Tree allometric relationships for structurally and species diverse forests, and that account for differences in climate

Allometric relationships are often required in forestry and ecology. For example, they are generally required when examining how stand structural variables (density, species composition ...) influence forest growth and functioning. They are also included in most forest growth models. However, despite the fact that allometric relationships are often influenced by stand structural variables, climate, edaphic conditions and age (1-10, & 12), this is often ignored and many of the published allometric relationships have been developed using data from monocultures or they are general relationships developed after combining data from different treatments, which thereby averages out the treatment effects. The use of such equations when quantifying mixing effects, or the effects of other stand structural attributes, might lead to biased predictions and conclusions (5).

In this project we examined how commonly used relationships between stem diameter and height, crown dimensions, leaf area or biomass (e.g. foliage, stem or root) were modified by their vertical position within the canopy (dominance), stand density, age, species composition and climate. Several European-wide data sets were used (9,10). One of the datasets used was developed from a meta-analysis of nearly 1000 published biomass equations for major European tree species (10). This dataset was provided as supplementary information so that it can be used to develop equations specific to the needs of individual studies. We found that:

*All stand structural or climatic variables significantly influenced the relationships, but their effects differed widely between the target species (9,10). The inter-specific variability was often correlated with species traits (wood density, shade tolerance, specific leaf area).

*Single “generalized” equations could be developed for each given species, which could be applied in any stand structure and species combination (9,10). This approach may improve predictions of biomass and carbon stocks in structurally and compositionally diverse forests.

As a second component of this work, we focused on developing generalized equations for many different species in Australia (6), several Chinese species (7) or world-wide (8). These studies included comparisons of predictions from species-specific equations and regional equations.

We also examined how stand-level allometry, in terms of self-thinning relationships, are influenced by species composition, the vertical structure of the forest (whether a species is in a dominant or suppressed position), site quality, and climatic conditions (13).

Lastly, the relationship between tree size and tree biomass growth were examined using a long-term Swiss dataset to find whether tree growth increases continuously with tree size. In particular, this study showed the importance of considering whether the individual tree growth refers to that of a single individual tree examined through time, or whether it refers to many trees examined at a single point in time; the size-growth relationships vary depending on which of these relationships is considered (15).

Journal articles related to this project:

1. Forrester, D.I., Collopy, J.J., Beadle, C.L., Baker, T.G. (2012). Interactive effects of simultaneously applied thinning, pruning and fertiliser application treatments on growth, biomass production and crown architecture in a young Eucalyptus nitens plantation. Forest Ecology and Management. 267, 104-116. doi:10.1016/j.foreco.2011.11.039

2. 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

3. Togashi, H.R., Prentice, I.C., Evans, B.J., Forrester, D.I., Drake, P., Feikema, P., Brooksbank, K., Eamus, D., Taylor, D. (2015). Morphological and moisture availability controls of the leaf area-to-sapwood area ratio: analysis of measurements on Australian trees. Ecology and Evolution 5, 1263-1270. doi:10.1002/ece3.1344

4. Guisasola, R., Tang, X., Bauhus, J., Forrester, D.I. (2015). Intra- and inter-specific differences in crown architecture in Chinese subtropical mixed-species forests. Forest Ecology and Management 353, 164-172. doi:10.1016/j.foreco.2015.05.029

5. Forrester, D.I., Pretzsch, H., 2015. Tamm Review: On the strength of evidence when comparing ecosystem functions of mixtures with monocultures. Forest Ecology and Management 356, 41-53. doi:10.1016/j.foreco.2015.08.016

