Browsing by Subject "SPECIES COMPOSITION"

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  • Brown, Hugh C. A.; Berninger, Frank A.; Larjavaara, Markku; Appiah, Mark (2020)
    High deforestation rates, especially in the tropics, currently result in the annual emission of large amounts of carbon, contributing to global climate change. There is therefore an urgent need to take actions to mitigate climate change both by slowing down deforestation and by initiating new sinks. Tropical forest plantations are generally thought to sequester carbon rapidly during the initial years but there is limited knowledge on their long-term potential. In this study, we assessed the carbon sequestration in old (42-47 years) timber plantations of Aucoumea klaineana, Cedrela odorata, Tarrietia utilis, and Terminalia ivorensis, and secondary forests of similar ages, by comparing their basal areas and above-ground carbon stocks (AGC) to that of nearby primary forests. Additionally, we estimated and compared timber volume and stumpage value in the three forest types. Systematic random sampling of ninety-three 20 m x 20 m plots in eleven forest sites (2 secondary forests, 2 primary forests, and 7 timber plantations) was undertaken to determine the effect of forest type on AGC, basal area, timber volume, and stumpage value. After 42 years of growth, mean AGC of the timber plantations (159.7 +/- 14.3 Mg ha(-1)) was similar to that of primary forests (173.0 +/- 25.1 Mg ha(-1)) and both were significantly higher than the mean AGC of the secondary forests (103.6 +/- 12.3 Mg ha(-1)). Mean basal area and timber volume of the timber plantations and secondary forests were similar to that of the primary forests, though in each case the timber plantations had significantly higher values compared to the secondary forests. Mean timber value of the plantations ($8577 ha(-1)) was significantly higher than both secondary ($1870 ha(-1)) and primary forests ($3112 ha(-1)). Contrary to our expectations, naturally regenerated trees (woody recruits) within the timber plantations had similar AGC levels, basal area, timber volume, and value compared to the secondary forests. Long-rotation tropical forest plantations under low-intensity management could achieve higher AGC levels and thus have higher climate change mitigation potential and timber values compared to naturally regenerated secondary forests, and are able to reach values similar to primary forests. Monoculture timber plantations could facilitate the successful colonization of their understoreys by native woody recruits that contribute considerably to stand AGC and timber values. Long-rotation forest plantations in the tropics therefore have a critical role to play in forest rehabilitation and climate change mitigation while having the potential to provide modest financial returns to landowners through selective harvesting of timber and/or payments for carbon sequestration.
  • Danquah, Jones Abrefa; Appiah, Mark; Ari, Pappinen (2011)
  • Berner, Annina Zihler; Fuentes, Susana; Dostal, Alexandra; Payne, Amanda N.; Gutierrez, Pamela Vazquez; Chassard, Christophe; Grattepanche, Franck; de Vos, Willem M.; Lacroix, Christophe (2013)
  • Reverte Saiz, Sara; Reverte Saiz, Sara; Arnan, Xavier; Roslin, Tomas; Stefanescu, Constanti; Antonio Calleja, Juan; Molowny-Horas, Roberto; Hernández-Castellano, Carlos; Rodrigo, Anselm (2019)
    Large-scale spatial variability in plant-pollinator communities (e.g. along geographic gradients, across different landscapes) is relatively well understood. However, we know much less about how these communities vary at small scales within a uniform landscape. Plants are sessile and highly sensitive to microhabitat conditions, whereas pollinators are highly mobile and, for the most part, display generalist feeding habits. Therefore, we expect plants to show greater spatial variability than pollinators. We analysed the spatial heterogeneity of a community of flowering plants and their pollinators in 40 plots across a 40-km(2) area within an uninterrupted Mediterranean scrubland. We recorded 3577 pollinator visits to 49 plant species. The pollinator community (170 species) was strongly dominated by honey bees (71.8% of the visits recorded). Flower and pollinator communities showed similar beta-diversity, indicating that spatial variability was similar in the two groups. We used path analysis to establish the direct and indirect effects of flower community distribution and honey bee visitation rate (a measure of the use of floral resources by this species) on the spatial distribution of the pollinator community. Wild pollinator abundance was positively related to flower abundance. Wild pollinator visitation rate was negatively related to flower abundance, suggesting that floral resources were not limiting. Pollinator and flower richness were positively related. Pollinator species composition was weakly related to flower species composition, reflecting the generalist nature of flower-pollinator interactions and the opportunistic nature of pollinator flower choices. Honey bee visitation rate did not affect the distribution of the wild pollinator community. Overall, we show that, in spite of the apparent physiognomic uniformity, both flowers and pollinators display high levels of heterogeneity, resulting in a mosaic of idiosyncratic local communities. Our results provide a measure of the background of intrinsic heterogeneity within a uniform habitat, with potential consequences on low-scale ecosystem function and microevolutionary patterns.
  • Mäki, Mari; Krasnov, D.; Hellén, H.; Noe, S. M.; Bäck, J. (2019)
    The forest floor is a significant contributor to the stand-scale fluxes of biogenic volatile organic compounds. In this study, the effect of tree species (Scots pine vs. Norway spruce) on forest floor fluxes of volatile organic compounds (VOC) was compared in boreal and hemiboreal climates.
  • Leppanen, Jaakko; Siitonen, Susanna; Weckstrom, Jan (2017)
    It is difficult to plan restoration projects or study the amount of disturbance in aquatic ecosystems if background conditions are not known. Zooplankton, especially cladocerans (water fleas), has proven highly useful as a reliable indicator of environmental change. Cladocerans preserve well in sediments and thus allow for the analysis of historical communities. To assess the stability of cladoceran communities in lakes with low human impact, we compared pre-industrial and modern cladoceran assemblages (top-bottom analysis) in 32 sub-Arctic lakes in NW Finnish Lapland. We used a dataset of measured environmental variables to determine their explanatory power on cladoceran assemblages. While cladoceran assemblages at the community level have remained relatively stable between the pre-industrial and modern samples, a clear change at the genus level was observed with a significant proportional increase in Bosmina (Eubosmina) spp. (Wilcoxon signed-rank test z = 2.75 p = 0.006). The amount of organic matter in the sediment [measured as loss on ignition (LOI)] explained the largest proportion of the variation in the cladoceran community. Since LOI is strongly correlated to climatic factors, the increased abundance of B. (Eubosmina) spp. may ultimately be related to climate warming. As the top-bottom approach is comprised of two temporal snapshots, it cannot provide the exact time of community change. This shortcoming is of special importance for restoration and management planning.