First Age-Estimation Model for Dracaena ombet and Dracaena draco subsp. caboverdeana

Research Highlights: The first model for crown age estimation was developed for Dracaena ombet Heuglin ex Kotschy and Peyr. and D. draco subsp. caboverdeana Marrero Rodr. and R. Almeida. Background and Objectives: Dracaena species are monocotyledon trees without annual tree rings. Most arborescent dragon tree species are endangered; thus, it is important to determine the age structures of these populations for proper conservation management strategies, and for modelling of population trends. For these reasons, it is necessary to develop a methodology of crown age estimation. Materials and Methods: Field data were collected in the Desa’a Forest (Ethiopia) and in Santo Antão (Cape Verde Islands). Trees within each age class, as expressed by the number of branch orders, were measured. The diameter at breast height, tree height, stem height, number of branch orders, number of all leaf rosettes and number of flowering leaf rosettes within the crown were recorded for each sampled tree. The flowering probabilities were counted as input data for the model used. Results: The duration of the interval between flowering events was 5.23 years for D. ombet and 4.94 years for D. draco subsp. caboverdeana. The crown of the oldest tree of D. ombet with 18 branch orders was estimated to be 94.2 years old, and the crown of the oldest tree of D. draco subsp. caboverdeana with 22 branch orders was estimated to be 108.6 years old.

Micropropagation to Conserve the Endangered Gabal Elba Dragon Tree (Dracaena ombet Heuglin ex Kotschy & Peyr)

Plant tissue culture offers opportunities for the rescue and conservation of endangered plant species. Here, we report the successful in vitro propagation of Dracaena ombet, an endangered plant. Several physical and chemical seed treatments were evaluated to develop a propagation approach. Germination of D. ombet seeds was monitored for 16 weeks by placing them onto Murashige and Skoog (MS) medium. Maximum seed germination (20%) was recorded when seeds were soaked-scarified, whereas all other treatments did not result in seed germination. Fragmented (longitudinally bisected) and intact in vitro shoots were cultured onto MS medium supplemented with various concentrations of 6-benzylaminopurine (BAP) and indole butyric acid (IBA) to induce axillary shoots. Longitudinal fragmentation of explants had a greater effect than the intact explants for shoot proliferation when cultured onto medium containing plant growth regulators. Fragmented shoots cultured onto MS medium supplemented with 2 mg·L−1 BAP and 0.5 mg·L−1 IBA treatment resulted in the highest amount of axillary shoots (seven shoots per explant). The intact shoots had the highest axillary shoots (1.8 shoots per explant) when cultured onto a medium supplemented with a combination of 1 mg·L−1 BAP and 0.5 mg·L−1 IBA. One hundred percent rooting was obtained using half strength MS medium supplemented with 0.5 or 1 mg·L−1 IBA. With full strength MS medium, a maximum rooting of 60% was obtained with 1 mg·L−1 IBA or naphthalene acetic acid (NAA) addition. The plantlets were acclimatized to ex vitro conditions with a 95% survival rate. This study offers a simple method for in vitro propagation of D. ombet, which is valuable to enable conservation of this endangered species.

Conservation status of the Endangered Nubian dragon tree Dracaena ombet in Gebel Elba National Park, Egypt

The Nubian dragon tree Dracaena ombet, which is categorized as Endangered on the IUCN Red List, is found on the highest slopes of Gebel Elba National Park in Egypt, with scattered populations in Sudan, Djibouti, Ethiopia and Somalia. The Gebel Elba population is threatened by drought. Surveys were conducted in the Park to assess the condition and document the distribution of the species to prepare a baseline for conservation efforts. Eight sites were surveyed during 2007–2009: trees were tagged and their locations were recorded using a global positioning system, and tree density, diameter at breast height and population status were estimated. Of 353 trees recorded only 46% (161 individuals) were alive and only 27% (96 individuals) were in a healthy condition. Only 1% (2 individuals) were young trees, indicating a low regeneration level. Field-based observations suggest that 80% of the D. ombet population in Gebel Elba may soon be extinct. A conservation action plan is needed for this flagship species in Egypt and throughout its range.