Estructura forestal de tres especies endémicas del género Polylepis (Rosaceae) en la Región Central del Perú

Polylepis (Rosaceae) is the dominant tree genus in High-Andean forest ecosystems. These ecosystems are severely threatened, but litle is known about their structure and functioning. We provide the first reports of the dasometric structure and spatial distribution of eight forests of Polylepis canoi, P. flavipila and P. rodolfo-vasquezii in the Central Peruvian Andes as fundamental information for management and conservation policies. We sampled all individuals ≥1 cm of diameter at ground level (DGL) in 20 plots of 10x10 m in each forest, and measured total height (TH) and DGL. Also, we mapped the spatial distribution of the individuals in two plots of 30x30 m (X and Y axes). We found differences in the dasometric structure between forests of the same species, which, in some cases, were associated with climate, soil or elevation variables. However, no well-defined pattern was found. The allometric relationships of the linear and non-linear models did not differ widely with respect to the R2 nor to the Akaike (AIC) scores, indicating that the forests did not show a saturation of tree height with increasing diameter. In the P. canoi forests, individuals with diameters ≥10 cm were the most abundant. In contrast, the forests of P. rodolfo-vasquezii showed a predominance of individuals with diameters ≤10 cm, whereas P. flavipila presented an altered structure with no relationship between DGL and TH in one of the evaluated forests. The analysis of spatial distribution according to the Ripley’s K function on a small scale revealed that P. flavipila and P. canoi presented random patterns, whereas P. rodolfo-vasqueziishowed an aggregate pattern. Finally, our results showed that even forests of the same species have different dasometric structures, whereas spatial patterns differ only between species. So, caution must be taken when extrapolating information between species or forests during ecological studies and conservation actions

Using dendrochronology to trace the impact of the hemiparasite Tristerix chodatianus on Andean Polylepis trees

The high Andean forests of the genus Polylepis (Rosaceae) are threatened by extinction due to anthropogenic effects such as timber extraction, burning, and overgrazing. Some species are also affected by Tristerix chodatianus (Loranthaceae), a hemiparasitic plant which induces progressive host damage. To understand this hemiparasitic process, we evaluated the impact of T. chodatianus on growth and the wood anatomy of Polylepis flavipila using growth rings and digital image processing. We found that P. flavipila has a xeromorphic wood anatomy and that the ecological indices of mesomorphism and vulnerability decrease at higher elevations to avoid embolisms and vessel cavitation. Tristerix chodatianus causes anatomical changes in the host wood, mainly in the last 13 years measured. Alterations include a reduction in the vessel density, and an increase in the vessel diameter and Vulnerability Index, all of which are more evident in downstream sections of parasitized branches. These changes in the xylem tissues increase the vulnerability of the parasitized branches to embolisms and cavitation, thus leading to progressive death of the tree crown. Our study confirms that the analysis of the wood anatomy of parasitized branches can be used to determine the years of colonization of a tree branch by a hemiparasite and that it can be a useful tool to monitor the phytosanitary state of parasitized Polylepis trees