Fgya 2009 02 technte effectsclimateonmortalityyoungplantedlodgepolepine by fRI Research

Foothills Growth and Yield Association Interim Technical Note February 2009

By: W.R. Dempster, R.P.F, PhD

Effects of Climate on Mortality of Young Planted Lodgepole Pine Introduction

Between the summer of 2000 and the spring of 2002, 9 member companies of the Foothills Growth and Yield Association (FGYA) installed and planted 102 one-hectare research plot clusters (“installations”) throughout the Eastern Slopes, in a large replicated experiment designed to monitor stand development of harvest-origin lodgepole pine in relation to site, initial spacing of planted stock, vegetation control (weeding) and density regulation (pre-commercial thinning). Results following the first 5 growing seasons were modeled, and reported in 2008.1 FGYA members make heavy investments in forest regeneration which are exposed to silvicultural risks and losses in the short-term, as well as longer-term threats from climate change. Climate and its interaction with other forest influences are not well understood, but are implicated in the risks and losses already being incurred. Understanding these relationships will not only assist managers in the short term, but potentially provide important insights on longer term implications of climate change. The influence of climate, directly or indirectly, on mortality in young trees is of particular interest. High levels of mortality were observed during the first 5 years of the regenerated lodgepole pine trial. The controlled experimental factors (site and treatment) generally explained little of the variation in early mortality, though significant differences were observed between the 5 ecological strata (“eco-classes”). Improved explanation of this variation will greatly assist our ability to develop useful decision-support tools for regeneration management.

Methods Exploratory analyses of the relationship between climate and mortality of regeneration were initiated using observations from the FGYA regenerated lodgepole pine trial, which was established between 2000 and 2002. ClimateAB2, a computer program integrating climate normals and historical data for genecology and climate change studies in Alberta, was used to extract 35 annual and seasonal temperature and precipitation related variables for each of the 85 planted experimental sites. Correlations were explored between total tree mortality (regardless of apparent cause) and the extracted climate variables over 3 time periods: 1. Average climate conditions for the year, and year following, planting; cumulative mortality over the first one or 2 growing seasons (depending on whether the site was planted in the summer or spring respectively); 2. Average climate conditions from 2001 to 2006; cumulative mortality over 5 growing seasons (to 2006); 3. Average climate conditions from 2001 to 2006; cumulative mortality over 7 growing seasons (to 2008). 1

Dempster, W.R. 2008. Regenerated lodgepole pine trial, analysis of crop performance five growing seasons atter planting. Foothills Growth and Yield Association Technical Report. 2 Wang, T., Hamann, A., Spittlehouse, D., and Aitken, S. N. 2006. Development of scale-free climate data for western Canada for use in resource management. International Journal of Climatology, 26(3):383-397. For more information on this or other FGYA Reports, please contact: Robert Udell Tel.: (780) 865 – 4532, Email: udellconsulting@shaw.ca, or visit www.foothillsresearchinstitute.ca.

Foothills Growth and Yield Association Interim Technical Note February 2009

By: W.R. Dempster, R.P.F, PhD

The correlation matrices indicated significant relationships between mortality and many of the climate variables, particularly when the data were partitioned by eco-class. However, many of the climate variables were highly correlated with each other. The strongest and most consistent relationships with mortality were explored by first selecting in each eco-class those climate variables showing:  Correlation coefficients exceeding 0.7071 (indicating that the variable explains at least 50% of the variation in mortality) during at least one of the 3 time periods;  Correlation coefficients exceeding 0.5 (indicating that the variable explains at least 25% of the variation in mortality) in at least 2 of the 3 time periods;  Consistent correlation direction (positive or negative) across all time periods. Most (28 out of 35) climate variables met these criteria. The eco-classes appeared to divide into 2 populations: one in which mortality decreased with increasing temperature (Ledum - Labrador tea - sites), and one in which it increased (all other sites). Further selection, pending more rigorous statistical analyses, was made by retaining only those variables for which the correlation coefficients exceeded 0.5 in all eco-classes within each population at 5 growing seasons after planting. This selection identified 4 variables having superior strength and consistency of correlation (see Table 1). Preliminary Results Table 1 shows correlation coefficients for the relationships between transformed3 mortality percent and the following climate variables selected as described above:  DD>5 degree-days above 5°C (growing degree-days);



DD5100

the Julian date on which DD>5 reaches 100 (budburst date for most plants);



MAT

mean annual temperature (°C);



DD<18

degree-days below 18°C.

Arc sine transformation was used to normalize the statistical distribution of % mortality. For more information on this or other FGYA Reports, please contact: Robert Udell Tel.: (780) 865 – 4532, Email: udellconsulting@shaw.ca, or visit www.foothillsresearchinstitute.ca.

