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Evaluation of White spruce growth response to partial harvest

DENDROECOLOGY GROUP

Forest productivity and management

Margarita Fernández, Javier Gibaja del Hoyo, Hilary Howard, Turtle May, Tom Monet

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Canada harvested 710,000 hectares in 2020
Quebec accounted for 28%
74% of the hectares harvested in Quebec each year is done by clear cutting the forest

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Introduction

simplify and homogenize forest, close to a monocrop

Javi

https://www.ecologyandsociety.org/vol2/iss2/art6/

VARIABILITY IN STAND COMPOSITION

A natural chronosequence covering > 230 yr after fire have been reconstructed for Quebec's southern boreal forest using fire areas originating in different years (Bergeron and Dubuc 1989, Leduc et al. 1995). Fig. 3 summarizes natural succession for mesic, "mixedwood" (MacDonald 1995) sites. Intolerant hardwoods (trembling aspen and white birch) dominate the canopy during the first 100 yr. Stand breakup occurs gradually over a number of years. Following their mortality, a second cohort of hardwoods, as well as fir and white spruce recruited in the understory, attain the overstory to form mixedwood stands. Only after 200 yr, following mortality of the second and even third intolerant hardwood cohort, are stands dominated by softwood species. Natural dynamics can thus be schematized by successive cohorts of hardwood, mixedwood, and softwood dominance. In some respects, current silviculture practices ignore natural ecosystem dynamics. In Quebec, provincial silvicultural standards require that cutovers be regenerated to a hardwood and softwood stocking level similar or superior to preharvest levels. The consequence of this approach is that it imposes a cyclical rotation of similarly composed stands, whereas succession in the natural system generally involves a transition of stand types.

During the development of mixedwoods, gaps that are generated by partial disturbances, such as insect outbreaks and windthrow, together with tree- and stand-level processes, such as competition and senescence, facilitate the establishment and growth of shade-tolerant conifers [8]. These species might stay suppressed in the understory for long periods before the formation of canopy gaps (and the concomitant increase in light availability) induces an acceleration of their growth rate. Thus, gap dynamics act as modulators of stand composition and structure in late-successional conifer stands [15,16]. Moreover, changes in canopy composition are the consequences of differential growth rates among species [17] and not just a replacement of species that is driven by numerous inhibition or facilitation processes.

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Introduction

Javi

https://www.ecologyandsociety.org/vol2/iss2/art6/

VARIABILITY IN STAND COMPOSITION

A natural chronosequence covering > 230 yr after fire have been reconstructed for Quebec's southern boreal forest using fire areas originating in different years (Bergeron and Dubuc 1989, Leduc et al. 1995). Fig. 3 summarizes natural succession for mesic, "mixedwood" (MacDonald 1995) sites. Intolerant hardwoods (trembling aspen and white birch) dominate the canopy during the first 100 yr. Stand breakup occurs gradually over a number of years. Following their mortality, a second cohort of hardwoods, as well as fir and white spruce recruited in the understory, attain the overstory to form mixedwood stands. Only after 200 yr, following mortality of the second and even third intolerant hardwood cohort, are stands dominated by softwood species. Natural dynamics can thus be schematized by successive cohorts of hardwood, mixedwood, and softwood dominance. In some respects, current silviculture practices ignore natural ecosystem dynamics. In Quebec, provincial silvicultural standards require that cutovers be regenerated to a hardwood and softwood stocking level similar or superior to preharvest levels. The consequence of this approach is that it imposes a cyclical rotation of similarly composed stands, whereas succession in the natural system generally involves a transition of stand types.

During the development of mixedwoods, gaps that are generated by partial disturbances, such as insect outbreaks and windthrow, together with tree- and stand-level processes, such as competition and senescence, facilitate the establishment and growth of shade-tolerant conifers [8]. These species might stay suppressed in the understory for long periods before the formation of canopy gaps (and the concomitant increase in light availability) induces an acceleration of their growth rate. Thus, gap dynamics act as modulators of stand composition and structure in late-successional conifer stands [15,16]. Moreover, changes in canopy composition are the consequences of differential growth rates among species [17] and not just a replacement of species that is driven by numerous inhibition or facilitation processes.

