Impact of silviculture on dead wood and on the distribution and frequency of tree microhabitats in montane beech-fir forests of the Pyrenees

Abstract

In forest ecosystems, the level of biodiversity is strongly linked to dead wood and tree microhabitats. To evaluate the influence of current forest management on the availability of dead wood and on the abundance and distribution of microhabitats, we studied the volume and diversity of dead wood objects and the distribution and frequency of cavities, dendrothelms, cracks, bark losses and sporophores of saproxylic fungi in montane beech-fir stands. We compared stands unmanaged for 50 or 100 years with continuously managed stands. A total of 1,204 live trees and 460 dead wood objects were observed. Total dead wood volume, snag volume and microhabitat diversity were lower in the managed stands, but the total number of microhabitats per ha was not significantly different between managed and unmanaged stands. Cavities were always the most frequent microhabitat and cracks the least frequent. Dendrothelm and bark loss were favored by management. Beech (Fagus sylvatica) carried many more microhabitats than silver fir (Abies alba), especially cavities, dendrothelms and bark losses. Fir very scarcely formed dendrothelms. Secondary tree species played an important role by providing cracks and bark losses. The proportion of microhabitat-bearing trees increased dramatically above circumference thresholds of 225 cm for beech and 215 cm for fir. Firs with a circumference of less than 135 cm did not carry microhabitats. In order to conserve microhabitat-providing trees and to increase the volume of dead wood in managed stands, we recommend conserving trees that finish their natural cycle over 10-20% of the surface area.

The dynamics and structure of dead wood in natural spruce-beech forest stand – a 40 year case study in the Krkonoše National Park

“…On the contrary, forest harvesting and most other conventional silvicultural interventions do not normally aim to produce large amounts of dead wood typically found in old-growth forest. Larrieu et al (2012) confirmed that management of montane beech-fir stands reduces the total volume of dead wood and the snag volume, modifies the pattern of decay stages and also reduces the tree species diversity and the diversity of tree microhabitats. Yet, in the framework of sustainable forest management, a better knowledge of the factor influencing the occurrence of dead wood would allow foresters to adopt scientifically-base practices to preserve biodiversity.…”

Protection against rockfall along a maturity gradient in mountain forests

“…In similar ecological contexts, i.e., French mountain forests with soils of medium to high fertility, local studies have found values comparable to ours: Pernot et al (2013), considering six distinct forest sites in French mountain forests found an average total volume of deadwood of 58 m 3 ha À1 in unmanaged areas. In the mountain beech fir forests of the central Pyrenees, Larrieu et al (2012) got a lower value (around 40 m 3 ha À1 ) but with a much higher counting limit for deadwood components (more than 60 cm in girth). In the beech fir forest in our study area, Grosso (2012) reported an average value of 114 m 3 ha À1 .…”

Coppice-with-standards with an overmature coppice component enhance saproxylic beetle biodiversity: A case study in French deciduous forests

“…In conclusion, the extension of the rotation age increases the amount of woody debris and alters the deadwood profile. Longer periods between harvesting let living trees grow large enough to bear more trunk microhabitats (Larrieu et al, 2011) and to generate woody debris, and encompass more natural disturbance events (strong wind, for example) (Jonsson et al, 2010). The rate of dead wood input is therefore driven by disturbance and tree mortality (Meyer and Schmidt, 2011).…”