A long-term impact of forest disturbance on spruce seedling regeneration on coarse woody debris

Abstract

Storm disturbance have huge impacts on subalpine forest ecosystems. However, long-term effects of such disturbance on regeneration of subalpine forests are poorly understood. Picea jezoensis var. hondoensis has limited and discontinuous distributions in subalpine central Japan. Thus, evaluating long-term effects of forest disturbance and their mechanisms have great conservation significance. Picea needs coarse woody debris (CWD) such as logs and stumps for their seedling colonization, and thus their establishment is greatly affected by CWD condition which largely depending on decay activity of decomposer fungal community. Recent studies in Europe found that frequency of occurrence of brown rot fungi, a certain functional group of fungi which decay wood holocellulose without decaying lignin, tends to be increase after forest dieback1), and that CWD decayed by brown rot fungi negatively affects spruce seedling density2). Because the decay process of CWD is known to be several decades long, we hypothesized that the effect of forest disturbance on fungal community and wood decay of CWD, and its negative effect on spruce seedling establishment would be long lasting. To test this hypothesis, we compared fungal communities within CWD and spruce seedling density among forest sites of the three different categories (control old-growth forest, damaged forest with the logs left, and damaged forest with the logs removed) in an old-growth subalpine coniferous forest in Mt. Yastugatake, central Japan. This forest had got a wide-range disturbance by a typhoon in 1959. We surveyed totally 95 logs in 9 sites (5, 2, and 2 sites for the forest categories held in above, respectively). Fungal communities within CWDs were documented using Illumina sequencing. Seedling and epiphytic bryophyte communities were recorded and were analyzed with CWD properties such as wood decay type (white rot, brown rot, and soft rot), pH, moisture, and bryophyte coverage. Illumina sequencing did not show obvious difference in fungal communities among the forest categories. Also, frequencies of the occurrence of wood decay type were not significantly different among the categories. None of these variables had significant association with spruce seedling density. However, experience of the disturbance certainly reduced current spruce seedling density. These results suggested that the forest disturbance do have a long lasting effect on spruces seedling regeneration on CWD, but the effect might not be attributable to their impacts on CWD fungal community and wood decay.

1)Vogel S, Alvarez B, Bassler C Müller J, Thorn S (2017) The Red-belted Bracket (Fomitopsis pinicola) colonizes spruce trees early after bark beetle attack and persists. Fungal Ecology 27:282-288.

2)Bače R, Svoboda M, Pouska V, Janda P, Červenka, J (2012) Natural regeneration in Central-European subalpine spruce forests: Which logs are suitable for seedling recruitment? Forest Ecology and Management 266:254-262.