Environmental changes in biodiversity hotspot ecosystems of
South Ecuador: RESPonse and feedback effECTs (FOR2730)

Abstract:

Few studies have analysed the effect of silvicultural treatments on tree growth in tropical montane forests (TMF). These forests have strong topographic gradients, which influence growth rates and can potentially interact with silvicultural treatments. The present study investigated the relative effects of silvicultural treatments and topography on growth rates at the tree level in a TMF. For this, we combined two distinct data sources: (1) field data from a silvicultural experiment in the Andes of southern Ecuador where liberation thinnings, i.e. the removal of the strongest crown competitors, were applied to potential crop trees (PCT) in 2004; and (2) topographic variables obtained from a high-resolution digital terrain model created from an airborne LIDAR survey. We fitted all data in a single linear mixed-effect model. Based on monitoring data from 174 released and 200 reference PCTs of 8 timber species, we calculated periodic annual increment (PAI) in DBH 6 years after the silvicultural treatment as our outcome variable. As topographic predictors, we used elevation and a topographic position index. To control for the by-species growth variability we included random intercepts for species and random slopes for the effect of treatment on species in our model. PAI was significantly influenced by the topographic predictors. Over the elevational gradient, growth rates declined on average by 0.73 mm a−1 per 100 m increase in elevation. For the topographic position, PCTs in valleys had an average PAI of 2.02 mm a−1 compared to 1.04 mm a−1 on ridges. The effect of the silvicultural treatment across all species was only marginally significant, but its effect size was nevertheless within the range, but at the lower end of values reported for other tropical forest ecosystems (reference trees: 1.35 mm a−1; released trees: 1.60 mm a−1). Between species, baseline growth rates as well as the treatment effect varied considerably. Best linear unbiased predictions of species effects suggested that 5 species responded positively to the silvicultural treatment, whereas 3 species showed no treatment effect. Overall, tree growth varied substantially as indicated by the large residual variance that remained unaccounted for in the model. Our findings indicate that positive effects of silvicultural treatments in TMF are likely to exist, but that they are possibly obfuscated by strong topographical gradients and large between-tree growth variability. Overall, our results suggest that “broad-brush” management prescriptions are not suited for sustainable forest management of TMF. Instead, granular and spatially explicit prescriptions that take the strong impact of topography on diameter growth as well as species-specific responses to silvicultural treatments into account should be favoured.

Abstract:

Uno de los aspectos importantes a considerarse en la producción eficiente de plántulas con fines de restauración es la calidad de semillas y su variabilidad. El objetivo de este estudio fue evaluar los parámetros de semillas de acuerdo con las reglas del “International Seed Testing Association” entre diferentes árboles madre o individuos de siete especies nativas (Cedrela montana, Morella pubescens, Inga acreana, Tabebuia chrysantha, Ocotea heterochroma, Oreocallis grandiflora y Myrcianthes rhopaloides) en dos bosques de montaña del sur del Ecuador. Estas especies fueron seleccionadas por la importancia ecológica, socioeconómica, y su gran potencial para la restauración. De un total de 35 árboles madre de todas las especies, se colectaron las semillas en sus respectivos periodos de fructificación, y en el laboratorio fueron analizados los siguientes parámetros: pureza, peso, contenido de humedad y germinación; adicionalmente se determinó el coeficiente de velocidad de germinación. Los resultados mostraron una similitud intraespecífica en cada especie para la mayoría de los parámetros; no obstante, el peso presentó alta variabilidad intraespecífica para todas las especies. El parámetro germinación obtuvo diferencias entre individuos para C. montana, T. chrysantha, O. heterochroma y M. rhopaloides. En cuanto a la velocidad de germinación, individuos de especies como O. grandiflora e I. acreana mostraron un alto coeficiente en contraste a los individuos de O. heterochroma y M. pubescens. La información generada en este estudio podría ser el primer paso en la formulación de pautas para la producción masiva de plántulas de especies nativas con fines de restauración.

Abstract:

