Black Alder
Alnus glutinosa
The black alder is a deciduous tree reaching heights of up to 30 meters, typically found along water bodies and in swampy forests. It is characterized by its dark, fissured bark and obovate leaves that are often notched at the apex. An ecological highlight is its symbiotic relationship with the bacterium Frankia alni in root nodules, allowing the tree to fix atmospheric nitrogen. This species is highly tolerant of waterlogging and plays a crucial role in stabilizing riparian zones.
Details
Oxygen production
Moderate (as a tree species, primarily relevant for CO2 sequestration).
Habitat function
Root system provides hiding spots for fish; nesting site for birds; host plant for the alder leaf beetle.
Nutrient uptake
Atmospheric nitrogen fixation; uptake of nutrients from waterlogged soils.
Food source for
Eurasian siskin (seeds), alder leaf beetle (leaves), various moth caterpillars.
Human use
Wood for furniture making, hydraulic engineering (extremely durable under water), historically used for dye extraction.
Ecology
Ecological role
Pioneer species in wetlands, nitrogen enrichment of the soil through symbiosis, habitat for specialized fungi and insects.
Competitor species
European ash (Fraxinus excelsior) on moist sites, willow species (Salix spp.).
Ecosystem service
Bank stabilization, flood protection through retention capacity, carbon sequestration in peat soils.
Threats
Phytophthora alder dieback (root rot), lowering of groundwater levels, drainage of wetlands.
Scientific profile
Profile
Protection & threats
Main threats
Groundwater depletion, river channelization (loss of dynamics), spread of Phytophthora alni, and hybridization with non-native provenances.