I know a researcher who calibrated her ability to estimate biomass. She gathered some samples (took all from a measured area, let's say 1 sq. m), dried and weighed them. Then she did it again (new sites of course), but this time she estimated the biomass before collecting the samples and recorded the estimates, then dried and weighed again. She did this several times until she had trained herself to be good at making the estimates without destroying the collection sites. Every now and then, she would check a sample again (i.e. harvest and weigh) to be sure she was still making good estimates. Of course, there is an error factor in doing it this way, but the size of the error can itself be estimated by using the data.

You could try this. You will have to have some metrics, such as % cover, species %, and depth of vegetation to guide you. If it is a spongy site (moss covered) then you could also feel the sponginess ... which might seem a bit "off the wall", but basically this method uses as many senses as possible so as to train the observer's ability.

I don't know whether this has been published, but you can check publications of E.C. Pielou (who was research supervisor in this case and a well respected quantitative ecologist). The method is not non-destructive, but is less destructive than the usual way which would be to harvest everything and weigh it.

We in Forest Research Institute Dehraun, India carried out non-destructive Biomass Estimation study of Natural Plantations of Sal, Teak & Pine in New Forest FRI Campus Dehradun...

U can go through the entire paper attached with my RG profile. Revert back for comments/suggestions, if any. Best Wishes!

Stem diameter may also be an estimator of plant biomass. In some vegetable crops (e.g. tomato), stem height has a higher correlation with plant biomass than plant height.

I guess all methods needs a calibration first... thank you very much for your suggestions!!

Hi Veronica,

While visual estimates of plant cover may give you a good first approximation, another non-destructive method which is perhaps more objective and quantitative is the point-intercept or point-quadrat method. It is a method which has been used for a long time (Levy & Madden 1933), and been shown to very accurately predict biomass of herbaceous species and small shrubs (Jonasson, Oikos,1988) even in very diverse plant communities (Barkaoui et al., Folia Geobotanica, 2013, see link below).

It basically consists in introducing a pin vertically in the foliage and count the number of times it hits a species's leaf or stem, and repeating this along a transect line or a grid within a quadrat. It is more time-consuming than visual estimates of percent cover, but not really not as bad as it seems, and it provides in addition very information-rich data including small scale spatial distribution of plants and aboveground biomass.

I would recommend it if you are interested in good quality aboveground biomass data, but maybe not if you are just looking for a quick estimate. It would of course be better to calibrate it, although as an indicator of relative abundance it might not be necessary.

Article Questioning the Reliability of the Point Intercept Method fo...

There are different sampling times and labour but I would not deprecate pim if calibration for plant functional types has been done; now blue band canopy analyzers use acually a ray tracing idea and also gap area fraction instrumentation theory has got relevant links to it. Grassland can mean modified roots, woody stolons, annual plants, ephemerals, resurrectional types. Possibly combining reflectance of stand, high resolution pictures taken on spot, and some massive excavation of random squares, with sieving organic fractions would serve. In the original Med there is a strong seasonality, phanerophitic evergreen shrubs and frequent fires, but this may not quite right for a mesquite or chaparral vegetation.

I might add that biodiversity studies diverge in some way from crop physiology. Respected scientists in both areas do not cross data. I read recently A good handbook of biodiversity of David Hill et al. that gives a good deal of space to quadrat or pim (pp217- on WEB) but no reference was given for optical methods. In Ag For Met journal in contrast, in the last 15 years there are several application of optical methods for leaf area ad now some crop analyzer is integrated with GIS; remote sensing makes very influential extimations of plant biomass following them. It is clear that if one counts also frogs and reptiles does not carry the same panoplia of a crop physiologist. Perhaps the need of below-ground measurements is a good common trait and in a mixed grassland can be a surprise. Then going to Karim Barkaoui et al. added question would say that Warren Wilson at CSIRO was quite a new approach in the 60's but DEMON (CSIRO again) and other types of procedures had since then the time of develop and disappear. Ray tracing and rendering tools offer now a cost effective way for using side and top pictures but depends on Software handling skill. Once done for a species a top picture would suffice for above ground biomass.

See:

Catchpole, W.R. and C.J. Wheeler. 2006. Estimating plant biomass: A review of techniques. Australian Journal of Ecology 17:121–131.

But you are correct that whatever method you use, calibration is important, and recalibration when making comparisons across times, treatments, gradients, etc.