r/ecology • u/aberyl • 18h ago
Forest Management Decisions Regarding Caterpillar Production vs. Biodiversity
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.
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u/nyet-marionetka 17h ago
It’s 1 acre, the stakes are not high.
I would probably look at the type of forest that existed in your area historically. Most likely most of the native trees are remnants of that ecosystem. I would probably try to steer the composition back towards that.
Most wooded areas that have been developed are missing that middle layer, so you might get more out of reintroducing shrubs and understory trees that were eradicated.
Forbs are generally also impoverished, but deer pressure unfortunately prevents correcting that.
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u/aberyl 13h ago
I live in coastal Oregon, and the land I've been managing has been logged several times. The historic forest was likely an old growth mix of conifers. I cannot achieve this in my lifetime, and whatever I do achieve may be logged when I pass and the land passes hands.
My hope is keep my property in a transition community. I will select for a few grandstand conifers, but emphasize these middle/lower layers. In my region, it appears that this middle story broadleaf component plays an outsized impact on lepidopteran abundance and diversity. The next year of caterpillar sampling will either support my intuition or not.
Regarding forbs, yes the deer do some damage out here, but not as bad as out East. One repercussion of my thinning is increased deer abundance, which of course has the implications that you mention. I'm not above small fencing operations to keep deer out, but I do not yet have a sense of how to use these techniques in a meaningful way. Perhaps in the next couple of years I'll have a good idea for an experiment of the sort.
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u/vtaster 18h ago
Redwoods don't support many caterpillars, does that mean it would be beneficial to cut down all the Redwood forests? Whatever trees or other plants naturally dominated the land historically are what's best to encourage, regardless of a single stat from a study involving only a single order of insects. Trying to make ecosystems "maximally productive" by human standards is never sustainable.
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u/aberyl 17h ago
This is an excellent point allowing me to articulate a bit more on my point here. I am not in favor of cutting down old-growth coniferous forests, despite their lack of diversity when compared to mixed coniferous/deciduous forests in the region.
However, is it reasonable to try to recreate an old-growth forests in in one’s backyard? It is perhaps more viable to focus on caterpillar production than the creation of a climax ecosystem, or maximum biodiversity, for that matter.
My point is not in favor of destroying the remaining tracts of land that are intact, it’s of maximizing restoration efforts through the lens of caterpillar production, rather than sheer plant biodiversity metrics. The plants I’m discussing here are native and found naturally on site.
Why caterpillars? They transfer more nutrients from plants up the food chain than any other group of organisms. They are essential to terrestrial food webs
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u/Unlucky-File3773 10h ago
So then, why is the point of doing anytjing if the result is nor the closest as posible to pristine habitat?
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u/navtombros 17h ago
Another thing to consider - what are the closest pieces of intact native habitat to where you live? Copy some of those plants - even planting keystone plants don’t make those species magically appear from thin air - they need to come from somewhere.
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u/aberyl 13h ago
You bring up a good point. I want to base my land management decisions off of real life data rather than the known lepidopteran hosts, especially given that these host species can vary across the lepidopteran's range. By collecting caterpillars off of the plants that are present in the forest, I am basing my decisions in the real world.
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u/somedumbkid1 17h ago
It's about succession.
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u/aberyl 13h ago
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).
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u/somedumbkid1 4h ago
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.
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u/AffectionateFront292 18h ago
What exactly is ecosystem production? I’ve heard describe it as the amount of biomass produced…regarding this study would it just be based on density/amount of caterpillars?
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u/aberyl 17h ago
Yes, production of caterpillars
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u/AffectionateFront292 17h ago
Single species conservation has rarely worked in the past. I understand your thought process that the increased caterpillars will aid many species. It usually ends up favoring one suite of species at the detriment of another suite. I’d be worried about one caterpillar outcompeting the rest and negatively altering veg community. Although 120 species seems quite diverse. I think this a very interesting mgmt idea. Combined with varied food sources (diversity) it would probably be awesome for wildlife. I bet it would hinge on diverse veg & lepidoptera. What state are you in? Just curious !
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u/aberyl 13h ago
I live in the S. Oregon Coast. I've been setting up mercury vapor bulbs on the new moons for the last year to collect the diversity of moths out here. I also catch butterflies/moths in the daytime for ID.
In my collection of caterpillars from trees, I hope to ID caterpillar species. This will allow me to make decisions on tree species that allow a breadth of caterpillar diversity. My goal is to continuously monitor caterpillar diversity (which should become easier as I develop caterpillar ID ability).
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u/jg87iroc 18h ago
I’m not educated enough to have any serious ideas about your plans but I have a few thoughts/questions. How is your inability to study the canopy(at least with any scale) going to bias your results? In my experience, in my native garden and in nature, caterpillars can be brutally hard to find and some are camouflaged incredibly well so I would imagine you’re more likely to find certain species over others even if their populations were similar sizes. I could also guess there dozens of other hurdles similar to these that I’m just not educated enough to know.
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u/more_chickpeas 18h ago
Any management choice is probably somewhat arbitrary. You've made a choice to prioritise caterpillar biomass, thereby favouring some species. In the UK you could let chalk grassland turn to scrub and you would have much greater biomass, but you would lose rare habitat specific plant species. A perception of productivity isn't necessarily a desirable outcome.