Central to the issue of harvest feasibility on the outer BC coast (CWHvh) is the question of whether sites, once harvested, can be regenerated, and whether the time period for replacement and subsequent growth is economically and environmentally acceptable. Since low productivity sites have not been harvested in the past, there is a lack of data to answer this question. We tried to provide an answer by assessing regeneration following natural disturbances. Small scale gap disturbances are the norm within old-growth stands. If regeneration is not a problem in gaps, then we have some evidence that regeneration should not be a problem upon implementation of our management practices. The objectives of this study were: (1) to develop baseline information on the mechanisms and the patterns of regeneration across a sequence of forest types; (2) to assess regeneration success with respect to productivity; and (3) to estimate future growth and productivity.

A method was developed for extending a fine-scaled forest gap model to a watershed-scaled landscape, using the Eastern Cross Timbers ecoregion as a case study for the method. A topographic wetness index calculated from digital elevation data was used as a measure of hydrologic across the modeled landscape, and the gap model modified to have with a topographically-based hydrologic input parameter. The model was parameterized by terrain type units that were defined using combinations of USDA soil series and classes of the topographic wetness index. A number of issues regarding the sources, grid resolutions, and processing methods of the digital elevation data are addressed in this application of the topographic wetness index. Three different grid sizes, 5, 10, and 29 meter, from both LiDAR-derived and contour-derived elevation grids were used, and the grids were processed using both single-directional flow algorithm and bi-directional flow algorithm. The result of these different grids were compared and analyzed in context of their application in defining terrain types for the forest gap model. Refinements were made in the timescale of gap model’s weather model, converting it into a daily weather generator, in order to incorporate the effects of the new topographic/hydrologic input parameter. The precipitation model was converted to use a Markov model to initiate a sequence of wet and dry days for each month, and then daily precipitation amounts were determined using a gamma distribution. The output of the new precipitation model was analyzed and compared with a 100-year history of daily weather records at daily, monthly, and annual timescales. Model assumptions and requirements for biological parameters were thoroughly investigated and questioned. Often these biological parameters are based on little more than assumptions and intuition. An effort to base as many of the model’s biological parameters on measured data was made, including a new technique for estimating optimal volumetric growth rate by measuring tree rings. The gap model was set up to simulate various terrain types within the landscape.

Em uma parcela permanente de 10,24 ha na Floresta Pluvial Atlântica Submontana do Parque Estadual Carlos Botelho (Sete Barras, SP, Brasil), este estudo teve o intuito de descrever o regime de distúrbio do dossel e avaliar a regeneração natural sob diferentes regimes de luz. Para tanto, foi realizado o levantamento de todas as clareiras da parcela, que foram mensuradas e tiveram sua idade aproximada estimada. Em seguida, foram instaladas 42 parcelas de 10x10m para avaliar a regeneração natural em três regimes luminosos: dossel contínuo (18 parcelas), clareiras pequenas a médias (11) e clareiras grandes com abundância de Guadua tagoara (Nees) Kunth (13). O regime de luz foi caracterizado por fotografias hemisféricas tomadas ao centro das parcelas. O estudo da regeneração natural foi divido em: estrato herbáceo (i.e., ervas menores que um metro de altura), avaliado através da cobertura do solo estimada pelo método de interceptação de linha; e estrato arbustivo, avaliado através dos indivíduos com altura maior que 1m, e com diâmetro à altura do peito menor que 5cm. Para estes indivíduos anotou-se a espécie, diâmetro, altura total e área de copa, além da presença de partes reprodutivas e substrato de germinação. Informações sobre hábito, grupo sucessional e síndrome de dispersão das espécies também foram obtidas. Após um ano, uma reavaliação permitiu analisar a mortalidade, danos, recrutamento e crescimento. Apesar de 67% das clareiras terem sido menores que 150 m2 , o regime de distúrbio foi atípico, principalmente pela contribuição de clareiras maiores que 750 m2 , e pela área média e total que variaram respectivamente de 419 a 799 m2 , e de 26 a 49%, dependendo do método de delimitação de clareira. A densidade foi de 6 clareiras.ha -1 e a taxa de recorrência variou entre 91 e 220 anos, dependendo dos métodos. Houve diferença significativa entre os ambientes para a maioria dos índices de luz, especialmente para a radiação total incidente com médias entre 909 e 2.400 mols.m-2.ano-1. Observou-se diferença significativa entre ambientes na cobertura por ervas, porém os resultados variaram entre espécies. No estrato arbustivo, houve diferença significativa na composição e abundância das espécies, inclusive entre clareiras médias e sub-bosque. A