摘要
Litsea glaucescens Kunth(Mexican bay leaf,laurel)has a wide distribution in Mexico,growing at both riparian and rupicolous environments in the mountainous region of the Central Highlands of the country.Sierra Fría-Sierra Laurel is a protected natural area covered by a dry forest.The Mexican bay leaf is associated with the oak forest,especially on ravines.The species has been considered at risk in recent years.This research is focused on analyzing the elements of the environment of the ravines,which are influencing the distribution and establishment of laurel populations in the region.Two mountainous regions of Aguascalientes were selected,Sierra Fría and Sierra Laurel.Three ravines of the basin were selected to obtain environmental data.Variables registered were topographic,edaphic,and biotic.Principal component analysis was used to identify ecological factors associated with the presence of L.glaucescens.Mexican bay leaf populations were registered in 10 ravines.At the structural level in the community,29 woody species were registered,Mexican bay leaf had an Importance Value Index of 15.8,ranking 10th among all species.Individuals of laurel were classified by size classes(S,individuals with heights ranging from 0 to 20 cm;S,heights ranging from 0.2 to 1.0 m;S,heights between 1 and 2 m with light trace of flowering;S,heights greater than 2 m with flowering greater than 30% of the canopy;and S,individuals with heights greater than 5 m,curved trunk and basal regrowth)to obtain the population structure.The importance index value for all the species in the riparian community was calculated to the community level.Edaphic factors that characterized the presence of Mexican bay leaf were a high percentage of rock coverage(90%),less mulch depth,and sandy loam shallow soils.Sites that showed higher cation exchange capacity had a higher presence of individuals of the S,S,and Ssize classes.Class Sindividuals were found in shady places with 97% of intercepted light.Individuals of classes Sand Sendure less shady places(75%–85% of intercepted light),and individuals class Sand Sare more frequent in open canopies and crag conditions.Regarding the ecological site factors,such as riverside stream,and rocks on mountain slopes,L.glaucescens life form is riparian and rupicolous.Cation exchange capacity,sodium and calcium levels play an important role in the presence of Mexican bay leaf.Distribution on the ravine and recruitment of the Mexican bay leaf populations are associated with shaded sites,mainly for individuals of size classes Sand S,versus sunny places for individuals of size classes Sand S.The overall population structure had a positive kurtosis with all plant size categories well represented;statistically,the population structure of L.glaucescens is very close to the normal distribution.The information obtained allows us to affirm that the laurel populations in the mountainous areas of Sierra Fría and Sierra Laurel from central Mexico are in good demographic condition.
基金
the Mexican National Council for Science and Technology(Consejo Nacional de Ciencia y Tecnología,CONACYT)for the scholarship granted to the first author
To Ofelia Castillo Díaz from the Mexican National Protected Areas Commission in the state of Aguascalientes for offering support and financing part of the field work。
