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Regeneration Niche: A Driving Force of Community Physiognomy

November 20, 2014
regeneration niche

Conifer seedlings on the forest floor. Photo Credit: Morguefile.com

When any one plant individual dies, a gap is created and new individuals ultimately take its place (Grubb, 1977). This is a general definition of regeneration niche that P.J. Grubbs says is an important stage in community shaping and richness development. “This replacement stage is of great importance not only for understanding species’ richness as such but also for understanding the basic processes of evolutionary divergence in plants and for the management of plant communities”(Grubb, 1977). Many plant communities are heterogeneous, meaning they are made up of different species. It is not always ensured the new plant that replaces the dead individual will be of the same species. One can see an example of this in our field site at coffin butte, as many white oaks have died and become snags on the ground. The species that has replaced them are different species as we have seen; Douglas firs, cherry trees, and I have even seen a holly tree in the understory. Regeneration niches could also contribute to the development of a community’s physiognomy moving from one successional stage to another. Physiognomy is defined as the form, structure, or appearance of a plant community (Gurevitch, 2006).

Mechanism that drive Regeneration Niches: (listed in Grubbs, 1977)

  • The Amount of light provided after an individual plant dies; if a whole tree is blown over one would think a shade intolerable species would replace it. In contrast, if only a diseased branch of a tree is broken off then one would think a shade tolerable species would begin to grow in place of it.
  • Production of a viable seed or the dispersal of the seed is also important. The timing in which the seed is made and if the seed is spaced out properly can influence how a certain species invades the gap.
  • Also, if there is establishment of a seedling nearby, it can give that species a faster and easier ability to take over the recently created gap provided.
Characteristics that can play a role on regeneration niches are: (listed in Grubbs, 1977)
  • The size and shape of the gap.
  • Nature of the soil.
  • The presents of other plants or animals in the community.
  • The presents of fungi, bacteria, or viruses in the community that can affect different species.
Douglas Fir 2

Douglas fir cone, in a squirrel’s mouth Photo Credit: Morguefile.com

Regeneration niche is defined as the set of environmental requirements necessary for germination and establishment of a plant species (Gurevitch, 2006). Now, I would like to bring this idea home with an example of how forest structure and composition can be changed through time because different plant species have different regeneration niches. On Vancouver Island, Stephen Getzin and his collogues did a study investigating the change in a Douglas fir (Pseudotsuga menziesii) community physiognomy as it went through different successional stages: immature, mature, and old growth. Their data analysis showed that Douglas firs accounted for 49% of the immature stand, and only 16% of the Old Growth stand. Although, regardless of their frequency Douglas firs had the largest diameter at breast height. In contrast, later successional species like Western Hemlock (Tsuga heterophylla) went from being 42% of immature stand frequency to 72% of old growth stand frequency, and Western Redcedar (Thuja plicata) went from being virtually absent in the immature stand to having about 9% frequency in the old growth stand (Getzin, 2006). Western Redcedar also had their highest frequency of 23% in the mature stand. Their data also showed that Doulas fir had the lowest segregation index, meaning that it could be close neighbors to other Douglas firs or different species. On the other hand, Western Hemlock and Western Redcedar had higher segregation indexes meaning that they prefer to have neighbors of the same species (Getzin, 2006). Getzin also points out that in the old growth stand, almost no Douglas fir seedlings can be found. A conclusion can be drawn from this data suggesting that Douglas firs are dominant early successional individuals and because they are shade intolerant species, they cannot regenerate very well in old growth stand. However, since Western Hemlock and Western Redcedar are shade tolerant species, this allows them to regenerate in later successional stages.

pine forest

coniferous Forest canopy Photo Credit: Morguefile.com

The understanding of different plant species’ regeneration niches can also help with conservation efforts. As we can use it to see how communities can be shaped and how their richness develops throughout different successional stages.

Works Cited:

 

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