densidade de ervas e arbustos foi maior nos ambientes mais iluminados, assim como a densidade de pioneiras e secundárias iniciais. O recrutamento em um ano (16%) apresentou diferenças nos ambientes, com 63% dos recrutas apenas nas grandes clareiras. O mesmo não ocorreu com a taxa de mortalidade cujas principais causas foram os danos físicos e dessecamento. Para os 13% de indivíduos danificados em um ano, houve destaque para danos ligados à extração de palmito. Apenas os danos físicos naturais apresentaram diferença entre ambientes, com grandes clareiras sendo as mais danosas. No geral e entre as 25 espécies avaliadas separadamente, houve uma tendência de crescimento maior com o aumento da incidência luminosa. Clareiras pequenas a médias tiveram significativamente maior riqueza, diversidade e menor dominância de espécies que o sub-bosque. Clareiras grandes com bambu tiveram menor riqueza e diversidade, mas contribuíram com a manutenção da diversidade beta da parcela permanente. / In a 10.24 ha permanent plot of Tropical Lower Montane Atlantic Rain Forest in the Carlos Botelho State Park (Sete Barras, SP, Brazil), this study aimed to describe the canopy disturbance regime and to assess natural regeneration under different light regimes. In order to do so, the plot was completely surveyed for canopy gaps that were measured and had their approximate age estimated. Then, 42 10x10 m plots were established to evaluate natural regeneration under three light regimes: understory (18 plots), small to medium canopy gaps (11 plots) and large gaps abundant in Guadua tagoara (Nees) Kunth (13 plots). The light regime was characterized through hemispherical photographs taken at each plot center. Natural regeneration was dived into: herb stratum (i.e., herbs below one meter in height) assessed through soil coverage using the line intercept method; and shrub stratum or all plant individuals taller than one meter high and thinner than 5 cm in diameter at breast height. All individuals were identified to species and measured for diameter, height, crown height and area, besides notes on the presence of reproductive structures and germination substrate. Information on growth form, dispersal syndrome and ecological group were also obtained for each species. After one year, one reevaluation was made to assess mortality, damages, recruitment and growth. Although 67% of gaps were smaller than 150 m2 , the plot disturbance regime was atypical mainly by the contribution of gaps bigger than 750 m2 and by the average and total gap area that varied respectively from 419 to 799 m2 , and from 26 to 49% depending on the gap delimitation method. Gap density was 6 gaps.ha-1 and the turnover rate varied from 91 to 220 years depending on the gap method employed. There was significant difference between environments among the light index, especially for total incident radiation with means varying from 909 and 2,400 mols.m-2.y-1. It was found significant differences on herb soil coverage between environments, although the results varied among species. In the shrub stratum, species composition and abundance was significantly different, even between small to medium canopy gaps and the understorey. Herb and shrub densities were bigger in the more enlightened environments, as well as pioneer and early secondary species densities. Recruitment over the year (16%) was different between environments with large gaps accounting for 63% of all recruits. Similar difference was not found for mortality rate that had physical damage and desiccation as main death causes. Amid the 13% of damage individuals in the course of one year, there was noticeable contribution of damages linked to illegal extraction of palm-heart. Differences between environments were present only for physical damages with large gaps being the most damaging environment. In general and among the 25 species evaluated separately, there was a tendency of bigger growth with enhancement in light incidence. Small to medium gaps had significantly higher species richness and diversity, and lower dominance compared to the understorey. Large gaps had lower richness and diversity, but they contributed to maintain beta diversity of the permanent plot.

Em uma parcela permanente de 10,24 ha na Floresta Pluvial Atlântica Submontana do Parque Estadual Carlos Botelho (Sete Barras, SP, Brasil), este estudo teve o intuito de descrever o regime de distúrbio do dossel e avaliar a regeneração natural sob diferentes regimes de luz. Para tanto, foi realizado o levantamento de todas as clareiras da parcela, que foram mensuradas e tiveram sua idade aproximada estimada. Em seguida, foram instaladas 42 parcelas de 10x10m para avaliar a regeneração natural em três regimes luminosos: dossel contínuo (18 parcelas), clareiras pequenas a médias (11) e clareiras grandes com abundância de Guadua tagoara (Nees) Kunth (13). O regime de luz foi caracterizado por fotografias hemisféricas tomadas ao centro das parcelas. O estudo da regeneração natural foi divido em: estrato herbáceo (i.e., ervas menores que um metro de altura), avaliado através da cobertura do solo estimada pelo método de interceptação de linha; e estrato arbustivo, avaliado através dos indivíduos com altura maior que 1m, e com diâmetro à altura do peito menor que 5cm. Para estes indivíduos anotou-se a espécie, diâmetro, altura total e área de