Summary1. Matrix models are popular tools for plant demographic studies, but their application to long-lived, slow-growing species is hampered by the fact that (i) model output is highly sensitive to category width and (ii) growth variation between individuals can only be partially accounted for. Integral Projection Models (IPMs) -an extension of matrix models -offer a solution to these problems. 2. Here, we introduce a new method to parameterize IPMs for trees -the 'integration method' -which allows constructing IPMs for long-lived, slow-growing species. This approach is more suitable than the 'midpoint rule', which is customarily used. 3. We built IPMs for six tree species from Vietnamese (sub)tropical forests. For four of these species, population growth rate (k) was highly sensitive to the number of categories in the transition matrix. Population growth stabilized for IPMs with 100-1000 categories, corresponding to categories of 0.1-1 cm in trunk diameter. This preferred width is much narrower than the 10-cm-wide categories customarily used in tree models. 4. The distribution of elasticity values over transition types (stasis, progression to next and further categories) is also highly sensitive to matrix dimension in IPMs. In addition, elasticity distribution is influenced by including or excluding growth variation. 5. Age estimates obtained from IPMs were also highly sensitive to matrix dimension: an IPM with 1000 size categories yielded 2-4 times higher age estimates for large trees than one with 10 size categories. Observed ages obtained from tree ring analyses for four of the study species allowed validating these estimates. IPMs with 10 categories strongly underestimated age, while those with 1000 categories yielded slight age overestimates. Underestimating age in small matrices is caused by the occurrence of unrealistically fast pathways through the life cycle and is probably widespread among tree models with broad categories. Overestimating ages in IPMs with narrow categories may be due to temporally autocorrelated growth or errors in fitting growth curves. 6. Synthesis. IPMs are highly suitable tools to analyse tree demography. We recommend that tree IPMs (and classical matrix models) apply narrow diameter categories (0.1-1 cm width) to obtain reliable model output.

Given that changes in population size are slow, information on future prospects of long‐lived tree species is necessarily obtained from demographic models. We studied six threatened tree species in four Vietnamese protected areas: the broad‐leaved Annamocarya sinensis, Manglietia fordiana and Parashorea chinensis, and the coniferous Calocedrus macrolepis, Dacrydium elatum and Pinus kwangtungensis. With data from a 2‐year field study on recruitment, growth and survival, we constructed matrix models for each species. All species showed continuous regeneration, as indicated by annual seedling recruitment and inverse J‐shaped population structures. To evaluate the future prospects of our study species, we calculated three parameters: (1) asymptotic growth rates (λ) from matrix models indicated significant population declines of 2–3%/year for two species; (2) population trajectories for 50–100 years showed slight population declines (0–3%/year) for five species; and (3) the reproductive period required for an adult tree to replace itself was excessive for three of the six species, suggesting that these species presently have insufficient recruitment. Overall agreement of the three parameters was low, showing that reliance on just one parameter is risky. Combining the three parameters we concluded that prospects are good for Dacrydium and Parashorea, worrisome for Annamocarya, Manglietia and Pinus, and intermediate for Calocedrus. We argue that conservation should involve strict protection of (pre‐)adult trees, as their survival is crucial for population maintenance in all species (high elasticity). For species with poor demographic prospects, active intervention is required to improve seedling and tree growth, enrich populations with seedlings from controlled germination, and restore habitat. Finally, our study suggests that these conservation measures apply to long‐lived trees in general, given that their demography is highly similar. Such measures should be taken before populations decline below critical levels, as long‐lived species will respond slowly to management.

Conservation of threatened tree species requires basic information on growth rates and ages. This information is lacking for many species, but can be obtained relatively easily from tree ring analysis. We studied four threatened Vietnamese species: three conifers from highelevation forests (Calocedrus macrolepis, Dacrydium elatum and Pinus kwangtungensis) and one broad-leaved species from lowland forest (Annamocarya sinensis). We collected increment cores from remnant populations in protected areas and measured ring width. We built chronologies and found significant correlations with rainfall (all species) and temperature (two species), indicating that rings were formed annually. Diameter-age trajectories showed that species reached reproductive size at 60-80 years. Maximum observed ages were 128-229 years. Some species showed large variation in long-term growth rates among individuals, which was partially explained by strong persistence of growth differences. We also assessed whether growth rates changed over time. For certain size categories in some species, we found higher recent growth rates of juvenile trees compared to those in the distant past. This shift requires a cautious interpretation, but is consistent with a CO 2 fertilization effect. For other size categories, we found contrasting results: extant large trees had higher growth rates as small juveniles compared to extant small trees. Such correlations, which we found for all species, suggest a 'juvenile selection effect': the preferential survival of fast-growing juveniles to the canopy. Information on ages, historical growth rates and juvenile selection effect is relevant for the planning of conservation actions.