Summary 1 We examined how seed size and seedling growth rate influence recruitment success of neotropical pioneer species. We investigated the soil seed bank, and followed seedlings from emergence and establishment to the sapling stage in artificially created gaps in secondary forest on the Barro Colorado Nature Monument, Panama. 2 To simulate microsite variation within gaps, litter addition/removal and soil disturbance treatments were applied to seedling plots in a factorial design. 3 Seedling emergence was almost three-fold higher in litter-free plots than in control plots. 4 We found a negative relationship between seed mass and seed abundance in the soil, seed mass was positively correlated with seedling emergence success from the seed bank and with seedling survival through to the end of the first dry season. 5 In the 18 months following the first dry season we observed an uncoupling of seed mass from seedling performance. Seedling mortality was now a function of maximum relative growth rate, with higher mortality of fast-growing species attributable to herbivory, notably by shoot-borers. 6 We propose that a seed size-dependent trade-off between dispersal success (selecting for large seed number), and emergence‐establishment success (selecting for large seed size) can explain the maintenance of wide variation in seed size among pioneer species. Secondarily, a trade-off between growth rate and susceptibility to herbivores acting at the post-establishment phase may contribute to observed differences in light requirements among pioneer species.

Seed size, growth rate and gap microsite conditions as determinants of recruitment success for pioneer species

Contributors. Methods in Ecology series. Preface. 1 Sampling theory and practice: Simon R. Leather & Allan D. Watt. 2 Sampling insects from roots: Alan C. Gange. 3 Pitfall trapping in ecological studies: B.A. Woodcock. 4 Sampling methods for forest understorey vegetation: Claire M.P. Ozanne. 5 Sampling insects from trees: shoots, stems, and trunks: Martin R. Speight. 6 Insects in flight: Mark Young. 7 Techniques and methods for sampling canopy insects: Claire M.P. Ozanne. 8 Sampling methods for water--filled tree holes and their artificial analogues: S.P. Yanoviak & O.M. Fincke. 9 Sampling devices and sampling design for aquatic insects: Leon Blaustein & Matthew Spencer. 10 Methods for sampling termites: David T. Jones, Robert H.J. Verkerk & Paul Eggleton. 11 Parasitoids and predators: Nick Mills. Index

Insect sampling in forest ecosystems.

Spanish Cedar (Cedrela odorata L.) is a globally important timber species which has been severely exploited in Mesoamerica for over 200 years. Using polymerase chain reaction–restriction fragment length polymorphisms, its chloroplast (cp) DNA phylogeography was studied in Mesoamerica with samples from 29 populations in six countries. Five haplotypes were characterized, phylogenetically grouped into three lineages (Northern, Central and Southern). Spatial analysis of ordered genetic distance confirmed deviation from a pattern of isolation by distance. The geographically proximate Northern and Central cpDNA lineages were genetically the most differentiated, with the Southern lineage appearing between them on a minimum spanning tree. However, populations possessing Southern lineage haplotypes occupy distinct moist habitats, in contrast to populations possessing Northern and Central lineage haplotypes which occupy drier and more seasonal habitats. Given the known colonization of the proto-Mesoamerican peninsula by South American flora and fauna prior to the formation of the Isthmus of Panama, it seems most likely that the observed population structure in C. odorata results from repeated colonization of Mesoamerica from South American source populations. Such a model would imply an ancient, pre-Isthmian colonization of a dry-adapted type (possessing the Northern lineage or a prototype thereof), with a secondary colonization via the land bridge. Following this, a more recent (possibly post-Pleistocene) expansion of moist-adapted types possessing the Southern lineage from the south fits the known vegetation history of the region.

Chloroplast DNA phylogeography reveals colonization history of a Neotropical tree, Cedrela odorata L., in Mesoamerica

Preface. Acknowledgement. 1. Resistance in trees to insects - An overview of mechanisms and interactions S. Larson. 2. Mechanisms of resistance in conifers and bark beetle attack strategies F. Lieutier. 3. Mechanisms of resistance in trees to defoliators K. Clancy. 4. Mechanisms of Resistance in Conifers against shoot infesting insects. The case of the white pine weevil Pissodes strobi (Peck): (Coleoptera: Curculionidae) R.I. Alfaro, et al. 5. Host tree resistance to wood-boring insects T.D. Paine. 6. Plant resistance against gall-forming insects: the role of hypersensititiy T.G. Cornelissen, et al. 7. The resistance of hybrid willows to specialist and generalist herbivores and pathogens: the potential role of secondary chemistry and parent host plant status J. Hjalten, P. Hallgren. 8. Deploying pest resistance in genetically-limited forest plantations: developing ecologically-based strategies for managing risk D.J. Robinson. 9. Deployment of tree resistance to insects in short-rotation Populus D.R. Coyle, et al. 10. Strategies for Deployment of Insect Resistant Ornamental Plants D.A. Herms. 11. Possibilities to utilize tree resistance to insects in forest pest management in central and western Europe C.H. Heidger, F. Lieutier. 12. Deployment of tree resistance to pests in Asia N. Kamata. 13. Using Resistance in Tropical Forest Plantations J.D. Nichols, et al. Index.

Mechanisms and deployment of resistance in trees to insects.

