Urban Landscaping and Slope Effects on Tree Seedling Dispersal

Urban Landscaping and Slope Effects on Tree Seedling Dispersal

Andrea Semlow

Urban landscaping has major impacts on the natural dispersal of plants and has shifted the population dynamics of plants. The effect of buildings on light coverage causes very different plants to succeed in a fragmented habitat. Consistent watering and other human activity adds to the sustainability of plants species in urban landscapes. This is especially relevant on the Grinnell College Campus because the region used to be covered by tallgrass prairie and is now manicured lawns, planted gardens, non-native trees, and concrete. The highly landscaped area have caused severe fragmentation of the populations and greatly shifted the community structure. The spatial distributions of seedlings of plants and trees are effected by a variety of factors, however, this blog focuses on the effect of slope on tree seed dispersal.

One study that gives an interesting discussion on the effect of steep versus gentle slopes on seed dispersal is titled, “Steep slopes promote downhill dispersal of Quercus crispula seeds and weaken the fine-scale genetic structure of seedling populations.” Q. crispula is a common tree species throughout cool temperate deciduous forests of southern Japan with large heavy seeds that are wind-pollinated. The study examined two questions:     

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1      1) In which direction and to what extent are seeds of Q. crispula dispersed on slopes?

2      2) Is genetic structure formed evenly on slopes? And if so is it weaker on flat sites?

The study was performed at University of Tokyo Forest on a southwest-facing hillside that had strong winds. The leaves of every adult and all seedlings that germinated in 2004 and 2005 were collected to detect and compare vertical dispersal on steep and gentle slopes. The endocarps, which is tissue from the seed of maternal origin, attached to seedlings were sampled to identify mother trees and genotypes. The mean horizontal and vertical dispersal distances were measured. The study found that most seeds were dispersed downwards and routes of some dispersed seeds crossed. Gentle slopes were limited to horizontal and vertical dispersal but steep slopes dispersed downwards. The genotypes of the adult population seemed to have no relation with topographical slopes. Neighboring seedlings are more likely to be related to each other on gentle slopes than on steeper slopes.

Site to access study:  http://hal.archives-ouvertes.fr/docs/00/88/40/92/PDF/hal-00884092.pdf

                

            This study relates to my own project because my group will be looking at the effect slopes and tree coverage have on tree seedling dispersal in one location on the Grinnell College campus. The area we have selected is a gentle slope and there is a diverse assortment of non-native mother trees surrounding the plot selected. We are going to measure how the slope has affected the growth of seedlings. In a future study if it were possible, looking at the genotypes of tree seedlings in the area, using the methods of the Q. crispula study, could help us better understand the effects of the urban landscaping as well as fragmentation on seedling dispersal and overall community structure.

               

 

Erin Callaway sampling from plot behind
Noyce at Grinnell College.