During the summer of 2006, many places in the UK experienced some of their highest temperatures ever recorded. July brought Central England its warmest monthly mean temperature since 1659. It gave Wales a new record with a temperature of 34.2ºC being recorded at Penhow near Newport. Scotland too, experienced its hottest month on record with a mean temperature of 15.6ºC (mean temperatures are derived from daily readings that span 09.00 - 09.00). Wisley in Surrey had the highest July figure anywhere in the UK at 36.5ºC. For a while, it was predicted that we could experience the highest temperature ever recorded in the UK. But it was not to be; that record still stands at 38.5ºC, reported in Faversham, Kent on 10th August 2003. July also heralded England’s sunniest month on record (301.5 hours), beating the previous record of 284 hours in June 1957. The exceptionally dry conditions of many areas aggravated the situation and added further pressure on turf managers, especially on those affected by the water restrictions.
Climate change or not?
In general, the south of the Country enjoyed weather that was more reminiscent of the Mediterranean region and, understandably, the abnormal temperatures and dryness stimulated a lot of speculation about climate change. A consequence of
global warming? An indication of what to expect in future summers? Or, a one- off phenomenon unlikely to be repeated in our lifetime? We might never experience such a summer again. On the other hand, it may be repeated during 2007. It may get even hotter! If hotter, drier summers are to become the norm, we must become more aware of the potential impact that drought and high temperatures have on the health and development of grasses and their communities. After all, the unusually high temperatures and prolonged period of heat that some counties experienced during the summer of 2006 were enough to cause substantial heat stress to cool-season turfgrasses.
Turfgrass Adaptations
Turfgrass species that grow throughout northern Europe are termed cool- season turfgrasses; as opposed to warm- season species that are adapted to sub- tropical and tropical climates, e.g., Bermudagrass, Zoysiagrass, Seashore Paspalum, St. Augustinegrass, Kikuyugrass, etc.
The optimum temperature range for cool-season turfgrass shoot growth is 15º to 24ºC and 10º to 18ºC for root growth. As temperatures drop below or rise above this range the plants will experience some stress. As might be expected, cool-season species are generally more tolerant of lower temperatures than they are of higher ones. Warm-season turfgrasses, in contrast, are well adapted to higher temperatures
but
far less tolerant of lower temperatures. The optimum temperature range for warm-season turfgrass shoot growth is 27º to 35ºC, and 24º to 29ºC for root growth. Problems of low temperature stress pertain more to warm-season species; whereas heat stress is of greater concern when managing cool-season species.
Drought resistance is not heat resistance
Some turf managers hold the incorrect belief that turfgrass species with good drought tolerance will inherently survive hot summer months. Whilst there is, to a degree, a correlation between drought resistance and heat resistance, the two terms are not synonymous. There are droughty environments
that are never subjected to heat stress. For example, mountainous districts with shallow soils may regularly experience drought conditions but rarely, if ever, encounter high temperatures. Similarly, coastal locations may be droughty but temperatures are constantly moderated by cooling sea breezes. Some species adapted to such ecosystems have not evolved to withstand high temperatures and can be prone to severe injury when cultivated in situations where high temperatures are commonplace. A number of fine-leaved fescues fall into this category (see Table 1). The inability to withstand heat stress is compounded where close mowing and excessive wear occurs.
High Temperature Stress
Heat stress in cool-season grasses occurs
typically at
Global warming is a ‘hot topic’ in more senses than one. Here, Martyn Jones, Secretary, British Turf & Landscape Irrigation Association, and Trustee, National Turfgrass Foundation, considers the possible implications that rising temperatures could have on turfgrass management in the UK.
WHEN THE
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