Cedrela odorata L. (Spanish cedar), an economically important timber species native to the American tropics, is the focus of increasing conservation concern due to high rates of deforestation within its native range. To assess the extent of the genetic diversity within and between populations of this species, samples were obtained from 10 widely dispersed populations within Costa Rica and analysed for random amplified polymorphic DNA (RAPD) variation. Fourteen 10-mer primers were used to generate 97 polymorphic RAPD bands. Presence/absence data for all bands were subjected to a pairwise genetic distance analysis, according to Jaccard's coefficient, then neighbour-joining cluster analysis was performed on these distances, as was an analysis of molecular variance (AMOVA), to assess levels of differentiation between populations and regions, and Shannon's Diversity Index was used to quantify levels of diversity within and between populations. Results indicated highly significant genetic differentiation (P < 0.004, AMOVA) between populations originating from the North Pacific and Atlantic/South Pacific regions of Costa Rica, with 35.3% of the total variation attributable to a difference between these areas. Little differentiation was recorded between populations from within the same region (P= 0.757, AMOVA), and 65.1% of the total variance was attributable to variation within populations. Estimated values for within-population diversity, calculated as Hpop/Hsp by means of Shannon's Diversity Index, were found to vary greatly between primers, but the overall within-population component of genetic diversity was 0.45. Possible reasons for the high degree of intraspecific genetic variation within this species are discussed and the implications of these results for the conservation and use of its genetic resources are described.

Genetic variation in Costa Rican populations of the tropical timber species Cedrela odorata L., assessed using RAPDs

Summary

1 Attack by shoot borers (Hypsipyla grandella Zeller) is the main factor limiting the cultivation of Cedrela odorata and Swietenia macrophylla, two economically important members of the mahogany family. No viable methods of pest control are currently available. To assess for genetic variation in susceptibility to pest attack, a combined progeny/provenance test of C. odorata and a provenance test of S. macrophylla were established separately at CATIE, Turrialba, Costa Rica, and assessed intensively over an 84-week period.



2 Variation in height growth between provenances was highly significant in both species, provenance means varying by a factor of 2.7 and 1.2 in C. odorata and S. macrophylla, respectively. Cedrela odorata also displayed provenance variation in foliar phenology, as 94.7% of the trees from a ‘wet zone’ provenance remained foliated, whereas > 35% of trees from three ‘dry zone’ provenances abscised their leaves during the dry season.



3 Both species displayed significant genetic variation in susceptibility to shoot borer attack. At the peak of attack during the second year of growth, the effect of provenance was highly significant in both species, the mean number of attacks per tree varying between 0.8–2.4 and 0.6–1.3 in different provenances of C. odorata and S. macrophylla, respectively. A provenance of C. odorata from San Carlos, Costa Rica, displayed consistently lower susceptibility to pest attack, being subjected to fewer attacks during the first year and demonstrating a higher mean height to first point of damage.



4 The nitrogen, total tannin and proanthocyanidin concentration of foliage varied significantly between C. odorata provenances: nitrogen concentration was significantly lower and tannin and proanthocyanidin contents were significantly higher in trees from the San Carlos provenance, Costa Rica. This study therefore suggests that proanthocyanidins may reduce susceptibility of C. odorata to H. grandella, at least during the early period of growth.



5 These results provide support for the development of plant resistance as a strategy for managing shoot borers. In particular, there may be scope for selecting for high foliar proanthocyanidin content and the ability to tolerate attack by vigorous apical growth.

Genetic variation in host susceptibility to attack by the mahogany shoot borer, Hypsipyla grandella (Zeller)

In order to evaluate the relationships between attacks by the mahogany shoot borer Hypsipyla grandella (Zeller) and host growth and phenology, field trials of Spanish cedar Cedrela odorata and American mahogany Swietenia macrophylla established in Costa Rica were assessed intensively over an 84 week period. Height growth of C. odorata was approximately twice that of S. macrophylla , with mean growth rates of 2.0 and 1.3 cm week −1 respectively. Cedrela odorata displayed pronounced temporal variation in leaf phenology, with a minimum of 51% of trees in leaf during a relatively dry period. In contrast, the minimum proportion of foliated S. macrophylla trees was 87%. No shoot borer attacks were recorded on S. macrophylla until week 50 after the onset of assessments, whereas initial attacks of C. odorata were recorded during week 6. By week 84, the proportion of trees attacked was 74% and 77%, respectively. In both species, attacks were concentrated in seasonal peaks, coinciding with the production of new shoots. Pronounced spatial variation in attack was observed in both species. At week 12, the number of attacks per block in C. odorata was negatively correlated with available calcium concentration (r=0.85, P C. odorata was positively correlated with available phosphate concentration (r=0.84; P C. odorata and 0.4% S. macrophylla remained undamaged to a height of 3 m. It is suggested that control methods for the mahogany shoot borer should take account of temporal dynamics in attack, and relationship to host phenology. Manipulation of the soil nutrient status may also form part of an integrated approach to pest management.

E.A. Corea

Papers

Genetic variation in host susceptibility to attack by the mahogany shoot borer, Hypsipyla grandella (Zeller)

Variation in attack by the mahogany shoot borer, Hypsipyla grandella (Lepidoptera: Pyralidae), in relation to host growth and phenology

Genetic variation in height growth and leaf colour of Eucalyptus deglupta Blume at ages up to 16 months in Costa Rica

Manual sobre mejoramiento genetico forestal con referencia especial a America Central