Tim Wardlaw_A gradient study at the Warra Supersite provides new knowledge to support the management of production forests to sustain biodiversity
Managing a production forest landscape to
sustain mature forest biodiversity?
Is the Regional Forest Agreement working?
Presentation by: Tim Wardlaw, Forestry Tasmania
What we want
Mature forest species to persist in
mature eucalypt forests
Mature forest species to
recolonise areas after disturbance
……….throughout forest landscapes
We have a lot of mature eucalypt
forests BUT it’s not evenly distributed
What about the recolonisation of
areas by mature forest species
Do mature eucalypt forests here
have a similar biodiversity
A mosaic of disturbance-driven
Interval between disturbance events
Other native forest
Increasing disturbance Native non-forest
Agricultural land SHORT
Landscape context: what’s in the neighbourhood?
Two patches of silvicultural
Frequent disturbance: Infrequent disturbance:
(mostly anthropogenic) (mostly natural)
• Non-forest • Rainforest
• Plantation • Mature eucalypt forest
• Silvicultural regeneration • Wildfire regrowth
The gradient of disturbance intensity
Proportion of landscape (% area)
• Mature eucalypt
70 • Wildfire regrowth
60 • Other native forest
20 • Silvicultural regen .
10 • Plantation
3 4 5 6 7
Most disturbed Context-class Least disturbed
Sampling the gradient Mature eucalypt
Proportion of landscape (% area)
90 Natural regeneration
70 7 7 7 7
50 7 7 7 7 2 forest types
0 7 replicates
3 4 5 6 7
Most disturbed Least disturbed
Response of disturbance-sensitive
elements to landscape disturbance
Context-class of 1 km radius landscape
3 4 5 6 7
Reduced abundance / richness Abundance / richness maintained
Biodiversity response to context-class
= response to mature eucalypt forest
Plot offorest birds
Dense Fitted Model Disturbance-sensitive beetles
Plot of Fitted Model Rainforest plants
Plot of Fitted Model
50 30 10
Number of beetle species
Number of birds counted
Number of plant species
10 5 2
0 0 0
0 10 20 30 40 50 60 0 10 20 30 40 50 60 0 10 20 30 40 50 60
Amount of mature eucalypt forest in 1 km landscape (% area)
• Poorer recolonisation in landscapes with little
mature eucalypt forest
• Maintain at least 20% mature eucalypt forest
Biodiversity response to context-class
= response to mature eucalypt forest
Number of rainforest species
0 500 1000 1500 2000 2500 3000 3500
Distance to nearest mature forest (m)
• More disturbance-sensitive species recolonise older
silvicultural regeneration when mature forest is nearby
To maintain mature forest biodiversity
in production forest landscapes
1. Retain patches of mature forest in reserves or
(Aim for at least 20% in 1 km radius landscape)
2. Configure retention so that a high proportion of
harvest areas are close to retained mature forest
(Aim for harvest areas to be within 400 m of
How does the RFA perform?
RFA: a mix of retention strategies
Disturbance context-class: priorities for
retention to sustain mature forest biodiversity
(context classes 7-10)
(context classes 1-4)
Decline in mature forest
Intermediate disturbance biodiversity. Retention to
(context classes 5-6)
provide more future mature
forest a high priority
Wood production areas
mature forest biodiversity
as minimally disturbed
Current and future mature eucalypt
forest in long-term retention
Amount in surrounding 1km landscape (% of area)
Mature in CAR Mature - excluded
Regrowth in CAR Regrowth - excluded
1 2 3 4 5 6 7 8 9 10
52% of total landscape
40% of total landscape
Proximity of available harvest areas to long-
95% of areas available for
harvest within 500m of
Is the RFA working?
• It’s increased long-term retention of eucalypt forest in
parts of the landscape where mature eucalypt forest is
• It’s retained sufficient mature forest in long-term
retention to sustain biodiversity in the less intensively
disturbed parts of the production landscape
• Not all retained eucalypt forest is mature
• Proximity benefits for recolonisation need to be
demonstrated in most disturbed landscapes
• The Tasmanian Parliament is currently
considering the Tasmanian Forests
• Aims to end forestry conflict in Tasmania
• Proposes a more “black and white” forest
• Conservation Science did not get considered
during negotiations to this agreement
The team • Ruiping Gao
• Marie Yee
• Dave McElwee
• Jordan Rendell
Simon Grove (FT) • Leigh Edwards
• Dick Bashford
Jayne Balmer (UTas) • Liam Hindrum
Andrew Hingston (FT) • Nita Ramsden
Lynne Forster (UTas) • Kevin Bonham
• Nicky Lynch
Christina Schmuki (UTas) • Lucile Baud
Rob Musk (FT) • Grégoire Thauvin
• Elsa Libis
Steve Read (FT)
• Chloe Hill
• Yijin Ong
Can production forests provide us with goods and services and still provide habitat for their dependent biodiversity, particularly the biodiversity dependent on mature forests? We have just completed a 3-year co-funded study with Forest and Wood Products Australia to see what the science says about this.
