Seed Viability and Potential Germination Rate of Nine Endemic Boswellia Taxa (Burseraceae) from Socotra Island (Yemen).

The endemic Boswellia species (Burseraceae) on Socotra Island (Yemen) are of great local significance due to their various local ethnobotanical uses. However, despite the fact that these trees are endangered, little is known about their biology. We tested seed germination rates in controlled experiments (trials of 21 days) for two subsequent years and for nine endemic taxa of Boswellia occurring on Socotra Island. For this, seeds were collected island-wide from a wide range of localities and for several populations per species. We observed differences in germination among Boswellia species, among species and localities and among both years, which indicates that the development of seeds is strongly affected by external ecological factors. Although we noted a large variation in seed germination (relatively high in Boswellia socotrana), and half of the species showed relatively low mean daily germination, our study indicated that all endangered endemic Frankincense Tree taxa of Socotra harbor the potential for in situ conservation through recruitment, given that known impacts can be reduced in local replantation areas (e.g., grazing).

Resprouting trees drive understory vegetation dynamics following logging in a temperate forest.

Removal of canopy trees by logging causes shifts in herbaceous diversity and increases invasibility of the forest understory. However, disturbed (cut) trees of many species do not die but resprout from remaining parts. Because sprouts develop vigorously immediately after disturbances, we hypothesized that sprouts of logged trees offset the changes in species richness and invasibility of the herbaceous layer by eliminating the rise in the resource availability during the time before regeneration from seeds develops. To test this, we analyzed data on herbaceous vegetation and sprout biomass collected in a broadleaved temperate forest in the Czech Republic before and for 6 years after logging. Sprouts that were produced by most of the stumps of logged trees offset large rises in species richness and cover of herbaceous plants and the resource availability that followed logging, but they affected the alien plants more significantly than the native plants. The sprouting canopy effectually eliminated most of the alien species that colonized the forest following a logging event. These findings indicate that in forests dominated by tree species with resprouting ability, sprouts drive the early post-disturbance dynamics of the herbaceous layer. By offsetting the post-disturbance vegetation shifts, resprouting supports forest resilience.

Terpenoid profiles of resin in the genus Dracaena are species specific.

Dragon's blood is the colloquial name for the red resin produced by tree species in the genus Dracaena (Asparagaceae), and the resin is directly involved in plant defensive mechanisms against pathogen and herbivore attack. It is also widely used in traditional folk medicine due to its antiviral, antimicrobial and antitumor activities. In the present work, a method using solid phase microextraction combined with two-dimensional gas chromatography with time-of-flight mass spectrometric detection was developed for the analysis of resin from five Dracaena species, namely Dracaena cinnabari Balf. f., D. serrulata Baker, D. ombet Heuglin ex Kotschy & Peyr., D. draco subsp. draco, and D. draco subsp. ajgal. Twenty terpenoid components in the resins of the five species were identified after comparative study of the volatile metabolite profiles. Monoterpenes were found to be species specific, and the observed differences might be further investigated as a possible means of identifying chemotaxonomic markers. In addition, for the first time, we describe the terpenoid volatile profiles of D. ombet and D. serrulata resins.

Growth dynamics of Dracaena cinnabari under controlled conditions as the most effective way to protect endangered species.

Dracaena cinnabari Balf. fil. is an endangered endemic species growing on the Yemeni island of Soqotra. Dracaena woodlands are considered as one of the oldest forest communities on Earth. Uncontrolled grazing unfortunately caused a lack of naturally occurring regeneration. Our two-year research was focused on the growth dynamics of Dracaena seedlings from two separate populations. One hundred of germinated seeds from two different altitudes from the island were sown and planted under the same conditions. Average increment and difference between the growth dynamics of plants from the two localities were investigated. The observed data on this plant species revealed very interesting, hitherto unknown results. (1) The seedlings germinated within a time period from four to ten weeks. Germination rate was 90% on the Firmihin highland plateau and 78% on the Scand Mountain. (2) Average plant length from both localities was almost the same (24.9 cm) at the end of measurement. Differences in values between the two populations proved as non-significant. (3) A significant difference was found in the number of leaves and in the sum of lengths of all leaves on one plant. While the seedlings from Firmihin featured a wide spreading above-ground part with a large number of leaves, the plants from Scand invested more energy into faster leaves elongation rate. (4) Growth dynamics reflected seasonal changes. Increments were slower or ceased during the period of vegetative rest from autumn to spring. (5) Average mortality rate was 13%. Most of the plants died during the period of vegetative rest. Further study on germination and regeneration under artificial conditions seems like the only way to prevent species extinction.

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.