Adjacent Old-growth Forest Research Articles

Understory vegetation response to alternative silvicultural systems in coastal British Columbia montane forests

This study is one of several investigating the biological effects of silvicultural systems at the Montane Alternative Silvicultural Systems (MASS) project located on Vancouver Island in British Columbia (BC). We compared understory vegetation cover and diversity under four silvicultural systems (clearcutting, patch cutting, dispersed retention, and shelterwood) to an adjacent old-growth forest. Long-term plots were measured pre-harvest and at intervals up to 26 years post-harvest. We also compared vegetation response to fertilization and vegetation control treatments. All harvesting resulted in a short-term reduction in understory cover from logging debris and ground disturbance. Recovery from disturbance varied by species, life-form and system. Understory tree species returned to pre-harvest cover after 15 years and significantly exceeded initial cover after 26 years. Shrubs returned to pre-harvest cover after 5–10 years and continued to increase in most systems. Herb cover was low in the pre-harvest forest but increased rapidly in years three through 10 due to herbaceous colonizers; this was least pronounced in the shelterwood. Herbs have declined rapidly since year fifteen. Forest floor bryophytes were reduced to less than 5% cover in all systems except the shelterwood and they remain at one-third or less of their pre-harvest cover. The shelterwood retained more stand structure and plant species from the original old-growth forest than other systems immediately after logging, except for the retained patches. All the harvesting treatments increased species richness and diversity compared to the pre-harvest forest. The increase in total species and abundance was highest for year 15 when early-seral colonizers were still present, and many pre-harvest species had returned. By year 26, richness and diversity began to decrease as early-seral species were lost. For overall species diversity of vascular plants and forest floor bryophytes, silvicultural system did not have an effect after 26 years. All the late-seral herbs that occur at MASS were present after harvesting but several were locally eliminated or had reduced abundance in cut areas. We found no significant edge effects into retention patches, which had comparable species richness and diversity to the pre-harvest old growth—suggesting that aggregated retention can be effective for maintaining late-seral species. Silvicultural system had more significant long-term effects on shrubs and bryophytes than early vegetation control.

Biodiversity Function and Resilience in Tropical Agroforestry Systems Including Shifting Cultivation

Agroforestry systems potentially deliver win–win solutions to production and biodiversity conservation in the tropics, but they need to be adapted to farmers’ needs. We reviewed the literature on functional roles of biodiversity and resilience in tropical agroforestry systems, and we evaluated the evidence base for the beneficial role of biodiversity on yield, and effects of farmer management practices. Most studies investigated the biodiversity of taxa assumed to have positive functions for farmers. Shaded commodities and shifting cultivation were the systems most frequently assessed. Half of studies investigated plants, while Hymenoptera and birds were other major groups. Many agroforests had lower diversity than forest, while less than half had higher diversity than agriculture. The effects of management within systems were rarely addressed, with shade level the most frequent factor. Papers on resilience, mainly from shifting cultivation systems, showed the positive influence of adjacent old-growth forest to biodiversity, and the negative effects of tillage. Better reporting of results for meta-analyses, and long-term experiments on key questions are needed to evaluate the potential of agroforestry more thoroughly.

The soil seed bank in abandoned tropical pastures: source of regeneration or invasion?

We assessed the availability of both pioneer and non-native species in the soil seed bank of old-growth forest and recently abandoned pasture, to evaluate whether the soil seed bank in these pastures represents a source of regeneration of species from adjacent old-growth forest or of invasion by non-native species. Our study was conducted at Selva Lacandona, Chiapas, Mexico. Soil samples were randomly collected from 6 sites in old-growth forest, and 6 sites in abandoned pastures. Seedlings from soil samples were identified and classified into pioneer, non-native (weeds/ graminoids), and other forest species. Pioneer species seeds were virtually absent in pastures, but represented ~30% of seeds in the forest. Non-native species comprised ~99% of the soil seed bank in pastures. In the forest, soil seed bank density of weeds and graminoids decreased with increasing distance (up to 4 km) from agricultural fields, and comprised up to 25% (Mean ± 1SE= 16 ± 7) of the seed bank. Our results show a near total elimination of pioneer species from the soil seed bank in pastures, and considerable invasion of the borders of the Montes Azules reserve by seeds of non-native species. Thus, in the region studied, the soil seed bank in abandoned pastures represents a source of invasion by non-native species into old-growth forest rather than a potential source of forest regeneration.

