Primrose Explosion

One of the more intriguing parts of land management is watching for (and trying to interpret) temporary explosions of abundance within various species.  Sometimes it’s pretty clear that the rapid increase in population had nothing to do with management decisions – e.g., the huge numbers of orange sulphur butterflies we saw last year – but other times it’s possible to make at least some tenous links to management.  For example, I’ve collected enough plant data to know that daisy fleabane (Erigeron strigosus) often flowers in abundance in the year following a burn in our patch-burn grazing system.  It appears to germinate during the year of the burn (and intensive grazing) and then flowers during the next season when another the cattle have shifted their grazing to the next burn patch.  Interestingly, though that fire/grazing disturbance certainly opens the door for germination of many plant species, only a few species actually track tightly with that burn/graze pattern.  Most others seem more strongly tied to weather conditions, though management appears important as well.  In other words, it’s hard to know which plant species will respond best when we do a particular management treatment.  (And that’s why it’s fun!)

In 2009, we burned two different patches of the same native sand prairie in the same year – one in the early spring and one in late July.  Cattle were on the site during the whole season and shifted their focus to each new burn patch as it greened up after its burn.  During the following year, it was interesting to see which plant species showed up most strongly in each of the two burn patches as the grazing shifted to yet another patch.  Deer vetch (an annual legume – Lotus unifoliolatus) was one that was particularly abundant in the summer burn patch in 2010 – though it also had a pretty good year elsewhere as well.  Anyway, I figured we’d seen the end of the big showy plant responses to that summer fire by the end of 2010, but now I think I was wrong.

Showy Evening Primrose (aka Four-Point Primrose or Oenothera rhombipetala) in sand prairie - Platte River Prairies, Nebraska.

 This week, that old summer burn area is just loaded with showy evening primrose (Oenothera rhombipetala), a biennial native wildflower that forms a rosette during its first season and blooms during its second.  I can’t be completely sure that it’s abundant because of the summer fire and grazing, but when I stood on a hill overlooking the area, the edges of the primrose explosion tracked right along the edges of the summer fire unit.  I’ve been trying to find out more about when this primrose germinates (fall or spring) to see if that makes sense with what I’m seeing, but haven’t found anything specific enough.  If it germinates in the spring, that would make sense, since the surrounding vegetation would have been weak in the spring of 2010 (because of the 2009 summer fire and subsequent grazing) and would have favored germination of plants like the primrose. 

Showy evening primrose is an easy species to notice, and it’s hard to miss it when it has these kinds of temporary population explosions.  Other plant species are less obvious, and I have to rely on my annual plant data collection to see patterns, but the primrose doesn’t hide its activity!  Makes me wonder how many insects and other species are responding strongly to our management but going unnoticed…

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About Chris Helzer

Chris Helzer is the Director of Science for The Nature Conservancy in Nebraska. His main role is to evaluate and capture lessons from the Conservancy’s land management and restoration work and then share those lessons with other landowners – both private and public. In addition, Chris works to raise awareness about the importance of prairies and their conservation through his writing, photography, and presentations to various groups. Chris is also the author of "The Ecology and Management of Prairies in the Central United States", published by the University of Iowa Press. He lives in Aurora, Nebraska with his wife Kim and their children.
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6 Responses to Primrose Explosion

  1. Dan Staehr says:

    Does the primrose attract butterflies? Have you done any on-going butterfly counts on your prairies?

    • Chris Helzer says:

      We did some counts last year for general species, and we’re doing regal fritillary counts for the second year running. I don’t know for sure, but was under the impression they were mainly pollinated by night-flying moths…

      • jtrager says:

        I think you’re right, Chris. Most of this group of Oenothera species are pollinated by sphinx moths, and have correspondingly long corolla/nectar tubes.

  2. Karen Hamburger says:

    Showy primrose gets very fragrant at night and I have had sphinx moths in the evening hours and the large hawk moths come to them after dark in my back yard. I have also observerd tiny white moths that I cant identify at night. I have also wondered about bats pollinating them.
    Durning the day its mosty the bee type polinatios but they favor the other flowers more. Humming birds seem to ignore them. I have wondered if they produce very little nectar during the day.
    Are there any studies about how and when different flowers produce their nectar ?
    Karen Hamburger

    • Chris Helzer says:

      Hi Karen – thanks for the moth info. I don’t know of any bats in Nebraska that are pollinators – I think they’re all insect feeders.

      Yes, I think there are studies of when/how flowers produce their nectar, and they do vary. I’m not really familiar with them other than I know that at least some studies exist! I think I remember reading that many plants can be depleted of their nectar by mid-morning (and replenish again overnight) and that others are more consistent about production…

  3. Karen Hamburger says:

    Hey Chris
    If you could point me in the right direction on finding the nectar studies I would apprecate it.
    The reason I wondered about bats is I have found flowers in the peak of blooming that have been chewed up during the night. I also suspect mice. There is no evidence as to who is the culprit.
    I am the only one in my extended neighborhood area that does not use chemicals so I have a higher density of insects and bats swooping in to my yard feasting on the bugs and I have found bats on the ground after hard down pours around the garden near the night blooming plants.
    Maby the bats have a sweet tooth??:^) I know the mice do!!! I have too many snakes that keep the mice population down…so I was just wondering.
    Perhaps we have another path to explore!!!!
    Thanks
    Karen

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