Factors determining distributions of tree species and plant functional types

Tropical forests represent an important pool in the global carbon cycle. Their biomass stocks and carbon fluxes are variable in space and time, which is a challenge for accurate measurements. Forest models are therefore used to investigate these complex forest dynamics. The challenge of considering the high species diversity of tropical forests is often addressed by grouping species into plant functional types (PFTs). We investigated how reduced numbers of PFTs affect the prediction of productivity (GPP, NPP) and other carbon fluxes derived from forest simulations. We therefore parameterized a forest gap model for a specific study site with just one PFT (comparable to global vegetation models) on the one hand, and two versions with a higher amount of PFTs, on the other hand. For an old-growth forest, aboveground biomass and basal area can be reproduced very well with all parameterizations. However, the absence of pioneer tree species in the parameterizations with just one PFT leads to a reduction in estimated gross primary production by 60% and an increase of estimated net ecosystem exchange by 50%. These findings may have consequences for productivity estimates of forests at regional and continental scales. Models with a reduced number of PFTs are limited in simulating forest succession, in particular regarding the forest growth after disturbances or transient dynamics. We conclude that a higher amount of species groups increases the accuracy of forest succession simulations. We suggest using at a minimum three PFTs with at least one species group representing pioneer tree species.

Download Full-text

Diversity of leaf phenology in a tropical deciduous forest in India

Journal of Tropical Ecology ◽

10.1017/s0266467404002032 ◽

2005 ◽

Vol 21 (1) ◽

pp. 47-56 ◽

Cited By ~ 33

Author(s):

C. P. Kushwaha ◽

K. P. Singh

Keyword(s):

Tree Species ◽

Deciduous Forest ◽

Plant Functional Types ◽

Deciduous Tree ◽

Tropical Deciduous Forest ◽

Leaf Fall ◽

Evergreen Species ◽

Functional Types ◽

Leaf Flush ◽

Strategy Index

Patterns of leaf phenological diversity were documented in nine key tree species of a tropical deciduous forest in the Vindhyan region of India. Monthly leaf counts on 160 tagged twigs on ten individuals of each species were made through two annual cycles. Tree species exhibited a gradient of deciduousness (∼leafless duration), ranging from semi-evergreen species (entire population never becoming leafless) to 7-mo-deciduous species. The semi-evergreen species initiated leaf flush (bud break of vegetative bud) earlier around the spring equinox. In all deciduous tree species synchronous leaf-flush initiation, with low inter-annual variability, occurred during the hot dry summer (May–June, day temperature >40 °C), prior to the onset of the rainy season. Based on the quantification of leafless period, leaf-flush duration, and leaf strategy index (leaf-flush rate/leaf-fall rate, proposed in this study) in different species, four plant functional types were recognized: (a) semi-evergreen, spring flushing, showing leaf exchange, with mean leafless period 8 d, leaf-flush duration 6–7 mo and leaf strategy index <0.5 (Shorea robusta); (b) <2-mo-deciduous, summer flushing, leafless period 3–8 wk, leaf-flush duration 5–6 mo, and leaf strategy index >0.5−<0.7 (Anogeissus latifolia, Diospyros melanoxylon and Hardwickia binata); (c) 2–4-mo-deciduous, summer flushing, leafless period 2–3 mo, leaf-flush duration 4–5 mo, and leaf strategy index >0.8−<1.0 (Acacia catechu, Lagerstroemia parviflora and Terminalia tomentosa); and (d) >4-mo-deciduous, summer flushing, leafless period >4–7 mo, leaf-flush duration 3–4 mo, and leaf strategy index 1.0 (Boswellia serrata and Lannea coromandelica). Conspecific trees showed asynchrony with respect to leaf-flush completion, initiation and completion of leaf-fall, and extent of leafless period. Leaf strategy index (indicating rate of resource use and conservation) was strongly related with the leafless period in different species (r=0.82) and can serve as a useful index in leaf phenological studies and classification of plant functional types.

Download Full-text