Recovery of Abies alba and Picea abies saplings to browsing and frost damage depends on seed source

Abstract

The density of wild ungulates has increased in the last century, and browsing has become a major driver of forest succession in the northern hemisphere. In addition, tree species are expected to respond differently to future climate conditions, especially an increased frequency of late frost events. The aim of this study was to analyze the influence of intraspecific genetic variation on the recovery of two tree species to frost and browsing. An experiment with saplings from 90 Abies alba and 72 Picea abies seed sources was conducted. Five‐year‐old saplings were clipped at three intensities before budburst in spring. Growth (height, diameter, leader shoot length, and biomass) and quality (e.g. stem form, multistemming, reaction type) were assessed before and 1–2 years after clipping or 3–4 years after natural frost events, and provenance differences were related to environmental differences at the seed source. For Abies, frost and clipping resulted in reduced height growth in the first year after the stress and reduced height for two (clipping) to four (frost) vegetation periods. Sapling biomass, diameter increment, and quality decreased after heavy clipping. For Picea, which grew twice as fast as Abies, such effects were only found after frost damage. Population differences were significant for both species for all investigated growth traits and for Picea also for some quality variables. The “reaction type” after browsing (e.g. new shoot, existing twig bending upward) seems to be species specific and independent of seed source. In contrast, the time lag between clipping and formation of a clear new leader shoot increased for Abieswith lower temperatures at the seed source. Lowland populations with warmer climates grew faster, and for Picea also qualitatively better, and recovered faster from leader shoot loss (Abies) or reacted at the uppermost meristem (Picea). Thus, the investigated stressors increased the existing differences among populations.

Recovery of silver fir (Abies albaMill.) seedlings from ungulate browsing mirrors soil nitrogen availability

“…Previous analysis of growth traits in the same common garden experiment showed that seedlings recovered from the stress caused by simulated ungulate browsing when only their terminal buds were browsed, but not after the removal of several shoots (i.e. heavy browsing) Kupferschmid & Heiri (2019). Here, we hypothesized that the e ect of simulated browsing on physiological traits related to C and N balance would be largely diminished.…”

“…1A and B). In March 2015, at the start of the third eld growing season, a simulated browsing experiment started to test seedlings' morphological response and capacity of recovery to ungulate browsing (Kupferschmid & Heiri, 2019) (Fig. 1B and C).…”

“…The most common e ects of ungulate browsing are the removal of buds, thus apical meristem tissue and the removal of shoots, which reduces the photosynthesizing leaf area and changes the root-to-shoot ratio (Hoogesteger & Karlsson, 1992;Rhodes & Clair, 2018). Trees are often found to recover well from light to moderate browsing stress via di erent compensatory mechanisms at the morphological level such as increased leaf size (Lehtilä et al, 2000), overcompensated growth in the leading bud (O'Reilly-Wapstra et al, 2014), growing side shoots (Kupferschmid & Heiri, 2019), but also in their reproductive strategy such as increased production of female strobili (Allison, 1990). However, browsing can also severely limit growth and cause seedling mortality (Kupferschmid, 2017;Rhodes & Clair, 2018).…”

“…In this study, we assessed the physiological response of silver r seedlings to simulated ungulate browsing two growing seasons after the treatment in an ongoing common garden experiment (Frank et al, 2017;Kupferschmid & Heiri, 2019;Csilléry et al, 2020b). In parallel, we assessed the same physiological traits in the source populations, whenever possible on the mother trees of the seedlings, in their home environments.…”

Abschätzung des Einflusses von Verbiss durch wildlebende Huftiere auf die Baumverjüngung

“…Review in Kupferschmid 2017). Weisstannen aus Hochlagenprovenienzen reagierten zum Beispiel zeitlich verzögert auf Triebschnitt (simulierter Verbiss), die Fichte hingegen nicht (Kupferschmid & Heiri 2019). Wildlebende Huftiere beeinflussen deshalb das Wachstum der Baumverjüngung je nach Baumart unterschiedlich, was deren relative Häufigkeit und damit deren Etablierungserfolg verändern kann (Krueger et al 2009).…”