 |
| Titel |
Drought-related tree mortality in drought-resistant semi-arid Aleppo pine forest |
| VerfasserIn |
Yakir Preisler, José M. Grünzweig, Eyal Rotenberg, Shani Rohatyn, Dan Yakir |
| Konferenz |
EGU General Assembly 2014
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250091485
|
| Publikation (Nr.) |
 EGU/EGU2014-5781.pdf |
|
|
|
|
|
| Zusammenfassung |
| The frequency and intensity of drought events are expected to increase as part of global
climate change. In fact, drought related tree mortality had become a widespread phenomenon
in forests around the globe in the past decades. This study was conducted at the Yatir
FLUXNET site, located in a 45 years old Pinus halepensis dominated forest that successfully
sustained low mean annual precipitation (276mm) and extended seasonal droughts (up
to 340 days between rain events). However, five recent non-consecutive drought
years led to enhanced tree mortality in 2010 (5-10% of the forest population, which
was not observed hitherto). The Tree mortality was characterized by patchiness,
showing forest zones with either >80% mortality or no mortality at all. Areas of
healthy trees were associated with deeper root distribution and increased stoniness
(soil pockets & cracks). To help identify possible causes of the increased mortality
and its patterns, four tree stress levels were identified based on visual appearance,
and studied in more detail. This included examining from spring 2011 to summer
2013 the local trees density, root distribution, annual growth rings, needle length
and chlorophyll content, rates of leaf gas exchange, and branch predawn water
potential. Tree phenotypic stress level correlated with the leaf predawn water potential
(-1.8 and -3.0 in healthy and stressed trees, respectively), which likely reflected
tree-scale water availability. These below ground characteristics were also associated, in
turn, with higher rate of assimilation (3.5 and 0.8 μmol CO2 m-2s1 in healthy
and stress trees, respectively), longer needles (8.2cm and 3.4 cm in healthy and
stressed trees, respectively). Annual ring widths showed differences between stress
classes, with stressed trees showing 30% narrower rings on average than unstressed
trees. Notably, decline in annual ring widths could be identified in currently dead or
severely stressed trees 15-20 years prior to mortality or tree degradation. These results
indicate, together with earlier results that showed a virtually close hydrological cycle
(ET~P) for this forest, that mortality was dominated by conditions at the level of
the single-tree or small group of trees. The dependency on belowground water
availability of individual trees emphasizes the difficulties in drawing process-based
conclusions from the mean response at the forest stand level and, alternatively, the need to
investigate drought stress and survival processes at the patch scale. The capabilities
of early identification, and of grading the stress level with simple tools, such as
tree-rings and pre-dawn water potential, can facilitate partitioning forest stands into
zones more relevant to the study and management of drought related mortality.
Ultimately, an integrated approach considering both the stand and patch scales
and which utilizes methodologies such as used in this study will be essential to
reliably predict ecosystem response to changes in precipitation regimes and climate. |
|
|
|
|
|
|