Annual mowing maintains plant diversity in threatened temperate grasslands

Abstract

Questions: Disturbance regimes shaped the evolution of grasslands but grazing exclusion and fire suppression have caused unprecedented increases in grassland biomass and biodiversity declines. Mowing reduces biomass but is not widely practiced in conservation reserves because of concerns about facilitating exotic plant invasion and altering ecosystem function. We asked whether regular mowing affected (1) the diversity of native and exotic functional groups, (2) spatial turnover in vegetation composition (β-diversity), (3) vegetation attributes relating to biomass and structural heterogeneity, (4) community composition and (5) the distribution and abundance of individual native and exotic species.Location: Five temperate grassland reserves, south-eastern Australia, encompassing C 3 and C 4 dominated communities.Methods: Vegetation within reserves had been cut to 10 cm, once per year, for 10 years in late spring/early summer to maintain access tracks. We surveyed plant communities in mowed areas and nearby (<5 m) unmowed control areas (40 subplots per reserve, 200 total) and used linear mixed-effects models to examine the effects of mowing. Results:Of 24 functional groups, the richness of 16 native and exotic groups significantly increased with mowing. In 14 of these cases, effects were consistent across C 3 -and C 4 -dominated grassland. Mowing reduced spatial turnover, but this did not reduce species richness at any spatial scale. When accounting for species abundance and evenness (Shannon diversity), effects of mowing were generally positive for native species and neutral for exotic species. Mowing increased native perennial grass cover and bare earth, decreased exotic perennial grass cover and litter, and changed community composition. Mowing reduced vegetation height but not structural heterogeneity. Mowing positively affected six individual native species and no exotic species.One native (Asperula conferta) and two exotic (Avena spp. and Nassella neesiana) species were found in lower abundance on mowed plots. Conclusions:Annual mowing can be a useful conservation tool for threatened temperate grasslands but should be heterogeneous to ensure the persistence of mowingsensitive native species. Good vehicle hygiene is essential and localized complementary management (e.g., herbicide) might be required to reduce exotic forbs and grasses. K E Y W O R D S community ecology, disturbance regime, functional ecology, invasive species, meadow, prairie, savanna, slashing 208 | Applied Vegetation Science SMITH eT al.

Regulation ofJacobaea vulgarisby varied cutting and restoration measures

“…Combination 2 also reached high evenness-indices, as did the flower cut treatment. In general, evenness was significantly higher under mowing regimes (flower cut, seed cut, and combination 2), in which more species were able to establish due to reduced competition by dominant grasses (61). Diversity patterns of the treatments changed over time.…”

Multivariate drivers of diversity in temperate Australian native grasslands

“…In degraded grasslands in the ACT, tussock thinning and litter removal favoured native forbs, but only when seeds were added (Johnson et al 2018). Positive effects of slashing at small spatial scales (a diversity), might not translate to larger scales (b diversity) (Smith et al 2018).…”

“…Mowing can result in aggregated litter which can have negative consequences unless slash is removed (Verrier and Kirkpatrick 2005;Morgan 2015). Slashing is generally viewed as unfavourable in temperate grasslands (Kirkpatrick 1986), particularly for taller species, but Smith et al (2018) show that annual mowing can have positive influences on plant diversity, and may promote structural heterogeneity when applied patchily, and can also favour some rare species (Gilfedder and Kirkpatrick 1997). Mowing increased cover of native species (including some rare or threatened species) and reduced exotic grass cover compared with grazing in Tasmania (Verrier and Kirkpatrick 2005).…”

A dataset of plant and microbial community structure after long-term grazing and mowing in a semiarid steppe

“…Unlike grazing, mowing does not selectively impact palatable plants and does not cause trampling or dung and urine deposition. Furthermore, although it has less of an impact on soil structure than grazing, mowing can produce a more uniform vegetative cover and remove plant aboveground biomass, reducing nutrient cycling to the soil 16 . However, due to the cumulative nature of mowing and grazing impacts, the effects on the plant and microbial community may only be significant after long-term exposure.…”