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.
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Claims 8
Claim · model-written summary
The dry weight rank method works well with relatively small quadrats holding only a few plants, irrespective of horizontal vegetation structure.
Verbatim
t0“Evaluation of the dry weight rank method for botanical analysis of grassland by means of simulation”
e1“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”
Claim · model-written summary
In vegetation with patchy species growth, the dry weight rank method gives satisfactory results with large quadrats of tens of plants.
Verbatim
t0“Evaluation of the dry weight rank method for botanical analysis of grassland by means of simulation”
e2“In vegetations where species grow patchwise, satisfactory results are also obtained using large quadrats with much more plants (i.e. tens) per quadrat”
Claim · model-written summary
Minor species compete successfully for first, second and third ranks in patchy vegetation, which keeps the method working with large quadrats.
Verbatim
t0“Evaluation of the dry weight rank method for botanical analysis of grassland by means of simulation”
e3“The reason is that in these cases also minor species can compete successfully for first, second and third ranks”
e2“In vegetations where species grow patchwise, satisfactory results are also obtained using large quadrats with much more plants (i.e. tens) per quadrat”
Claim · model-written summary
Only a certain degree of patchiness is necessary for the dry weight rank method to work.
Verbatim
t0“Evaluation of the dry weight rank method for botanical analysis of grassland by means of simulation”
e4“However, it appeared that only a certain degree of patchiness is necessary”
Claim · model-written summary
A very small sampling quadrat, smaller than 1 dm2, could be used in recently sown grasslands.
Verbatim
t0“Evaluation of the dry weight rank method for botanical analysis of grassland by means of simulation”
e5“in principle a very small sampling quadrat (smaller than 1 dmsuperscript 2) could be used”
Claim · model-written summary
The correction for missing ranks functions almost always perfectly, so the condition of at least three species per quadrat is not necessary.
Verbatim
t0“Evaluation of the dry weight rank method for botanical analysis of grassland by means of simulation”
e6“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”
Claim · model-written summary
Multipliers calculated from simulation data satisfactorily mimic the original multipliers of the dry weight rank method.
Verbatim
t0“Evaluation of the dry weight rank method for botanical analysis of grassland by means of simulation”
e7“Multipliers calculated from simulation data could satisfactorily mimic the original multipliers of DWR given by 't Mannetje & Haydock”
Claim · model-written summary
The dry weight rank method is well suited for studying vegetation changes in old, floristically diverse grasslands.
Verbatim
t0“Evaluation of the dry weight rank method for botanical analysis of grassland by means of simulation”
e4“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”