Biology Reference
In-Depth Information
The flower loss may have allowed the Phlox to compensate by increasing seed set,
which has shown to be resource limited in other species [21], in the remaining
flowers. The relationship between seed mass and flower number is much stronger
in Rosa than in Phlox (Figure 3a), and Rosa, possibly because of its woody nature,
was unable to compensate for the flower loss by generating new shoots and flow-
ers or by increasing seed set in the remaining flowers. Therefore, the significance
of this treatment is most likely due to a combination of how many buds remained
after meristem removal as well as the allocation of remaining resources for repro-
duction.
Conclusions
High levels of defoliation reduced total seed weight in Phlox, Rosa, and Rhus,
all of which are found in Minnesota prairies. The removal of meristems along
with defoliation caused a greater response than defoliation alone in both Phlox
and Rosa. This suggests that loss of meristems is more important than defoliation
alone in its influence on the reproductive success of these species. All three species
studied are preferred by large mammal herbivores (primarily white tailed deer).
These results suggest that both defoliation, which limits the resources available for
reproduction, and meristem removal may be partly responsible for the compara-
tive rarity of the study species outside fenced enclosures.
Materials and Methods
Study Site and Study Species
The study was conducted at Cedar Creek Natural History Area (CCNHA) in
central Minnesota. For a detailed description of the study site, see Tilman [22].
The four species studied include smooth sumac (Rhus glabra), wild rose (Rosa
arkansana), bushy vetch (Lathyrus venosus), and phlox (Phlox pilosa). Smooth
sumac is a perennial shrub (1-4 m tall). Wild rose is a short woody perennial
shrub (1 m or shorter). Lathyrus venosus is a perennial legume (1.5 m or shorter).
Phlox is anherbaceous perennial (30 cm or shorter). These species was chosen
because they were abundant inside the fenced area and absent or rare outside the
fence (see methods below). There is also evidence that Rhus[23], Lathyrus[15],
Phlox (Haarstad, personal communication), and Rosa[24] are all browsed by deer.
The density of deer in this area has been minimally estimated to be 0.16 deer per
ha [25]. This density is similar to other protected areas, where deer herbivory has
caused changes in plant composition [25]. Target species were located inside ex-
closures which kept out large herbivores.
