Moss-driven facilitation promotes species coexistence in Andean páramo peatlands

doi:10.21203/rs.3.rs-6743870/v1

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Moss-driven facilitation promotes species coexistence in Andean páramo peatlands

https://doi.org/10.21203/rs.3.rs-6743870/v1

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Andean páramo peatlands are fragile high-altitude ecosystems shaped by frequent fog, intense solar radiation, strong diurnal temperature fluctuations, water saturation stress, and low nutrient availability. These harsh conditions make them ideal systems for studying plant–plant facilitation. We examined a peatland in Chingaza National Park (Colombia) to assess how mosses and species associations influence microclimate, water dynamics, and soil nutrients. At the peatland scale (820 m²), we recorded 65 species and 5,368 individuals; 89% of individuals and 54% of species occurred on moss-dominated hummocks, which covered only 29% of the area. These hummocks, primarily formed by Chusquea tessellata, Sphagnum magellanicum, Kurzia capillaris, Breutelia squarrosa, and S. cuspidatum, showed strong species co-occurrence (χ² = 11091.77, p < 0.001), suggesting facilitative interactions drive community structure. Across 170 hummocks, we found 5,299 species interactions and identified nine non-vascular species as potential facilitators. Generalized linear models showed that non-vascular richness significantly predicted vascular plant diversity, especially when interacting with hummock area (AIC = 654.95). Mosses integrated structural and abiotic influences, regulating water capture, infiltration, and nutrient dynamics. Species differed in their effects: K. capillaris and B. squarrosa enhanced soil nitrogen, phosphorus, and carbon more than S. magellanicum. Upper moss layers promoted water input, while lower layers retained moisture and buffered nutrient availability. Our results show that moss-dominated hummocks act as facilitative microhabitats, enhancing biodiversity through microenvironmental modification. These results underscore the role of moss-driven facilitation in shaping species-rich microsites, offering key insights for biodiversity conservation and the restoration of Andean peatlands.

Andean páramo

peatlands

ecological facilitation

mosses

plant–plant interactions

soil–water dynamics

Facilitation—an ecological interaction in which at least one species benefits without harming the other—plays a critical role in shaping plant communities (Stachowicz, 2001). This interaction is widespread and has been well documented across diverse ecosystems, including deserts, tundra, alpine zones, and marshes (Callaway, 2007; Brooker et al., 2008). In many of these systems, facilitation emerges when "nurse" species mitigate environmental stress by buffering temperature extremes, reducing desiccation, intercepting moisture, retaining nutrients, or improving substrate structure.

Over the past two decades, a growing body of empirical evidence has highlighted facilitation as a key mechanism sustaining biodiversity in stressful environments (Michalet et al., 2006; Brooker et al., 2008). A significant part of this effect stems from niche construction—the process by which organisms actively modify their surroundings in ways that benefit other species, especially when niche differentiation is pronounced (Ardichvili et al., 2025).

Building on this framework, Hacker and Gaines (1997) proposed that facilitation promotes biodiversity by enhancing species survival under stress, fostering ecosystem resilience, and enabling novel interaction networks. From this perspective, facilitation is not merely a secondary outcome of coexistence but a key driver of community structure, diversity, and stability in extreme environments (Brooker et al., 2008).

Páramos—high-elevation tropical ecosystems of the northern Andes (ca. 3,000–5,000 m)—are biodiversity hotspots with remarkable species richness and endemism (Londoño et al., 2014; Peyre et al., 2018, 2021). Brooker et al. (2008) proposed that facilitation plays a key role in community assembly under stressful conditions, such as high mountain environments. The high plant diversity in these systems cannot be fully explained by environmental filtering and competition alone, and emerging evidence highlights the importance of facilitation in shaping páramo plant communities. Facilitation by páramo shrubs has been documented, particularly in species of Hypericum (Ayarza-Páez et al., 2022; Bueno & Llambí, 2015; Farji-Brener et al., 2009). Shrub canopies mitigate abiotic stress by buffering temperature extremes, reducing solar radiation, and increasing ambient humidity, enhancing seedling regeneration. Similarly, nurse cushion plants (Llambí et al., 2018) and mosses (Smith, 1984) improve microsite conditions by accumulating biomass and nutrients, stabilizing soils, and protecting seedlings from frost, wind, and herbivory. Studies from other tropical Andean ecosystems indicate that positive interactions involving cushions and mosses are crucial for plant colonization under high-stress conditions (Anthelme et al., 2021; Zimmer et al., 2018). In the periglacial zones of both Patagonia (Gavini et al., 2020) and the páramo (Llambí et al., 2021; Pérez, 1997), biological soil crusts formed by mosses and lichens enhance substrate stability and water retention, facilitating early plant establishment. These findings suggest that mosses may play a central role in ecological facilitation, particularly in wet environments dominated by non-vascular plants.

