Can the Riparian Invader, Arundo Donax, Benefit

DOI: 10.1111/wre.12036

Can the riparian invader, Arundo donax, beneﬁt from clonal integration?

L KUI*†, F LI*, G MOORE* & J WEST* *Department of Ecosystem Science and Management, Texas A & M University, College Station, TX, USA, and †College of Environmental Science and Forestry, State University of New York, Syracuse, NY, USA

Received 30 April 2013 Revised version accepted 3 June 2013 Subject Editor: Francesco Tei, Perugia, Italy

objective was to determine whether clonal integration Summary enhanced growth and survival of A. donax ramets. We Resource sharing through rhizomes of clonal plants compared growth-related responses in paired 1 m2 supplements locally available nutrients to enhance plots with severed and intact rhizomes. In the first recruitment and growth in resource-limited environ- 19 days, rhizome severing nearly doubled ramet ments. We investigated whether Arundo donax,an density, while by 77 days, the intact rhizomes pro- invasive clonal plant, can benefit from clonal integra- duced 67% taller stems with 49% greater diameter tion. Sharing resources between ramets can facilitate and showed higher survival rate after flooding. This resprouting from mowing, fire and herbicide treat- study provides initial evidence that physiological inte- ments, but it is unknown whether clonal integration gration could be an important mechanism in A. donax, contributes to A. donax invasion success. Our first which can enhance its competitive abilities, accelerate objective was to determine whether A. donax rhizomes rates of encroachment and strengthen its capability to transported water between ramets. Hydrogen isotopic– recolonise disturbed areas. Our results highlight an enriched water was applied on three 1 m diameter important consideration of clonal invasive species in areas, and rhizome and soil samples were collected weed management. beyond the watering zone after 5, 24 and 48 h of the Keywords: giant reed, translocation, invasive species, last watering. Logistic modelling indicated that water plant response, isotopes, rhizome severing. was able to move laterally at least 3.5 m. The second

KUI L, LI F, MOORE G&WEST J (2013). Can the riparian invader, Arundo donax, beneﬁt from clonal integration? Weed Research 53, 370–377.

transport nitrogen through the interconnected rhizomes Introduction (de Kroon et al., 1996, 1998). Clonal plants that remain interconnected belowground Physiological integration among clones can signifi- have the potential for physiological integration, the cantly improve the survival of a local population (Xiao translocation of water resources, nutrients or carbohy- et al., 2011), enhance fitness (Du et al., 2010) and drates from a donor ramet to a recipient ramet (Caraco support the growth of ramets into harsher environments & Kelly, 1991; de Kroon et al., 1998). For example, (Yu et al., 2008). Despite all those benefits, the existence using stable isotope labelling in pot experiments, Carex and extent of physiological integration differs among hirta L. and Carex flacca Schreb. were found to species (Williams & Briske, 1991; Dong, 1999), size of

Correspondence: L Kui, College of Environmental Science and Forestry, State University of New York, Syracuse, NY, USA. Tel: (+1) 3154704831; Fax: (+1) 3154706535; E-mail: [email protected]

