The influence of canopy-layer composition on understory plant diversity in southern temperate forests

Background： Understory plants represents the largest component of biodiversity in most forest ecosystems and plays a key role in forest functioning.Despite their importance, the influence of overstory-layer composition on understory plant diversity is relatively poorly understood within deciduous-evergreen broadleaved mixed forests.The aim of this work was to evaluate how tree overstory-layer composition influences on understory-layer diversity in three forest types（monospecific deciduous Nothofagus pumilio（Np）, monospecific evergreen Nothofagus betuloides（Nb）, and mixed N.pumilio-N.betuloides（M） forests）, comparing also between two geographical locations（coast and mountain） to estimate differences at landscape level.Results： We recorded 46 plant species： 4 ferns, 12 monocots, and 30 dicots.Canopy-layer composition influences the herb-layer structure and diversity in two different ways： while mixed forests have greater similarity to evergreen forests in the understory structural features, deciduous and mixed were similar in terms of the specific composition of plant assemblage.Deciduous pure stands were the most diverse, meanwhile evergreen stands were least diverse.Lack of exclusive species of mixed forest could represent a transition where evergreen and deciduous communities meet and integrate.Moreover, landscape has a major influence on the structure, diversity and richness of understory vegetation of pure and mixed forests likely associated to the magnitude and frequency of natural disturbances, where mountain forest not only had highest herb-layer diversity but also more exclusive species.Conclusions： Our study suggests that mixed Nothofagus forest supports coexistence of both pure deciduous and pure evergreen understory plant species and different assemblages in coastal and mountain sites.Maintaining the mixture of canopy patch types within mixed stands will be important for conserving the natural patterns of understory plant composition in southern beech mixed forests.

Flowering and seeding patterns in pure and mixed Nothofagus forests in Southern Patagonia

Introduction:Variation in reproductive phenology among species is an important mechanism for maintaining species coexistence.In mixed forests,the impact of limiting(biotic and abiotic)factors on tree reproductive success regulates the maintenance of species in balanced proportions or the conversion towards monospecific forests.This study offer a significant first approach to the reproductive phenology of mixed forests,assessing flowering,seeding and loss factors on reproductive success in three forest types(pure deciduous Nothofagus pumilio(Np),evergreen Nothofagus betuloides(Nb)and mixed(M)forests),comparing also between two geographical locations(coast and mountain),during one growing season.Results:Flowering falling started early in Np.Seed fall occurred first and more concentrated in Np,while in Nb,it was progressive during autumn.Phenology in M combined both patterns,but with better reproductive performance of both species.Seed production was greater in Nb(42,900,000 ha^(−1))than in Np(710,000 ha^(−1)),while M presented intermediate values(31,900,000 ha^(−1)).Abortion was greatest in Np(19% of female flowers and 10% of immature fruits),while fruit predation was low(7-9%)in all forest types.Empty seed was the main loss factor,but with low net values for each species in M.Regarding geographical location,sea proximity generated a quick starting of the growing season in coast compared to mountain sites.However,we detected forest types×location interactions in flowering and seeding patterns(e.g.in male flower production and in empty and viable seeds),with differences in species response according to location.Conclusions:Both deciduous and evergreen species have reproductive advantages in mixed compared to pure forests.However,mixed were more similar to pure evergreen forests in their reproductive traits and the incidence of the limiting factors.The study of only one growing season does not allow us to conclude whether mixed forests are stable communities,but we contribute to understand the roles of reproductive phenology in mixed forest dynamics.