6. Paul, K.I., Roxburgh, S.H., Chave, J., England, J.R., Zerihun, A., Specht, A., Lewis, T., Bennett, L.T., Baker, T.G., Adams, M.A., Huxtable, D., Montagu, K.D., Falster, D.S., Feller, M., Sochacki, S., Ritson, P., Bastin, G., Bartle, J., Wildy, D., Hobbs, T., Larmour, J., Waterworth, R., Stewart, H.T.L., Jonson, J., Forrester, D.I., Applegate, G., Mendham, D., Bradford, M., O'Grady, A., Green, D., Sudmeyer, R., Rance, S.J., Turner, J., Barton, C., Wenk, E.H., Grove, T., Attiwill, P.M., Pinkard, E., Butler, D., Brooksbank, K., Spencer, B., Snowdon, P., O'Brien, N., Battaglia, M., Cameron, D.M., Hamilton, S., McAuthur, G., Sinclair, J. (2016). Testing the generality of above-ground biomass allometry across plant functional types at the continent scale. Global Change Biology, 22, 2106-2124. doi:10.1111/gcb.13201

7. Xiang, W., Zhou, J., Ouyang, S., Zhang, S., Lei, P., Li, J., Deng, X., Fang, X., Forrester, D.I., (2016). Species-specific and general allometric equations for estimating tree biomass components of subtropical forests in southern China. European Journal of Forest Research, 135, 963-979, doi:10.1007/s10342-016-0987-2

8. Jucker, T., Caspersen, J., Chave, J., Antin, C., Barbier, N., Bongers, F., Dalponte, M., Ewijk, K.Y.v., Forrester, D.I., Haeni, M., Higgins, S.I., Holdaway, R.J., Iida, Y., Lorimer, C., Marshall, P.L., Momo, S., Moncrieff, G.R., Ploton, P., Poorter, L., Rahman, K.A., Schlund, M., Sonké, B., Sterck, F.J., Trugman, A.T., Usoltsev, V.A., Vanderwel, M.C., Waldner, P., Wedeux, B.M.M., Wirth, C., Wöll, H., Woods, M., Xiang, W., Zimmermann, N.E., Coomes, D.A. (2017). Allometric equations for integrating remote sensing imagery into forest monitoring programs. Global Change Biology 23, 177-190. doi:10.1111/gcb.13388

9. Forrester, D.I., Benneter, A., Bouriaud, O., Bauhus, J. (2017). Diversity and competition influence tree allometry - developing allometric functions for mixed-species forests. Journal of Ecology, 105, 761-774. doi:10.1111/1365-2745.12704

10. Forrester, D.I., Tachauer, I.H.H., Annighoefer, P., Barbeito, I., Pretzsch, H., Ruiz-Peinado, R., Stark, H., Vacchiano, G., Zlatanov, T., Chakraborty, T., Saha, S., Sileshi, G.W. (2017). Generalized biomass and leaf area allometric equations for European tree species incorporating stand structure, tree age and climate. Forest Ecology and Management. 396, 160-175. doi:10.1016/j.foreco.2017.04.011

11. Forrester, D.I., (2021). Does individual-tree biomass growth increase continuously with tree size? Forest Ecology and Management 481, 118717. doi: 10.1016/j.foreco.2020.118717

12. Forrester, D.I., Dumbrell, I.C., Elms, S.R., Paul, K.I., Pinkard, E.A., Roxburgh, S.H., Baker, T.G., (2021). Can crown variables increase the generality of individual tree biomass regressions? Trees Structure and Function, 35, 15:26. doi: 10.1007/s00468-020-02006-6

13. Forrester, D.I., Baker, T.G., Elms, S.R., Hobi, M.L., Ouyang, S., Wiedemann, J.C., Xiang, W., Zell, J., Pulkkinen, M., (2021). Self-thinning tree mortality models that account for vertical stand structure, species mixing and climate. Forest Ecology and Management 487, 118936. doi: 10.1016/j.foreco.2021.118936

14. Xiang, W., Li, L., Ouyang, S., Xiao, W., Zeng, L., Chen, L., Lei, P., Deng, X., Zeng, Y., Fang, J., Forrester, D.I., (2021). Effects of stand age on tree biomass partitioning and allometric equations in Chinese fir (Cunninghamia lanceolata) plantations. European Journal of Forest Research 140, 317-332 doi:10.1007/s10342-020-01333-0

15. Forrester, D.I., (2021). Does individual-tree biomass growth increase continuously with tree size? Forest Ecology and Management 481, 118717. doi:10.1016/j.foreco.2020.118717