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Can the life-history strategy explain the success of the exotic trees Ailanthus altissima and Robinia pseudoacacia in Iberian floodplain forests?

Castro-Díez P, Valle G, González-Muñoz N, Alonso Á - PLoS ONE (2014)

Bottom Line: Ailanthus altissima and Robina pseudoacacia are two successful invasive species of floodplains in central Spain.A. altissima and R. pseudoacacia showed reproductive traits (late flowering phenology, insect pollination, late and long fruit set period, larger seeds) different from P. alba and other native trees, which may help them to occupy an empty reproductive niche and benefit from a reduced competition for the resources required by reproductive growth.If so, these invaders may benefit from the reduced gap formation rate of flood-regulated rivers of the study region.

View Article: PubMed Central - PubMed

Affiliation: Department of Life Sciences (U.D. Ecology), University of Alcalá, Alcalá de Henares, Madrid, Spain.

ABSTRACT
Ailanthus altissima and Robina pseudoacacia are two successful invasive species of floodplains in central Spain. We aim to explain their success as invaders in this habitat by exploring their phenological pattern, vegetative and sexual reproductive growth, and allometric relations, comparing them with those of the dominant native tree Populus alba. During a full annual cycle we follow the timing of vegetative growth, flowering, fruit set, leaf abscission and fruit dispersal. Growth was assessed by harvesting two-year old branches at the peaks of vegetative, flower and fruit production and expressing the mass of current-year leaves, stems, inflorescences and infrutescences per unit of previous-year stem mass. Secondary growth was assessed as the increment of trunk basal area per previous-year basal area. A. altissima and R. pseudoacacia showed reproductive traits (late flowering phenology, insect pollination, late and long fruit set period, larger seeds) different from P. alba and other native trees, which may help them to occupy an empty reproductive niche and benefit from a reduced competition for the resources required by reproductive growth. The larger seeds of the invaders may make them less dependent on gaps for seedling establishment. If so, these invaders may benefit from the reduced gap formation rate of flood-regulated rivers of the study region. The two invasive species showed higher gross production than the native, due to the higher size of pre-existing stems rather than to a faster relative growth rate. The latter was only higher in A. altissima for stems, and in R. pseudoacacia for reproductive organs. A. altissima and R. pseudoacacia showed the lowest and highest reproductive/vegetative mass ratio, respectively. Therefore, A. altissima may outcompete native P. alba trees thanks to a high potential to overtop coexisting plants whereas R. pseudoacacia may do so by means of a higher investment in sexual reproduction.

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Climatic conditions and plant phenology.A) Climatic diagram showing monthly mean temperature and precipitation during 2011 (Torrejón de Ardoz weather station). B) Diagrams of phenological activity of the three species in 2011. Different letters across species for the beginning or end of each phenophase indicate significant differences after a pairwise Watson-Williams multisample test (P<0.05). Missing letters means that comparisons could not be performed for all species due the lack of variation between replicates.
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pone-0100254-g001: Climatic conditions and plant phenology.A) Climatic diagram showing monthly mean temperature and precipitation during 2011 (Torrejón de Ardoz weather station). B) Diagrams of phenological activity of the three species in 2011. Different letters across species for the beginning or end of each phenophase indicate significant differences after a pairwise Watson-Williams multisample test (P<0.05). Missing letters means that comparisons could not be performed for all species due the lack of variation between replicates.

Mentions: This study was conducted in the floodplains of a medium-low stretch of the Henares River in central Spain (Province of Madrid), which is a public non protected area where no permit access is required. The study area spans over 22 km, from Alcalá de Henares to Mejorada del Campo. Environmental conditions and vegetation structure along this stretch are considered to be homogeneous [50]. Soils are luvisols and fluvisols [65] with a pH near 8 and a percentage of organic matter of 4.6–9 [61]. Altitude ranged from 554 to 602 m above sea level. Climate is continental Mediterranean with hot and dry summers and cold winters. Mean annual temperature and annual precipitation in the study area were 14.1°C and 528.5 mm in 2010 and 15.1°C and 411.1 mm in 2011 (Fig. 1) (data from “Torrejón de Ardoz” weather station, National Institute of Meteorology). In the study area the riparian forest is mostly constrained to a narrow band due to the occupation of floodplains by crops, industry and human settlements. The main dominant tree in the native community is Populus alba, which is accompanied by S. alba and to a minor extent, P. nigra, F. angustifolia and U. minor[50]. Among them, patches of the exotics A. altissima and R. pseudoacacia are frequent, mainly in human-disturbed areas [51]. P. alba has been found to be an exotic invasive species in other regions, such as Australia and South Africa [66], [67].


