Tansley Review No. 114

Abstract

A cyclic behaviour in the intensity of maritime conditions which varies with the periodic behaviour of the North Atlantic oscillation has recently become apparent in the climatic record of northern Europe. Periodic increases in oceanicity are usually viewed as having a positive effect on plant survival, as milder winters, reduction of temperature extremes, low risk of exposure to frost, and freedom from drought reduce many aspects of environmental stress. However, warmer winters in maritime environments may also have a powerful influence in creating habitats that are unfavourable for many species. The dangers of long periods of soil saturation for overwintering plants, soaking injury to germinating seeds, premature bud burst in spring, depression of treelines by increased cloud cover and high lapse rates, as well as the constant leaching of soils, are all negative aspects of the maritime environment. Woody species in which root dormancy is delayed by mild winters are particularly vulnerable to the consequences of winter flooding. Subsequent re-exposure to oxygen as water tables fall in spring can aggravate flooding damage through post-anoxic injury, leading to severe dieback of anchoring roots. Soil leaching, particularly after human disturbance, can induce nutrient deficiencies and the establishment of oligotrophic communities with reduced productivity. Podzolization and iron pan formation have in the past facilitated the processes of paludification in oceanic regions. The resulting spread of bogs and acid moorlands can further reduce the potential for productivity in both agriculture and natural plant communities. Given the probability that current climatic trends may increase the degree of oceanicity in western and northern regions of Europe, the potentially negative consequences of such a climatic change need to be considered in relation to future ecological changes and their consequences for conservation and land use.

Dendroclimatic relationships and possible implications for mountain birch and Scots pine at treeline in northern Sweden through the 21st centuryThis article is a contribution to the series Tree recruitment, growth, and distribution at the circumpolar forest–tundra transition.

“…The negative response of Scots pine to summer precipitation at three of our study sites also corresponds with previous work (Gunnarson and Linderholm 2002;Linderholm and Chen 2005). Crawford (2000) speculated that anoxic conditions developing in the soil due to excessive snowmelt and precipitation might account for the negative response of pine growth to summer precipitation. Kullman and Kjällgren's (2006) prediction that pines would overtake birch due to an increasingly continental climate is only partially supported on the basis of climatering width relationships presented here and published by others.…”

Climate, changing phenology, and other life history traits: Nonlinearity and match–mismatch to the environment

“…Surprisingly, milder winters may sometimes lead to more frost damage, as not all parts of the plants are equally prone to freezing, and reduced snow cover during mild winters may result in more exposure. For example, mild periods in winter may generate premature spring growth and cause severe dieback of nonhardy shoots (24). During years with lower snow accumulation, an early-blooming herbaceous perennial (Delphinium nelsonii) experienced colder temperatures between the period of snowmelt and flowering (25).…”

Record-low primary productivity and high plant damage in the Nordic Arctic Region in 2012 caused by multiple weather events and pest outbreaks

“…Several recent anomalous events of biogenic, physical and anthropogenic origin have been documented from the NAR. Increasing precipitation rates, and accordingly paludification, have been suggested as drivers of vegetation change in maritime regions (Crawford 2000). Events of long-distance dispersed air pollution from sources in Central Europe have shown to reduce ecosystem health within the NAR recently (Potter et al 2007, Karlsson et al 2013.…”

“…From this perspective, it is highly uncertain whether the ongoing greening trends of high-latitude continental areas in the Arctic will persist, unless the effects of increasing summer temperatures and northward migration of more thermophilous plants with higher leaf area become so strong that this will mask the stress effects of anomalous weather events and pest outbreaks. For warmer continental and oceanic regions north of the Arctic Circle where primary productivity is less dependent on summer temperatures (Xu et al 2013; see also figure 3(b)), the predicted increase in frequency of extreme climatic events (Jentsch et al 2007, Smith 2011, Stocker et al 2013 may cause a shift from stable to browning trends (Crawford 2000). There is therefore immediate need for more attention to the role of steadily increasing weather events and climate changeinduced pest outbreaks in regulating productivity and ecosystem change in the Arctic.…”