Production ecology of plantations and forests

The production ecology equation provides an excellent framework to quantify the processes that influence forest growth.

The production ecology equation: Tree and stand growth is related to the availability of light, water and nutrients, the acquisition of those resources and the efficiency with which they are used to fix carbon or to produce biomass or wood. The relationship between these variables can be described using the production ecology equation (3, Monteith, 1977; Binkley et al., 2004):

Gross primary productivity

= resource supply x proportion of resource captured x efficiency of resource use

The growth of mixed species stands is often described using concepts such as facilitation, competitive reduction and complementarity. These can be difficult to quantify and separate because they usually occur simultaneously. The production ecology helps to show the contribution of different processes to differences in growth rates. We have often used this framework to study mixed-species forests.

Measuring the water use of a Eucalyptus globulus tree using the compensation heat pulse technique.

Studies where we have studied the production ecology of forests, and the main findings:

*Mixtures of Eucalyptus globulus and the nitrogen-fixing species Acacia mearnsii where mixtures were significantly more productive than monocultures. The acacia fixed about 40 kg of nitrogen per year in mixtures (this page, or this paper) and rates of nutrient cycling were also greater in mixtures than in eucalypt monocultures (this page, or this paper). By applying the production ecology equation we found that the mixtures also intercepted more light, and used that light more efficiently to produce wood than monocultures (5). The mixtures also used more water and used it more efficiently to produce wood (2). Based on this particular experiment it would be possible to use mixtures to produce the same amount of wood, but on only about half the land area and with about 2/3 of the water that a eucalypt monoculture would use.

*A literature review of all studies that have compared the growth and water use of mixed-species stands to monocultures (11). It was found that if the growth of a given species increases in mixture, then it will also use more water and/or be more water-use efficient; when growth increases there will not be a reduction in transpiration or water-use efficiency. When growth does not change for a given species in mixture, there is generally no change in its water use or water-use efficiency. In this review, data from the Eucalyptus globulus and Acacia mearnsii mixtures were also analysed at the tree and neighbourhood levels to show that within a stand, trees of a given species can show contrasting growth and transpiration responses depending on their size (diameter) and the density of their neighbourhood. That is, the stand-level patterns are the average of several different tree-level responses that are not evident at the stand level.

*The production ecology approach was also used to examine how differences in crown architecture and canopy structure influence the light absorption and light-use efficiency in mixed Picea abies and Abies alba forests (10). The main aim was to examine how these factors change along a productivity gradient. These species both grew faster in mixtures than monocultures on productive sites but not on poor sites (this page or this paper). This increase in complementarity as site productivity increased may result when the interactions between the trees improve light absorption or light-use efficiency. That is, as water and nutrient availability increase, stand leaf area may also increase resulting in intense competition for light, so any interactions that improve light absorption or light-use efficiency will become increasingly useful. Using the Maestra model to predict individual tree light absorption, we found that for a given tree size, light absorption and light-use efficiency were greater for trees in mixed-species neighbourhoods than monospecific neighbourhoods (10). This complementary effect increased as climatic conditions improved. This also resulted from inter- and intra-specific differences in tree allometry and changes in stand structure. Similar studies were done in Pinus sylvestris and Fagus sylvatica forests (12), and several different species mixtures in a biodiversity experiment (13).

*We also applied the production ecology equation to silvicultural treatments such as thinning, pruning and fertiliser application to understand how these treatments interacted and how silvicultural regimes might be refined in eucalypt plantations (4,7,8). This was also summarized in a review (8). Pruning reduced growth, light interception and transpiration, but the growth reduction was small and disappeared 3 years after pruning because the reduction in light and water use was counted by an increase in light- and water-use efficiency. Thinning had the greatest effect on growth, which increased by about 50%. Light and water use, and light- and water-use efficiencies of the crop trees also all increased following thinning. For all treatments the physiological responses in terms of photosynthesis and resource-use efficiencies were shorter lived than the structural changes, such as larger crowns and tree allometry. This showed that as the stands developed the relative contribution of physiological differences to growth responses declined relative to structural changes (e.g. crown sizes). Changing stand structure can significantly influence the growth of individual trees within these plantations, and if the management aim is to maximise the size of crop trees, this is best done by thinning early and intensively to ensure the retained trees develop large crowns.

*In any evenaged monospecific forest growth and leaf area start low, then increase before peaking relatively early and declining for the rest of the rotation (Ryan et al., 1997). Since faster growing trees of a given species generally use more resources and/or are more resource-use efficient, we examined whether this pattern also occurred as two stands developed by measuring light absorption and transpiration. In the first stand, growth, transpiration and water-use efficiency all increased early before peaking at about age five years and then declining (1). In the second stand, growth and light-use efficiency increased until peaking at about 4-5 years, although light absorption continued to increase until age 7 years (7).

