Hana Habrová

A comparative structural and functional study of leaf traits and sap flow in Dracaena cinnabari and Dracaena draco seedlings

Water relations for two remote populations of Dracaena tree species from the dragon tree group, Dracaena cinnabari Balfour f. and Dracaena draco (L.) L., were studied to test our hypothesis that morphological and anatomical differences in leaf structure may lead to varied functional responses to changing environmental conditions. Sap flow measurements were performed using the heat field deformation method for four Dracaena seedlings grown in one glasshouse and two greenhouses, and leaf traits related to plant-water relationships were characterised. All traits studied confirmed that D. cinnabari leaves are more xeric in their morpho-anatomical structure compared with D. draco leaves. No radial sap flow variability was detected in D. draco plant stems, whereas sap flow was found to be higher in the inner part of D. cinnabari stems. The regular occurrence of reverse sap flow at night in both Dracaena species was consistent with a staining experiment. Vapour pressure deficit (VPD) was found to be the main driver for transpiration for both Dracaena species. However, the relationship between VPD and sap flow appeared to be different for each species, with a clockwise or no hysteresis loop for D. draco and a counter-clockwise hysteresis loop for D. cinnabari. This resulted in a shorter transpiration cycle in D. cinnabari. The observed superior water-saving strategy of D. cinnabari corresponds to its more xeric morpho-anatomical leaf structure compared with D. draco.

Field Survey of Dracaena Cinnabari Populations in Firmihin, Socotra Island: Methodology and Preliminary Results

Abstract Between 2010 and 2011 a field survey dedicated to Dracaena cinnabari (DC) population was conducted in Firmihin, Socotra Island (Yemen). It’s main goal was to collect data that would make it possible to unbiasedly estimate main characteristics of the local DC population. Our motivation was to provide reliable information to support decision-making processes as well as other research activities. At the same time we were not aware of a survey which could provide this kind of statistical-sound estimates for the whole population covering an area of almost 700 ha. This article describes how the survey has been planned and carried out in practice. In addition, we also provide a set of preliminary estimates of the main DC population figures - totals and per hectare densities of stems, overall and partitioned according to predicted crown age. Among estimated parameters there are also mean crown age and proportions of predefined age classes on the total number of living DC stems. These estimates provide an explicit information on age structure of the whole DC population in Firmihin. Although we collected data on more than one hundred randomly located plots, the reported accuracy of our estimates is still rather limiting. We discuss several possibilities to obtain more accurate results or at least to approach the supposedly lower true variance that can’t be calculated by approximate techniques applied here. The design and concept of our survey makes it possible to evaluate changes over time on stem by stem bases and to generalize these stem-level details to the whole population. Mortality, regeneration and even change of population’s mean crown age can be estimated from a future repeated survey, which would be extremely useful to draw firm conclusions about the dynamic of the whole DC population in Firmihin.

Dynamic response of woody vegetation on fencing protection in semi-arid areas; Case study: Pilot exclosure on the Firmihin Plateau, Socotra Island.

Woody vegetation dynamics and Dracaena cinnabari regeneration have been studied for five years in the conditions of Socotra Island. Woody plants were measured regularly inside and outside the exclosure area, and the growth and survival of D. cinnabari seedlings were observed. In the exclosure of about 1000 m2 a total of 49 species were identified, including 23 endemics, growing in the average density of 3.82 specimens per m2. The fenced area was overgrown relatively rapidly by dense grass cover – reaching approx. 2.7 t/ha. Species growth dynamics inside and outside the exclosure shows that grazing had a marked impact, leading to the elimination of trees and shrubs. All grazed species grew noticeably in the exclosure, in the average of 50 cm in 5 years. D. cinnabari as the dominant flagship species of Socotra has been studied with regards to regeneration dynamics. Observations indicate that probability of its seedlings survival increases with their age. No seedlings germinated from the seeds sown in the experiment, however, outplanted seedlings performed relatively well. Field observations show that D. cinnabari seed germination is triggered when the seed reaches a protected micro-habitat with a developed humus layer and high relative humidity in the soil lasts for at least two days.

Overview of Biotope Types of Socotra Island

Abstract The study describes main biotopes of Socotra Island. The biotopes were distinguished and described during complex field observations on more than 250 localities of Socotra between years 1999-2004. Classification of biotopes is based on differences in physiognomy, structure and species composition of the vegetation component of present biocoenoses. Groups of biotope types differ, above all, in the physiognomy and structure of vegetation. Biotope types are divided according to composition of dominant species. In this manner, 13 groups of biotopes and 39 biotope types were distinguished and described

Application of the Czech Methodology of Biogeographical Landscape Differentiation in Geobiocoenological Concept – Examples from Cuba, Tasmania and Yemen

Abstract Within the area of Central Europe, and especially in the Czech Republic (and former Czechoslovakia), geobiocoenological landscape differentiation has been applied for more than 40 years to create a spatial model of the natural (potential) condition of geobiocoenoses in the landscape. Because long-term objective of geobiocoenology is to contribute to the creation of harmonic cultural landscape by gradual development of a comprehensive system of groundworks for sustainable landscape use, and as Mendel University experts work in various countries, adaptions of geobiocoenology were used also outside Europe, in tropical areas. Examples of such a work could be shown on islands such as Socotra (belonging politically to Yemen), Tasmania, and Cuba.

Growth Dynamics of Endemic Dracaena cinnabari Seedlings In Situ on Socotra Island

Dragon ́s blood tree, a flagship endemic species of Socotra, is threatened with extinction 23 due to lack of natural regeneration, likely because of goat herbivory and/or climatic factors. Loss of 24 dragon ́s blood tree would result in loss of other native flora, heightening the importance of 25 formulating a conservation strategy for it. Although artificial afforestation might be used to offset 26 the lack of natural regeneration, it would have to overcome the same threats faced by naturally 27 occurring seedlings. Moreover, there is no published information on the growth dynamics of 28 seedlings in plantations in situ on Socotra. To fill this information gap, we compared seedling 29 growth over an 8-year period after planting at three sites that differed in the degree to which goats 30 were excluded and in whether they were watered regularly over the period. In addition to 31 developing a new classification of the growth stages, which will enable better tracking of population 32 dynamics, we found that continuous goat exclusion was necessary to prevent seedling mortality. 33 Also, although seedling growth overall was slow, growth parameters of regularly irrigated 34 seedlings ranged from 156 % to 446 % of those not regularly watered, suggesting that this treatment 35 can speed seedlings’ escape from goat browsing. 36