Can the life-history strategy explain the success of the exotic trees Ailanthus altissima and Robinia pseudoacacia in Iberian floodplain forests?

Castro-Díez P, Valle G, González-Muñoz N, Alonso Á - PLoS ONE (2014)

Climatic conditions and plant phenology.A) Climatic diagram showing monthly mean temperature and precipitation during 2011 (Torrejón de Ardoz weather station). B) Diagrams of phenological activity of the three species in 2011. Different letters across species for the beginning or end of each phenophase indicate significant differences after a pairwise Watson-Williams multisample test (P<0.05). Missing letters means that comparisons could not be performed for all species due the lack of variation between replicates.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4061096&req=5

pone-0100254-g001: Climatic conditions and plant phenology.A) Climatic diagram showing monthly mean temperature and precipitation during 2011 (Torrejón de Ardoz weather station). B) Diagrams of phenological activity of the three species in 2011. Different letters across species for the beginning or end of each phenophase indicate significant differences after a pairwise Watson-Williams multisample test (P<0.05). Missing letters means that comparisons could not be performed for all species due the lack of variation between replicates.
Mentions: This study was conducted in the floodplains of a medium-low stretch of the Henares River in central Spain (Province of Madrid), which is a public non protected area where no permit access is required. The study area spans over 22 km, from Alcalá de Henares to Mejorada del Campo. Environmental conditions and vegetation structure along this stretch are considered to be homogeneous [50]. Soils are luvisols and fluvisols [65] with a pH near 8 and a percentage of organic matter of 4.6–9 [61]. Altitude ranged from 554 to 602 m above sea level. Climate is continental Mediterranean with hot and dry summers and cold winters. Mean annual temperature and annual precipitation in the study area were 14.1°C and 528.5 mm in 2010 and 15.1°C and 411.1 mm in 2011 (Fig. 1) (data from “Torrejón de Ardoz” weather station, National Institute of Meteorology). In the study area the riparian forest is mostly constrained to a narrow band due to the occupation of floodplains by crops, industry and human settlements. The main dominant tree in the native community is Populus alba, which is accompanied by S. alba and to a minor extent, P. nigra, F. angustifolia and U. minor[50]. Among them, patches of the exotics A. altissima and R. pseudoacacia are frequent, mainly in human-disturbed areas [51]. P. alba has been found to be an exotic invasive species in other regions, such as Australia and South Africa [66], [67].

Bottom Line: Ailanthus altissima and Robina pseudoacacia are two successful invasive species of floodplains in central Spain.A. altissima and R. pseudoacacia showed reproductive traits (late flowering phenology, insect pollination, late and long fruit set period, larger seeds) different from P. alba and other native trees, which may help them to occupy an empty reproductive niche and benefit from a reduced competition for the resources required by reproductive growth.If so, these invaders may benefit from the reduced gap formation rate of flood-regulated rivers of the study region.

View Article: PubMed Central - PubMed

Affiliation: Department of Life Sciences (U.D. Ecology), University of Alcalá, Alcalá de Henares, Madrid, Spain.

ABSTRACT
Ailanthus altissima and Robina pseudoacacia are two successful invasive species of floodplains in central Spain. We aim to explain their success as invaders in this habitat by exploring their phenological pattern, vegetative and sexual reproductive growth, and allometric relations, comparing them with those of the dominant native tree Populus alba. During a full annual cycle we follow the timing of vegetative growth, flowering, fruit set, leaf abscission and fruit dispersal. Growth was assessed by harvesting two-year old branches at the peaks of vegetative, flower and fruit production and expressing the mass of current-year leaves, stems, inflorescences and infrutescences per unit of previous-year stem mass. Secondary growth was assessed as the increment of trunk basal area per previous-year basal area. A. altissima and R. pseudoacacia showed reproductive traits (late flowering phenology, insect pollination, late and long fruit set period, larger seeds) different from P. alba and other native trees, which may help them to occupy an empty reproductive niche and benefit from a reduced competition for the resources required by reproductive growth. The larger seeds of the invaders may make them less dependent on gaps for seedling establishment. If so, these invaders may benefit from the reduced gap formation rate of flood-regulated rivers of the study region. The two invasive species showed higher gross production than the native, due to the higher size of pre-existing stems rather than to a faster relative growth rate. The latter was only higher in A. altissima for stems, and in R. pseudoacacia for reproductive organs. A. altissima and R. pseudoacacia showed the lowest and highest reproductive/vegetative mass ratio, respectively. Therefore, A. altissima may outcompete native P. alba trees thanks to a high potential to overtop coexisting plants whereas R. pseudoacacia may do so by means of a higher investment in sexual reproduction.

Show MeSH
Related in: MedlinePlus