The Effects of Overstory Mortality on Snow Accumulation and Ablation


Project Leader

Funding Agency

Pat Teti, P.Geo.,
B.C. Ministry of Forests and Range
Natural Resources Canada,
Mountain Pine Beetle Initiative

Introduction


Mountain pine beetles have killed a large percentage of mature Lodgepole pine trees over an area of more than 14 million hectares in the B.C. Interior (B.C. Ministry of Forests and Range, 2008). Research has shown that this can increase the magnitude of spring runoff (Uunila et al., 2006). Forest licensees are also permitted to log beetle-attacked pine stands at an accelerated rate (BC Ministry of Forests and Range, 2004). The net effect is that most of B.C.’s mature pine stands will be changing rapidly over the next decades due to deterioration of the overstory, natural regeneration, clearcut harvesting, and managed reforestation.
This project is documenting differences in structure between pine stands at different stages of growth and deterioration, changes within stands over time, and the effects of those differences on snow hydrology at the stand-level. This will help watershed modellers predict possible changes in stream flow due to pine beetles and forest management. The map below shows the locations of 5 study areas where this work is being done.

 

Location Map of study areas

 

The following shows a conceptual model of how a beetle-attached pine stand might change over several decades if it were left to develop naturally versus how
it would be expected to change if it were logged and reforested.

 

 

 

This is a photo of a stand in which the mature Lodgepole pine trees were killed about 20 years earlier. The dead trees have fallen and the site is recovering naturally due to pine and spruce that established both before and after beetle attack.
This stage of development corresponds with the fourth frame from the top in the left hand side of the figure above.

 

Top
 

Rationale


Resource managers are concerned about hydrologic changes due to beetle-related stand deterioration, as well as accelerated timber harvesting for the purpose of utilizing the affected timber before it deteriorates.

When pine trees die and deteriorate, more snow and rain reach the ground and less soil moisture is removed by transpiration. This can lead to wetter soils and increased runoff. However, dead trees still intercept some precipitation and eventually, the forest will regenerate. Clearcut harvesting also reduces interception and transpiration but the effects are greater and occur faster than those associated with overstory mortality. On the other hand, forest regeneration on a clearcut is faster than that in a beetle-killed stand. We need to quantify the magnitudes of hydrologic changes due to beetles versus logging and the different rates of recovery after those changes.

This B.C. Government web page discusses forest stewardship considerations associated with accelerated pine salvage logging.

Top

Project Description


In order to make watershed management decisions, managers need professional advice on the expected hydrologic effects of pine beetles and logging under different scenarios. The quality of such advice can be improved with the application of a watershed runoff model that accurately represents what is happening at the stand-level.


This project is improving our understanding of stand-level processes by quantifying snow hydrology and stand characteristics in natural and managed pine stands at different stages of deterioration and recovery. Each study area has at least five plots including one in a recent clearcut, at least one in a partially-recovered clearcut, and at least three in a natural pine stands. The Rosita and Vanderhoof study areas also include immature natural pine stands recovering from wildfire. The Rosita study area includes two stands that were severely attacked by beetles in the early 1980s. Differences in snow accumulation and ablation are being compared with stand properties derived from tree surveys, ground-based canopy photography, and high resolution aerial photography.

Top

Progress


A total of 29 plots in 5 study areas have been monitored since the spring of 2006. Snow storage and ablation rates have been documented in each plot for 3 years.  Vegetation and coarse woody debris were surveyed in 2007. A variety of radiation parameters have been calculated from fisheye canopy photos taken in the summers of 2006 and 2008. Aerial photography has been used to document rates of snow disappearance, stand structure, and changes in stand structure over time.
The effects of plot characteristics on snow hydrology have been described in publications listed in the next section.

 

Publications


Redding, T., R. Winkler, P. Teti, D. Spittlehouse, S. Boon, J. Rex, S. Dubé, R.D. Moore, A. Wei, M. Carver, M. Schnorbus, L. Reese-Hansen, and S. Chatwin. 2008. Mountain pine beetle and watershed hydrology. In Mountain Pine Beetle: From Lessons Learned to Community-based Solutions Conference Proceedings, June 10–11, 2008. BC Journal of Ecosystems and Management 9(3):33–50. 4.3 MB pdf file

Teti, P., 2008. Effects of overstory mortality on snow accumulation and ablation. Natural Resources Canada, Canadian Forest Service, Pacific Forestry Centre, Victoria, BC. Mountain Pine Beetle Working Paper 2008-13. 34 p. 795 kb pdf file

Teti, P. 2009 (in press). Effects of mountain pine beetles and timber harvesting on stand attributes and snow on the B.C. Interior Plateau. Proceedings of the 77th Western Snow Conference, Canmore, Alberta.  http://www.westernsnowconference.org/proceedings/index.htm

Teti, P. and R. Winkler. 2008. Snow hydrology and solar radiation in growing and deteriorating pine stands. In Mountain Pine Beetle: From Lessons Learned to Community-based Solutions Conference Proceedings, June 10–11, 2008. BC Journal of Ecosystems and Management 9(3):136–138.  URL: same as Redding, et al., above.

References and More Information


B.C. Ministry of Forests and Range. 2004. Quesnel Timber Supply Area Rationale for Allowable Annual Cut (AAC) Determination by the Chief Forester. 63 p. https://www.for.gov.bc.ca/hts/tsa/tsa26/tsr3/rationale.pdf

B.C. Ministry of Forests and Range. 2008. https://www.for.gov.bc.ca/hfp/mountain_pine_beetle/facts.htm

The Effects of Forest Structure on Snow Accumulation and Melt in South-Central
British Columbia
(Thesis abstract)

The Upper Penticton Creek Watershed Experiment (web page)
      
Uunila, L., B. Guy, and R. Pike. 2006. Hydrologic Effects of Mountain Pine Beetle in the Interior Pine Forests of British Columbia: Key Questions and Current Knowledge. Streamline Watershed Management Bulletin. Volume 9(2):1-6.
http://www.forrex.org/publications/streamline/ISS31/streamline_vol9_no2.pdf

Winkler, R. and J. Roach. 2005. Snow Accumulation in BC’s Southern Interior Forests. Streamline Watershed Management Bulletin, Volume 9 Number 1. http://www.forrex.org/streamline/ISS30/streamline_vol9_no1_art1.pdf

 


Contact: Pat Teti
Research Hydrologist
Southern Interior Region
Williams Lake Service Centre
Phone: 250 398-4752, eMail: pat.teti@gov.bc.ca