Vegetational Changes in the California Annual Type

The objectives of the study were to describe fluctuations in the California annual type that occur within a growing season and from one year to the next. These are given for three sites. Other changes that are related to mulch manipulation, grazing, and tire are discussed. Not only does this type of information have value in itself but it also has value in the interpretatiori of studies on the management of the vegetation for forage production. If sampling can be done at one time only, vegetational changes during the growing season necessitate that the sampling date be selected carefully. Otherwise, seasonal differences may be unknowingly confounded with those due to other causes. That the annual-type vegetation differs greatly in any given place from one year to another is well known. Annual vegetation also changes with season and the pattern may differ from one site to another. The three types of changes are superimposed and must be determined before the effect of manipulation can be accurately evaluated. The magnitude of these changes was measured inl terms of number of plants per unit of area on plots located on the Hopland Field Station in Mendocino County. The results, therefore, are from a restricted area and are presented as such. They are not offered as norms to describe the "average California annual type." However, the principles found are in essential agreement with the work of others. Together they may be interpreted as giving the basic sequences and (lirections of change. It is assumed that these sequences are not fortuitous and that they would show a significant relation to those of other areas and years despite diversities between individual situations. The term "California annual type" is used in this paper to denote that vegetation in California which is composed primarily of annuals. The type is a mixture of many species of grasses and broadleaved herbs, and species that are native and introduced. Although many perennial species are present, individual perennial plants are scarce. The type is located below the 4,000 foot level in the Central Valley and intermittently in the Coast Ranges. It is the understory in the open areas of oak-woodland and to some extent in the chaparral types. Actually the type is a very broad one. It contains many sub-types which can be delineated by species composition or other characteristics, and related to the differences in soil and climate. The term "vegetation" is used to signify a group of individual plants growing together. The size of area and complexity of the group is indicated only by the context in which the term appears. The term "vegetational change" is used to specify changes over time in the number of plants per unit of area or in relative species composition on a percentage basis. Sincere appreciation is extended to members of the Faculty Seminar in Ecology at the University of California who offered many helpful suggestions during discussions of this paper.