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Introduction

DRIVING FACTORS

Javi

https://www.ecologyandsociety.org/vol2/iss2/art6/

VARIABILITY IN STAND COMPOSITION

A natural chronosequence covering > 230 yr after fire have been reconstructed for Quebec's southern boreal forest using fire areas originating in different years (Bergeron and Dubuc 1989, Leduc et al. 1995). Fig. 3 summarizes natural succession for mesic, "mixedwood" (MacDonald 1995) sites. Intolerant hardwoods (trembling aspen and white birch) dominate the canopy during the first 100 yr. Stand breakup occurs gradually over a number of years. Following their mortality, a second cohort of hardwoods, as well as fir and white spruce recruited in the understory, attain the overstory to form mixedwood stands. Only after 200 yr, following mortality of the second and even third intolerant hardwood cohort, are stands dominated by softwood species. Natural dynamics can thus be schematized by successive cohorts of hardwood, mixedwood, and softwood dominance. In some respects, current silviculture practices ignore natural ecosystem dynamics. In Quebec, provincial silvicultural standards require that cutovers be regenerated to a hardwood and softwood stocking level similar or superior to preharvest levels. The consequence of this approach is that it imposes a cyclical rotation of similarly composed stands, whereas succession in the natural system generally involves a transition of stand types.

During the development of mixedwoods, gaps that are generated by partial disturbances, such as insect outbreaks and windthrow, together with tree- and stand-level processes, such as competition and senescence, facilitate the establishment and growth of shade-tolerant conifers [8]. These species might stay suppressed in the understory for long periods before the formation of canopy gaps (and the concomitant increase in light availability) induces an acceleration of their growth rate. Thus, gap dynamics act as modulators of stand composition and structure in late-successional conifer stands [15,16]. Moreover, changes in canopy composition are the consequences of differential growth rates among species [17] and not just a replacement of species that is driven by numerous inhibition or facilitation processes.

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SAFE Project

Professor Brian Harvey

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Treatment 1 (T1): 33% partial cut

Cutting from below

Treatment 2 (T2) : 66% partial cut

Cutting the most vigorous trees

Control 1 & 2: unmanaged stands

Aspen stand of SAFE 1

Forest from treatment 2

SAFE PROJECT

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Research questions:

How do stand structure variables differ between managed and unmanaged stands?
How sensitive to climate are these white spruce (Picea glauca) stands?
How does harvest intensity impact white spruce secondary growth after 22 years?

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Treatment 2: 2/3 removal of basal area

Two-thirds of the stems were harvested with priority given to the most vigorous stems. The trees left standing, combined with the ability of aspen to regenerate by root suckering after cutting, and the response of understory softwoods to canopy opening, should allow the stand to evolve towards a structure and composition similar to that of older natural stands.

Treatment 1 : ⅓ removal of basal area

Priority given to the removal of the lowest quality stems.

The stand thus retains most of the attributes of natural stands while seeing its mortality reduced.

Partial cuts come from Europe

The response 20 years after a partial cut over a boreal forest and white spruce has not been studied yet

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PERMANENTE PLOT – SAFE PROJECT

EXPERIMENTAL DESIGN

METHODS

100 m

Control

Treatment 1

(1/3 Partial cut)

Treatment 2

(2/3 Partial cut)

Aussenac et al. 2016 Journal of Ecology

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PERMANENTE PLOTS – SAFE PROJECT-

100 m

FOREST STAND INVENTORY

METHODS

Plot area = 400 m²

Radius = 11.28 m

100 m

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PERMANENTE PLOTS – SAFE PROJECT

FOREST STAND INVENTORY

METHODS

Plot area = 400 m2

Radius = 11.28 m

100 m

DBH (Diameter at 1.3 m): Trees above 5 cm DBH

Tree’s social status: Dominant, codominant, suppressed

State (alive or dead)

Species composition

VARIABLES :

All trees above 9 cm DBH were

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PERMANENT PLOTS – SAFE PROJECT- COMPETITION

SUB-INVENTORY

METHODS

Micro-plot area = 4 m²

We selected white spruce trees and used them as the center of our subplots

Hegyi’s competition index

DBH of all the trees within the subplot and distance to the focal tree

VARIABLES :

Target species: White spruce

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Methodology

Core sampling

Mount and dry

Sanding

Cross-Dating

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Methodology

Treatment 2

Treatment 1

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Methodology- Stand Structure

Basal area per plot per species: m²per hectare

Basal area formula = π x (DBH/200)²

Tree density per plot per species: Number of trees per hectare

Species in our plots:

Balsam fir (Abies balsamea)

Trembling aspen (Populus tremuloides)

White spruce (Picea glauca)

White cedar (Thuja occidentalis)

Black spruce (Picea mariana)

White birch (Betula papyrifera)

Mountain Maple (Acer spicatum)

Jack Pine (Pinus banksiana)

Ash (Fraxinus species)

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DOWNLOADING OF CLIMATE DATA

Raphaël → ClimateNA

Specific Location

Interpolates data from stations

Monthly accuracy

Temp, Precip and Solar radiation

Monthly Drought Code (MDC)

Tongli Wanget al., 2016

Raphaël D. Chavardès et al., 2019

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R e s u l t s

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How do stand structure variables differ between managed and unmanaged stands?
How sensitive to climate are these white spruce (Picea glauca) stands?
How does harvest intensity impact white spruce secondary growth after 22 years?

