A National Multi-Scale Assessment of Regeneration Deficit as an Indicator of Potential Risk of Forest Genetic Variation Loss

Genetic diversity is essential because it provides a basis for adaptation and resilience to environmental stress and change. The fundamental importance of genetic variation is recognized by its inclusion in the Montréal Process sustainability criteria and indicators for temperate and boreal forests. The indicator that focuses on forest species at risk of losing genetic variation, however, has been difficult to address in a systematic fashion. We combined two broad-scale datasets to inform this indicator for the United States: (1) tree species occurrence data from the national Forest Inventory and Analysis (FIA) plot network and (2) climatically and edaphically defined provisional seed zones, which are proxies for among-population adaptive variation. Specifically, we calculated the estimated proportion of small trees (seedlings and saplings) relative to all trees for each species and within seed zone sub-populations, with the assumption that insufficient regeneration could lead to the loss of genetic variation. The threshold between sustainable and unsustainable proportions of small trees reflected the expectation of age–class balance at the landscape scale. We found that 46 of 280 U.S. forest tree species (16.4%) may be at risk of losing genetic variation. California and the Southeast encompassed the most at-risk species. Additionally, 39 species were potentially at risk within at least half of the seed zones in which they occurred. Seed zones in California and the Southwest had the highest proportions of tree species that may be at risk. The results could help focus conservation and management activities to prevent the loss of adaptive genetic variation within tree species.

Climate Warming Impacts on Distributions of Scots Pine (Pinus sylvestris L.) Seed Zones and Seed Mass across Russia in the 21st Century

Research highlights: We investigated bioclimatic relationships between Scots pine seed mass and seed zones/climatypes across its range in Russia using extensive published data to predict seed zones and seed mass distributions in a changing climate and to reveal ecological and genetic components in the seed mass variation using our 40-year common garden trial data. Introduction: seed productivity issues of the major Siberian conifers in Asian Russia become especially relevant nowadays in order to compensate for significant forest losses due to various disturbances during the 20th and current centuries. Our goals were to construct bioclimatic models that predict the seed mass of major Siberian conifers (Scots pine, one of the major Siberian conifers) in a warming climate during the current century. Methods: Multi-year seed mass data were derived from the literature and were collected during field work. Climate data (January and July data and annual precipitation) were derived from published reference books on climate and climatic websites. Our multiple regression bioclimatic models were constructed based on the climatic indices of growing degree days > 5 °C, negative degree days < 0 °C, and annual moisture index, which were calculated from January and July temperatures and annual precipitation for both contemporary and future climates. The future 2080 (2070–2100) January and July temperatures and annual precipitation anomalies were derived from the ensemble of twenty CMIP5 (the Coupled Model Intercomparison Project, Phase 5) global circulation models (GCMs) and two scenarios using a mild RCP (Representative Concentration Pathway) 2.6 scenario and an extreme RCP 8.5 scenario. Results: Site climate explained about 70% of the seed mass variation across the Scots pine range. Genetic components explained 30% of the seed mass variation, as per the results from our common garden experiment in south central Siberia. Seed mass varied within 3.5 g (min) and 10.5 g (max) with the mean 6.1 g (n = 1150) across Russia. Our bioclimatic seed mass model predicted that a July temperature elevated by 1 °C increased seed mass by 0.56 g, and a January temperature elevated by 5 °C increased seed mass by 0.43 g. The seed mass would increase from 1 g to 4 g in the moderate RCP 2.6 and the extreme RCP 8.5 climates, respectively. Predicted seed zones with heavier seed would shift northwards in a warming climate. However, the permafrost border would halt this shifting due to slower permafrost thawing; thus, our predicted potential for Scots pine seed zones and seed mass would not be realized in the permafrost zone in a warmed climate. Our common garden experiment in central Siberia showed that trees of northerly origins produced lighter seeds than local trees but heavier ones than the trees at the original site. Trees of southerly origins produced heavier seeds than local trees but lighter seeds than the trees at the original site. Conclusions: The findings from this study could serve as blueprints for predicting new landscapes with climatic optima for Pinus sylvestris to produce better quality seeds to adjust to a warming climate.

Modelling Shifts and Contraction of Seed Zones in Two Mexican Pine Species by Using Molecular Markers

A seed zone or provenance region is an area within which plants can be moved with little risk of maladaptation because of the low environmental variation. Delineation of seed zones is of great importance for commercial plantations and reforestation and restoration programs. In this study, we used AFLP markers associated with environmental variation for locating and delimiting seed zones for two widespread and economically important Mexican pine species (Pinus arizonica Engelm. and P. durangensis Martínez), both based on recent climate conditions and under a predicted climate scenario for 2030 (Representative Concentration Pathway of ~4.5 Wm−2). We expected to observe: (i) associations between seed zones and local climate, soil and geographical factors, and (ii) a meaning latitudinal shift of seed zones, along with a contraction of species distributions for the period 1990–2030 in a northward direction. Some AFLP outliers were significantly associated with spring and winter precipitation, and with phosphorus concentration in the soil. According to the scenario for 2030, the estimated species and seed zone distributions will change both in size and position. Our modeling of seed zones could contribute to reducing the probabilities of maladaptation of future reforestations and plantations with the pine species studied.

