Land management is required to maintain natural ecosystems (when natural disturbance regimes are altered) and to maintain land for human use and development. In either case, the management method and schedule may vary. Timing of management, in particular, can have demographic and therefore population dynamics implications. Plant resource availability and allocation patterns shift phenologically, so that depending on the stage in the growing season when management is applied, there may be increased impacts in the ability for regrowth or seed production. Meadows in fields and roadsides are managed with mowing, and in these habitats, common milkweed (Asclepias syriaca) is of conservation concern due to its strong linkages with monarchs (Danaus plexippus) for oviposition and as larval food source. I asked, does timing of clipping (as a proxy for mowing) affect plant re-sprouting and re-growth or seed pod production? I implemented a manipulative study of common milkweed (Asclepias syriaca) with three treatments: unclipped control, clipped in June and clipped in July. I measured plants and determined reproductive output (flowers in June and pod in July and August). Vegetative reproduction was quantified.
Results/Conclusions
Plants across the three treatments did not differ in any of the size measurements or flower umbel counts before the first treatment application (stem length, number of leaves, umbel, P>0.5). After being clipped in June, plants were not able to recover their growth and were significantly smaller (stem length, number of leaves, P<0.0001) with fewer flower umbels (P<0.0001). By August, plants in the no-clip control were the only plants to produce seed pods. Stem length of plants clipped in June were intermediate to control plants and July-clipped plants, thereby indicating some regrowth for early cut plants (P<0.0001). The number of leaves was similar for control and July-clipped plants, but the mechanism differed: control plants were beginning to senesce, and July-clipped plants had not re-grown leaves (P<0.0001). Plants clipped in July did show some re-growth potential: in August, 14 of the 30 root sprouts that had emerged from underground were in the July clipped plots. So far, this work demonstrates an impact of timing of clipping on plant growth and reproduction. Especially for plants of conservation concern, like common milkweed, considering the demographic responses to timing of management may contribute to the persistence of the population.