© 2013 European Weed Research Society 53, 370–377 Clonal integration of Arundo donax 371 ramet (Caraco & Kelly, 1991; Brezina et al., 2006), root many riparian areas may provide continuous access to development (Matlaga & Sternberg, 2009) and resource groundwater even during drought, and thus, integra- availability (de Kroon et al., 1996; Guo et al., 2011). tion may not exist under mesic or homogeneous Clonal integration may benefit rhizomatous plants conditions (Matlaga & Sternberg, 2009). growing in systems with pronounced resource gradients This study examined the existence and potential (Dong, 1999; Xiao et al., 2010). In semi-arid riparian benefits of clonal integration in A. donax on the flood- zones, water availability gradients provide conditions plain of lower Rio Grande River, USA. The first for clonal plants to transport water from river banks objective was to determine whether A. donax shared and distribute it throughout floodplains (Shumway, soil resources (here water) through its rhizome 1995). In turn, oxygen can be transported from terres- networks at lateral distances up to 3.5 m, using a trial ramets to the lower submerged ramets (Amsberry deuterium-labelling experiment. If clonal integration et al., 2000; Xiao et al., 2010). In some riparian habi- existed in A. donax, the second objective was to assess tats, clonal integration may allow clonal invasive the effects of clonal integration on plant’s recruitment plants to grow faster and expand more rapidly than and growth by conducting a rhizome-severing experi- the non-clonal native plants (Wang et al., 2009). Plant ment. Our goal was to better understand the mecha- invasion has become a serious ecological issue in ripar- nisms for successful invasion by large clonal plants ian zones, and riparian restoration and management such as A. donax. projects have been carried out to control the expansion of invasive species (Richardson et al., 2007). Efforts to Materials and methods restore riparian zones and manage non-native riparian vegetation would benefit from improved understanding Site description of physiological and biological characteristics of clonal invasive species. Clonal plants may be more difficult to Research sites were located on an c. 1300 m wide flood- control using fire, mowing or herbicide treatments plain on the lower Rio Grande River (29°14′ N, 100°47′ because of vigorous resprouting from rhizomes (De W) of the USA–Mexico border. All experimental plots Cauwer & Reheul, 2009), and clonal integration may were located within the lower/active floodplain terrace, further enhance resprouting potential by translocating which was occupied by a continuous, nearly monocul- resources from robust rhizomes to weaker ramets. ture stand of naturally populated A. donax with sparse This study focuses on Arundo donax L. (giant reed), (<1%) Prosopis glandulosa Torr. The land on the high a clonal perennial grass that invades in North America terrace outside of our study site is managed as range- and frequently inhabits riparian zones (Dudley, 2000). land with cattle and sheep grazing. However, grazing Like many clonal invasive species, it has robust persis- was excluded from our study area for the past several tent rhizomes and propagates solely by vegetative decades through the construction of fever tick perma- means (Khudamrongsawat et al., 2004). Arundo donax nent quarantine/buffer zones (Pound et al., 2010). Our is characterised by rapid growth rates (up to 70 cm per site is located on alluvial soils that are generally well week), high biomass production, a tendency towards stratified, calcareous, sandy to silt loams (SSURGO, community dominance in many habitats and tolerance 2013). Gravelly layers have been encountered at depth to a wide range of environmental conditions (Dudley, during soil coring operations for other research efforts 2000). Any of these might be attributed, at least in on the site. The soil surface elevations in our sites were part, to clonal integration (Cushman & Gaffney, about 3–5 m above the average river water level. Arun- 2010). Using the network of robust persistent rhi- do donax may have been promoted by fire (Coffman zomes, it is reasonable to expect A. donax can extend et al., 2010), which occur commonly in the region. growth during dry conditions by transporting water There was evidence of previous fire events at our site, from moist areas to the neighbour ramets on flood- although none occurred at our site during the study. plains. If this is true, clonal integration may provide Amistad Dam at Del Rio, TX, about 50 km upstream an important mechanism to explain why many semi- of our research site, was completed in 1969. Altered arid riparian zones have been extensively occupied by flow regimes following dam construction probably also A. donax (Yang et al., 2011). contributed to the expansion of exotic species, including On the other hand, although A. donax maintains A. donax, into the riparian zones (Purchase et al., physical connection between ramets, it may not be nec- 2001). essary for A. donax to maintain physiological integra- The climate in this region is semiarid with average tion in all riparian environments (Caraco & Kelly, annual rainfall of 470 mm (NOAA, 2010). In 2010, a 1991). Arundo donax roots can penetrate to a depth of summer flood happened from 7 to 15 July. It was up to about 3 m (personal observation), which in caused by significant releases from the Amistad Dam

© 2013 European Weed Research Society 53, 370–377 372 L Kui et al. and heavy local precipitation associated with Hurri- cane Alex. The total precipitation from June to August was 152 mm, similar rainfall amount compared with 30-year averages for those months (NOAA, 2010). However, the precipitation in July was 120 mm, three times the average for July.

