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Fragmentation

Basic Info on Fragmentation:

Habit fragmentation is defined as "the simultaneous reduction of the area of the focal habitat and increased isolation of the remaining habitat patches" (Ranta et al. 1998). In short, fragments are areas of forest surrounded by deforested area.

Many species are lost during and immediately following fragmentation, but there are also many long-term effects which can be caused by changes in processes such as pollination, predation, territorial behaviour and feeding habits, in addition to changes in microclimate affecting solar radiation, humidity and wind pattern. In general, fragments have a much greater proportion of edge zone (in comparison to closed forest), which is physically different from interior forest, thus changing ecological properties of the fragment. Fragments usually can not support many species assemblages that exist in closed forest, and smaller fragments suffer more loss in biodiversity.

Effect of fragmentation on Epiphytes:

Survival of epiphytes subsequent to fragmentation is largely dependent on the size of the tree in which a species resides, the size of the fragment and also the relation of the fragment to closed forest (distance). In fragmented forest, there is a much greater loss in biodiversity of epiphytes than loss of presence in the fragment (thus we could not monitor the health of epiphytes in fragmented forest merely by measuring chemical output, we would have to determine species richness). The size and shape of a fragment will determine how the exchange of diaspores and pollen is carried out within and between fragments, and can lead to isolation of subpopulations.

Although the slow growth and long cycles of epiphytes make them more vulnerable to high rates of disturbance, it allows them to survive better in the mid-term if they can get past initial conditions. This increases their chance of success for colonization of second-forest in deforested areas as long as these reforested patches are not to far from larger fragments. In addition, their sensitivity makes them "suitable indicators of changes in local climate, forest structure and ecosystem health" (Hietz 1998).

Long-term effects of fragmentation on different types of flora:

In the Singapore Botanic Gardens a 4 hectare fragment of lowland tropical rain forest has been preserved since 1859. Initially, an inventory was taken of all woody stems greater than 5 cm in diameter at breast height and all vascular flora. Recently, another inventory was taken and the two were compared. The researchers identified trees by collecting foliage samples or fallen leaves and made collections of other vascular flora.

They found that of 448 initial species, 220 remained.

	Number of original species	Number of lost species	% extinction
Trees	286	121	42.3%
Climbers	104	63	60.6%
Epiphytes	6	4	66.7%
Shrubs	38	28	73.7%
Herbs	14	12	85.7%
Total	448	228	50.9%

Although the researchers considered human disturbance as a possible cause for this loss of biodiversity, they consider it much more probable that the main contributing factors are those related to isolation. The extinction consists of death of individuals and failure of new recruitment (often due to uneven competition). The latter result is evident in the finding that some areas of the fragment resembled logged forest in which climbers had taken over (possibly due to increased light penetration). They found that in this particular fragment, forest structure and floristic composition were similar in the periphery and the center of the fragment. The researchers also note that fragments can act as refuges for species for long (but not indefinite) periods of time.

Data from fragments of the Atlantic rain forest of Brazil:

Researchers studied geographical characteristics of 1839 forest fragments in an area of 623 km^2 (which were in the final stage of fragmentation) surrounded by sugar-cane fields in the Atlantic rain forest of Brazil. They found that in general the fragments were small and close together.

They analyzed the fragments by degree of isolation, edge effects and shape using GIS software. They grouped the fragments based on the distance (d) from one fragment to another for d = 50m, 75m, 100m, 150m, 250m, and 350m. For d = 50m, there were 1580 groups which contained 49% of the total forest area, for d = 250m, the groups contained 95% of forest area, and for d = 350m, 98% was included. Some fragments acted as important bridges or stepping stones between blocks of fragments.

The researchers discussed the geographical characteristics of the fragments in the context of island biogeography theory, which states that:

one large reserve is better than one small one
one large reserve is better than several small ones of equal total area (because the latter has a higher proportion of edge zone)
fragments close together are better than those that are far apart for species survival
corridors help improve species survival and biodiversity
round reserves are better than reserves of other shapes

They found that the habitat type of the matrix is important for dispersing species (thus we could reforest uninhabitable matrix to reduce isolation of populations). Additionally, they found that in simulations, reforestation of fields between the fragments resulted in an increase of forest area by 48% and an increase in interior area by 166%.

They recommend protection of large fragments, reforestation to connect fragments, and second-growth forest to improve the matrix.

Plans for Reforestation in Scotland woodland:

The Scottish National Heritage is attempting to network woodland habitats to counteract fragmentation using the ECONET approach. Most of the current fragmentation is the result of anthropogenic factors such as clearing land for agriculture, and logging. They plan to develop nodes and links of forest according to four possible procedures.

(1.) planting of new wood as far from existing wood as possible, resulting in maximum edge and isolation, but quickly developing connections.
(2.) starting with one wood and adding to it concentrically, resulting in early development and minimum edge effect, but bad initial connectivity.
(3.) starting with a few individual evenly distributed woods and adding to them concentrically, with results somewhere between the first two options.
(4.) starting with a strip of wood and widening it, resulting in good connectivity in one direction and a minimum edge effect, but low initial interior conditions.

Sources:

Hietz, Peter. "Diversity and Conservation of Epiphytes in a Changing Environment." International Union of Pure and Applied Chemistry (IUPAC). 1998. Volume 70: Issue 11. Available at: http://www.iupac.org/symposia/proceedings/phuket97/hietz.html

Turner, I.M.; Chua, K.S.; Ong, J.S.Y.; Soong, B.C.; Tan, H.T.W. "A century of plant species loss from an isolated fragment of lowland tropical rainforest." Conservation Biology. August 1996. Volume 10: Issue 4, pgs. 1229-1244.

Ranta, Pertti; Blom, Tom; Niemela, Jari; Joensuu, Elina and Siitonen, Mikko. "The fragmented Atlantic rain forest of Brazil: size, shape and distribution of forest fragments." Biodiversity and Conservation. 1998. Volume 7, pgs. 385-403.

Hampson, A.M. and Peterken, G.F. "Enhancing the biodiversity of Scotland's forest resource through the development of a network of forest habitats." Biodiversity and Conservation. 1998. Volume 7, pgs. 179-192.