Dynamics of forest stand

Introduction

• Forest dynamics : Forest models and tree models (Shugart and west 1980)

• The study of change in forest stand structure with time, including stand behaviour

during and after disturbance (human-caused or natural) - every management

action (Willson, 2014)

• Studied through Compositional change - relay floristics (the classical successional

model) (Johnstone et al. 2010)

• Stand dynamics is the study of changes in forest stand structure over time,

including stand behavior during and after disturbances (Smith et al. 1997)

What are the Foundations - Forest Stand Dynamics? / need

Observation

Ecology, physiology, morphology, anatomy, environmental

factors

Facilitates study of Interactions –i.e., tree-tree, species-

species, tree-site.

Enables understanding of Stand Growth and Succession

Why is Forest Stand Dynamics important for foresters?

• Aids understanding of forest development and responses to natural disturbance

• Basis for understanding the interactions and responses to planned interventions

– Predicting productivity and future yield

– Predicting future structure and composition

– Controlling silvicultural costs

– Habitat and conservation values

– Enhancing landscape-scale values

• Forests are complex systems and need to be managed to be both resilient (to minimise

effects of climate change, pests and diseases) and sustainable (social, economic, ecological

and environmental factors)

• Principles of forest stand dynamics apply to all forest types and forest biomes

Succession - "Relay floristics" - Balsam fir is replacing trembling aspen

• Composition of forest does

not changes so completely

or in a singular direction

• Mode of replacement is

strongly dependent on the

composition of the stand

and site type

Change through "gap replacement"

Canopy gap replacement• If a stand is a mixture of mid- tolerant

(e.g., red oak white ash) and tolerant (e.g., sugar maple) species, and occurs on a rich mesic site, any canopy gaps that occur through death of single trees are likely to be "captured" by tolerant species.

• This is because tolerant species are likely to be better represented in the reproduction layer and their growth rates are optimal on such sites.

• If a similar stand develops on a drier, less fertile site, the mid-tolerant species have a greater chance to fill gaps because on these sites their growth rates exceed those of the more moisture and nutrient demanding tolerant species

Canopy gap replacement as a function of chance occurrence of seedlings in the gap area and differential growth rate of species on a dry-mesic site.

SM=sugar mapleWA=white ash

RO=red oak

Resilience and response dynamics - ecosystem feedbacks (Kilchenmann, 2013)

Alternate successional cycles - Black spruce domain

Alternate successional cycles – Broadleaf forest domain

Forest dynamics models- schematic diagram illustrates assumptions that are associated with model classification

(Shugart,1984)Mode of classification Phenomena

schematic

Category

Age structure

Diversity

space Regeneration

Growth

Geometric competition

Resource competition

Mortality

Tree Mixed Mono Spatial ** *Tree Mixed Mono Nonspatial **Tree Mixed Mono Nonspatial * **Tree Mixed Mono Spatial ** *Tree Mixed Mono Nonspatial ** * * **Tree Mixed Mono Spatial * ** ** * **Tree Mixed Mono Nonspatial ** ** **Gap Mixed Mono Nonspatial ** **Gap Mixed Mono Spatial ** ** * * *

** strong emphasis, * some emphasis and a blank no or little emphasis

Mixed aged, Mixed-species non spatial tree model - Principal subroutines in the FOREST model

• MAIN• INPUT• STANGN• HOWFAR• COMPE• YIELD• STAT• CUT• OUTPUT• REPRO• PSEED• SEEDYR• DSTRIB• GRAMIN8• GROW

MAIN Determines height, diameter, and crown development of over story trees

INPUT Accepts parameter values for each species primarily for over story development

STANGN Accepts real tree input data or generates spatial patterns and tree characteristics for each species

HOWFAR Determines the distance between points on main plot and buffer zone that are needed for evaluation of competition and seed and sprout distribution

COMPE Evaluates the tree competition

YIELD Calculates the timber product yields based on individual tree dimensions, specific gravity and bark characteristics

STAT Computes parameters of distribution of tree and stand characteristics for summary output

CUTOrders tres by size or increment for pruning or harvest treatments and implements these treatments on individual trees by species. Harvest includes row thinning, selection according to specified criteria, spacing rules, cuts to basal area levels and combinations above. The timing and degree of cutting may be set by the user or allowed to vary as dictated by stand development

OUTPUT Prepare table, stem map, and graphic output that describe stand development

REPRO Accepts input of initial reproduction status, reproduction parameters for each species, and specifications for degree and timing of any changes in reproduction parameters to be implemented during the run

PSEED Determines seed and sprout production for each over story tree as a function of species, size and threshold stage

SEEDYR Generates seed year multiplier for each species (i.e., frequency of good, moderate and poor seed years)