Deuterium-labelling experiment The deuterium-labelling experiment was conducted in an area located c. 100 m from the water course within a continuous stand of A. donax. The experiment began in mid-August 2010, one month after the summer flood. The experimental site was not inundated during flooding but did experience shallow groundwater (~1.5 m Fig. 1 Plot layout for the watering experiment. The centre dark from the soil surface). After the flood receded and colour marks the 1 m diameter watering area. Outside rings 20 days had passed without precipitation, we set up were situated at four distances away from the labelled ramets. three replicate circular plots (Fig. 1) spaced 10 m apart. Samples were collected at the intersection of each ring along In each plot, five rhizome and five soil samples were col- five direction lines (N, NE, NW, SE, SW). lected for background isotopic determination prior to the experiment on 16 August 2010. Those background directions, which were treated as replicate samples for samples were located randomly along the 3.5 m ring of corresponding distances. In each plot, Three additional each plot to prevent potential rhizome damage within post-watering soil samples were collected within the the harvesting area later in the experiment. At each watering zone on 18 August (top 10 cm), 19 August sample point, rhizome samples c. 5 mm in diameter and (10, 20 and 30 cm depths) and 20 August (top 10 cm). 10 mm long were collected from the nearest rhizome Samples were processed at the Stable Isotopes for using an increment borer. Soil samples were collected Biosphere Science Laboratory at Texas A&M Univer- from the upper 10 cm adjacent to each rhizome. To sity (http://sibs.tamu.edu) for determination of deute- minimise evaporative isotopic fractionation, soil and rium content as follows. Water from soil and rhizome rhizome samples were sealed in scintillation vials with samples was extracted using the cryogenic vacuum Polyseal cone caps (Qorpak, Bridgeville, PA, USA) fol- distillation method (West et al., 2006). The hydrogen lowed by Parafilm sealing to prevent cap loosening. stable isotope ratios of soil water and rhizome water Then, all the samples were kept in the shade until were then analysed with a Delta V Isotope Ratio Mass moved into a freezer (4°C) at end of the day. Samples Spectrometer coupled to a High Temperature Conver- were kept frozen until water extraction. sion Elemental Analyzer (TC/EA-IRMS; Thermo Immediately after pre-sampling, 18.4 L of deute- Fisher Scientific, Waltham, MA, USA). Hydrogen sta- rium-enriched water (dD ~ 1800 &) was sprayed uni- ble isotope ratios are expressed in delta notation (dD) formly inside the watering zone, a 1 m diameter circle in parts per thousand (&) relative to the internation- area in the centre of each plot (Fig. 1). Care was taken ally reference standard, Standard Mean Ocean Water to avoid any overflow outside the watering zone by (Werner & Brand, 2001; Coplen & Qi, 2009) as applying water at a slow and constant rate. For every follows: plot, the watering process was repeated on three dD ð&Þ¼ðR =R 1Þ1000& ð1Þ successive days between 08:00 and 10:00 (1618 sample sample standard

August). To simulate natural rainfall conditions, the where Rsample and Rstandard are the D/H ratio in the amount of water (18.4 L 9 3 days) summed to sample and standard respectively. The labelled water 70.3 mm, which was approximately the 20-year mean (~1800&) was produced by mixing 53.5 mL of 99.95% rainfall for August (70 mm; NOAA, 2010). heavy water (D2O) and 170 L of local tap water. 2 To trace the movement of H2O, five rhizome sam- Long-term precision for natural abundance values is ples inside the watering zone and 20 samples beyond c. 2& (1r). the zone were collected at 5, 24 and 48 h after the last day of watering. There were four concentric rings at Rhizome-severing experiment distances of 0.5, 1.0, 1.5 and 3.5 m from the edge of watering zone (Fig. 1). The five sampling points The rhizome-severing experiment began prior to the located on each ring were aligned in five cardinal deuterium-labelling experiment in May 2010 and

