No 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.

No abstract

length: 236 words 2Number of references: 54 3 Tables and Figures: 3 figures and 1 table 4 5 Supplementary material: 6Appendix S1-5: 3 supplementary tables and 2 supplementary figures 7 5 ABSTRACT 1 Understory herbs and soil invertebrates play key roles in soil formation and nutrient cycling 2 in forests. Studies suggest that diversity in the canopy and in the understory are positively 3 associated, but they often confound the effects of tree diversity with those of tree species 4 identity and abiotic conditions. We combined extensive field sampling with structural 5 equation modeling to evaluate the simultaneous effects of tree diversity on the species 6 diversity of understory herbs, beetles, and earthworms. The diversity of earthworms and 7 saproxylic beetles was directly and positively associated with tree diversity, presumably 8 because species of both these taxa specialize on certain species of trees. Tree identity also 9 strongly affected diversity in the understory, especially for herbs, likely as a result of 10 interspecific differences in canopy light transmittance or litter decomposition rates. Our 11 results suggest that changes in forest management will disproportionately affect certain 12 understory taxa. For instance, changing canopy diversity will affect the diversity of 13 earthworms and saproxylic beetles more than changes in tree species composition, whereas 14 the converse would be expected for understory herbs and detritivorous beetles. We conclude 15 that the effects of tree diversity on understory taxa can vary from positive to neutral and may 16 affect biogeochemical cycling in temperate forests. We recommend to maintain high tree 17 diversity, thereby promoting the diversity of multiple understory taxa, and to reduce the 18 abundance of tree species that may reduce understory diversity. 19 20 21

No abstract