Evaluation of the dry weight rank method for botanical analysis of grassland by means of simulation

Abstract

With the Dry Weight Rank (DWR) method of 't Mannetje and Haydock [see Journal of British Grassland Society (1963) 18, 268-275] for botanical analysis in pastures, the dry weight proportions of species are estimated from their first, second and third ranks in dry weight in single quadrats. The yield correction of Haydock and Shaw [see Australian Journal of Experimental Agriculture and Animal Husbandry (1975) 15, 663-670] is used additionally to solve the problem of the respective under- and overestimates of the dry weight proportions of high and low yielding species when these grow in patches. In this paper the DWR method is evaluated by means of computer simulation. Main element of the simulation model is a computer sampling program with which a fictitious vegetation can be sampled with a circular quadrat. The output shows that the DWR method works well using relatively small sampling quadrats with, on average, only a few plants per quadrat, irrespective of the horizontal vegetation structure. In vegetations where species grow patchwise, satisfactory results are also obtained using large quadrats with much more plants (i.e. tens) per quadrat. The reason is that in these cases also minor species can compete successfully for first, second and third ranks. However, it appeared that only a certain degree of patchiness is necessary, and with the usually applied quadrat sizes up to 25 dmsuperscript 2, probably in most vegetations this condition is fulfilled. Care should be taken in applying the DWR method for estimating species composition in recently sown grasslands where species usually occur more or less at random. In those cases, in principle a very small sampling quadrat (smaller than 1 dmsuperscript 2) could be used. However, this has practical limitations since the quadrat size should not be too small for realistic yield estimations, needed for the Haydock & Shaw yield correction. The simulations revealed that one condition (i.e., that the sampling quadrat should be at least as large that it usually contains three or more species) is not necessary because of the almost always perfect functioning of the correction for missing ranks. Generally speaking, a sampling quadrat should be chosen not larger than is strictly necessary from the viewpoint of horizontal vegetation structure and from the viewpoint of realistic yield estimations. Multipliers calculated from simulation data could satisfactorily mimic the original multipliers of DWR given by 't Mannetje & Haydock. It is postulated that the DWR method is well suited for studying vegetation changes in old, floristically diverse grasslands with dominant species often in moderate dry weight proportions and species usually growing in patches.

A variant of the dry‐weight rank method for botanical analysis of grassland with dominance‐based multipliers

“…This is because the probability of a species being assigned the first rank is small if it has only a small part in the mixture (0% of dominance may be compatible with 15% of weight, but 0% of weight is not compatible with 15% of dominance). So in Figure 1 a sigmoid relationship, resembling the theoretical relationship reported by Neuteboom et al . (1998) between (1:0:0) EDW and ODW, may be drawn.…”

“…A compromise between subjectively estimating and objective measuring is the dry‐weight rank method ( Mannetje and Haydock, 1963; Kruijne et al ., 1967 ; Neuteboom et al ., 1998 ). It uses ranking of species according to the biomass occupied per species.…”

Plant and soil fungal but not soil bacterial communities are linked in long-term fertilized grassland

“…These proportions are multiplied by 0.702, 0.211 and 0.87, respectively, culminating in the following equation: DWA% = 0.702 (A1%) + 0.211 (A2%) + 0.087 (A3%). This method was tested with different sampling methods, including small samples, and it was concluded that the DWR method is well suited for studying vegetation changes in old, floristically diverse grasslands 36 , such as ours. For each plant species, the functional classification was noted (grass, herb, legume or forb).…”

The potential of parasitoid Hymenoptera as bioindicators of arthropod diversity in agricultural grasslands

“…Data were collected from 50 randomly located circular quadrats (3 dm 2 ) per pasture, using the dry‐weight‐rank (DWR) method (‘t Mannetje & Haydock 1963) with yield correction (Jones & Hargreaves 1979). This method was developed to provide a rapid and accurate estimate of the botanical composition of heterogeneous agricultural grassland swards on a dry‐weight basis, without requiring the clipping and hand sorting of constituent species (‘t Mannetje & Haydock 1963; Neuteboom, Lantinga & Struik 1998). The DWR method assumes that when a large number of samples are taken, the dominant species will on average account for 0·702, the second for 0·211 and the third for 0·087 of total herbage mass.…”

“…Species were identified according to Stace (1997). Further details on the DWR method of botanical assessment are provided in ‘t Mannetje & Haydock (1963) and Neuteboom, Lantinga & Struik (1998). Mean vegetation height was estimated within each sampled sward by recording height measurements at 50 randomly selected locations using a Filips Folding Plate Pasture Meter (http://www.jenquip.co.nz).…”