Vegetation (weeds) control

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At the planting site, weeds are those herbaceous and woody species that compete with planted seedlings for energy, water, and nutrients (Ivetić and Devetaković 2016[1]). However, not all existing vegetation at planting sites should be considered weeds (Facilitation by Nurse Plants), and not all of them should be controlled. At planting site, herbaceous vegetation control has more effect than woody vegetation control (Rose et al. 1999[2]). Effect of existing vegetation on planting site can be twofold. Betula papyrifera Marshall reduces growth of shade-intolerant conifers but facilitates growth of shade-tolerant conifers (Simard and Vyse 2006[3]).

Due to high costs and environmental issues (especially with herbicide use), decisions about vegetation control application should be based on a cost-benefit analysis. For example, growth and yield simulations using treatment-specific site index curves suggested that site preparation or post-planting vegetation control could reduce rotation length of Picea glauca by 12–16 years, but untreated areas were predicted to produce an equivalent volume if left to grow to mean annual increment culmination age (Boateng et al. 2009[4]). Knowledge of the maximum (a level of vegetation cover where additional control will not increase tree performance) and minimum (a level of vegetation cover that must be reached before additional control will increase tree performance) response thresholds can be used to improve herbicide prescriptions (Wagner et al. 1989[5]). A minimum response threshold level of 20% cover has been suggested (Wagner 2005[6]). The response thresholds are species and site specific. Pinus contorta Dougl. var. latifolia Engelm. height and diameter growth and Picea glauca × Picea sitchensis diameter growth increased dramatically when cover of Rubus parviflorus Nutt. was below 5%, suggesting a response threshold (LePage and Coates 1994[7]). Mortality of Betula pendula Roth and Pinus sylvestris seedlings increased significantly once the cover of competing vegetation reached 60% (Hytönen and Jylhä 2005[8]; Jylhä and Hytönen 2006[9]). Such thresholds should be considered during the decision making process on application of any method of vegetation control.

Another issue to consider is how many years after planting vegetation control is beneficial to seedlings performance. Intensive vegetation control in first couple of years after planting is critical for seedling field performance. The critical period in the establishing phase differs with species: 1-2 years after planting for shade-intolerant Pinus banksiana Lamb. and Pinus resinosa Sol. Ex Aiton, 1-4 years for more shade-tolerant Picea mariana (Mill.) B.S.P. and Pinus strobus L. (Wagner et al. 1999[10]). Rose and Ketchum[11] (2003) found no observable effect of vegetation control in third year after planting on Pseudotsuga menziesii growth. Additional time aspect to consider is duration of vegetation control effect. Positive effect of weed control with herbicides last up to 11 (Hytönen and Jylhä 2005[8]) and 30 (Wagner 2005[6]) years after planting.

Vegetation control generally has a positive effect on seedling performance but efficiency depends on method and size of the control area. Competitive vegetation can be controlled physically by mulching, mechanically by cultivation, and chemically by herbicides (Tab. 1).

Table 1. Reported positive effects of vegetation control to seedlings survival and growth (Ivetić and Devetaković 2016[1]).

Type Method Positive effect on

survival (S) and growth (G)

Physical Mulching S Navaro Cerrillo et al. 2005[12]; Hytönen and Jylhä 2005[8]; Ceacero et al. 2014[13]
Mechanical (M) Cultivation S Navaro Cerrillo et al. 2005[12]; Ceacero et al. 2014[13]
Removal G Klossas et al. 2012[14]
Chemical     (C) Herbicide S Navaro Cerrillo et al. 2005[12]; Ceacero et al. 2014[13]
G Balneaves et al. 1996[15]; Rosner and Rose 2006[16]; Klossas et al. 2012[14]
S+G Hytönen and Jylhä 2005[8]; Hytönen and Jylhä 2008[17]
M + C G Sutton 1995[18]

Chemical vegetation control significantly improved seedling growth compared to the manual cutting (LePage and Coates 1994[7]), tillage (Groninger et al. 2004[19]), mulch and cover crop (Jylhä and Hytönen 2006[9]). Combination of weed control methods can result in synergic effect. Rey Benayas et al.[20] (2005) found a clear positive synergic effect of shading and weed mowing on seedling performance of three Quercus species (Q. coccifera L., Q. ilex, and Q. faginea Lam.).

Increasing in area of vegetation control has positive effect on seedling growth. Mean stem volume, basal diameter, and height of seedlings increased significantly with increasing area of vegetation control, and the magnitude of difference between treatments increased with time (Rose and Ketchum 2002[21]).

The vegetation control efficiency depends on seedling stocktype as well: promoting survival of small and growth of large seedlings. Although the highest stand volumes of 15-years old Picea abies were obtained with the combination of large bareroot seedlings (4-year-old) and effective vegetation control, 2-year-old container seedlings because of their smaller size benefited more from vegetation control in terms of survival (Hytönen and Jylhä 2008[17]). The volume return from increased weed control is maximized by planting the largest possible seedlings (Rosner and Rose 2006[16]). On sites released from competitive vegetation larger seedlings grow quickly and occupy site resources during establishment due to greater level of incoming radiation and their greater photosynthetic capability (Grossnickle 2005[22]).

Chemical control of herbaceous competition in the first couple of years after planting promotes small seedlings survival and large seedlings growth. Decision on type, method, area, and number of applications should be made on species specific response thresholds and site specific conditions (e.g. vegetation cover, environmental restrictions, and erosion control).


