The sampling of aquatic vegetation

Interest in the description of aquatic vegetation in Britain began with Tansley (1911), though he willingly admitted to having insufficient data for anything like a systematic scheme of classification. What Types of British Vegetation contains is, in fact, an outline of a few distinctive assemblages of aquatic species grouped by growth form and characteristic of broadly contrasting types of fresh waters, moving and still, the accounts relating for the most part to a small number of particular sites. Especially prominent was the contribution of Pallis (1911) on the aquatics of the Norfolk broads and rivers, in whose account an interest in the hydroserai succession is very prominent.

There are more data on aquatic vegetation in Tansley (1939), assembled from a variety of studies in the intervening years, some on river vegetation (Butcher 1927, 1933) but mostly on ponds and lakes (Walker 1905, Matthews 1914, Godwin 1923), with Esthwaite and other Cumbrian lakes (Pearsall 1918, 1921) now being added to Broadland as classic sites for description of aquatic assemblages, swamps and fens. Among these various accounts, the definition of vegetation types is uneven. Sometimes, there are simply lists of species associated with particular conditions of water depth, quality and speed of movement or substrate character, usually with a DAFOR rating (dominant, abundant, frequent, occasional, rare) to denote relative abundance. In other cases, assemblages are more precisely defined as associes or consocies with dominance playing a large part in distinguishing the more species-poor vegetation types. Again, there is a strong preoccupation with the dynamics of succession.

Since these accounts were published, more phytosociological descriptions of aquatic communities have been very few. In some cases, aquatic vegetation has been sampled and characterised as part of a comprehensive survey of particular areas, like Skye (Birks 1973), where it makes but a minor contribution, and only in Spence (1964) and the work of the Macaulay Institute, as it then was (Birse & Robertson 1976, Birse 1980, 1984), has there been any attempt at more extensive data collection and definition of communities, less strictly phytosociological in the former, more so in the latter.