Change season/timing of cutting/mowing: freshwater marshes
Overall effectiveness category Awaiting assessment
Number of studies: 4
Background information and definitions
Cutting/mowing could have different effects on vegetation depending on the time of year at which it is done. For example, it might be beneficial to avoid disturbance when certain plants are young/flowering so that they can grow/reproduce and contribute to the community. The season of disturbance can also affect nutrient levels and impacts to soils by trampling or vehicles.
To be summarized as evidence in this section, studies should have compared a fixed frequency and intensity of cutting/mowing, but in different seasons (e.g. summer vs winter) or in different temporal patterns (e.g. 50% of plants cut every summer vs 100% of plants cut every other summer).
Related actions: Change season/timing of vegetation harvest, including studies of cutting where vegetation is removed; Reduce frequency of cutting/mowing; Reduce intensity of cutting/mowing; Cut/mow herbaceous plants to maintain or restore disturbance; Use cutting/mowing to control problematic herbaceous plants.
Supporting evidence from individual studies
A replicated, randomized, paired, controlled study in 1983–1986 in two wet meadows in Switzerland (Buttler 1992) reported that summer and winter mowing had similar effects on overall plant community composition and structure, but different effects on some individual plant species. Statistical significance was not assessed. Over 3–4 years, plots mown in summer and winter experienced similar changes in overall plant community composition (partial data reported as a graphical analysis). Both mowing regimes were associated with a significant increase in the proportion of vegetation in lower layers. This was true for vegetation overall, and the dominant species in each community (partial data reported, as number of times survey pins touched living vegetation). Some individual species responded differently to each mowing regime. For example, common reed Phragmites communis developed more, thinner shoots and lower above-ground biomass over four years of summer mowing, but developed fewer, thicker shoots and greater above-ground biomass over three years of winter mowing (see original paper for partial data). Methods: Two pairs of plots (each 121–169 m2) were established in two historically mown, but abandoned, lakeside wet meadows. In each pair, one random plot was mown in winter (from early 1983) and one random plot was mown in late summer (from 1983). Cuttings were removed. Vegetation was surveyed each summer 1983–1986 (before mowing, where applicable).Study and other actions tested
A replicated, randomized, paired, controlled study in 1989–1991 of four farmland ditches in the Netherlands (Best 1994) found that vegetation cutting had similar effects on the plant community in the emergent wetland zone, whether it was done in May or November. The season of cutting had no significant effect on the overall plant community composition in two of three years, and had only a small effect in the other year (data reported as statistical model results). The season of cutting had no significant effect on plant species richness in 11 of 12 comparisons (for which May-cut: 10–49; November-cut: 8–47 species/ditch). The study also identified 18 common emergent and terrestrial plant species whose cover was significantly affected by the season of cutting in at least one of the four ditches (data not reported). Methods: Between 1989 and 1991, vegetation was cleared from two 20 m sections of each ditch: one section each May and one section each November. Vegetation was cut within the ditch and on its margins, then dumped higher up on the ditch banks. Each July, plant species and their cover (excluding mosses) were recorded in the emergent wetland zone (influenced by water, parts seasonally flooded) bordering each ditch.Study and other actions tested
A replicated, paired, controlled, before-and-after study in 1986–1988 in five wet grasslands in Belgium (Dumortier et al. 1996) reported mixed effects of single annual mows, between June and November, on plant species richness and biomass. Statistical significance was not assessed. Over two years, plant species richness increased in plots mown between July and October (from 15–19 to 18–20 species/6 m2). It declined in plots mown in November (from 19 to 18 species/6 m2) and was stable in plots mown in June (17 species/6 m2). Total above-ground biomass (including litter) declined in plots mown between August and October (from 550–730 g/m2 to 480–560 g/m2). It increased in plots mown in June, July or November (from 310–660 g/m2 to 410–780 g/m2). The study also reported data on the cover of some example individual plant species (see original paper). Methods: In spring 1986, six 7 x 7 m plots were established in each of five adjacent wet grasslands (mown annually for the previous 10 years). From 1986, one plot/grassland was mown in each month between June and November. Cuttings were removed. Plant species were recorded each summer between 1986 and 1988. Biomass was cut and collected from five 30 x 30 cm quadrats/plot/year, immediately before mowing (so not at the same time in all plots), then dried and weighed.Study and other actions tested
A controlled, before-and-after study in 2000–2001 of a riparian reedbed near Tokyo, Japan (Asaeda et al. 2006) reported that cutting in June suppressed common reed Phragmites australis biomass and density more, over the second growing season after cutting, than cutting in July. Unless specified, statistical significance was not assessed. Before cutting, common reed abundance was statistically similar in both plots (density: 91–102 shoots/m2; above-ground biomass: 40–660 g/m2). In the first growing season after cutting, common reed abundance showed similar responses in both June-cut and July-cut plots: initial decline, then recovery to similar levels (see original paper for data). In the second growing season after cutting, June-cut plots contained fewer reed shoots than July-cut plots at four of six time points (for which June-cut: 140–156 shoots/m2; July-cut: 168–218 shoots/m2) and less reed biomass at three of seven time points (for which June-cut: 370–800 g/m2; July-cut: 710–1070 g/m2). At all other times, reed abundance was similar in June- and July-cut plots. Methods: In April 2000, two 6 x 10 m plots were established in a mature riparian reedbed. Reeds were cut in early June 2000 in one plot and early July 2000 in the other (20–30 cm above ground level; cuttings removed). Reed shoots were cut, counted, dried and weighed every 1–2 months between April and December 2000 and 2001 (three 0.125-m2 quadrats/plot/survey).Study and other actions tested