Effects of Climate and Atmospheric Deposition on Tree Growth in a Boreal Peatland

Background

Boreal peatlands are major carbon sinks and are important components of regional biodiversity.
Peatlands are often threatened by tree encroachment as a result of climate change and atmospheric deposition.
Understanding how this encroachment proceeds from initial tree establishment to fully mature forested bogs is crucial for the long term management of these systems.

Objectives

Determine the timing of release from the shrub stage to the erect tree stage, and how that timing was related to climate and atmospheric deposition.
Model growth patterns against climate and atmospheric deposition variables to potentially inform conservation efforts for boreal peatlands.

Species studied

Picea mariana - Black Spruce
Larix laricina - Eastern Larch

Study location

Shingle Shanty Preserve and Research Station

Methods

Cookies from small trees were collected.

Black Spruce (PIMA) Cookie

These were analyzed using standard dendrochronological techniques.
The annual growth rings were detrended and crossdated.
I then modeled growth patterns against climate and atmospheric deposition data variables to determine how these factors are associated with both release events and subsequent growth.

Tree Growth Models

Ring width chronologies of a) Black Spruce and b) Eastern Larch.

Black Spruce model results. The final linear model (R2 =0.46) included 8 predictor variables (3 temp., 4 deposition, and pH). Three of these are shown here with Ring Width Index plotted against the predictor, and each predictor variable plotted through time.

Figure 4. Larch model results. The final linear model (R2 =0.46) included 4 predictor variables (3 temp., and 1 deposition). Three of these are shown here with Ring Width Index plotted against the predictor, and each predictor variable plotted through time.

Conclusions

Bogs depend on atmospheric deposition in order to get nutrients. The recent decrease in these nutrients may explain the decrease in growth for both species.
Rising temperatures have a positive effect on Black Spruce growth but a negative effect on Larch growth.
Rising pH had a negative effect on Black Spruce growth.
Atmospheric deposition variables retained in the models were sodium, which had a negative effect on Black Spruce, and nitrate which had a positive effect on Larch.
So many countering factors make it difficult to observe direct trends. However, understanding the process of tree encroachment is crucial for the long term management of boreal peatlands.

Thank you Dr. Lesser and Stephen Langdon for advising me throughout this study and thank you all for listening!

Effects of Climate and Atmospheric Deposition on Tree Growth in a Boreal Peatland Anna Skolnick