Our LocationsMine Lease, Planning and ApprovalsThe Mining and Rehabilitation ProcessEnvironmental ManagementCommunityOur PeopleHistoryNews and Events
Flora Monitoring

There are two flora monitoring programs undertaken in the rehabilitated mined areas each year.  In March when the rehabilitation is 9 months old the areas are monitored to check that the number of established plants meets standards agreed by the Department of Environment and Conservation (DEC) and Alcoa.  The standard for eucalypt density is between 600 and 2500 stems per hectare with a target of 1300 stems per hectare.  The target for legumes is 1 plant every 2 square metres.  Legumes include wattles and other native shrubs that add nitrogen to the soil.  Areas of erosion or weeds are also identified at this stage and treated if required.  The timing of this monitoring allows for any reseeding or replanting that is required, to be carried out before the next winter.
 
The second monitoring occurs in the second spring after establishment, when the rehabilitation is 15 months old).  Between 90 and 150 plots, each 80 square meters in total area, are placed randomly in that year’s rehabilitated areas.  In each of these 80 square meter plots all plant species are identified and counted.  Weeds or introduced species are not included in this species count.  The results form these plots are compared to control plots in un-mined forest and this comparison is used each year to determine if we have reached our internal target known as the Botanical Milestone.  The Botanical Milestone is:
 
“The average number of indigenous plant species in 15 month old rehabilitation is ≥100% of the number found in representative jarrah forest sites, with at least 20% of these from the recalcitrant species priority list.”
 
Recalcitrant species are those that are common in the unmined forest but are difficult to propagate and return to the rehabilitated mined areas.  These species do not re-establish from top soil.  These species may not produce much seed, or we do not yet understand what treatment is required to get the seeds to germinate.  Instead, these species are grown from cuttings or tissue culture at Alcoa’s Marrinup Nursery and planted in the rehabilitation each year.  Given the difficulties in returning these species, they are often under-represented in the rehabilitated areas.
 
Each year, a selection of these 15 month rehabilitation monitoring plots are permanently pegged and become part of a long term vegetation monitoring program.  These plots are remonitored at 1, 6, 15, 20, 30 and 50 years of age.  In these plots the density and cover of all plants is recorded as well as the vegetation structure and tree growth.  Since 1990, more than 900 permanent monitoring plots have been established.  These plots allow us to monitor long term changes in the vegetation and the information is used to continually improve our rehabilitation practices.
 
 


botanist in field with transect

Click image to enlarge.


A botanist assessing a monitoring plot in 15 month old rehabilitation.

forest where monitoring conducted

Click image to enlarge.


A permanent vegetation monitoring plot in 1988 rehabilitation. The plot is 19-years-old.