Foothills Growth and Yield Association Interim Technical Note February 2009

By: W.R. Dempster, R.P.F, PhD

Table 1. Correlations (r-values) between mortality and selected climate variables Population

Climate Variable

Ledum sites

DD>5 DD5100

Other sites

MAT

DD<18

Eco-class (moisture / nutrient status) 2 5 2 5 1 3 4 1 3 4

mesic / poor hygric / poor mesic / poor hygric / poor submesic / medium - low mesic / medium subhygric / rich submesic / medium - low mesic / medium subhygric / rich

Growing Season 1-2 5 -0.75 -0.84 -0.68 0.31 0.72 0.82 0.66 0.55 0.72 0.64 0.73 0.94 -0.55 -0.72 -0.64 -0.72 -0.93

7 -0.80 -0.53 0.76 0.54 0.79 0.28 0.90 -0.79 -0.29 -0.89

Note that:  All 4 retained climate variables are directly calculated or derived measures of annual temperature;  On Ledum sites (eco-classes 2 and 5) mortality decreased with increasing temperature;  On all other sites (eco-classes 1, 3 and 4) mortality increased with increasing temperature;  In eco-classes 3 and 5 the relationship has weakened over time;  In eco-classes 1 and 2 the relationship has strengthened over time;  In eco-class 4 the strength of the correlation appears to have peaked;  The relationship was most consistently strong on rich sites (i.e. eco-class 4). Figures 1 and 2 illustrate trends of % mortality with temperature on Ledum and other sites respectively. Each point in the scatter diagrams represents an installation (1 ha cluster of 4 treatment plots). Overall trends are shown for each population, explaining 64% of the total mortality variation in Figure 1, and 52% in Figure 2. Note that the trends are based on a single x-variable in each case, and pooling of eco-classes and treatments (planting density and weeding). Exploratory stepwise multiple regressions suggested that adding more climate variables, and / or stratifying the data by eco-class or other site factors, could increase the proportion of mortality variation explained. No significant treatment effects on mortality have yet been observed.

For more information on this or other FGYA Reports, please contact: Robert Udell Tel.: (780) 865 – 4532, Email: udellconsulting@shaw.ca, or visit www.foothillsresearchinstitute.ca.

Foothills Growth and Yield Association Interim Technical Note February 2009

By: W.R. Dempster, R.P.F, PhD

Figure 1. Trend of mortality with temperature on Ledum sites after 5 growing seasons 18

% Mortality

Eco-class 2 Eco-class 5 Trendline

0 900

950

1000

1050

1100

1150

1200

Degree-days above 5°C

Figure 2. Trend of mortality with temperature on all other sites after 5 growing seasons 30

% Mortality

Eco-class 1 Eco-class 3 Eco-class 4 Trendline

0 1.8

2.2

2.4

2.6

2.8

3.2

Mean Annual Temperature (°C)

For more information on this or other FGYA Reports, please contact: Robert Udell Tel.: (780) 865 – 4532, Email: udellconsulting@shaw.ca, or visit www.foothillsresearchinstitute.ca.

Foothills Growth and Yield Association Interim Technical Note February 2009

By: W.R. Dempster, R.P.F, PhD

Interpretation The absolute range in average temperatures across the 85 sites was quite small (1.5 degrees annual, 3 degrees summer). Small differences in average temperature are associated with large changes in mortality, especially on the better sites at higher temperatures, and explain more of the variation in mortality than have other site and treatment factors. The nature and cause of the apparent climatic effects are far from clear. Assessment of tree health and recently-dead trees, both in the FGYA and earlier studies, suggests that direct causes of mortality are frequently biotic e.g. root disease, root collar weevils and rusts. Climate effects on mortality may be both direct (e.g. summer drought, winter desiccation) and indirect (i.e. resulting from climate affecting pathogen dynamics or pre-disposing trees to pathogens). One possible explanation for the trend observed in Figure 2 is that the increase in mortality simply reflects faster stand development and onset of self thinning on better and warmer sites. This was not supported by investigation. Apart from the fact that most of the plots are not yet showing much indication of crown competition and that the opposite trend was observed on Ledum sites (Figure 1), there was no indication that mortality was positively linked to stand height. In fact a weak but statistically significant negative relationship was observed between mortality and average height. Incorporation of climate variables into regeneration models may provide a significant improvement in our ability to forecast mortality and survival. This has practical implications because:  Knowledge of probable mortality is key to operational decision-making regarding achievement of regeneration performance targets;  It was previously feared that mortality would be too chaotic and random for prediction;  Localized values for climate data can be easily calculated for any opening in Alberta providing the geographic location (latitude, longitude and elevation) is known.

For more information on this or other FGYA Reports, please contact: Robert Udell Tel.: (780) 865 – 4532, Email: udellconsulting@shaw.ca, or visit www.foothillsresearchinstitute.ca.

Foothills Growth and Yield Association Interim Technical Note February 2009

By: W.R. Dempster, R.P.F, PhD

The preliminary study was confined to planted stock. Observed mortalities are generally higher than those reported for natural regeneration.4 Evaluation of relative trends in natural regeneration will be given high priority, notwithstanding present limitations imposed by the protracted ingress period encountered on most of the sites under study. Continued and expanded research will improve predictions of regeneration success, silvicultural investment risks, and the implications of climate change for silvicultural practice.

Ives, W.G.H. and C.L. Rentz. 1993. Factors affecting the survival of immature lodgepole pine in the foothills of westcentral Alberta. Forestry Canada Information Report NOR-X-330. 4

For more information on this or other FGYA Reports, please contact: Robert Udell Tel.: (780) 865 â&#x20AC;&#x201C; 4532, Email: udellconsulting@shaw.ca, or visit www.foothillsresearchinstitute.ca.