Effects of simulated moose browsing on growth, mortality, and fecundity in Scots pine: relations to plant productivity

Abstract

Current theory on plant–animal interactions predicts that the outcome of herbivory on plant performance will be dependent on plant productivity. Thus, slow-growing plants should be less able to compensate for biomass losses than fast-growing plants, and therefore be more susceptible to herbivory if attacked. We simulated winter browsing by moose (Alcesalces (L.)) on Scots pine (Pinussylvestris L.) along a gradient of plant productivity and addressed the following questions: (1) Does herbivory affect growth independently of plant productivity? (2) Is herbivory a more important mortality factor for slow-growing than for fast-growing plants? (3) Is there any effect of herbivory on fecundity, and is it related to plant productivity? Two clipping regimes simulated different intensities of moose winter browsing. Mortality was followed annually, and after 4 years we measured tree growth and fecundity on control as well as on treatment pines. The effect of clipping on growth was related with both clipping intensity and plant productivity. In the light-clipping treatment mortality was restricted to the slow-growing pines, in contrast with the severe treatment, where it occurred across the whole range of plant growth. Moreover, in the light-clipping treatment most mortality occurred within 1 year after treatment, whereas tree death occurred over 2 or more years in the severe treatment. We found no effect of age on mortality within growth-rate classes. The proportion of trees with cones increased with growth rate for control trees but not for treated trees, indicating that herbivory more strongly affects fecundity on fast-growing than on slow-growing trees. Our results confirm the hypothesis that herbivory affects plant performance differently across a gradient of plant productivity. We suggest that mammalian herbivores can increase mortality of plant genets after the seedling stage primarily in stands on low-productivity sites, especially in combination with a high density of the herbivore.

Der Wald-Wild-Konflikt

“…Nadelbaumarten, mit Ausnahme der Lärche, zeigen diese Reaktion nur sehr begrenzt (Eiberle 1975). Während einmaliger leichter Verbiss offenbar kompensiert werden kann (Cunningham et al 2006), ist die Fähigkeit vieler Nadelbaumarten, Triebe nach mehrmaligen Verbiss oder einmaligen starken Verbiss zu regenerieren, gering (Edenius et al 1995, Hódar et al 2008. Entsprechend erwiesen sich in den Untersuchungen von Weise (1997) durch simulierten Verbiss verursachte Höhenwachstums-und Durchmesserwachstumsreduktionen als dauerhaft.…”

Yew (Taxus baccata L.) regeneration is facilitated by fleshy-fruited shrubs in Mediterranean environments

“…We did not consider the habitats pine and yew in the case of saplings because very few saplings were found growing under these tree species, and all of them were simultaneously growing under¯eshy-fruited shrubs (and, thus, were classi®ed under this category). In addition, we estimated the age of the saplings as the number of whorls of the main shoot [for this procedure with other conifers, see Edenius et al (1995);]. …”

Density and population structure of the natural regeneration of Scots pine (Pinus sylvestris L.) in the High Ebro Basin (Northern Spain)

“…Gong et al [12] reported that in native pinewoods at Glen Tanar, Aberdeenshire (Scotland), the dominant seedlings, defined as the tallest 10 percent of seedlings in each plot, when aged 12 (61.5 cm height) were 22 cm higher in fenced than in unfenced plots. Slow-growing Scots pine plants are less able to compensate for biomass losses and, therefore, they have less chances to survive when attacked [8]. In consequence, damage is more detrimental in poor sites, thus increasing regeneration difficulties.…”