Drivers of trembling aspen (Populus tremuloides) mortality and productivity decline in boreal forests of interior Alaska
Abstract
Increasing forest die-back has been documented worldwide as a result of climate change, particularly longer and more intense drought. Higher temperatures and drought are also associated with increasing insect outbreaks, which have been identified as a contributing factor to tree mortality and productivity decline. In response to warming and insect infestation, trembling aspen (Populus tremuloides) in the boreal forest has experienced recent productivity declines and mortality. Here we study the influence of insects and moisture deficits on aspen growth and mortality in interior Alaska using tree radial growth measurements. We also assessed if tree mortality events and trends are reflected in remote sensing indices of vegetation productivity (NDVI).
We sampled dead and live aspen from long term inventory sites in interior Alaska that are a part of the Cooperative Alaska Forest Inventory (CAFI) network and had recently documented mortality events. We assessed the radial growth response of both dead and live trees to insect outbreaks and a climate moisture index (CMI) from 1950 - 2013. We found that the majority of aspen died between 2000 and 2010, and lifetime productivity was significantly less in dead than live trees. Dead and live trees exhibited similar growth responses to climate and insects prior to the mid-1990s yet different responses afterwards. Specifically, we saw increased growth with higher annual CMI and low insect damage from 1950 to 1995 among both groups. From 1995 to 2013, a period during which severe and sustained damage by the aspen leaf miner (Phyllocnistis populiella) occurred, live trees exhibited the same growth response as they did prior to the outbreak, but trees that died were no longer influenced by moisture. We also found that summer NDVI showed a positive correlation with ring width, which supports the utility of NDVI for monitoring tree growth and insect outbreaks at large scales. Our results suggest that moisture limits aspen radial growth and that sustained insect herbivory can directly and indirectly (by de-coupling growth from climate) influence aspen mortality. These results indicate that the productivity of aspen in boreal forests may decline and mortality may increase as temperatures rise, moisture becomes more limiting, and insect outbreaks increase in frequency and severity.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.B31F2556B
- Keywords:
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- 0414 Biogeochemical cycles;
- processes;
- and modeling;
- BIOGEOSCIENCESDE: 0439 Ecosystems;
- structure and dynamics;
- BIOGEOSCIENCESDE: 0475 Permafrost;
- cryosphere;
- and high-latitude processes;
- BIOGEOSCIENCESDE: 1640 Remote sensing;
- GLOBAL CHANGE