Tree planting is the process of transplanting tree seedlings, generally for forestry, land reclamation, or landscaping purposes. It differs from the transplantation of larger trees in arboriculture and from the lower-cost but slower and less reliable distribution of tree seeds. Trees contribute to their environment over long periods of time by improving air quality, climate amelioration, conserving water, preserving soil, and supporting wildlife. During the process of photosynthesis, trees take in carbon dioxide and produce oxygen.
In silviculture, the activity is known as "reforestation", or "afforestation," depending on whether the area being planted has recently been forested or not. It involves planting seedlings over an area of land where the forest has been harvested or damaged by fire, disease, or human activity. Trees are planted in many different parts of the world, and strategies may differ widely across nations and regions and among individual reforestation companies. Tree planting is grounded in forest science and, if performed properly, can result in the successful regeneration of a deforested area. However a planted forest rarely replicates the biodiversity and complexity of a natural forest.
Because trees remove carbon dioxide from the air as they grow, tree planting can be used to help limit climate change. Desert greening projects are also motivated by improved biodiversity and reclamation of natural water systems, as well as improved economic and social welfare due to an increased number of jobs in farming and forestry.
Types of trees planted
The type of tree planted may have great influence on the environmental outcomes. It is often much more profitable to outside interests to plant fast-growing species, such as eucalyptus, casuarina or pine (e.g., Pinus radiata or Pinus caribaea), even though the environmental and biodiversity benefits of such monoculture plantations are not comparable to native forest, and such offset projects are frequently objects of controversy.
To promote the growth of native ecosystems, many environmentalists advocate only indigenous trees be planted. A practical solution is to plant tough, fast-growing native tree species which begin rebuilding the land. Planting non-invasive trees that assist in the natural return of indigenous species is called "assisted natural regeneration." There are many such species that can be planted, of which about 12 are in widespread use in the US.
Alternatively, farmer-managed natural regeneration (FMNR), involves farmers preserving trees (not replanting), and is considered to be a more cost-effective method of reforestation than regular tree planting.
Season of planting
Bareroot stock The classical silvicultural literature unanimously advocates spring as the time to plant bareroot stock, with lifting and outplanting taking place while the trees are still apparently dormant.Sutton, R.F. 1984. Plantation establishment in the boreal forest: glyphosate, hexazinone, and manual weed control. For. Chron. 60:282–287. This view, in which spring planting is implicit, was epitomized by Toumey and Korstian (1942):Toumey, J. W. and Korstian, C.F. 1942. Seeding and planting in the forestry practice. Ed. 3. John Wiley & Sons Inc., New York. "Almost without exception the most favourable time for ... planting is 2 weeks or more before buds [of the planting stock] begin their growth". Soil moisture conditions are generally favourable at the time when the growing season is about to begin, while dormant stock is less subject to mechanical injury and physiological shock.Stiell, W.M. 1976. White spruce: artificial regeneration in Canada. Dep. Environ., Can. For. Serv., Ottawa ON, Inf. Rep. FMR-X-85. 275 p.
If the size of the planting program allows, there is little doubt that such scheduling would be advantageous in that it satisfies one, and commonly 2, of the factors essential for success: (1) the use of planting stock that is physiologically capable of responding to a growth environment at planting, and (2) planting when site factors favour tree survival and growth. The 3rd factor a good planting job, and although desirable in all plantings, is probably somewhat less critical in conventional spring plantings than at other times. If, however, a planting program cannot be completed in this way, there are other options: conventional fall planting with fresh-lifted stock; summer planting with fresh-lifted stock; and spring and summer planting with stored spring-lifted or fall-lifted stock.
Conventional spring planting with fresh spring-lifted stock In the context of regeneration silviculture, "spring", "summer", etc. lack precise meaning. Typically, the spring planting season begins as soon as lifting becomes possible in the nursery, and ends with the completion of the program. At this time, planting stock is physiologically attuned to the oncoming growing season, and the outplant has the whole of that season in which to establish its root system before it is challenged by any frost heaving. In practice, ideals are seldom attained. That stock is normally dormant when spring-planted is a widespread fallacy. Active growth is commonly obvious at the time of planting, but in any case the metabolic activity increases in planting stock before the tops give visible expression to this. The difficulty of obtaining, in quantity, spring-lifted stock in dormant condition increases with increasing continentality of climate. In many areas, the period of springlike weather is unreliable and often short. As well, the soil moisture advantage claimed for spring planting is also insecurely founded. Soils that are sandy or gravelly, and shallow soils of any texture are highly dependent on current weather due to their limited available water capacities. Nor will a plentiful supply of soil moisture benefit an outplant whose roots are enveloped in anaerobic and/or cold soil, and mortality of trees outplanted into soil colder than about 6 °C may be excessive.Sutton, R.F. 1968. Ecology of young white spruce (Picea glauca [Moench] Voss). Ph.D. thesis, Cornell Univ., Ithaca NY, Univ. Microfilms, Ann Arbor, Michigan MI, 68–11645. 500 p.Sutton, R.F. 1969. Form and development of conifer root systems. Commonw. For. Bureau, Oxford, U.K., Tech. Communication No. 7. 131 p.
