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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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Species branch production in 2011.Left: Allometric relationships between previous-year stem mass and current year stem (A), leaf (C), inflorescence (E) and infrutescence (G) mass (note the log-scale of both axes). The Likelihood Ratio Statistic (LRS) comparing slopes across species and its significance is shown in each chart. Different letters indicate significant slope differences (P<0.017, after Bonferroni correction). Right: relative production of current-year stem (B), leaf (D), inflorescence (F) and infrutescence (H) mass, expressed per unit of previous-year stem mass. Different letters across species indicate significant differences (Tukey test, see Table 3 for more details).
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pone-0100254-g002: Species branch production in 2011.Left: Allometric relationships between previous-year stem mass and current year stem (A), leaf (C), inflorescence (E) and infrutescence (G) mass (note the log-scale of both axes). The Likelihood Ratio Statistic (LRS) comparing slopes across species and its significance is shown in each chart. Different letters indicate significant slope differences (P<0.017, after Bonferroni correction). Right: relative production of current-year stem (B), leaf (D), inflorescence (F) and infrutescence (H) mass, expressed per unit of previous-year stem mass. Different letters across species indicate significant differences (Tukey test, see Table 3 for more details).

Mentions: The mass of every branch organ in either cohort was the largest in A. altissima and the smallest in P. alba, although FLt and FRt did not differ between A. altissima and R. pseudoacacia in 2011 and 2010, respectively (Table 2). However, when organ mass was relativized by St−1, A. altissima tended to show larger relative production only for stems, but lower for reproductive organs (Fig. 2 right, Fig. S2). In 2011, linear mixed models showed that St/St−1 was the largest in A. altissima and similar between P. alba and R. pseudoacacia (Fig. 2B). Lt/St−1 was similar across species, being marginally smaller in R. pseudoacacia than in P. alba (P = 0.07). By contrast, FLt/St−1 and FRt/St−1 followed the ranking R. pseudoacacia ≥ P. alba ≥ A. altissima (Fig. 2F, H). This ranking was consistent independently of whether any or both sexes were considered in A. altissima (data not shown). In 2010 comparisons between A. altissima and R. pseudoacacia showed similar trends, but less often significant (Fig. S2). Among all analyses, DBH was only significant in the case of St/St−1 of 2011, where it showed a negative slope (i.e. thicker trees tended to produce less stem mass). In 2011, the random factor (tree) explained between 37 and 57% of the variance not explained by the fixed factors, while in 2010 this proportion varied from 6% to 83% (Table 3).


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)

Species branch production in 2011.Left: Allometric relationships between previous-year stem mass and current year stem (A), leaf (C), inflorescence (E) and infrutescence (G) mass (note the log-scale of both axes). The Likelihood Ratio Statistic (LRS) comparing slopes across species and its significance is shown in each chart. Different letters indicate significant slope differences (P<0.017, after Bonferroni correction). Right: relative production of current-year stem (B), leaf (D), inflorescence (F) and infrutescence (H) mass, expressed per unit of previous-year stem mass. Different letters across species indicate significant differences (Tukey test, see Table 3 for more details).
© Copyright Policy
Related In: Results  -  Collection

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

pone-0100254-g002: Species branch production in 2011.Left: Allometric relationships between previous-year stem mass and current year stem (A), leaf (C), inflorescence (E) and infrutescence (G) mass (note the log-scale of both axes). The Likelihood Ratio Statistic (LRS) comparing slopes across species and its significance is shown in each chart. Different letters indicate significant slope differences (P<0.017, after Bonferroni correction). Right: relative production of current-year stem (B), leaf (D), inflorescence (F) and infrutescence (H) mass, expressed per unit of previous-year stem mass. Different letters across species indicate significant differences (Tukey test, see Table 3 for more details).
Mentions: The mass of every branch organ in either cohort was the largest in A. altissima and the smallest in P. alba, although FLt and FRt did not differ between A. altissima and R. pseudoacacia in 2011 and 2010, respectively (Table 2). However, when organ mass was relativized by St−1, A. altissima tended to show larger relative production only for stems, but lower for reproductive organs (Fig. 2 right, Fig. S2). In 2011, linear mixed models showed that St/St−1 was the largest in A. altissima and similar between P. alba and R. pseudoacacia (Fig. 2B). Lt/St−1 was similar across species, being marginally smaller in R. pseudoacacia than in P. alba (P = 0.07). By contrast, FLt/St−1 and FRt/St−1 followed the ranking R. pseudoacacia ≥ P. alba ≥ A. altissima (Fig. 2F, H). This ranking was consistent independently of whether any or both sexes were considered in A. altissima (data not shown). In 2010 comparisons between A. altissima and R. pseudoacacia showed similar trends, but less often significant (Fig. S2). Among all analyses, DBH was only significant in the case of St/St−1 of 2011, where it showed a negative slope (i.e. thicker trees tended to produce less stem mass). In 2011, the random factor (tree) explained between 37 and 57% of the variance not explained by the fixed factors, while in 2010 this proportion varied from 6% to 83% (Table 3).

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