The State of BC’s Forests The Indicators Ecosystem dynamics — PDF print version

Indicator 3 – Ecosystem dynamics

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Why is this important?

Altering the dynamics of forest ecosystems may reduce environmental stability and resilience, leading to detrimental economic and social impacts.

Overview

• Ecosystems are dynamic – their non-living elements change, and their living elements grow and die. Despite dramatic changes in individual elements, ecosystems can be resilient and stable.
• Since 1950, the dynamics of British Columbia’s forest ecosystems have been subject to climate change, wildfire suppression and increased timber harvests.
• Changes in the dynamics of B.C.’s forest ecosystems appear to be reducing ecosystem stability and resilience.

STATE

mixed

TREND

deteriorating

INFORMATION

partial

Questions about ecosystem dynamics

3-1	What are the main dynamics in B.C.’s forests?
3-2	How are the main dynamics changing forest age?
3-3	How are the main dynamics changing forest biomass?
3-4	How fragmented are B.C.’s forest ecosystems?
	Ministry of Forests and Range’s assessment

Related indicators

• Pressures that affect ecosystem dynamics include fire management, logging, reforestation, invasive plants and animals, and climate change (see Timber harvest, Silviculture, Exotic species, Greenhouse gases).
• Altering ecosystem dynamics can disrupt wildlife habitat and economic activity (see Species diversity, Forest products, Jobs and communities).
• Management responses include protected areas (see Protected forests), research to improve understanding (see Management capacity), ecosystem restoration and prescribed fires.

Indicator 3-1

What are the main dynamics in B.C.’s forests?

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Why is this important?

Managing the combined effects of established and new ecosystem dynamics requires understanding their relative importance and their interactions.

State and Trend

• Fires, insects and diseases that kill trees are part of the natural dynamics of ecosystems. Humans reduce some disturbances (e.g., fire suppression) and add other disturbances (e.g., timber harvests).
• From 1950 to 2000, fire suppression reduced the area disturbed by fires, while the area disturbed by timber harvests increased. Their combined area averaged 170,000 ha per year. This is forecast to increase to 190,000 ha annually in 2001–2050.
• The current mountain pine beetle epidemic, enabled by climate change³, is forecast to disturb an average 2,000,000 ha per year in 2001–2050 (an area may be disturbed more than once). This is 40 times the 1951–2000 average and 10 times the forecast area of fire and harvest disturbance. The actual area disturbed in 2005 was 8,700,000 ha, and the actual average for 2001–2005 is twice the forecast level.
• Other insects primarily reduce growth rates. They affected 340,000 ha per year in 1951–2000, and generally had lesser impacts.
• Diseases attack tree roots, stems and foliage. They cause both growth loss and mortality. An introduced stem disease, white pine blister rust, has greatly reduced the occurrence of mature western white pine. Climate change triggered an epidemic of a endemic foliage disease⁴.
• Disease impacts are widely dispersed and difficult to reduce.
• Maps: Pine Volume Killed – 2004 Observed (PDF), 2011 Projection (PDF)

Information

• Past assumptions about mountain pine beetles have proven wrong.
• The effects of climate change are new, complex and hard to predict.
• References: MFR’s MPB; CFS’s Disturbances, MPB Initiative
• Related international and national indicators: MP 3.a; CCFM 2.3

Indicator 3-2

How are the main dynamics changing forest age?

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Why is this important?

Maintaining a mix of forest ages over time supports a variety of habitats for plants and animals, and the capacity of ecosystems to recover from disturbances.

State and Trend

• Wildfire, insect and disease disturbances affect forest age across the province, but timber harvests affect the age of forests primarily on the timber harvest land base (THLB).
• From 1951 to 2000, the proportion of forests over 80 years old increased on the THLB and the non-THLB (non-commercial and explicitly reserved forests). Effective suppression of wildfires allowed the aging of large forest areas burned in the late 1800s (see Indicator 1-3).
• Over the next 50 years, a decrease in the proportion of forests over 80 years old is forecast on the THLB, caused by increased areas harvested.
• In contrast, ongoing aging is forecast for forests on the non-THLB until 2050, when about 90% of these forests will be over 80 years old. As a result, fuel for wildfires and food for insects will increase.
• Wildfires now account for a small proportion of total disturbances, so doubling the average area burned by 2050 changes the forecast little. However, the severe 2003 fire season increased the average for 2001–2005 six-fold.
• Maps: Forest Age (PDF)

Information

• Past and future forest ages were modelled with the federal government’s national carbon budget model, using forest inventories for 2000.
• The model treated all insect disturbances as partial disturbances – forests with a mix of tree species continue to age after mountain pine beetle kills all the pine. This modelling is inaccurate for pure pine forests if all trees are killed.
• References: MFR’s VRI; CFS’s CBM-CFS2
• Related international and national indicators: MP 1.1.b, 2.a; CCFM 1.1.1

Indicator 3-3

How are the main dynamics changing forest biomass?

