Development of stand structural heterogeneity and growth dominance in thinned Eucalyptus stands in Brazil

Abstract

Higher tree size heterogeneity in forests has been linked to lower productivity, especially in monocultures. Thinning the stand can directly manipulate tree size variability, thereby changing growth partitioning across tree dominance classes and consequently changing the development of stand structural heterogeneity compared to its course in unthinned stands. We used three thinning-intensity experiments to assess how stand heterogeneity and growth dominance develop through time and across different thinning intensities in Eucalyptus stands in one of the most productive regions of Brazil. The experiments were established along a three-site gradient in productivity. The plots were thinned from below at ages 58 and 146months. The thinning intensities included the removal of 20%, 35% and 50% of basal area and an additional treatment of 35% removal plus pruning concomitantly to thinning. Thinning reduced stand heterogeneity and growth dominance as well as their development through time and this reduction was greater the more intense the thinnings were. Stand structural heterogeneity and growth dominance both increased before and after the first thinning, but the rates of increase after the first thinning were lower than they were before the first thinning. After the second thinning, heterogeneity tended to remain constant, whereas growth dominance tended to decrease, reaching negative values. This was contrary to our expectations of observing the same trends in both variables. Our results show that thinning from below not only reduces heterogeneity and growth dominance by removing the smaller trees, but can also slow the development of stand heterogeneity and growth dominance in Eucalyptus stands and potentially other monocultures.