4.9.1 A graphic analysis of plant functional types
The concentrations of major leaf nutrients, their internal ratios and main morphological characteristics of trees in the four land use types and of certain families and species were illustrated as radial values in radial diagrams. The radial axis for each parameter corresponds to the span of observed values for that parameter in a sample. The centre of the circle
represents the lowest value of each parameter in the topical sample (entering 0% of the
Urticaceae
Figure 4.36 A graphic overview of the relative values of some important leaf traits in the five most frequent families of the random sample. Average values of the individuals included in the random sample for each family were used. The radial axis for each parameter corresponds to the span of observed values in the topical sample. Thus, the centre of the circle represents the lowest value of that parameter occurring in the sample (entering 0% of the range). The outer edge of the circle represents the highest value achieved in the sample, thus 100% of the range. The values for δ13C are denoted as absolute numbers, therefore 100% corresponds to the most negative value. (SLA – Specific leaf area, LS – Leaf size, LW – Length-width ratio)
4 RESULTS
range). The outer edge of the circle represents the highest values of the parameters found in the sample, thus 100% of the range. This form of illustration turned out to be useful for comparative overviews at a given level. It can immediately be recognized that the graphic pattern of different species are dissimilar also within a given land use type. On the other hand, other groups of similar species can be recognised across the land use types.
4.9.1.1 Groups of species with similar trait profiles
Vast differences between species can be observed in Figure 4.37. The profiles of the different species illustrated do not universally coincide within the land use types, and also not necessarily within a family. Certain groups with common patterns can however be discerned.
The three Euphorbiaceae species illustrated all showed different patterns that neither looked like the family means pattern, nor like the respective forest type, in which the species occurred. For example, Homalanthus populneus formed a pattern dissimilar to any other species illustrated. Its high P and SLA were common with the general secondary forest pattern, but the low mineral nutrient concentrations rather reminded on late stage, natural forest species. The overall strikingly low concentration of nutrients in the huge-leaved Macaranga hispida is interesting, and was not seen in any of the other illustrated species.
Trema orientalis, Grewia glabra and Gliricidia sepium showed a similar pattern,
characterized by small leaf sizes, high δ13C, low C/N ratio, high K concentration and a rather high P-concentration and SLA. This pattern could also be recognized as the mean pattern for the agroforestry system. Pipturus argentus was also similar to this group, only diverging through a lower K concentration and higher Ca concentration than the others.
Another group of similar species was formed by the three natural forest species
Lithocarpus sp., Semecarpus forstenii and Litsea sp.. The common traits in this group were low concentrations of both N and P, but high N/P ratio, very low concentrations of all three nutrients and, concerning morphology, very low SLA. These were all late stage natural forest species that mainly diverged from the natural forest means profile through their higher C/N ratios and their strikingly low Mg and K concentrations.
Aglaia argentea and Bischofia javanica both had rather high Mg and K concentrations, which separated them from the other natural forest species illustrated, but cohered with the mean pattern for natural forest. These two still did not form a homogenous group, because of the remarkable differences in C/N and length-with ratio.
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NF
Figure 4.37 A graphic overview of the relative values of some important leaf traits in the four land use types studied and in 12 abundant species. The radial axis for each parameter corresponds to the span of observed values in the topical sample. Thus, the centre of the circle represents the lowest value of that parameter occurring in the sample (entering 0% of the range). The outer edge of the circle represents the highest value achieved in the sample, thus 100% of the range. The values for δ13C are denoted as absolute numbers, therefore 100% corresponds to the most negative value. (SLA – Specific leaf area, LS – Leaf size, LW – Length-width ratio)
4 RESULTS
4.9.2 Division of 107 tree species into functional groups
The cluster analysis based on the five main predictors for leaf physiology resulted in a model where the 107 species in the study were divided into ten functional groups (clusters).
The species belonging to each cluster are listed in Appendix 9. The cluster centroid values (or seeds) of each of the underlying leaf traits, the frequency of each functional group, as well as information on neighbouring groups are presented in Table 4.17.
Table 4.17 Ten functional groups identified through a disjoining cluster analysis. The model, comprising 107 tree species of four different land use types, has an expected R2 value of 0.97. C – cluster (group) number, F – number of species in each cluster, SLA - specific leaf area [cm2 g-1], Size - leaf size [cm2], δ13C – carbon isotope ratio [‰], N – foliar nitrogen concentration [g kg-1], P – foliar phosphorus concentration [g kg-1], Max dist – maximum distance of an observation (species) from the cluster centroid, Next C – nearest other cluster, Dist – distance from centroid to nearest other cluster centroid, Typical species – examples of characteristic species of each cluster.
C F SLA Size δ13C N P Max dist Next
C Dist Typical species
1 4 236 38 -29.7 41 2.6 51 7 85 Erythrina sp., Homalanthus populneus 2 23 150 141 -31.1 22 1.6 41 6 50 Solanum sp., Trema orientalis, Cananga
odorata
3 3 177 322 -27.8 40 4.1 40 5 64 Mallotus mollissimus, Tabernamontana macrocarpa, Pipturus argentus 4 1 161 1251 -26.9 27 2.9 0 10 646 Macaranga tanarius
5 5 77 307 -29.7 17 1.6 48 3 64 Dysoxylum sp.1, Chisocheton sp.1 6 22 53 81 -31.4 29 2.2 38 7 42 Aralia sp., Siphonodon celastrineus 7 28 135 25 -31.9 19 1.3 60 6 42 Ficus spp., Terminalia sp., Meliosma
sumatrana
8 2 129 412 -26.3 45 6.5 17 3 101 Dendrocnide sp.2, Elmerillia tsiampacca 9 15 41 195 -29.9 22 2.3 54 2 80 Semecarpus forstenii, Cryptocarya
crassinervia, Lithocarpus sp., Theobroma cacao
10 4 109 647 -28.6 18 2.5 39 8 211 Dendrocnide stimulan, Macarnaga hispida
The first group was characterized by small leaves with high SLA and high N. The species closest to the cluster centroid was Erythrina sp.. The second group was dominated by secondary forest species like Trema orientalis and Solanum sp., but did also contain the species Cananga odorata, which occurred in the natural forest. The groups 3 and 4 consisted of species more or less exclusively occurring in the secondary forest. They were the only groups comprising species from just one land use type. These groups, which comprised only a few species, were characterized by large leaf sizes, relatively high SLA and high δ13C
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values. Species with relatively large, coriaceous leaves (low SLA), with corresponding low δ13C that are poor in N and P formed the fifth group. The sixth group was similar, but with smaller leaves with intermediate N and P concentrations. Both these types were typical for medium sized natural forest trees. The groups 7 and 9 contained species from all four land use types. The eighth functional group applied to two species in this sample only, which had remarkably high P and high δ13C. The tenth type was characterised by large leaves with low N.
5 DISCUSSION