Ecosync
The Validity of an Estimation of Biomass. Guggenmoos, S., Shaw, H.J.W.,
Johnson, R.E., 1989.
Herbicide efficacy for
brush control has generally been determined by assessing treated stems for stem
kill. The stem kill is measured by determining the condition of the cambium
layer. The bark is stripped back on treated stems and a rating number is
assigned (ie. 0-100%) based on how far down from the apex the cambium has been
rendered non-viable. This method is reasonable for many herbicides which are
most active in meristematic tissue and where the brush species under study does
not have a strong proclivity to reproduce vegetatively.
When the tree species under
study readily reproduces vegetatively stem kill of the treated stems is an
incomplete and inadequate measure of control. The measurement of stem kill does
not yield information relevant to the persistence of the control. It is, in
fact, the persistence of the control which is of material interest to the
vegetation manager. For the pipeline or power line manager it is the amount and
speed of regrowth of the targeted species which determines the maintenance
cycle. For the forest manager the amount and speed of regrowth determines the window
of opportunity available to the crop trees. What these vegetation managers
require is not so much an assessment of kill but an assessment of the duration
of control. This requires examining to what degree the target species exist and
are proliferating.
A measure of the biomass of
the targeted species would constitute significant information for the
vegetation manager. In agricultural research this number is usually determined
by harvesting the competing weeds, oven drying them and recording dry weights.
Although, this approach would work for brush control the logistics of removing
woody plants and transporting them from often remote areas to a laboratory
becomes inhibiting. It would be desirable to have a measure of biomass which
does not require the removal, transportation and further handling of the
regrowth.
It was established that a
count of the viable stems of a target species and the maximum or average sprout
height were data easily gathered in the field. To determine if these data could
be used as a reasonable estimate of biomass a trial was undertaken. Twenty 4
square metre plots were randomly selected. For each plot all the viable poplar
species stems were counted and the average height recorded. These two values
were multiplied and labeled the Sprout Factor. All the viable poplar stems were
removed from each plot and weighed to establish the actual biomass.
The biomass and the Sprout
Factor were tested for correlation. This test yielded an r value of 0.87. Given
that such a strong correlation exists it may be concluded that the number of
sprouts multiplied by the sprout length is a reasonably good estimate of the
biomass.
Herbicide efficacy ratings
based on stem kill and a biomass indicator, such as the sprout factor, will
yield information more pertinent to future vegetation management requirements.
In addition one of the data used for the derivation of the sprout factor,
sprout height, yields information about expected maintenance cycles. (TransAlta
Utilities Corporation, Sherwood Park, Alberta).