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2. Tropical Monsoon Forest (medium height, deciduous or mainly deciduous forest of warm climates)

(not corresponding closely to an Olson et al. category; but approximately a sub-division of seasonal tropical forest).

References directly cited in these pages (does not at present include secondary citations)

The deciduous or monsoon tropical forests in the present world, in south Asia and central America for example (together with the evergreen tropical Eucalyptus forests in Australia), appear to be merely remnants of the much more extensive areas that would once have existed before large-scale human interference (Walter 1971). In fact, the deciduous forests that we do see at present are often the product of human disturbance of semi-evergreen or semi-deciduous forests (Walter 1971). Given the degraded state of many of these tropical deciduous forests, and the relatively small areas they now occupy, it is particularly difficult to reconstruct their 'natural' carbon storage. The values here are from sites chosen to represent forests that have not been heavily logged or grazed in the recent past.

Suggested summary values for the preanthropogenic state

Storage (tC/ha) Ecosystem component
10 tC/ha Dead standing trees, coarse woody litter, leaf litter and other debris
150 tC/ha Above and below-ground vegetation
100 tC/ha Soil organic carbon
260 tC/h Total carbon storage

Litter

Storage (tC/ha) Location Author(s)
3 tC/ha (1.) Dry forests (litter) Brown & Lugo (1992)
10 tC/ha (2.) Monsoon forests (coarse woody debris) Harmon (pers. comm.)

(1.) Defined as tropical lowland dry forests with 1000-1700mm annual pptn. Based on a global literature survey. A standard error of +/- 0.25 is given, but the number of samples is not indicated.

(2.) An ad hoc estimate of carbon in coarse woody debris.

Vegetation

The natural fire frequency in monsoon forests is generally thought to be very low (Mueller-Dombois 1978), and not a major factor in suppressing the natural steady-state biomass. For example Mueller-Dombois notes that in his observations on Sri Lankan monsoon forests, grass fires were frequent in cleared areas but these never entered the forest. Charred trunks or charcoal were almost never found in this forest type. Mueller-Dombois suggests that year-round litter decomposition and lack of undergrowth tends to prevent ground fires from spreading, and that this in turn prevents the more destructive crown fires. An exception may be the Australian Eucalyptus forest which accumulate dense, flammable litter and in which fire adaptations are frequent.

Storage (tC/ha) Location Author(s)
140 tC/ha (1.) Global seasonal tropical forest Olson et al. (1983)
171 tC/ha (2.) Indian monsoon forests Iversen et al. (1994)

(1.) 100 (low) - 140 (medium) -170 (high estimate). May include a great deal of what is categorized here as 'rainforest' (i.e. evergreen and semi-evergreen forest; category 1 in this inventory), and also disturbed regenerating forest due to the relatively intense human activity in monsoon forest regions.

(2.) For the 'natural' non-anthropogenic average mass of carbon in vegetation. Based on a large number of site inventories of eastern Indian monsoon forests. Iverson et al. have reached their conclusion of a relatively high natural biomass from those stands which have 'equilibrium' age structure, apparently indicating relatively light human disturbance. The above ground biomass figure of Iverson et al. is 300 t/ha, with an extra 20% added for roots is 360t/ha and x0.475 to convert to carbon is 171 tC/ha. The rainfall in this area is somewhat higher than in the Ganges plain of northern India, but lower than much of north-eastern India and Bangladesh, so hopefully the biomass value may represent a reasonable average of the monsoon forest region overall.

Soil

Storage (tC/ha) Location Author(s)
110 tC/ha (1.) Seasonal forests Post et al. (1985)
110 tC/ha (1.) Seasonal forests Zinke et al. (1985)
71 tC/ha (2.) Dry forests (1000-1700mm pptn) Brown & Lugo (1992)

(1.) Based on extensive literature survey.

(2.) These are from lowland tropical dry forests with annual precipitation between about 1000 and 1700mm, putting them in the 'monsoon forest' range. The average figure is based on 7 samples in literature survey. One standard error of +/- 12.