Does Defoliation Affect Reproductive Output in Herbaceous Perennials and Woody Plants in Different Ways?

After defoliation, plants may compensate for loss of tissue (Crawley 1983, 1988; Hendrix 1988). However, there appears to be considerable variation in the extent and nature of this response, and some species do not respond at all (Belski 1986; Verkaar 1988). A number of compensating mechanisms may be proposed. For example, any resulting increase in the sink demand of the plant may be met by an increase in the photosynthetic rates of the tissues (Gifford & Evans 1981; Mooney & Chiariello 1984; Watson & Casper 1984; Garnier 1991). Similarly, compensation might include allocation to sexual reproduction (Crawley 1983; Paige & Whitham 1987; Hendrix 1988; and the compensation hypothesis of Tuomi, Hakala & Haukioja 1983). However, growth and reproduction often compete, and there may be trade-offs between vegetative and reproductive growth (Waller 1988; Lovett-Doust 1989). Further, the cost of reproduction has two major components: cost paid in survival and cost paid in future reproduction. The trade-off between reproductive investment and both these costs will govern the compensatory response, but unfortunately, few studies consider long-term costs. Despite the costs, after considerable leaf damage, some herbaceous perennials show a short-term compensation for reproduction. In this paper, I review the available information concerning reproductive output after leaf removal, and discuss possible underlying mechanisms that may affect the variation in the responses observed.