Estimation and Uncertainty of the Mixing Effects on Scots Pine—European Beech Productivity from National Forest Inventories Data

Abstract

An increasing amount of research is focusing on comparing productivity in monospecific versus mixed stands, although it is difficult to reach a general consensus as mixing effects differ both in sign (over-yielding or under-yielding) and magnitude depending on species composition as well as on site and stand conditions. While long-term experimental plots provide the best option for disentangling the mixing effects, these datasets are not available for all the existing mixtures nor do they cover large gradients of site factors. The objective of this study was to evaluate the effects and uncertainties of tree species mixing on the productivity of Scots pine–European beech stands along the gradient of site conditions in Europe, using models developed from National and Regional Forest Inventory data. We found a positive effect of pine on beech basal area growth, which was slightly greater for the more humid sites. In contrast, beech negatively affected pine basal area growth, although the effects switched to positive in the more humid sites. However, the uncertainty analysis revealed that the effect on pine at mid- and more humid sites was not-significant. Our results agree with studies developed from a European transect of temporal triplets in the same pine–beech mixtures, confirming the suitability of these datasets and methodology for evaluating mixing effects at large scale.

Productivity Estimations for Monospecific and Mixed Pine Forests along the Iberian Peninsula Aridity Gradient

“…Hence, density is key in the assessment of both stand growth and species competition. Regarding the influence of species composition, numerous studies report a positive effect of species mixing on productivity or overyielding [23,24], although this effect depends on species composition and might vary with environmental conditions [25][26][27][28].…”

Simulating Araucaria angustifolia (Bertol.) Kuntze Timber Stocks With Liocourt’s Law in a Natural Forest in Southern Brazil

“…where: PAIM% vtci = mean annual percentage of volume increments up to the crown, with bark; Vt i = total volume increments up to the crown in the d i class in m 3 •ha −1 , with bark; PAI% vtcii = annual percentage of volume increments up to the crown in the d i class.…”

“…where: Vt = total volume at the end of the period in m 3 •ha −1 , with bark; Vr = remaining volume at the beginning of the period in m 3 •ha −1 , with bark; i = annual growth rate; cc = cutting cycle in years.…”

“…Considering the data shown in Table 2 for the diametric class of 27.5 cm, four trees per hectare can be harvested, with an estimated production of 1.6 m 3 •ha −1 . In this scenario, the trees had a total increment up to the crown of 15.3 m and 11.1 m. Therefore, 0.0% of the timber stocks' volume may be classified in assortments S1 and S2, 72.1% (corresponding to three units) in S3, and 27.9% or 0.4406 m 3 •cc in S4, referring to timber destined for the energy or wood industry. According to the same data, for a class center of 52.5 cm, the trees' height would be 19.1 m, with 51.1% (corresponding to one unit) of the timber stocks' volume being classified in assortment S1, 46.8% (corresponding to three units) in S2, 0% in S3, and 2.1% or 0.0437 m 3 •cc in S4.…”

“…Mixed-species stands provide greater ecological and socio-economical services since they can be more resistant to natural disturbances [1,2], more stable with regard to climate change or disease control [3], and more productive than homogeneous stands [4,5]. Despite this, quantitative silvicultural guidelines facilitating the efficient management of mixed-species stands are still largely based on research information pertaining to pure even-aged stands [6].…”