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TPH for Control and Treatment Units

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BA for Control and Treatment Units

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TPH for White Spruce (Picea glauca) in Control and Treatment Units

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BA for White Spruce (Picea glauca) in Control and Treatment Units

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How do stand structure variables differ between managed and unmanaged stands?
How sensitive to climate are these white spruce (Picea glauca) stands?
How does harvest intensity impact white spruce secondary growth after 22 years?

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Tree ring analysis: Spaghetti Plot

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No significant correlation with climate…

Climate-growth analyses

Drought code

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How do stand structure variables differ between managed and unmanaged stands?
How sensitive to climate are these white spruce (Picea glauca) stands?
How does harvest intensity impact white spruce secondary growth after 22 years?

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Tree Ring Growth for Different Treatments

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Tree Ring Growth for Different Treatments

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Basal Area Increment for Different Treatments

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Impact of Competition on Growth for Treatment 2

HEGYI’s COMPETITION INDEX:

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Differences on mean tree Ring Growth after Harvest between treatments

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Differences on mean Tree Ring Growth Pre and Post Silviculture Treatments:

ANOVA results

Growth (mm yr-1)

A

C

B

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Generalized Additive Models

fit_pigl <- bam(log(BAI)~ s(log(cBA)) + s(log(AgeCore2)) + s(MDC6) + Plot+s(year) + s(year,by=Plot) + ti(log(cBA),log(AgeCore2)) + s(treecore, bs='re'), correlation=corAR1(form=~1|treecore), data=treatcontrol2,select=TRUE, method="ML)

Tipping point

Increased in growth only during the first years after the treatments

Fixed effects:

Cumulative growth x Cambial age
Drought index
(Control vs Treatment) x Year

Random effects:

Treecore

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Impact of Competition on Growth for Treatment 1

HEGYI’s COMPETITION INDEX:

(Mailly, Turbos, & Pothier, 2003)

showing relationship between competition and growth after harvest. we used the Hegyi’s competition index because it is the most strongly correlated with basal area growth in black spruce stands and we are doing whitre spruce which is similar. The distance (Distij) and DBH of each neighbouring tree (j) within a 4 m radius of the subject tree (i) were measured to calculate the CIi:

also note here that the competition index on the x-axis is very high, it goes all the way to 16

used linear model in R

Turtle

(Mailly, Turbos, & Pothier, 2003).

Daniel Mailly, Sylvain Turbis, and David Pothier

Hegyi’s competition index (CIi) was selected because it is the most strongly correlated with basal area growth in black spruce stands [24]. →Competition data were by position classes (edge and interior trees), 10 years a.c. for black spruce trees (n = 240). Hegyi’s competition index (CIi) was selected because it is the most strongly correlated with basal area growth in black spruce stands [24]. The distance (Distij) and DBH of each neighbouring tree (j) within a 4 m radius of the subject tree (i) were measured to calculate the CIi:

CIi=∑j=1n(DBHiDBHJ×1Distij)

TAKES DISTANCE OF COMPETITION SPECIES

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Take Home Messages

Methodological implications

Ecological implications

Management implications

methods conclusions: dendrochronology is a valuable tool to investigate and evaluate the growth response of different silviculture treatments

ecological conclusions: harvest has an impact on white spruce growth in boreal forests, but there are other driving factors besides harvesting, particularly competition

management conclusions: partial harvest can be used to promote growth response in boreal forests

overall take home messages: tom speaks very good spanish

We learnt how to collect and process wood samples to analyze tree-rings
We found significant differences between treated and control plots 22 years after the silvicultural treatments
dramatic growth response of white spruce after silvicultural treatments for both treatment prescriptions
22 years after harvest, growth starts to plateau and return to pretreatment growth trends

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¡El mejor equipo!

Merci beaucoup !

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Average Tree Ring Growth from 1976-1998

(22 years before harvest)