Growth dynamics of endemic Dracaena cinnabari Balf. f. of Socotra Island suggest essential elements for a conservation strategy

Abstract

Dragon’s blood tree, a flagship endemic species of Socotra, is threatened with extinction due to lack of natural regeneration, likely because of goat herbivory and/or climatic factors. Loss of dragon’s blood tree would result in loss of other native flora, heightening the importance of formulating a conservation strategy for it. Although artificial afforestation might be used to offset the lack of natural regeneration, it would have to overcome the same threats faced by naturally occurring seedlings. Moreover, there is no published information on the growth dynamics of seedlings in plantations in situ on Socotra. To fill this information gap, we compared seedling growth (total plant height, leaves number, stem height, stem diameter) over an 8-year period after planting at three sites that differed in the degree to which goats were excluded and in whether they were watered regularly over the period. In addition to developing a new classification of the growth stages, which will enable better tracking of population dynamics, we found that continuous goat exclusion was necessary to prevent seedling mortality. Also, although seedling growth overall was slow, growth parameters of regularly irrigated seedlings ranged from 156% to 446% of those not regularly watered, suggesting that this treatment can speed seedlings’ escape from goat browsing. For the dragon’s blood tree and likely for other taxa within this group, extremely slow growth and long generation times suggest that conservation and restoration efforts will require a commitment to active management that will last decades, rather than a short-term approach.