Further Observations on the Effects of Excluding Rabbits from Grassland A in East Anglian Breckland: The Pattern of Change and Factors Affecting it (1936-73)
On release in 1936 from intensive grazing by rabbits the biotic potential of Grassland A emerges over 38 yr in a sequence of physiognomic dominants (Festuca ovina, Hieracium pilosella, Thymus drucei), and the entry of 17 spp. additional to the original 11 in the permanent plot. The relationships of the dominants to each other, to the subordinate species and of both to weather factors is discussed and used in the interpretation of the phenomena of change. [The following species were studied: Catapodium rigidum, Galium parisiense, Minuartia hybrida, Agrostis, Cerastium semidecandrum, Senecio jacobaea, Acinos arvensis, Arenaria serpyllifolia, Festuca ovina, Koeleria cristata, Taraxacum, Cirsium vulgare, Erigeron acer, Crepis capillaris, Hieracium pilosella, Botrychium lunaria, Luzula campestris, Zerna erecta, Leontodon taraxacoides, Linum catharticum, Thymus drucei, Carlina vulgaris, Plantago lanceolata, Erophila verna, Centaurium minus, Sagina nodosa, Astragalus danicus, Lotus corniculatus.] Changes in the abundance of species are compared with meteorological data for ground frost (Dec. to March), frost-heaving and rainfall (Sept., Oct., Nov.), and with data for germination (May and June) and for survival in spring, all factors that were important during charting of the plot at all times of the year from 1961 to 1969, and now applied to the interpretation of the graphs for the whole period 1936-73. Of similar significance is the competitive power of the dominants, in which emphasis is placed on population structure and behavior. Based on the relative importance of the weather factors and period of physiognomic dominance a sequence of the following 4 regimes is recognized and analyzed: Festuca, Hieracium, Interregnum, and Thymus.