Coarse Woody Debris in Primary and Secondary Middle Taiga Spruce Forests

Restoration of the pool of coarse woody debris after disturbances is one of the mechanisms for maintaining the stability of forest biogeocenoses. The studies of coarse woody debris have been carried out in the “Vepssky Forest” Reserve in the Leningrad Region on 8 sample plots established in primary forests (4 sample plots) and in secondary forests of the 1st generation after logging in 1973–1974 (4 sample plots), where the composition and structure of the stand, as well as the site conditions have been identical to those in primary forests. The coarse woody debris has been inventoried on transects. The stocks of coarse woody debris in primary stands have ranged from 104 to 233 m3 ha–1. Windfall and leaning trees have prevailed. The proportion of deadwood in both primary and secondary forests has been low. Clear cutting has significantly changed not only the stock of coarse woody debris, but also its distribution by decay classes and substrate categories. The stocks of coarse woody debris in secondary forests have ranged from 8 to 40 m3 ha–1, and have been mainly represented by stumps. The coarse woody debris of the 4th and 5th decay classes has almost been absent in primary forests, while in secondary forests the proportion of highly decomposed wood remaining after cutting has been about 50 %. The ratio of coarse woody debris and growing stocks has been on average 1:1 and 1:5 in the biogeocenoses of primary and secondary forests, respectively. The annual carbon balance of coarse woody debris (the difference in fluxes due to the loss of growing forest and the decay of coarse woody debris) has ranged from 0,40 to 2,80 t C ha–1 year–1, averaging 1,75 and 0,63 t C ha–1 year–1 in secondary and primary forests, respectively. The positive annual carbon balance in the coarse woody debris is due to the predominance of the rate of the loss of growing forest over the rate of the decay of coarse woody debris in primary forests as a result of wind disturbances and as a result of self-thinning of the stand in secondary forests

Mineralization and fragmentation rates of bark attached to logs in a northern boreal

a b s t r a c t Predicting the characteristics of coarse woody debris (CWD) and its importance for biodiversity, carbon and nutrient cycling requires narrowing the uncertainties in bark decomposition rate assessments. We estimated bark decomposition rates and compared them to wood decomposition rates of birches (Betula pubescens and Betula pendula), Siberian fir (Abies sibirica), Siberian pine (Pinus sibirica) and Siberian spruce (Picea obovata) in the northern boreal forest of the Komi Republic, Russia. Estimates were made based on the mass loss of bark attached to above-ground fallen and leaning logs dated to have fallen from 1 to 168 years previous to sampling. A single-exponential model was used to estimate the mass loss of bark attached to the logs. Decomposition rate estimates of all log bark included mass loss due to fragmentation. Mineralization rate as mass loss per surface area was estimated for non-fragmented bark pieces. The initial bark mass of the tree base was higher compared to that of the rest of the log; it did not depend neither on the tree species nor on the log size. The proportional rate of bark mineralization was the same for Siberian fir, Siberian pine and Siberian spruce logs -0.040 yr À1 . The mineralization rate of birch bark was 0.009 yr À1 . Bark fragmentation accelerated mass loss. Variation in bark decomposition rates was explained by tree species and log diameter and did not depend on tree mortality mode. The bark turnover time (t 95 ) was 302, 224, 149, 140 and 117 years for birch, fir, spruce, Siberian pine with diameter more than 41 cm, and Siberian pine with diameter less than 40 cm, respectively. Bark decomposed faster than wood for fir (0.034 vs. 0.026 yr ). The different decomposition rates of wood and bark suggest that considering wood and bark together as one substrate can result in a less accurate portrayal of decomposition patterns. These bark decomposition rates can be used for modelling carbon dynamics in similar ecosystems. Knowing the turnover time of log bark for these tree species also facilitates the prediction of the quality of CWD in biodiversity studies in boreal forests

Decaying Picea abies log bark hosts diverse fungal communities

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Types and rates of decomposition of Larix sibirica trees and logs in a mixed European boreal old-growth forest

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Carbon and nitrogen dynamics along the log bark decomposition continuum in a mesic old-growth boreal forest

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Coupled effect of temperature and mineral additions facilitates decay of aspen bark

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