Two decades of variable retention in British Columbia: a review of its implementation and effectiveness for biodiversity conservation

Stand-level retention is an important component of sustainable forest management which aims to balance ecological,social and economic objectives.Long-term retention of mature forest structures at the time of harvesting(variable retention)is intended to produce future forest stands that more closely resemble conditions that develop after natural disturbances,thereby maintaining greater diversity of habitats for a variety of organisms.Structure includes features such as live and dead trees representing multiple canopy layers,undisturbed understory vegetation and coarse woody debris.Over the past two decades,variable retention has become common on forest lands in the temperate rainforests of coastal British Columbia(BC)and has been applied to a lesser extent in inland forest types.Our review of studies in BC and in similar forest types in our region indicates that both aggregated and dispersed retention can contribute to biodiversity conservation by providing short-term‘life-boating’habitat for some species and by enhancing the structural characteristics of future stands.For example,greater abundance of species present in the pre-harvest forest have been documented for vegetation,birds,carabid beetles,gastropods,ectomycorrhizal fungi and soil fauna in retention cutblocks compared to clearcuts.There are,however,some negative consequences for timber production such as wind damage to retained trees and reduced growth rates of tree regeneration compared to clearcuts.The authors suggest an adaptive management approach for balancing competing objectives when faced with uncertainty.This includes monitoring the implementation and effectiveness of various strategies for achieving goals.Over two decades of experience applying variable retention harvesting to industrial-scale management of forest lands in BC suggests that it is possible to balance production of wood with biodiversity conservation.

Variable retention harvesting in Victoria’s Mountain Ash (Eucalyptus regnans) forests (southeastern Australia)

Variable retention harvesting is a silvicultural system that focuses on retaining key elements of stand structure at the time of logging and is increasingly being used worldwide.We describe the design and establishment of a variable retention harvesting experiment established in the Mountain Ash(Eucalyptus regnans)forests of the Central Highlands of Victoria,south-eastern Australia.The experiment was instigated in 2003,and the work to date has shown that it has environmental benefits for certain groups of small mammals,birds,and vascular plants.The experiment has been integrated with an ongoing long-term monitoring program as well as other experiments such as those in post-fire salvage-logged areas.Collectively,the results of various studies suggest that the potential value of variable retention harvesting extends beyond green-tree logging to post-fire salvage logging environments.We outline some of the challenges in,and new perspectives derived from,implementing and maintaining our experiment.This included difficulties protecting islands from high-intensity post-harvest regeneration burns and threat of declining funding undermining ongoing project viability.A critically important perspective concerns the ecological and economic context in which variable retention harvesting is implemented.In the particular case of Mountain Ash forests,assessments using formal IUCN criteria classify the ecosystem as being Critically Endangered under the Red Listed Ecosystem approach.As a result,Mountain Ash forests are at a high risk of ecosystem collapse.Further logging will increase that risk,making the basis for continued harvesting questionable.In addition,economic analyses suggest that the value of natural assets,like water production,far outweigh the value of the wood products harvested from the Mountain Ash ecosystem,again leading to questions about the viability of ongoing harvesting.We therefore conclude that whilst variable retention harvesting has the potential to contribute to biodiversity conservation in Mountain Ash forests,broader ecological and economic contextual issues(such as the values of competing resources like water yields and the heavily degraded state of the forest)may erode the case for its broader application.

Variable retention harvesting in the Douglas-fir region

Variable retention harvesting evolved in the Douglas-fir region of the Pacific Northwest gradually in response to increasing dissatisfaction with the ecological consequences of clear-cutting,from the standpoint of wildlife habitat and other important forest functions.It is a harvesting technique that can provide for retention(continuity)of such structures as large and old live trees,snags,and logs.Variable retention is based on the natural model of the biological legacies that are typically left behind following natural disturbances,such as wildfire,wind,and flood.Variable retention is also an important technique for fulfilling the first silvicultural principle of ecological forestry,that of providing for continuity in structure,function,and composition between forest generations.The history and current application of variable retention approaches on forests in western Washington and Oregon states(USA),where many of the fundamental concepts were first developed and applied,is described in this article.

Variable retention forestry in European boreal forests in Russia

We explored whether,and to what extent,variable retention(VR)forestry has been applied in European boreal forests in northwestern Russia.Our survey revealed VR since 1910.Between 1910 and the 1960s,the statistics showing how much was retained are largely missing.However,for example,in the 1950s,on a large scale in the Republic of Karelia,up to 200-ha-sized harvesting areas,18–33%,were retention patches with a mean growing stock of 30–40m3 ha−1.In the fellings defined as“incomplete clear fellings,”which were the most common final felling type at that time,11–40%of the growing stock was left.Between the 1960s and the early 1990s,with more efficient harvesting and skidding techniques,conventional clear fellings with a much lower amount of retention were practiced.Concern about the regeneration of harvested areas gradually led to smaller(maximum 50 ha)harvesting areas and the increase of silvicultural activities.Until now,to ensure natural regeneration,patches of understory and 20–25 seed trees(i.e.,ca.15–25m3)per ha have been left permanently in harvesting areas.Landscape-scale retention for protecting ecosystem functions and biodiversity was legislated in 1978 by preserving key biotopes up to 1000 ha in size.Since 2001,promoted by forest certification,the key biotopes,such as paludified forest patches,buffers around water bodies,and habitats of red-listed species,have also been retained in harvesting areas,together with a dispersed retention of different elements.Quantitative estimates of the amount of key biotopes are largely missing.However,estimates of 1–13%in harvesting areas and 23%in whole managed landscapes have been given.VR applied during the last century has emulated natural disturbances and created diverse uneven-aged forest structures with high amounts of diverse coarse woody debris.We conclude that an analysis of past and current retention practices is essential for estimating the global role of Russian forestry.Further decisions on the general direction of Russian forestry and,specifically,retention practices are important to address the global challenges of biodiversity loss and climate change.