22/12/2025
Every so often nature delivers a wee treat (early Xmas gift 🎁)to the river ecology.
A whole tree, root wad and all is a very beneficial gift to aquatic life. 🤩
This one has recently arrived, delivered by high water to the River Tummel just by the road bridge near Ballinluig.
In ecology, whether we’re talking about forests, soil, or in this case rivers, what is required - in order to maximise how much life can live there - is lots of different kinds of physical space.
This is also known as habitat mosaic or sometimes structural heterogeneity.
Different depths, different substrate sizes, different speeds of flow all offer opportunities to varying organisms. Or one organism at different stages in its life cycle.
Using salmon as one example - though many other organisms also benefit here’s a wee list:
This tree will cause some scour, which will create deeper holding water for larger fish.
It will give some shade which will help keep aquatic invertebrates 🐛 alive (many of which have a lower tolerance to high temperatures than fish). Such shade also helps keep fish at temperatures they can tolerate and reduces evaporation.
These bugs (stonefly, mayfly, caddis, freshwater shrimp) are the main food for juvenile salmon
It will provide some complex structure to allow smaller fish, like salmon parr, a place to evade fish eating birds, like sawbills or cormorants.
It will be home to a huge number of bugs and fungi which will provide decades of food to salmon as well as birds like woodpeckers 🐟 🐦. The water facilitates the decay process creating a unique habitat when compared to dry deadwood.
It will help grade sediments by their size creating improved spawning conditions for both salmon and trout, and maybe lamprey too.
This sediment grading also offers opportunities to still more aquatic invertebrates (salmon food) in the resulting gravels and silts. Mayflies tend to like faster moving water over small pebbles whereas choronomids like slow water and silt. The caddisfly larvae love being on the wet wood. So the whole area becomes a tapas bar for fish.
It represents an interruption to flow which slows the flow down. Slowed flows during floods means the river is less erosive and can lower the flood peak. One tree on its own doesn’t do much but each one adds a small beneficial effect. If we had hundreds (as we used to before folks started ’tidying up’) the cumulative effect would be significant.
So let’s hope this stays in place and doesn’t fall victim to the (often well intentioned) chainsaw wielding folks.
As a side note, if you do ever feel the need to use a chainsaw in the river, make sure your using chain oil which is plant based.
This bit if the Tummel will have a happier Christmas and (if it stays) a happy year to come. We wish you the same!
That’s all for now. 😊🐛🐟🍄🟫🌳💚