Peatlands are wetlands dominated by mosses, particularly Sphagnum, where saturated and acidic conditions promote organic matter accumulation but limit nutrient availability, thereby promoting oligotrophic conditions and restricting vascular plant establishment (Aldous, 2002; Heijmans et al., 2001; Laberge et al., 2015). Many peatlands exhibit a characteristic microtopography of hummocks and valleys (previously referred to as hollows), which differ in moisture and nutrient availability (Andrus et al., 1983; Rydin & Jeglum, 2013). Hummocks are elevated microforms in peatlands, mainly formed by peat mosses, which create drier and more aerated conditions than adjacent hollows, influencing species composition and ecosystem processes (Rydin & Jeglum, 2013). This microtopographic heterogeneity supports niche partitioning among Sphagnum species (Gong et al., 2020; Mulligan & Gignac, 2002; Rydin, 1993). Studies by Rydin (1993) and Gong et al. (2020) show that Sphagnum species coexist along vertical gradients from valleys to hummocks by occupying distinct niches defined by moisture-related physiological traits, such as water retention and desiccation tolerance. For example, Sphagnum fuscum commonly occurs on drier hummocks, whereas S. balticum and related species are more frequent in wetter depressions, though they tend to decline under desiccation stress (Rydin, 1993). These habitat preferences help reduce direct competition and foster species coexistence through trait-based niche partitioning (Gong et al., 2020; Rydin, 1993). Beyond their spatial distribution, Sphagnum mosses actively modify their environment, creating microhabitats that facilitate the establishment and persistence of a wide array of organisms—including non-vascular plants (Albinsson, 1997), vascular plants (Heijmans et al., 2001; Laberge et al., 2015), and microbial communities (Hooper, 1981). For instance, liverworts such as Kurzia often colonize relatively stable microhabitats formed by Sphagnum in boreal peatlands (Albinsson, 1997). Microbial communities—particularly algae and cyanobacteria—also establish on Sphagnum mats, where they can influence nutrient availability and, in turn, affect interactions among vascular plants (Hooper, 1981).

Páramo peatlands have developed under high productivity conditions in the equatorial zone, resulting in substantial peat accumulation (Benfield et al., 2021). These Andean wetlands are crucial for water regulation and biodiversity conservation (Suárez et al., 2023) and exhibit greater floristic richness than their temperate counterparts (Cleef, 1981). Angiosperm assemblages display pronounced heterogeneity driven by elevation, water chemistry, and disturbance (Cleef, 1981; Suárez et al., 2023). In contrast, temperate peatlands are typically more nutrient-limited and support lower plant diversity (Baker & Boatman, 1990; Breeuwer et al., 2009). As in temperate mires, Sphagnum species often dominate in some páramo peatlands, forming hummocks and influencing nutrient dynamics, potentially explaining the occurrence of localized nutrient hotspots (Bosnian et al., 1993). Mycorrhizal fungi may mediate additional facilitative effects (Silva et al., 2023).

Despite this background, facilitation remains understudied in páramos, and even less is known about its role in peatlands. These systems are ideal for exploring how facilitation structures plant communities under extreme conditions. This study tests the premise that facilitation is a key mechanism for maintaining páramo biodiversity, with a subset of species disproportionately influencing diversity through environmental buffering. Four hypotheses are proposed: (1) Vegetation patterns in peatlands are non-random and associated with diversity-rich hummocks;(2) Hummocks offer vertical microhabitat stratification that supports species coexistence via complementary strategies;(3) Mosses mediate facilitation by modifying abiotic conditions; and (4) These mechanisms are linked to environmental variables such as temperature, humidity, nutrients (C, N, P), and water retention capacity. Hypotheses 1–2 were evaluated through spatial and hummock-scale association analyses; hypotheses 3–4 were tested using data on moss dominance, hummock characteristics (height, area, moss layers), microclimatic variables, and soil nutrient concentrations.

