Disturbances and Climate Drive Structure, Stability, and Growth in Mixed Temperate Old-growth Rainforests in the Caucasus
The Colchic rainforest of the Western Caucasus is one of the few temperate rainforests dominated by broadleaf deciduous trees. Understanding natural dynamics of broadleaf-dominated temperate rainforests is essential for their conservation and management. Here, we investigate for the first time the structure, natural disturbance, and recruitment dynamics of a mixed Colchic old-growth rainforest, dominated by Fagus orientalis and Picea orientalis. We used forest inventories and dendrochronological analysis of tree growth in five 30-m-radius plots to quantify forest structure, growth, and disturbances. For the last 400 years, the forest experienced a mixed disturbance regime dominated by frequent small gaps superimposed onto medium disturbances with about a 25-year recurrence period, with no evidences of stand-replacing disturbances. This disturbance regime favored the dominance of shade-tolerant, late successional species with slow tree canopy access through multiple growth releases. These dynamics impose low growth rates and continuous recruitment of spruce and beech, and contributed to a high heterogeneity of tree ages and sizes that result in stable forest structure, as suggested by the low stand slenderness. Spruces were the oldest (up to 427 years) and fastest growing trees in the forest, suggesting that their low presence in the forest is due to low disturbance rates that limit their recruitment. Spring climate conditions that promoted beech growth were detrimental for spruce growth, suggesting that interspecies interactions may condition the effect of climate on forest growth and development. The dynamic equilibrium state we reconstructed in this old-growth forest could likely be disrupted by anthropogenic disturbances or management.
KeywordsDisturbance Forest dynamics Dendroecology Mixed forest Old-growth forest Recruitment Growth Stability
We thank Daniel Bishop, Marco Mina, and Timothy Thrippleton for their help during fieldwork. In addition, we are also grateful to Cengiz Cihan and the Turkish General Directorate of Forestry (OGM) in Borçka, Artvin, for sampling permission and assistance in the field. Dario Martin-Benito was funded by Marie-Curie IEF Grant (EU-Grant 329935), ETH Zurich fund PA2350-404, and a project AGL2015-73190-JIN from the Spanish Ministry of Economy, Industry and Competitiveness. Mehmet Doğan was partly supported by TÜBİTAK (the Scientific and Technological Research Council of Turkey) International Postdoctoral Research Fellowship Programme (Grant No. 1059B191600826). The Climate Center of the Lamont-Doherty Earth Observatory at Columbia University provided funds for the exploratory work of this study. The datasets generated and analyzed in the current study are available from the corresponding author on reasonable request.
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