From the perspective of management we want the mature forest we retain to continue to function as mature forest and support the suit of species characteristic of that successional stage. We also want forests to recover after disturbance, whether it be from forestry or natural events, and be recolonised by those late-successional species.We also want these two processes to happen throughout the forest landscape – from forest landscapes that are largely natural with little human modification through to forest landscapes that have been substantially modified by human activities.
There is still a lot of mature eucalypt forest in the Tasmanian landscape but it’s not distributed evenly through the landscape. Do the mature forests in parts of the landscape less rich in mature forest have similar biodiversity as those parts where mature forests are rich? Does silvicultural regeneration acquire a similar biodiversity in those contrasting parts of the landscape?
We established the Southern Forests Experimental Forest Landscape in 2007 as a place where we could attempt to answer such landscape-level questions.This 110,000 ha landscape, dominated by tall, wet E. obliqua forest, extends from the Tasmanian Wilderness World Heritage Area in the west to the Huon Estuary in the east and is anchored to the Warra Tall Eucalypt Supersite.
It contains a mosaic of vegetation types that have developed from a long history of natural disturbance and a more recent history of European land-use. (mouse click) Each vegetation type is maintained in that state by a particular interval between disturbance events: where there are very long intervals between disturbance events rainforests persist, while at the other extreme there tend to be short intervals between disturbance events on agricultural land.(mouse click)The patterns of natural disturbance and European land-use have played out to provide a gradient of disturbance intensity in a relatively uniform biophysical environment. This gradient allows us to examine how the intensity of disturbance in the surrounding landscape affects biodiversity: specifically whether mature forest species can persist in retained patches of mature forest and whether they can recolonise forest areas after disturbance.
Landscape context is the term used to describe the characteristics of the region in which a patch sits. Landscape context helps us to explain how something we observe at a point is influenced by things beyond that point. For example if we see a wedge tail eagle flying over a paddock it means that the paddock is situated within the territorial range of the mature eucalypts it needs for nesting. We developed a context-class score to measure landscape context in terms of the intensity of disturbance in the surrounding landscape. In this example we have two patches of forest in the centre of landscapes of varying size represented by the concentric circles. Both patches are in the same forest type - older silvicultural regeneration. However they are located in landscapes with contrasting disturbance context-classes.On the left, the patch in context-class 4 is embedded in a landscape that has a high intensity of disturbance: a high proportion of the area in the surrounding different sized landscapes is of vegetation types typified by relatively short intervals between disurbance events, such as plantations shown as the blue areas; buttongrass plains, shown as the yellow areas, and silvicultural regeneration shown as the light green areas. On the right, the patch in context-class 6 is embedded in a landscape that has a low intensity of disturbance: a high proportion of the area in the surrounding landscapes is of vegetation types that reflect relatively long intervals between disturbance events, such as rainforest shown in blue and mature eucalypt forest shown in red.
The gradient of disturbance intensity we sampled in the SFEFL ranged between context-class 3 – the most intensely disturbed landscapes, to context-class 7 – least disturbed landscapes. You can see how the composition of the surrounding landscapes changes across this gradient.
We located patches of mature eucalypt forest and 30-50 years-old silvicultural regeneration in the centre of landscapes ranging between context-class 3 and context-class 7. Each plot type sampled four context-classes with three of those context-classes overlapping. There were seven replicate patches of each plot type in each of the four context-classes they sampled – a total of 56 plots.
In each of the 56 plots we did intensive surveys to measure the species-richness and abundance of three focal groups – birds, flighted beetles and vascular plants.We chose these groups because past research, particularly at Warra, has found them to be biodiverse in these forests and they are responsive to disturbance.
In the surveys we recorded 44 species of birds, 619 species of flighted beetles and 107 species of vascular plants.(mouse click)A small subset of species in each of the three groups were sensitive to the intensity of disturbance in the surrounding landscape.The subset of disturbance-sensitive bird species was dominated by ground-foragers that prefer wet sclerophyll forest and rainforest.The subset of disturbance-sensitive plant species was dominated by rainforest plants.The subset of disturbance-sensitive beetles was ecologically more diverse suggesting a variety of traits confer a sensitivity to disturbance.
