Solidago altissima subsp. areas, L.

Rim, Hojun, Lee, Minhyun & Song, Uhram, 2023, Mowing inhibits the invasion of the alien species Solidago altissima and is an effective management strategy, Management of Biological Invasions 14 (1), pp. 63-79 : 67-72

Comparison of vegetation between S. altissima-dominant areas and uninvaded areas

In the area dominated by S. altissima , we detected 44 and 37 plant species in 2018 and 2019, respectively ( Table S2 ). Many species belonged to Asteraceae , followed by Gramineae and Rosaceae . The most dominant species was S. altissima in this area. In the area dominated by native species, we found 53 plant species in 2018 ( Table S2 ). Many species belonged to Asteraceae , followed by Gramineae and Fabaceae . The most dominant species was Glycine soja in this area. All species detected in the areas dominated by S. altissima or native species in 2018 and 2019 are listed in Table S2 .

The average relative coverage of S. altissima was 74.77% in S. altissima - dominant sites, compared with 5.65% at sites dominated by native species ( Figure 1a ). The average number of total species per quadrat differed significantly between S. altissima -dominated and native species-dominated areas (i.e., 6.02 and 7.82, respectively) ( Figure 1b ). The average number of native species also differed significantly between S. altissima -dominated and native species-dominated areas (i.e., 4.44 and 6.01, respectively) ( Figure 1b ). The proportion of non-native species was 26.2% in S. altissima -dominant areas and 23.3% in native species-dominated areas.

In the area dominated by S. altissima , the importance value was highest for S. altissima (0.409), followed by Pueraria lobata (0.141) and Artemisia princeps (0.087) in July 2018 ( Table S3 ). In the area dominated by native species, Glycine soja (0.166), P. lobata (0.158), and Erigeron canadensis (0.154) had the highest importance values. The importance value for S. altissima was 0.104, ranking 6 th in July 2018 ( Table S4 ).

Management of S. altissima -dominated community by repeated mowing and eco-friendly herbicide application

The coverages of S. altissima did not differ significantly between 2018 and 2019, regardless of the treatment applied to quadrats ( Figure S2 ). The quadrats that were mowed three times in 2018 had a lower S. altissima coverage in 2019 than in 2018; however, the variance was high and the difference was not statistically significant. Therefore, mowing treatment for 1 year did not affect the coverage of S. altissima , regardless of mowing frequency.

The importance value for S. altissima changed significantly after mowing treatment for 1 year. The importance value for S. altissima was 0.409 in 2018 and decreased to 0.321 in 2019. Consistent results were obtained at all sites subjected to mowing (Table S 5).

In July 2018, 2 months after the first treatment (mowing or Eco200), the height of S. altissima in the mowing group was significantly different from that of the control group, with no difference in the height of S. altissima between the Eco 200 treatment and control group (Table S 6). After 1 year of mowing or Eco 200 treatment, in April 2019, the height of the dead shoots differed significantly between the control group and the Mowing 1, Mowing 2, and Mowing 3 groups ( Table 1 ). In particular, the average heights in the Mowing 2 and Mowing 3 groups were one-tenth that of the control group ( Table 1 ). However, the height of the dead shoots in the Eco 200 group was not significantly different from that in the control group and was larger than those in the mowing treatment groups.

We continued the experiment to determine the effects of mowing on the growth of S. altissima in 2019. We measured the height of shoots of S. altissima in May, July, and September, before each mowing treatment. The height of the shoot already differed between the control and Mowing 2 or Mowing 3 groups in May 2019, before mowing ( Table 2 ). Height did not differ between the Mowing 1 and control groups. In July, heights in the Mowing 2 and Mowing 3 groups were significantly different from that in the control group, with no difference between the Mowing 1 and control groups (Table S 7). In September, heights in all treatment groups were significantly different from that in the control group ( Table 3 ).

The number of shoots of S. altissima did not differ significantly between groups in March 2018 before the experiment started ( Figure 2 ). After 1 year of mowing or Eco 200 treatment, the number of shoots of S. altissima was significantly lower in the Mowing 3 group than in the control group in April 2019 ( Figure 2 ). Mowing 1, Mowing 2, and Eco 200 treatments did not reduce the number of shoots compared with the number observed in the control group.

The number of leaves was lower in mowing treatment groups than in the control group (Table S 8). Mowing 3 (mowed twice before harvesting) had the fewest leaves between the control and treatment groups. The aboveground biomass of S. altissima was also significantly lower in the mowing treatment groups than in the control group. However, there were no significant differences between mowing treatments ( Figure 3a ).

