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.
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 tosustain mature forest biodiversity?Is the Regional Forest Agreement working?Presentation by: Tim Wardlaw, Forestry Tasmania
What we wantMature forest species to persist inmature eucalypt forestsMature forest species torecolonise areas after disturbance ……….throughout forest landscapes
We have a lot of mature eucalyptforests BUT it’s not evenly distributed As here? What about the recolonisation of areas by mature forest species after disturbance? Do mature eucalypt forests here have a similar biodiversity
A mosaic of disturbance-drivenvegetation types Rainforest LONG Interval between disturbance events Wildfire eucalypt (mature) Wildfire eucalypt (regrowth) Other native forest Older silvicultural regeneration Younger silvicultural regeneration PlantationIncreasing disturbance Native non-forest Agricultural land SHORT Huon River
Landscape context: what’s in the neighbourhood? Two patches of silvicultural regeneration Frequent disturbance: Infrequent disturbance: (mostly anthropogenic) (mostly natural) • Non-forest • Rainforest • Plantation • Mature eucalypt forest • Silvicultural regeneration • Wildfire regrowth
The gradient of disturbance intensity 100Proportion of landscape (% area) 90 Natural • Rainforest 80 • Mature eucalypt 70 • Wildfire regrowth 60 • Other native forest 50 40 30 20 • Silvicultural regen . Anthropogenic 10 • Plantation • Agricultural 0 3 4 5 6 7 Most disturbed Context-class Least disturbed
Sampling the gradient Mature eucalypt 100 Older silviculturalProportion of landscape (% area) 90 Natural regeneration 80 70 7 7 7 7 60 50 7 7 7 7 2 forest types 40 X 30 4 context-classes 20 Anthropogenic 10 X 0 7 replicates 3 4 5 6 7 Context-class Most disturbed Least disturbed
The biodiversity 44 species 619 species 107 species3133 observations 85,740 specimens Responsive to landscape disturbance intensity 5 species 38 species 13 species
Response of disturbance-sensitiveelements to landscape disturbance Context-class of 1 km radius landscape 3 4 5 6 7 Increasing disturbance in surrounding landscape
Response of disturbance-sensitiveelements to landscape disturbance Context-class of 1 km radius landscape 3 4 5 6 7 Reduced abundance / richness Abundance / richness maintained Mature Silvicultural Mature Silvicultural Mature Silvicultural
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 speciesNumber of birds counted Number of plant species 40 25 8 20 30 6 15 20 4 10 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 10 8 Number of rainforest species 6 4 2 0 -2 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 biodiversityin production forest landscapes 1. Retain patches of mature forest in reserves or long-term retention (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 mature forest) How does the RFA perform?
RFA: a mix of retention strategies Formal reserves Informal reserves Off-reserve management
Disturbance context-class: priorities forretention to sustain mature forest biodiversity Minimally disturbed (context classes 7-10) Intensively disturbed (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 provide comparable mature forest biodiversity as minimally disturbed areas
Current and future mature eucalypt forest in long-term retention 80 Amount in surrounding 1km landscape (% of area) Mature in CAR Mature - excluded 70 Regrowth in CAR Regrowth - excluded 60 50 40 30 20 10 0 1 2 3 4 5 6 7 8 9 10 Context-class 52% of total landscape 40% of total landscape
Proximity of available harvest areas to long- term retention 95% of areas available for harvest within 500m of long-term retention
Is the RFA working?Mostly….. • It’s increased long-term retention of eucalypt forest in parts of the landscape where mature eucalypt forest is deficient • It’s retained sufficient mature forest in long-term retention to sustain biodiversity in the less intensively disturbed parts of the production landscapeBut, • Not all retained eucalypt forest is mature • Proximity benefits for recolonisation need to be demonstrated in most disturbed landscapes
Postscript• The Tasmanian Parliament is currently considering the Tasmanian Forests Agreement• Aims to end forestry conflict in Tasmania• Proposes a more “black and white” forest landscape.• Conservation Science did not get considered during negotiations to this agreement
With:The team • Ruiping Gao • Marie Yee • Dave McElwee • Jordan RendellSimon Grove (FT) • Leigh Edwards • Dick BashfordJayne Balmer (UTas) • Liam HindrumAndrew Hingston (FT) • Nita RamsdenLynne Forster (UTas) • Kevin Bonham • Nicky LynchChristina Schmuki (UTas) • Lucile BaudRob Musk (FT) • Grégoire Thauvin • Elsa LibisSteve Read (FT) • Chloe Hill • Yijin Ong