Boreal moss communities: succession and implications for establishment after fire in Alberta’s spruce-dominated forests Progress Report, Year 1 (April 2003) By Michael Simpson and Dr. M.R.T. Dale INTRODUCTION This report describes activities funded through Year 1 of the Chisholm-Dogrib Fire Research Initiative. It includes an outline of these activities, the methods used, preliminary results and a brief analysis of these results. The report will conclude with an outline of activities planned for Year 2. Two projects occupied Year 1: (a) the commencement of a survey of species of moss and site characteristics within 2 stands burned in the Chisholm fire of 2001, and (b) laboratory experiments comparing the probability of germination and seedling survival of selected vascular plant species on burned feather moss material and mineral soil. METHODS Biotic and abiotic surveys of two stands burned in the Chisholm fire: This survey was part of a longer term study to describe post-fire successional changes in boreal moss communities in Picea glauca-dominated boreal forests in central Alberta. The Chisholm sites represent an early-successional scenario. Older stands will be surveyed over the next 2 summers. Sites at Chisholm were selected on the basis that each had a pre-fire tree species composition of at least 80% Picea glauca, pre-fire crown closure of 51-70% and an average tree height of 20-25 m (data from Canadian Forestry Service). Both sites were within 7.5 km of Chisholm town site. Site 1, designated Chisholm Main Road (CMR), was approximately 0.5 km south of the main unpaved road to Chisholm. The stand was bordered on two sides by stands of burned Picea mariana, on one side by a dirt road on which salvage logging activities were proceeding, and on one side by a stand of burned P. glauca that was subsequently salvage logged. Site 2, designated Chisholm Back Road (CBR), was approximately 3 km north of the secondary unpaved road to Chisholm (north of the main road). The stand was bordered on one side by a cut line, which was substantially overgrown by herbaceous plants, and on all other sides by P. glauca-dominated woodland that graduated into P. glauca-Populus sp. mixed wood on the north side. Within each stand I marked out a 50 m2 plot in an area that I considered to be representative of the stand in terms of understory vegetation and structural components. I then subdivided this plot into 10 m x 10 m subplots to allow for restricted randomised sampling. For data recording, I used a 0.5 m x 0.5 m quadrat subdivided into 25 10 cm x 10 cm sub-quadrats. Four quadrats were surveyed at randomly located points within each subplot, giving a total of 100 quadrats and 2500 subquadrats per plot. The variables I recorded are given in Table 1. Analysis of moss data is in progress. I performed a provisional analysis of litter data from a random subset of subquadrats from each plot with descriptive statistics using Microsoft Excel v.10 (Microsoft Corp. 2002), and SPSS for Windows v. 11.5 (SPSS Inc. 2002). Preliminary analysis of a subset of the data on other plants (including vascular plants and
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liverworts) produced a provisional species list for each plot, and, for CBR only, the percentage of quadrats within the subset occupied by each species. Aerial diaspore sampling: This experiment was part of a longer term study to test the hypothesis that differences in relative cover of selected species over successional time is not due to changes in their relative establishment from the diaspore rain. I located 3 50 m transects at 12.5, 50.0 and 37.5 m distance along one plot boundary. At 0 m and every 5 m thereafter along each transect (total: 11 plates per transect), I placed 1 open 100 mm diameter Petri plate containing an agar mixture taken from Kimmerer (1991). At 0 m and every 10 m along each transect, I also placed 1 unopened agar plate (total: 6 per transect) to test for pre-contamination. Six unopened plates that were not removed from the bags in which the plates were transported to the site were also set aside as controls. This exercise was conducted on 11 July and 29 August. At Plot 1, plates were exposed for 6.5 – 7 hours on both occasions. At Plot 2, plates were exposed for 6.5 hours on the first occasion and only for 5.5 hours on the second due to rain. When exposure times were complete, lids were put on open plates and all plates were sealed in air-tight bags before being placed in a cooler for transport. On both occasions, plates were placed in a growth chamber not more than 24 hours after exposure. Growth chamber conditions were: day temperature 24oC; night temperature 10oC; RH 75%; lights on at 6.00 am with light intensity of 250 mE s-1 m-2; lights off at 9 pm. One week after plates were placed in the growth chamber, counting of emerged protonemata began and continued until all plates had been examined. Data were analysed