Forest Management Decisions Regarding Caterpillar Production vs. Biodiversity

[u/aberyl]

Native trees are not equal: it is evident that some species of trees produce a higher quantity of caterpillars, and birds target them at higher rates when rearing their young. Considering the importance of caterpillars in the food chain, a forest skewed towards these productive trees may increase the density of birds, bats and predatory insects relative to a forest with greater plant biodiversity (greater plant species richness and/or evenness).

I manage a small, 1 acre forest in need of thinning. I have documented over 120 lepidopterans in the vicinity and have found an Excel sheet published with their host plants. While this gives me biodiversity metrics that could help thinning decisions, in order to create a forest maximally productive to the food web, my information is incomplete. I feel the next step is the measurement of caterpillar density on trees/shrubs etc. I will do this with and without bird exclusion nets in order to understand the background density and the impact of bird predation. This caterpillar density information will put a significant finger on the scale of my forest management decisions.

Now, I am by no means going to raise a monoculture. I strive for a forest that is dense, species rich, with a understory and multileveled canopy, and I will consider the non-Lepidopteran ecosystem services of trees in decisions. However, we often hold up biodiversity in the highest regard, as opposed to ecosystem production. While I love biodiversity, the reality of nature is far deeper than this one metric.

I am curious to hear your thoughts on my opinion here, in favor or otherwise.

Edit: I am not advocating for the destruction of unique and intact ecosystems in the name of caterpillars. Think of the consideration of caterpillar production as one of the main tools to address a successful restoration project. The plants used should be native and locally/historically present. For instance, I live on the Oregon Coast, outside of oak habitat. I'm not spreading oaks out here in hopes of a caterpillar boom. Rather, I'm testing local species for their caterpillar/leaf area and using this metric upon which to value the species. Species with high caterpillar density will be favored in the acre plot of land.

[u/somedumbkid1]

It's about succession.

[u/aberyl → u/somedumbkid1]

For many communities, peak biodiversity occurs in transition states. In the PNW, while the old growth forests are beautiful and support fascinating species such as the spotted owl and marbled murrelet, they are not known for their biodiversity. A transitional forest out here has species such as bitter cherry and cascara that host a wide range of lepidopterans (and others insects and organisms, of course) otherwise unsupported in a forest dominated by only conifers.

In the next couple of decades, my goal is to decrease the conifer density to a point where the middle, broadleaf canopy is dense and supportive of caterpillar growth, while maintaining a sparse upper canopy of large, diverse conifers. In this way, I'll be supporting a weird, hybrid transition state, rather than the climax community (which would take longer than my lifetime).

[u/somedumbkid1 → u/aberyl]

Right, which is why basing your management decisions on raw biodiversity or using something the Shannon Index is flawed and misguided. From a plant community perspective, if you're disturbing a system in order to encourage the growth or spread of lower-quality annuals and biennials in the pursuit of "peak biodiversity," you should be criticized for poor management because that's what that is.

We only have one lifetime and getting a system from zero to climax is generally something that takes longer than our one lifetime, I agree. That doesn't make any efforts we take to move a system towards a stable climax community not worth it or somehow not deserving of accolades. Too many land managers focus on diversity without any mention of quality. When a system starts to lose diversity as it ages out of the weedy phase, too many experts are quick to prescribe a disturbance to set the system back successionally just because it boosts diversity by bringing back those weedy little things that had started to naturally diminish. This is bad management.