Thanks to Brilliant for supporting  this episode of SciShow.

To take your STEM skills to the next level, go to Brilliant.org/SciShow for 20%  off an annual premium subscription! [ ♩ Intro ] Wildfires are all over the news these days. In North America, the number of  forest fires has increased four-fold in the last couple of decades, with fires lasting longer and  getting bigger every year.

And wildfires are an inconvenience  and a danger for many creatures, including us humans, but they’re not always a  bad thing for all animals. One creature we might not expect  wildfires to affect much at all are fish. You know, since they live in water, which is one place that fire tends to not do well.

But despite that, researchers have found that wildfires can change the lives of  our aquatic friends in a lot of ways. In fact, we now know that even though  wildfires have a lot of downsides , some types of wildfires can be beneficial, or even necessary, for their ecosystem to thrive. Sure, when a wildfire happens, a pond or stream doesn’t actually burn up.

But immediately after a fire, the  quality of life in streams, lakes, and rivers temporarily gets worse  for the creatures that live there. The water quality drops, and when the surrounding  trees are burned badly enough to die off, their roots are no longer there  to hold the landscape in place, which can cause it to become unstable. And that often results in a large amount of  debris falling into nearby bodies of water, or being washed into them by the  next big rainfall.

Stuff like   burned trees, large boulders and mud. This can also carry a lot  of nutrients into the water, which can trigger a massive algal bloom – when the microscopic algae that live in the  water all grow very quickly, all at once. And at first , an algal bloom  sounds like it would be great for the ecosystem.

A lot of creatures use it as  their primary source of food. But the vast majority of the algae that doesn’t get eaten eventually  dies and sinks to the bottom and as it decomposes, those  decomposers consume a lot if not all of the oxygen in the water. Which is pretty bad news for the aquatic  animals that need that oxygen to survive.

But there are some benefits. In the long term, those trees and  rocks can establish new habitats for fish and other creatures in the water. For example, increased numbers  of logs, known as logjams, can improve the quality of a stream  or river by creating more hiding spots for juvenile fish species.

All those logs and boulders can also  help to create deeper pools of water, where the water can be  cooler than in the shallows. And that’s great for fish species that need  those cooler temperature ranges to survive. Swimming around in warmer water temperatures  can be very stressful for these fish.

It increases their energy  expenditure and need for food, which may or may not be available. So  having places to chill out is vital. Sometimes, though, it’s not just nature that disturbs  fish’s ecosystem during a wildfire.

Occasionally, humans get involved and  try to contain or extinguish the flames. When a fire needs to be brought under control, firefighters will manually combat the spread  by pouring dirt or water on the flames, or by removing or wetting all of the  underbrush before the wildfire gets there. But when the fires become too big and too intense, bigger fire suppression methods like  chemical fire retardants have to be used.

These contain nitrogen-heavy compounds  which, in high enough concentrations, can be toxic to fish and other creatures that live  in the water and create even more algal blooms. Now, putting out wildfires before  they cause all this ecological chaos might sound like the obvious choice. But researchers in the  Pacific Northwest have found that suppressing all wildfires  can be counterproductive.

In the Wenatchee River basin, for example, that approach is actually having a negative  impact on some fish species in the area. Their studies suggest that allowing  little to no wildfire near streams may be limiting habitat for salmon. Without the upheaval that fire brings, there are fewer logjams and  boulders creating an ecosystem that these creatures evolved to thrive in.

This has contributed to the  decline of threatened fish species like Chinook salmon and bull trout, in combination with other  factors like the fragmentation and loss of their habitats. The good news is that in 2015, these researchers were able to model  how these vulnerable fish populations might recover if we humans changed  up our fire-management strategy. They modeled scenarios with different  fire sizes and habitat connectivity.

And they predicted that in  a future, warmer climate, bull trout would fare better when some wildfires were allowed to do their thing  and create habitat variety, including those colder pools  of water they need to live. Instead of us trying to completely prevent fires, they argued that managing  forests and allowing regular, small burns would help support these  vulnerable species in a warmer climate.   Here’s the sticking point, though. Hot, high-intensity fires are becoming more common thanks to the climate crisis.

And those are a way bigger problem  than slower, lower-burning fires. You see, low burning fires help clear  out the underbrush in the landscape – the stuff that otherwise becomes fuel  for a bigger, more devastating fire. They improve the diversity and  richness of an ecosystem over time, both on land and in the water, whereas the high-intensity variety  just demolishes everything in sight.

With high-intensity fires  becoming more and more prevalent, it looks like future fire management efforts  need to literally fight fire with fire. Research has shown that by  starting controlled burns, which mimic low-intensity wildfires, forest managers can eliminate some of the fuel for super intense fires capable of  wiping out the entire forest ecosystem. Smokey the Bear may tell has told us  that only we can prevent wildfires.

But it’s worth keeping in mind that they  are an important part of many ecosystems. With proper management, fires  can help ecosystems thrive. Even in places where they can’t burn at all.

Today we talked about a pretty  unexpected interaction in nature. But if you’re not done  learning surprising new things, you might enjoy a course from  today’s sponsor, Brilliant. Brilliant is an interactive STEM-learning platform that helps you to truly  understand concepts in math, science, and computer science by guiding  you through engaging, hands-on courses.

They’re always working to make their  courses more engaging and more interactive. And with their new course Everyday Math, you can brush up on all the math skills  that never quite stuck in grade school – or maybe just gotten a little rusty. So to join their community of  learners and educators today, click the link in the description down  below or visit Brilliant.org/SciShow.

You’ll get 20% off the annual Premium  subscription by using that link. [ ♩ outro ]