Remember, reductions in context-class reflect patches with increasing levels of disturbance in their surrounding landscape. (mouse click)
In patches of mature eucalypt forest disturbance sensitive birds and plants persisted in the most intensively disturbed landscapes at comparable abundance and richness as in the least disturbed landscapes. Disturbance-sensitive beetles showed a decline in richness in the most disturbed landscapes compared to landscapes with intermediate or low levels of disturbance. This decline was associated with both a long history of more frequent natural disturbance and more intensive post-European land-use.(mouse click)In patches of older silvicultural regeneration, disturbance-sensitive species of all three groups showed declines in abundance and richness in the most disturbed landscapes compared to landscapes with intermediate or low levels of disturbance.(mouse click)To maintain the abundance and richness of disturbance-sensitive species we need to ensure our land-use coupled with natural disturbance does not exceed intermediate levels, represented here by context-class 5.
In our study landscape, differences in disturbance context-class were strongly correlated with the amount of mature eucalypt forest in the surrounding landscape. This was reflected in strong positive correlations in the abundance and species-richness of the disturbance-sensitive elements of the three focal groups recolonising older silvicultural regeneration with the amount of mature eucalypt forest in the surrounding landscape; in this case the surrounding 1 km radius landscape.(mouse click)Those correlations were strongly influenced by consistently low biodiversity values for the three groups in parts of the landscape with little or no mature eucalypt forest in the surrounding 1 km landscape.(mouse click)These results suggest that be maintaining a minimum of 20% mature eucalypt forest in the 1 km landscape should ensure allow mature forest biodiversity to recolonise areas after disturbance.
The response of disturbance-sensitive species recolonising previously harvested areas was also affected by the proximity of that harvested area to the nearest patch of mature forest. Here the number of rainforest plant species recolonising the harvested area generally remains low when the harvested areas are distant to the nearest mature forest but increases rapidly once the harvested area is closer. (mouse click)In this case, we see more rainforest plant species recolonising harvested areas that are within 400 metres of the nearest patch of mature forest.The amount of mature forest in the surrounding landscape and the distance of the harvested area to the nearest patch of mature forest were
The amount of mature forest in the surrounding landscape and the distance of the harvested area to the nearest patch of mature forest were strongly correlated. So it’s safer to consider both when consider how much mature forest should be retained in the landscape and where.For the groups we looked at in our study landscape the response of the disturbance-sensitive species indicate we should be aiming for at least 20% retention of mature eucalypt forest in the surrounding landscape AND we should be configuring that retention to ensure as much of future harvest areas will be within 400 m of mature forest.(mouse click)How has the RFA performed in providing these levels of retention of mature forest in our study landscape?
From our findings we can use landscape disturbance context-class to see where the priorities for conservation of mature forest biodiversity are, at least in our experimental landscape. (mouse click)Production forest areas kept to an intermediate intensity of disturbance can maintain a mature forest biodiversity that is comparable with a minimally disturbed landscape.(mouse click)In intensively disturbed parts of the landscape though, mature forest biodiversity has declined. We want these areas to eventually become grey. To do this we need more mature forest here, so we need to retain the remaining mature forest and augment this by retaining additional younger forest and allowing it to mature.
I just want us to focus on the public forests, particularly State forest.
The network of informal reserves does extend into the more intensively disturbed parts of the production forestry landscape so provides retention of either currently mature forest or regrowth forest that may become mature. There are still large areas the are too distant to the retention to get the benefit of proximity to mature needed for mature forest species to recolonise areas after disturbance. Note here, that we are only considering retention on public land. Covenants and other long-term retention measures on private land have not been considered here.
Exclusions provided, for example, through Forest Practices Code provisions provide retention at smaller spatial scales and within the most intensively disturbed parts of the landscape.
52% of the study area had sufficient mature eucalypt forest in CAR reserves or set asides outside of reserves to meet the 20% retention target. A further 40% of the study area relies on regrowth forest to meet some of the 20% retention target.
We also want the current or future mature forest retained to be close enough to harvest areas assist mature forest species recolonise areas after harvest. For most of the areas currently available for harvesting most of that proximity benefit to assist recolonisation is provided by informal reserves and areas outside reserves that have been excluded from harvesting – shown here in pink. Only a small proportion of the areas available for harvesting receive a proximity benefit from formal reserves – shown as yellow or brown areas.