G. W. 1981. Nutrient conserva­ tion in ·forestry: A perspective. So. J.
App1. For. 5(2):50-59.
Blackmon, B.G., J. B. Baker, and D. T.
Cooper. 1979. Nutrient use geographic sources of eastern by three cottonwood.
Can. J. For. Res. 9:532-534.
Fight, R. D., and G. F. Dutrow. 1981. Fin­ ancial comparison of forest fertilization in the Pacific Northwest and Southwest.
J. For. 79:214-215.
Fisher, R. F., and W. S. Garbett. 1980.
Response of seminature slash and loblolly pine plantations to fertilization with nitrogen and phosphorus. Soil
Sci. Soc. Amer. J. 44:850-854.
Gordon, J. C., C. T. Wheeler, and D. A.
Symbiotic nitrogen fixation in the management of temperate
Proceedings of symposium on impact of intensive harvesting rient cycling held SUNY Call.
Sci. and Forestry. A. L. Leaf,
State
1979. Use improve and forest soils. on nut­ of Environ. ed. Syra­
55 cuse, NY.
Hall, T. H., R. V. Quenet, C. R. Layton, R.
J. Robertson. 1980. Fertilization and thinning effects on a Douglas-fir ecosystem at Shawnigan Lake: 6-year growth response. For. Serv., Pac. For.
Res. Cen., BC-X-202, 31 p.
Langdon, 0., and W. H. McKee. 1981. Can fertilization of loblolly pine on wet sites reduce the need for drainage? p.
212-218. In Proceedings of the First
Biennial Southern Silvicultural Research
Conference. J. P. Barnett, ed. USDA
For. Servo Gen. Tech. Rep. SO-34 , p.
Southern Forest Exp. Stn., New Orleans,
LA.
Miller, R. E., and R. D. Fight. 1979.
Fertilizing Douglas-fir forests. USDA
For. Servo Gen. Tech. Rep. PNW-83, 29 p.
Miller, R. E., and M. D. Murray. 1978.
The effects of red alder on growth of
Douglas-fir, p. 283-306. In Utilization and Management of Alder.
D7
G. Briggs,
D. S. DeBell, and W. A. Atkinson
(compilers). USDA For. Servo Gen. Tech.
Rep. PNW-70. Pac. Northwest For. and
Range Exp. Stn., Portland, OR.
Pope, P. E. 1979. The effect of genoty e on biomass and nutrient content in ll-year-old loblolly pine plantations.
Can. J. For. Res. 9:224-230.
Pritchett, W. L. 1979. Properties and management of forest soils. John Wiley &
Sons, New York, NY. 500 p.
Ruehle, J. L., and D. H. Marx. 1979.
Fiber, food, fuel, and fingal symbionts.
Science 206:419-422.
Shumway, J., and W. A. Atkinson. 1978.
Predicting nitrogen fertilizer response in un thinned stands of Douglas-fir.
Comm. Soil Sci. Plant Anal. 9(6):529-539.
Strand, R. F., and D. S. DeBell. 1979.
Growth response to fertilization in relation to stocking levels of
Douglas-fir, p. 102-106. In proceedings
Forest Fertilization Conference. S. P.
Gessel, R. M. Kenady, and W. A. Atkinson, eds. University of Washington, College of Forest Resources, Institute of Forest
Resources Contrib. No. 40. Seattle.
Switzer, G. L., L. E. Nelson, and J. B.
Baksr. 1976. Accumulation and distri­ bution of dry matter and nutrients in
Aigeros poplar plantations. p. 359-369.
In Thielges, B. A., and S. B. Land
(eds.). Proceedings of a symposium on eastern cottonwood and related species.
Louisiana State University, Baton Rouge.
U.S.A.
Tarrant, R. F., and R. E. Miller. 1963.
Accumulation of organic matter and soil nitrogen beneath a plantation of red alder and Douglas-fir. Soil Sci. Soc.
Am. Proc. 27:231-234.