Phenology

Phenology (or phaenology) is the study of the dates on which seasonal plants alter their appearance (and also of dates on which insects, birds and other animals come into view). The dates vary: by place according to the climate and in time according to the vagaries of the weather. Phenology is obviously of interest to the succession gardener, since it concerns itself with the broad structure of succession, not only of garden plants but also of weeds and dominant tree species. A reading list dealing with phenology topics is a good way to get familiar with the topic.
In Germany, phenology - like most other hobbies - has even developed its own government budget, bureaucracy, periodicals, academic departments, vocational training programmes and textbooks and has thus ceased to be something shared and enjoyed by ordinary folk. News media attention in Japan to the cherry-blossom front is an example of phenology as public enjoyment. In English-speaking lands, phenology continues to be best known as a hierarchy-free hobby, practised for the sheer joy of observing, though it is also a part of the science of agricultural metereology.
The German Weather Service phenological calendar and the Wikipedia article on the topic demonstrate the systematized German approach, with a strict categorization (drawn up back in 1955) of the whole year as follows:

• Pre-spring (end of February and start of March): Galanthus nivalis flowers appear; flowering of Corylus avellana and Alnus glutinosa; peaking of Jasminum nudifolium; flowering of Salix caprea signals the end of the phase.
• Early spring: blossoms of Forsythia suspensa, Ribes uva-crispa, R. nigrum and R. rubrum, followed by Prunus avium, P. domestica, P. spinosa, Pyrus, and some species of Acer on leafless branches; the greening of lawns and fields; appearance of leaves on Aesculus hippocastanum and Betula pendula, followed a week later by slow-to-show leaves of Fagus sylvatica, Tilia cordata und Acer.
• Full-on spring: blossoms of Malus and Syringa x chinensis, later of Rubus idaeus; leaves of Quercus robur, which is among the last deciduous trees to turn green.
• Early summer (June): flowers of grasses including Alopecurus pratensis, of Sambucus nigra, Crataegus monogyna and Aruncus dioicus, and of Papaver orientale.
• Mid-summer: flowers of Tilia platyphyllos and Cichorium intybus; fruit of Ribes rubrum.
• Late summer: this phase is reckoned to begin when the first flowers of Calluna vulgaris appear; ripening of fruits of some varieties of Malus domestica and Prunus domestica, Amelanchier and Sorbus aucuparia; flowering of Anemone japonica.
• Early autumn: flowering of Colchicum autumnale; ripening of fruit of Sambucus nigra, Corylus avellana and Pyrus domestica.
• Mid-autumn: ripening of the fruits of Quercus robur, Aesculus hippocastanum and Juglans regia; leaves of Aesculum hippocastanum, Fagus sylvatica, Quercus, Fraxinus excelsior and Parthenocissus quinquefolia take on autumn colours, while orchard trees lose leaves.
• Late autumn: leaves change colour on Quercus robur and Aesculus hippocastanum, beginning a phase reckoned to last into mid-November.
• Winter: said to begin when the leaves of Quercus robur fall and the needles of Larix deciduaare shed.

Curiously, the Germans have also elaborated a "succession of aspects" which attempts to offer a more rounded ecological approach. "Aspects" are a further example of German scientists' attempts to systematize their observations in the light of late 20th century interest in ecology. The textbook writers have assembled their phenological observations into what they consider to be distinguishable stages in the development of a typical ecosystem. They record data about the plants as communities, often adding in data about the insects and other arthropods that feed on and breed in the plants. Aspects also place more emphasis than phenology does on the dull times of the year, when there are fewer or no garden blooms. The outcome of all this academic data-crunching is a canonical list of six stages in the annual life-cycle of plants and insects in the northern temperate zone of the Earth (just outside the windows of all those German, Austrian and Swiss scientists). Here is the list:

• Hiemal or winter aspect: From November to March, when many plants and insects are dormant, and there is a thick, intact layer of leaf litter on the ground.
• Prevernal aspect: corresponds to phenology's early spring, usually March and April, when early blossoms appear, but main trees are not yet in leaf, and the first arthropods on and in the ground become active.
• Vernal aspect: corresponds to spring, from the start of May to mid-June; a period when leaves return to deciduous trees, evergreens grow new leaves or needles, and birds and insects reproduce.
• Aestival aspect: corresponds to the mid-summer, from mid-June to mid-July, when plants and animals grow fastest.
• Serotinal aspect: the late summer from mid-July to mid-September, when leaves of deciduous trees visibly age and darken, and large populations of insects and migratory birds are evident.
• Autumnal aspect: from September to mid-October, when leaves begin to fall and populations of arthropods in leaf litter soar.

This is one of those curious examples in which a textbook-style prescription seems to remove the fun from one of life's little pleasures, and also divides us all into those who have learned the "proper" way and the merely ignorant.
There are two phenological gardens in close proximity, at Wulfsdorf and Quickborn, and I'll report on them when I have had a chance to visit them.