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Catalin Petritan I.,University of Gottingen | Catalin Petritan I.,Transilvania University of Brasov | von Lupke B.,University of Gottingen | Petritan A.M.,University of Gottingen | Petritan A.M.,Institute of Forest Research and Management
Investigacion Agraria Sistemas y Recursos Forestales | Year: 2011

The horizontal and vertical distribution of live fine roots (diameter < 2 mm) of overstory Norway spruce [Picea abies (L.) Karst.] and their influence on diameter and height growth of underplanted beech (Fagus sylvatica L.) and Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco) saplings were studied on experimental plots in the Solling Mountains (Germany).The aims of this study were to investigate how overstory fine root density varies with stand density, and how it influences growth of the underplanted saplings to changes in belowground resources availability in connection with simultaneously changing light availability. Most fine roots were concentrated in the humus layer (more than 45%) and in the top mineral soil (0-5 cm, about 15%). Fine root biomass increases with overstory basal area and decreases with rising distance from the nearest overstory tree, reaching about zero within ca. 8 m distance. Over the whole two-year study period, light availability alone was the decisive factor for growth of the beech saplings (5 resp. 6 years of age) while growth of the Douglas-fir saplings in the first study year (6 years of age) was additionally affected by a shortage of belowground resources due to root competition in a season with less than average rainfall. This species-specific response of underplanted saplings to changes in above and belowground resources is of silvicultural importance for the establishment of a mixed stand beneath a mature canopy: the more sensitive Douglasfir should be planted on the central parts of openings with little or none belowground competition while the less sensitive beech can be placed below the denser parts of the overstory.

Petritan A.M.,University of Gottingen | Petritan A.M.,Institute of Forest Research and Management | Von Lupke B.,University of Gottingen | Petritan I.C.,University of Gottingen
Annals of Forest Science | Year: 2010

Construction cost (g glucose g-1), chemical composition and morphology of leaves of beech (Fagus sylvatica L.) and two co-occurring valuable broadleaved species (sycamore maple - Acer pseudoplatanus L. - and ash - Fraxinus excelsior L.) were investigated along a horizontal light gradient (3-60% of above canopy radiation) and from top to bottom within the crowns in a fairly even-aged mixed-species thicket established by natural regeneration beneath a patchy shelterwood canopy. • Construction cost and carbon concentration increased with irradiance in ash and sycamore maple and were independent of irradiance in beech. Leaf traits expressed on an area basis, like construction cost, nitrogen content and leaf mass (LMA) increased significantly with irradiance in all three species and decreased from top to bottom within crowns. • The shade tolerant beech invested more glucose to produce a unit foliar biomass, but less to build a unit foliar area due to lower LMA. Thereby beech was able to display a greater total leaf area, what at least in parts counterbalanced the lower values of Na as compared to ash and sycamore maple. © INRA, EDP Sciences, 2010.

Petritan I.C.,University of Gottingen | von Lupke B.,Transilvania University of Brasov | Petritan A.M.,Institute of Forest Research and Management
Baltic Forestry | Year: 2011

Effects of shelterwood and two types of low vegetation cover (shrubs and gramineous) on frost occurence and degree of damages were investigated in young beech (Fagus sylvatica L.) and Douglas-fir (Pseudotsuga menziesü [Mirb.] Franco) plantations. A late frost event was registered at the end of April 2007 which did not affect saplings below a spruce shelterwood (on strip cutting or target diameter cutting plots), but frost damages occurred in open field conditions (on clear cutting plots). The probability of frost damage occurrence increased significantly with light availability in both species, whereas the degree of frost damages (%, proportion of damaged beech leaves and damaged new Douglas-fir needles) decreased with increasing seedling height for both species. A significant influence of field vegetation type (shrubs and gramineous) on the probability of frost occurrence could be detected in beech: in small shrubs the probability was lower than in gramineous species (0.48 vs. 0.76). The degree of frost damage decreased from gramineous to small shrubs type in both species, but significantly only in Douglas-fir saplings (from 28.6 % to 15 %, in beech from 30.7 % to 25.2 %). We concluded that at sites which are prone to late spring frost the early regeneration needs protection for successful establishment, and that this protection can be provided by strip cutting along with shelterwood or on clear-cut areas by a dense ground vegetation of small shrubs.

Petritan I.C.,University of Gottingen | Petritan I.C.,Transilvania University of Brasov | von Lupke B.,University of Gottingen | Petritan A.M.,University of Gottingen | Petritan A.M.,Institute of Forest Research and Management
European Journal of Forest Research | Year: 2011

In Central Europe, the conversion of pure Norway spruce stands (Picea abies [L.] Karst.) into mixed stands with beech (Fagus silvatica L.) and other species like e. g. Douglas fir (Pseudotsuga menziesii [Mirb.] Franco) is accomplished mainly by underplanting of seedlings beneath the canopy of overstorey spruce trees after partial cutting treatments what means exposure to shade and below-ground root competition by the overstorey to the seedlings. Particularly about the second factor, our knowledge is limited. Therefore, we carried out a below-ground competition exclusion experiment by root trenching and investigated the effects on soil resources, growth, and biomass partitioning of underplanted beech and Douglas fir saplings under target diameter and strip cutting treatments. The exclusion of overstorey root competition by trenching increased the soil water potential in the second year that had a fairly dry growing season and led to significantly higher foliar concentrations of most nutrients, particularly in Douglas fir, indicating an amended nutrient supply. Both improvements were accompanied by an increase in length and diameter increment of the underplanted saplings, appearing in both species only after having surpassed a species-specific threshold light value (Douglas fir 16% of above canopy radiation, beech 22%). We also found significant interactions between trenching and light for specific fine root length and further biomass and morphological parameters. Judged by the much steeper increase in height and diameter growth with increasing light after release from below-ground competition, Douglas fir saplings appeared to be more sensitive to root competition than beech saplings what conforms to older findings for beech. According to our results, a strip cutting seems to be more appropriate than a target diameter cutting treatment to replace a pure spruce stand by a mixed stand with beech and Douglas fir. © 2011 The Author(s).

Petritan I.C.,University of Gottingen | Petritan I.C.,Transilvania University of Brasov | von Lupke B.,University of Gottingen | Petritan A.M.,University of Gottingen | Petritan A.M.,Institute of Forest Research and Management
Journal of Forest Research | Year: 2012

The reaction of young beech (Fagus sylvatica L.) and Douglas fir (Pseudotsugamenziesii (Mirb.) Franco) saplings on competition of two types of vegetation-(1) gramineous with mainly Agrostis capillaries, Calamagrostis epigejos, Deschampsia flexuosa, and (2) small shrubs with mainly Rubus fruticosus and R. idaeus-on clear cuts on two sites was studied for 2 years. Half the sample saplings were released from competing vegetation by repeated herbicide applications. This treatment significantly raised the diameter increment in both species at the site with higher competition intensity, and more strongly after the removal of small shrubs than after the removal of grasses. Sapling length increment was not significantly affected. After being released from small shrubs, saplings of both species developed a smaller specific fine root length (cm g -1 fine root biomass) than unreleased saplings during the second year which was characterized by low rainfall. Root nitrogen concentration significantly increased after weed control in both vegetation types. Sapling foliar content of main nutritional elements was negatively related to dry mass and total chemical content of surrounding ground vegetation. Based on these results, a release from ground vegetation could be a useful tool to improve growth of planted beech and Douglas-fir saplings on sites with well-developed small shrubs competition (mainly by Rubus fruticosus and R. idaeus), or under fairly dry conditions. © 2011 The Author(s).

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