J. Corbera, L. Faidella, M. Guardiola, M. Jover, M. Llobet, E. March i F. Sabater. L’aloc (Vitex agnus-castus) al Maresme: distribució, abundància i amenaces a la seva conservació
L'Atzavara, 15: 175-182

The chasteberry (Vitex agnus-castus) in the Maresme: distribution, abundance and threats on its conservation.

Between 2003 and 2005, more than 70 km of streams of the Maresme (eastern Catalonia) were studied. The study was conducted from June to October, corresponding to the flowering period of the chasteberry (Vitex agnus-castus), in 59 streams belonging to 22 hydrographical basins. Along sections of 25-m, we characterized stream morphology, type and conservation state of vegetation, as well as presence and abundance of the chasteberry and threats to this shrub. A total of 2986 sections were studied. The chasteberry was present in 17.8% of the sections, and had been introduced in other 8.5% of them. The presence of the chasteberry (measured as a percentage in the studied sections of each stream) varied from 0% to 72.7%. Streams with higher abundances were: the Can Cabanyes Torrent (72.7%) and the Ameia Creek (64.6%) in Argentona, the Can Solé Torrent (57.4%) and the Salamandra Torrent (52.2%) in Mataró, the Teixoneres Gully (54.6%) in Canet, and the Sant Ou Torrent (50.0%) in Tordera. The distribution of the chasteberry density (measured as percentage of metres occupied by this species for each section) for these six streams is presented. On the other hand, the chasteberry is threatened in more than 70% of the stream sections where it grows. The main threat, affecting 31.6% of the sections, is the presence of the giant reed (Arundo donax), an invasive alien species that reduces sunlight availability to the chasteberry, affecting its development. Big trees, present in 30.7% of the sections, affect the chasteberry in the same way than the giant reed. Periodic pruning affect the chasteberry more aggressively, but with a lower percentage (11.3% of sections). Because of the low abundance of the chasteberry in the Maresme and the high percentage of threatened populations, it is proposed that streams with a better degree of conservation become object of some kind of protection.

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