Study site

Chingaza National Natural Park (PNN Chingaza) is located on the eastern flank of the Cordillera Oriental in Colombia, in the northern Andes of South America (Fig. 1). Its landscape, shaped by glacial processes, features U-shaped valleys, cirques, moraines, and glacial lagoons (Vargas & Pedraza, 2004). The study site (4.51696001° N, -73.706069° W) is a high Andean peatland dominated by Sphagnum moss species, forming swamp communities that gradually transition to drier areas. Like other páramos, the site is characterized by extreme environmental conditions, including acidic and shallow soils, permanent water saturation, marked daily temperature fluctuations, high ultraviolet radiation, extreme humidity, and strong winds (Monasterio & Reyes, 1980).

The sampling site is located at 3415 meters above sea level and exhibits the characteristic microtopography of a high-Andean peatland, with well-defined hummocks, hollows, and mats (Cleef, 1981; Schmidt-Mumm & Vargas Ríos, 2012). The climate is humid, with annual precipitation ranging from 2800 to 3000 mm, and a unimodal rainfall regime marked by a short dry season from December to March (Vargas & Pedraza, 2004). Frequent fog and dew, especially during drier periods, play a key role in maintaining moisture availability (Berrones et al., 2024).

The vegetation is dominated by Chusquea tessellata, a grass species well adapted to flooded conditions. Its branching structure supports the establishment of various bryophyte species, contributing to the formation of mounds that rise above the water table. These hummocks show vertical stratification, with Sphagnum mosses prevailing in wetter sections, and other bryophytes—such as Pleurozium schreberi, Campylopus spp., and Breutelia spp.—more commonly found along the drier upper margins (Sánchez-M. et al., 1989).

Peatland-scale species associations

To analyze the spatial distribution patterns of vegetation at the peat scale, four 20 × 2 m transects, and an additional 50 × 10 m transect were established, with a total sampling area of 820 m². In each transect, all present plant species were recorded. The number of individuals of each species growing on different mosses, liverworts, and lichens was counted. Plants growing directly on decaying peat biomass or submerged in water (up to 5 cm deep) were also recorded, corresponding to open-space conditions outside the hummocks. For each individual, total height was measured from the stem base to the apex of the leaf crown, according to the growth habit.

Hummock-scale species associations

We established two 20 × 2 m transects and recorded all hummocks present to assess patterns of interspecific spatial association. A total of 170 hummocks were examined, including counts of vascular and nonvascular plants growing atop other plants. Each individual's vertical position within the hummock profile—from the water table to the canopy—was recorded to characterise vertical species distribution.

Environmental variables

Microclimatic monitoring

Temperature and relative humidity were recorded every 30 minutes over 12 days at four vertical levels within the hummock structure. Measurements were taken using HOBO dataloggers. Sensors were placed in microsites dominated by different moss and plant species at each hummock level: the basal layer dominated by Sphagnum cuspidatum (Sphcus-Basal, < 20 cm), the lower interior by S. magellanicum (Sphmage-Interior, 20–40 cm), the upper interior by Frullania convoluta (Frullcon-Interior, 40–60 cm), and the canopy by Chusquea tessellata (Chutess-Canopy, > 60 cm).

Nutrient content analysis

Composite substrate samples (n = 5 per species, total n = 25) were collected from five dominant moss species: Sphagnum cuspidatum, S. magellanicum, Kurzia capillaris, Breutelia squarrosa, and Frullania convoluta. Total carbon (Ct) was determined using the Walkley and Black method, total nitrogen (Nt) by Kjeldahl, and phosphorus (P) and potassium (K) through calcination. Analyses were conducted at the Water and Soils Laboratory of the National University of Colombia (CIER).

