An exceptionalCalluna vulgariswinter die-back event, Abernethy Forest, Scottish Highlands

Abstract

Background: Calluna vulgaris is a woody shrub forming plant communities of economic and international conservation importance. Following winter 2002-2003, there was exceptional Calluna die-back in the central Scottish Highlands. Aim: To understand the effects and causes of this die-back event at Abernethy Forest Nature Reserve, Cairngorms National Park. Methods: Patterns of weather, foliage moisture and microclimate were interpreted in relation to patterns of Calluna vulgaris die-back. Vegetation development was investigated over 4 years, based on pre-existing monitoring plots. Results: February 2003 included a period of exceptionally low air humidity, during which unusually low Calluna shoot moisture readings were made, particularly in areas that subsequently had severe die-back. In monitored areas, Calluna cover declined by a third, with minimal recovery after three growing seasons. Die-back was more severe where Calluna was longer-stemmed and less abundant, and where topography was flatter or more north-facing. These topographical features, and die-back, were correlated with colder winter microclimates. A doubling in Vaccinium myrtillus cover in forest plots was strongly correlated with the pattern of Calluna die-back. Meteorological data showed an eight-fold increase in the variability of winter humidity minima since 1983-1984. Conclusions: Die-back probably followed severe 'winter desiccation', caused by extreme low humidity conditions, combined with low temperatures, lack of snow cover, and Calluna vulnerability due to age. It led to a major vegetation change in the direction of management aims at this site, but contrary to aims at many other Calluna-dominated sites. The importance of climatic variability as a potential driver of major vegetation change is emphasised.

Testing prescribed fire as a tool to promote Scots pine Pinus sylvestris regeneration

“…Subsequently, there was a steady increase in live vegetation cover in burnt plots, which reached around 66% after 5 years. In unburnt vegetation, an unusual natural heather die-back episode in early 2003 (Hancock 2008), resulted in lower means and higher variance in vegetation cover in that year, with some recovery in the following years. There were only minor diVerences in vegetation cover between plots with and without deer.…”

Using cattle for conservation objectives in a Scots pine Pinus sylvestris forest: results of two trials

“…Each of these events occurred, or probably occurred, over large areas (1,000s of km 2 ) (Keeling et al 2001;Broome et al 2007;Hancock 2008). Therefore, paradoxically, had we been able to establish a single year, spatially replicated cattle experiment, in place of each of our single-plot trials, with replicates dispersed over an area no larger than this (e.g., within the 3,800 km 2 Cairngorms National Park), then the impacts of these events on the scientific study of the focal hypotheses could have been much greater.…”

“…Such approaches may have cost and biodiversity advantages, depending on site constraints and objectives. Consideration should also be given to the implications of natural heather die-back, and subsequent bilberry increase, observed at Abernethy during this study (see also Hancock 2008). Although hard to predict, such events may, in time, deliver site objectives in the absence of costly management.…”

“…Heather that was clearly trampled and discoloured was distinguished on the first post-grazing visit. In late winter 2002/3, much heather died due to a spell of exceptional weather (Hancock 2008), and this recently dead (reddish-brown) heather was distinguished in winter 2003/4, from live (green) and long-dead (grey) heather.…”

Investigation of the fungi associated with dieback of prickly acacia (Vachellia nilotica subsp. indica) in Northern Australia

“…Chilling alters plant physiology mainly in two ways (a) intracellular freezing: causes disruption of cell membrane leading to cell necrosis and (b) intercellular freezing or ice formation in intercellular spaces: causes vascular cavitation, cell dehydration, cell contraction and finally collapse of the dehydrated and contracted cells (Palta & Weiss 1993;Ristic & Ashworth 1993). Such physiological damage often leads to the expression of a range of physical symptoms including those associated with dieback (Zhu et al 2000;Hancock 2008;Cech et al 2010;Strasser 2011;Weber & Entrop 2013). In addition, chilling also predisposes the affected plants to infection by certain low temperature loving fungi and bacteria and also insect infestation which often lead to development of dieback symptoms (Cambours et al 2005;Pukacki & Przyby 2005;La Spina et al 2013;PerezSierra et al 2013).…”