Mark G. Neyland

Retention Forestry to Maintain Multifunctional Forests: A World Perspective

The majority of the worlds forests are used for multiple purposes, which often include the potentially conflicting goals of timber production and biodiversity conservation. A scientifically validated management approach that can reduce such conflicts is retention forestry, an approach modeled on natural processes, which emerged in the last 25 years as an alternative to clearcutting. A portion of the original stand is left unlogged to maintain the continuity of structural and compositional diversity. We detail retention forestrys ecological role, review its current practices, and summarize the large research base on the subject. Retention forestry is applicable to all forest biomes, complements conservation in reserves, and represents bottom-up conservation through forest manager involvement. A research challenge is to identify thresholds for retention amounts to achieve desired outcomes. We define key issues for future development and link retention forestry with land-zoning allocation at various scales, expanding its uses to forest restoration and the management of uneven—age forests.

A synthesis of outcomes from the Warra Silvicultural Systems Trial, Tasmania: Safety, timber production, economics, biodiversity, silviculture and social acceptability

Summary The Warra Silvicultural Systems Trial was established in southern Tasmania from 1998 to 2007 in tall wet Eucalyptus obliqua forest to compare seven alternatives to the traditional clear-fell, burn and sow (CBS) harvesting method. The alternatives included CBS with understorey islands, patch-fell, strip-fell, dispersed retention, aggregated retention, single-tree/small-group selection and group selection. The effects of the treatments were compared at age three years against six criteria: safety for harvesting crews, rate of timber recovery, economic returns to the forest owner, old-growth biodiversity, regeneration and growth of eucalypts (silviculture), and social acceptability. Combining all criteria, aggregated retention performed best, and is suggested to be the most suitable alternative for routine use in wet eucalypt forests if a management objective is to maintain old-growth structures and biodiversity at the stand (coupe) level. Aggregated retention presented no novel safety issues even though coupes contained a relatively greater amount of forest edge; harvesting was relatively productive, although total forest management costs increased by about

Survival and growth of Nothofagus pumilio seedlings under several microenvironments after variable retention harvesting in southern Patagonian forests

5 per tonne or cubic metre compared to clear-felling. Biodiversity outcomes were much superior to clear—felling, both at three years of age and (predicted) at rotation age, and the system had greater visual appeal and social acceptability than clear-felling. Regeneration burns in the aggregated retention treatments were operationally more difficult than with clear-felling and were somewhat less effective in creating a suitable seedbed, resulting in lower densities of eucalypt stems in the regenerating forest although stocking standards were still attained. Old-growth biodiversity in commercial forests can be managed at the landscape level, through retention between coupes and through wildlife habitat strips that connect larger ecological reserves. However, internationally there is increasing recognition that maintaining old-growth elements at the coupe level is a worthwhile complementary practice for maintaining biodiversity in commercially-managed native forests. Managers of tall wet eucalypt forests need to balance the difficulties of regeneration burning and costs of aggregated retention against its ecological and social acceptability benefits.

Early impacts of harvesting and burning disturbances on vegetation communities in the Warra silvicultural systems trial, Tasmania, Australia

ContextVariable retention prescriptions for Nothofagus pumilio forests provide for biodiversity conservation and natural regeneration by controlled opening of the canopy. Harvesting generates different microenvironments which present dissimilar conditions for seedling establishment, due to positive or negative influences over biotic and abiotic factors.AimsThis study evaluated seedling survival and performance in different microenvironments within the harvested stands. Tested hypotheses stated that seedling stress and performance were influenced by harvesting due to changes in forest structure, microclimate, soil properties, and nutrient availability.MethodsIn the stands harvested by variable retention, five contrasting microenvironments were selected as treatments for the experiments and sampling. Environmental variables were related to ecophysiological, seedling survival, and performance.ResultsThe modification of forest structure (crown cover and tree density) and the presence of coarse woody debris greatly affect the effective rainfall and global radiation reaching understorey level, influencing seedling stress and consequently survival and performance. Harvesting also modifies soil properties (e.g., soil bulk density) and coarse woody debris accumulation which in turn influences soil moisture and/or solar radiation levels. Analyses showed that seedlings received benefits of microenvironment variation after harvesting. Areas covered with middle or fine woody debris presented regeneration with better ecophysiological response and seedling performance, although dispersed retention areas (far away from remnant trees) and roads could also present suitable conditions for seedling survival and performance.ConclusionsThe proportion of different microenvironments in the harvested forests will determine the amount of natural recruitment of regeneration and consequently the success of proposed silvicultural management. Forest practices must be manipulated to increase the proportion of favorable microenvironments (e.g., woody debris), allowing greater natural regeneration success during the first years after harvesting.

