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Fortier J.,University of Quebec at Montreal | Gagnon D.,University of Quebec at Montreal | Truax B.,Fiducie de recherche sur la foret des Cantons de lEst | Lambert F.,Fiducie de recherche sur la foret des Cantons de lEst
New Forests | Year: 2011

Understory plant biomass, species richness and canopy openness were measured in six-year old hybrid poplar riparian buffer strips, in the understory of two unrelated clones (MxB-915311 and DxN-3570), planted along headwater streams at three pasture sites of southern Quebec. Canopy openness was an important factor affecting understory biomass in hybrid poplar buffers, with lower understory biomass observed on sites and under the clone with lower canopy openness. Although tree size was an important factor affecting canopy openness, relationships between total stem volume and canopy openness, for each clone, also support the hypothesis of a clonal effect on canopy openness. Understory biomass and canopy openness as low as 3.6 g m -2 and 7.6% in 1 m 2 microplots were measured under clone MxB-915311 at the most productive site. This reduction of understory plant growth could compromise important buffer functions for water quality protection (runoff control, sediment trapping and surface soil stabilisation), particularly were concentrated runoff flow paths enter the buffer. On the other hand, tree buffers that maintain relatively low canopy openness could be interesting to promote native and wetland plant diversity. Significant positive relationships between canopy openness and introduced species richness (R 2 = 0.46, p < 0.001) and cover (R 2 = 0.51, p < 0.001) were obtained, while no significant relationship was observed between canopy openness and native (wetland) species richness and cover. These results suggest that planting riparian buffer strips of fast-growing trees can rapidly lead to the exclusion of shade-intolerant introduced species, typical colonisers of disturbed habitats such as riparian areas of pastures, while having no significant effect on native (wetland) diversity. Forest canopy created by the poplars was probably an important physical barrier controlling introduced plant richness and abundance in agricultural riparian corridors. A strong linear relationship (R 2 = 0. 73) between mean total species richness and mean introduced species richness was also observed, supporting the hypothesis that the richest communities are the most invaded by introduced species, possibly because of higher canopy openness, as seen at the least productive site (low poplar growth). Finally, results of this study highlight the need for a better understanding of relationships between tree growth, canopy openness, understory biomass and plant diversity in narrow strips of planted trees. This would be useful in designing multifunctional riparian buffer systems in agricultural landscapes. © 2011 Springer Science+Business Media B.V.

Fortier J.,University of Quebec at Montreal | Gagnon D.,University of Quebec at Montreal | Truax B.,Fiducie de recherche sur la foret des Cantons de lEst | Lambert F.,Fiducie de recherche sur la foret des Cantons de lEst
Biomass and Bioenergy | Year: 2010

In this paper the potential of five hybrid poplar clones (Populus spp.) to provide biomass and wood volume in the riparian zone is assessed in four agroecosystems of southern Quebec (Canada). For all variables measured, significant Site effects were detected. Survival, biomass yield and volume yield were highest at the Bromptonville site. After 6 years of growth, total aboveground biomass production (stems+branches+leaves) reached 112.8tDM/ha and total leafless biomass production (stems+branches) reached 101.1tDM/ha at this site, while stem wood volume attained 237.5m3/ha. Yields as low as 14.2tDM/ha for total biomass and 24.8m3/ha for total stem volume were also observed at the Magog site. Highest yields were obtained on the most fertile sites, particularly in terms of NO3 supply rate. Mean stem volume per tree was highly correlated with NO3 supply rate in soils (R2=0.58, p<0.001). Clone effects were also detected for most of the variables measured. Total aboveground biomass and total stem volume production were high for clone 3729 (Populus nigra×P. maximowiczii) (73.1tDM/ha and 134.2m3/ha), although not statistically different from clone 915311 (P. maximowiczii×P. balsamifera). However, mean whole-tree biomass (including leaves) was significantly higher for clone 3729 (38.8kgDM/tree). Multifunctional agroforestry systems such as hybrid poplar riparian buffer strips are among the most sustainable ways to produce a high amount of biomass and wood in a short time period, while contributing to alleviate environmental problems such as agricultural non-point source pollution. © 2010 Elsevier Ltd.

Fortier J.,University of Quebec at Montreal | Gagnon D.,University of Quebec at Montreal | Truax B.,Fiducie de recherche sur la foret des Cantons de lEst | Lambert F.,Fiducie de recherche sur la foret des Cantons de lEst
Agriculture, Ecosystems and Environment | Year: 2010

Riparian vegetation has a critical role to play in non-point source pollution abatement and water quality protection within watersheds in agricultural areas. In addition to their water quality function, riparian buffers also have the potential to sequester large amounts of carbon (C). In this study, the C and nutrient sequestration by five unrelated hybrid poplar (Populus spp.) clones growing in the riparian zone of four southern Quebec (Canada) agroecosystems is measured aboveground after 6 years of growth and compared to free-growing (unmanaged) herbaceous buffer strips. Very large differences in C sequestration and nutrient accumulation in hybrid poplar buffers were observed across the four agricultural riparian sites. For all variables measured in this study, the largest effect detected by the ANOVA was the Site effect. While C sequestration, N and P accumulation in total aboveground biomass were, respectively 52 t ha-1, 770 kg ha-1 and 82 kg ha-1 at the Bromptonville site, these values were as low as 6.4 t ha-1, 90 kg ha-1 and 10 kg ha-1 at the Magog site. Site fertility, in terms of NO3 supply rate, was the main factor controlling biomass growth, and consequently C sequestration and nutrient accumulation in hybrid poplars. Although Site effect was by far the largest effect in this study, the Clone effect was also important, with clone 3729 (Populus nigra L. × Populus maximowiczii A. Henry) being the most effective for C and nutrient sequestration. Across the four study sites, total aboveground C sequestration, N and P accumulation at the site level could be, respectively enhanced by 31-37%, 29-41% and 30-38% with the sole use of clone 3729. Site × Clone interactions for the variables tested in this study were generally not significant, or significant but small in magnitude compared to main effects (Site and Clone). Important C and nutrient accumulation differences exist after 6 years of growth between hybrid poplar buffers and unmanaged herbaceous buffers. Compared to an unmanaged herbaceous buffer, the distinct advantage of hybrid poplar buffers is that C and nutrient sequestration greatly increase with increasing site fertility, whereas they do so to a much lesser extent in herbaceous buffers. © 2010 Elsevier B.V. All rights reserved.

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