Leaf fall and strandings at Southend

November 27, 2006. After a windy week and previous night Chalkwell beach showed a gravel ridge formed in front of a strandline of algae and diverse deciduous leaves. They included a greenish yellow leaf of the Hawthorne Crataegus monogyna Jacquin, shed by one tree in my garden from November 14 to 18 this year, and from the same tree in 1997 from November 7 to 16. Smaller Hawthorn trees and hedges still retained many yellow leaves today and in previous years (1996 and 2005) they only started to fall on December 1st and had gone within a week. Static floatation tests on the December 2000 insitu and fallen Hawthorne leaves yielded average times of 0.6 and 0.7 days, little more than one tidal cycle duration and a maximum time in a sample of 59 of 2.40 days. In the rough sea environment there is probably a long enough flotation time for these and many other deciduous leaves to cross the Thames from the opposite Kent coast (6 km) when the wind is from that southerly direction. However Oak and some evergreen leaves (i.e. Holly, Ivy) can float for over a week in tests and can come from a greater distance down the River Thames and other estuaries before being sunk or stranded. These leaves are seen in smaller numbers on strandlines throughout the year, usually after rain and in the case of evergreens, probably because of dumping of garden waste in the Thames.

A diverse leaf assemblage was studied at Chalkwell on November 28 2003 by collecting a mass of stranded algae and picking all the leaves out of it. The 57 leaves included 14 oak (12 Quercus robur L. and 2 of the local forest species Q. petraea (Mattuschka) and 30 serrated elongated leaves which may have included the other local forest tree Hornbeam Carpinus betulus L. In addition, there were 3 leaves of Poplar (Populus) which probably came from a tree near the beach, 2 or 3 Maple (Acer campestre L. and single leaves of Willow (Salix) and Horsechesnut (Aesculus). These three are common ornamental and street trees in Southend-on-Sea but seemed unlikely to have been blown into the sea from these more distant trees by the gentle south and west winds developed on the night of November 27/28 2003. Maple, Horsechesnut and a Sycamore (or Plane Tree?) leaves were observed in the strandline today and seem unlikely to have come directly from the land into stronger onshore wind.

The question of whether these leaf fall and stranding observations illuminate global warming is problematical since the botany textbooks relate the change in colour and strength of the leaves to reduced day length not temperature (i.e. via the plant hormone auxin). Looking at the common Southend street trees today (Aescules) there was evidence of still green leaves on branches of otherwise bare trees adjacent to streetlights. On the other hand, there were many entirely bare trees situated beside the lights and some retaining some leaves further away. None of the trees, except those suffering from a new disease in Horsechesnut had lost leaves on November 4, although many were partly yellow and brown by that date. Probably temperature and previous dehydration has an effect additional to that due to day length, but it is difficult to make general observations.