Tuesday, May 1, 2012

Summary of Preliminary Study of Mayapple Seeds

     Mayapple seeds are relatively rare. To do a full blown seed study has not been feasible. I hope that I can purchase seeds that have not been dried as I need them for the portion of my study looking at where in the forest is best for mayapple seed germination.  I have talked to the supplier of the seeds and they assured me that they will reevaluate their mayapple seed storage conditions. 
     At any rate, this poster summarizes my findings. These findings have informed my research decisions and will allow me to better interpret my data.
Full size poster

Another Hypothesis

     This spring I am collecting data to help determine what makes a good microhabitat for mayapple. I have observed it growing in a wide variety of locations. I have observed it making reproductive shoots in a wide variety of locations. I do not find mayapple growing in places like this:
Dry south facing slope (no mayapple).
 But, after taking the above photo, I turned around, and a little lower on this slope there is a depression where it is slightly wetter and I saw this:
Mayapple patch in moist depression on an otherwise dry south-facing slope.
There are a couple of reproductive shoots in this patch also.

     It appears that mayapple grows best in locations that are moist.  I have not seen mayapple growing in the saturated soil of stream bottoms however. I do find shoots and sparse colonies in dry locations, but I believe that it spreads into these locations by rhizome growth and not by seeds. 

     I hypothesize that if the seeds can stay moist in the fall and winter, that mayapple seeds will grow just about anywhere from lawns to soil-filled depressions in boulders. There may be other limiting factors in the environment besides moisture, but visually, I cant tell what they are. My hope is that the measurements I am taking will capture the difference between good mayapple habitat and not-so-good mayapple habitat.

     I often find small mayapple patches at the base of trees. I bet that they got there in raccoon poop.

An isolated mayapple patch at the base of a tree.

Thursday, March 8, 2012

Hypotheses to date:
Observed: A mayapple fruit begins green and firm and gradually lightens as it increases in size. When it ripens it turns soft, yellow and odorous. The change from whitish green and firm to yellow and soft happens within a day or two. Most fruit are eaten in early June when they are not ripe. Seeds that come from these fruit appear to be nonviable. Seeds that are taken from unripe fruit at the end of July or early August (starting to ripen but still firm but a day to a week short of ripening) have a germination rate half that of seeds taken from on-the-plant-ripened fruit.
Based on Jen's camera pictures and on my observations of leaf and fruit removal in early June, deer are responsible for the the unripe fruit removal.

Observed: Deer mechanically destroy (chew up) close to 100% of seeds ingested.
Hypothesis: Deer are seed predators and contribute little to the distribution of mayapple.

Observed: One seed (out of two) from ripe fruit  recovered from the deer poop germinated. The other seed appeared viable but remained dormant.
Hypothesis: Since deer probably eat ripe fruit also, they may occasionally disperse viable mayapple seeds.

Observed: Seeds allowed to dry are 99% dead. Only two out of hundreds germinated after rehydration. The rest molded and became mush within a week. These two seeds were part of a batch of 30 that were kept hydrated for 10 months, including 7 months at warm temperatures before drying out. They were dry for several weeks. All the rest (of the hundreds that quickly molded) were dried after fruit removal and stored dry for months before rehydration.

Hypothesis: Mayapple seeds need to be dispersed to locations that do not dry out between the time of dispersal (late July - mid August) and the time of germination (late February - March).

Other observations and hypotheses:
Mayapple form the most dense and reproductive colonies (based on percentage of flowering shoots) in moist areas. This will be tested quantitatively in the next few months.

Mayapple colonies are found most often under a closed canopy.They are occasionally found in open areas near the edge of a forest where humans have cleared the vegetation such as power line corridors and mowed areas on road sides.

Deer defecate preferentially in open areas - not a lot of  brush and foliage cover below a meter.  Perhaps this is because they don't want a lot of brush to poke their rear or they prefer an open field of view during a vulnerable moment? Caveats: I made a determined effort to search thoroughly in brushy sections of my transects, slowly and systematically sweeping aside the brush up to two meters on either side but I do recognize the possibility that I missed more poo in the brushy areas. The majority of my transects were in relatively open understory areas.

Deer defecate preferentially on flat or gently sloped ground. I did find a few pellet groups on deer trails angled up the side of a slope however. The vast majority of poop was found on ridge tops or terraces. Very few pellet groups were found in the bottoms or near streams.  The data are still being analyzed.

Raccoons defecate all over it seems. I have confirmed that they prefer to go at the base of trees and they  use the same spot more than once. It is difficult to intuit anything else from the data which is still being analyzed.

 The poo disintegrates within a few months. The seeds are moved by water (observed up to 70 cm in prelim study) and perhaps mice/chipmunks?  I am going to begin more rigorous secondary dispersal studies soon. Hopefully I will be able to purchase some cameras to watch the poo too!

I will collect data in the next few months to characterize the locations in which mayapple grows most successfully.

Statistical analysis is something I am learning as I go, and I haven't gone very far.