Is Active Management the Key to the Conservation of Saproxylic Biodiversity? Pollarding Promotes the Formation of Tree Hollows

Abstract

Trees with hollows are key features sustaining biodiversity in wooded landscapes. They host rich assemblages of often highly specialised organisms. Hollow trees, however, have become rare and localised in Europe. Many of the associated biota is thus declining or endangered. The challenge of its conservation, therefore, is to safeguard the presence of hollow trees in sufficient numbers. Populations of numerous species associated with tree hollows and dead wood are often found in habitats that were formed by formerly common traditional silvicultural practices such as coppicing, pollarding or pasture. Although it has been occasionally mentioned that such practices increase the formation of hollows and the availability of often sun-exposed dead wood, their effect has never been quantified. Our study examined the hollow incidence in pollard and non-pollard (unmanaged) willows and the effect of pollarding on incremental growth rate by tree ring analysis. The probability of hollow occurrence was substantially higher in pollard than in non-pollard trees. Young pollards, especially, form hollows much more often than non-pollards; for instance, in trees of 50 cm DBH, the probability of hollow ocurrence was ∼0.75 in pollards, but only ∼0.3 in non-pollards. No difference in growth rate was found. Pollarding thus leads to the rapid formation of tree hollows, a habitat usually associated with old trees. It is therefore potentially a very important tool in the restoration of saproxylic habitats and conservation of hollow-dependent fauna. If applied along e.g. roads and watercourses, pollarding could also be used to increase landscape connectivity for saproxylic organisms. In reserves where pollarding was formerly practiced, its restoration would be necessary to prevent loss of saproxylic biodiversity. Our results point to the importance of active management measures for maintaining availability, and spatial and temporal continuity of deadwood microhabitats.

Spatial analysis of the habitat and distribution of Osmoderma eremita (Scop.) in trees outside of woodlands

“…With regards to oaks, Ranius et al (2009) described a very slow process, with about 200-300 years required for 50% of trees to develop cavities and 400 years are required for all oaks to develop cavities. In a study on Salix alba, Sebek et al (2013) found a probability of cavity formation of approximately 80% in pollards with a diameter of 30-60cm, but only approximately 30% of non-pollards of the same diameter class developed cavities. On the landscape scale, Kirby (2015 suggested a model of regeneration as a series of episodic events, rather than a continuous recruitment of young trees.…”

Monitoring and management of Cerambyx cerdo in the Mediterranean region – a review and the potential role of citizen science

“…Therefore, forest management of SCIs should aim at maintaining or restoring the typical biological diversity associated with habitat structure and functions, with appropriate management plans (Article 6). How habitat structure and associated saproxylic beetle communities should be maintained or restored is a challenging question (Vodka et al 2008, Sebek et al 2013, with particular e) The conservation status of a natural habitat will be taken as "favourable" when: -its natural range and areas it covers within that range are stable or increasing and -the specific structure and functions which are necessary for its long-term maintenance exist and are likely to continue to exist for the foreseeable future and -the conservation status of its typical species is favourable as defined in (i); i) The conservation status will be taken as "favourable" when: -population dynamics data on the species concerned indicate that it is maintaining itself on a long-term basis as a viable component of its natural habitats and -the natural range of the species is neither being reduced nor is likely to be reduced for the foreseeable future and -there is, and will probably continue to be, a sufficiently large habitat to maintain its populations on a long-term basis; reference to the Mediterranean basin which has high and poorly known levels of diversity and endemism (Baselga 2008). The long lasting association of C. cerdo with old and decaying trees (Buse et al 2007(Buse et al , 2008a suggests that trees colonised by C. cerdo represent keystone structures (Tews et al 2004) to maintain saproxylic diversity and functions associated with Mediterranean protected oak habitats (Sirami et al 2008).…”

“…Retention forestry is also emerging as a practical way to harvest forest and maintain or restore old-growth features of landscapes (Fedrowitz et al 2014, Mason andZapponi 2015). Management options to protect C. cerdo and related habitat structures and functions range therefore from strict protection of old growth forests, to conservation of habitat trees over managed landscapes, and to forest harvesting coupled with grazing and retention (Sirami et al 2008, Vodka et al 2008, Sebek et al 2013, Fedrowitz et al 2014, Mason and Zapponi 2015. Traditional forest management practices are thus seen as potential conservation tools to protect saproxylic communities (Buse et al 2007, Vodka et al 2008, as well as sustainable and viable production systems (Scarascia-Mugnozza et al 2000, Sjölund andJump 2013).…”

What is the impact of active management on biodiversity in boreal and temperate forests set aside for conservation or restoration? A systematic map

“…Full development or restoration of coppiced or pollarded stands may require decades to centuries, however. So far, these processes have rarely been investigated beyond pure observations [62].…”