Abstract
BackgroundUnderstory 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.ResultsWe 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.ConclusionsOur 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.
Highlights
Understory plants represents the largest component of biodiversity in most forest ecosystems and plays a key role in forest functioning
Canopy cover and basal area were significantly higher in mountain than in coastal sites, while differences were not significant between locations for the other variables
We expected the highest level of solar radiation in deciduous forest, because the canopy of N. pumilio is quite sparse and their leaves are substantially thinner than N. betuloides
Summary
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. In temperate deciduous forests, trees drop their leaves in autumn allowing high seasonal variation in light availability for the understory; while in evergreen broadleaved forests -more commonly found in the Southern Hemisphere- trees keep their leaves year round, understory plants are adapted to low light availability in all seasons. In both broadleaved forest types, understory plants have adapted to maximize their light/energy capture in different ways. There is little information about particularities of understory composition, structure and distribution patterns in mixed deciduous-evergreen broadleaved forests (see Kuninaga et al 2015)
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