Nature's Timings
Richard reviews recent research
A number of interesting scientific papers about phenology have been published in recent months. They consider potential consequences of species responding to climate change...
‘As nature’s calendar responds to climate change we anticipate problems for life cycles loss of synchrony and changes in competitive advantage between species’, says Richard Smithers, the Woodland Trust’s UK conservation adviser.
‘Examples are the vulnerability of early frogspawn to sporadic late frosts, scope for butterflies to emerge before caterpillar food-plants are sufficiently well-grown as insects react to warmer temperatures quicker than plants, and substantial differences in when oak and ash are coming into leaf’.
Creation of two races
An American study of the goldenrod gall fly, published in the ‘Journal of Evolutionary Biology’, considered whether phenology limits its choice of plants for egg-laying.
Researchers found that the fly lays most eggs on middle-aged plants of its usual host, early goldenrod, and on young plants of its alternative host, Canadian goldenrod.
They suggest this may provide opportunity for natural selection to create two distinct races of the fly.
Trees in France
In ‘Agricultural and Forest Meteorology’, a French team compared the sensitivity to temperature of trees coming into leaf within and between species (silver fir, sycamore, hornbeam, beech, ash, holly and sessile oak).
The timing of first leaf was monitored over two years along two altitudinal gradients in the Pyrenees and over 22 years in Fontainebleau forest (just south of Paris).
All species came into leaf earlier with decreasing altitude, ranging from 11 to 34 days per 1000m for beech and oak respectively.
‘In keeping with results reported for Nature’s Calendar in the UK’, says Richard Smithers, ‘they also found that, although some trees are coming into leaf substantially earlier than in 1976, there is considerable variation between species with oak being the most, and beech the least, sensitive to temperature’.
Results from the Pyrenees and Fontainebleau were very similar and led the researchers to conclude that such responses to climate change might be consistent, in spite of species being locally adapted.
Leafing in America
A model has been used to predict and compare the rate at which 22 North American tree species come into leaf in the 20th and 21st centuries, published in ‘Global Change Biology’.
The model suggests almost all will be affected by climate change, with leaves appearing five to nine days earlier, on average.
The model also suggests that this response might be even faster but for lack of sufficient chilling to break dormancy, which could even lead to abnormal budburst in some years.
They predict that early-leafing trees will respond more quickly to rising temperatures than those that come into leaf later in the season.
Yo-yoing up 
‘Most researchers have been focused on how species will respond to the general trend for increasing temperatures’, says Richard, ‘but there is increasing appreciation that, as our climate changes, it may also become more variable and that extreme weather events may have particularly important consequences’.
German researchers reporting on an experiment in ‘Global Change Biology’ have identified that severe drought and heavy rain may both cause changes in the timing of flowering in grassland and heathland species as great as ten years of gradual warming.
All these studies highlight the importance of getting a better grasp of what is happening to nature’s calendar and we will be publishing further analyses of all the valuable data that you have recorded over the months and years to come.