The spruces may be planted not only throughout the spring planting period provided that the period of most active shoot elongation is avoided, but virtually throughout the whole growing season, with little loss of performance other than some reduction in increment.Mullin, R.E. 1971. "Some effects of root dipping, root exposure and extended planting dates with white spruce." For. Chron. 47(2):90–93.
Conventional fall planting with fresh-lifted stock The fall planting season is generally considered to begin when nursery stock has hardened off and soil moisture reserves have been replenished by autumnal rain. It then continues until the planting program has been completed or is terminated by freeze-up or heavy snow. The advantages of fall planting were once considered "To outweigh those of spring so certainly" that in the National Forests of the Lake States almost all planting was done in the fall, but in spite of some success, operational fall plantings in North America have tended to be less successful than operational spring plantings.LeBarron, R.K.; Fox, G.; Blythe, R.H. 1938. The effect of season of planting and other factors on early survival of forest plantations. J. For. 36:1211–1215. On certain sites, a major disadvantage of fall planting is that the root systems of outplants have little time in which to become firmly anchored before being subjected to frost heaving. Such plants are also vulnerable to "winter browning", which may occur in the fall soon after planting, especially among stock having high shoot:root ratios.Rudolf, P.O. 1950. Cold soaking – a short-cut substitute for stratification? J. For. 48(1):31–32. Relationships between dormancy progression and physiological condition, including root-growth capacity, are much less clear in the spruces than in the pines, but certainly there is good evidenceBaldwin, H.I. 1938. Planting experiments in the northeast. J. For. 36:758–760.Mullin, R.E. 1968. Comparisons between seedlings and transplants in fall and spring plantings. Ont. Dep. Lands For., Res. Div., Toronto ON, Res. Rep. 85. 40 p.Sinclair, C.; Boyd, R.J. 1973. Survival comparisons of three fall and spring plantings of four coniferous species in northern Idaho. USDA, For. Serv., Intermount. For. Range Exp. Sta., Ogden UT, Res. Pap. INT-139. 20 p.McClain, K.M. 1975. Continuous planting of seedling black spruce. p. 177–194 in Black Spruce Symp. Proc., Can. Dep. Environ., Can. For. Serv., Sault Ste. Marie ON, Symp. Proc. O-P-4.McClain, K.M. 1979. A review on the possibility of extending the planting season. Ont. Min. Nat. Resour., Northern For. Res. Unit, Thunder Bay ON. 44 p. that, in the absence of frost heaving, plantings of spruces can be just as successful in fall as in spring.
Summer planting with fresh-lifted stock Conceptually and logistically, the simplest way of extending the conventional planting season is to extend lifting and planting of fresh stock through summer until the planting program has been competed. Summer planting has also been successful in a number of research studies with white spruce, e.g., Crossley 1956;Crossley, D.I. 1956. The possibility of continuous planting of white spruce throughout the frost-free period. Can. Dep. Northern Affairs National Resour., For. Branch, For. Res. Div., Ottawa ON, Tech. Note 32. 31 p. Ackerman and Johnson 1962;Ackerman, R.F.; Johnson, H.L. 1962. Continuous planting of white spruce throughout the frost-free period. Can. Dep. For., For. Res. Branch, Ottawa ON, Tech. Note 117. 13 p. Decie 1962 cited by Revel and Coates 1976;Revel, J.; Coates, H. 1976. Planting white spruce throughout the growing season on high site areas in the Sub-Boreal Forest Region of B.C. B.C. For. Serv., Res. Div., Victoria BC, Rep. E.P.668. 37 p. Burgar and Lyon 1968;Burgar, R.J.; Lyon, N.F. 1968. Survival and growth of stored and unstored white spruce planted through the frost-free period. Ont. Dep. Lands Forests, Toronto ON, Res. Rep. 84. 37 p. Mullin 1971, 1974;Mullin, R.E. 1974. Some planting effects still significant after 20 years. For. Chron. 50:191–193. Revel and Coates 1976. Success depends on minimizing stresses to planting stock at all stages from lifting through planting and on planting when site conditions are conducive to survival and growth.
Spring and summer planting with stored stock Refrigerated storage of planting stock has been developed largely with the aim of overcoming problems experienced in using flushed planting stock. Storage provides a means of holding stock for use when fresh stock is either unavailable or at a stage of development that renders it unsuitable for planting. It also offers possibilities of manipulating the physiological condition of the stock. However, there are problems associated with storage, e.g., mold, cold injury, desiccation, and depletion of food reserves. The rate of deterioration depends very much on the physiological condition of the planting stock at the time of lifting, as well as on the storage environment and duration of storage.Mullin, R.E. 1978. "Tests of frozen spring storage for white spruce and red pine planting stock." USDA, For. Serv., Tree Plant. Notes 29(4):26–29.