copa, além da presença de partes reprodutivas e substrato de germinação. Informações sobre hábito, grupo sucessional e síndrome de dispersão das espécies também foram obtidas. Após um ano, uma reavaliação permitiu analisar a mortalidade, danos, recrutamento e crescimento. Apesar de 67% das clareiras terem sido menores que 150 m2 , o regime de distúrbio foi atípico, principalmente pela contribuição de clareiras maiores que 750 m2 , e pela área média e total que variaram respectivamente de 419 a 799 m2 , e de 26 a 49%, dependendo do método de delimitação de clareira. A densidade foi de 6 clareiras.ha -1 e a taxa de recorrência variou entre 91 e 220 anos, dependendo dos métodos. Houve diferença significativa entre os ambientes para a maioria dos índices de luz, especialmente para a radiação total incidente com médias entre 909 e 2.400 mols.m-2.ano-1. Observou-se diferença significativa entre ambientes na cobertura por ervas, porém os resultados variaram entre espécies. No estrato arbustivo, houve diferença significativa na composição e abundância das espécies, inclusive entre clareiras médias e sub-bosque. A densidade de ervas e arbustos foi maior nos ambientes mais iluminados, assim como a densidade de pioneiras e secundárias iniciais. O recrutamento em um ano (16%) apresentou diferenças nos ambientes, com 63% dos recrutas apenas nas grandes clareiras. O mesmo não ocorreu com a taxa de mortalidade cujas principais causas foram os danos físicos e dessecamento. Para os 13% de indivíduos danificados em um ano, houve destaque para danos ligados à extração de palmito. Apenas os danos físicos naturais apresentaram diferença entre ambientes, com grandes clareiras sendo as mais danosas. No geral e entre as 25 espécies avaliadas separadamente, houve uma tendência de crescimento maior com o aumento da incidência luminosa. Clareiras pequenas a médias tiveram significativamente maior riqueza, diversidade e menor dominância de espécies que o sub-bosque. Clareiras grandes com bambu tiveram menor riqueza e diversidade, mas contribuíram com a manutenção da diversidade beta da parcela permanente. / In a 10.24 ha permanent plot of Tropical Lower Montane Atlantic Rain Forest in the Carlos Botelho State Park (Sete Barras, SP, Brazil), this study aimed to describe the canopy disturbance regime and to assess natural regeneration under different light regimes. In order to do so, the plot was completely surveyed for canopy gaps that were measured and had their approximate age estimated. Then, 42 10x10 m plots were established to evaluate natural regeneration under three light regimes: understory (18 plots), small to medium canopy gaps (11 plots) and large gaps abundant in Guadua tagoara (Nees) Kunth (13 plots). The light regime was characterized through hemispherical photographs taken at each plot center. Natural regeneration was dived into: herb stratum (i.e., herbs below one meter in height) assessed through soil coverage using the line intercept method; and shrub stratum or all plant individuals taller than one meter high and thinner than 5 cm in diameter at breast height. All individuals were identified to species and measured for diameter, height, crown height and area, besides notes on the presence of reproductive structures and germination substrate. Information on growth form, dispersal syndrome and ecological group were also obtained for each species. After one year, one reevaluation was made to assess mortality, damages, recruitment and growth. Although 67% of gaps were smaller than 150 m2 , the plot disturbance regime was atypical mainly by the contribution of gaps bigger than 750 m2 and by the average and total gap area that varied respectively from 419 to 799 m2 , and from 26 to 49% depending on the gap delimitation method. Gap density was 6 gaps.ha-1 and the turnover rate varied from 91 to 220 years depending on the gap method employed. There was significant difference between environments among the light index, especially for total incident radiation with means varying from 909 and 2,400 mols.m-2.y-1. It was found significant differences on herb soil coverage between environments, although the results varied among species. In the shrub stratum, species composition and abundance was significantly different, even between small to medium canopy gaps and the understorey. Herb and shrub densities were bigger in the more enlightened environments, as well as pioneer and early secondary species densities. Recruitment over the year (16%) was different between environments with large gaps accounting for 63% of all recruits. Similar difference was not found for mortality rate that had physical damage and desiccation as main death causes. Amid the 13% of damage individuals in the course of one year, there was noticeable contribution of damages linked to illegal extraction of palm-heart. Differences between environments were present only for physical damages with large gaps being the most damaging environment. In general and among the 25 species evaluated separately, there was a tendency of bigger growth with enhancement in light incidence. Small to medium gaps had significantly higher species richness and diversity, and lower dominance compared to the understorey. Large gaps had lower richness and diversity, but they contributed to maintain beta diversity of the permanent plot.

No description available.