Proximity is not a proxy for parentage in an animal-dispersed Neotropical canopy palm

We used parentage analysis to estimate seedling recruitment distances and genetic composition of seedling patches centred around reproductive trees of the animal-dispersed Neotropical canopy palm Iriartea deltoidea in two 0.5 ha plots within second-growth forest and one 0.5 ha plot in adjacent old-growth forest at La Selva Biological Field Station in north-eastern Costa Rica. Seedlings were significantly spatially aggregated in all plots, but this pattern was not due to dispersal limitation. More than 70 per cent of seedlings were dispersed at least 50 m from parent trees. Few seedlings were offspring of the closest reproductive trees. Seedling patches observed beneath reproductive trees originate from dozens of parental trees. Observed patterns of seedling distribution and spatial genetic structure are largely determined by the behaviour of vertebrate seed dispersers rather than by spatial proximity to parental trees.

MULTIGENERATIONAL GENETIC ANALYSIS OF TROPICAL SECONDARY REGENERATION IN A CANOPY PALM

Iriartea deltoidea (Arecaceae) is an abundant canopy palm with a wide geographic distribution in Neotropical wet forests. We analyzed the genetic profile across three generations of Iriartea within a 43-ha area encompassing two areas of second-growth and adjoining old-growth forest at La Selva Biological Field Station in northeastern Costa Rica. A total of 311 reproductively mature trees, 99 large saplings, 207 small saplings, and 601 seedlings were genotyped using 141 AFLP loci. Parentage analysis revealed high dispersal distances, both for seed (over 2.3 km) and pollen (over 3.8 km), indicating a large genetic neighborhood within La Selva Biological Station. In a 20-ha area of second growth, the founding palm population was dominated by a small number of parental trees located in the adjacent old-growth forest; two old-growth trees contributed 48% of the second-growth genes. The genetic diversity of reproductively mature trees in this second-growth forest was significantly reduced compared to adjacent old-growth forest. Within 400 m of the border with old-growth forest, we observed a similar reduction of genetic diversity in saplings, and an even greater loss of genetic diversity in the second generation of seedlings. Nearly half of these seedlings were offspring of local parents. In contrast, in the distant portion of second-growth forest (400-800 m from the old-growth border), parentage analysis showed that 40% of seedlings originated from outside the study area and only 10% were offspring of local parents. These high levels of gene flow maintained genetic diversity in saplings and seedlings similar to levels observed in old-growth forest. Our findings highlight the importance of gene flow from diverse seed and pollen sources for sustaining levels of genetic diversity of tree populations in second-growth forests.

Genetic Consequences of Tropical Second-Growth Forest Regeneration

Secondary forests are more extensive than old-growth forests in many tropical regions, yet the genetic composition of colonizing populations is poorly understood. We analyzed the parentage of a founder population of 130 individuals of the canopy palm Iriartea deltoidea in a 24-year-old second-growth forest in lowland Costa Rica. Among 66 trees in adjacent old-growth forest, only two individuals contributed 56% of the genes in founders. Second-growth trees had lower genetic diversity and larger patches of similar genotypes than old-growth trees. Recovery of genetic diversity of populations in tropical second-growth forests may take many generations and will require continued dispersal from genetically diverse source populations.

