WEWeb EcologyWEWeb Ecol.1399-1183Copernicus GmbHGöttingen, Germany10.5194/we-15-1-2015Plant–plant interactions: from competition to facilitationMontesinosD.daniel.montesinos@uc.ptUniversidade de Coimbra, Centre for Functional Ecology, Coimbra, PortugalD. Montesinos (daniel.montesinos@uc.pt)24March201515112This work is licensed under a Creative Commons Attribution 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by/3.0/This article is available from https://we.copernicus.org/articles/15/1/2015/we-15-1-2015.htmlThe full text article is available as a PDF file from https://we.copernicus.org/articles/15/1/2015/we-15-1-2015.pdf
The way plant species influence the composition of their surrounding plant
community has been a subject of interest since Alexander von Humboldt
developed the foundations of biogeography in the 19th century. In
the same century, Adolphe Dureau de la Malle introduced a
preliminary idea of succession (1825), formally developed by the
end of the century by Henry Chandler Cowles (1899) and
founded on the importance of environmental constraints and plant–plant
competitive interactions. The view of plant–plant interactions as primarily
competitive was nearly exclusive until the end of the 20th century,
when Bertness and Callaway formally established the concept of facilitation,
as opposed to competition, to stress the importance of mutualism among plant
species in shaping plant communities (Bertness and
Callaway, 1994; Callaway, 1995). Those foundational papers started an
important movement devoted to the study of positive interactions among
plants, and Web Ecology, first published in the year 2000, has played a
significant role in propagating those ideas in its pages since then; this
includes a broad range of studies and authors, including several works by
R. M. Callaway and many of his collaborators.
Interestingly, most of Web Ecology's papers dealing with plant–plant
interactions focused on the study of facilitation, but competition naturally
also found space in our pages. For instance, Rey Benayaset et al. (2007) studied different
management techniques of the use of low-cost, low-impact techniques on
restoration of Quercus coccifera oak forests, finding that competition had a strong impact
on oak recruitment and that simple clipping of competing vegetation
resulted in similar effects to those of more thorough and expensive
treatments of competition removal. Other studies (Li et al., 2007) did try to
detect facilitation between pairs of species but found prevailing competition
between two species inhabiting mobile dunes, although the presence of one species
created a wind barrier that modified prevailing airstreams and strongly influenced
the spatial pattern of seed dispersal of the second species.
This provided further evidence of the effect of shrubs as a source of spatial heterogeneity.
Some facilitation studies made important contributions to the management and
conservation of a single keystone species. Arrieta and Suárez (2001) reported the
facilitative effect of nurse Ilex aquifolium (holly) shrubs and successfully related the
observed spatial pattern to differences in light, dispersal, and
disturbance, with important implications for holly conservation in southern
Europe. Other studies had a large-scale vision and embraced the study of
plant–plant interactions at landscape levels, even comparing similar
habitats across continents. For instance, Marañón et al. (2009) studied the ecological factors
influencing Mediterranean oak savannas occurring in either California or the
Iberian Peninsula. They discussed the complex facilitative and competitive
interactions that explain the coexistence of oak trees and herbaceous species
in Mediterranean savannas and dehesas. Different factors acted at different
spatial scales, from large-spatial-scale rainfall and water availability to
local- and patch-scale factors related to disturbance, water distribution, and
fire, proposing different models integrating complex facilitative and
competitive interactions. Other important ecological generalizations were
also established in our pages. Reid et al. (2010) performed a systematic review of the
ecological literature on cushion plants, which were found to be real
champions of facilitation due to the microclimatic conditions found within
their compact and prostrate canopies and the particular importance of
those more favorable conditions on the highly stressful environments that
they inhabit, making them keystone species in the ecosystems they inhabit.
Ariza and Tielbörger (2012) found that biomass explained
the intensity of facilitative interactions but not of competitive ones. The
assumption that increased biomass results in increased competition was
challenged by intra-specific tests with three different annual herbs, for
which a consistent pattern of size-dependent facilitation interactions was
observed across life stages, explained as predominantly aboveground
facilitation via water stress alleviation and predominant below-ground
competition for water. Saiz et al. (2014)
evaluated the interaction between grazing and aridity on the patch structure
of gypsophila plant communities and the role of specialists as
facilitators of other plant species. Specialist gypsophila plants were
significant facilitators, but their relative importance depended on grazing
and aridity.
Despite the short timespan since the formal study of facilitation was
established, it has been a hot topic in the ecological literature
with a considerable impact among researchers. Lortie and Callaway (2009) studied the relative abundance and quality of
scientific literature dealing with competition (metaphorically described as
Goliath) and facilitation (David), finding that although the long tradition
of the study of competition has produced a much higher net amount of papers dealing
with competition, papers dealing with facilitation received a similar mean
number of citations. This very clearly illustrated the fact that quality is more important
than quantity for the relevance of scientific studies – a
vision that we fully embrace in Web Ecology.
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