The biomass of rhizomes was significantly affected by mowing treatment and by the frequency of mowing after 2 years ( Figure 3b ). Plants subjected to mowing once a year had 933.6 g /m 2 rhizomes, similar to the rhizome content of control plants (987.7 g /m 2). However, plants that were mowed two or three times had 732.0 g/m 2 or 535.3 g /m 2 rhizomes, respectively, which were significantly lower than the estimate for control plants.

Effects of mowing frequency on reproductive characteristics

We found that flowering rates of S. altissima were affected by mowing. All individuals in the Mowing 1 group had flowers and a flowering rate significantly higher than the flowering rate of the control group (93 ± 7%). However, the flowering rates in the Mowing 2 (0%) and Mowing 3 groups (20%) were significantly lower than that in the control group in Fall 2019 ( Figure 4 ).

Effects of mowing frequency and eco-friendly herbicide application on the early establishment of S. altissima invasion

Although there were no statistically significant differences in cover between the control and treatment groups due to high variances, patches of S. altissima showed the greatest expansion in the control group, followed by the 20% Eco 200 and 100% Eco 200 groups ( Table 4 ). In particular, 100% mowing and Eco 200 treatment decreased the patch area of S. altissima .

The flowering rate decreased with the frequency of mowing in the patches (sites 8–10) of S. altissima ( Figure S3 ). Most individuals flowered in the control quadrats. The flowering rate in the Mowing 3 group was 13%, which was significantly lower than that in the control group. The flowering rate in Eco 20% group had higher than Mowing 3 group and Eco 100% patches had no flowering individuals ( Figure S3 ).

Allelopathic effect of S. altissima

Solidago altissima extract adversely affected the germination rates of Lactuca sativa L. and Oenothera biennis L. (Table S 9). For L. sativa , the germination rate was 32.9% at 3 days and increased to 44.3% at 6 days in the control group. For O. biennis , the germination rate was 45.7% at 6 days and increased to 65.7% at 12 days in the control group. However, when treated with the extract of S. altissima , the germination of seeds of both plants was delayed or did not occur. L. sativa seeds did not germinate until 9 days after treatment with a 20% dilution of the S. altissima extract and did not germinate at all when treated with a 50% dilution of the S. altissima extract. The seeds of O. biennis showed similar responses to S. altissima extract, although small numbers of seeds germinated, even when treated with 50% S. altissima extract (Table S 9). The growth of roots of both plants was also significantly reduced by treatment with the S. altissima extract (Table S 10). Lactuca sativa seedlings showed root elongation of only 0.8 mm 12 days after treatment with a 20% dilution of S. altissima extract. The roots of O. biennis seedlings did not grow when treated with S. altissima extract, regardless of the concentration.

Figures

Figure 1. (a) Coverage of S. altissima and (b) the average number of species per quadrat in the S. altissima-dominant areas or uninvaded areas. Data are presented as means ± standard errors of 14 replicates. Bars with different letters are significantly different at p <0.05 (Student’s t-test).

Figure 2. Number of shoots of S. altissima in March 2018 and April 2019. Mowing 1: mowed once in July; Mowing 2: mowed twice in May and September; Mowing 3: mowed three times in May, July, and September; Eco 200: 30% of shoots in the quadrats were cut near the ground, and the cut surfaces were covered with Eco 200 block. Data are presented as means ± standard errors of 14 replicates. Bars with different letters are significantly different at p <0.05 (ANOVA with post hoc Tukey’s test).

Figure 3. (a) Aboveground biomass of S. altissima in September 2019. (b) Biomass of rhizomes of S. altissima in September 2019. Mowing 1: mowed once in July; Mowing 2: mowed twice in May and September; Mowing 3: mowed three times in May, July, and September. Data are presented as means ± standard errors of 14 replicates. Bars with different letters are significantly different at p <0.05 (ANOVA with post hoc Tukey’s test).

Figure 4. Effects of control practices on flowering rates of S. altissima in October 2019. Mowing 1: mowed once in July; Mowing 2: mowed twice in May and September; Mowing 3: mowed three times in May, July, and September. Data are presented as means ± standard errors of 14 replicates. Bars with different letters are significantly different at p <0.05 (ANOVA with post hoc Tukey’s test).

Tables

Table 2. Heights of S. altissima before mowing treatment in May 2019.

