POPULATION BIOLOGY OF THE CLONAL MOSS HYLOCOMIUM SPLENDENS IN NORWEGIAN BOREAL SPRUCE FORESTS .1. DEMOGRAPHY

1 Hylocomium splendens is a perennial clonal moss with annual periodic ity in the emergence of new modules. New growing points usually emerge in spring and develop into mature segments their second summer. Popul ation increase is brought about by ramification (branching) of the you ngest segment or by regeneration from older parts of the shoot system. 2 A technique for nondestructive re-identification of segments in per manent plots is devised. Precise demographic information on 9206 growi ng points and 7602 mature segments was obtained by following 119 local populations in seven Norwegian reference areas for monitoring during 3 years. The dry weight of each mature segment was estimated from morp hological field measurements. 3 The potential of each mature segment f or production of new growing points was strongly size-dependent; c. 40 % of the variation in a segment's size was explained by the size of it s mother segment. Integration within segment chains was largely restri cted to neighbouring segments. The number offspring growing points (by ramification as well as regeneration) was positively size-dependent, while termination risk was negatively size-dependent. Mature segments produced by regeneration were smaller, while segments produced by rami fication were larger than the average segment. Strong apical dominance was demonstrated. 4 Mortality and branching rates, averaged over popu lations, areas and years, are reported. Annual recruitment was 32.3%; 23.3% by regeneration, 7.5% by ramification, and 1.5% by accidentally introduced shoots. Annual mortality was 19.7%. 6.8% by loss, 1.9% by g razing, and 11.0% by termination for other reasons.5 Demographic data for growing points and mature segments were analysed separately by sta ge-structured transition matrix models. The total population increased every year (average lambda = 1.10-1.11). Vital rates were strongly si ze-dependent. The contributions of ramification and regeneration to in crease in lambda are equal as ramification occurred in large segments with high probability for survival. 6 Ramification is considered impor tant for maintenance of size and risk-spreading among ramets under fav ourable conditions, while high regenerative ability facilitates resili ence to, and recovery after, disturbance. The ecological significance of size is discussed. 7 Hylocomium splendens is closely similar to clo nal forest vascular plants in major demographic traits, e.g. size-depe ndence of fitness and branching patterns.