CORRIDORS AND MAMMAL COMMUNITY STRUCTURE ACROSS A FRAGMENTED, OLD-GROWTH FOREST LANDSCAPE

We studied the influence of corridors on the community structure of old- growth forest mammals across a fragmented ecosystem, the Olympic National Forest, Wash- ington, USA. This region of once contiguous forest has been transformed by logging into a mosaic of landscape features including clearcuts, second-growth forest, and old-growth forest patches and corridors. To assess corridor utility, we quantified among- and within- corridor variability in community structure, landscape indices, and habitat descriptors. Discriminant analyses showed that the four corridors studied differed significantly both in species assemblages (P , 0.05) and in habitat characteristics ( P , 0.005). Changes along individual corridors were primarily associated with adjacent habitat. The proportion of adjacent old-growth forest significantly decreased along two of the four corridors, re- flecting this system's fragmentation gradient of an increasingly disturbed landscape matrix. The number of forest species found in corridor sites was significantly correlated with this matrix: less old-growth forest surrounding a corridor site resulted in fewer forest-dependent species. Width of the corridor at a site and site isolation often acted singly or in combination with the fragmentation gradient as an influence on community structure. This was also the case for many individual species. Demographic measures suggested that, while reproduction is occurring along these corridors, levels are lower than in continuous forest. Finally, data showed that, while forest species richness and occurrence of specific forest species were consistently higher in corridors than in the surrounding matrix, these patterns were driven primarily by differences between corridors and clearcuts. These results suggest that, al- though these corridors appear to be effective and may possibly serve as demographic sources of individuals, they should not be considered equivalent to one another. Only by considering corridors individually can their respective value be determined. For the Olympic National Forest, this value is significant, with the use of a combination of different corridors com- prising a viable supplement to maintaining continuous forest for long-term preservation of

An empirical model for predicting diurnal air-temperature gradients from edge into old-growth Douglas-fir forest

Edge — the boundary line between clearcut and adjacent old-growth forest — is one of the critical landscape elements in the highly fragmented forest landscapes of North America's Pacific Northwest. Ecological phenomena at edges may be better understood by examining the physical environments near the edge. To further this objective diurnal air temperature gradients were measured along 16 gradients from the edge into the interior old-growth Douglas-fir [ Pseudotsuga menziesii (Mirb.) Franco] forest over the 1989 and 1990 growing seasons and analyzed effects of edge orientation (relation of edge-facing to the azimuth) and macroclimate (local weather conditions of the clearcut) on these gradients were also explored through regression analysis. The air temperature gradient was expressed with a simple exponential equation involving three intermediate variables of interest: air temperature in the interior forest ( TEMPIF), difference in air temperature between the edge and inside the forest (Δ AT), and changing ratio of temperature along the gradient ( SLOPE). Linear or nonlinear regression equations were developed to predict TEMPIF, Δ AT, and SLOPE. Correlation analysis always preceded regression analysis, in which the relationships between the regression parameters and independent variables representing edge orientation and macroclimate were further explored. A computer model developed from the final empirical relationships successfully predicted air temperature gradients, circumventing the need for time-consuming field measurements with expensive meteorological instruments, and generated new information about the influences of edge orientation and macroclimate on air temperatures. TEMPIF, Δ AT, and SLOPE were shown to be highly sensitive to the dependent variables. Although model application should be limited to edges created by recent (10- to 15-year-old) clearcuts adjoining old-growth Douglas-fir forest, the modeling approach could be applied to edges with different characteristics by modifying the relationships.

The abundance of salamanders in forest stands with different histories of disturbance

Because of the importance of salamanders in forest food chains, the effects of forest management practices on populations of these animals warrant consideration. We compared the numbers and activity patterns of salamanders in areas of a deciduous forest in central New York State that had been cut selectively for firewood, or clearcut, or planted with conifers. Numbers of salamanders were lower in three recently distrurbed habitats than in adjacent old-growth control stands. The frequency of above-ground activity by both species of salamanders was positively correlated with the density of understory vegetation and the depth of leaf litter. Small-scale habitat disruption associated with harvesting firewood increased the numbers of the terrestrial eft stage of the red-spotted newt ( Notophthalmus viridescens) but had no effect on numbers of red-backed salamanders ( Plethodon cinereus). A recently clearcut area had fewer red-backed salamanders than adjacent old-growth forest had, but the numbers of salamanders in a 60-year-old second-growth forest were indistinguishable from those in the adjacent old-growth forest. Populations of salamanders in a conifer plantation were low. Thus, salamanders seem to be resilient to limited disturbance of forests, but major changes are likely to affect populations of salamanders and, consequently, of birds and mammals that depend on salamanders for food.