© 2013 European Weed Research Society 53, 370–377 Clonal integration of Arundo donax 373 continued through mid-August. A transect was set up through interconnected rhizomes. The observed proba- 30 m away from the deuterium experimental site and bility was calculated by considering a binary response perpendicular to the river, beginning 0.5 m from the variable where 1 represented the rhizomes that received river and ending at 100 m. A randomised complete enriched water with dD > 20& and 0 represented block experimental design (Ott & Longnecker, 2010) rhizomes with dD < 20&. We chose a threshold of was used to account for any elevation and soil mois- 20& for determining whether rhizomes had enriched ture gradients from the river inland. Five blocks with signal, because that value was the highest rhizome’s 20 m intervals were spaced evenly along the transect. deuterium concentration prior to watering, and it was Each block consisted of two 1 9 1 m plots, one also nearly two standard deviations (28& + 2 9 severed and one control. The severed plot was ran- 3.52&) above the background rhizome deuterium signal domly assigned and spaced 6 m apart from its control established prior to labelling. counterpart. The plot (P) receiving enriched water, the distance Initial conditions prior to treatment were docu- (l) in metres from the watering area and the number of mented on 1 June 2010 by harvesting aboveground days (t) since watering were included as explanatory biomass in all plots and measuring the diameters of variables, where P was a factor with three levels, and l live stems and dry-weight of plot-level stems. One day and t were continuous variables. after harvest (2 June 2010), underground rhizome con- Model selection was performed by calculating nections were severed around the perimeter of all treat- Akaike information criteria (AIC; Burnham & Anderson, ment plots using a narrow saw blade to the depth of 2002) among 11 candidate models (the lower AIC the 30 cm, which is well below the typical depth of better the model), including the full model with all the rhizome connections based on observations of river above three explanatory variables, plus all their bank cutaways. In the control plots, soils around the two-way interactions. For the best model, the exponen- perimeters were disturbed using a thin iron bar, insert- tiated parameters for each explanatory variable repre- ing to the depth of 30 cm but avoiding damage to rhi- sent odds ratios and were used for interpretation. The zomes. The reason for soil disturbance in control plots odds ratio was the factor by which the odds increased was to account for any effects on plant performance or decreased for a 1 unit increase in the explanatory var- resulting from it alone. Any displaced soils and litter iable (continuous variables, such as distance) or when were moved back into place after rhizome severing or factors change from one level to the other (category surface soil disturbance. variables, such as plot). Nineteen and 51 days after rhizome severing (on 21 For the rhizome-severing experiment, because the June and 20 July respectively), stem heights and basal data were not normally distributed, we used the paired diameters of regrowth were measured in situ and stem Wilcoxon signed rank test to determine the effects of numbers were counted. The flood occurred between rhizome severing using stem density, plot-level above- these two sets of measurements from day 3542. Three ground biomass, stem diameter and plant height as of the five blocks located closest to the water course response variables. were temporarily inundated during the flooding period. The other two blocks experienced shallow groundwater. A comparison of the plots that were not fully Results inundated to those that were revealed no statistical difference, and so, all plots were treated the same in Deuterium-labelling experiment the subsequent statistical analyses. On the 77th day (18 Prior to watering, the dD of background rhizome and August), stems were harvested, and the same plant soil water was 28 3.52& (mean SD). At the growth-related measures were repeated in the same time of the experiment, the isotopic composition of manner described for pre-treatment measurements. rhizome and soil water did not differ. After applying deuterium-enriched water, the dD of top 10 cm soil Statistical analyses inside the watering area increased to 1223&, 1472& Data from both experiments were analysed in R (R and 1415& for plot 1, 2 and 3 respectively. Mean dD Core Team, 2011). For the deuterium-labelling experi- of soils gradually decreased to 147& with depth at ment, we constructed a generalised linear model (‘glm’ 30 cm. As the water percolated into the soil profiles, it function with binomial family and logit link; Bolker, was depleted in deuterium by dilution with pre-existing 2008). The dependent variable was the logarithm of the soil water along its path. odds, that is, the logarithm of the ratio P/(1–P), where The probability of finding rhizomes with labelled P is the probability of rhizome receiving enriched water, water was affected by distance from the watering area