Local was best: sourcing tree seed for future climates

As climate change accelerates, foresters are looking to ever warmer climates to secure sources of climatically adapted tree seed with which to establish healthy and productive plantations. However, as seed procurement areas approach jurisdictional boundaries (states, provinces, nations), across which seed and seed transfer systems are not typically shared, innovative approaches are required to identify those plantation areas for which suitable domestic provenances will be lacking, and areas in neighbouring jurisdictions with matching warmer, future climates that could fill domestic seed supply gaps. We describe a straightforward, climate envelope approach to locate these areas, using British Columbia (BC), Canada, and the Pacific Northwest (PNW) USA to illustrate the analysis. We find that 21% of BC’s ecosystems (seed zones) will be at moderate or high risk of lacking adapted domestic provenances for plantation establishment by 2040. Importantly, however, we find large areas in the PNW that should be able to fill most of BC’s domestic seed supply gaps. Spatial analyses of this type will inform seed suppliers, managers and policymakers where alternative seed procurement arrangements are needed and underscore the operational and policy barriers to acquiring seed from warmer jurisdictions. More broadly they also highlight the need for inter-jurisdictional cooperation in matters pertaining to resource management.

Establishment of a Genetically Diverse, Disease-Resistant Acacia koa A. Gray Seed Orchard in Kokee, Kauai: Early Growth, Form, and Survival

Background and Objectives: Koa (Acacia koa A. Gray) is an economically, ecologically, and culturally valuable tree species endemic to Hawaii. A vascular wilt disease caused by the fungal pathogen Fusarium oxysporum f. sp. koae Gardner (FOXY) induces high rates of mortality in plantings and threatens native koa forests as well. Landowners are reluctant to consider koa for reforestation purposes in many areas due to the risk of mortality caused by FOXY. Producing seeds with genetic resistance to FOXY is vital to successful koa reforestation and restoration. The Hawaii Agriculture Research Center (HARC), with both public and private partners, operates a tree improvement program to develop wilt-resistant koa populations in Hawaii. The population genetics of koa is poorly understood and seed zones are evolving. Thus, HARC uses provisional seed zones based on genetic and biogeographic variables and has selected wilt-resistant koa populations that are locally found in Kokee, Kauai (eco-regions) of Hawaii. Materials and Methods: To make these selections, virulent FOXY isolates were used in previous seedling inoculation trials to evaluate resistance levels among koa families in greenhouse experiments, and the most resistant families were used in the field trial reported here. Results: In this trial, survival rates two years after planting varied by family, and ranged from 45% to 95%, but all resistant families had greater survival rates than the susceptible control (25%). The trial has been converted to a seed orchard. Conclusions: The higher survival rates of the families are encouraging and seeds coming from the orchard will improve the success of future restoration and reforestation efforts. Within these resistant families it was also possible to make some selections based on height, growth, diameter, and stem form. Thus, the establishment of a wilt-resistant seed orchard results in locally adapted, eco-region specific, disease-resistant koa seed that will allow for the restoration of this iconic species and provide plant material for commercial reforestation opportunities at the landscape level.

ON THE POSSIBILITY OF APPLYING A NEW SET OF SINGLE-NUCLEIC POLYMORPHISMS LOCI TO THE OPTIMIZATION OF THE FOREST SEED AREA OF PEDUNCULATE OAK

We tested 95 new, geographically informative nuclear SNP loci of pedunculate oak in order to identify genetic differences of populations in the same seed zone. In a cluster analysis all individuals of the two studied stands are divided into two distinct groups. We observed statistically significant genetic differentiation of two populations (genetic distance d_0 = 0.170, parameter of differentiation 〖delta〗_T = 0.1696, genetic fixation F_ST = 0.0687) and higher genetic variability in the lowland stand (P = 91,58%, observed heterozygosity H_O = 0.364, expected heterozygosity H_E = 0.330, diversity of alleles υа = 1.58) in comparison to the oak stand in the Volga uplands (P = 77,89%, H_O = 0.327, H_E = 0.272, υа = 1.47). We concluded that these oak forests should be subdivided into different seed zones. Continuing the research by using the set of SNP loci and expanding the set of studied populations will supply Russian forestry by genetic information to optimize the forest seed zoning of the pedunculate oak.