Succession and management - Ecological Applications: Toward a Sustainable World - page 225

In the case of nurse plants that are legumes, the associated bacteria serve to
increase nitrogen availability to target plants. Fungi may also increase nutrient
availability in situations where plant nutrients are a limiting factor. Most plants
do not have roots as such, they have mycorrhizas - intimate mutualisms
between fungi and root tissue. The fungal networks in mycorrhizas capture
nutrients from the soil, which are transported into the roots to the benefi t of
the plants and, in return, the fungi gain access to the photosynthetic products
of the plant.
Tropical dry forests in places like the Yucatan Peninsula of Mexico have been
converted to agriculture and pasture, with less than 10% of mature forest remaining.
And as a result of a rapidly increasing human population, accidental fi res have
increased in frequency, tending to convert much of the remaining primary forest to
secondary forest with less biodiversity and lower conservation value. It would be
impracticable to undertake large-scale restoration to mature forest, but small patches
can be improved to augment and link the remaining forest fragments. Allen et al.
(2005) planted seeds of six important climax trees in a site that had been recently
subject to a severe fi re. They wanted to determine whether seedling success would
be facilitated by mycorrhizal fungi. Thus, seeds were planted in three experimental
treatments: in steam-sterilized soil (initially lacking mycorrhizal fungi), in soil
inoculated with mycorrhizal fungi that are characteristic of early forest succession
(principally Glomus spp.) or in soil inoculated with mycorrhizal fungi from late
succession (including species of Scutellospora , Gigaspora and Acaulospora ). In each
case, seedling growth was enhanced by fungal inoculation of the soil, and in most
cases mycorrhizal species associated with late-successional soils facilitated growth
most (Figure 8.8). It is clear that the common plant nursery practice of sterilizing
soil is not always appropriate when community restoration is the objective.
Pollination is another kind of mutualism with implications for restoration time-
tables and reinstatement of proper community functioning. Hay meadows represent
some of the most species-rich plant communities in the UK, but well over 90% have
disappeared as a result of agricultural intensifi cation. You saw earlier that meadows
are being restored by returning to much less intensive patterns of grazing and
mowing, as well as by planting desirable species (Section 2.4.2). Forup and Memmott
(2005) compared plant-pollinator interactions in two ancient British hay meadows
and in two restored hay meadows to discover whether patterns of insect visitation
and pollen transport had been regained in the restoration process. In each meadow
they identifi ed and counted all insect-pollinated fl owers, noted which insects visited
which fl owers and identifi ed to plant species the pollen grains attached to the
insects' bodies. Their analysis included 42 plant species and 85 fl ower-visiting insect
species, dominated by two-winged fl ies (Diptera) and bees and wasps (Hymenop-
tera) with somewhat fewer beetles (Coleoptera), bugs (Hemiptera) and butterfl ies
and moths (Lepidoptera).
The results are shown as fl ower-visitation webs in Figure 8.9. All meadows were
similar, although a marginally higher proportion of all conceivable fl ower-insect
links is realized in ancient meadow. There was no difference in the proportion of
fl ower species visited, and visited plants all had more than a single species of insect
visitor. Furthermore, there were no differences between old and restored meadows
in the total amount of pollen transported or the average number of grains per insect.
Despite differences in plant community composition among the meadows, the