DSTRIB Distributes seeds and sprouts (root suckers and basal sprouts) from each overstory tree to subplots within main plot

GRMIN8 Calculates seed germination as a function of microsite and over story cover conditions

GROW Controls growth and mortality of reproduction until surviving individual reproduction stems reach overstory status - then MAIN assumes control of stem development

Contd.,

Gap model - 450 years change on a single simulated plot (BRIND model) for alpine ash zone of the Brindabela mountains

(Shugart 1984)

The species are drawn to scale by height, and the width of plot in 32 m

Die back regeneration cycle shown in simplified form for Metrosiderous polymorpha on hawaiian islands

(Shugart, 1984)

Severely declining stand of ohia

Stand of mature healthy ohia

Forest Gap models - importance1. Forests are represented as a collection of small patches. The

forest successional stage and age vary across patches.2. Patches are independent of their neighborhoods and do not

interact with other patches. Thus, dynamic processes such as tree recruitment, growth and mortality are calculated separately for each patch.

3. All patches are homogeneous in size and resource level (i.e., light reaching the upper canopy). The size of one patch is usually chosen according to the extent of the largest possible tree crown (e.g., 20 m x 20 m). Intra- or interspecific interactions are simulated for all trees in a patch rather than tree-by-tree, as tree positions are not included.

4. Leaves are modeled as thin disks on top of each tree. Trees standing within one patch compete for light due to asymmetric shading

Forest based models – Forest dynamics (Fischer et al., 2016)

FORMIX

FORMIND

GRASSMIND

FORMIX• Applied to tropical forests in South-East Asia. FORMIX

accounts for biomass and tree numbers in five distinct canopy layers (each layer has some representative trees similar to size class models). (Huth et al., 2001)

FORMIND• Is the process- and individual-based successor of the FORMIX

model, in which the concept of distinct layers was discarded. FORMIND was developed in the late 1990’s to simulate tropical forest dynamics more realistically than before. (Fischer et al., 2016)

MAIN PROCESSES OF FORMIND

• Establishment

• Growth

• Mortality

• Competition and environmental limitations

• Disturbances

• Carbon cycle

Simulation of species-rich forests with the growth model FORMIND (Fischer et al., 2016)

Individual-based means that growth is calculated for each tree individually. Trees in high diversity forests are aggregated into different plant functional types in order to

facilitate the parameter definition of similar-behaving species and to reduce computing time.

Output - Allows to simulate forests of high heterogeneity

The model area (1 to 50 ha) is divided into 20m x 20m patches. Forest gaps are

implemented to simulate forest structure and dynamics. Gaps occur- dying trees or external disturbances – leads to establishment of LD

spp.

• This image shows a visualization of a mountainous tropical forest in Ecuador.

• Tree species are aggregated into seven plant functional types. • Trees colored in red are of late successional stage (shade-tolerant

species), trees colored in green are of early successional stage (light-demanding species) and trees in blue are of intermediate successional stage.

GRASSMIND - Simulation of species-rich grasslands with GRASSMIND

• The individual-based approach of forest gap models offer a high degree of flexibility to be adapted to different environments (e.g., temperate forests) or even other ecosystem types (e.g., temperate grassland

• GRASSMIND designed for simulating the structure and dynamcis of herbaceous communities including:– competition between individual plants for light, space, soil water and

nitrogen– different management regimes (mowing, irrigation, fertilization)– climatic changes (drought events, increased temperatures, etc.)

individual plants compete for light and space aboveground and for soil water and nitrogen belowground. So, the GRASSMIND is coupled with the soil model CANDY.

Studying practically the forest stand dynamics concept

Facilitating learning in forest stand dynamics

• Part 1 : field (site inspection and data collection)• Part 2 : data collection, presentation, analysis and

interpretation

Basic measurements• Complete measurements in

100m2 or 200 m2 plots (trees and ground vegetation)

Session 2 : Analysis and Interpretation

• Introduction – Outline the learning goals, objectives and structure of the session– review and reflect on key aspects of session 1

• Fast facts lecture– Theory and terminology

• Explain the task– Distribute handout and data sheets– Explain steps required to complete the exercise

• Student activity– Summarise and collate data– Present results in graphical format– Creat a stand profile diagram

• Review and reflect– Group and class discussion– Reviw of learning outcomes and reflect on application of knowledge to forestry

practice

References

• http://harvardforest.fas.harvard.edu/blog/forest-dynamics-former-plantations

• http://www.ufz.de/index.php?en=36279• http://formind.org/mode• http://dialog.ua.edu/2014/11/seeing-both-the-for

est-and-the-trees/

• http://baloun.entu.cas.cz/png/wanang/forest-dynamics-plot

• http://www.ctfs.si.edu/site/Mudumalai

Thank you…..