Site	Control	Mowing 1	Mowing 2	Mowing 3
Site 1	101.0 ± 3.2a	101.0 ± 3.0a	81.1 ± 2.6b	64.9 ± 3.1c
Site 2	116.5 ± 4.7a	111.8 ± 4.7a	82.9 ± 4.1b	72.5 ± 6.6b
Site 4	89.1 ± 2.2a	74.8 ± 2.2b	49.5 ± 3.1d	59.8 ± 1.6c
Site 5	93.5 ± 2.5a	99.5 ± 2.3a	78.0 ± 2.0b	77.1 ± 2.0b
Site 6	125.3 ± 5.2a	117.0 ± 3.0a	86.5 ± 3.0c	105.0 ± 3.4b
Site 7	123.3 ± 3.3a	119.3 ± 2.9ab	111.3 ± 2.8bc	110.3 ± 3.1c
Site 8	96.0 ± 4.0a	94.5 ± 4.1ab	84.5 ± 3.3bc	81.0 ± 3.1c

* Mowing 1: mowed once in July; Mowing 2: mowed twice in May and September; Mowing 3: mowed three times in May, July, and September. Data are presented as means ± standard errors of 10 replicates. Means within a row followed by different letters are significantly different at p <0.05 (ANOVA with post hoc Tukey’s test). Units: cm.

Table 3. Heights of S. altissima before mowing in September 2019.

Site	Control	Mowing 1	Mowing 2	Mowing 3
Site 1	168.0 ± 3.27a	64.0 ± 3.32c	100.5 ± 9.14b	67.5 ± 3.1c
Site 2	192.0 ± 11.3a	79.0 ± 4.07c	111.0 ± 6.9b	73.0 ± 7.61c
Site 3	159.0 ± 4.99a	123.0 ± 7.12b	84.5 ± 5.89c	47.0 ± 2.71d
Site 4	190.0 ± 2.98a	102.0 ± 3.89b	112.5 ±8.07b	62.0 ± 5.33c
Site 5	217.0 ±10.23a	87.5 ± 4.9c	137.0 ± 4.96b	62.5 ± 3.1d
Site 6	177.5 ± 6.76a	97.5 ± 5.44c	120.5 ± 4.97b	60.0 ± 2.58d
Site 7	143.5 ± 12.2a	81.0 ± 2.77b	138.5 ± 3.5a	62.0 ± 4.67b

* Mowing 1: mowed once in July; Mowing 2: mowed twice in May and September; Mowing 3: mowed three times in May, July, and September. Data are presented as means ± standard errors of 10 replicates. Means within a row followed by different letters are significantly different at p <0.05 (ANOVA with post hoc Tukey’s test). Units: cm.

Table 4. Change in areas occupied by S. altissima in patch-type communities from March 2018 to March 2019.

Control	Mowing 3	Eco 20%	Eco 100%
205.2 ± 107.3	24.7 ± 44.0	104.5 ± 85.2	− 31.7 ± 13.0

Mowing 3: mowed three times in May, July, and September; Eco 20%: 20% of shoots were mowed and treated with Eco 200; Eco 100%: 100% of shoots were mowed and treated with Eco 200. Data are presented as means ± standard errors of six replicates.

Table 1. Heights of dead shoots of S. altissima after 1 year of treatment in April 2019.

Site	Control	Mowing 1	Mowing 2	Mowing 3	Eco 200
Site 1	162.8 ± 6.62a	85.7 ± 5.52b	29.5 ± 2.74c	21.3 ± 2.09c	77.9 ± 8.94b
Site 2	213.2 ± 12.08a	87.1 ± 7.33c	38.4 ± 2.17d	29.0 ± 2.01d	144.8 ± 9.57b
Site 3	163.4 ± 7.31a	66.3 ± 4.55c	40.7 ± 2.57d	33.4 ± 2.11d	143.4 ± 7.13b
Site 4	191.6 ± 3.84a	160.8 ± 7.90b	59.2 ± 1.66d	81.9 ± 6.50c	166.9 ± 12.33b
Site 5	181.7 ± 4.76a	114.7 ± 2.90b	89.5 ± 10.23c	46.6 ± 5.12d	183.8 ± 9.00a
Site 6	174.8 ± 4.34a	82.9 ± 4.49c	39.7 ± 2.51d	31.6 ± 2.47d	153.3 ± 3.12b
Site 7	165.5 ± 4.79a	91.2 ± 6.02b	64.7 ± 3.24c	44.0 ± 3.67d	153.8 ± 7.25a

* Mowing 1: mowed once in July; Mowing 2: mowed twice in May and September; Mowing 3: mowed three times in May, July, and September; Eco 200: 30% of shoots in the quadrats were cut near the ground, and the cut surfaces were covered with the Eco 200 block. Data are presented as means ± standard errors of 20 replicates. Means within a row followed by different letters are significantly different at p <0.05 (ANOVA with post hoc Tukey’s test). Units: cm.