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Why is this important?

Changes in forest biomass imply changes in ecosystem functions, stability and resilience.

State and Trend

• The quantity of living organisms in an ecosystem can be measured as the amount of carbon in above-ground and below-ground biomass. The quantity of dead organisms or dead organic matter is also important.
• In B.C.’s forests, biomass amounts to less than one third of total ecosystem carbon. Merchantable parts of trees amount to about 10%.
• Total ecosystem carbon in B.C.’s forest ecosystems increased from 1951 to 2050 in the scenario used for Indicators 3-1 and 3-2.
• On the non-THLB, assuming no harvesting and minor natural disturbances, total ecosystem carbon increases 18% from 1951 to 2050.
• On the THLB, total ecosystem carbon is relatively stable over the 100 years. A decrease of about 5% from 2000 to 2050 is caused by ongoing timber harvests replacing older forests with second-growth forests.
• Wildfires and timber harvests decrease total ecosystem carbon by directly removing carbon from forest ecosystems. Harvests have the biggest impact on total ecosystem carbon.
• Mountain pine beetle, and other insects and diseases, affect total ecosystem carbon indirectly. They change biomass to dead organic matter, with no immediate effect on total ecosystem carbon. This leads to increased carbon release from decomposition, and decreases carbon absorption from the atmosphere.
• Maps: Forest Land (PDF)

Information

• The model may be overestimating carbon increases before 2000⁵.
• Information on the impacts of diseases is limited.
• References: MFR’s VRI; CFS’s CBM-CFS2
• Related international and national indicators: MP 2.b, 5.a; CCFM 2.1, 4.1.2

Indicator 3-4

How fragmented are B.C.’s forest ecosystems?

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Why is this important?

Fragmentation of forests disrupts ecosystem functions, reduces habitat quantity and quality, and reduces populations of some species.

State and Trend

• Road density is a common indicator of fragmentation and related human activities. Roads can cause a direct loss of habitat, degrade habitat quality, reduce the size of habitat patches, create barriers that isolate populations, reduce habitat use because animals avoid related noise and activity, decrease populations through road kills and increased legal and illegal hunting, and help disperse predators and invasive species.
• The road density categories shown represent areas that are 1) undeveloped, without roads, 2) minimally affected by few roads, 3) unsuitable for some large carnivores such as grizzly bear and wolves, 4) rural areas unsuitable for all large carnivores, and 5) urban areas.
• Undeveloped watersheds covered 44% of B.C. in the 1980s, an estimated 26% in 2005, and are expected to cover 18% in the long term.
• Undeveloped and minimally affected watersheds combined covered 73% of B.C. in the 1980s and an estimated 61% in 2005.
• Other developments, such as seismic lines for oil and gas exploration, cause additional fragmentation, especially in north-eastern B.C.⁶
• Large areas away from all developments (regardless of watershed locations), called intact areas, are important habitat for large wildlife.
• Maps: Intact Areas (PDF)

Information

• Province-wide road data were systematically collected by government in the 1980s, and updated for about 34% of the province during the 1990s. Since then, voluntary contributions from industry have provided updates, but it is not known where road information is complete or incomplete.
• References: MAL’s LRDW
• Related international and national indicators: MP 1.1.e; CCFM (none)

 

Indicator 3 – Ecosystem dynamics Ministry of Forests and Range’s assessment State mixed B.C.’s varied forest ecosystems have evolved with periodic disturbance by fire, insects and diseases. Forest management over the last 50 years has suppressed some of these disturbances and introduced increasing levels of disturbance from timber harvests. On balance, the amount of forest over 80 years old is greater now, as is the total ecosystem carbon. The current epidemic of mountain pine beetle has, however, created an unprecedented level of disturbance that is threatening numerous aspects of environmental, economic and social sustainability. Ecosystem fragmentation has increased, but substantial areas still exist that are undeveloped or only minimally affected by roads. Trend deteriorating Fire suppression, timber harvests and climate change are changing ecosystem dynamics across the province. Their combined effects are not easy to anticipate and, as in the case of mountain pine beetles, can have catastrophic impacts. The changing proportions and geographic distribution of forests over and under 80 years old can be expected to have various known, uncertain and currently unknown impacts on ecosystem functions. In combination with climate change, this is changing susceptibility to wildfires, insects, diseases and invasive species. Increasing impacts from these agents can be expected. Ecosystem fragmentation is also expected to increase. Information partial Locations of historical wildfires and many insect outbreaks are well documented. Their impacts on timber volumes are less well known, as are the locations and impacts of tree diseases. A detailed and complex model of provincial-level forest ecosystem dynamics is available, and while some input data and assumptions are not accurate, the model and data are constantly being improved. Systematic, province-wide inventories of roads are not being maintained, so monitoring of ecosystem fragmentation will need to rely on satellite imagery. Climate change is known to be occurring in B.C., but the nature of the change is variable and its likely impact on forest ecosystem dynamics is hard to predict.