© 2013 European Weed Research Society 53, 370–377 374 L Kui et al. and location (plot), as indicated by the best model. The best model suggested that odds of finding labelled water were negatively associated with distance from 3.2 0.06 0.4 0.06 5.9 0.58 the watering area (Table 1). The odds of finding 703 1 labelled water in a rhizome at 1.0 m were estimated to be 11 times as large as finding it at 2.0 m {[exp (1.79–1 9 2.38)/exp(1.79–2 9 2.38)]} and 384 times as large as the odds of finding labelled water in a rhizome 2.6 13.3 0.9 3.2 3.7 5.6 { – 9 – 9 1031 732 at 3.5 m [exp(1.79 1 2.38)/exp(1.79 3.5 2.38)]; Table 1}. In addition, the odds of finding labelled water outside the watering zone was overall 19 times 816 higher in plot 2 and two times higher in plot 3, compared with plot 1 (Table 1). This is probably due to differences in soil texture. The probability of a given 4.1 1 8.9 0.8 0.31 1.92 rhizome chosen randomly at a distance of 3.5 m from 4.8 0.20 6.4 the watering zone to contain enriched water can be up to 2.8%, in the case of plot 2 [exp (1.79 + 2.96– 3.5 9 2.38)/(1 + exp(1.79 + 2.96–3.5 9 2 .38)], indicat- 3.4 11.9 1.0 2.18 ing rhizomes can move water laterally at distance of at 2.9 5.6 least 3.5 m, but that it would be relatively unusual to observe movement beyond this distance.

Rhizome-severing experiment Prior to the experiment, plant growth were similar 3.8 1 11.6 0.1 0.06 1.75 6.1 0.06 7.8 among paired plots (Table 2). New stems sprouted in all plots 1 week after the treatment. In the initial

19 days, rhizome severing increased the recruitment of -value from the paired Wilcoxon signed rank test, which is the probability of wrongly rejecting null P

A. donax ramets by 98% compared with rhizomes- is 2.1 10.9 0.1 0.52 7.9 7.2 intact plots (Table 2). However, new ramets with intact P ). rhizomes were 49% taller compared with their severed C counterparts. Stem diameters did not differ on day 19 between treatments (Table 2). After ﬂooding occurred, by day 51 of the experiment, 45% of stems had died in the severed plots compared with only 22% mortality in the control plots. On day 51, all growth-related param- 2.0 0.90 10.5 0.4 1 0.35 9.7 1 14.2 1326 1 eters were equal among all paired plots (Table 2). On

day 77, ramets with intact rhizomes were 67% taller ) and intact control plots ( and 49% larger in diameter than their severed T SD) measured in the rhizome severing experiment on 1 June, 21 June (i.e. 19 days after rhizome severing, DARS), 20 July (51 DARS) and 4.0 16.4 0.8 3.5 3.8 20.8 1501 2855 Table 1 Parameter estimates for the generalised linear model . Aboveground biomass was not collected on day 19 and 51. Flood happened between day 35 and 42

(binomial with logit link) with the lowest AIC value (see text for C model selection results). The probability of a rhizome receiving 1 June 2010Pre-experimentTCPTCPTCPTCP 19 21 June 2010 20 July 2010 51 18 August 2010 77 and

enriched water was driven by the distance to the watering area )2868 T 2 and locations of the plots. The intercept is the log odds for plot 1 at distance 0 m; the estimated value for plot 2 was the log odds ratio for plot 2 respect to plot 1; and the estimated value for growth parameters (mean ) 21.6 distance was log odds ratio for every 1 m increase in distance 2 Estimated value SE z Value Pr

