New Forests

, Volume 42, Issue 2, pp 241–265 | Cite as

Understory plant diversity and biomass in hybrid poplar riparian buffer strips in pastures

  • Julien FortierEmail author
  • Daniel Gagnon
  • Benoit Truax
  • France Lambert


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 m2 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.


Plant species richness Canopy openness Light Native species Wetland species Introduced (exotic) species Agroforestry Afforestation 



We gratefully acknowledge funding and planting stock received from the Ministère des Ressources naturelles et de la Faune du Québec, and funding from the Ministère de l’Agriculture, des Pêcheries et de l’Alimentation du Québec, Agriculture and Agri-Food Canada, and the Conférence régionale des élus de l’Estrie. We are very grateful to the landowners (M. Beauregard, A. Doyon, J. Lamontagne) who allowed the planting of the buffers on their farms. We would also like to thank C. Bélisle, M. Bélisle, P.-O. Émond, G. Fleury, E. Flores, M.-C. Giroux and L. Godbout who assisted with field work. Thanks are also due to C. Vasseur of the Biodôme de Montréal for facilitating soil analyses, as well as to S. Hay of the Marie-Victorin Herbarium (Université de Montréal) for verifying our plant specimen identifications, and identifying many sedges and grasses. We also acknowledge two anonymous reviewers whose constructive comments helped improve this paper. J. Fortier wishes to thank the Fiducie de recherche sur la forêt des Cantons-de-l’Est for the scholarship awarded.


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Copyright information

© Springer Science+Business Media B.V. 2011

Authors and Affiliations

  • Julien Fortier
    • 1
    Email author
  • Daniel Gagnon
    • 1
    • 2
  • Benoit Truax
    • 2
  • France Lambert
    • 2
  1. 1.Centre d’étude de la forêt (CEF), département des sciences biologiquesUniversité du Québec à MontréalMontréalCanada
  2. 2.Fiducie de recherche sur la forêt des Cantons-de-l’EstSt-Benoît-du-LacCanada

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