A phylogenetic classification of the world’s tropical forests

Knowledge about the biogeographic affinities of the world’s tropical forests helps to better understand regional differences in forest structure, diversity, composition and dynamics. Such understanding will enable anticipation of region specific responses to global environmental change. Modern phylogenies, in combination with broad coverage of species inventory data, now allow for global biogeographic analyses that take species evolutionary distance into account. Here we present the first classification of the world’s tropical forests based on their phylogenetic similarity. We identify five principal floristic regions and their floristic relationships: (1) Indo-Pacific, (2) Subtropical, (3) African, (4) American, and (5) Dry forests. Our results do not support the traditional Neo- versus Palaeo-tropical forest division, but instead separate the combined American and African forests from their Indo-Pacific counterparts. We also find indications for the existence of a global dry forest region, with representatives in America, Africa, Madagascar and India. Additionally, a northern hemisphere Subtropical forest region was identified with representatives in Asia and America, providing support for a link between Asian and American northern hemisphere forests

An estimate of the number of tropical tree species

The high species richness of tropical forests has long been recognized, yet there remains substantial uncertainty regarding the actual number of tropical tree species. Using a pantropical tree inventory database from closed canopy forests, consisting of 657,630 trees belonging to 11,371 species, we use a fitted value of Fisher’s alpha and an approximate pantropical stem total to estimate the minimum number of tropical forest tree species to fall between ∼40,000 and ∼53,000, i.e. at the high end of previous estimates. Contrary to common assumption, the Indo-Pacific region was found to be as species-rich as the Neotropics, with both regions having a minimum of ∼19,000–25,000 tree species. Continental Africa is relatively depauperate with a minimum of ∼4,500–6,000 tree species. Very few species are shared among the African, American, and the Indo-Pacific regions. We provide a methodological framework for estimating species richness in trees that may help refine species richness estimates of tree-dependent taxa

Phylogenetic classification of the world's tropical forests

Knowledge about the biogeographic affinities of the world’s tropical forests helps to better understand regional differences in forest structure, diversity, composition, and dynamics. Such understanding will enable anticipation of region-specific responses to global environmental change. Modern phylogenies, in combination with broad coverage of species inventory data, now allow for global biogeographic analyses that take species evolutionary distance into account. Here we present a classification of the world’s tropical forests based on their phylogenetic similarity. We identify five principal floristic regions and their floristic relationships: (i) Indo-Pacific, (ii) Subtropical, (iii) African, (iv) American, and (v) Dry forests. Our results do not support the traditional neo- versus paleotropical forest division but instead separate the combined American and African forests from their Indo-Pacific counterparts. We also find indications for the existence of a global dry forest region, with representatives in America, Africa, Madagascar, and India. Additionally, a northern-hemisphere Subtropical forest region was identified with representatives in Asia and America, providing support for a link between Asian and American northern-hemisphere forests.</p

Stem anatomy and relative growth rate in seedlings of a wide range of woody plant species and types

Stem traits were analysed in laboratory-grown seedlings of 80 European woody and semiwoody species of known potential relative growth rate (RGR) and of similar ontogenetic phase. The objectives were, firstly, to assess the relation between stem structure and plant growth potential and, secondly, to explore how stem structure varies among species differing in life form and leaf habit. Hydraulic conductance was represented by the mean diameter of the widest xylem conduits (Dmax), and structural strength by the percentage of xylem tissue occupied by cell wall material (CWx) or stem tissue density (SD). Across all species RGR showed a weak positive correlation with Dmax and weak negative ones with CWx and SD, with slow-growers showing great dispersion of stem trait values. In the RGR-Dmax relationship this dispersion disappeared when trees were removed from the analysis. None of the relationships were significant among tree species alone. It was suggested that fast-growers require a xylem with wide conduits (high Dmax) to achieve high hydraulic conductivity, and 'cheaply' constructed stems (low CWx and SD) to maximise allocation to leaves. However, the possession of such traits does not guarantee fast growth, as other factors may constrain RGR elsewhere in the plant. Deciduous seedlings showed higher Dmax and lower CWx than evergreens. Higher Dmax could reflect an innate higher tolerance of conductivity loss by freeze-induced embolism in deciduous plants, which are not burdened by the maintenance of foliage in winter. In contrast, life forms were differentiated most clearly by SD. For instance, shrub seedlings had less dense stem tissues than tree seedlings, possibly because they need less investment in long-term strength and stature