Canopy Studies - Overview

The study of canopy environments in wet-belt forests poses many challenges and opportunities. Traditionally, studies of biological diversity have been ground-based, leaving many gaps in our knowledge of canopy inhabitants and their life-cycles. This is particularly true for the interior cedar-hemlock forests, where individual trees can reach heights of 55 to 60 m, necessitating specialized canopy access techniques.

In coastal forests of the Pacific Northwest, major infrastructure such as canopy cranes have previously been used to facilitate canopy studies. Within interior wet-belt forests of northern B.C. modified single-rope climbing techniques have provided a lower-cost environmentally sensitive way of studying canopy environments.

Actively growing lichen thalli of Alectoria sarmentosa during winter snowmelt event.One of the major groups of organisms that have been studied in the canopy of interior wet-belt forests are canopy epiphytes, especially lichens and mosses. As Pacific storm systems move over the interior mountain ranges in British Columbia, they create a zone of high precipitation, which favors the growth and development of canopy epiphyte communities. These epiphytes, mainly lichens, rely upon their host trees for support, but are wholly dependent upon rainwater and snowmelt for moisture to support growth and reproduction.

Left: Actively growing lichen thalli of Alectoria sarmentosa during winter snowmelt event.


Widely spaced trees in old-growth cedar-hemlock forest encourage lichen growth in lower canopy positions.The development of canopy lichen communities is strongly influenced by the age of the forest stand within which they reside and the continuity of forest cover on a given site. In even-aged younger forest stands, the greater density of foliage in mid- to upper canopy positions reduces light availability in the lower canopy, limiting growth of most canopy lichens. The denser foliage in younger stands also intercepts more rain and snowfall (much of which then evaporates before dripping through to the lower canopy), creating drier conditions for canopy epiphytes.

Right: Widely spaced trees in old-growth cedar-hemlock
forest encourage lichen growth in lower canopy positions.

In contrast, within older wet-belt forest stands, not only do individual trees attain greater stature, but the forest stand is characterized by gaps, created by past treefall events, where sun flecks can penetrate through the canopy to the humid environment near the forest floor surface. This promotes the establishment and growth of a suite of old-growth lichen indicator species, including species such as the canopy cyanolichen (cyanolichens are lichens that contain a blue-green, sometimes called cyanobacterial, algal component) Nephroma helveticum (see image below).

The distribution of lichens within the canopy of wetbelt forests is therefore closely linked to vertical gradients of temperature, moisture and light availability. In the upper canopy of cedar-hemlock forests, where exposure to sun and wind creates drier conditions for growth, the more dessication tolerant hair lichens are abundant, providing a valuable forage source for mountain caribou when blown to the forest floor surface. In mid- to lower canopy positions, rich cyanolichen communities develop, including large foliose lichens such as Lobaria pulmonaria.

Left: The foliose lichen Lobaria pulmonaria is common on branches in the lower canopy of old-growth wet-belt cedar-hemlock forests.

Many canopy lichens in wetbelt forests are limited to specific microhabitats. Large cottonwoods, for instance, often grow as isolated individuals in conifer dominated wet-belt forest stands, where they create dripzone effects, releasing nutrients to passing rainwater that can enhance the growth of cyanolichens on surrounding trees. Additionally, rainwater channels directly on the bark of large cottonwoods can support unique communities of gelatinous cyanolichens, such as Collema. At the other extreme are many of the pin-lichens, or stubble lichens, that only grow on the underside of large snags, where they are protected from direct contact with rainfall or meltwater.

Site continuity, or the length of time between major disturbance events, is also a major factor influencing the development of canopy lichen communities in wetbelt forests. Successful long-distance dispersal of many old-growth dependant lichens appears to occur only rarely. Thus forests that develop in wet or protected microsites, such as in toe-slope positions or in protected side-valleys where fire occurs less frequently, often contain more diverse canopy lichen communities, including many rare species, for some of the Calcicoid lichens, that normally have more oceanic affinities. These forests, a subset of old-growth forests, have been denoted as antique forests in pioneering studies by Trevor Goward. Current studies on the distribution of these forests within regional landscapes of BCs inland rainforest (see Stand structural attributes and canopy lichen diversity) suggest that they represent an endangered landscape element and should be regarded as a high conservation biology priority. Many of the lichens found within these stands share affinities with lichen populations from coastal wet temperate rainforests worldwide (see South Temperate Rainforests).

Canopy biodiversity is being evaluated within partial-cut harvesting trials at Lunate Creek, in wet-belt forests of the upper Fraser River Valley. (photo M. Geertsema).The knowledge that is now being obtained from canopy studies in interior wet-belt forests will provide valuable information on the ecological function and biodiversity of this little known ecosystem and will help guide local communities in making land-use planning decisions.

Above: Canopy biodiversity is being evaluated within partial-cut harvesting trials at Lunate Creek, in wet-belt forests of the upper Fraser River Valley. (photo M. Geertsema).

Among questions that are being posed in this regard: Are some old-growth forests more valuable than others (eg. antique forests), in terms of preserving canopy biodiversity and as potential candidates for protection? Can forest harvesting be adapted using partial-cut harvesting techniques to retain elements of canopy structure required by old-growth dependant organisms and minimize edge effects in adjacent unharvested stands?

Antique forest dependant lichen Nephroma helveticum (photo by Anna L. Roberts)Many gaps remain in our knowledge of canopy biology in wet-belt forests. Little is known, for instance, about the diversity or ecological role of insects (eg. spider guilds) within wetbelt forests. Further, basic information on many aspects of ecosystem function, such as canopy nutrient cycling, for instance from lichenized nitrogen fixation, remains largely unknown within the interior wet-belt forests.



Above: Antique forest dependant lichen Nephroma helveticum (photo by Anna L. Roberts)

 
 

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Canopy biologist at UNBC using single-rope climbing techniques to carry out lichen biodiversity studies in canopy of cedar-hemlock forest.
Canopy biologist at UNBC using single-rope climbing techniques to carry out lichen biodiversity studies in canopy of cedar-hemlock forest.

 
 
 
 
 

Measurements of canopy microclimate in UNBC study on old-growth wet-belt cedar-hemlock forests.
Measurements of canopy microclimate in UNBC study on old-growth wet-belt cedar-hemlock forests.

 
 
 
 
 

Pendulous mats of the hair lichen Bryoria in the upper canopy of a cedar-hemlock forest.
Pendulous mats of the hair lichen Bryoria in the upper canopy of a cedar-hemlock forest.

 
 
 
 

Collema (a gelatinous cyanolichen) growing in the drainage track of a large Poplar.
The canopy lichen Lobaria retigera can be found in antique forest stands within BCs inland wet temperate rainforest and in BCs coastal rainforests. It also occurs in rainforests of New Zealand, Queensland (Australia), and Papau New Guinea.

 
 
 
 

Antique forest stand located within a sheltered small side-valley tributary of the Upper Fraser River (photo M. Nash).
Antique forest stand located within a sheltered small side-valley tributary of the Upper Fraser River (photo M. Nash).

 
 
 
 

Canopy enclosures are being used to study lichen growth rates in studies conducted at UNBC.
Canopy enclosures are being used to study lichen growth rates in studies conducted at UNBC.

The University of Northern British Columbia