A review of dipterocarps - Center for International Forestry Research
A review of dipterocarps - Center for International Forestry Research
A review of dipterocarps - Center for International Forestry Research
Create successful ePaper yourself
Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.
Root Symbiosis and Nutrition<br />
is actively being pursued in Southeast Asia. However, the<br />
same cannot be said <strong>of</strong> research into dipterocarp mineral<br />
nutrition requirements. With the present interest in<br />
establishing plantations <strong>of</strong> <strong>dipterocarps</strong>, fertilisers are<br />
being applied with the hope <strong>of</strong> producing enhanced or<br />
more rapid growth without a clear understanding <strong>of</strong><br />
dipterocarp mineral nutrition requirements. This very<br />
important aspect <strong>of</strong> dipterocarp silviculture needs to be<br />
studied in much more detail. This is reflected in the<br />
current state <strong>of</strong> knowledge discussed above and in the<br />
identification <strong>of</strong> research priorities discussed below.<br />
A word <strong>of</strong> caution be<strong>for</strong>e discussing future research<br />
priorities: results <strong>of</strong> many <strong>of</strong> the dipterocarp mycorrhizal<br />
studies carried out in this region, <strong>for</strong> example, the BIO-<br />
REFOR proceedings, are <strong>of</strong>ten difficult to interpret or<br />
not verifiable because <strong>of</strong> poor experimental design, lack<br />
<strong>of</strong> statistical analysis, or incomplete monitoring and<br />
reporting. Experiments need to be more carefully<br />
planned, controlled and monitored, to ensure that the<br />
observed effects are genuinely due to the inoculated<br />
ectomycorrhizal fungi and not from other contaminants.<br />
In view <strong>of</strong> the multi-faceted and some yet unknown<br />
aspects <strong>of</strong> dipterocarp mycorrhizas and nutrition, and the<br />
current ef<strong>for</strong>ts to establish dipterocarp plantations in the<br />
region, the following research priorities have been<br />
identified. Many paraphrase the recommendations made<br />
by Malajczuk et al. (undated) in their Annex 1 -<br />
Recommended <strong>Research</strong> Programme on Mycorrhizal<br />
Management, as these are found to be very relevant to<br />
dipterocarp mycorrhizal research. The following should<br />
be the future research priorities <strong>for</strong> dipterocarp<br />
mycorrhizas and nutrition:<br />
1. There is a need <strong>for</strong> more integrated studies on<br />
dipterocarp mineral nutrient requirements and<br />
mycorrhizal infection <strong>for</strong> seedling/cutting<br />
establishment in the field.<br />
Most fertiliser trials carried out thus far have ignored<br />
the role <strong>of</strong> mycorrhizas. They have a significant role<br />
to play in plant mineral uptake and are being<br />
considered in some quarters as possible fertiliser<br />
substitutes/supplements. Results from pot<br />
experiments have limited applicability in field<br />
conditions especially if plants in the field are<br />
interconnected by mycorrhizal links. These intact<br />
mycelial networks constitute the main source <strong>of</strong><br />
inoculum when seedlings are grown near an<br />
established tree (Newton and Pigott 1991b,<br />
107<br />
Alexander et al. 1992, Yasman 1995) as is likely to<br />
occur in re<strong>for</strong>estation <strong>of</strong> selectively logged<br />
dipterocarp <strong>for</strong>ests.<br />
2. The mycorrhizal dependency <strong>of</strong> <strong>dipterocarps</strong> <strong>for</strong><br />
re<strong>for</strong>estation should be determined <strong>for</strong> each species<br />
at various ages in various habitats (different light<br />
regimes, soil nutrient levels, water retention, organic<br />
substrates).<br />
Mycorrhizal fungi like vascular plants may vary in<br />
their ecological and physiological requirements and<br />
under given circumstances, some fungi may benefit<br />
particular hosts more than others. The ability <strong>of</strong> a<br />
particular mycorrhizal fungus to enhance the foliar<br />
nutrient content <strong>of</strong> the host may not be indicative <strong>of</strong><br />
the isolate’s ability to improve seedling growth and<br />
subsequent outplanting per<strong>for</strong>mance (Mitchell et al.<br />
1984). Surveys and identification <strong>of</strong> ectomycorrhizal<br />
fungi associated with <strong>dipterocarps</strong> should be<br />
continued and the results shared among workers in<br />
the region.<br />
3. Field studies should be conducted to determine the<br />
influence <strong>of</strong> nutrition and mycorrhizal infection on<br />
dipterocarp seedling survival, and their roles in<br />
determining <strong>for</strong>est composition.<br />
It has been suggested that the ‘nursing’ phenomenon<br />
(Read 1991), i.e. regeneration <strong>of</strong> seedlings in the<br />
vicinity <strong>of</strong> parent trees whereby they become<br />
incorporated into a mycelial network, reduces tree<br />
species diversity (Alexander 1989). It is believed that<br />
because mycorrhizal fungi have a great influence on<br />
plant survival in new and reclaimed sites, tree health<br />
and site quality, they are the cornerstone to proper<br />
establishment <strong>of</strong> functional <strong>for</strong>est ecosystems<br />
(Malajczuk et al. undated).<br />
4. Isolation and pure culture <strong>of</strong> indigenous<br />
ectomycorrhizal fungi should be intensified, and<br />
species associated with the desired host plant species<br />
both in unlogged and logged over <strong>for</strong>est requiring<br />
rehabilitation should be determined.<br />
There is evidence that some <strong>of</strong> the easily manipulated<br />
exotic mycorrhizal fungi such as P. tinctorius may<br />
be out competed by indigenous (co-evolved)<br />
mycorrhizal fungi in the field (see Chang et al. 1996).<br />
Moreover, fungi which are beneficial to the host in<br />
the natural <strong>for</strong>est may not be adapted to the degraded<br />
site where re<strong>for</strong>estation will be carried out. It has<br />
been suggested that successful establishment <strong>of</strong><br />
indigenous ectomycorrhizal trees is limited to areas