Tropical forests and the trees as their principal components have been investigated in detail. However, due to its complexity, their interactions, adaptations and response to climate variations require much more research. In this study, dendrochronological techniques were applied to evaluate the potential of tree-rings from tropical tree species as climate records. Two ecosystems with very distinct climate scenarios were selected from a dry and humid forest in southern Ecuador. A comparative analysis between these two forest types was performed by applying three dendrochronological methods. First, Tree Ring Width (TRW) measurements from tree species with distinct ring boundaries were dated to develop ring-width chronologies. Second, stable carbon isotopes (?13C) were measured from whole-wood and alpha-cellulose of dated annual tree-rings. Finally, concentrations of more than 23 chemical elements were determined from individual dated tree-rings after dissolving the wooden material in HNO3. The results showed the high potential of tropical tree species as climate archives, Bursera graveolens and Maclura tinctoria for the dry forest and Cedrela montana for the humid forest. Radial growth variations in tree species from the dry forest revealed a strong and reliable precipitation signal. Then, for these tropical regions, the first ring-width based wet-season precipitation reconstruction over the past century was developed, and spatial correlations unraveled a strong connection to the climatic conditions of the central Pacific precipitation and temperature variability. Interseries correlations of the TRW from the trees of the humid forest revealed a weak common signal. Stable carbon isotopes evidenced higher climate sensitivity than TRW measurements in the humid forest. However, to infer a reliable climate reconstruction from stable carbon isotopes, more ?13C time series were needed. ?13C values from whole-wood and alpha-cellulose reflected local and regional signals of precipitation and humidity. Meanwhile, nutrient concentration in the wood was higher in the dry forest, but common patterns and trends of nutrients were more distinct in the humid forest. For both study sites, two groups of nutrients with opposite radial distribution were identified (Group 1: Ca, Sr, Ba, Ga; and Group 2: K, P, Rb). In conclusion, TRW of tree species from the dry forest have a high paleoclimate potential, especially to reconstruct precipitation amounts in arid zones of southern Ecuador. Stable carbon isotopes constitute a promising tool to perform climatic reconstructions in both ecosystems. Finally, the valuable historical information of nutrient concentration evidenced in tree-rings opens promising ways to study tree growth dynamics especially in the humid forest.

Abstract:

Zwar lieferten die Analysen in dieser Arbeit keine eindeutigen Antworten auf die Fra-gestellung, dennoch bietet sie Ansatzpunkte für weitere Untersuchungen zu diesem Thema. Zum einen wäre die genaue Erforschung des Reliefs vor Ort sinnvoll. Dabei könnte einerseits der Verlauf der Fließgewässer überprüft werden, andererseits könn-ten die Einzugsgebiete auf Hangrutschungen untersucht werden, welche die Boden-verhältnisse stören können. Des Weiteren kann umliegende Vegetation, die die Bäume möglicherweise beeinflussen könnte, erforscht werden. Die aufgestellte Hypothese wird in dieser Arbeit vollständig abgelehnt, da keinerlei räumliche Muster in der topographischen Lage der Bäume erkennbar sind. Grund da-für sind vor allem eingeschränkten Möglichkeiten in ArcGIS die Topographie des Ge-bietes detailliert untersuchen zu können. Zum anderen scheint Lage der Bäume im Relief keine ausschlaggebende Ursache für deren Isotopenverhältnisse darzustellen. Sehr wahrscheinlich sind die lokalen Bodenverhältnisse entscheidend für das Isoto-pensignal der Bäume. Da die örtliche Bodenbeschaffenheit zum Teil durch Rutschkör-per gestört sein kann, ist eine Untersuchung dieser maßgeblich für zukünftige For-schungen.

Abstract:

Cedrela montana is a deciduous broad-leaved tree species growing in the humid mountain rainforests of southern Ecuador. High-resolution dendrometer data indicate a regular seasonal growth rhythm with cambial activity during January to April. Amplitudes of daily radial stem diameter variations are correlated with the amount of the maximum daily vapour pressure deficit. During humid periods, daily stem diameter variations are considerably smaller than during drier periods. This indicates that cambial activity is limited by available moisture even in such a very humid mountain climate. Wood anatomical studies on microcores show the formation of a marginal parenchyma band at the beginning of the growth period. This parenchyma band can be used to delineate annual growth rings. We were able to establish the first ring-width chronology from Cedrela montana which covers the time until 1840. However, the chronology is presently statistically robust back to 1910 only. Correlation functions calculated with NCEP/NCAR data indicate a significantly positive relationship of tree growth with temperatures during the growth period during January to April. However, only 8% of the growth variance is explained by this climatic factor. In the future, this relationship may be useful to reconstruct past temperature conditions of the study area.

Abstract:

Abstract: For the first time in tropical mountain rain forest, arbuscular mycorrhizal fungal richness and community composition was investigated from planted seedlings of Cedrela montana, Heliocarpus americanus, Juglans neotropica and Tabebuia chrysantha in reforestation plots on degraded pastures. A segment of fungal 18S rDNA was sequenced from the mycorrhizas. Sequences were compared with those obtained from mycorrhizas of adult trees of 30 species in the neighboring, pristine tropical mountain rain forest. In total, 193 glomeromycotan sequences were analyzed, 130 of them previously unpublished. Members of Glomeraceae, Acaulosporaceae, Gigasporaceae and Archaeosporales were found in both habitats, with Glomus Group A sequences being by far the most diverse and abundant. Glomus Group A sequence type richness did not appear to differ between the habitats; a large number was observed in both. Glomus Group A sequence type composition, however, was found distinctly different. Seedlings were rarely colonized by fungi of the pristine forest but trapped a number of fungi known from other areas, which were rarely found in the pristine forest.