Water retention and infiltration rate

To assess moisture regulation by mosses, four samples per species were collected using plastic cylinders (5 cm in diameter and 5 cm in height). The infiltration rate was tested by applying water at a constant rate and recording the percolation time. Water retention was calculated from the dry and saturated weights after oven-drying (160°C, 110 min) and rehydration (50 ml water in airtight bags).

Statistical analysis

To test spatial associations between species, chi-square (χ²) tests were applied using observed counts versus expected counts based on moss cover. Expected values were calculated as the product of the total individuals by the proportional cover of each moss species. Species with expected counts < 5 were grouped as "rare species". Standardized residuals (|Res| > 2) indicated significant positive or negative associations (Greig-Smith, 1983; Valiente-Banuet & Verdú, 2007). The same method was applied to analyse the spatial pattern of hummocks, with the area estimated using an inverted cone model.

To evaluate the drivers of vascular plant richness in hummocks, generalized linear models (GLMs) with Poisson errors and a log link were employed. The response variable was vascular species richness, while the explanatory variables included non-vascular richness, hummock structural traits (height, area, moss layers), soil nutrients, and humidity and temperature ranges. Principal component analysis (PCA) was used to reduce the dimensionality of the nutrient variables. Seven candidate models (including null, additive, and interaction structures) were tested to examine the relationship between vascular richness and biotic and abiotic predictors. A full description of the model structures is provided in Appendix S1 (Table S1). Model selection was based on Akaike’s Information Criterion (AIC) and adjusted R². All analyses were conducted in RStudio (RStudio Team, 2024).

Peatland structure and species distribution

The studied peat bog exhibits a microtopography characterised by hummocks dominated by Sphagnum magellanicum, and valleys covered by mats of Sphagnum cuspidatum and Kurzia capillaris—the latter being the only species capable of persisting under waterlogged conditions (Fig. 2). The hummocks also contain a structural framework formed by Chusquea tessellata, a giant bamboo-like grass commonly found in high Andean ecosystems.

A total of 65 plant species and 5,368 individuals were recorded. Plant cover reached 91%, with Sphagnum cuspidatum being dominant. Hummocks, which covered only 29% of the sampled area, supported 89% of the individuals and 54% of all species.

A strong preference for hummock microhabitats was detected (Fig. 3, Table 1), as confirmed by a chi-squared test (χ² = 11091.77, p < 0.001). Observed and expected individual counts differed markedly: 4,618 individuals were recorded in hummocks, far exceeding the expected 1,330, while only 750 were observed in valleys, compared to an expected 3,986 (Supplementary Table S2). Standardized residuals confirmed that nearly all species exhibited positive spatial associations with hummocks and negative associations with the valley microhabitat dominated by S. cuspidatum (Table 1).

Table 1

The 20 most abundant species recorded across hummock and valley microhabitats accounted for 91.5% of all individual observations in the peatland. See Supplementary Table S2 for complete data on standardized residuals and spatial associations for all species recorded during vegetation sampling. StaRes = standardized residuals; Obs = number of observed individuals; Exp = number of expected individuals; H = hummock; V = valley. Values in **bold** indicate significant positive associations (StaRes > 2); values < − 2 indicate negative associations.
Species	Hummock Obs	Hummock Exp	Valley Obs	Valley Exp	ResEst (H / V)	Total individuals
Calamagrostis bogotensis	1114	323	179	970	135.0 / -31.4	1293
Pernettya prostrata	650	174	44	520	103.7 / -24.1	694
Melpomene flabelliformis	427	107	0	320	86.4 / -20.1	427
Sphagnum magellanicum	357	96	27	288	73.9 / -17.2	384
Puya cryptantha	311	108	121	324	54.5 / -12.7	432
Geranium lainzii	193	48	0	145	56.8 / -13.2	193
Poa sp1	151	49	44	146	39.9 / -9.3	195
Frullania convoluta	97	24	0	73	39.9 / -9.3	97
Pleurozium schreberi	79	20	2	61	35.2 / -8.2	81
Chusquea tessellata	122	41	42	123	34.4 / -8.0	164
Kurzia capillaris	113	37	33	109	34.3 / -8.0	146
Breutelia squarrosa	145	40	15	120	45.1 / -10.5	160
Vaccinium floribundum	78	22	9	65	32.5 / -7.6	87
Rhynchospora ruiziana	114	56	110	168	21.2 / -4.9	224
Sphagnum cuspidatum	60	28	50	82	16.7 / -3.9	110
Pentacalia flosfragans	43	12	4	35	24.5 / -5.7	47
Campylopus bryotropii	43	11	1	33	25.9 / -6.0	44
Plagiochila bifaria	54	14	0	40	29.6 / -6.9	54
Gentianella corymbosa	37	11	8	34	20.6 / -4.8	45
Nertera granadensis	31	9	4	26	20.2 / -4.7	35

