SEGUIMIENTO Y EVALUACIÓN

Distribution and frequency of species offer some hints about their likely habitat requirements, but not about the environmental parameters that may be limiting the observed range of a given species. Broadly distributed species are more easily tested for association with various habitat parameters. Comparison of their abundance across micro- habitats over time or space may also be useful for identification of microclimate change.

Six species with a broad distribution over the Weinmannia host were chosen as potential microclimate change indicators. Each had a characteristic pattern of abundance (Table 23).

Table 23. Frequency in zone samples of six species with wide distribution on the Weinmannia sp.

Species 1 2.1 2.2 3 4 5

Lejeunea subgen. Nanolejeunea sp. 1 0.5 0.1 0.4 0.1 0.1

Macrolejeunea pallescens 1 1 0.8 0.7 0.8 0.2

Plagiochila stricta 0.8 1 0.5 0.7 0.1

Omphalanthus filiformis 0.1 0.7 0.5 1 0.9 0.8

Frullanoides densifolia subsp. densifolia 0.3 0.1 1 1 0.8

Frullania riojaneirensis 0.1 0.3 0.4 1

Zone

Lejeunea subgen. Nanolejeunea sp. is likely to be a facultative epiphyte, predominantly growing on the lower trunk. Macrolejeunea pallescens is an obligate epiphyte, with highest frequency on the lower and upper trunk. Plagiochila stricta was most commonly found along the upper trunk, but not in the outer crown. Omphalanthus filiformis appears to prefer mid-crown conditions. Frullanoides densifolia subsp. densifolia had highest frequency in the mid and mid-outer crown, while Frullania riojaneirensis is a high light specialist that was most frequently found in the outer crown.

Frequency of L. subgen. Nanolejeunea was most strongly correlated with the relative humidity values and diameter. All other variables did not have significant correlations (Table 24). This species has demonstrated a preference for the lower trunk habitat and may require high humidity or long periods of leaf wetness.

Chapter 5. Environmental variables and species distribution

The abundance pattern of Macrolejeunea pallescens was most strongly, but negatively correlated with VisSky and the radiation variable, particularly the diffuse below fraction of below crown radiation. This is not surprising as all these variables, including LAI have been shown to be highly correlated. VisSky is very highly correlated with DifBe (r = 0.995). It appears radiation intensity, and especially diffuse radiation, more than RH or temperature, may have a negative impact on M. pallescens abundance.

Table 24. Pearson’s correlation coefficients for associations of frequency of selected bryophyte species and environmental parameters: height above ground, diameter of branches and trunk, temperature, proportion of visible sky, leaf area index and total below, direct below and diffuse below radiation recorded on a Weinmannia sp. host. All associations shown were significant (P < 0.05).

Height Dia RH Temp VisSky LAI TotBe DirBe DifBe

L. subgen. Nano. 0.80 0.82 M. pallescens -0.87 0.82 -0.84 -0.81 -0.86 P. stricta -0.84 -0.88 0.84 -0.88 -0.87 -0.88 O.filiformis 0.84 -0.88 -0.90 F. densifolia 0.90 -0.89 -0.91 0.91 -0.86 0.80 F. riojaneirensis 0.87 -0.84 0.82 0.96 -0.89 0.95 0.93 0.95

Radiation intensity was also strongly correlated with the frequency of P. stricta, but for this species, the negative relationship was nearly as strong with both the diffuse and direct fraction of below crown radiation. The frequency of P. stricta drops off quickly in the mid-crown, apparently affected by high irradiation and rising temperature, suggested by the high negative correlation to VisSky and temperature, which themselves were shown to only have a moderately strong association (Table 20). Curiously, this species was most frequently found on the sheltered side of the trunk and not on the less illuminated lower trunk, suggesting a narrow range of irradiation tolerance and a preference for moderate radiation intensity.

Frequency of Omphlanthus filiformis was most closely aligned with the relative humidity, but also with branch diameter and height above ground. The negative relationship with Dia and RH suggests a low tolerance for lower trunk sites where the humidity is high. Its high frequency in the upper crown indicates a tolerance of, if not a requirement for high

Chapter 5. Environmental variables and species distribution

The negative correlation of F. densifolia with Dia, RH and LAI reflects its highest frequency in the mid-outer crown. Its requirement for moderately high radiation intensity is suggested by the strong negative correlation with LAI and a positive relationship with DirBe. A reduction in frequency in the outer crown may indicate the prevalence of suboptimal light conditions (excessive radiation) or desiccation regimes in that section of the crown. Preferred position of F. densifolia and the high correlation with temperature may indicate a physiological requirement for temperatures higher than those found near the forest floor.

High radiation intensity was a possible requirement for F. riojaneirensis. Its frequency was most strongly correlated with VisSky and the radiation variables. The observed preference of this species for the twiggy outer crown is confirmed by the negative correlation with Dia (Table 24).

5.3 Discussion

The selected environmental variables were well correlated with each other, resulting in low dimensionality in the ordination space. Temperature had the weakest associations of any variable tested. Lee and La Roi (1979) found that bryophytes were much more sensitive to fluctuations in moisture than temperature. There was less than 0.5˚C difference in mean temperature between the coolest and warmest sections of the host. During the warmest part of the day, a little over 1˚C separated the sheltered side of the trunk, the coolest part of the Weinmannia and the highly irradiated upper crown. The small temperature gradient on this host may not directly have a significant impact on species physiology and distribution. However, the relative humidity gradient is co- dependent on temperature. The importance of relative humidity to spatial distribution of epiphytic species is discussed below.