Quantitative characterization of the thorn system of the common shrubs Sarcopoterium spinosum and Calicotome villosa

Abstract

Thorny, spiny, and prickly plants including annuals, hemicryptophytes, shrubs, and trees dominate many habitats in the Near East, as the outcome of a long history of large-scale grazing. This study focuses on the quantitative aspect of the number of thorns per plant and per unit ecosystem area. Specifically, we quantitatively characterized the thorn system of two common shrub species, the low and compact Sarcopoterium spinosum and the taller and less compact Calicotome villosa. For each species we sampled 25 plants of various sizes, in each of two populations (for a total of 50 plants of each species). Large S. spinosum shrubs covering an area of more than 0.5 m² had ca. 9,700-19,000 thorns per plant. We found that in S. spinosum there were more thorns per unit plant area on average in the grazed population (26,000 per m²) than in the non-grazed population (16,228 per m²). This, if repeated in additional populations and ecologies may serve as an indication that, thorns in S. spinosum, as well as in other taxa, may increase in number as an induced defense response to browsing. In C. villosa, large shrubs taller than 1.0 m had ca. 900-22,500 thorns per plant. The average thorn density per m² was 6,290 in one population and 10,950 in the other.

Keywords:

• Calicotome villosa
• defense
• herbivory
• Sarcopoterium spinosum
• thorns