While previous studies focused on tree growth in pure stands, we reveal that tree resistance and resilience to drought stress can be modified distinctly through species mixing. Our study is based on tree ring measurement on cores from increment boring of 559 trees of Norway spruce (Picea abies [L.] Karst.), European beech (Fagus sylvatica [L.]) and sessile oak (Quercus petraea (Matt.) Liebl.) in South Germany, with half sampled in pure, respectively, mixed stands. Indices for resistance, recovery and resilience were applied for quantifying the tree growth reaction on the episodic drought stress in 1976 and 2003. The following general reaction patterns were found. (i) In pure stands, spruce has the lowest resistance, but the quickest recovery; oak and beech were more resistant, but recover was much slower and they are less resilient. (ii) In mixture, spruce and oak perform as in pure stands, but beech was significantly more resistant and resilient than in monoculture. (iii) Especially when mixed with oak, beech is facilitated. We hypothesise that the revealed water stress release of beech emerges in mixture because of the asynchronous stress reaction pattern of beech and oak and a facilitation of beech by hydraulic lift of water by oak. This facilitation of beech in mixture with oak means a contribution to the frequently reported overyield of beech in mixed versus pure stands. We discuss the far-reaching implications that these differences in stress response under intra- and inter-specific environments have for forest ecosystem dynamics and management under climate change.

Resistance of European tree species to drought stress in mixed versus pure forests: evidence of stress release by inter-specific facilitation.

https://cyberleninka.org/article/n/1198847.pdf

Canopy space filling and tree crown morphology in mixed-species stands compared with monocultures

The spatial and temporal dynamics of species interactions in mixed-species forests: From pattern to process

Through complementarity interactions, mixed-species forests can be more productive than monocultures, and this effect can increase with tree-species richness. However, this is not always the case. This review examines the processes and stand structural attributes that can influence diversity-productivity relationships (DPRs); how they influence resource availability, resource uptake, and resource-use efficiency; and also describes some important differences between tree-diversity versus grassland-diversity experiments. The size of the complementarity effects caused by these processes and stand structures varies along spatial and temporal gradients in resource availability and climate. These spatial and temporal dynamics have now been examined in many studies, and the general patterns are summarized using a simple framework; complementarity is predicted to increase as the availability of resource “X” declines (or climatic condition X becomes harsher) if the species interactions improve the availability, uptake, or use efficiency of resource X (or interactions improve climatic condition X). Importantly, this framework differs from the stress-gradient hypothesis to account for a wider range of inter-specific plant interactions (not only facilitation) by considering contrasting methods used to quantify species interactions while accounting for stand structure. In addition, complementarity (as opposed to facilitation) for a given species combination can increase as growing conditions improve in forests, contrary to predictions of the stress-gradient hypothesis with regards to facilitation. This review indicates that while the effects of tree-species diversity on growth and other forest functions are now receiving a lot of attention, far less is known about the effects of structural diversity on growth or forest functioning. Direct measurements of the processes, as opposed to focusing mainly on growth responses, could greatly contribute to our understanding of structural diversity effects.

/pdf/a-review-of-processes-behind-diversity-productivity-hw7vwm4ng6.pdf

A Review of Processes Behind Diversity—Productivity Relationships in Forests

Mixed-species versus monocultures in plantation forestry: Development, benefits, ecosystem services and perspectives for the future

• Existing growth and yield plots of pure and mixed stands of Norway spruce (Picea abies (L.) H. Karst.) and European beech (Fagus sylvatica L.) were aggregated in order to unify the somewhat scattered sources of information currently available, as well as to develop a sound working hypothesis about mixing effects. The database contains information from 23 long-term plots, covering an ecological gradient from nutrient poor and dry to nutrient rich and moist sites throughout Central Europe.• An empirically formed interaction model showed, that depending on the site conditions, dry mass growth in mixed stands can range from − 46% to +138 % of the growth yielded by a scaled combination of pure stands at equal mixing proportions.• Drawing from the interaction model, overyielding of the mixed stands appears to be triggered by two separate mechanisms. On poor sites, where significant overyielding is commonly found, facilitation by beech offsets nutrient-related growth limitations in spruce. In contrast, overyielding of mixed stands occurs less frequently on rich sites, and appears to be based on an admixture effect, with spruce reducing the severe intra-specific competition common in pure beech stands.• It was concluded that silviculture can accelerate growth of spruce by beech admixtures on poor sites, while growth of beech can be promoted by admixture of spruce, particularly on excellent sites.

/pdf/comparison-between-the-productivity-of-pure-and-mixed-stands-4f8hugf1jf.pdf

Comparison between the productivity of pure and mixed stands of Norway spruce and European beech along an ecological gradient

The mixture of beech (Fagus sylvatica L.) and oak (sessile oak, Quercus petraea (Matt.) Liebl., and pedunculate oak, Q. robur L.) is of considerable importance in Europe and will probably become even more important under climate change. Therefore, the performance of oak and beech in mixture was compared with the species’ growth in pure stands. Data from 37 long-term mixing experiments in Poland, Germany and Switzerland were pooled for analysis of mixing effects on stand productivity and possible interrelationships with mixing portions or site conditions. We found that on average, mixed stands of oak and beech exceeded biomass productivity in pure stands by 30 % or 1.7 t ha−1 year−1, as the growth of both species was benefitted by the mixture. However, that the interaction actually ranged from facilitation and overyielding on poor sites to underyielding on fertile sites triggered by competition. An empirically derived interaction model showed volume and dry mass growth changing in mixed stands from gains of 50 % to losses of 10 % depending on site conditions. It is concluded that the analysed mixture grows in accordance with the stress-gradient hypothesis and that our results suggest a site-specific relationship between species mixture and biomass productivity. As a consequence, an adequate species mix should result in increased productivity under steady state as well as climate change.

