Plants growing in confined spaces

In many cases of urban horticulture practice and domestic gardens, plants grow in conditions that are not optimal. These conditions are soil quality and quantity, nutrient availability, light exposure, surrounding vegetation, surrounding buildings and water availability. Plants will compete for water, light and nutrients and in confined spaces, this competition, may have adverse effects on certain plant species.

In a case such as the planting arrangement below (see photo), an elm tree (Ulmus procera) is the dominant species in a corner garden bed that includes maple trees (Acer palmatum), Azalea sp., and start jasmine climbers (Trachelospermum jasminoides); the plants grow within the restrictions of the garden bed.

During summer, the garden bed requires additional watering as the area within 2 meters from the Elm tree is drier than the rest of the garden. Also, the plant species included in the photo are experiencing slower growth in comparison with same species in another part of the same garden.

Belowground competition occurs when plants decrease the growth, survival, or productiveness of neighbour hooding plants by reducing available soil resources. Competition be-low ground can be stronger and involve many more nearby plants than above ground competition.

Belowground competitive ability is correlated with such attributes as root density and surface area either in root growth or in the properties of enzymes involved in nutrient uptake. Unlike competition for light, in which larger plants have a disproportionate advantage by shading smaller ones, competition for soil resources is apparently more symmetric. Belowground competition often decreases with increases in nutrient levels, but it is premature to generalize about the relative importance of above- and belowground competition across resource gradients. Although shoot and root competition are often assumed to have additive effects on plant growth, some studies provide evidence to the contrary, and potential interactions between the two forms of competition should be considered in future investigations.

Plant growth competition.

Much of the competition among garden plants takes place underground. In contrast to above ground competition which primarily involves a single resource, light, plants compete for a broad range of soil resources, including water and essential mineral nutrients in the soil. Below ground competition often reduces plant performance more than does above ground competition.

The above photo indicates the  primary importance in below ground competition is the occupation of soil space. The ability to occupy space depends on several root characters, including relative growth rate, biomass, fine root density, and total surface area.

Openings in the below ground root zone activity are likely to be important for plant establishment. The extent to which root gaps are associated with canopy openings and the role of root gaps in the dynamics of gap succession have only recently been researched.