Silvicultural monitoring in uneven-aged highland dry Eucalyptus delegatensis forests in Tasmania

Impacts on the understorey vegetation of a range of silvicultural alternatives to clearfelling in lowland Eucalyptus obliqua wet forest were studied over a decade in the Warra silvicultural systems trial in southern Tasmania. The treatments were clearfell with understorey islands, patchfell, stripfell, dispersed retention, aggregated retention, and single-tree/small-group selection. High intensity burning, low intensity burning and no burning were variously applied as part of these treatments. Three understorey types were studied, including one wet sclerophyll community and two rainforest communities. Wherever burning occurred across the research trial, the regenerating vegetation was floristically wet sclerophyll with an incipient composition consistent with that of the pre-harvest wet sclerophyll community. Sites previously occupied by rainforest understoreys retained occasional rainforest elements, but the regeneration was overwhelmingly sclerophyll in nature. There were no consistent differences in the floristic composition of the regenerating vegetation, after burning or harvesting disturbance, that could be attributed to the silvicultural system. However, field observations and the results of a related, subsequent study suggest that, in designing silvicultural trials similar to the present one, close attention should be paid to the size of quadrats in relation to the level at which disturbance impacts are operating. The response of the vegetation at edges created by the treatments, and in the undisturbed forest beyond, supports the finding that edge effects on the vascular flora extend for less than 10 m into the undisturbed forest.

Is continuous-cover silviculture, as practised in Bavaria, suitable for use in wet eucalypt forests in Tasmania, Australia?

Summary Poor early establishment and growth of regeneration following clearfelling of highland dry Eucalptus delegatensis forests in Tasmania in the 1970s led to the development of alternative practices. Shelterwood retention, shelterwood removal, potential sawlog retention and advance growth retention systems were developed and implemented by forest owners as preferable alternatives to clearfelling in most instances. Less than optimal outcomes following partial harvesting led to the development of formal monitoring procedures. These procedures assess the pre-harvesting forest structure, guide development of the harvesting prescription, follow the course of harvesting, return information on progress to the harvesting contractor, and allow for continuous improvement of operations. Together they ultimately provide improved outcomes for the forest grower. The paper discusses the development of uneven-aged management and describes the processes used to develop and monitor the outcomes.

Variable-retention harvesting in Tasmania: regeneration success?

Summary Appropriate silviculture, based on natural forest dynamics and ecological attributes of tree species, is fundamental to the sustainable management of native (natural and semi-natural) forests for wood production. Continuous-cover silviculture works well in shade-tolerant spruce–fir–beech forests of Central Europe (in this paper, we use the German state of Bavaria as a typical example) and can be regarded as ‘close-to-nature’, particularly where there is a focus on maintaining some old-growth elements for long-term retention. Continuous-cover silviculture, however, cannot be regarded as ‘close-to-nature’ for Australian wet eucalypt forests, which are dominated by shade-intolerant eucalypts that are dependent on intensive disturbance, usually associated with fires, for their regeneration. While the prevailing technique of clearfelling, burning and sowing of eucalypt seed has some affinities with natural regeneration processes stimulated by bushfires, it differs substantially from natural disturbances in that it is more uniform than bushfires and removes most ‘legacy’ structures such as live and dead trees, which are important to maintain some continuity of ecosystem functioning between forest generations. Variable retention silviculture, which retains mature stand elements for incorporation in the new stand, better approximates ‘close-to-nature’ silviculture for wet eucalypt forests. Silvicultural trials and recent operational experience show that variable retention can be applied successfully in wet eucalypt forests in some situations. Although Tasmania has much higher levels of formal ecological reserves than Bavaria (49% compared to just 3%), its use of native forests, particularly wet eucalypt forests, for wood production struggles for acceptance by the general public. We suggest that high levels of social acceptance of forestry in Bavaria, and low levels in Tasmania, cannot be explained purely by ecological and silvicultural differences of the forest types. Other influential factors in Bavaria compared with Tasmania include higher levels of private forest ownership, practical forest knowledge, domestic processing, established forest road networks and profitability.

A major shift to the retention approach for forestry can help resolve some global forest sustainability issues

Summary Society’s changing expectations for forest management and an improved understanding of wet-forest ecology have led to the adoption of variable-retention silviculture in Tasmania’s old-growth wet eucalypt forests. Aggregated retention (ARN) retains patches of forest after harvesting to help maintain biodiversity and ecosystem function at the site level, but these ecological goals must be balanced against silvicultural considerations such as achieving successful regeneration. We sampled 38 ARN coupes that were harvested and regenerated from 2007 to 2010 and 31 paired clear-fell, burn and sow (CBS) coupes. Despite more complex boundary shapes and thus much higher levels of forest edge influence, the development of successful ‘slow burning’ methods combined with the adoption of aerial sowing in all ARN coupes has resulted in early regeneration densities and growth rates that are very comparable with those in clear-felled coupes. The longer-term effects of ARN harvesting on eucalypt productivity require further research, but these early results indicate that the initial silvicultural goals for eucalypt regeneration can be met after ARN harvesting in wet eucalypt forests.