Hummock-scale species associations

Within the 170 hummocks, we recorded 46 plant species (54.4% vascular, 45.6% non-vascular) and 5,299 species co-occurrences. Contingency table analysis identified nine non-vascular species with potential facilitative roles (Table 2). These species were associated with 100% of the vascular species and 98.8% of all individuals recorded in hummocks, and the chi-squared test indicates this pattern is not explained by chance (χ² = 4397.96, p < 0.001). Given their frequency and widespread presence, Sphagnum magellanicum, S. cuspidatum, K. capillaris, and Breutelia squarrosa emerged as key structural and functional species in hummock development and diversity maintenance.

Table 2

Observed and expected individuals (Obs/Exp) and standardized residuals (StaRes) for facilitated species (rows) and facilitators (columns) across 170 hummocks (n = 5,299). Facilitators accounted for 100% of species and 98.8% of recorded individuals. Bold indicates significant positive associations (StaRes > 2); values < − 2 indicate negative associations. Abbreviations: *Sphagnum cuspidatum* (Sphacusp), *S. magellanicum* (Sphamage), *Kurzia capillaris* (Kurzcapi), *Campylopus bryotropii* (Campbryo), *Fuscocephaloziopsis crassifolia* (Fusccras), *Breutelia squarrosa* (Breusqua), *Plagiochila bifaria* (Plagbifa), *Herbertus sendneri* (Herbsend), *Frullania convoluta* (Frullconv), and other hummock mosses (Other). Species with fewer than 50 observed individuals are grouped as “Other”, including *Alobiellopsis dominicensis*, *Breutelia karsteniana*, *Chelilolejeunea filiformis*, *Cladia aggregata*, *Cora arachnoidea*, *Hypotrachyna* sp. 1, M147a, M149, *Plagiochila rutilans*, *Pleurozium schreberi*, and *Syzigiella rubricaulis*.
Especie	Sphacusp	Sphamage	Kurzcapi	Campbryo	Fusccras	Breusqua	Plagbifa	Herbsend	Frulconv	Other	Total n_i
Calamagrostis bogotensis Obs/Exp	456/435	474/239	295/134	8/32	47/7	93/277	60/108	34/44	24/170	13/57	1504
StaRes	23.5	17.2	13.2	6.7	3.1	19.4	12.2	7.8	15.3	8.9
Pernettya prostrata Obs/Exp	337/323	384/177	222/99	2/24	41/5	60/206	22/80	26/33	14/126	8/43	1116
StaRes	19.6	14.4	10.9	5.5	2.6	16.0	10.0	6.4	12.6	7.3
Puya cryptantha Obs/Exp	144/125	148/69	98/39	0/9	29/2	10/80	2/31	1/13	1/49	0/16	433
StaRes	11.5	8.5	6.4	3.2	1.5	9.3	5.8	3.7	7.3	4.2
Melpomene flavelliformis Obs/Exp	41/111	97/61	51/34	23/8	9/2	54/71	42/27	17/11	38/43	11/15	383
StaRes	10.8	8.0	6.0	3.0	1.4	8.7	5.4	3.5	6.8	4.0
Geranium lainzii Obs/Exp	16/65	98/36	21/20	1/5	4/1	37/41	28/16	14/7	3/25	3/9	225
StaRes	8.2	6.1	4.6	2.3	1.0	6.6	4.1	2.6	5.2	3.0
Rhynchospora ruiziana Obs/Exp	70/53	48/29	49/16	0/4	11/1	3/34	0/13	2/5	0/21	0/7	183
StaRes	7.4	5.5	4.1	2.0	0.9	5.9	3.7	2.4	4.6	2.7
Gentianella corymbosa Obs/Exp	63/46	44/25	33/14	0/3	7/1	5/29	0/11	6/5	0/18	0/6	158
StaRes	6.8	5.1	3.8	1.9	0.9	5.5	3.4	2.2	4.3	2.5
Other vascular plants (n = 18) Obs/Exp	118/148	195/81	122/45	1/11	13/2	29/94	12/37	17/15	3/58	0/19	510
StaRes	12.6	9.3	7.0	3.5	1.6	10.2	6.3	4.1	8.0	4.6
Other non-vascular plants (n = 21) Obs/Exp	150/228	238/125	123/70	23/17	31/4	52/145	40/56	31/23	39/89	60/30	787
StaRes	16.0	11.8	8.9	4.5	2.1	13.0	8.1	5.2	10.2	5.9
Total	1395/1533	1726/842	1014/472	58/114	182/25	343/976	206/379	148/156	122/600	95/202	5299