descriptively using Microsoft Excel v.10 (Microsoft Corp. 2002). Seedling survival on burned moss: This experiment was conducted by a student, Nyja Thordarson, under the supervision of the Principal Investigator, Dr. Mark Dale, and myself. It was designed to test the hypothesis that a covering of burned feather moss will reduce the establishment potential of some vascular plant species in the early stages of post-fire succession because a lower percentage of their seedlings will survive on this substrate than on mineral soil. Five boreal plant species were selected as study species on the basis that they are common in central Alberta, produce abundant seeds, and seeds were readily obtainable. The species were Larix laricina, Picea glauca, Petasites palmatus, Geranium bicknellii and Viola adunca. Both G. bicknellii and V. adunca were subsequently withdrawn from consideration due to low germination. Seeds were pre-germinated in 60 mm Petri plates on one sheet of Whatman #1 filter paper moistened with 2 ml distilled water. Seedlings were considered germinated when the radical tip could be seen to have emerged from the testa. After germination, 10 seeds of one of the study species were randomly allocated to 20 4-inch pots of each of 3 substrate treatments: mineral soil, burned feather moss material, and sub soil extracted from beneath burned moss. This procedure was repeated for each species (4 species x 10 seedlings x 3 substrates x 20 replicates per species). Because of poor germination, only 7 pots of each treatment could be prepared for Petasites. Pots were randomly distributed among trays and placed in a growth chamber with conditions as given above. Pots were watered every 3 days and trays were rearranged after watering. Seedling survival was recorded after 4, 10 and 14 weeks. At 14 weeks shoot length and shoot biomass of all survivors were recorded. After harvesting, the pH of 7 randomly selected pots of each substrate was recorded using litmus paper and converted to estimated H+ concentrations. 2
All substrates were collected in October, 2002, from within the boundaries of the House River fire. The sub soil treatment was used to try to separate the effects of soil from the effects of burned moss. When transferring material to pots, an attempt was made to maintain its vertical structure so that burned material remained on the surface. Root length and total biomass could not be recorded because roots could not be extracted from some material. Survival was compared between treatments and counting dates with a goodness of fit test using SPSS for Windows v. 11.5 (SPSS Inc. 2002). Analysis of shoot length and shoot biomass data is in progress. Seed germination on burned moss: This experiment was also conducted by Nyja Thordarson under the supervision of the Principal Investigator, Dr. Mark Dale, and myself. It was designed to test the hypothesis that a covering of burned feather moss will reduce the establishment potential some vascular plant species fewer seeds will germinate on this substrate than on mineral soil. In order to be able to relate the results of this experiment to the seedling survival study described above, 3 of the same species were used: L. laricina, Picea glauca and Petasites palmatus. Linum lewisii was substituted for G. bicknellii and V. adunca because of the low germination of these species in the seedling survival study. Four seeds of each of the study species were sown in each of 144 4 cm2 plastic pots containing one of the 3 substrate treatments used in the seedling survival study. The smallest separable unit into which pots could be divided was 6 pots. Each 6-pot unit contained only one treatment. Seeds were sown such that a row of 3 pots in a 6-pot unit contained one species, and the adjacent row contained a different species. L. lewisii was sown adjacent to P. palmatus, and L. laricina adjacent to P. glauca. Hence, randomization between treatments and species was restricted. However, units were randomly distributed among 8 trays. Pots were watered with distilled water at the start of the experiment and trays were covered with plastic to maintain humidity. Watering was repeated once a week thereafter. Units were rerandomized among trays after each watering. With the commencement of germination, the number of new germinants of each species was recorded daily. Germinants were marked with toothpicks to prevent recounting. Material for each of the treatments was collected with that used in the seedling survival study. Analysis of data is in progress. PRELIMINARY RESULTS Biotic and abiotic surveys: Provisional species lists from each of the surveyed plots are given in Tables 2 and 3. Twentyfive species have been positively identified from the first plot, and 32 species from the second plot. Twenty-one species were recorded in both plots. The most frequently recorded species in the analysed subset of subquadrats (n=600) from CBR were Equisetum scirpioides, which occurred in 62% of subquadrats, Equisetum arvense (42%) and Marchantia polymorpha (37%). Twenty-one species were found in less than 10% of subquadrats. These data are not yet available for CMR. Five species of moss have been positively identified from CBR and 4 from CMR. Observations suggested that Ceratodon purpureus was the most common moss in both plots and C. purpureus and Bryum argenteum were the species most commonly found not in contact
