Open Access
CO2 fertilization plays a minor role in long-term carbon accumulation patterns in temperate pine forests in the southwestern Pyrenees
(Elsevier, 2019) Lo, Yueh-Hsin; Blanco Vaca, Juan Antonio; González de Andrés, Ester; Imbert Rodríguez, Bosco; Castillo Martínez, Federico; Institute for Multidisciplinary Research in Applied Biology - IMAB
Isolating the long-term fertilization effect of CO 2 from other climate- and site-related effects on tree growth has been proven a challenging task. To isolate long-term effects of [CO2] on water use efficiency at ecosystem level, we used the FORECAST Climate forest model, calibrated for Scots pine (Pinus sylvestris L.) forests in the southwestern Pyrenees, growing at a Mediterranean montane site and at a continental subalpine site. Future climate scenarios (RCP 4.5 and RCP 8.5) were generated using a battery of six climate models to estimate daily values of temperature and precipitation in a 90-year series. A factorial experiment was designed to disentangle the importance on C pools of three growing limiting factors (nitrogen limitation, climate (temperature + precipitation) limitation and atmospheric CO 2 concentration). The relative importance of each factor was quantified by comparing the scenario with the limitation of each individual factor turned on with the non-limitation scenario. Positive CO 2 fertilization due to improvement in water use efficiency was detected by the model, but its quantitative impact improving tree growth was minimum: its average increase in ecosystem C pools ranged from 0.3 to 0.9%. At the site with cooler climate conditions (continental), the main limitation for tree growth was climate. Such limitation will be reduced under climate change and the ecosystem will store more carbon. At the site with milder climate conditions (Mediterranean), N availability was the main limiting factor albeit modulated by water availability. Such limitation could be reduced under climate change as N cycling could accelerate (higher litterfall production and decomposition rates) but also increase if droughts become more frequent and severe. In addition, the magnitude of the uncertainty related to climate model selection was much more important than CO 2 fertilization, indicating that atmospheric processes are more important than tree physiological processes when defining how much carbon could be gained (or lost) in forests under climate change. In conclusion, due to the small changes in forest C pools caused by variation of atmospheric CO 2 concentrations compared to changes caused by other growth limiting factors (nutrients, climate), reducing uncertainty related to climate projections seems a more efficient way to reduce uncertainty in tree growth projections than increasing forest model complexity.
Open Access
¿Están los bosques mixtos pirenaicos de pino silvestre y haya en el camino hacia la saturación por nitrógeno?
(Asociación Española de Ecología Terrestre, 2017) Blanco Vaca, Juan Antonio; San Emeterio Garciandía, Leticia; González de Andrés, Ester; Imbert Rodríguez, Bosco; Larrainzar Rodríguez, Estíbaliz; Peralta de Andrés, Francisco Javier; Lo, Yueh-Hsin; Castillo Martínez, Federico; Ciencias del Medio Natural; Natura Ingurunearen Zientziak
Las actividades humanas causan altos niveles de deposición atmosférica crónica de N que pueden estar trastornando el ciclo del N en los bosques de los Pirineos occidentales. Para probar esta hipótesis, se han investigado los efectos de la deposición de N atmosférico en el ciclo de N en dos bosques mixtos de pino silvestre y haya en Navarra. Un bosque está situado a 1350 m de altitud y tiene un clima continental, mientras que el otro está situado a 650 m y tiene un clima mediterráneo húmedo. Pruebas preliminares indicaron una fijación biológica de N 2 atmosférico indetectable, así como la casi nula presencia de plantas con simbiontes fijadores como en la actividad de fijadores libres. Por lo tanto se asumió que la principal entrada de N en estos bosques es la deposición atmosférica. Se estimó la dependencia de la productividad de estos ecosistemas de la deposición por medio del modelo ecológico FORECAST, calibrado para estos sitios. Se simularon seis escenarios con tasas de deposición en un rango de 5 a 30 kg ha -1 año -1 . Los resultados indicaron que la productividad de estos bosques es dependiente de la deposición de N, pero indicios de saturación por N (aumento de lixiviación y carencia de aumento de productividad) indican que pueden saturarse a partir de 20-25 kg N ha -1 año -1 , unos 5-10 kg N ha -1 año -1 por encima de los niveles observados actualmente.

Castillo Martínez, Federico

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