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The Effects of Environmental Features and Overstory Composition on the Understory Species Assemblage in Sub-Mediterranean Coppiced Woods : Implications for a Sustainable Forest Management

Tardella F. M., Postiglione N., Vitanzi A., Catorci A.

Polish Journal of Ecology

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2017

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Vol. 65, nr 2

167--182

EN

Understanding the relationship among environmental factors, overstory and understory is a key step for the improvement of sustainable forest management. Our aim was to understand how environmental features (topographic factors) and overstory (tree species) composition affect understory (shrub and herb species) assemblage in sub-Mediterranean coppiced woods. The study area lies in the Monti Sibillini National Park (central Italy). In 205 plots (20 × 20 m) we collected topographic features and species cover values; moreover, we defined the Social Behaviour Type (SBT — i.e. species ecological and dynamic features) of each understory species. Data were analysed using Redundancy Analysis and Generalized Linear Modeling. We found that topographic factors shaped percentage cover of different tree species and hence determined forest community type. Topography-related factors were further mediated by the tree layer composition, in filtering understory assemblage, on the basis of species SBT. We found no effect of overstory species diversity on understory species diversity. However, the presence of tree species different from the dominant ones increased understory species richness. This effect was particularly notable in evergreen woods, dominated by Quercus ilex. We conclude that, to improve the management sustainability, coppicing management should be focused on the achievement of the greater tree species diversity.

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Structural Diversity Closely Associated with Canopy Species Diversity and Stand Age in Species-Poor Montane Forests on Loess Plateau of China

Liu N., Wang H., Nan H.

Polish Journal of Ecology

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2017

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Vol. 65, nr 2

183--193

EN

High species diversity is often accompanied with and supported by a diversified stand structure in species-rich natural forests. However, the relationship between species diversity and stand structural diversity is less examined in species-poor forests. In montane forests on Loess Plateau of north-central China in a semi-arid climate zone, canopy species diversity and vertical structure of 57 broadleaves, conifer and mixed stands, with varying stand ages and site conditions, were randomly sampled. Canopy species diversity was represented by Shannon's index (H'). Stand structural diversity was represented by two indices respectively, i.e. coefficients of variation of diameter measurements at breast height (CVdbh) and Shannon's index of diameter classes (H'dbh). Structural equation models (SEMs) were constructed to explore multiple relationships between stand structural diversity and canopy species diversity, stand age and elevation. Both stand structural diversity indices increased directly with H' and stand age. However, indirect positive effect of stand age via increasing H' was only significant on CV. H'dbh provided positive feedback on H', while effect of stand age was only indirect via increasing structural diversity. Elevation significantly affected coefficients of variation of diameter, which was probably a sampling effect due to narrow distribution of broadleaves-conifer stands in altitudinal range. In conclusion, the results showed that stand structural diversity and canopy species diversity and stand age are closely associated with the species-poor montane forests like these on Loess Plateau of north-central China.

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The Effect of Fallow Period Length on the Abundance and Diversity of Usable Plant Assemblages in Shifting Cultivation System (Swidden Agriculture) in Northern Laos

Delang C. O., Weiyi X., Brooke B., Chun K. P.

Polish Journal of Ecology

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2016

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Vol. 64, nr 3

350--356

EN

Shifting cultivation, or swiddening, involves alternating cycles of cropping and fallow periods. Rather than being abandoned, the fallow swidden fields provide a source of important plant products for remote, forest-dwelling human communities. In northern Laos, the traditional length of fallow periods used to range between five and 11 years, depending on the availability of land and quality of the soil. Fallow periods are currently being shortened because of population pressures and government policies. To determine the potential impacts of shorter fallow periods, 128 swidden fallows of various ages (up to 20 years), located at altitudes between 400 and 800 m a.s.l. in northern Laos were sampled for usable plants. The impact of fallow length on plant abundance and species diversity was analysed. The number of usable plant species was found to increase with the fallow age until it was 11–12 years old, and then decline, while the abundance of usable plants increased beyond that period. We conclude that shorter fallows will result in a significantly smaller usable plant abundance and species diversity for the villagers. We propose that 11–12-year-long fallows should be considered in order to fully exploit the greater plant volume of older fallows as well as the compositional shift of species in fallows over time.