Invisible factors making certain plants do better or worse in certain years?

I notice that certain years, certain plants seem to do better than others.

For example, two years ago there was a massive explosion of this native, annual weedy plant Bidens frondosa. There was a meadow near me where it was the dominant plant, and it was showing up all over the place.

The next year though? There was much less of it. This year? Still much less. Both years there were only a few isolated plants, here and there, and it was nowhere dominant.

Sometimes there are factors that I can observe that clearly explain why certain plants do better in certain years. One year there was a spell of about 6 weeks with no rain, and that hugely hindered the growth of plants that rely on that time-period for germination and establishment. I noticed that that year, the drought killed a lot of stuff in spring and early-summer, and annuals that establish a bit later, like Erechtites hierachifolia or the various Acalypha sp. did better that year, whereas garlic mustard was set back, and it also harmed the native black raspberry a lot. Some years are wetter than average and I see moisture-loving annuals like jewelweed moving onto drier ground, or the moisture-loving perennial honewort establishing on usually-drier sites. On consistently dry years I see areas that are normally wetlands filling in with drought-loving annuals like partridge pea.

Sometimes there is a clear masting year for a certain tree, like last year, the northern red oaks in my area were masting, and accordingly, this year, there are a ton of small red oak seedlings everywhere. Two years ago, beech was masting, and I saw more beech seedlings last year, and this year I have not seen a single one.

But sometimes, I’m just perplexed. I cannot figure out why Bidens frondosa had such an amazing year two years back, and why there was so little of it the following year. Where did all those seeds go, did they not germinate? Did animals eat them? Did they germinate but the plants got out-competed? Do the seeds persist in the seed bank and germination only gets triggered under certain conditions, so some years more germinate than others?

Last year, my parsley crop failed. I planted four plants in different location and all four struggled and eventually died. My parents, about 50 miles away, 250 feet elevation higher, completely different soil type (fine, silty limestone-based soils, compared to my coarser, slightly more acidic soils) had the same thing happen that year. Why?

This year, in my area, I notice Elymus grasses (wild-ryes) are doing really well. I am seeing more of them than ever before, of multiple species. I’m also seeing first-year plants with really good seed production, whereas in the past seed production is usually poor on first-year plants.

I want to understand this stuff, and I’m curious for factors to look into other than weather conditions. Are these things affected by periodic insect outbreaks? Our area had 17-year cicadas this year. One year some sort of caterpillar infestation defoliated many of the Catalpa trees, but only those. One year there were a lot of Japanese beetles, and they defoliated certain plants, including evening primroses (Oenothera sp.), Roses (mostly the invasive multiflora rose), and various Hibiscus sp. This year, besides the cicadas, there are no disproportionate insect outbreaks that I notice.

I wonder if there are invisible factors though, that I’m not noticing, like maybe microscopic pathogens that are dominating in some years, or maybe insect infestations going on underground, things eating the root systems of various plants?

I find this stuff fascinating but I feel like I’m barely beginning to understand it because it’s so incredibly complex.

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I’ve got plenty of Japanese beetles again this year if you want some of mine… I think biotic interactions do play an important role for certain plants. In my area, you can see marked differences in vegetation depending on deer browsing. If the winter has been tough and the deer had to spread out more to find food, certain plants in the understory may appear to have been wiped out for the year. In my yard, I’ve got a bumper crop of black walnut saplings coming up this year because last year was a mast year for my big old tree and the squirrels buried them everywhere. Powdery mildew seems to be much more prevalent this year than in previous years and it’s having a damaging effect on certain plants but not others. Another fungus that seems to be doing well unfortunately is lily leaf spot, so I expect to be seeing much fewer lilies blooming in the woods because most are wilting before they can reproduce. This will affect the seed bank so some of these effects may still be seen several years into the future.

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It can be all kinds of things, but the fact Bidens frondosa lives for 1 year only it could mean something happened to how its seeds wintered, was the winter 2 years ago any different than usual? And maybe 3 years ago better than usual for those plants?

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I say yes to all that. If you have an abundance of an annual plant one year, it could be that it was the previous year’s conditions that particularly suited it, so more seeds were set and dispersed.

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That’s a good point. I checked the germination requirements and Bidens frondosa seeds require a two-month cold period to break dormancy. Winter weather and temperatures may affect how many of the seeds germinate in a given year.

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I don’t have much to add, but like @cazort my garden is very bad this year and I don’t know why. I planted carrots, beans, peas and they are either gone or not growing. Rabbits are possibly one factor, but many of my seeds did not germinate. Potatoes seem to be doing fine, though.
The wild plants are even more stressed, though. We basically have had no rain since April and an aphid infestation has coated many plants with a very sticky, dry exudate. Berries are not maturing, elms with DED are doing badly, and so are many oaks. I can water my garden, but the wild plants are on their own.

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In nearly all Carex sedge species, the buds for flowering stems are produced in later summer or fall. Their development depends on growing conditions in that summer. Then next year, they expand. If year 1 is terrible, it sets few buds, so it produces few flowering stems in year 2 even if year 2 is great. If year 1 is great lots of buds are produced. If year 2 is terrible, flowers abort.

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This all makes sense, and thanks much for the new ideas and observations! I think I under-appreciate the degree to which the effect of previous years’ weather fluctuations can affect what happens in a given year.

I have definitely noticed the effect of winter cold on germination rates when trying to germinate seeds myself.

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i notice a lot of this sort of thing since we are lucky/privileged to own a field of about 1 acre. Different plants do better or worse in different years, sometimes specific to our property, sometimes it seems to hold true for the entire state, the same thing holds for being an ecologist through Vermont, different plants in wetlands do better or worse on a given year. This year the goldenrods got off to a strong start due to a dry spring, but now it is wet. The milkweed is having a miserable year, just small with no vigor and lots of yellowed sick plants. Swamp aster is not doing well either due to dry start or heavy deer pressure. Jewelwed seems to be having a somewaht feeble year but too early to say. Lots of plants bloomed early but some sedges were very late. Etc etc.

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