Browsing by Subject "Nebelwald"

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Radial tree growth dynamics and xylem anatomy along an elevational gradient in the El Sira Mountains, Peru
(2019) Niessner, Armin; Küppers, Manfred
The explicit purpose of this study was to (1) characterize climate and vegetation along the western slope of the Cerros del Sira (Peru), (2) evaluate radial tree growth along this slope in response to seasonal rainfall anomalies, (3) reveal how the meteorological environment controls tree radial stem growth, and (4) to investigate how xylem anatomy relates to dynamics of tree growth. From May 2011 until September 2015, radial stem growth of 67 trees was monitored using point-dendrometers, and meteorological parameters were measured within five sites along an elevational gradient. Additionally, tree dimensions (stem diameter, stem height) and xylem anatomical traits (mean vessel diameter, vessel frequency, cumulative vessel area and potential hydraulic conductivity) were determined. The transect extends from lowland terra firme forests (ca. 250 m asl) over submontane forests, late and mid successional montane cloud forests up to exposed elfin forests (ca. 2200 m asl). Continuous rainfall records for remote tropical areas are extremely rare and measurements along this transect are also incomplete. Monthly rainfall estimates by the TRMM PR satellite ("product 3B42") were highly correlated with rain gauge observations, although they underestimate rainfall at high elevations. Different intra-annual tree growth patterns could be identified within each elevational forest type, showing species/individuals with seasonally independent continuous or alternating growth patterns and strictly seasonal growth. Stem growth at each site was typically higher during rainy seasons, except for in the elfin forest. The rainy season from October 2013 to March 2014 was extraordinarily dry, with only 73 % of long-term mean precipitation received, which resulted in reduced tree radial growth rates, again with the exception of the elfin forest. Different analytical approaches revealed that precipitation is the main growth-controlling factor at lower elevations, especially during rainy seasons. Growth within montane and cloud forests positively correlates to solar radiation. Tree growth within the elfin forest is only weakly correlated to meteorological parameters, but dry conditions during dry seasons promote growth. It was hypothesized that (1) individuals/species with large vessel diameters and low vessel frequencies have higher radial growth rates, but are more vulnerable to relatively dry periods. Therefore, (2) they are more likely to grow seasonally and predominantly during rainy seasons, (3) their growth during the exceptionally dry rainy season 2013/14 was more constrained, and (4) their growth is generally closer correlated to meteorological parameters. Larger trees tend to have larger vessel diameters, which positively relates to radial growth rates, and they also tend to grow more seasonal. As hypothesized, trees having large vessel diameters are more sensitive to droughts, as indicated by stronger positive correlations with rainfall and negative with solar radiation. However, in mountainous forests, relations between xylem anatomical traits and tree growth dynamics seem to be more complex. In late-successional cloud forests, growth of trees with large vessel diameter is positively, while of trees with small vessel diameter negatively related to solar radiation. Sensitivity to the dry rainy season 2013/14, expressed as relative reduction in growth compared to "normal" rainy seasons, could not be explained by xylem anatomical traits, contradicting the preceded hypothesis. Tropical lowland rainforest species, especially individuals with large vessels, will likely suffer from increasing drought frequencies and intensities. How montane forest ecosystems will react to a (globally) changing climate is rather uncertain, especially in exposed elfin forests. Results of this study suggest that species of late-successional tropical montane forests may profit from higher temperatures. While montane tropical rain forests may also suffer from prolonged droughts, exposed ridges covered by elfin forests still receive plenty of precipitation and may benefit from receiving more solar radiation for photosynthesis and, thus, grow faster.
Vergleichende Betrachtung von Mikroklima, Struktur und aus dem Xylemsaftfluss von Bäumen hochskalierter Transpiration eines tropisch-montanen Regenwaldes und eines Wolkenwaldes in Südost-Ecuador
(2010) Ohlemacher, Christian; Küppers, Manfred
In a tropical montane rain forest 1990 m a.s.l. and a cloud forest 2240 m a.s.l. in the Andes of Southeast Ecuador, tree stand structure (tree height, tree basal area, tree sapwood area, tree crown ground projection area and leaf area index (LAI)) was registered and the sap flow rate of trees, the microclimate (photosynthetically active radiation, temperature, air moisture) inside and above the canopy, and short term stem radius changes were measured. The period of measurement was one year, and synchronous measurements exist from 7 months. To investigate, whether the stand conductance for water differs between the two sites, their stand structure, xylem sap flow and microclimate were compared. Annual stand transpiration was calculated by means of upscaling the xylem sap flow, under inclusion of the site specific microclimate, with the basal area as scaling parameter. Mean radial stem growth was derived from stem radius changes. Radial stem growth is higher in the montane rain forest than in the cloud forest by a factor 3-5. No clear hints were found for different conductivity of trees between the investigated stands. The lower annual stand transpiration of the higher sited cloud forest (238 mm/a^-1) than that of the lower sited montane rain forest (438 mm/a^-1) is caused by a lower stand and foliage density (LAI = 1,6 in the cloud forest vs. LAI = 3,7 in the montane rain forest) and the higher air moisture at the higher sited stand. The crown area-related sap flow rate of single trees is approximately equal at both stands.