A variety of responses to climate change have been reported for northern tree populations, primarily from tree-ring and satellite-based studies. Here we employ provenance data to examine growth and survival responses of northern populations (defined here as those occurring north of 52oN) of black spruce (Picea mariana) and Jack pine (Pinus banksiana) to southward seed transfers – a space for time substitution that affords insights into potential climate change responses by these important northern tree species. Based on previous work, we anticipated relatively flat response curves that peak at much warmer temperatures than those found at seed source origin. These expectations were generally met for growth-related responses, with peak growth associated with seed transfers to environments 2.2^oC and 3.6^oC warmer than seed source origin for black spruce and jack pine, respectively. These findings imply that northern tree populations harbor a significant amount of resilience to climate warming. However, survival responses told a different story, with both species exhibiting reduced survival rates when moved to warmer and drier environments.  Together with the growth-based results, these findings suggest that the warmer and drier conditions expected across much of northern Canada under climate change may reduce survival, but surviving trees may grow at a faster rate up until a certain magnitude of climate warming has been reached. We note that all relationships had high levels of unexplained variation, underlining the many factors that may influence provenance study outcomes and the challenges in predicting tree responses to climate change. Despite certain limitations, we feel that the provenance data employed here provide valuable insights into potential climate change outcomes for northern tree populations.

Black spruce provenance data were obtained from measurements on a portion of the Canadian Forest Service’s (CFS) long-term black spruce provenance trial, which originally incorporated 202 seed sources across 34 test sites in Canada and the United States.  Measurements of height and diameter of all surviving trees at each test site were made in 2003, at 33 years of age from seed. These data were obtained through a collaborative research agreement with William H. Parker at Lakehead University, Thunder Bay, Ontario. In total, 192 seed sources at 18 test sites in Canada and one test site in Minnesota were included in the measurement.

Jack pine provenance data were obtained from measurements on a portion of the CFS 255 series rangewide provenance trial, which consisted of 99 seed sources planted in various combinations at test sites across eastern Canada, the United States, and Europe. During the summer of 2005, at 39 years of age from seed, all 16 remaining viable test sites in Canada and the United States were remeasured. We obtained these data through a collaborative research agreement with William H. Parker at Lakehead University, Thunder Bay, Ontario.

This dataset contains measurements of the average height and survival of black spruce and jack pine provenances (or seed sources) planted at a variety of test sites in eastern North America. Also included are estimates of climate at the test site and at provenance origin.  Following is a brief explanation of the variables found in the dataset:

Species - Name of the tree species associated with the data
Test_Name - Test site identifier
Test_Long - Longitude of the provenance (decimal degrees)
Test_Lat - Latitude of the provenance (decimal degrees)
Test_Elev - Elevation of the provenance (m)
Prov_Name - Provenance or seed source identifier
Prov_Long - Longitude of the provenance (decimal degrees)
Prov_Lat - Latitude of the provenance  (decimal degrees)
Prov_Elev - Elevation of the provenance (m)
Height - Average height of provenance at test site(m)
Survival - Average survival of provenance at test site (%)
AMEANT_T - Average annual mean temperature at test site for period spanning year of plantation establishment through year of height measurement(C)
ANNP_T - Average annual precipitation at test site for period spanning year of plantation establishment through year of height measurement(mm)
CMIANN_T - Average annual climate moisture index at test site for period spanningyear of plantation establishment through year of height measurement (cm)
GSLENGTH_T - Average growing season length at test site for period spanning year of plantation establishment through year of height measurement (days)
AMEANT_P - Mean annual temperature at provenance over the 1961-1990 period (C) 
ANNP_P- Average annualprecipitation at provenance location for 1961-1990 period (mm)
CMIANN_P- Average annual climate moisture index at provenance location for 1961-1990 period (cm)
GSLENGTH_P- Average growing season length at provenance location for 1961-1990 period (days)

Notes:
Details on the climate moisture index can be obtained from Hogg et al. (1997).
Details on all other  climate variables can be obtained from McKenney et al. (2011).
Details on the provenance remeasurement can be obtained from Thomson et al. (2009) and Thomson and Parker (2008).

Acknowledgements:
The data provided here was collected and compiled by Dr. William H. Parker and students at Lakehead University. He kindly shared the data with us and agreed to having it published online.

References:
Hogg, E. H. Temporal scaling of moisture and the forest-grassland boundary in western Canada. Agricultural and Forest Meteorology, 84, 115-122 (1997).
McKenney, D.W., et al. Customized spatial climate models for North America. Bulletin of the American Meteorological Society, 92, 1611-1622 (2011).
Thomson, A.M., Riddell, C.L., & Parker, W.H. Boreal forest provenance tests used to predict optimal growth and response to climate change: 2. Black spruce. Canadian Journal of Forest Research, 39, 143-153 (2009).
Thomson, A. M., & Parker, W. H. (2008). Boreal forest provenance tests used to predict optimal growth and response to climate change. 1. Jack pine. Canadian Journal of Forest Research, 38(1), 157-170.