Abiotic and biotic factors and their interactions as causes of oak decline in Central Europe

Abstract

Incidences of oak decline have occurred repeatedly during the past three centuries as well as in the most recent decades. On the basis of historical records and dendrochronological measurements, oak decline in Central Europe has been attributed to the single or combined effects of climatic extremes (winter frost, summer drought), defoliating insects, and pathogenic fungi. Starting from a literature review, we discuss the possible roles of various abiotic (air pollution, nitrogen eutrophication, soil chemical stress, climatic extremes, site conditions) and biotic factors (insect defoliation, borer attack, infection by pathogenic fungi, microorganisms) that have been related to oak decline. On the basis of investigations on Quercus petraea and Quercus robur at three different levels (from experiments with young trees to monitoring on a supraregional scale), we suggest a conceptual model of the interaction of abiotic and biotic factors responsible for the onset of oak decline. This model should be valid for Central European oak stands at more acidic sites (soil pH (H 2 O) £ 4.2; on soils with higher pH, pathogenic Phytophthora species may contribute to oak decline). The combination of severe insect defoliation in at least two consecutive years with climatic extremes is the most significant complex of factors in the incidence of oak decline. Combined with defoliation, summer drought or winter ⁄ spring frost or both have to occur within the same year or in consecutive years to trigger major outbreaks of decline. Important additional stress factors are the following: (1) hydromorphic site conditions which, particularly in the case of Q. robur, render the trees more susceptible to drought stress as a result of an impairment of root growth in the subsoil; and (2), possibly, excess nitrogen which, in combination with drought stress, results in distinct decreases in the foliar concentrations of allelochemicals in Q. robur, thereby probably making the trees more susceptible to insect defoliation. Air pollution, soil chemical stress (including excess manganese), and nitrogen-induced nutritional imbalance do not seem to be important causal factors in the complex of oak decline. On the basis of the model, the appearance of the most recent oak decline in North-western Germany can be adequately explained.

The altitude-for-latitude disparity in the range retractions of woody species

“…Elevated temperature and drought can directly elevate mortality [4,27,30,31,48,53,55,56], increase the susceptibility of species to attack by pests and pathogens [5,28,49,57], or favour outcompetition owing to reduced reproduction and relative competitive ability [12,26,29,55].…”

“…This phenomenon explains the historically conservative adaptive response of tree species to climate change [41,94,95] and should caution against assuming that phenotypic plasticity will enable range-edge populations to tolerate substantial future environmental changes. 12 A frequent feature of the dieback events recorded in woody species is that elevated temperatures and drought often predispose tree populations to outbreaks of bark beetles, wood-boring insects [4,5,28,30,49,57] and fungal pathogens, including Phytopthora species and the canker-causing Valsa sordida [28,30,49,57], resulting in mass mortality. Given that increases in global temperature and increasing frequency of severe drought events are predicted to continue [60], future increases in the frequency, severity and spatial extent of pest and pathogen outbreaks are likely within trailing range-edge populations.…”

The anatomical traits of trunk wood and their relevance to oak (Quercus robur L.) vitality

“…photosynthetic CO 2 uptake). This can cause severe structural anomalies which could lead to the elimination of this tree species (Wargo 1996;Thomas et al 2002). On the other hand, oak species are known to show morphological and physiological adaptations that enable them to delay the impact of unfavourable factors (e.g.…”

Gefährdungen der Ökosystemdienstleistungen von Wäldern

“…Der Bezug zum Vorjahr ergibt sich dabei aus der häufig beobachteten zeitlichen Verzögerung von Zuwachsreaktionen und lässt sich auf Carry-over-Effekte bezüglich Kohlenstoffspeicherung und auf mastinduzierende Knospenbildung zurückführen (DROBYSHEV et al 2010, FRIEDRICH et al 2009, GRUBER 2003, LEBOURGEOIS et al 2005, PIOVESAN u. ADAMS 2001, REICHSTEIN et al 2013, VAN DER MAATEN 2012 Buchen-BZE II-Standorte während der Klimanormalperiode 1961-1990und der Jahre 1948, 1960, 1976und 2004 Betrachtet man einzelne der im Modell berücksichtigten klimatisch-hydrologischen Buchen-BZE II-Standorte während der Klimanormalperiode 1961-1990und der Trockenjahre 1947, 1959, 1976und 2003(a) (vgl. FRIEDRICHS et al 2009, LEUZINGER u. KÖRNER 2007, THOMAS et al 2002. Trotz dieser Einschränkungen wurden anhand der Ergebnisse der für die Modellierung der JRBabw geeigneten 39 Buchen-BZE II-Standorte für den Zeitraum 1932Trockenstressrisikostufen abgeleitet.…”