Modern day forests represent a new type of anthropogenic ecosystem. Humans have been shifting the species composition of forests since the genesis of our own species, nearly 200,000 years ago. However, in more recent times our manipulation of forest ecosystems has even increased further with funded organizations, the division of natural habitats into private property and advancements in forestry equipment. Species diversity is greatly reduced with deforestation and forest thinning, but some species actually are better off in the face of anthropogenic forest manipulation. Lactarius deliciosus is the stunning species featured in today’s edition of Fungi Friday and its abundance actually increases with forest thinning.
Lactarius deliciosus is a mycorrhizal species that specializes in sharing scant soil resources with conifers (mainly Pinus sp.) in return for a sugar reward. It is a highly regarded choice edible across Europe, where it likely originated from. Its fitting Latin epithet deliciosus means exactly what it sounds like. Like other species from the genus Lactarius, fresh specimens exude a milky substance when cut or scratched. Different Lactarius species produce different colored, “milk” and sometimes the consistency and odor vary too. Lactarius deliciosus produces an orange-red slightly sticky substance.
Lactarius deliciosus group. Photo by Diane (mcgd).
As forests become more and more managed by humans, many mushroom species are taking a major hit. There’s only a small area of old growth forests left in the contiguous United States compared to the unforested/unmanaged area of just one hundred years ago. Species diversity not just for mushrooms, but most other kingdoms of organisms increases with forest age. Contrary to this basic ecological concept, some species actually do better with some forest management operations. As I mentioned before the abundance of Lactarius deliciosus increases with certain forestry practices.
One study published in 2011 by Bonet et al. looked at 30 different pine dominated plots with varying degrees of forest thinning over two years. Their findings clearly suggest that the production of Lactarius deliciosus fruiting bodies are significantly higher in plots that have been recently thinned. To be more exact, the study reveals that L. deliciosus mushroom biomass was five times greater the first year after thinning took place and double the biomass the second year after thinning compared to forest plots that were not thinned.
Fernández-Toirán et al. in 2006 also helps describe this pattern that the 2011 publication picked up on. The 2006 paper looked into the fungal community of Pine dominated ecosystems across central Spain and found that L. deliciosus is actually more of an early successional species. As we thin forests, we in a way, reverse forest succession as many larger trees are removed. After forest thinning, the ecosystem resembles more of an early successional forest. The canopy opens and more light penetrates the forest floor. Temperatures are slightly higher, and with less large trees soaking up water, there happens to be more available water. These factors result in higher yields of L. deliciosus fruitbodies.
A factor neither paper mentions is that the increased mushroom production could be perceived a stress response. Many species fruit when conditions specific to them are perfect. Oppositely, many species fruit when they face adverse conditions. We see individuals’ fruit when their resources are running out and we see large fruiting events after soaking rains as fungal mycelia encounter little oxygen. So, although you might see a glorious, robust, healthy looking mushroom, that individual could actually be quite stressed. That individual may be producing a spore bearing surface as a last-ditch effort to reproduce. L. deliciosus is without a doubt an early successional species, but forest thinning may procure a threat response as its tree host that provides the fungus with sugars might have just been removed, thinned by us humans.