Thesis (MSc(For))--University of Stellenbosch, 2005. / ENGLISH ABSTRACT: Recognizing the biological significance of gaps, the South African Department of Water Affairs and Forestry (DWAF) in 1989 initiated a Gap Dynamics Project in the indigenous forests of Tsitsikamma (Eastern Cape, South Africa). This consists of three sub-projects: Koomansbos (9300 m2), created by a ground fire in 1989; Plaatbos (1600 m2), made by a Podocarpus falcatus (Thunb.) R. Br. ex Mirb. (Podocarpaceae) windfall in 1994; and nine gaps of different sizes, artificially created by selective tree felling in 1995: three small (100-150 m2), three medium (300-500 m2) and three large (800-1000 m2). All the gaps were surveyed after creation and permanent plots were established for subsequent monitoring. The current timber harvesting system practiced in South African indigenous forests attempts to minimize gap size. It has been proposed by Euston-Brown et al. (1996) that this practice is likely to benefit the more shade tolerant species, but may inhibit the regeneration of less shade tolerant plants in the forest. Therefore, the present study aimed to verify two hypotheses: gaps may close in a process that is determined by their size, their origin and the plant species characteristics; soil quality might change inside those gaps. For the purpose of the study, the gaps cited above were re-surveyed between 2002 and 2003. It was found that: 1) there was little clear difference in the community structure of plant species between gaps of different sizes and origins; as expected from the species-area relationship, large gaps had higher species richness, plant diversity and herbaceous percentage cover than medium and small gaps; diversity indices were higher in the large windfall gap than in the large fire and artificial gaps; generally, context and stochastic events were largely more important in determining gap diversity and regeneration than gap sizes and origins; 2) diversity indices in the gaps were higher than recorded previously; 3) soil pH and Electrical Conductivity were respectively lower and higher inside the gaps than adjacent to them; these variations were statistically significant. Present data on the vegetation in the gaps were compared to past measurements, and future vegetation structure has been predicted, as a function of current gap vegetation. Recommendations have been made for sustainable management of the indigenous forest of Tsitsikamma. / AFRIKAANSE OPSOMMING: Voortspruitend uit die erkenning van die biologiese belang van gapings, het die Suid-Afrikaanse Departement van Waterwese en Bosbou (DWB) in 1989 'n projek oor gapingsdinamika in die inheemse woude van Tsitsikamma (Oos-Kaap, Suid-Afrika) geïnisieer. Dit bestaan uit drie subprojekte: die gaping in Koomansbos (9300 m2) wat in 1989 deur 'n grondvuur geskep is; die gaping in Plaatbos (1600 m2) wat veroorsaak is toe bome van die spesie Podocarpus falcatus (Thunb.) R. Br. ex Mirb. (Podocarpaceae) in 1994 omgewaai is; en nege gapings van verskillende groottes wat in 1995 kunsmatig deur geselekteerde boomkappery geskep is: drie is klein (100-150 m2), drie mediumgrootte (300-500 m2) en drie groot (800-1000 m2). Alle gapings is ná hulle ontstaan opgemeet en ondersoek en permanente terreine is vir daaropvolgende monitering gevestig. Die stelsel wat tans vir die oes van hout in Suid-Afrikaanse inheemse woude gebruik word, poog om die grootte van gapings te minimaliseer. Euston Brown et al. (1996) doen aan die hand dat hierdie praktyk spesies wat meer skaduweeverdraagsaam is waarskynlik sal bevoordeel, maar die regenerasie van plante in die woud wat minder skaduweeverdraagsaam is, kan inhibeer. Hierdie studie het dus ten doel gehad om twee hipoteses te verifieer: Gapings kan toegroei in 'n proses wat deur hul grootte, oorsprong en die eienskappe van die plantspesies bepaal word; en die gehalte van die grond binne daardie gapings kan verander. Die gapings waarna hierbo verwys is, is vir die doel van hierdie studie tussen 2002 en 2003 weer gemonitor. Daar is bevind dat: 1) daar min duidelike verskille was tussen die gemeenskapstruktuur van plantspesies tussen gapings van verskillende groottes en oorsprong; soos van die verhouding tussen spesies en area verwag kan word, het groter gapings 'n hoër spesierykheid, plantdiversiteit en persentasie niehoutagtige dekking as medium- en klein gapings gehad; diversiteitsindekse was hoër in die groot Plaatbosgaping as in die groot Koomansbosgaping of die kunsmatige gapings; in die algemeen was konteks en stochastiese gebeure grootliks belangriker in die bepaling van gapingsdiversiteit en -regenerasie as gapingsgrootte of -oorsprong; 2) diversiteitsindekse in die gapings was hoër as wat voorheen aangeteken is; en 3) grond-pH en elektriese geleidingsvermoë was onderskeidelik laer en hoër binne die gapings as neffens hulle; hierdie variasies was statisties beduidend. Huidige data oor die plantegroei in die gapings is met vorige metings vergelyk, en 'n toekomstige plantegroeistruktuur is as 'n funksie van huidige gapingsplantegroei voorspel. Aanbevelings is gemaak rakende die volhoubare bestuur van Tsitsikamma se inheemse woud.