Facilitation and predictors of vascular richness

Generalized linear models (GLMs) revealed that non-vascular species richness significantly predicts vascular plant richness. Model 1, which included only non-vascular richness, was highly significant (p < 2e–16, AIC = 674.83). Model 2, incorporating both abiotic and structural variables, improved the model fit (AIC = 657.82), with non-vascular richness (p = 0.027), hummock height (p = 0.0067), and area (p = 0.0109) identified as significant predictors. Model 3, which included only structural and abiotic variables, also identified hummock height, area, and the number of vegetation layers as significant predictors, had a higher AIC (660.64), indicating a less parsimonious fit.

The best-supported model (Model 4, AIC = 654.95) included a significant interaction between non-vascular plant richness and hummock area (p = 0.0239), indicating a context-dependent facilitation effect. Specifically, the positive influence of non-vascular richness on vascular plant richness was stronger in larger hummocks, where spatial structure likely enhances microsite differentiation and establishment opportunities. This pattern underscores that facilitation is not uniform across microsites but modulated by hummock size, reinforcing the role of spatial heterogeneity in shaping plant community assembly. Notably, even in hummocks with moderate non-vascular richness, vascular richness increased more steeply with hummock area, suggesting that facilitative effects are amplified by structural attributes rather than solely by non-vascular diversity (Fig. 4).

Environmental drivers of facilitation

The richness of non-vascular plants was best explained by a combination of structural and fine-scale microclimatic variables. Model 5 (AIC = 598.77) identified hummock area (p = 0.0019), number of vegetation layers (p = 0.0017), nutrient availability (p = 8.79e–05), humidity range (p < 0.0001), and temperature range (p = 0.0112) as significant predictors. In contrast, Model 6, which excluded microclimatic variables, had a significantly poorer fit (AIC = 616.80), underscoring the critical role of local climatic heterogeneity in shaping non-vascular diversity.

Beyond these environmental correlations, dominant non-vascular species created soils with contrasting nutrient profiles. Substrates beneath Kurzia capillaris, Breutelia squarrosa, and Sphagnum cuspidatum contained higher nitrogen and organic carbon concentrations than those associated with S. magellanicum (Fig. 5a–d). K. capillaris had the highest phosphorus levels, while S. cuspidatum showed elevated potassium content.

Significant differences were also detected in hydrological traits among moss substrates (infiltration rate: F = 22.74, p < 0.001; water holding capacity: F = 4.33, p < 0.001). K. capillaris, S. magellanicum, and S. cuspidatum allowed rapid infiltration, whereas Fissidens convolutus and B. squarrosa exhibited exceptional water retention (> 400% of dry weight; Fig. 6).

Mats of S. magellanicum (Sphmage-Interior) retained solar heat and exhibited elevated nighttime temperatures, suggesting effective thermal buffering. S. cuspidatum and F. convolutus displayed similar, though less pronounced, patterns. In contrast, canopy sensors on Chusquea tessellata recorded the widest diurnal temperature ranges (Fig. 7a). Relative humidity at the hummock base remained near saturation, but F. convoluta experienced higher variability than S. magellanicum. At canopy level, relative humidity dropped markedly at midday, with fluctuations exceeding 20% (Fig. 7b), reinforcing the importance of microclimatic stabilization in moss-dominated substrates.