Intercept 1.79 0.41 4.31 1.6e-05

Plot2 2.96 0.60 4.92 8.6e-07 Arundo donax Plot3 0.77 0.45 1.71 0.086 Distance 2.38 0.36 6.58 4.7e-11 Aboveground biomass (g m Stem diameter (mm) 15.6 18 August 2010 (77 DARS) in severed treatment plots ( Plant height (m) 3.5 hypothesis of difference between Date DARS Stem density (n m Table 2

© 2013 European Weed Research Society 53, 370–377 Clonal integration of Arundo donax 375 counterparts (Table 2). However, plant density and on observations of river bank cutaways. We believe aboveground biomass were similar. that this topic of alternative modes of horizontal transport deserves further study. After finding that A. donax can transport resources Discussion among ramets, the observed differences in ramet We determined that A. donax shared water through growth rates under similar environmental conditions interconnected rhizomes to a distance of at least 3.5 m are believed to be due to the effects of rhizome sever- and that this sharing had important consequences for ing. Initially, the rapid increase of ramet resprouting growth and response to flooding in two associated indicated that the loss of rhizome connection might experiments. Our results suggest that rhizome integra- stimulate a shoot propagation response. This phenom- tion likely benefits ramets living in patchy riparian enon is commonly observed in a variety of clonal areas, enhances competitive abilities of A. donax and plants, such as Ammophila breviligulata Fern. (Maun, contributes to its frequent dominance and invasion of 1984), Solidago canadensis L. (Schmid & Bazzaz, 1987) these systems (Quinn et al., 2007). and Scirpus maritimus L. (Charpentier et al., 1998). While the exact distance of water transported through The increased ramet propagation following rhizome rhizome pathways in A. donax is challenging to quantify severing has been attributed to loss of apical in situ, we found clear evidence of intrarhizome trans- dominance within the clone (Wang et al., 2009). port. de Kroon et al. (1996) suggested that Carex spp. Rhizome severing was associated with higher mor- rhizomes transport 30–60% of water from resource- tality from natural disturbances. The unexpected 8-day abundant ramets to resource-poor ramets. Because flood contributed to ramet mortality, which provided A. donax has large rhizomes and deep roots, sharing of useful insights into additional benefits from clonal water and nutrients may be necessary only when soil integration. Although plants commonly exhibit dec- resources become limited. reased productivity during and after flooding due to We observed water transported to distances of at limited oxygen supply to roots (Kozlowski, 1984), clo- least 3.5 m, which was the farthest distance sampled in nal integration can enhance the flood tolerance of rhi- our experiment. However, the chance for such zomatous species. For example, Phragmites australis long-distance transport was small (up to 2.8%). It is (Cav.) Trin. ex Steud. (Amsberry et al., 2000) and important to recognise that the complexity of rhizome Spartina alterniflora Loisel. (Xiao et al., 2010) proba- networks (de Kroon et al., 1991) results in an increas- bly cope with anoxic soils by transporting oxygen ing likelihood of sampling rhizomes that are not part from their taller mother ramets to the rhizosphere. of networks that have roots in the labelled soil with Further studies focusing on oxygen transport could increasing distances from the watering area. Thus, it is explore the role of clonal integration in conferring possible that we have underestimated maximum water flood tolerance. Clonal integration also increased transport that could exceed the distances in our experi- ramets’ height and diameter. A similar pattern was ment. However, as only one of 45 samples was found found in S. maritimus (Charpentier et al., 1998). We to have enriched signal, we expect that our estimate is did not observe measurable differences in plot-scale reasonably robust. It should be noted that some water biomass by the end of experiment. Longer-term studies may possibly move via non-rhizome pathways. Mycor- are needed to determine the plant growth and effects rhizal fungi can colonise clonal plants and distribute of intraspecific competition after one or more growing nutrients in heterogeneous environments (Du et al., seasons. 2009). It is possible that the enriched water reached From the riparian vegetation management perspec- long-distance rhizomes were transported through tive, because of rhizome integration, we expect that mycorrhizal networks. Additionally, hydraulic redistri- A. donax grows better in harsh environments, such as bution is common in many grasses (Caldwell et al., riparian zones in semi-arid regions (Cushman & Gaff- 1998). A study on sand dune community dominated ney, 2010). Our results suggest that the effects of frag- by Hedysarum leave Maxim. revealed that rhizomes of mentation under non-flooded conditions are similar to that species can transport nutrients long distances and those reported in other systems (Dong et al., 2012), in redistribute nutrients back to the soil (Yu et al., 2010). which fragmentation may lead to greater proliferation If this happens horizontally, it is possible that enriched of ramets and perhaps accelerate expansion. Fragmen- water would then be taken up by secondary lateral tation prior to flooding might result in decreased roots (Nobel & Huang, 1992). We believe this is productivity and greater mortality of ramets. However, unlikely given the spatial heterogeneity in soil water flooding is also likely to significantly increase the potentials that would be required. Also, it is not movement of viable fragmentation and accelerate likely that A. donax roots grow 3.5 m laterally, based colonisation in downstream regions.