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with other mosses. Colonies of all species were never extensive, and where species grew together boundaries between them were diffuse. Litter was recorded as belonging to one of the 10 categories given in Table 4. In the subset of subquadrats analysed from CMR the most common litter category was Twigs (Figure 1). Twigs comprised 50% or more of the litter present in 77% of subquadrats. The next most common category was Herbaceous and deciduous leaves (29%). Every other litter type was recorded in less than 4% of subquadrats. Twigs was also the most common litter category in the subset of subquadrats analysed from CBR. It comprised 50% or more of litter present in 52% of subquadrats (Figure 1). The next most common category was dry matted organic material. This material was characterized as being composed of thin, highly intertwined roots or fungal hyphae with a woody texture, spongy consistency and low moisture retention. It comprised 50% or more of litter present in 50% of subquadrats. Herbaceous and deciduous leaves (12%) and coniferous needles (12%) were the only other categories that were recorded in more than 10% of subquadrats. In CMR litter covered >50% of a subquadrat in 35% of cases and >75% in 17% of cases. In CBR litter covered >50% of a subquadrat in 50% of cases and >75% in 35% of cases (Figure 2). The most frequent litter depth category was 1-10 mm in both plots (63% of subquadrats in CMR, 66% in CBR) (Figure 3). Aerial diaspore sampling: An overall mean number of protonemata was calculated for each plot and each sampling date from all exposed Petri plates regardless of within-plot location (transect or distancealong-transect). A 2-tailed t-tests showed that for both July and August there was a highly significant difference between plots (t=-8.040, df=34.29, P<0.001; t=-2.992, df=33.15, P<0.005). For CMR but not CBR there was a highly significant difference in mean protonemata counts between July and August (2-tailed t-test, t=--5.988, df=64, P<0.001; t=1.118, df=55.82, P=0.268). Variances were unequal in all comparisons except between July and August for CMR. No other transects showed significant differences in either plot. Figure 4 shows the distribution of protonemata counts along each transect in each plot. Further analysis on this data is in progress. Seedling survival on burned moss: Petasites palmatus: P. palmatus showed a high short-term germination rate, but stopped germinating altogether before enough seedlings were produced for transplant. Additional seeds were subsequently sown but none germinated. Survival was poor on all substrates. After 4 weeks, survival on mineral soil was 16%, burned moss 10% and sub soil 6% (Figure 5(a)). After 10 weeks, seedlings were surviving only on mineral soil (14% of seedlings planted) (Figure 5(b)), and there was no survival on any substrate after 14 weeks (Figure 5(c)). Of the 16% of seedlings that were surviving on mineral soil after 4 weeks, 87.5% survived for 10 weeks but none were alive after 14 weeks (Figure 6). Larix laricina: A 3-way Pearson Chi-Square comparison of the proportion of transplanted seedlings surviving at each count date showed very highly significant differences between treatments (Table 5). Post-hoc 2-way Pearson Chi-Square comparisons showed very highly significant differences between mineral soil and sub soil, mineral soil and burned moss, and sub soil and burned moss after 4, 10 and 14 weeks (Table 5). A 3-way Pearson Chi-Square comparison of the proportion of transplanted seedlings surviving on each substrate showed very highly significant differences between count dates (Table 6). Post-hoc 2-way Pearson 4
Chi-Square comparisons showed that the proportion surviving significantly decreased between 4 and 10 weeks, but not between 10 and 14 weeks (Table 6). Of the 51.0% of seedlings that were surviving on burned moss after 4 weeks, 43.8% survived for 10 weeks. Of these, 89.4% survived for 14 weeks (Figure 6). The same trend was observed in the other treatments, but differences in percent survival between dates were less pronounced. Picea glauca: A 3-way Pearson Chi-Square comparison of the proportion of transplanted seedlings surviving at each count date showed a significant difference between treatments only at 14 weeks (Table 5). Post-hoc 2-way Pearson Chi-Square comparisons showed a highly significant difference only between mineral soil and burned moss (Table 5). A 3-way Pearson Chi-Square