Phenological observations

On page 15 of volume II of this work, under the title ‘Phenology’, mention is made of several articles on this subject from the pen of the distinguished botanist Carlos Azevedo de Meneses. One of them, published in the former review Portugal Agrícola, was judged worth reproducing in these pages, and is transcribed here. ‘The little that is known about the phenology of Madeira is owed to the observations of Dr Oswald Heer, made in 1850 and 1851, and to those we have been making on this island since 1902. The observations for the period from September 1902 to early April 1905 were published in a French botanical review. Today our task is limited to presenting the data gathered after that date, with the aim of shedding a little more light on the phenological behaviour of various tree species introduced into the island that thrive in our climate. Of the four species mentioned in the Instructions of Hoffmann–Ihne, only the oak (Quercus pedunculata) is common in Funchal and its surroundings. It stands out from all the other species we have had the opportunity to observe for the truly extraordinary earliness of its leafing.

Of the many oaks planted on the left bank of the Ribeira de São João, two came into bud on 3 December 1905. By the 23rd of the same month two-thirds of these oaks had new leaves, and many of them were already fairly well in leaf. By the end of January of the following year every specimen grown in Funchal had leaves, but they did not become fully green until the first fortnight of March.

We saw the first yellow leaves on 16 September. Once yellow, the leaves remain on the trees and fall only very late, when the new leafing is already well advanced. In the parish (freguesia) of Monte (‘hill’), which lies at an altitude of 600 metres, the oaks did not begin to leaf until 15 January, that is, 43 days later than in Funchal.

Of the horse chestnut (Æsculus Hippocastanum), also mentioned in Hoffmann–Ihne’s Instrucções, we were able to observe only two specimens planted in Funchal. The leaves began to lose their colour on 3 September, and the first new leaves appeared on 12 March. The flowers began to appear in the first eight days of April. In Platanus occidentalis, Vitis vinifera and V. Labrusca, leaf colouring set in on 14, 15 and 21 September respectively, and budding took place on 24, 22 and 20 February of the current year. The leafing of the plane trees began in the parish (freguesia) of Monte on 6 March, that is, 12 days later than in Funchal. The leaves of the plane trees also stayed on the trees for a long time after turning yellow, but they always fall before the new leafing begins.

In Robinia Pseudo acacia leaf colouring began on 15 October, in Tilia argentea on the 18th of the same month and in Ficus Carica on 2 November; the leafing of these same trees began on 27 January, 12 March and 24 January respectively. All these observations refer to Funchal; in Monte the budding of the species mentioned took place on 19 February, 19 March and between 21 and 25 February.

On the cherimoya trees (anoneira) (Anona cherimolia) of Funchal, the first yellow leaves appeared on 14 February of the current year and the first new leaves on 9 April. The chestnut trees of Monte budded on 20 April and the walnut trees between 30 April and 5 May.

We were unable to gather precise data on when the leaves of the trees change colour in the surroundings of Funchal, but we have noticed more than once that this colouring comes later the higher the spot where the trees stand.

From the above, then, it can be seen that the length of winter dormancy in the period covered by our latest observations was 163 days for the plane, 160 for the vine, 152 for the Labrusca vine, 170 for the horse chestnut, 78 for the oak, 104 for the robinia, 145 for the lime, 83 for the fig and 54 for the cherimoya tree. For the period from 1903 to 1905 we found the following mean figures for the winter dormancy of the same species: plane 168 days, vine 162, Labrusca vine 156, horse chestnut 192, oak 123, robinia 112, lime 166, fig 125 and cherimoya tree 50.

According to the phenological notes published by Mr Adolpho Frederico Moller in the Boletim da Sociedade Broteriana, the mean length of winter dormancy in Coimbra, in the period from the end of 1903 to the beginning of 1905, was 140 days for the plane, 154 for the vine, 136 for the horse chestnut, 154 for the oak, 146 for the robinia and 156 for the lime. Comparing these figures with some of the earlier ones, one concludes that the robinia and the oak rest longer in Coimbra than in Funchal, whereas the reverse is true of the other species.

It may seem surprising at first sight that certain species at the latitude of Madeira should have a longer dormancy, and consequently shorter periods of vegetative activity, than in more northerly countries. Yet the case is in no way abnormal and is easily explained, as we shall see.

In the first place, rainfall is not distributed in Coimbra in the same way as in Funchal. While that city records on average 79 millimetres of rain during the summer months, Funchal records only 16.9. The mean rainfall measured by the rain gauge of the Coimbra observatory is 19.4 millimetres in July and 15.3 millimetres in August, whereas in Funchal it is 1.1 and 2.4 millimetres respectively. In that mainland city there are 21.5 days of rain during the summer months; in Funchal, only 4.2.

Since prolonged droughts during the hottest season of the year are therefore one of the characteristics of the climate of Funchal, and since they must bring about an early suspension of the plants’ vital activity, it is clear that leaf fall must occur here sooner than in Coimbra, and all the earlier the more sensitive the trees are to drought.

This, then, is one of the causes of the long periods of dormancy recorded in Madeira. The other lies in a peculiarity of certain trees cultivated here: they begin to bud only after receiving a sum of temperature considerably greater than that which brings them into growth in their countries of origin.

This late budding, in which A. de Candolle wished to see an adaptation of the trees to the climate and A. Grisebach the survival of habits ingrained in the species, is not, however, observed in all species. The oak, for example, seems to be an exception to the rule, and an exception all the more surprising given that it also occurs at the island’s middle altitudes.

It should be noted, however, that although the budding of the oak begins extraordinarily early in Madeira, general leafing is completed only after a fairly long interval, as we showed at the beginning of this article. This seems to indicate a certain tendency in the species, caused by hereditary habits, to resist the influence of normal leafing temperatures.

From September onwards, many premature shoots frequently appear both on the trunks of oaks and on vine canes. As these shoots are not accompanied by a general swelling of the buds, they must not be mistaken for the start of the new leafing.

Comparing the data gathered from 1903 to 1905 with those from our own observations of 1905 to 1906, we find that in the latter period many trees in Funchal budded considerably earlier, the advance being greater in the oak than in the other species. As humidity is one of the factors of periodicity, and as rainfall was extremely abundant in the last months of 1905, unlike in previous years, it may be presumed that this was the reason why these trees came into growth earlier.’

The botanical journal referred to above is the ‘Bulletin de l'Academie Intern. de Geogr. Botanique du Mans’, nos 189 and 190 of 1905.