Blog Post 5. Design Reflections

My initial field data involved the identification of lichen genera, and the collection of presence-absence data for epiphytic lichen growing on the trunk bark of 4 different tree families (Pinaceae, Cupressaceae, Aceraceae, Betulaceae) within the south western region (10-19m elevation) of Stanley Park. Individual tree trunks from each family were sampled at sites systematically, along a transect (Lees Trail). A total of 5 replicate stations along Lees trail were chosen based on accessibility, at regular intervals of approximately 150 m to span the entire ~ 1km long transect. At each point along the transect, a random number of steps were taken into the forested area (>10m) and one individual from each tree family (if available) was selected for observation. The lichen genera present on the tree trunk (< 1.4m height) were identified (using a guide), and the presence/absence was recorded for each tree.

Did you have any difficulties in implementing your sampling strategy? If yes, what were these difficulties?

I had difficulties finding trees within the deciduous families (hardwood/angiosperm) Aceraceae and Betulaceae. Often there was only one individual of either  family at each station, and coniferous members of the Pinaceae and Cupressaceae famiies always dominated the stand. Additionally, all vine maples (family Aceraceae) were much younger than the other trees measured, making it difficult to compare lichen data across tree families.

It was difficult to differentiate Hemlock and Douglas fir tree species, and they often had the same lichen genera present on their bark. I solved this in the field by grouping observations by tree family. It was difficult to identify lichen in the field, and the differentiation between Cladonia sp. (squamulose) and Platismatia sp. (foliose) lichen had to be done using photographs and physical samples upon return from the field.

It was time consuming to photograph and identify lichen on 3-4 trees, per replicate station. A recent seasonal change in weather has made spending time in Stanley Park more difficult due to the increased amount of rain.

Was the data that you collected surprising in any way?

I found it surprising that all tree families measured, had visible dust lichen (Lepraria sp.) except for the two maple trees (family Aceraceae). Western Red Cedars seemed to have the most diverse genera of lichen present on the trunk bark.

Squamulose lichen was present with and without secondary thallus structures (podetia). The Cladonia genus is known to develop cup-shaped fruticose podetia. Cladonia sp. (identified as Cladonia ochroclora ) had developed visible fruticose podetia (secondary thallus) more frequently on Western Red Cedar (family Cupressaceae) and Alder (family Betulaceae) compared to Douglas Fir and Western Hemlock (family Pinaceae).

Do you plan to continue to collect data using the same technique, or do you need to modify your approach? If you will modify your approach, explain briefly how you think your modification will improve your research.

I will continue selecting replicates systemically along the length of each trail. However, I plan to change my method by selecting trees along the very edge of the trail, to reduce any potential confounding edge- effects on lichen distribution. This type of sample selection will improve my research because replicates will be more comparable. Overall, by selecting replicates at the very edge of the trail (stand), the replicate data will be more comparable due to the potentially reduced confounding effects of location within the stand, aspect, humidity, and differential exposure to radiation.

I plan to sample 10 Western Red Cedars (Cupressaceae) and 10 Douglas fir or Western Hemlock (Family Pinaceae), within each sub-area. I plan to sample trees randomly along each trail transect, using a random number generator to select a number of steps greater than 10, but less than 20. This will maintain an aspect of random sampling in my sample selection method.

I will maintain the same data collection technique; presence absence of lichen genera below 1.4m trunk height, on all aspects of the tree trunk (north, east, west, and south- facing sides). To help identify lichen genera in the field, I plan to collect unit shape category for each replicate. I will record whether the lichen is: powdery, crustose, squamulose, foliose, or fruticose in nature. This adds a categorical morphological response variable, and also provides an alternative identification method if the genera cannot be resolved in the field.

I plan to start collecting the circumference at breast height of every tree sampled, to approximate tree age. Age will represent a potential biotic predictor variable. I will also note a description of the ground cover at each site, ranging from soil and decaying organic matter (ie. branches, woody debris, and leaves/needles) to dense vegetation (ie. understory and young trees).