comparison of the proportion of transplanted seedlings surviving on each substrate showed a significant difference between count dates only for burned moss (Table 6). A post-hoc 2-way Pearson Chi-Square comparison showed that the proportion surviving was significantly different between 4 and 10 weeks, but not between 10 and 14 weeks (Table 6). Of the 72.0% of seedlings that were surviving on burned moss after 4 weeks, 84.9% survived for 10 weeks. Of these, 91.8% survived for 14 weeks (Figure 6). The same trend was observed in the other treatments (Figure 6). There were no significant differences in mean H+ concentration between treatments (one-way ANOVA, F2,18=1.659, P=0.218) (Table 7). DISCUSSION The two field plots showed differences in several characteristics. However, the species composition of mosses was largely the same. From observation, it appeared that the moss with the greatest cover in both plots was Ceratodon purpureus, a common species of waste ground and disturbed sites. There appeared to be high relative cover also of Funaria hygrometrica, which is typical of recently burned ground. All of the species identified were acrocarpous and widely recognised as early successional annuals or short-lived perennial colonists or fugitives (sensu During 1979). Leprobryum pyriforme was not identified in CMR. However, the surveying protocol covered only 1% of each 50 m x 50 m plot, so its presence cannot be ruled out. Moreover, a combination of unfamiliarity with this species in the field, and the considerable morphological variability of other species, particularly Ceratodon, may have led to some misidentification. These explanations might also account for a failure to record some other early successional species, such as Pohlia nutans which would be expected in these circumstances. Observations indicated that CBR had considerably higher cover of mosses than CMR. The high percentage of quadrats occupied by Marchantia polymorpha and Equisetum sp., in CBR suggests that this plot had a history of being slightly moister than CMR. Gravimetric soil moisture readings taken late in the season support this proposition (data not presented here).It was not explicitly apparent, however, perhaps due to the unusually dry season. Tree diameter at breast height was also lower in this plot (data not presented here). Marchantia colonies were much larger and were often observed growing in isolation, in contrast to those in CMR, which were almost always observed growing in contact with moss colonies. In both plots Ceratodon purpureus and Bryum argenteum were the only species frequently found growing in isolation from other species, perhaps suggesting that they were better able to tolerate exposure. All species were usually found growing in mixed colonies. Higher moisture level in CBR might also account for the lower severity of burning this plot apparently experienced. All trees within the stand were dead, but a couple bordering an adjacent cut-line retained some dead needles. Moreover, a large proportion of the forest floor was covered by dry matted organic material, often to a depth of over 5 cm. This 5
material appeared to be much less frequent in CMR, and was never recorded in any subquadrats in that plot. Mosses were rarely observed to grow on dry matted organic material or the surfaces of fallen burned logs. Surface pH of these substrates was not recorded, but may not have been conducive to colonization. Also, the bark of the latter had often become detached, leaving a smooth rounded surface that would not readily retain propagules. In CBR, at least, mosses appeared to be most lush where there was a high proportion of ash in the substrate. In both sites the high proportion of twigs (many of which were charred) in litter indicates that fine woody debris could be an important source of nutrients in burned plots across a range of burn severities. This topic will be further explored in the integrated project being undertaken by myself, Barb Kishchuk, at Natural Resources Canada, and Tyler Cobb, at the University of Alberta Department of Renewable Resources, as part of this research initiative. Populus sp. regeneration was much greater in CBR, but a higher cover of Populus was not evident in the canopy. This also might reflect reduced mortality of below-ground regenerative structures at this site, possibly as a result of the lower average depth of burn. Assuming that protonmeta counts are representative of spore dispersal, Figure 4 indicates that dispersal was highly random across both plots in July and August. The between-month difference in the overall mean number of protonemata in CMR might have been due to an increase in the number of mature sporophytes later in the season. Funaria capsules were abundant and matured towards the end of July. However, it is not clear why this pattern was not reproduced in CBR, where Funaria appeared to be more frequent. It seems unlikely that contamination