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  • Author: Martin Šenfeldr x
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Abstract

This paper studies non-indigenous dwarf pine stands in the Hrubý Jeseník Mountains, from the perspective of their spatial and genetic relations to slope phenomena of deformation character. The paper contains a typology of regional slope deformations, data on their spatial distribution and specific properties, including risk estimates of their origination or further development in case of potential future dwarf pine stand clearings, as well as a three-stage categorization of dwarf pine stands based on this tendency. The results were processed using data from literary sources, map documents and aerial photos, as well as an extensive field survey. Three main types of slope deformations were distinguished on sites with highly variable geomorphological features - extensive complex phenomena with numerous subforms, linear debris flows and local shallow landslides. The acquired data show that while dwarf pine stands have no great effect on the development of large slope phenomena, they play a more significant reinforcement role in the prevention of smaller surface deformations, the origination of which is predominantly related to steeper slopes. The results of this study can serve for future decision making on the management of dwarf pine stands

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.