Quantifying the effect of pine mistletoe on the growth of Scots pine

Abstract

Summary Mistletoe infection results in substantial growth losses in mistletoe‐infected forests. This study reports and evaluates the results of retrospective analyses of radial growth of Scots pine (Pinus sylvestris) in relation to the level of infection of pine mistletoe (Viscum album ssp. austriacum). A total of 43 Scots pine trees were destructively sampled from different sites. Of these trees, 14 were uninfected and 29 were infected. Infection classes were determined using six‐class dwarf mistletoe rating system (DMRS). All needle and mistletoe biomass were removed completely and weighed for each sampled tree. Subsamples from needles and all mistletoe biomass were taken to the laboratory for oven‐dried weight determinations. Five‐cm‐thick wood discs were cut from the stem at the breast height (1.3 m) to determine annual basal area increment for the last 25 years. In addition to DMRS, new infection classes were created using mistletoe‐to‐needle biomass (MB/NB) ratio. The results showed that the radial growth losses could be as much as 41% to 64% at different infection levels. The rate of growth loss in relation to DMRS and MB/NB ratio was similar, but with a larger variability in DMRS values. The results showed that both DMRS rating and MB/NB ratio seem to be important for quantifying growth loss on Scots pine trees infected with mistletoe. The results of this study can also be invaluable in modelling the effects of mistletoe on the growth of Scots pine trees.

Impact of Common Mistletoe (Viscum album L.) on Scots Pine Forests—A Call for Action

“…Nutrients absorbed by trees-macroelements N, K, Ca, P, and S and trace elements Mg, Fe, Cu, Zn, Mo, B, Na, and N-accumulate in mistletoe, making them inaccessible to the host, especially in needles, increasing the adverse impact of drought [57]. It was found that the total chlorophyll content in pine needles affected by mistletoe increased from April to June, then decreased to September, whereas in healthy plants it increased from April to October [56]. In needles of infected pines, the decrease in chlorophyll content resulted in a decrease in photosynthetic efficiency and damage to chloroplasts resulted from Fe + deficiency [57].…”

“…Mistletoe infection causes crown thinning by reducing foliage biomass (Figure 3). Bilgili et al [56] reported that needle biomass may be reduced by as much as 40% in infected trees. Decreased chlorophyll content in foliage of infected trees [58,94] leads to significant reduction of photosynthetic capacity [95] and results in growth losses of host trees [96,97].…”

“…The loss of water and mineral nutrients is manifested in host plants by water deficiency, decreased biomass increment, shortened needles, and poorer quality of seeds [52,53]. The rate of transpiration of water in mistletoe is higher than in the host plant [54], which reduces the efficiency of water use by the host by up to 9 times [37,55,56]. Stress resulting from water use by mistletoe causes water deficit in the host, which reduces food resources in needles due to reduced host plant photosynthesis, especially during summer drought [55,[57][58][59].…”

Dwarf Mistletoe Infection Interacts with Tree Growth Rate to Produce Opposing Direct and Indirect Effects on Resin Duct Defenses in Lodgepole Pine

“…Yet, evidence from comparisons of P. contorta killed by bark beetles versus those that survived suggests that investing in larger resin ducts is a better defensive strategy for this species than increasing the number of resin ducts [65]. Thus, my findings offer a potential mechanism underlying prior reports of increasing rates of bark beetle attack and pest-related mortality resulting from mistletoe infection (e.g., [24,30,32,33]). My results also highlight the need for additional studies, similar to that of Klutsch and Erbilgin [34], that consider multiple measures of resin defense in pines infected by mistletoe and then work to unravel the various direct and indirect pathways through which abiotic and biotic factors shape these defenses in conifers.…”

“…The indirect negative effect of mistletoe infection on resin duct defenses, which results from the suppression of tree growth by mistletoe infection, adds a mechanistic explanation to prior reports of lower growth rates and higher mortality linked to mistletoe infection level [21,22,[25][26][27][28][29][30]32,33]. Given that bark beetles are more likely to attack and kill trees with fewer or smaller resin ducts [4][5][6], the suppression of resin duct sizes and total area by mistletoe infection could help to explain the higher rates of attack by bark beetles on pines with severe mistletoe infections [23,24].…”