Species proportions by area in mixtures of Scots pine (Pinus sylvestris L.) and European beech (Fagus sylvatica L.)

Abstract

Scots pine (Pinus sylvestris L.) and European beech (Fagus sylvatica L.) dominate many of the European forest stands. Also, mixtures of European beech and Scots pine more or less occur over all European countries, but have been scarcely investigated. The area occupied by each species is of high relevance, especially for growth evaluation and comparison of different species in mixed and monospecific stands. Thus, we studied different methods to describe species proportions and their definition as proportion by area. 25 triplets consisting of mixed and monospecific stands were established across Europe ranging from Lithuania to Spain in northern to southern direction and from Bulgaria to Belgium in eastern to western direction. On stand level, the conclusive method for estimating the species proportion as a fraction of the stand area relates the observed density (tree number or basal area) to its potential. This stand-level estimation makes use of the potential from comparable neighboring monospecific stands or from maximum density lines derived from other data, e.g. forest inventories or permanent observations plots. At tree level, the fraction of the stand area occupied by a species can be derived from the Forest Res (2017) 136:171-183 DOI 10.1007/s10342-016-1017 proportions of their crown projection area or of their leaf area. The estimates of the potentials obtained from neighboring monospecific stands, especially in older stands, were poorer than those from the maximum density line depending on the Martonne aridity index. Therefore, the stand-level method in combination with the Martonne aridity index for potential densities can be highly recommended. The species' proportions estimated with this method are best approximated by the proportions of the species' leaf areas. In forest practice, the most commonly applied method is an ocular estimation of the proportions by crown projection area. Even though the proportions of pine were calculated here by measuring crown projection areas in the field, we found this method to underestimate the proportion by 25% compared to the stand-level approach.Eur J

Difference in shade tolerance drives the mixture effect on oak productivity

“…abiotic factors limiting species growth, growing stock and species developmental stage, see Figure ). As recommended by recent studies (Dirnberger et al., ; Huber, Sterba, & Bernhard, ), we calculated the proportion of Q. petraea in a mixture as the ratio between the DI of Q. petraea and the total DI of the plot. If p is the proportion of Q. petraea in the mixture, the expected productivity of Q. petraea in mixture ( E ) based on its productivity in pure stands is then (Loreau, ):where is the productivity of Q. petraea under mixed stand conditions predicted from the growth model developed in pure stands with abiotic factors limiting species growth, growing stock and species developmental stage of the mixed stand as input data (Equation ).…”

“…abiotic factors limiting species growth, growing stock and species developmental stage, see Figure S3). As recommended by recent studies (Dirnberger et al, 2017;Huber, Sterba, & Bernhard, 2014), we calculated the proportion of Q. petraea in a mixture as the ratio between the DI of Q. petraea and the total DI of the plot. If p is the proportion of Q. petraea in the mixture, the expected productivity of Q. petraea in mixture (E) based on its productivity in pure stands is then (Loreau, 1998):…”

Changes in structural heterogeneity and stand productivity by mixing Scots pine and Maritime pine

“…The processes involved in the positive relationship between crown complementarity and over-yielding in mixed stands have been associated with maximized light capture and/or light-use efficiency (Forrester et al, 2017a;Williams et al, 2017). Both process are closely related to crown size characteristics (Binkley et al, 2013); for example, crown projection area has been used to measure species growing-space occupancy and study growing-space efficiency as a proxy for light interception in mixed stands (Dirnberger et al, 2017;Mainwaring and Maguire, 2004;Pretzsch and Schütze, 2009). Following this approach with the same Scots pine-Mar itime pine triplets dataset used in the present work, Cattaneo et al, (2017) found that P. pinaster increased its growth efficiency at the tree level by growing in mixture with P. sylvestris, which showed no benefits from growing in mixture and agreed with the stand-level results mentioned above.…”

EuMIXFOR empirical forest mensuration and ring width data from pure and mixed stands of Scots pine (Pinus sylvestris L.) and European beech (Fagus sylvatica L.) through Europe

“…The original data set covers attributes at the tree level, increments cores, stand and triplet characteristics and has been used for different purposes by Pretzsch et al (2015Pretzsch et al ( , 2016, Río et al (2016bRío et al ( , 2017, Dirnberger et al (2016) and Forrester et al (2017). The data set presented here describes the original data, but ongoing projects can complement the published data by additional measurements of resource supply, nutritional status and wood properties.…”

“…Furthermore, it has the potential to reveal the effect of site conditions on the mixing responses at the stand, species and individual tree level. Available spatial information allows analyses of crown projection (Dirnberger et al 2016), crown architecture or light regimes. The available core data allow retrospective analyses and can be linked to corresponding tree attributes, e.g.…”