Main findings and hypotheses

Our findings support all four hypotheses. First, vegetation in the peatland is non-randomly distributed, with species-rich hummocks indicating structured spatial patterns. Second, vertical microhabitat differentiation—driven by water saturation and nutrient gradients—supports species coexistence through complementary strategies. Third, mosses, particularly Sphagnum spp., function as ecological facilitators by modifying abiotic and structural conditions, promoting vascular and non-vascular species establishment. Lastly, facilitation is closely linked to environmental drivers such as moisture, infiltration, and nutrient availability, underscoring the foundational role of mosses in habitat formation and maintenance.

Hummocks are distinct microhabitats structured by interactions among mosses and vascular plants. Species such as Sphagnum cuspidatum, Kurzia capillaris, Chusquea tessellata, and Breutelia squarrosa act as keystone facilitators that modulate soil, temperature, and water dynamics—thereby driving plant community assembly.

Facilitation and community diversity

Although hummocks occupy only 31.5% of the peatland surface, they harbor 89% of all individuals and over half of the recorded species. Pioneer mats of non-vascular plants provide the structural and edaphic conditions required for vascular plant colonization. Mosses stabilize the substrate, retain moisture, and accumulate nutrients, generating favorable microsites for recruitment. These findings support the framework of niche construction theory (Ardichvili et al., 2022) and are consistent with successional patterns observed in oligotrophic environments (Cleef, 1981; Silva et al., 2023).

Chusquea tessellata—a tall, hollow-stemmed bamboo—exhibits functional traits suggesting a distinct facilitation mechanism. In wetland grasses such as Phragmites australis, wind-induced convection through culms (Venturi effect) promotes oxygen flow to the rhizosphere, enhancing soil aeration and supporting microbial oxidation in waterlogged conditions (Armstrong et al., 1992). Given Chusquea’s rigid structure and frequent occurrence in wind-exposed cloud condensation zones (Cleef, 1981), a similar mechanism may operate in high Andean peatlands. This possibility remains unexplored and merits investigation as a potentially key driver of soil oxygenation, biogeochemical cycling, and community assembly in these ecosystems.

Moss-mediated environmental modulation

Our analyses indicate that non-vascular plant richness is a stronger predictor of vascular species richness than abiotic variables alone. This finding suggests that larger hummocks—harboring more diverse bryophyte communities—generate a broader range of microsites. Such increased environmental heterogeneity likely promotes the establishment and coexistence of other plant species. In this context, non-vascular plants may act as ecosystem engineers, reshaping their surroundings through water retention, nutrient accumulation, and thermal buffering (Laberge et al., 2015). In particular, our results indicate that Sphagnum magellanicum contributes to the stabilization of temperature and moisture regimes, while Kurzia capillaris and Breutelia squarrosa are associated with nutrient-enriched substrates that may enhance seedling establishment. The observed interspecific variation in peat nutrient content points to contrasting facilitation strategies—ranging from nutrient sequestration to active rhizosphere enrichment (Heijmans et al., 2002).

In addition to nutrient enrichment and thermal buffering, differences in water dynamics among species also shape microsite availability. Mosses occupying distinct vertical layers within hummocks regulate both infiltration and moisture retention, generating fine-scale gradients that influence species zonation. Upper hummock bryophytes such as Frullania convoluta may function as fog or dew collectors, contributing to moisture availability during dry periods (Glime, 2017; Proctor, 2000). In contrast, basal mosses like Kurzia capillaris and Sphagnum spp. exhibit high field capacity (Montenegro et al., 2005; Berrones et al., 2024), effectively retaining rainwater and runoff.

These patterns illustrate how mosses and liverworts construct complex microenvironments that facilitate vascular plant colonization. The vertical stratification of hummocks—reflected in both species turnover and environmental gradients—underscores the central role of facilitation in shaping peatland biodiversity.

Future directions

Our study demonstrates that moss-mediated facilitation plays a central role in shaping community structure in Andean peatlands. However, several key knowledge gaps remain. Future research should address seasonal variation in facilitative dynamics, the role of fog interception, and nutrient fluxes over temporal scales. Chusquea tessellata may also influence seedling establishment through its potential effects on nutrient availability, mycorrhizal associations, and microbial activity (Díaz et al., 2024), and this functional role warrants further exploration. Experimental approaches examining moss responses to environmental change will be crucial to guide peatland restoration under future climate scenarios. Finally, comparative studies across different páramo systems are needed to assess the generality of these patterns and inform regional conservation strategies.

