Distribution of Maidenhair Fern in a Cedar Grove (Site Visit 2)

Blog Post 3: Distribution of Maidenhair Fern in a Cedar Grove (Site Visit 2)

SV2 Verona

Introduction:

Before visiting the backyard burn scar for the second time, I decided to focus on the unburned (but for five burn piles) western redcedar grove beginning at the toe of the slope. This would be the southern half of the initial project area.

Upon entering the grove, I realized that my initial prediction about higher relative abundance of northern maidenhair fern (Adiantum pedatum) immediately downslope of a burn pile had little merit. It was present in similar densities throughout the grove. I also quickly identified the other fern species using a field guide; it is western sword-fern (Polystichum munitum). While the primary focus of my study will revolve around the maidenhair fern, towards the end of the site visit I began to wonder whether maidenhair and sword-fern are mutualistic or competitive. I observed that maidenhair was perhaps present in greater relative abundance than sword-fern near the burn piles – so sword-fern is an important aspect of the study, too.

Highlights of the three observed gradients:

1. Topography Gradient. Maidenhair density did not seem to vary much relative to aspect (varying from SW to SE, southern aspect of low-to-moderate slope). Slope percentage did not seem an immediate process of maidenhair pattern, although it should be noted maidenhair was not present on the slight “knob” in the middle of the grove. This led me to wonder if maidenhair has a preference for concave, therefore water-funneling, slopes over convex ones.
2. The Log. In continuing the potential preference of maidenhair for “microdrainages” of moister soil, a half-decomposed, branchless log was observed. It was ~10m in length and lay about 10° from the fall line of the mellow slope. Maidenhair was only present on the eastern side, or side where the log may have funneled water relative to its blockage of the fall line.
3. Sunlight Gradient. Maidenhair fern was not observed in the upper, northern, half of the project area. This is the old burn scar, which I have learned occurred ~5-7 years ago. It is still a very open stand with a few live grand firs, standing dead, and copious brush. It appears too sunny for maidenhair, a shade-tolerant species. This observation led me to focus more on the cedar grove in the southern half of the unit. Interestingly, maidenhair persisted in a small meadow (~90m in diameter) in the far SE side of the cedar/fir grove.
4. Burn Piles Gradient. There are five total burn piles in the cedar grove. One is alone and contains half-burned large logs. The other four are in two groups of two, with the separation between the two in a group ~2-4 meters. Initial observation suggested no discernible change in vegetation amount relative to proximity to burn pile. A final observation, however, suggests a difference in the quantity of maidenhair fern relative to sword-fern near piles.
5. Maidenhair and Sword-fern – Mutualistic, or Competing? The burn piles suggested that maidenhair out-competes sword-fern immediately downslope of a pile. Sword-fern and maidenhair often grow near or amongst each other. This is present as either individual clumps of maidenhair fronds and sword-fern fronds, forming “bush-like” clusters, or with smaller maidenhair fronds growing beneath mature sword-fern fronds. In the latter instance, the maidenhair fronds were noticeably smaller than in mature clumps. Downslope of burn piles, however, there appeared to be a preference towards maidenhair.

Patterns, processes, hypotheses, and predictions:

Based on my varied observations, need for literature review, and the early stage of the project, I elected to postulate two hypotheses loosely based on competition between maidenhair and sword-fern (perhaps literature will reveal that these two species are mutualistic instead). Currently, I am keener to study the second hypothesis, although this may change with available literature.

1. Hypothesis 1: Maidenhair fern is better adapted to moist soils than sword-fern.
   1. Patterns: Maidenhair fern and sword-fern often grow together in western redcedar forest. Maidenhair fern may be observed relatively more as a population percentage, and with greater growth, in concave slopes and areas of water catchment. Sword-fern may found more on concave/drier slopes.
   2. Processes: The abiotic micro-topography of an area affects its soil moisture. Plant species differ in their soil moisture preferences.
   3. Prediction: The proportion of maidenhair fronds is higher in topographical concavities.
   4. Response variable: The percentages of frond densities of maidenhair fern and sword-fern relative to total frond density. A continuous variable.
   5. Explanatory variable: Concave or convex slope relative to ability to moisten soil. A categorical variable.
   6. Statistics required: ANOVA.
2. Hypothesis 2: Maidenhair fern has either a preference for the nutrients present in redcedar burn piles, or has a faster uptake mechanism for nutrients necessary for both it and sword-fern.
   1. Patterns: Maidenhair fern seems to appear in greater relative abundance immediately downslope or adjacent to one-year-old burn piles of western redcedar.
   2. Processes: Burn piles are known nutrient cyclers. Maidenhair fern either has a preference for their available nutrients, or is able to uptake them faster than sword-fern.
   3. Prediction: The proportion of maidenhair fronds relative to a total community including sword-fern, is higher adjacent to burn piles than in the general area of the cedar grove.
   4. Response variable: The percentages of frond densities of maidenhair fern and sword-fern relative to total frond density. A continuous variable.
   5. Explanatory variable: Presence of burn pile (categorical), or perhaps distance from burn pile (continuous).
   6. Statistics required: ANOVA or regression.

Concluding thoughts:

While mutualism may be present, the growth of mature maidenhair clumps, in absence of sword-fern, in the sunnier meadow of the cedar grove suggests that maidenhair needs more sunlight than is present underneath a sword-fern frond. This would potentially put the two species in competition for sunlight, rather than in a mutualistic relationship. Perhaps maidenhair fern and sword-fern are competitive in other regards, whether soil moisture or proximity to a nutrient source (burn pile).

SV2 Verona