Journal articles related to this project:

1. Forrester, D.I., Collopy, J.J., Morris, J.D., (2010). Transpiration along an age series of Eucalyptus globulus plantations in southeastern Australia. Forest Ecology and Management 259, 1754-1760. doi:10.1016/j.foreco.2009.04.023

2. Forrester, D.I., Theiveyanathan, S., Collopy, J.J., Marcar, N.E., (2010). Enhanced water use efficiency in a mixed Eucalyptus globulus and Acacia mearnsii plantation. Forest Ecology and Management 259, 1761-1770. doi:10.1016/j.foreco.2009.07.036

3. Richards, A.E., Forrester, D.I., Bauhus, J., Scherer-Lorenzen, M. (2010). The influence of mixed tree plantations on the nutrition of individual species: a review. Tree Physiology 30, 1192-1208. doi:10.1093/treephys/tpq035

4. Forrester, D.I., Collopy, J.J., Beadle, C.L., Warren, C.R., Baker, T.G. (2012). Effect of thinning, pruning and nitrogen fertiliser application on transpiration, photosynthesis and water-use efficiency in a young Eucalyptus nitens plantation. Forest Ecology and Management. 266, 286-300. doi:10.1016/j.foreco.2011.11.019

5. Forrester, D. I., Lancaster, K., Collopy, J. J., Warren, C. R., Tausz, M. (2012). Photosynthetic capacity of Eucalyptus globulus is higher when grown in mixture with Acacia mearnsii. Trees-Structure and Function 26, 1203-1213. doi:10.1007/s00468-012-0696-5

6. Binkley, D., Campoe, O. C., Gspaltl, M., Forrester, D.I. (2013). Light absorption and use efficiency in forests: Why patterns differ for trees and forests. Forest Ecology and Management. 288, 5-13. doi:10.1016/j.foreco.2011.11.002

7. Forrester, D.I., Collopy, J.J., Beadle, C.L., Baker, T.G. (2013). Effect of thinning, pruning and nitrogen fertiliser application on light interception and light-use efficiency in a young Eucalyptus nitens plantation. Forest Ecology and Management. 288, 21-30. doi:10.1016/j.foreco.2011.11.024

8. Forrester, D.I. (2013). Growth responses to thinning, pruning and fertiliser application in Eucalyptus plantations: A review of their production ecology and interactions. Forest Ecology and Management 310, 336-347. doi:10.1016/j.foreco.2013.08.047

9. Forrester, D.I. (2014). The spatial and temporal dynamics of species interactions in mixed-species forests: From pattern to process. Forest Ecology and Management 312, 282-292. doi:10.1016/j.foreco.2013.10.003

10. Forrester, D.I., Albrecht, A.T. (2014). Light absorption and light-use efficiency in mixtures of Abies alba and Picea abies along a productivity gradient. Forest Ecology and Management. 328, 94-102. doi:10.1016/j.foreco.2014.05.026

11. Forrester, D.I. (2015). Transpiration and water-use efficiency in mixed-species forests versus monocultures: effects of tree size, stand density and season. Tree Physiology 35, 289-304. doi:10.1093/treephys/tpv011

12. Forrester, D.I., Ammer, C., Annighöfer, P.J., Barbeito, I., Bielak, K., Bravo-Oviedo, A., Coll, L., Río, M.d., Drössler, L., Heym, M., Hurt, V., Löf, M., Ouden, J.d., Pach, M., Pereira, M.G., Plaga, B., Ponette, Q., Skrzyszewski, J., Sterba, H., Svoboda, M., Zlatanov, T., Pretzsch, H. (2018). Effects of crown architecture and stand structure on light absorption in mixed and monospecific Fagus sylvatica and Pinus sylvestris forests along a productivity and climate gradient through Europe. Journal of Ecology. 106, 746-760. doi:10.1111/1365-2745.12803

13. Forrester, D.I., Rodenfels, P., Haase, J., Härdtle, W., Leppert, K.N., Niklaus, P.A., Oheimb, G.v., Scherer-Lorenzen, M., Bauhus, J., (2019). Tree species interactions increase light absorption and growth in Chinese subtropical mixed-species plantations. Oecologia, 191, 421-432. doi:10.1007/s00442-019-04495-w

14. Forrester, D.I., (2019). Linking forest growth with stand structure: Tree size inequality, tree growth or resource partitioning and the asymmetry of competition. Forest Ecology and Management 447, 139-157. doi:10.1016/j.foreco.2019.05.053

15. Bottero, A., Forrester, D.I., Cailleret, M., Kohnle, U., Gessler, A., Michel, D., Bose, A.K., Bauhus, J., Bugmann, H., Cuntz, M., Gillerot, L., Hanewinkel, M., Lévesque, M., Ryder, J., Sainte-Marie, J., Schwarz, J., Yousefpour, R., Zamora-Pereira, J.C., Rigling, A., (2021). Growth resistance and resilience of mixed silver fir and Norway spruce forests in central Europe: Contrasting responses to mild and severe droughts. Global Change Biology 27, 4403-4419 doi:10.1111/gcb.15737

16. Forrester, D.I., Schmid, H., Nitzsche, J., (in press). Growth and structural changes in Swiss uneven-aged forests over 100 years, and comparisons between 15 uneven-aged forest types of Europe, North America and Australia. Forestry. doi:10.1093/forestry/cpab042