Patrick Pyttel

Growth and form of Quercus robur and Fraxinus excelsior respond distinctly different to initial growing space: results from 24-year-old Nelder experiments

Initial growing space is of critical importance to growth and quality development of individual trees. We investigated how mortality, growth (diameter at breast height, total height), natural pruning (height to first dead and first live branch and branchiness) and stem and crown form of 24-year-old pedunculate oak (Quercus robur [L.]) and European ash (Fraxinus excelsior [L.]) were affected by initial spacing. Data were recorded from two replicate single-species Nelder wheels located in southern Germany with eight initial stocking regimes varying from 1,020 to 30,780 seedlings·ha−1. Mortality substantially decreased with increasing initial growing space but significantly differed among the two species, averaging 59% and 15% for oak and ash plots, respectively. In contrast to oak, the low self-thinning rate found in the ash plots over the investigated study period resulted in a high number of smaller intermediate or suppressed trees, eventually retarding individual tree as well as overall stand development. As a result, oak gained greater stem dimensions throughout all initial spacing regimes and the average height of ash significantly increased with initial growing space. The survival of lower crown class ashes also appeared to accelerate self-pruning dynamics. In comparison to oak, we observed less dead and live primary branches as well as a smaller number of epicormic shoots along the first 6 m of the lower stem of dominant and co-dominant ashes in all spacing regimes. Whereas stem form of both species was hardly affected by initial growing space, the percentage of brushy crowns significantly increased with initial spacing in oak and ash. Our findings suggest that initial stockings of ca. 12,000 seedlings per hectare in oak and 2,500 seedlings per hectare in ash will guarantee a sufficient number of at least 300 potential crop trees per hectare in pure oak and ash plantations at the end of the self-thinning phase, respectively. If the problem of epicormic shoots and inadequate self-pruning can be controlled with trainer species, the initial stocking may be reduced significantly in oak.

Fully Mechanized Harvesting in Aged Oak Coppice Stands

Coppice is a traditional forest management system used all over the world. It takes advantage of fast early growth and the vegetative reproduction of the respective trees. Coppice forests provide firewood and many other products and services, especially to rural communities. In Central Europe, regular periodic cutting and management of coppice forests was abandoned due to socioeconomic changes in recent decades, resulting in aged stands that have gradually lost their coppice characteristics. Today, coppice forests are recognized again not only for their growth potential but also for their benefits for biodiversity and nature conservation. Together with the rising demand for energy wood, this recognition could result in a renaissance of the traditional coppice management system. Several stands grow on relatively easily accessible terrain where fully mechanized systems (harvester, forwarder) could be used. However, there is no current information regarding the technical feasibility and productivity of moder...

Silvicultural Options for Mixed-Species Stands

Silvicultural approaches for mixed-species stands typically aim at creating and maintaining stand compositional and structural diversity to provide the desired ecosystem function. An important aim of regeneration and tending is to develop stable mixtures that facilitate the anticipated interactions among the participating tree species and at the same time require little silvicultural input to maintain the composition of compatible tree species. To ensure survival and vigorous growth of trees in mixture in the long term, it is often necessary to separate species in space and time during the regeneration phase. Weaker competitors can be given a head start through advance regeneration or may be regenerated in patches that protect the majority of individuals from interspecific competition. In managed forests, tree species in mixture may also have a service function. For example, nurse crops may be used to facilitate establishment of sensitive tree species and to accelerate ecosystem recovery following disturbances. Trainer species are typically used to improve the quality development of stems of economically important species. Whereas the regeneration of mixtures has received considerable attention in research, there is little specific information regarding the thinning of mixed-species stands, which are often treated like an agglomerate of monospecific stands of the companion species. In the absence of quantitative information on optimal tree spacing, stand density, or the growth response to thinning in mixtures, crop tree thinning approaches are recommended. These facilitate the maintenance of desired species proportions as well as stand stability and development of quality attributes in crop trees through simple indicators. Although it is often assumed that the development of stem quality in mixtures is inferior to that in monospecific stands, there is so far little solid evidence to support this assumption. Rather, it appears that stem quality depends on specific interactions between species and the structural heterogeneity of stands.

Croissance de l’Alisier torminal dans les forêts du Nahebergland issues d’anciens taillis

Son impact esthetique pendant la floraison et en automne, sa valeur environnementale et economique et sa rarete sont les criteres a l’origine du choix de l’Alisier torminal (Sorbus torminalis (L.) Crantz) comme arbre de l’annee 2011 en Allemagne. La disparition des regimes du taillis et du taillis-sous-futaie est souvent citee comme la principale cause de la tres faible presence aujourd’hui de l’Alisier torminal dans les forets allemandes. Toutefois, l’existence d’un lien direct entre ces traitements desormais historiques et la conservation de l’Alisier reste a ce jour incertaine.