Although spine variation within cacti species or populations is assumed to be large, the minimum sample size of different spine anatomical and morphological traits required for species description is less studied. There are studies where only 2 spines were used for taxonomical comparison amnog species. Therefore, the spine structure variation within areoles and individuals of one population of Gymnocalycium kieslingii subsp. castaneum (Ferrari) Slaba was analyzed. Fifteen plants were selected and from each plant one areole from the basal, middle and upper part of the plant body was sampled. A scanning electron microscopy was used for spine surface description and a light microscopy for measurements of spine width, thickness, cross-section area, fiber diameter and fiber cell wall thickness. The spine surface was more visible and damaged less in the upper part of the plant body than in the basal part. Large spine and fiber differences were found between upper and lower parts of the plant body, but also within single areoles. In general, the examined traits in the upper part had by 8–17% higher values than in the lower parts. The variation of spine and fiber traits within areoles was lower than the differences between individuals. The minimum sample size was largely influenced by the studied spine and fiber traits, ranging from 1 to 70 spines. The results provide pioneer information useful in spine sample collection in the field for taxonomical, biomechanical and structural studies. Nevertheless, similar studies should be carried out for other cacti species to make generalizations. The large spine and fiber variation within areoles observed in our study indicates a very complex spine morphogenesis.

Cette étude s’est déroulée dans une plan- tation forestière en Amérique centrale, proche de la ville de Diriamba au Nica- ragua, où des plantations de teck sur 48,9 ha, dans une zone de reboisement de 76,5 ha, sont renouvelées depuis 2006 (2006 : 7,90 ha ; 2007 : 13,63 ha    ;2008 : 11,93 ha ; 2009 : 12,87 ha ; 2010 :21,70 ha). Cette plantation sort de l’ordi- naire du fait de l’espacement de 1 x 1 m des arbres et des facteurs écologiques limitants de cette zone tropicale aride. L’espacement de 1 x 1 m a été  choisi pour favoriser la croissance en hauteur et obtenir ainsi des tiges de haute taille, et pour limiter les ramifications afin d’éviter la formation de houppiers importants. Cela permet de démarrer une production de poteaux de teck, adaptés à certaines constructions, dès la première coupe d’éclaircissement. Les paramètres de croissance des tecks (hauteur, circonfé- rence) ont été mesurés dans les placettes expérimentales mises en place en 2011. Des données complémentaires (morta- lité, arbres cassés ou tordus) ont égale- ment été relevées. Une méthodologie de terrain a été développée et les résultats restitués sous forme de tableaux et gra- phiques. Une évaluation statistique des paramètres de croissance a été menée à partir des mesures prises sur les placettes expérimentales délimitées dans la planta- tion. Les jeunes arbres plantés la même année ont été comparés selon leur prove- nance en termes de hauteur, de circonfé- rence, de productivité et de mortalité. Au total, 10 955 arbres sur 143  placettes  ont été mesurés. Sur ces peuplements de 1 à 5 ans d’âge, le bois sur pied total est estimé à 1 287,89 m3, la masse moyenne de bois à l’hectare à 17,89 m3, la hauteur moyenne des peuplements à 3,03 m et la circonférence moyenne à hauteur de poitrine à 2,74 cm. Les arbres cassés représentent 5,64 %, les arbres tordus 5,66 % et la mortalité moyenne s’établit à 21,48 %.

Growth simulators (GS) or mathematical models focusing on forest stand development can be used as an important instrument of decision making when collecting data for forest management. Currently, the main source of information for the forest owner or the forest manager is Forest Management Plans (FMP). The problem is that FMPs are static works, created for 10 years, which do not directly deal with the modelling of mensurational variables. Therefore the informative value of FMP for the owner is rather limited. FMP offer very exact information in the first year of their validity, but they do not enable to determine the development and behaviour of mensurational variables during the whole period while the plan is still valid, and thus give a more accurate information base for successful forest management. This problem could be solved by mathematical modelling of development of mensurational variables, or rather complicated growth simulators, which would supply the above-mentioned information. These problems are not new, KNEIfl (2000) and SIMON (2001) mentioned them in their works.PRETZSCH et al. (2002) approached the term model as a system of equations and relations describing tree growth and competitive relationships, while simulator is an implementation of the model into a computer program, which enables us to interactively influence the process of simulation. The main objectives of the growth process modelling are prognosis of forest stand development and determination of optimum management strategy.Based on the known and given behaviour regularities of the individual growth processes, simulation models enable to foresee the condition in which the given forest stand will be with certain probability under the conditions of quantitatively chosen factors.Many Czech authors were dealing with mathematical modelling and its possible utilisation in their works. To name the most important: POLÁK (1972), SIMON et al. (1996) and ZACH (2001). On the international level, the following authors focused on forming the growth simulators -PRETZSCH and KAHN (1998), NAGEL (1975), and STERBA and MONSERUD (1995). As PRETZSCH et al. (2002) presents, it is difficult to use foreign models because of different environment and that is why such models do not give realistic results. The main problem of creating a GS that would be possible to use for simulation of greater territory units, is the need for enormous database and validation, which demands extensive measuring. This is, of course, very demanding and becomes an obstacle when constructing the GS. However, it is possible to use quite simple mathematical models that can be created while processing the FMP. On the one hand, their utilisation restricted is to the given property, but they give valuable information for the management and also for the processing of FMP.For the mathematical modelling of development of mensurational variables it is necessary to create mock time series from non-mixed forest stands of the same age on the given estate. According to ZACH (2001) the mock time se...