what effect does habbit fragmentation have onthe growth of plants?

Answer 1

If a habitat is broken down into small, isolated regions the ability to mix genes is reduced. With a smaller allele pool & less variability there will be less ability to respond to disease, climate changes, or predation by herbivores.
Pollinators may not be as readily available leading to reduced reproduction in some plants. This will give a reproductive advantage to those with pollinators and wind pollinators.
As the area decreases the ratio of edge to area increases. This means there will be a great deal of invasive seed intrusion. This will increase competition for resources with native plants.
Resource allocation will shift dramatically when ever there is habitat loss. This will result in selection towards those favored by the new habitat restrictions. The habitat populations will change leading to loss of species diversity through local extinction.

Compare this habitat fragment to an island and you will expect to see similar responses.

Answer 2

The fragmentation of land with a population of native plants disturbes their natural living-conditions. They can either adapt - p.e. grow smaller - or die.
Here the definition of habit fragmentation, which explains it:
Habitat fragmentation is frequently caused by humans when native vegetation is cleared for human activities such as agriculture, rural development or urbanization. Habitats which were once continuous become divided into separate fragments. After intensive clearing, the separate fragments tend to be very small islands isolated from each other by crop land, pasture, pavement, or even barren land. The latter is often the result of slash and burn farming in tropical forests. In the wheatbelt of central western New South Wales, Australia 90% of the native vegetation has been cleared and over 99% of the Tallgrass prairie of North America has been cleared, resulting in extreme habitat fragmentation.

The term habitat fragmentation can be considered to include six discrete processes:

Reduction in the total area of the habitat
Increase in the amount of edge
Decrease in the amount of interior habitat
Isolation of one habitat fragment from other areas of habitat
Breaking up of one patch of habitat into several smaller patches
Decrease in the average size of each patch of habitat

There are more publications, but this one is the clearest.