by rainwater inhibited germination, although algal growth was most extensive in some rain-contaminated plates. The higher overall means for CBR might be explained by the higher apparent cover of mosses in this plot. The poor performance of Petasites in the seedling survival study suggests that although this species produces huge numbers of seeds, establishment by this mechanism is rare. Rhizomes protected from fire beneath the soil surface might be more important for regeneration. Preliminary data from the seed germination study, where Petasites failed to germinate on any substrate, support this hypothesis. Forb seeds appear to have done particularly badly on burned moss (data analysis in progress). Petasites seeds may require constant saturation, like that they received in the Petri-plates during pre-germination. Low survival in the seedling study was probably partly due to difficulties in transplanting this species. Radicals often became detached from the cotyledons, and many germinated seedlings were discarded if this was evident. Because the early roots are practically invisible to the naked eye, however, this was not always clear. A test using Sphagnum moss but not included in the final analysis suggests this may be only a partial explanation, however. Several seedlings transplanted into this substrate survived until the end of the experiment. Petasites is often seen growing out of burned over Sphagnum hummocks after fire. Larix laricina did particularly poorly on burned moss. This species prefers wetter habitats and seedlings may not be well adapted to surviving on a substrate with poor absorptive capacity. There was no significant difference in pH between substrates at the end of the experiment, but no reading was taken in the first 4 weeks, when mortality was highest for this species. On the basis of this evidence, it can be expected that the distribution of Larix might be restricted to areas where fire has been sufficiently severe to remove any surface covering of burned moss. The highest proportion of Larix seedlings survived on sub soil extracted from beneath burned moss, which suggests that soil from which moss has been removed by fire might be most conducive to the establishment of this species. The results of 6
the experiment do not suggest why this might be so. The notable features of this soil that distinguished it from surface mineral soil were an absence of surface charcoal and a higher sand content. It is not clear why the percentage of living seedlings that subsequently died was higher between 4 and 10 weeks than in earlier and later periods. Unlike L. laricina, Picea glauca showed the same establishment potential on all of the substrates tested. Moreover, the number of seedlings alive as a percentage of those transplanted was highest on mineral soil, not sub soil, at every count date. Percent survival was always lowest on burned moss, but only significantly so when compared with mineral soil at 14 weeks. The proportion of seedlings surviving between dates increased throughout the experiment in accordance with expectations. The vulnerability of seedlings apparently decreased with increasing maturity. Picea, however, grew more slowly than Larix. The significant difference in percentage survival between top soil and burned moss at 14 weeks for the former might have been due to the inability of some large individuals to sustain themselves because their roots had still failed to reach the mineral soil FUTURE ACTIVITIES Summer 2003: Field surveys of mosses, vascular plants and site characteristics will resume in May. Field experiments will be set up under conditions representing different successional stages to compare the establishment potential of 3 species of moss (Pleurozium schreberi, Ptilium crista-castrensis, Ceratodon purpureus), and to sample the diaspore rain and soil diaspore bank. The surveying protocol will be amended to facilitate the completion of more sites. The seed germination and seedling survival experiments will be repeated in the field. An experiment to test the effects of mosses and saproxylic beetles on the decomposition rate of woody debris will be set up in co-operation with Barbara Kishchuk and Tyler Cobb as part of an ongoing integrated research project. Fall 2003-Spring 2004: Experiments designed to test the effects of light and desiccation on fragment germination, protonema survival and early gametophyte growth of 3 species of moss will be set up in a growth chamber at the University of Alberta. Summer 2004: Species surveys and the moss establishment, diaspore sampling and woody debris field experiments will be completed. LITERATURE CITED During, H.J. 1979. Life strategies of bryophytes; a preliminary review. Lindbergia 53:2-18. Kimmerer, R.W. 1991. Reproductive ecology of Tetraphis pellucida II: differential success of sexual and asexual propagules. Bryologist 94: 284-288.
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