Amending Soil with Mulched European Buckthorn (Rhamnus cathartica) Does Not Reduce Reinvasion

Abstract

We conducted a three-year field experiment to determine if amending soils with mulched European buckthorn (Rhamnus cathartica) can limit reinvasion, and whether two methods of incorporation-tilling or surface application-produce similar results. Mulch (a high carbon:nitrogen [C:N] material) may reduce reinvasion by stimulating soil microbial immobilization of N. Converting the woody waste generated during buckthorn removal into mulch would also eliminate both the need to remove this waste from restoration sites and the expense of acquiring amendments from elsewhere. We found that adding buckthorn mulch to soils, whether tilled or not, did not decrease either buckthorn reinvasion or soil N availability. The mechanical disturbance of tilling, however, caused a large, prolonged reduction in reinvasion by killing a previously unrecognized but major contributor to reinvasion-small buckthorn individuals (most < 5 cm tall) that were undetected during initial removal. Recruitment of new individuals occurred during the experiment, but recruitment rate decreased rapidly over time, suggesting that buckthorn seeds are short-lived. Three major recommendations emerge: (1) buckthorn mulch should not be used to limit reinvasion; (2) tilling can greatly reduce reinvasion by killing buckthorn individuals that are undetected during initial removal; and (3) because buckthorn seeds appear to be short-lived, reinvasion can be reduced by repeated, annual follow-up control of undetected and newly recruited individuals.

Increased light availability due to forestry mowing of invasive European buckthorn promotes its regeneration

“…As a result, the number of germinants alive in spring did not differ between mulch depths, and the effects of mulch on buckthorn germinants were transient. These results are similar to those of Iannone et al (), who found mulch to suppress buckthorn only for an 8‐week period, although that period fell fully within the growing season. Despite differences in buckthorn germination rates, it is therefore unlikely that forestry mowing mulch will directly promote or inhibit buckthorn establishment.…”

“…These combined impacts of buckthorn leave invaded forests with abundant residual propagule pressure from buckthorn with little‐to‐no native species present to resist buckthorn reestablishment (Naeem et al ; Klionsky et al ; Rejmánek ). Therefore, emergence from the seedbank poses a significant threat to forest restoration (Iannone et al ). Management plans following buckthorn removal must account for continued propagule pressure from the seedbank despite the absence of fruiting individuals nearby.…”

“…In sum, forestry mowing likely has legacy effects on buckthorn regeneration that vary over time as mulch depth, light, and soil moisture change. Indeed in a multi‐year study of germinant, yearling, and resprouting buckthorn, Iannone et al () found that surface application of buckthorn mulch led to transient decreases in buckthorn reinvasion, but that mulch had no lasting impact on buckthorn reinvasion. However, this is the only experimental test of the effects of mulch on buckthorn performance to our knowledge, and it is unclear whether these results are constrained by the depth of mulch used or how these results may be dependent on changes in light conditions caused by buckthorn removal.…”

Region-specific patterns and drivers of macroscale forest plant invasions

“…Additionally, as illustrated both theoretically (Guo & Symstad, 2008;Catford et al, 2012) and empirically from local to subcontinental scales (Kennedy et al, 2002;Stohlgren et al, 2003), deeper insights can be gained by quantifying and analysing multiple invasion measures [e.g. devising better management practices by detecting varying effects of the same factor on different invader life stages (Iannone & Galatowitsch, 2008;Iannone et al, 2013)].…”

Below‐ground causes and consequences of woodland shrub invasions: a novel paired‐point framework reveals new insights

“…soil mulch amendments) will not benefit restorations, the latter being confirmed by a recent field experiment (Iannone et al . ). Nonetheless, knowing that buckthorn preferentially establishes in soils having these characteristics can help to develop better focused monitoring programmes, aiding in the prevention of further buckthorn spread.…”