The patterns observed in this Andean peatland demonstrate that hummocks harbor disproportionately high species richness and abundance despite being limited in spatial extent. This study contributes a novel perspective by integrating environmental and structural variables, moving beyond traditional floristic inventories to better understand these systems' spatial and ecological organization. Our models reveal that non-vascular plant richness, more than environmental variables or hummock size, best explains vascular plant diversity, emphasizing the central role of ecological facilitation. Vertical zonation within hummocks reflects functional differentiation: basal species such as Sphagnum cuspidatum and Kurzia capillaris are associated with higher nutrient concentrations, while mid- and upper strata dominated by Sphagnum magellanicum, Frullania convoluta, and Breutelia squarrosa regulate temperature and moisture dynamics. S. magellanicum acts as a thermal buffer, and F. convoluta and B. squarrosa enhance water retention, particularly during the dry season when fog is the primary moisture source. Together, these findings show that mosses facilitate the establishment and persistence of companion species by improving microhabitat conditions. This facilitative effect shapes plant community structure and contributes directly to the biodiversity and resilience of high-mountain peatlands.

Clinical trial number: not applicable.

Funding

This paper is part of the requirements for obtaining a Doctoral degree at the Posgrado en Ciencias Biológicas, Universidad Nacional Autónoma de México (UNAM) by L.A.R. We thank the Secretaría de Ciencia, Humanidades, Tecnología e Innovación (SECIHTI) for funding this research through a graduate scholarship to L.A.R. (1157884). We also acknowledge support from DGAPA-UNAM via the Programa de Apoyo a Proyectos de Investigación e Innovación Tecnológica (PAPIIT IN205723).

Competing Interests

The authors declare no competing interests.

Author Contributions

Liz Ávila-Rodríguez and Alfonso Valiente-Banuet conceived the ideas; Liz Ávila-Rodríguez, Alfonso Valiente-Banuet, and Tania Sánchez-Ortiz designed the methodology and collected the data; Liz Ávila-Rodríguez, Tania Sánchez-Ortiz, and Miguel Martínez-Ramos analyzed the data; Liz Ávila-Rodríguez and Clara Tinoco-Ojanguren led the writing of the manuscript. All authors contributed critically to the drafts and approved the final version for publication.

Acknowledgements

We thank the Chingaza National Natural Park staff, especially Erika Hernández and Pedro Camargo. We are also grateful to botanists Julio Betancur, Diego Giraldo Cañas, Orlando Rivera, and José Aguilar Cano at the Instituto de Ciencias, Universidad Nacional de Colombia, for their support in identifying the herbarium specimens. We thank Jacinto Triviño, Daniela Ardila, Rosa Holguín, Andrés Murcia, and Lady Vallejo for their invaluable assistance in the field. We also thank Noé Flores, Iván Reséndiz, and Juan Pablo Castillo at Departamento de Ecología de la Biodiversidad, Instituto de Ecología (UNAM) for their technical support during this research.

Ethics Approval

Not applicable.

Consent to Participate

Not applicable.

Consent for Publication

Not applicable.

Data Availability

The datasets generated and analyzed during the current study are available from the corresponding author upon reasonable request.

Supplementary Information

The online version contains supplementary material available at [insert DOI link if provided by the journal].

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Moss-driven facilitation promotes species coexistence in Andean páramo peatlands

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Abstract

Figures

Introduction

Materials and methods

Study site

Peatland-scale species associations

Hummock-scale species associations

Environmental variables

Microclimatic monitoring

Nutrient content analysis

Water retention and infiltration rate

Statistical analysis

Results

Peatland structure and species distribution

Hummock-scale species associations

Facilitation and predictors of vascular richness

Environmental drivers of facilitation

Discussion

Main findings and hypotheses

Facilitation and community diversity

Moss-mediated environmental modulation

Future directions

Conclusion

Declarations

References

Additional Declarations

Supplementary Files

Status:

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