Sustainable Land Use Management Needed to Conserve the Dragon’s Blood Tree of Socotra Island, a Vulnerable Endemic Umbrella Species

Abstract

Unsustainable overgrazing is one of the most important threats to the endemic and endangered population of dragon’s blood tree (Dracaena cinnabari) on Socotra Island (Republic of Yemen). However, there is a lack of information about the exact population size and its conservation status. We estimated the population size of D. cinnabari using remote sensing data. The age structure was inferred using a relationship between crown projection area and the number of branch sections. The conservation importance of each sub-population was assessed using a specially developed index. Finally, the future population development (extinction time) was predicted using population matrices. The total population size estimated consists of 80,134 individuals with sub-populations varying from 14 to 32,196 individuals, with an extinction time ranging from 31 to 564 years. Community forestry controlled by a local certification system is suggested as a sustainable land management approach providing traditional and new benefits and enabling the reforestation of endemic tree species on Socotra Island.

Micro-Hotspots for Conservation: An Umbrella Tree Species for the Unique Socotran Reptile Fauna

“…This study demonstrated that D. cinnabari was a suitable habitat for half of the native reptile community of Socotra Island, but we could not disregard the occurrence of other unexplored endemic fauna living in the bark and canopy of the tree species. Although few trees have been proposed as umbrella species (however, see [19,25]), we supported the consideration of D. cinnabari as an umbrella species for vertebrates as well. This was due to its ecological, environmental, and evolutionary functions for the Socotra endemic reptiles, in addition to its historical economic and social role for local people that harvest D. cinnabari resin, which is an activity that could be sustainable if carefully regulated.…”

“…Although a significant part of the island was covered extensively with dragon's blood trees, their original range was reduced as a result of overgrazing and overmaturity (lack of natural regeneration and a large proportion of old and dead trees) [18]. Dracaena cinnabari meets the requirements for being considered an umbrella species [19] due to its size, shape, and distribution throughout Socotra, as well as its rarity and sensitivity to human disturbance [2]. Reptiles could be the target beneficiary taxon, as this tree was referred to as being occasionally used by some reptile species and the exclusive habitat of the Critically Endangered Hemidactylus dracaenacolus Rösler & Wranik, 1999 [11].…”

Local Management System of Dragon’s Blood Tree (Dracaena cinnabari Balf. f.) Resin in Firmihin Forest, Socotra Island, Yemen

“…Similarly, many authors have mentioned the lack of regeneration in dragon's blood tree forests and woodlands on Socotra [53,54]. Trees with heights of less than 2.9 m and diameters of less than 8 cm are absent, which supports the hypothesis of gradual extinction [9,16] over the hypothesis of sudden mass extinction [10]. There is a sufficient number of Dracaena trees available, with an average cover of 67 trees ha -1 .…”

“…According to Adolt et al [14], the mortality was less than 1% (0.82%), but this study showed four times higher mortality, reaching 3.41%. Additionally, a study published by Maděra et al [9] estimated that the mortality was less than 1%, which differed substantially with the age of the trees. Despite the long-term morphological, anatomical, and physiological adaptations of the DC trees to arid climate conditions [22,[28][29][30]32,55], the present tree populations do have an evidently unbalanced age structure with a largely disorganized woodland structure and a lack of natural regeneration [16].…”

“…Hubálková [12] and Habrová et al [16] published predictive models of the future development at selected localities based on a detailed description of the stand structure by Habrová and Maděra [56] and the original methodology of the DC crown age estimation by Adolt and Pavliš [10] and Adolt et al [13]. Authors have predicted that the DC abundance will decrease by 36%, according to Hubálková [12], or 37%, according to Habrová et al [16], over the next 100 years, but both studies underestimated the mortality of dragon's blood trees in the oldest age classes in the population extinction models used by Maděra et al [9].…”