Starting dates and basic temperatures in phenological observations of plants

Abstract

Several methods have been used in plant phenology to find the best starting date in spring and the best threshold or basic temperature for growth and development of perennial plants. In the present paper the date giving the highest correlation coefficient for development to various phenophases, in relation to 24-hourly mean air temperatures was chosen as the best starting value in further analyses. For many woody plants this date was very often found to be 1 April based on phenological and climatological observations at about 60 sites in western Norway (at about 61°N). The early flowering species Corylus avellana and Salix caprea and the early leaf-bud breaking Prunus padus seemed to start development earlier in Spring, while the late sprouting Fraxinus excelsior showed the highest correlation coefficient using 15 April. If daytime temperatures were used in the calculations, the "best" starting date was generally found to be later than for the 24-hour mean temperatures. This variation must be seen as resulting from the different basic temperatures for the development of various species. Estimates of basic temperatures in various species and periods may be given, for example by finding the value having the least variance in heat sums or by various regression analyses. A technique has been developed to minimise the influence of significance of correlation, using the intercept with the temperature axis by merging the two least squares rectilinear regression lines that can be found between plant development and mean air temperature (from the estimated best starting date) at r=+1 or -1. The basic temperature seemed to vary from -5.9°C for leaf-bud break of P. padus to 5.5°C for leaf-bud break of F. excelsior, with basic temperatures of several other woody plants having intermediate values. These values are compared with those found by other methods.& k w d : Key words Phenology · Starting date · Threshold temperature · Basic temperature · Woody plants& b d y :Prepared in conjunction with a presentation made at the ISB

Using phenology to assess urban heat islands in tropical and temperate regions

“…Therefore, we also found slightly stronger correlations with mean nighttime temperature than with mean temperature (exception > 50% leaves unfolded) and no statistically significant correlation with maximum temperature. This is in accordance with Wielgolaski (1999) and Mimet et al (2009) 38 37 37 37 37 37 37 ui, urban index; T m , mean temperature; T night , mean nighttime temperature; T max , maximum temperature; DTR, diurnal temperature range; RH, relative humidity; a, absolute humidity, in March (=3), August (=8) and September (=9); BBCH 61, beginning of flowering; BBCH 65, full flowering; BBCH 10, mouse-ear stage; BBCH 15, >50% of leaves unfolded; n, number of sites; P , significance, bold values: significant coefficients at the 5% level; bold and italic values: significant coefficients at the 10% level.…”

Spatial structure of the 8200 cal yr BP event in northern Europe

“…The tree taxa that show strong responses to the 8200 cal yr BP event, Alnus, Corylus, and Ulmus, start flowering in early spring, in central Europe often in February-March and in southern and central Fennoscandia in March-April (Jäger et al, 1996;Kasprzyk et al, 2004). The start of their flowering and plant development is in general dependent on air temperature (Wielgolaski, 1999;Aasa et al, 2004) and if an abrupt change to cold winters and cold (Hammarlund et al, 2003Seppä et al, 2005), Rouge , and Tibetanus (Hammarlund et al, 2002). See Fig.…”

Spring phenology of European beech (Fagus sylvatica L.) in a submountain beech stand with different stocking in 1995-2004

“…On the basis of this fact we calculated temperature sums from 1 February to the onset of BB. The threshold temperature value has not been unified (Murray et al 1989;VonWuehlisch et al 1995;Wielgolaski 1999). We used the values of 0°C, 5°C, 8°C and 10°C for this purpose.…”