  1. 1.0 1.1 Ivetić V, Devetaković J (2016) Reforestation challenges in Southeast Europe facing climate change. Reforesta 1: 178-220. DOI:
  2. Rose R, Ketchum JS, Hanson DE (1999) Three-year survival and growth of Douglas-fir seedlings under various vegetation-free regimes. For Sci 45: 117-126.
  3. Simard S, Vyse A (2006) Trade-offs between competition and facilitation: A case study of vegetation management in the interior Cedar–Hemlock forests of Southern British Columbia. Can J Forest Res 36 (10): 2486-2496. doi:10.1139/x06-150.
  4. Boateng OJ, Heineman LJ, Bedford L, Harper JG, Linnell Nemec FA (2009) Long-term effects of site preparation and postplanting vegetation control on Picea glauca survival, growth and predicted yield in boreal British Columbia. Scand J Forest Res 24:111-129. doi:10.1080/02827580902759685.
  5. Wagner GR, Petersen DT, Ross WD, Radosevich RS (1989) Competition thresholds for the survival and growth of Ponderosa pine seedlings associated with woody and herbaceous vegetation. New Forest 3: 151-170. doi:10.1007/BF00021579.
  6. 6.0 6.1 Wagner GR (2005) Top 10 principles for managing competing vegetation to maximize regeneration success and long-term yields. In Colombo SJ (ed) The Thin Green Line: A Symposium on the State-of-the-Art in Reforestation, Ontario Ministry of Natural Resources, Forest Research Information Paper 160. pp 32-36.
  7. 7.0 7.1 LePage P, Dave CK (1994) Growth of planted lodgepole pine and hybrid spruce following chemical and manual vegetation control on a frost-prone site. Can J Forest Res 24: 208-216. doi:10.1139/x94-031.
  8. 8.0 8.1 8.2 8.3 Hytönen J, Jylhä P (2005) Effects of competing vegetation and post-planting weed control on the mortality, growth and vole damages to Betula pendula planted on former agricultural land. Silva Fenn 39: 365-380.
  9. 9.0 9.1 Jylhä P, Hytönen J (2006) Effect of vegetation control on the survival and growth of Scots pine and Norway spruce planted on former agricultural land. Can J Forest Res 36: 2400–2411. doi:10.1139/x06-053.
  10. Wagner GR, Mohammed HG, Noland LT (1999) Critical period of interspecific competition for northern conifers associated with herbaceous vegetation. Can J Forest Res 29: 890-897.
  11. Rose R, Ketchum JS (2003) Interaction of initial seedling diameter, fertilization and weed control on Douglas-fir growth over the first four years after planting. Ann Forest Sci 60: 625-35. doi:10.1051/forest:2003055.
  12. 12.0 12.1 12.2 Navarro Cerrillo RM, Fragueiro B, Ceaceros C, Del Campo A, De Prado R (2005) Establishment of Quercus ilex L. subsp. ballota [Desf.] Samp. using different weed control strategies in Southern Spain. Ecol Eng 25: 332-342. doi:10.1016/j.ecoleng.2005.06.002.
  13. 13.0 13.1 13.2 Ceacero CJ, Navarro-Cerrillo RM, Díaz-Hernández JL, Del Campo AD (2014) Is tree shelter protection an effective complement to weed competition management in improving the morphophysiological response of holm oak planted seedlings? iForest 7: 289-299.
  14. 14.0 14.1 Klossas G, Kyriazopoulos A, Koukoura Z (2012) Post-planting treatments and shading effects in a Fraxinus angustifolia Vahl. silvopastoral system. Ann For Res 56: 179-186.
  15. Balneaves J, Menzies M, Hong S (1996) Establishment practices can improve longer – term growth of Pinus radiata on a dry-land hill forest. New Zealand Journal of Forestry Science 26: 370-379.
  16. 16.0 16.1 Rosner LS, Rose R (2006) Synergistic stem volume response to combinations of vegetation control and seedling size in conifer plantations in Oregon. Can J Forest Res 35: 930-944.
  17. 17.0 17.1 Hytönen J, Jylhä P (2008) Fifteen-year response of weed control intensity and seedling type on Norway spruce survival and growth on arable land. Silva Fenn 42: 355-368.
  18. Sutton RF (1995) White spruce establishment: initial fertilization, weed control, and irrigation evaluated after three decades. New Forests 9: 123-133.
  19. Groninger WJ, Baer GS, Babassana DA, Allen HD (2004) Planted green ash (Fraxinus pennsylvanica Marsh.) and herbaceous vegetation responses to initial competition control during the first 3 years of afforestation. Forest Ecol Manag 189: 161-170. doi:10.1016/j.foreco.2003.07.039.
  20. Rey Benayas MJ, Navarro J, Espigares T, Nicolau MJ, Zavala AM (2005) Effects of artificial shading and weed mowing in reforestation of Mediterranean abandoned cropland with contrasting Quercus species. Forest Ecol Manage 212: 302-314. doi:10.1016/j.foreco.2005.03.032.
  21. Rose R, Ketchum JS (2002) Interaction of vegetation control and fertilization on conifer species across the Pacific Northwest. Can J Forest Res 32: 136-52. doi:10.1139/x01-180.
  22. Grossnickle SC (2005) Seedling size and reforestation success. How big is big enough? In: Colombo SJ (Compiler), The thin green line: a symposium on the state-of-the-art in reforestation, Forest Research Information Paper 160, Ontario Forest Research Institute, Ontario Ministry of Natural Resources, Sault Ste. Marie, Ontario, Canada. pp 138–144.