Seasonality of above-ground net primary productivity along an Andean altitudinal transect in Peru

Solar irradiance and precipitation are the most likely drivers of the seasonal variation of net primary productivity (NPP) in tropical forests. Since their roles remain poorly understood, we use litter traps, dendrometer bands and census data collected from one hectare permanent plots to quantify the seasonality of above-ground NPP components and weather parameters in 13 sites distributed along a 2800-m altitudinal gradient ranging from lowland Amazonia to the high Andes. We combine canopy leaf area index and litterfall data to describe the seasonality of canopy production. We hypothesize that solar irradiance is the primary driver of canopy phenology in wetter sites, whereas precipitation drives phenology in drier systems. The seasonal rhythm of canopy NPP components is in synchrony with solar irradiance at all altitudes. Leaf litterfall peaks in the late dry season, both in lowland (averaging 0.54 ± 0.08 Mg C ha y−1, n = 5) and montane forests (averaging 0.29 ± 0.04 Mg C ha y−1, n = 8). Peaks in above-ground coarse woody NPP appears to be triggered by the onset of rainfall in seasonal lowland rain forests (averaging 0.26 ± 0.04 Mg C ha y−1, n = 5, in November), but not in montane cloud forests.

Cost-benefit analysis of industrial and homemade dendrometer bands

Dendrometer bands are used to make repeated measurements of tree radial growth. Two types of dendrometers are used worldwide, the industrial and the homemade. Homemade dendrometers prevail in Brazilian forestry studies, but researchers have trouble constructing and installing them. An easier solution is to use industrial dendrometer bands, but they are not produced in Brazil and, therefore, are expensive and might not be appropriate for local environmental conditions. We analyzed trunk growth measurements each month (from February 2008 to January 2009) using both industrial (imported) and homemade (national components) dendrometer bands installed on 20 trees of Acacia tenuifolia in a seasonally dry forest on limestone outcrops in central Brazil. Cost-benefit comparative analysis of measurements and prices indicates that homemade dendrometer bands have all benefits, and none of the problems, of the imported industrial dendrometer bands, such as the following: (1) similar precision of measurements (correlation analysis: r > 0.930, P < 0.01; permutation t-test: P > 0.55), (2) much lower costs (10 to 15 times cheaper), (3) easily manipulated and installated in the field, and (4) absence of some damage to tree trunks that are caused by industrial dendrometers.

Liana loads and their association with Bertholletia excelsa fruit and nut production, diameter growth and crown attributes

We investigated the association between lianas and Bertholletia excelsa (Brazil nut), a long-lived, emergent tree of significant ecological and economic importance in Amazonia. Our objectives were: (1) to determine the relationship between crown liana load and liana number, basal area, and origin in relation to the B. excelsa host; and (2) to determine the relationship between liana load and B. excelsa fruit and nut production, diameter growth, and crown form, position and area. One hundred and forty trees (≥50 cm dbh) were selected with representatives of 10 diameter classes and four liana load categories. To quantify fruit and nut production, fruit counts and nut fresh weights per tree were measured in 2002 and 2003, and annual diameter growth was quantified using dendrometer bands. Trees with lianas produced significantly fewer fruits and had reduced nut fresh weights than liana-free trees. Trees with the most extensive liana loads (>75% crown coverage) were 10.2 times more likely to have crown forms categorized as less than half-crowns or few branches than trees with reduced liana loads. No statistically significant relationship was found between liana load and tree diameter growth. Results suggest that liana cutting might increase B. excelsa fecundity and commercial nut yields.

Growth assessment in tropical trees: large daily diameter fluctuations and their concealment by dendrometer bands

Tree stems contract and expand as stem water is depleted and replaced. Band-dendrometer studies suggest that such daily changes are small (<0.2 mm diameter), and they are ignored in most growth measurements. However, several studies using other approaches note larger changes (even >1 cm diameter), suggesting that significant biases are possible. An exploratory study examined the pattern and magnitude of daily stem changes and whether commercial band-dendrometers were able to reveal them. A method involving multiple precision measurements on eight trees in a Bornean hill dipterocarp forest revealed daily shrinkage and expansion of girth of around 1 mm. Fluctuations were greater in bright weather. Band-dendrometers detected these changes but revealed less than a tenth of their magnitude. An analytical model for dendrometer error is presented that predicts how measurement biases can be reduced. Tropical trees can fluctuate appreciably in stem diameter over the day. These reversible changes are of sufficient magnitude to merit concern in growth studies. Influential biases seem especially likely when measurement intervals are short and involve systematic differences in timing and weather. Further study is required to gauge the more general influence of these measurement problems.

Two-year tree growth patterns investigated from monthly girth records using dendrometer bands in a wet evergreen forest in India

With the aim of characterizing tree growth patterns, this paper re-examines the growth data of 100 selected trees belonging to 24 species that were recorded monthly in a 0.2-ha plot of a wet evergreen forest in the Western Ghats of India during the period 1980–82 using dendrometer bands. The mean growth profile, combining all of the selected trees, showed: (a) a significantly lower annual growth rate during the second year of survey which seemed to be negatively related to monsoon precipitation; (b) significant intra-annual growth variation clearly related to the regular alternation between a period of heavy rain and a quite long dry season of the monsoon climatic regime. Analysis of the variability of the individual smoothed growth profiles representing the 2-y trend of the growth data showed that: (a) the mean growth rate depended on a combination of an intrinsic endogenous variable (the structural class grouping species according to their maximum size), a tree size variable (tree diameter at breast height, dbh) and a neighbourhood variable (the number of taller neighbours in a 10-m radius); (b) the sudden change in growth rate from one year to the other was not predictable using these variables. The amplitude of the seasonal variations, investigated from the detrended growth profiles, appeared to be dependent on a combination of tree dbh and the number of taller neighbours in a 10-m radius. A co-inertia analysis of the smoothed and the detrended growth profiles indicated that the trees with fast growth also exhibited high seasonal variation. It is suggested that fast growing trees are those with favourable crown positions, which are consequently subject to high transpiration rates due to radiation and wind exposure.

Accuracy of tree growth measurements using dendrometer bands

Dendrometer bands are commonly used to make repeated measurements of tree circumference despite their tendency to underestimate first-year growth. Underestimates of growth are generally attributed to slack remaining in the bands after installation. To test for first-year measurement errors, 60 trees were fitted with a second dendrometer band 2 years after installation of the first band. The new bands consistently showed significantly less growth than the old bands (old-band measurements were assumed to represent true growth). Regression equations were developed to relate new-band estimates to true growth. There were no significant differences in regression intercepts for the three tree species tested, but significant differences in regression slopes were detected. Comparisons between canopy and subcanopy trees and between angiosperm species (Nyssaaquatica L. and Nyssasylvatica var. biflora (Walter) Sargent) and a gymnosperm (Taxodiumdistichumn (L.) Rich.) explained 95.7% of the variance in regression slopes for the individual species. It appears that in addition to band slack, part of the first-year error in dendrometer band data may result from species differences that are related to bark and stem characteristics.