It is critical to understand clonal plant physiological CALDWELL MM, DAWSON TE & RICHARDS JH (1998) and biological characteristics before implementing Hydraulic lift: consequences of water efflux from the roots – invasive plant control (Radosevich et al., 1984). The of plants. Oecologia 113, 151 161. CARACO T&KELLY CK (1991) On the adaptive value of fire and mowing removal of aboveground parts of physiological integration in clonal plants. Ecology 72, A. donax can decrease stem density in the short term. 81–93. Partial damage on rhizome networks might induce CHARPENTIER A, MESLEARD F&THOMPSON JD (1998) The denser ramet recruitment. Frequent mowing should effects of rhizome severing on the clonal growth and clonal decrease plant productivity by consuming stored architecture of Scirpus maritimus. Oikos 83, 107–116. energy in large rhizomes (De Cauwer & Reheul, 2009). COFFMAN GC, AMBROSE RF & RUNDEL PW (2010) Wildfire However, fragments remain viable and can resprout promotes dominance of invasive giant reed (Arundo donax) – and so any removal regime must have strategies for in riparian ecosystems. Biological Invasions 12, 2723 2734. COPLEN TB & QI HP (2009) Quality assurance and quality effective disposal of A. donax fragments (Decruyenaere control in light stable isotope laboratories: a case study of & Holt, 2001). Additionally, due to clonal integration, Rio Grande, Texas, water samples. Isotopes in herbicide (e.g., through rhizome/stem injection) may be Environmental and Health Studies 45, 126–134. translocated within clones and can be an efficient CUSHMAN JH & GAFFNEY KA (2010) Community-level approach to control plant’s productivity (Delbart consequences of invasion: impacts of exotic clonal plants et al., 2012). on riparian vegetation. Biological Invasions 12, 2765–2776. Given that a 1 m2 patch growing in sufficient soil DE CAUWER B&REHEUL D (2009) Impact of land use on vegetation composition, diversity and potentially invasive, moisture can potentially support larger surrounding 2 nitrophilous clonal species in a wetland region in Flanders. patches (up to 50 m based on our estimate of the Agronomy for Sustainable Development 29, 277–285. effective clonal integration distance), any altered DECRUYENAERE JG & HOLT JS (2001) Seasonality of clonal systems with levees, diversions or drainage ditches propagation in giant reed. Weed Science 49, 760–767. would potentially benefit and facilitate the expansion DELBART E, MAHY G, WEICKMANS B et al. (2012) Can land of A. donax and result in a loss of upland biodiversity managers control Japanese knotweed? Lessons from and reduction of riparian recreation value (Amsberry control tests in Belgium. Environmental Management 50, 1089–1097. et al., 2000). 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