Abstract
In the province of Chubut in Patagonia, Argentina, Nothofagus pumilio forests (locally known as lenga), are managed through selective cuts, which imply the opening of canopy gaps. This management scheme is carried out without taking into consideration the sapling requirements changes through neither a cutting cycle nor the precipitation gradient in which these forests thrive. To analyze these changes, we inferred the facilitation-competition balance between the canopy and regeneration studying the effects of precipitation levels, gap size and gap age on saplings growth in height on 45 canopy gaps artificially created between 1960 and 1993. Results shown that during the first 20 years since the gap opening, the regeneration growth is determined by light availability in mesic sites and by water availability in dry sites. However, the difference due to the precipitation levels gradually decreases over time. Moreover, in the period between 20 and 35 years after gap opening, in both mesic and xeric sites, light is the limiting factor to growth. This means that in xeric sites, saplings shift from a water-dependent to a light-dependent growth. The average closing rate of gaps due to lateral growth of trees bordering the gap is high enough so that within the proposed gap size range, the gap healing can occur before regeneration reaches the upper stratum. Consequently, in mesic sites the gap opening can be done by a single operation that generates gaps with diameters of approximately twice the average height of the canopy (D/H). While in xeric environments, lenga seedling establishment and initial growth require the cover of small gaps, but advanced regeneration requires bigger gaps to reach the canopy. For this reason, gaps should be opened in two stages: the first gaps should be opened with a D/H between 0.8 and 1, and after a cutting cycle of 35 years, these openings should be enlarged to a D/H between 1.5 and 2. The close relationship is maintained between the new cohort and the upper strata require special considerations regarding the evolution of the balance between positive and negative interactions during development. Our work highlights the need to adjust management practices to these spatial and temporal variations so as to achieve an optimal growth along the entire production cycle.
Highlights
The dynamics of canopy gaps, in which the fall of one or several trees that produces the gap is the main disturbance event, has been widely studied in different forests of the world (Runkle, 1985; White and Pickett, 1985; Pickett et al, 1999)
For gaps up to 20 years old, the analysis of variance for precipitation and the gap size on height growth showed no significant differences for main effects, while their interaction showed that the effect of gap size is different according to their location in xeric and mesic sites, respectively (p = 0.012 and p = 0.032 at gaps of 10 and 20 years old, respectively) (Figure 3)
The growth in height of dominant saplings as a function of gap age found in mesic and xeric sites, and in small and big gaps is shown in figure 3 and figure 4
Summary
The dynamics of canopy gaps, in which the fall of one or several trees that produces the gap is the main disturbance event, has been widely studied in different forests of the world (Runkle, 1985; White and Pickett, 1985; Pickett et al, 1999). In Andean Patagonia in Argentina, Nothofagus pumilio forests (locally known as lenga forests) develop over a wide distribution range, covering a great variety of ambient conditions and presenting different structures and regenerative dynamics These dynamics are mainly associated to the frequency, magnitude, and severity of disturbances, and to the productivity of the site (Donoso Z., 1995). In sites presenting summer water deficit (the northern area of its distribution in the provinces of Río Negro, Neuquén, and northern Chubut), lenga regeneration does not establish in areas in which vegetation cover is below 20% (Bava and Puig, 1992) In these sites, survival of lenga seedlings and saplings is frequently limited by the availability of water, and its establishment occurs in small gaps, product of tree fall that creates microsites showing low evapo-transpiration rates (Rusch, 1992; Heinemann et al, 2000)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