Productivity of mixed versus pure stands of oak (Quercus petraea (Matt.) Liebl. and Quercus robur L.) and European beech (Fagus sylvatica L.) along an ecological gradient

Die Verwendung von Holzrohstoffen ist in Deutschland in den letzten Jahrzehnten beträchtlich angestiegen (MANTAU, 2013). Insbesondere der Energieholzmarkt ist stark gewachsen, da durch die Entwicklung neuer Techniken und effizienter Logistik die Bereitstellungskosten für Energieholz gesunken und gleichzeitig die Preise aufgrund der Verknappung und Verteuerung fossiler Brennstoffe gestiegen sind (HAKKILA, 2004; VORHOLT, 2010). Vor diesem Hintergrund haben sich neue Märkte für die Verwendung von schwächeren Holzsortimenten und Reisig entwickelt. Hierdurch werden zunehmend auch solche Teile von Bäumen genutzt, die in den letzten Jahrzehnten noch im Wald und damit im Nährstoffkreislauf der Ökosysteme geblieben sind. Auch bei herkömmlichen Derbholzsortimenten ist die Nutzung aufgrund der zunehmenden Nachfrage, aber auch aufgrund des beschleunigten Wachstums der Wälder (KAHLE et al., 2008; PRETZSCH et al., 2014) erheblich angestiegen (SEINTSCH, 2010).

Nährstoffentzüge durch die Holz- und Biomassenutzung in Wäldern. Teil 1: Schätzfunktionen für Biomasse und Nährelemente und ihre Anwendung in Szenariorechnungen

Export of nutrients from forest ecosystems by harvesting timber and biomass. Part 1: Functions for estimating tree biomass and nutrient content and their application for scenario analyses.

Wie viel holzige Biomasse sich in einem forstlichen
Okosystem befindet, ist fur verschiedenste okonomische und
okologische Fragestellungen relevant. Da detaillierte Messungen
aufwendig und daher nicht grosflachig durchzufuhren sind, ist
man bei ihrer Bestimmung auf Schatzfunktionen angewiesen, die
allerdings eine Reihe von Schwachen aufweisen: Erstens liegen
unterschiedlich viele Untersuchungen zu den einzelnen Baumarten
vor, die zudem nicht gleichmasig auf die Verbreitungsgebiete und
Alterstufen der Baumarten verteilt sind. Zweitens basieren die
vorliegenden Funktionen zumeist auf Untersuchungen, die in
Reinbestanden durchgefuhrt worden sind. Die Frage der
Ubertragbarkeit solcher Ergebnisse auf gemischte, starker
strukturierte Bestande konnte bisher auf Grund fehlender
Vergleichsdaten nicht beantwortet werden. Drittens wird die
Masse der Rinde haufig nicht als separates Kompartiment erhoben.
Dies ist insbesondere von Bedeutung, wenn auser der
Biomasseproduktion auch die Nahrstoffinhalte von Interesse sind,
da die Rinde eine besonders hohe Nahrstoffkonzentration
aufweist. In der vorliegenden Arbeit werden die bisherigen
Untersuchungen durch Erhebungen in zwei Bestanden mittleren
Alters, die in Ober- und Unterschicht untergliedert sind
(Traubeneiche/Buche und Kiefer/Buche), erganzt. Dabei steht die
Biomasseerhebung im Vordergrund, womit eine Voraussetzung fur
spatere Nahrstoffbilanzen geschaffen werden soll, die in diesen
Bestanden in Abhangigkeit von der Bewirtschaftung durchgefuhrt
werden sollen. Insgesamt wurden 15 Eichen (10–33 cm
Brusthohendurchmesser), 15 Kiefern (10–30 cm) und 20 Buchen
(4–16 cm) gefallt und die holzige Biomasse in den wichtigsten
oberirdischen Kompartimenten bestimmt. Die Raumdichte-Messungen
zielen auf die Schatzung der Trockenmasse im Kern- und
Splintholz. Die Nicht-Derbholzbiomasse wurde auf der Basis von
Stichprobenerhebungen durch Trocknen und Wiegen bestimmt.
Auserdem wurde die Rindenbiomasse des Derbholzes durch
systematische Messung der Rindenstarke im Stamm- und
Kronenbereich quantifiziert. Die Ergebnisse bestatigen im Allgemeinen die
allometrischen Zusammenhange zwischen Grundflache in 1,3 m Hohe
uber dem Boden und holziger Biomasse aus alteren
Reinbestands-Untersuchungen. Die nicht-linearen Ausgleichskurven
weisen hohe Bestimmtheitsmase zwischen 0,97 und 0,99 auf und
lassen keinen Bias erkennen. Die Derbholz- und Rindenanteile
lassen sich dabei am besten mit linearen Zusammenhangen zur
Gesamtbiomasse bzw. Gesamt-Derbholzbiomasse beschreiben. Durch
Anwendung entsprechender Multiplikatoren, in welchen der
Nahrstoffgehalt pro Trockenmasse steckt, lassen sich die so
schatzbaren Biomassen in Nahrstoffmengen umrechnen.

Oberirdische holzige Biomasse in Kiefern-/Buchen- und Eichen-/Buchen-Mischbeständen

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